Welding Technology I - Script

ISF – Welding Institute RWTH – Aachen University

Lecture Notes

Welding Technology 1 Welding and Cutting Technologies

Prof. Dr.– Ing. U. Dilthey

Table of Contents

Chapter Subject Page

0. Introduction 3

1. Gas Welding 6

2. Manual Metal Arc Welding 17

3. Submerged Arc Welding 31

4. TIG Welding and

Plasma Arc Welding 48

5. Gas– Shielded Metal Arc Welding 60

6. Narrow Gap Welding,

Electrogas - and

Electroslag Welding 76

7. Pressure Welding 88

8. Resistance Spot Welding,

Resistance Projection Welding

and Resistance Seam Welding 104

9. Electron Beam Welding 119

10. Laser Beam Welding 133

11. Surfacing and Shape Welding 150

12. Thermal Cutting 165

13. Special Processes 182

14. Mechanisation and Welding Fixtures 196

15. Welding Robots 208

16. Sensors 216

Literature 226

0.

Introduction

0. Introduction 4

2005

Welding fabrication processes are classified in accordance with the German Standards

DIN 8580 and DIN 8595 in main group 4 “Joining”, group 4.6 “Joining by Welding”, Figure

0.1.

Welding: permanent, positive joining method.

The course of the strain lines is almost ideal.

Welded joints show therefore higher strength

properties than the joint types depicted in

Figure 0.2. This is of advantage, especially in

the case of dynamic stress, as the notch ef-

fects are lower.

4.6.2Fusion welding

1Casting

5Coating Changing of

materialsproperties

62Forming

3Cutting

4Joining

4.4Joining by

casting

4.1Joining by

composition

4.7Joining bysoldering

4.6Joining bywelding

4.3Joining bypressing

4.2Joiningby filling

4.8Joining byadhesivebonding

4.6.1Pressure welding

4.5Joining by

forming

Production Processes acc. to DIN 8580

br-er0-01.cdr

Figure 0.1

© ISF 2002

Connection Types

Screwing

Riveting

Adhesivebonding

Soldering

Welding

br-er0-02.cdr

Figure 0.2

0. Introduction 5

2005

Figures 0.3 and 0.4 show the further subdivision of the different welding methods accord-

ing to DIN 1910.

Production processes

4Joining

4.6Joining by welding

4.6.2Fusion welding


4.6.1.1Welding

bysolid bodies

Heated toolwelding

4.6.1.2Weldingby liquids

Flow welding

4.6.1.3Weldingby gas

Gas pressure-/roll-/ forge-/

diffusionwelding

4.6.1.4Welding byelectrical

gas discharge

Arc pressurewelding

4.6.1.6Welding

by motion

Cold pressure-/shock-/ friction-/

ultrasonicwelding

4.6.1.7Welding by

electric current

Resistancepressurewelding

Joining by Welding acc. to DIN 1910Pressure Welding

© ISF 2002br-er0-03.cdr

Figure 0.3

Production processes

4Joining

4.6Joining by welding

4.6.2Fusion welding


4.6.2.2Welding

by liquids

4.6.2.3Weldingby gas

4.6.2.5Weldingby beam

4.6.2.4Welding byelectrical

gas discharge

4.6.2.7Welding by

electric current

Cast welding Gas welding Arc welding Beam weldingResistance

welding

Joining by Welding acc. to DIN 1910Fusion Welding

br-er0-04.cdr

Figure 0.4

1.

Gas Welding

1. Gas Welding 7

2005

Although the oxy-acetylene process has been introduced long time ago it is still applied for its

flexibility and mobility. Equipment for oxyacetylene welding consists of just a few ele-

ments, the energy necessary for welding can be transported in cylinders, Figure 1.1.

Process energy is obtained from the exothermal chemical reaction between oxygen and a

combustible gas, Figure 1.2. Suitable combustible gases are C2H2, lighting gas, H2, C3H8 and

natural gas; here C3H8 has the highest calorific value. The highest flame intensity from point

of view of calorific value and flame propagation speed is, however, obtained with C2H2.

© ISF 2002

Equipment Componentsfor Gas Welding

acetylene hose

oxygen cylinder with pressure reducer

welding rod

oxygen hose

welding nozzle

welding torch

acetylene cylinder with pressure reducer

welding flame

workpiece

1

9

7

2

6

4

5

3

8

19

7

2

64

5

3

8

br-er1-01.cdr © ISF 2002

Properties of Fuel Gas inCombination with Oxygen

27702850

3200

0

200

400

600645

0

ignition temperature [ C]O

oxygen

air

0.5

1.0

1.5

2.0

2.5

0

density in normal state [kg/m ]3

pro

pane

2.0

0.9

oxygen

1.43

ace

tyle

ne

1.17

air

1.29

300335

510490

645

flame temperature with O2

flame efficiency with O2

flame velocity with O2

KW/cm

2 cm/s

43

10.3

8.5

1350

370

330

br-er1-02.cdr

natu

ral gas

pro

pane

ace

tyle

ne

natu

ral g

asna

tura

l gas

pro

pane

ace

tyle

ne

°Ck

Figure 1.1 Figure 1.2

1. Gas Welding 8

2005

C2H2 is produced in acetylene gas genera-

tors by the exothermal transformation of cal-

cium carbide with water, Figure 1.3. Carbide

is obtained from the reaction of lime and car-

bon in the arc furnace.

C2H2 tends to decompose already at a pres-

sure of 0.2 MPa. Nonetheless, commercial

quantities can be stored when C2H2 is dis-

solved in acetone (1 l of acetone dissolves

approx. 24 l of C2H2 at 0.1 MPa), Figure 1.4.

Acetone disintegrates at a pressure of more

than 1.8 MPa, i.e., with a filling pressure of

1.5 MPa the storage of 6m³ of C2H2 is possi-

ble in a standard cylinder (40 l). For gas ex-

change (storage and drawing of quantities up

to 700 l/h) a larger surface is necessary,

therefore the gas cylinders are filled with a

porous mass (diatomite). Gas consumption

during welding can be observed from the

weight reduction of the gas cylinder.

© ISF 2002

Acetylene Generator

loading funnel

material lock

gas exit

feed wheel

grille

sludge

to sludge pit

br-er1-03.cdr

Figure 1.3

© ISF 2002

Storage of Acetylene

acetone acetylene

porous mass

acetylene cylinder

filling quantity :

acetone quantity :

acetylene quantity :

~13 l

6000 l

15 bar

up to 700 l/h

cylinder pressure :

br-er1-04.cdr

N

Figure 1.4

1. Gas Welding 9

2005

Oxygen is produced by

fractional distillation of

liquid air and stored in cyl-

inders with a filling pres-

sure of up to 20 MPa, Fig-

ure 1.5. For higher oxygen

consumption, storage in a

liquid state and cold gasifi-

cation is more profitable.

The standard cylinder (40 l) contains, at a

filling pressure of 15 MPa, 6m³ of O2 (pres-

sureless state), Figure 1.6. Moreover, cylin-

ders with contents of 10 or 20 l (15 MPa) as

well as 50 l at 20 MPa are common. Gas

consumption can be calculated from the pres-

sure difference by means of the general gas

equation.

© ISF 2002

Principle of Oxygen Extraction

air

cooling

nitrogen

gaseous

cylinder

bundle

oxygen

oxygenliquid

air

nitrogenvaporized

liquid

tank car

pipeline

cleaning compressor separationbr-er1-05.cdr

supply

Figure 1.5

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Storage of Oxygen

50 l oxygen cylinder

protective cap

cylinder valve

take-off connection

gaseous

p = cylinder pressure : 200 bar

V = volume of cylinder : 50 l

Q = volume of oxygen : 10 000 l

content control

Q = p V

foot ring

user

gaseous

still

liquid

vaporizer

manometersafety valve

fillingconnection

liquid

N

Figure 1.6

1. Gas Welding 10

2005

In order to prevent mistakes, the gas cylinders are colour-coded. Figure 1.7 shows a survey

of the present colour code and the future colour code which is in accordance with DIN EN

1089.

The cylinder valves are

also of different designs.

Oxygen cylinder connec-

tions show a right-hand

thread union nut. Acetylene

cylinder valves are

equipped with screw clamp

retentions. Cylinder valves

for other combustible

gases have a left-hand

thread-connection with a

circumferential groove.

Pressure regulators re-

duce the cylinder pressure

to the requested working

pressure, Figures 1.8 and

1.9.

Figure 1.7

© ISF 2002

Single Pressure Reducing Valve during Gas Discharge Operation

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cylinder pressure working pressure

Figure 1.8

© ISF 2006

Gas Cylinder-Identificationaccording to DIN EN 1089

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old condition DIN EN 1089

oxygen techn.

white

blue (grey)

blue

acetylene

brownyellow

nitrogen

darkgreen

darkgreen

black

argon

dark green

grey

grey

old condition DIN EN 1089

grey

grey

brown

helium

carbon-dioxide

grey grey

grey

grey

argon-carbon-dioxide mixture

vivid green

hydrogen

redred

1. Gas Welding 11

2005

At a low cylinder pressure (e.g. acetylene cylinder) and low pressure fluctuations, single-

stage regulators

are applied; at higher cyl-

inder pressures normally

two-stage pressure regula-

tors are used.

The requested pressure is

set by the adjusting screw.

If the pressure increases

on the low pressure side,

the throttle valve closes the

increased pressure onto

the membrane.

The injector-type torch consists of a body with valves and welding chamber with welding

nozzle, Figure 1.10. By the selection of suitable welding chambers, the flame intensity can be

adjusted for welding different plate thicknesses.

The special form of the mixing chamber guarantees highest possible safety against

flashback, Figure 1.11.

The high outlet speed of

the escaping O2 gener-

ates a negative pressure

in the acetylene gas line,

in consequence C2H2 is

sucked and drawn-in.

C2H2 is therefore avail-

able with a very low

pressure of 0.02 up to

0.05 MPa -compared

with O2 (0.2 up to

0.3 MPa).

© ISF 2002

Single Pressure Reducing Valve,Shut Down

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discharge pressure locking pressure

Figure 1.9

© ISF 2002

Welding Torch

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welding torchinjector or blowpipe

coupling nuthose connection

for oxygenA6x1/4" rightmixer tube mixer nozzle oxygen valve

injector

pressure nozzle

suction nozzle

fuel gas valvewelding nozzle

hose connectionfor fuel gas

A9 x R3/8” left

welding torch head torch body

Figure 1.10

1. Gas Welding 12

2005

A neutral flame adjustment allows the differentiation of three zones of a chemical reaction,

Figure 1.12:

0. dark core: escaping gas mixture

1. brightly shining centre cone: acetylene decomposition

C2H2 -> 2C+H2

2. welding zone: 1st stage of combustion

2C + H2 + O2 (cylinder) -> 2CO + H2

3. outer flame: 2nd stage of combustion

4CO + 2H2 + 3O2 (air) ->

4CO2 + 2H2O

complete reaction: 2C2H2 + 5O2 ->

4CO2 + 2H2O

© ISF 2002

Injector-Area of Torch

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acetylene

oxygen

acetylene

welding torch head injector nozzle pressure nozzle

coupling nut torch body

Figure 1.11

1. Gas Welding 13

2005

By changing the mixture ratio of the volumes

O2:C2H2 the weld pool can greatly be influ-

enced, Figure 1.13. At a neutral flame ad-

justment the mixture ratio is O2:C2H2 = 1:1. By

reason of the higher flame temperature, an

excess oxygen flame might allow faster

welding of steel, however, there is the risk of

oxidizing (flame cutting).

Area of application: brass

The excess acetylene causes the carburising

of steel materials.

Area of application: cast iron

© ISF 2002

discharging velocity and weld heat-input rate: low

nozzle size: for plate thickness of 2-4 mmbalanced (neutral) flame

welding flame

2

soft flame

moderate flame

hard flame

discharging velocity and weld heat-input rate: middle

discharging velocity and weld head-input rate: high

3

4

br-er1-14.cdr

Effects of the Welding Flame Depending on the Discharge Velocity

Figure 1.14

© ISF 2002

excess ofacetylene

normal(neutral)

excess of oxygen

welding flameratio of mixture

effects in welding of steel

sparking foaming spattering

reducing oxidizingconsequences:

carburizinghardening

Effects of the Welding Flame Depending on the Ratio of Mixture

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Figure 1.13

© ISF 2002

Temperature Distributionin the Welding Flame

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welding flamecombustion

welding nozzle

welding zone

centre cone outer flame

3200°C

2500°C

1800°C

1100°C

400°C

2 - 5

Figure 1.12

1. Gas Welding 14

2005

By changing the gas mixture outlet speed the flame can be adjusted to the heat requirements

of the welding job, for example when welding plates (thickness: 2 to 4 mm) with the welding

chamber size 3: “2 to 4 mm”, Figure 1.14. The gas mixture outlet speed is 100 to 130 m/s

when using a medium or normal flame, applied to at, for example, a 3 mm plate. Using a

soft flame, the gas outlet speed is lower (80 to 100 m/s) for the 2 mm plate, with a hard

flame it is higher (130 to 160 m/s) for the 4 mm plate.

Depending on the plate thickness are the working methods “leftward welding” and “rightward

welding” applied, Figure 1.15. A decisive factor for the designation of the working method is

the sequence of flame and welding rod as well as the manipulation of flame and welding rod.

The welding direction itself is of no importance. In leftward welding the flame is pointed at

the open gap and “wets” the molten pool; the heat input to the molten pool can be well con-

trolled by a slight movement of the torch (s ≤ 3 mm).

© ISF 2002

welding-rod flame welding bead

weld-rod flame

Rightward welding ist applied to a plate thickness of 3mmupwards. The wire circles, the torch remains calm.

Advantages: - the molten pool and the weld keyhole are easy to observe- good root fusion- the bath and the melting weld-rod are permanently protected from the air- narrow welding seam- low gas consumption

Leftward welding is applied to a plate thickness of up to 3 mm.The weld-rod dips into the molten pool from time to time,but remains calm otherwise. The torch swings a little.

Advantages:easy to handle on thin plates

Flame Welding

br-er1-15e.cdr

Figure 1.15

© ISF 2002

gappreparations denotation sym-

bol

plate thicknessrange s [mm]from to

1,5

1,0

1,0 4,0

3,0 12,0

1,0 8,0

1,0 8,0

1,0 8,0

flange weld

plain buttweld

V - weld

corner weld

lap seam

fillet weld

1 - 2

1 - 2

Gap Shapes for Gas Welding

s+

1~ ~ r

= s

br-er1-16.cdr

Figure 1.16

1. Gas Welding 15

2005

In rightward welding the flame is directed

onto the molten pool; a weld keyhole is

formed (s ≥ 3 mm).

Flanged welds and plain butt welds can be

applied to a plate thickness of approx.

1.5 mm without filler material, but this does

not apply to any other plate thickness and

weld shape, Figure 1.16.

By the specific heat input of the different

welding methods all welding positions can be

carried out using the oxyacetylene welding

method, Figures 1.17 and 1.18

When working in tanks and confined

spaces, the welder (and all other persons

present!) have to be protected against the

welding heat, the gases produced during

welding and lack of oxygen ((1.5 % (vol.) O2

per 2 % (vol.) C2H2 are taken out from the

ambient atmosphere)), Figure 1.19. The addi-

tion of pure oxygen is unsuitable (explosion

hazard!).

A special type of autogene method is flame-

straightening, where specific locally applied

flame heating allows for shape correction of

workpieces, Figure 1.20. Much experience is

needed to carry out flame straightening proc-

esses.

The basic principle of flame straightening de-

pends on locally applied heating in connec-

tion with prevention of expansion. This proc-

© ISF 2002

PA

PB

PFPG

PC

PE

PD

butt-welded seams ingravity position

gravity fillet welds

horizontal fillet welds

vertical fillet and butt welds

vertical-upwelding position

vertical-down position

horizontal on vertical wall

overhead position

horizontal overhead position

Welding Positions I

br-er1-17.cdr

fs

Figure 1.17


PA

PB

PC

PD

PE

PG

PF

Welding Positions II

Figure 1.18

1. Gas Welding 16

2005

ess causes the appearance of a heated zone. During cooling, shrinking forces are generated

in the heated zone and lead to the desired shape correction.

© ISF 2002

5. after welding: Removing the equipment from the tank

4. illumination and electric machines: max 42volt

3. second person for safety reasons

2. extraction unit, ventilation

1. requirement for a permission to enter

protective measures / safety precautions

Hazards through gas, fumes, explosive mixtures,

electric current

Safety in welding and cutting inside oftanks and narrow rooms

br-er1-19e.cdr

Gas Welding in Tanks andNarrow Rooms

Figure 1.19

© ISF 2002

welded parts

first warm up bothlateral plates, then belt

butt weld

3 to 5 heat sourcesclose to the weld-seam

double fillet weld

1,3 or 5 heat sources

Flame straightening

Flame Straightening

br-er1-20.cdr

Figure 1.20

2.

Manual Metal Arc Welding


2005

Figure 2.1 describes the burn-off of a cov-

ered stick electrode. The stick electrode

consists of a core wire with a mineral cover-

ing. The welding arc between the electrode

and the workpiece melts core wire and cover-

ing. Droplets of the liquefied core wire mix

with the molten base material forming weld

metal while the molten covering is forming

slag which, due to its lower density, solidifies

on the weld pool. The slag layer and gases

which are generated inside the arc protect the

metal during transfer and also the weld pool

from the detrimental influences of the sur-

rounding atmosphere.

Covered stick electrodes

have replaced the initially

applied metal arc and car-

bon arc electrodes. The

covering has taken on the

functions which are de-

scribed in Figure 2.2.

br-er2-01.cdr ISF 2002c

Weld Point

electrode core

electrode coating

air(O , N , etc.)2 2

liquid slag

solid slag

Smoke and gas

Figure 2.1

Figure 2.2


2005

The covering of the stick electrode consists of a multitude of components which are mainly

mineral, Figure 2.3.

For the stick electrode manufacturing mixed ground and screened covering materials are

used as protection for the core wire which has been drawn to finished diameter and subse-

quently cut to size, Figure 2.4.

© ISF 2002

Influence of the Coating Constituents on Welding Characteristics

br-er2-03.cdr

coating raw material effect on the welding characteristics

quartz - SiO2 to raise current-carrying capacity

rutile -TiO2to increase slag viscosity,good re-striking

magnetite - Fe O3 4 to refine transfer of droplets through the arc

calcareous spar -CaCO3to reduce arc voltage, shielding gas emitter and slag formation

fluorspar - CaF2to increase slag viscosity of basic electrodes,decrease ionization

calcareous- fluorspar -K O Al O 6SiO2 2 3 2

easy to ionize, to improve arc stability

ferro-manganese / ferro-silicon deoxidant

cellulose shielding gas emitter

kaolin -Al O 2SiO 2H O2 3 2 2

lubricant

potassium water glassK SiO / Na SiO2 3 2 3

bonding agent

Figure 2.3

1 2 3

raw wirestorage wire drawing machine

and cutting system

inspection

to the pressing

plant

electrodecompound

raw material storagefor flux production

jawcrusher

magneticseparation

cone crusherfor pulverisation

sieving

to further treatment like milling, sieving, cleaning and weighing

sieving system

weighingand

mixing

inspection

wet mixer

descaling

inspection

example of a three-stage wire drawing machine

drawing plate

Ø 6 mm Ø 5,5 mm 3,25 mmØ 4 mm

© ISF 2002

Stick Electrode Fabrication 1

br-er2-04.cdr

Figure 2.4


2005

The core wires are coated

with the covering material

which contains binding

agents in electrode extru-

sion presses. The defect-

free electrodes then pass

through a drying oven and

are, after a final inspection,

automatically packed, Fig-

ure 2.5.

Figure 2.6 shows how the moist extruded cov-

ering is deposited onto the core wire inside an

electrode extrusion press.

Stick Electrode Fabrication 2

© ISF 2002br-er10-33e.cdr

core wiremaga-

zine

electrodecompound

inspection

inspection inspection

inspection

inspection

the pressing plant

drying stove

TODELIVERY

packinginspection

electrode-press

compound

nozzleconvey-ingbelt

wiremagazine

wirefeeder

pressinghead

Figure 2.5

core rodcoatingpressing nozzlepressing cylinderpressing cylinder

pressing mass core rod guide

Production of Stick Electrodes

br-er2-06.cdr

Figure 2.6


2005

Stick electrodes are, according to their covering compositions, categorized into four differ-

ent types, Figure 2.7. with concern to burn-off characteristics and achievable weld metal

toughness these types show fundamental differences.

The melting characteristics of the different coverings and the slag properties result in further

properties; these determine the areas of application, Figure 2.8.

© ISF 2002

Characteristic Features of Different Coating Types

br-er2-07.cdr

cellulosic type acid type rutile type basic typ

celluloserutilequartzFe - Mnpotassium water glass

40202515

magnetitequartzcalciteFe - Mnpotassium water glass

50201020

rutilemagnetitequartzcalciteFe - Mnpotassium water glass

TiO2SiO2

Fe OSiOCaCO

3 4

2

3

TiOFe OSiOCaCO

2

3 4

2

3

fluorsparcalcitequartzFe - Mnpotassium water glass

4510201015

4540105

CaFCaCOSiO

2

3

2

almostno slag

slag solidification time: long

slag solidificationtime: medium

slag solidification time: short

droplet transfer :

toughness value:

medium- sizeddroplets

good normal good very good

fine dropletsto sprinkle

medium- sized to fine droplets

medium- sized to big droplets

droplet transfer : droplet transfer : droplet transfer :

toughness value: toughness value: toughness value:

Figure 2.7

© ISF 2002

Characteristics of Different Coating Types

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coating typesymbol

gap bridging ability

current type/polarity

welding positions

sensitivity ofcold cracking

weld appearance

slag detachability

characteristic features

cellulosic typeC

acid typeA

rutile typeR

basic typeB

very good moderate good good

PG,(PA,PB,PC,PE,PF)

PA,PB,PC,PE,PF,PG

PA,PB,PC,PE,PF,(PG)

PA,PB,PC,PE,PF,PG

low high low very low

moderate good good moderate

good very good very good moderate

spatter,little slag,

intensive fumeformation

high burn-outlosses

universalapplication

low burn-out losses

hygroscopic predrying!!

~ / + ~ / +~ / + = / +

Figure 2.8


2005

The dependence on

temperature of the slag’s

electrical conductivity

determines the reignition

behaviour of a stick elec-

trode, Figure 2.9. The

electrical conductivity for a

rutile stick electrode lies,

also at room temperature,

above the threshold value

which is necessary for

reignition. Therefore, rutile

electrodes are given pref-

erence in the production of

tack welds where reigni-

tion occurs frequently.

The complete designation

for filler materials, follow-

ing European Standardi-

sation, includes details–

partly as encoded abbre-

viation – which are rele-

vant for welding, Figure

2.10. The identification

letter for the welding proc-

ess is first:

E - manual electrode welding G - gas metal arc welding

T - flux cored arc welding W - tungsten inert gas welding

S - submerged arc welding

© ISF 2002

Conductivity of Slags

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co

nd

uctivity

temperature

reignition threshold

high rutile-containing slag

semiconductor

acid sla

g

high

-tem

pera

ture

cond

ucto

r

basi

c slag

high

-tem

pera

ture

cond

ucto

r

Figure 2.9

© ISF 2002

Designation Example for Stick Electrodes

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The mandatory part of the standard designation is: EN 499 - E 46 3 1Ni B

hydrogen content < 5 cm /100 g welding depositbutt weld: gravity positionfillet weld: gravity positionsuitable for direct and alternating currentrecovery between 125% and 160%basic thick-coated electrodechemical composition 1,4% Mn and approx. 1% Niminimum impact 47 J in -30 Cminimum weld metal deposit yield strength: 460 N/mmdistinguishing letter for manual electrode stick welding

3

o

2

DIN EN 499 - E 46 3 1Ni B 5 4 H5

Figure 2.10


2005

The identification numbers give information about yield point, tensile strength and elongation

of the weld metal where the tenfold of the identification number is the minimum yield point

in N/mm², Figure 2.11.

The identification figures for the minimum impact energy value of 47 J – a parameter for the

weld metal toughness – are shown in Figure 2.12.

© ISF 2002

Characteristic Key Numbers of Yield Strength, Tensile Strength and Elongation

br-er2-11.cdr

key number minimum yield strengthN/mm

2

tensile strengthN/mm

2

minimum elongation*)%

35

38

42

46

50

355

380

420

460

500

440-570

470-600

500-640

530-680

560-720

22

20

20

20

18

*) L = 5 D0 0

Figure 2.11

Characteristic Key Numbers for Impact Energy

br-er2-12.cdr

characteristic figure minimum impact energy 47 J [ C]0

no demands

+20

0

-20

-30

-40

-50

-60

-70

-80

Z

A

0

2

3

4

5

6

7

8

The minimum value of the impact energy allocated to the characteristicfigures is the average value of three ISO-V-Specimen, the lowest value of whitch amounts to 32 Joule.

Figure 2.12


2005

The chemical composition

of the weld metal is shown

by the alloy symbol, Figure

2.13.

The properties of a stick

electrode are characterised

by the covering thickness

and the covering type. Both

details are determined by

the identification letter for

the electrode covering,

Figure 2.14.

Figure 2.15 explains the additional identifica-

tion figure for electrode recovery and applica-

ble type of current. The subsequent identifi-

cation figure determines the application possi-

bilities for different welding positions:

1- all positions

2- all positions, except vertical down

postion

3- flat position butt weld, flat position fillet

weld, horizontal-, vertical up position

4- flat position butt and fillet weld

5- as 3; and recommended for vertical

down position

© ISF 2002

Alloy Symbols for Weld MetalsMinimum Yield Strength up to 500 N/mm

2

br-er2-13.cdr

alloy symbol chemical composition*)

%

Mn Mo Ni

without 2,0_ -

Mo

MnMo

1 Ni

2 Ni

3 Ni

Mn 1 Ni

1 Ni Mo

1,4

>1,4 - 2,0

1,4

1,4

1,4

>1,4 - 2,0

1,4

0,3 - 0,6

0,3 - 0,6

-

-

-

-

0,3 - 0,6

-

-

0,6 - 1.2

1,8 - 2,6

2,6 - 3,8

0,6 - 1,2

0,6 - 1,2

Z other specified compositions

*) companion elements: Mo 0,2; Ni 0,5; Cr 0,2; V 0,08; Nb 0,05; Cu 0,3; Al 2,0

(applies only to self-shielded flux-cored electrodes).

single values are maxima

£

Figure 2.13

© ISF 2002

Key Letters forElectrode Coatings

br-er2-14.cdr

key letter type of coating

A

B

acid coating

basic coating

C cellulose coating

R rutile coated(medium thick)

RR rutile coated (thick)

RA rutile acid coating

RB rutile basic coating

RC rutile cellulose coating

Figure 2.14


2005

The last detail of the Euro-

pean Standard designation

determines the maximum

hydrogen content of the

weld metal in cm³ per 100

g weld metal.

Welding current amper-

age and core wire diame-

ter of the stick electrode

are determined by the

thickness of the workpiece

to be welded. Fixed stick

electrode lengths are as-

signed to each diameter,

Figure 2.16.

Figure 2.17 shows the

process principle of man-

ual metal arc welding.

Polarity and type of current

depend on the applied

electrode types. All known

power sources with a de-

scending characteristic

curve can be used.

Since in manual metal arc welding the arc length cannot always be kept constant, a steeply

descending power source is used. Different arc lengths lead therefore to just minimally al-

tered weld current intensities, Figure 2.18. Penetration remains basically unaltered.

© ISF 2002

Additional Characteristic Numbersfor Deposition Efficiency and Current Type

br-er2-15.cdr

additional

characteristic number

1

2

3

4

5

6

7

8

deposition efficiency

%

current type*)

<105

<105

>160

>160

>105 125

>105 125

>125 160

>125 160

alternating and direct current

direct current

*) To prove the suitability for direct current,

the tests have to be run with a no-load voltage of max. 65 V.


direct current


direct current


direct current

Figure 2.15

© ISF 2002

Size and Welding Currentof Stick Electrodes

br-er2-16.cdr

diameter

length

current

2,0 2,5 3,25 4,0 5,0 6,0

250/300 350 350/450 350/450 450 450

40-80 50-100 90-150 120-200 180-270 220-360

20 x d 30 x d 35 x d

d

mm

l

mm

I

A

min.

max. 40 x d 50 x d 60 x d

rule-of -thumbfor current[A]

Figure 2.16


2005

Simple welding transformers are used for a.c. welding. For d.c. welding mainly converters,

rectifiers and series regulator transistorised power sources (inverters) are applied. Convert-

ers are specifically suitable

for site welding and are

mains-independent when

an internal combustion en-

gine is used. The advan-

tages of inverters are their

small size and low weight,

however, a more compli-

cated electronic design is

necessary, Figure 2.19. © ISF 2002

Principle Set-up of MMAW Process

br-er2-17.cdr

work piece

arc

stick electrode

electrode holder

power source

= or ~

- (+)

+ (-)

Figure 2.17

© ISF 2002

Operating Point atDifferent Arc Lengths

br-er2-18e.cdr

U

1

2

2 1 I

A2 A1

A2

A1

characteristicof the arc

power sourcecharacteristic

Figure 2.18

© ISF 2002

Power Sourcesfor MMAW

br-er2-19.cdr

arc weldingconverter

transformer

rectifier

invertertype

Figure 2.19


2005

Figure 2.20 shows the standard welding pa-

rameters of different stick electrode diameters

and stick electrode types.

The rate of deposition of a stick electrode is,

besides the used current intensity, dependent

on the so-called “electrode recovery”, Figure

2.21. This describes the mass of deposited

weld metal / mass of core wire ratio in per-

cent. Electrode recovery can reach values of

up to 220% with metal covering components

in high-efficiency electrodes.

A survey of the material spectrum which is

suitable for manual metal arc welding is given

in Figure 2.22. The survey comprises almost

all metals known for technical applications and

© ISF 2002

Medium Weld Current andVoltages for Stick Electrodes

br-er2-20.cdr

medium weld current

mediu

m w

eld

voltage

B15

B53

RA12

RR12

RA73

RR73

100 200 300 400

6

3,25

4

5

=

=

=

=20

25

30

35

40

45

A

V

Figure 2.20

© ISF 2002

Burn-Off Rateof Stick Electrodes

br-er2-21.cdr

c = high-performance electrodesb = basic-coated electrodes, recovery <125%a = A- and R- coated electrodes, recovery 105%

0

1

2

3

4

5

6

7

burn

-off r

ate

at 100%

duty

cycle

welding amperage

kg/h

100 200 3000 400 500A

= RR12 - 5 mmX = RR73 - 5 mm

thick-

coate

d

thin

-coate

d

220%

depo

sitio

nef

ficie

ncy

160%

depo

sitio

nef

ficie

ncy

X

c

b

a

Figure 2.21

© ISF 2002

Suitable Materials forManual Metal Arc Welding

br-er2-22.cdr

constructional steels

shipbuilding steels

high-strength constructional steels

boiler and pressure vessel steels

austenitic steels

creep resistant steels

austenitic-ferritic steels (duplex)

scale resistant steels

wear resistant steels

hydrogen resistant steels

high-speed steels

cast steels

combinations of materials (ferritic/ austenitic)

steel:

cast iron: cast iron with lamella graphite

cast iron with globular graphite

nickel: pure nickel

Ni-Cu-alloys

Ni-Cr-Fe-alloys

Ni-Cr-Mo-alloys

copper: electrical grade copper (ETP copper)

bronzes (CuSn, CuAl)

gunmetal (CuSnZnPb)

Cu-Ni-alloys

aluminium: pure aluminium

AlMg-alloys

AlSi -alloys

Figure 2.22


2005

also explains the wide ap-

plication range of the

method.

In d.c. welding, the concen-

tration of the magnetic

arc-blow producing

forces can lead to the de-

flection of the arc from

power supply point on the

side of the workpiece, Fig-

ure 2.23. The material

transfer also does not oc-

cur at the intended point.

Arc deflection may also occur at magnetiz-

able mass accumulations although, in that

case, in the direction of the respective mass,

Figure 2.24.

Figures 2.25 and 2.26 show how by various

measures the magnetic arc blow can be

compensated or even avoided.

The positioning of the electrodes in opposite

direction brings about the correct placement of

the weld metal. Numerous strong tacks close

the magnetic flux inside the workpiece. By ad-

ditional, opposite placed steel masses as well

as by skilful transfer of the power supply point

the various reasons for arc deflection can be

eliminated. The fast magnetic reversal when

a.c. is used minimises the influence of the

magnetic arc blow.

Arc Blow Effect through Concentrationof Magnetic Fields

br-er2-23e.cdr

Figure 2.23


Arc Blow Effecton Steel Parts

inwards at the edges

close to current-connection

close to large workpiece masses

in gaps towards the weld

Figure 2.24


2005

Depending on the electrode covering, the wa-

ter absorption of a stick electrode may vary

strongly during storage, Figure 2.27. The ab-

sorbed humidity leads during subsequent

welding frequently to an increased hydrogen

content in the weld metal and, thus, increases

cold cracking susceptibility.

© ISF 2002

Remedy AgainstArc Blow Effect 1

br-er2-25.cdr

tilting of electrode

the weldingsequence

great number of tacks

tacks

Figure 2.25

© ISF 2002

Remedy AgainstArc Blow Effect 2

br-er2-26.cdr

through additional blocks of steel

through relocating the current-connection (rarely used)

through usinga welding transformeralternating current (notapplicable for alltypes of electrodes)

Figure 2.26

© ISF 2002

Water Absorption of DifferentBasic-Coated Electrodes

br-er2-27.cdr

Time of storage

Wa

ter

co

nte

nt

of

the

co

atin

g

1 10 100Days0,10

1,0

2,0

3,0

4,0

%

20°C / 70% RF

Figure 2.27


2005

Stick electrodes, particularly those with a basic, rutile or cellulosic cover have to be baked

before welding to keep the water content of the cover during welding below the permissible

values in order to avoid

hydrogen-induced cracks,

Figure 2.28. The baking

temperature and time are

specified by the manufac-

turer. Baking is carried out

in special ovens; in damp

working conditions and

only just before welding are

electrodes taken out from

electrically heated recepta-

cles.

© ISF 2002

Water Content of the Coatingafter Storage and Baking

br-er2-28.cdr

basic-coated electrode(having been stored at18 - 20°C for one year)

storage and baking

0,74

0,39

0,28

AWS A5.5

Wa

ter

conte

nt of th

e c

oatin

g

1,0

0,9

0,8

0,7

0,6

0,5

0,4

0,3

0,2

0,1

030 40 50 60 70 80%

%

Figure 2.28

3.

Submerged Arc Welding


2005

In submerged arc welding a mineral weld flux layer protects the welding point and the

freezing weld from the in-

fluence of the surrounding

atmosphere, Figure 3.1.

The arc burns in a cavity

filled with ionised gases

and vapours where the

droplets from the continu-

ously-fed wire electrode

are transferred into the

weld pool. Unfused flux can

be extracted from behind

the welding head and sub-

sequently recycled.

Main components of a submerged arc welding unit are:

the wire electrode reel, the wire feed motor equipped with grooved wire feed rolls which are

suitable for the demanded wire diameters, a wire straigthener as well as a torch head for cur-

rent transmission, Figure 3.2.

Flux supply is carried out via a hose from the flux container to the feeding hopper which is

mounted on the torch head. Depending on the degree of automation it is possible to install a

flux excess pickup behind

the torch. Submerged arc

welding can be operated

using either an a.c. power

source or a d.c. power

source where the electrode

is normally connected to

the positive terminal.

Welding advance is pro-

vided by the welding ma-

chine or by workpiece

movement.

© ISF 2002

Assembly of a SA Welding Equipment

br-er3-02e.cdr

AC or DC current supplywire straightenerwire feed rollsflux supplyindicatorswire reel

power sourcewelding machine holder

Figure 3.2

© ISF 2002

Process Principle of Submerged Arc Welding

br-er3-01e.cdr

base metal

weld metal

solid slag

flux

arc

weld cavitymolten poolliquid slag

electrode

contact piece

flux hopper

Figure 3.1


2005

Identification of wire electrodes for submerged arc welding is based on the average Mn-

content and is carried out in steps of 0.5%, Figure 3.3. Standardisation for welding filler mate-

rials for unalloyed steels as well as for fine-grain structural steels is contained in DIN EN 756,

for creep resistant steels in DIN pr EN 12070 (previously DIN 8575) and for stainless and

heat resistant steels in DIN pr EN 12072 (previously DIN 8556-10).

The proportions of additional alloying elements are dependent on the materials to be welded

and on the mechanical-technological demands which emerge from the prevailing operating

conditions, Figure 3.4. Connected to this, most important alloying elements are manga-

nese for strength, molybdenum for high-temperature strength and nickel for toughness.

The identification of wire electrodes for submerged arc welding is standardised in DIN EN

756, Figure 3.5.

During manufacture of fused welding fluxes the individual mineral constituents are, with

regard of their future composition, weighed and subsequently fused in a cupola or electric

furnace, Figure 3.6. In the dry granulation process, the melt is poured stresses break the

© ISF 2002

Wire Electrodes forSubmerged Arc Welding

br-er3-03e.cdr

commercial wireelectrodes

main alloying elementsMn Ni Mo Cr V

alloy type

Mn

MnMo

Ni

NiMo

NiV

NiCrMo

S1S2S3S4

0,51,01,52,0

S2MoS3MoS4Mo

1,01,52,0

0,50,50,5

S2Ni1S2Ni2

1,01,0

1,02,0

S2NiMo1S3NiMo1

1,01,5

1,01,0

0,50,5

S3NiV1 1,5 1,0 0,15

S1NiCrMo2,5S2NiCrMo1S3NiCrMo2,5

0,51,01,5

2,51,02,5

0,60,60,6

0,80,50,8

From a diameter of 3 mm upwards all wire electrodes haveto be marked with the following symbols:

S1

Si

Mo

S6:

:

:

I IIIIII_ _

Example:

S2Si:

S3Mo:

II

III

Figure 3.3

© ISF 2002

Properties and Application Areas for WireElectrodes in Submerged Arc Welding

br-er3-04e.cdr

DIN EN 756mat.-no.

Referenceanalysisapprox.weight %

Properties and application

S11.0351

CSiMn

= 0,08= 0,09= 0,50

CSiMn

= 0,11= 0,15= 1,50

CSiMn

= 0,10= 0,30= 1,00

CSiMnMo

= 0,10= 0,15= 1,00= 0,50

CSiMnNi

= 0,09= 0,12= 1,00= 1,20

CSiMnNi

= 0,10= 0,12= 1,00= 2,20

CSiMnMoNi

= 0,12= 0,15= 1,00= 0,50= 1,00

For lower welding joint quality requirements;in:boiler and tank construction, pipe production,structural steel engineering, shipbuilding

= 0,10= 0,10= 1,00

CSiMn

S21.5035

S31.5064

S2Si1.5034

S2Mo1.5425

S2Ni1

S2Ni2

S3NiMo1

For higher welding joint quality requirements; in:pipe production, boiler and tank construction,sructural steel engineering, shipbuilding.Fine-grain structural steels up to StE 380.

For high-quality welds with mediumwall-thicknesses.Fine-grain structural steels up to StE 420.

Especially suitable for welding of pipe steels,no tendency to porosity of unkilled steels.Fine-grain structural steels up to StE 420.

For welding in boiler and tank construction andpipeline production with creep-resistant steels.Working temperatures of up 500 °C. Suitablefor higher-strength fine-grain structural steels.

For welding low-temperature fine-grainstructural steels.Non-ageing.

Especially suitable for low-temperature welds.Non-ageing.

For quenched and tempered fine-grainstructural steels.Suitable for normalising and/or re-quenchingand tempering.

Figure 3.4


2005

crust into large fragments. During water granulation the melt hardens to form small grains

with a diameter of ap-

proximately 5 mm.

As a third variant, com-

pressed air is additionally

blown into the water tank

resulting in finely blistered

grains with low bulk weight.

The fragments or grains

are subsequently ground

and screened – thus bring-

ing about the desired grain

size.

Identification of a Wire Electrodein Accordance with DIN EN 756

br-er3-05e.cdr

Wi re e le c t ro de D I N EN 75 6 - S2Mo

DIN main no.

Symbols of the chemicalcomposition:S0, S1...S4, S1Si, S2Si, S2Si2, S3Si,S4Si, S1Mo,..., S4Mo, S2Ni1, S2Ni1.5,S2Ni2, S2Ni3, S2Ni1Mo, S3Ni1.5,S3Ni1Mo, S3Ni1.5Mo

Figure 3.5

© ISF 2002

Production of FusedWelding Fluxes

br-er3-06e.cdr

lime quarz rutile bauxite magnesite

silos

balance

roasting kiln

coke

coke

air

raw material

molten metal

tapping

coal-burning stoveelectrical furnace

granulation tub

foaming air

screen

balance

cylindrical crusher

drying oven

Figure 3.6

© ISF 2002

Production of AgglomeratedWelding Fluxes

br-er3-07e.cdr

rutile Mn - ore fluorspar magnesite alloys

sintering furnace

silosball mill

balance

mixer

dish granulator

gas

drying oven

heat treatment furnace

cooling pipe

screen

balance

Figure 3.7


2005

During manufacture of agglomerated weld

fluxes the raw materials are very finely

ground, Figure 3.7. After weighing and with

the aid of a suitable binding agent (water-

glass) a pre-stage granulate is produced in the

mixer.

Manufacture of the granulate is finished on a

rotary dish granulator where the individual

grains are rolled up to their desired size and

consolidate. Water evaporation in the drying

oven hardens the grains. In the annealing fur-

nace the remaining water is subsequently re-

moved at temperatures of between 500°C and

900°C, depending on the type of flux.

The fused welding fluxes are characterised by

high homogeneity, low sensitivity to moisture,

good storing properties and high abrasion re-

sistance. An important advantage of the agglomerated fluxes is the relatively low manufactur-

ing temperature, Figure 3.8. The technological properties of the welded joint can be improved

by the addition of temperature-sensitive deoxidation and alloying constituents to the flux. Ag-

glomerated fluxes have, in

general, a lower bulk weight

(lower consumption) which

allows the use of compo-

nents which are reacting

among themselves during

the melting process. How-

ever, the higher susceptibil-

ity to moisture during stor-

age andprocessing has to

be taken intoconsideration. Different Welding Flux Types

According to DIN EN 760

br-er3-09e.cdr

MS

CS

ZS

RS

AR

AB

AS

AF

FB

Z

MnO + SiOCaO

2 min. 50%max. 15%

manganese-silicate

CaO + MgO + SiOCaO + MgO

2 min. 55%min.15%

calcium-silicate

ZrO + SiO + MnOZrO

2 2

2

min. 45%min. 15%

zirconium-silicate

TiO + SiOTiO

2 2

2

min. 50%min. 20%

rutile-silicate

Al O + TiO2 3 2 min. 40% aluminate-rutilel

Al O + CaO + MgOAl OCaF

2 3

2 3

2

Al O + SiO + ZrOCaF + MgOZrO

2 3 2 2

2

2

Al O + CaF2 3 2

CaO + MgO + CaF + MoSiOCaF

2

2

2

min. 40%min. 20%max. 22%

aluminate-basic

min. 40%min. 30%min. 5%

aluminate-silicate

min. 70% aluminate-fluoride-basic

min. 50%max. 20%min. 15%

fluoride-basic

other compositions

Figure 3.9

© ISF 2002

Properties of Fused andAgglomerated Welding Fluxes

br-er3-08e.cdr

Properties

uniformity of grainsize distribution

grain strength

homogeneity

susceptibilityto moisture

storing properties

resistance to dirt

current carrying capacity

slag removability

high-speed weldingproperties

multiple-wire weldability

flux consumption

1)assessment : -- bad, - moderate, + good, ++ very good

2)core agglomerated flux

Fused fluxes1) Agglomerated

fluxes1)

+/++

+/++

+/++

+/++

+/++

+/++

-/++

-/+

-/++

-/++

-/++

-- /++2)

+/++

+/++

+/++

+/++

+/++

--/+

-/+

-/+

-/++

+/++

Figure 3.8


2005

The SA welding fluxes are, in accordance with

their mineralogical constituents, classified into

nine groups, Figure 3.9. The composition of the

individual flux groups is to be considered as in

principle, as fluxes which belong to the same

group may differ substantially with regards to

their welding or weld metal properties.

In addition to the groups mentioned above

there is also the Z-group which allows free

compositions of the flux.

The calcium silicate fluxes are recognized by

their effective silicon pickup. A low Si pickup

has low cracking tendency and liability to rust,

on the other hand the lower current carrying

capacity of these fluxes has to be accepted.

A high Si pickup leads to a high current cur-

rying capacity up to 2500 A and a deep

penetration. Aluminate-basic fluxes have,

due to the higher Mn pickup, good mechani-

cal properties. With the application of wire

electrodes, as S1, S2 or S2Mo, a low crack-

ing tendency can be obtained.

Fluoride-basic fluxes are characterised by

good weld metal impact values and high

cracking insensitivity. Figures 3.10a and

3.10b show typical properties and applica-

tion areas for the different flux types.

© ISF 2002

Classification of Fluxes for SAWelding According to DIN EN 760 (I)

br-er3-10ae.cdr

MS - high manganese and silicon pickup- restricted toughness values- high current carrying capacity/ high weld speed- unsusceptible to pores and undercuts- unsuitable- suitable for high-speed welding and fillet welds

for thick parts

CS acidic types

basic types

- highest current carrying capacity of all fluxes- high silicon pickup- suitable for welding by the pass/ capping method of thickparts with low requirements

- low silicon pickup- suitable for multiple pass weldingcurrent carrying capacity decreases with increaseingbasicity

ZS - high-speed welding of single-pass welds

RS - high manganese pickup/ high silicon pickup- restricted toughness values of the weld metal- suitable for single and multi wire welding- typical: welding by the pass/ capping pass method

AR - average manganese and silicon pickup- suitable for a.c. and d.c.- single and multi wire welding- application fields: thin-walled tanks, fillet welds forstructural steel construction and shipbuilding

Figure 3.10a

© ISF 2002

Classification of Fluxes for SA WeldingAccording to DIN EN 760 ( )II

br-er3-10be.cdr

AB - medium manganese pickup- good weldability- good toughness values in welding by the pass/ cappingpass method

- application field:unalloyed and low alloyed structural steels- suitable for a.c. and d.c.- applicable for multilayer welding or welding by thepass/ capping pass method

AS - mainly neutral metallurgical behavior- manganese burnoff possible- good weld appearance and slag removability- to some degree suitable for d.c.- recommended for multi layer welds for high toughnessrequirements

- application field: high-tensile fine grain structural steels,pressure vessels, nuclear- and offshore components

- mainly neutral metallurgical behaviour- however, manganese burnoff possible- highest toughness values right down to very lowtemperatures

- limited current carrying capacity and welding speed- recommended for multi layer welds- application field: high-tensile fine-grain structural steeels

FB

AF - suitable for welding stainless steels and nickel-base alloys- neutral behaviour as regards Mn, Si and otherconstituents

Z - all other compositions

Figure 3.10b


2005

Figure 3.11 shows the identification of a welding flux according to DIN EN 760 by the ex-

ample of a fused calcium silicate flux. This type of flux is suitable for the welding of joints as

well as for overlap welds. The flux can be used for SA welding of unalloyed and low-alloy

steels, as, e.g. general structural steels, as well as for welding high-tensile and creep resis-

tant steels. The silicon

pickup is 0.1 – 0.3% (6),

while the manganese

pickup is expected to be

0.3 – 0.5% (7). Either d.c.

or a.c. can be used, as, in

principle, a.c. weldability

allows also for d.c. power

source. The hydrogen con-

tent in the clean weld

metal is lower than the

10 ml/100 g weld metal.

The flux classes 1-3 (table 1) explain the suitability of a flux for welding certain material

groups, for welding of joints and for overlap welding. The flux classes also characterise the

metallurgical material be-

haviour. In table 2 defines

the identification figure for

the pickup or burn-off be-

haviour of the respective

element. Table 4 shows

the gradation of the dif-

fusible hydrogen content

in the weld metal, Figure

3.12.

Identification of a Welding FluxAccording to DIN EN 760

br-er3-11e.cdr

we l d i ng f l ux D I N E N 76 0- S F C S 1 67 AC H 10

DIN main no.

flux/SA welding

method of manufacture F fused A agglomerated M mechanically mixed flux

flux type(figure 3.9)

flux class 1-3 (table 1)

metallurgicalbehaviour (table 2)

hydrogen content (table 4)

type of current

Figure 3.11

Parameters for Flux IdentificationAccording to DIN EN 760

br-er3-12e.cdr

unalloyed andlow-alloyed steel

generalstructural steel

high-tensile & creepresistant steels

welding of joints

hardfacing

stainless and heatresistant steelsCr- & CrNi steels

pickup of elementsas C, Cr, Mo

flux class1 2 3

table 1

table 2

metallurgialbehaviour

identificationfigure

proportion flux inall-weld metal

%

1234

over 0,70,5 up to 0,70,3 up to 0,50,1 up to 0,3

burnoff

5pickup orburnoff

0 up to 0,1

6789

0,1 up to 0,30,3 up to 0,50,5 up to 0,7over 0,7

pickup

table 4

identificationhydrogen content

ml/100g all-weld metalmax.

H5

H10

H15

5

10

15

Figure 3.12


2005

Figure 3.13 shows the identification of a wire-flux combination and the resultant weld

metal. It is a case of a combination for multipass SA welding where the weld metal shows a

minimum yield point of 460

N/mm² (46) and a minimum

metal impact value of 47 J at

–30°C (3). The flux type is

aluminate-basic (AB) and is

used with a wire of the qual-

ity S2.

The tables for the identifica-

tion of the tensile properties

as well as of the impact en-

ergy are combined in Figure

3.14.

The chemical composition of the weld metal and the structural constitution are dependent on

the different metallurgical reactions during

the welding process as well as on the used

materials, Figure 3.15. The welding flux influ-

ences the slag viscosity, the pool motion and

the bead surface. The different combinations

of filler material and welding flux cause, in di-

rect dependence on the weld parameters (cur-

rent, voltage), a different melting behaviour

and also different chemical reactions. The di-

lution with the base metal leads to various

strong weld pool reactions, this being depend-

ent on the weld parameters.

The diagram of the characteristics for 3 dif-

ferent welding fluxes assists, in dependence

of the used wire electrodes, to determine the

pickup and burn-off behaviour of the element

Identification of a Wire-Flux CombinationAccording to DIN EN 756

br-er 3-13e.cdr

chemicalcomposition of the wire electrode

wi re - f l ux c om bi na t i onD I N EN 756 - S 4 6 3 AB S2

standard no.

wire electrode and/orwire-flux combinationfor submerged arcwelding

strength andfracture strain

(table1 and 2)

impact energy(table 3)

type of flux(figure 3.10)

Figure 3.13

© ISF 2002

Parameter for Weld Metal IdentificationAccording to DIN EN 756

br-er3-14e.cdr

table 2

identifi-cation

minimum base metalyield strength

N/mm2

minimum tensilestrengthN/mm2

2T

3T

4T

5T

275

355

420

500

370

470

520

600

Identification for strength properties of welding by thepass/ capping pass method welded joints

identification minimum yield pointn/mm2

tensile strengthN/mm2

minimum fracture strain%

440 up to 570

470 up to 600

500 up to 640

530 up to 680

560 up to 720

355

380

420

460

500

35

38

42

46

50

22

20

20

20

18

table 1 Identification for strength properties of multipass weld joints

table 3Identification for the impact energy of clean all-weld metal or of welding bythe pass/ capping pass method welded joints

Z

nodemands

A 0 2 3 4 5 6 7 8

-80-70-60-50-40-30-200+20

identification

temp. for minimumimpact energy 47J

°C

Figure 3.14


2005

manganese, Figure 3.16.

For example: A welding

flux with the mean charac-

teristic and when a wire

electrode S3 is used, has a

neutral point where neither

pickup nor burn-off occur.

The pickup and burn-off

behaviour is, besides the

filler material and the weld-

ing flux, also directly de-

pendent on the welding

amperage and welding

voltage, Figure 3.17. By the example of the selected flux a higher welding voltage causes a

more steeply descending manganese characteristic at a constant neutral point. Silicon pickup

increases with the increased voltage. The influence of current and voltage on the carbon con-

tent is, as a rule, negligible.

Inversely proportional to the voltage is the rising characteristic as regards manganese in de-

pendence on the welding

current, Figure 3.18.

Higher currents cause the

characteristic curve to flat-

ten. As the welding volt-

age, the welding current

also has practically no in-

fluence on the location of

the neutral point. Silicon

pickup decreases with in-

creasing current intensity. Manganese-Pickup and Manganese-BurnoffDuring Submerged Arc Welding

br-er 3-16e.cdr

S1

1,0% 3,0% Mn in wire2,0%

Mn-burnoff

Mn-pickup

S2 S3 S4 S5 S6

Figure 3.16

Metallurgical Reactions DuringSubmerged Arc Welding

br-er 3-15e.cdr

droplet reaction

dilution

weld pool reaction

welding flux welding filler metal

slag

weld metal

base metal

welding data

welding data

welding data

Figure 3.15


2005

The Mn-content of the weld metal can be de-

termined by means of a welding flux dia-

gram, Figure 3.19.

In this example, the two points on the axis

which determine the flux characteristic are

defined for the parameters 580A welding cur-

rent and 29V welding voltage, with the aid of

the auxiliary straight line and the neutral point

curve (MnNP). In this case, the two points are

positioned at 0.6% ∆Mn and 1.25% MnSZ.

Dependent on the manganese content of the

used filler material, the pickup or burn-off

contents can be recognized by the reflection

with respect to the characteristic line (0.38%

Figure 3.19


© ISF 2006

Pickup and Burnoff Behaviour in Dependenceon Welding Voltage and Wire Electrode

br-er3-17e.cdr

weld flux LW 280 current intensity 580 Awelding speed 55 cm/min

(DIN EN 760 SF CS 1 76 AC H 10)

neutral point

% Mn wire

% Si wire

% C wire

pic

ku

p/

bu

rno

ff

X in

we

igh

t %

�

33 V 36 V

25 V

0,5 1,0 2,0 2,5

27 V

29 V

25 V

36 V

0,05 0,1 0,15 0,2 0,25 0,3 0,35 0,4 0,45

0,05 0,15 0,20 0,25

25 - 36 V

0,6

% Mn

0,2

0

-0,2

-0,4

-0,6

0,6

% Si

0,2

0

-0,2

-0,4

0,05

0

-0,05

-0,10

-0,15

© ISF 2006

Pickup and Burnoff Behaviour in Dependenceon Welding Current and Wire Electrode

br-er3-18e.cdr

weld flux LW 280 arc voltage 29 Vwelding speed 55 cm/min

(DIN EN 760 SF CS 1 76 AC H 10)

pic

ku

p/

bu

rno

ff

X in

we

igh

t %

�

neutral point

% Mn wire

% Si wire

% C wire

% XSZ

0,6

% Mn

0,2

0

-0,2

-0,4

-0,6

0,6

% Si

0,2

0

-0,2

-0,4

0,05

0

-0,05

-0,10

-0,15

450 A

650 A 580 A

700 A

0,5 1,0 2,0 2,5

800 A

450 A

800 A

800 A

0,15 0,20 0,25

450 A

0,05 0,1 0,15 0,2 0,25 0,3 0,35 0,4 0,45

© ISF 2002

Welding Flux Diagramm for Determinationof the Mn Content in the Weld Metal

br-er3-19e.cdr

flux diagramm LW 280

manganese(DIN EN 760 SF CS 1 76 AC H 10),

wire electrode 4 mm acc. to Prof. Thier

= 580 A U = 29 V Mn = 0.48 % Mn Mn = 1.69 % Mn

example: I

SZ1

SZ2

Ø


2005

Mn-pickup with a wire containing 0.5%Mn, 0.2% Mn-burnoff with a wire containing 1.75%Mn).

The structure of the characteristic line for the

determination of the silicon pickup con-

tent, is, in principle, exactly the same as de-

scribed above, Figure 3.20. As silicon has

only pickup properties and therefore no neu-

tral point exists, the second auxiliary straight

line must be considered for the determination

of the second characteristic line point.

Weld preparations for multipass fabrication

are dependent on the thickness of the plates

to be welded, Figure 3.21. If no root is

planned during weld preparation and also no

support of the weld pool is made, the root

pass must be welded using low energy input.

When welding very thick plates which are accessible

from both sides, the dou-

ble-U butt weld may be

applied, Figure 3.22. Be-

fore the opposite side is

welded, the root must be

milled out (goug-

ing/sanding). This type of

weld cannot be produced

by flame cutting and is, as

milling is necessary, more

expensive, although exact

weld preparation and cor-

rect selection of the weld-

ing parameters lead to a

high weld quality.

Welding Procedure Sheets for Single-V Butt Welds, Single-YButt Welds with Broad Root Faces and Double-V Butt Welds

br-er 3-21e.cdr

preparation geometry weld buildup

manual metal arc welding

manual metal arc weldingmanual metal arc welding

andSASA

SASASASA

SASASASA

Figure 3.21

Figure 3.20

© ISF 2006

Welding Flux Diagram for Determinationof the Si Content in the Weld Metal

br-er3-20e.cdr

flux diagramm LW 280

silicon(DIN EN 760 SF CS 1 76 AC H 10),

wire electrode 4 mm acc. to Prof. Thier

= 580 A U = 29 V Si = 0.16 % Si

example: I

SZ

Ø

auxiliary

straight line

auxiliary

straight line


2005

Another variation of heavy-

plate welded joints is the

so-called „steep single-V

butt weld”, Figure 3.23.

The very steep edges keep

the welding volume at a

very low level. This tech-

nique, however, requires

the application of special

narrow-gap torches. The

geometry during slag de-

tachment and also during

reworking weld-related de-

fects may cause problems. Here, high demands are made on torch manipulation and process

control. Special narrow-gap welding fluxes facilitate slag removal.

The most important weld-

ing parameters as regards

weld bead formation are

welding current, voltage

and speed, Figure 3.24. A

higher welding current

causes higher deposition

rates and energy input,

which leads to reinforced

beads and a deeper pene-

tration. The weld width re-

mains roughly constant.

The increased welding volt-

age leads to a longer arc

which also causes the bead to be wider. The change in welding speed causes - on both sides

of an optimum - a decrease of the penetration depth. At lower weld speeds, the weld pool

running ahead of the welding arc acts as a buffer between arc and base metal. At high

speeds, the energy per unit length decreases which leads, besides lower penetration, also to

narrower beads.

© ISF 2002

Welding Procedure Sheetfor Double-U Butt Welds

br-er3-22e.cdr

preparation geometry weld buildup

manual metal arc weldingturning and sandingmanual metal arc welding

turn

turn

turn

side 1

side 2

SASA

SASA

SASA

SASA

Figure 3.22

© ISF 2002

Welding Procedure Sheetfor Square-Edge Welds

br-er3-23e.cdr

GMA welding

GMA welding

SA welding

SA welding

oscillated

Figure 3.23


2005

Weld flux consumption is dependent on the selected weld type, Figure 3.25. Due to geo-

metrical shape, the flux consumption of a fillet weld is significantly lower than that of a butt

weld. Because of their lower bulk weight, the specific consumption of agglomerated fluxes is

lower than that of fused

fluxes.

Two different control con-

cepts allow the regulation

of the arc length (the prin-

ciple is shown in Figure

3.26). The application of

the appropriate control sys-

tem is dependent on the

available power source

characteristics.

© ISF 2002

Control of the Arc Length

br-er3-26e.cdr

1 2 3

direction of welding

L1

L2

L3

Figure 3.26

© ISF 2002

Welding Flux Consumption in Dependenceon Current Intensity and Seam Shape

br-er3-25e.cdr

2,4

2,2

2,0

1,8

1,6

1,6

1,4

1,4

1,2

1,2

1,0

1,0

0,8

0,8

0,6

0,6

0,4

0,4

0,2

0,2

0

400

400

0500

500

600

600

700

700

800

800

900

900

1000

1000

1100

1100

consum

ption k

g flu

x / k

g w

ire

consum

ption k

g flu

x/ kg w

ire

A) flat weld - I square butt joint

current intensity (A)

current intensity (A)

B) fillet weld

fused composition fluxes

fused composition fluxes

agglomerated fluxes

agglomerated fluxes

Figure 3.25

© ISF 2002

Influence of the Weld Parameterson Penetration Depth and Weld Width

br-er3-24e.cdr

constant:

plate thickness:wire electrode:flux:

welding current ( )I

constant:

arc voltage (U)

constant:

welding speed (v)

penetr

ation d

epth

tin

mm

p

weld

wid

th w

in m

m

w

tp

I

w

tp

I

w

te

12

10

8

6

4

2

0

12

10

8

6

4

2

0

12

10

8

6

4

2

0

30

20

10

30

20

10

400 500 600 700 800 Amp.

28 30 32 34 36 38 40 Volt

30 40 50 60 70 80 90 100 110 cm/min

U = 32 Voltv = 60 cm/min

I = 600 Amp.v = 60 cm/min

I = 600 Amp.U = 32 Volt

25 mm4 mm

MS-Typ

Figure 3.24


2005

The external regulation of the arc length by

the control of the wire feed speed requires a

power source with a steeply descending char-

acteristic, Figure 3.27. In this case, the short-

ening of the arc caused by some

process disturbance, entails a strong voltage

drop at a low current rise. As a regulated quan-

tity, this voltage drop reduces the wire feed

speed. Thus, the initial arc length can be regu-

lated at an almost constant deposition rate. In

contrast, the internal regulation effects, when

the arc is reduced, a strong current rise at a

low voltage drop (slightly descending charac-

teristic). At a constant wire feed speed the ini-

tial arc length is independently regulated by the

increased burn-off rate which again is a conse-

quence of the high current.

The reaction of the internal regulation to

process disturbance is very fast. This process

is self regulating and does not require any

machine expenditure.

In submerged arc welding of butt joints, it is,

depending on the weld preparation, neces-

sary to support the liquid weld pool with a

backing, Figure 3.28. This is normally done

with either a ceramic or copper backing with a

flux layer or by a backing flux. Dependent on

the shape of the backing bar, direct formation

of the underside seam can be achieved.

When welding circumferential tubes, the in-

clination angle of the electrode has a direct

br-er3-28e.cdr

Examples of WeldPool Backups

backing flux

ceramic backing bar

flux copper backing

Figure 3.28

© ISF 2002

Control System forConstant Length of Arc

br-er3-27e.cdr

A

A´

I

I

I´

I´

U

U

U0

U0

US

US

ID

ID

IS

IS IK I

I

external regulation D U-regulation)(

AA´

UD

UD

internal self regulation D I-regulation)(

Figure 3.27


2005

influence onto the formation of the weld bead,

Figure 3.29. For external as well as for internal

tube welds, the best weld shapes may be ob-

tained with an adjusted angular position of the

torch. If the advance is too low, the molten

bath runs ahead and produces a narrow weld

with a medium-sized ridge, too high an ad-

vance causes the flowback of the molten bath

and a wide seam with a formed trough in the

centre. The processes described here for ex-

ternal tube welds are, the other way round,

also applicable to internal tube welds.

To increase the efficiency of submerged

arc welding, different process variations are

applied, Figure 3.30. In multiwire welding,

where up to 6 wires are used, each welding

torch is operated from a separate power

source. In twin wire welding, two wire electrodes are connected in one torch and supplied

from one power source. Dependent on the application, the wires can be arranged in a parallel

or in a tandem.

In submerged arc welding

with iron powder addition

can the deposition rate be

substantially increased at

constant electrical parame-

ters, Figure 3.31. The in-

creased deposition rate is

realised by either the addi-

tion of a currentless wire

(cold wire) or of a pre-

heated filler wire (hot wire).

The use of a rectangular

Process Variations ofSubmerged-Arc Welding

single wire tandem

parallel twinwire

tandem, twinwire


Figure 3.30


b2 b3b1

t 1 t 2 t 3

a3

a2

a1= 0°

0° - 30°

inclusion

Wire Position in SA-Welding

for Circumferential Tube Welds

Figure 3.29


2005

strip instead of a wire elec-

trode allows a higher cur-

rent carrying capacity and

opens the SA method also

for the wide application

range of surfacing.

However, the mentioned

process variations can be

combined over wide

ranges, where the elec-

trode distances and posi-

tions have to be appropri-

ately optimised, Figure

3.32. Current type, polarity, geometrical co-ordination of the individual weld heads and the

selected weld parameters also have substantial influence on the weld result.

Process Variations ofSubmerged-Arc Welding

iron powder/chopped wire

hot wire

cold wire

strip


Figure 3.31


tandem welding

three-wire welding

three-wire, hot wirewelding

four-wire welding

1. WH

1. WH

1. WH

2. WH

2. WH 3. WHHW

=

=

=

~

~

~~~~

3. WH

~

~

2. WH

~

65°

65°

12..16

12..1635

10 101535 12..16

75°80°

1215 18

Position of Wire Electrode inSubmerged-Arc Multi-Wire Welding

Figure 3.32


0 500 1000 1500 2000 2500 A 35000

10

20

30

40

50

60

70

80

kg/h

100

de

po

sitio

n r

ate

current intensity

we

ld m

eta

l voltage = 30 V

speed = 40 cm/min

wire protrusion = 10dlength

current intensity

Æ3,0 mm

Æ 4,0 mm

Æ5,0 mm

12

9

6

30

300 400 500 600 A 800

~~

kg/h

single wire+ metal powder

single wire+ hot wire

double wire

single wiretandem

three-wire

four-wire

Application Fields forSubmerged-Arc Process Variants

Figure 3.33


2005

The description of these individual process variations of submerged arc welding shows that

this method can be applied sensibly and economically over a very wide operating range, Fi-

gure 3.33. It is a high-efficiency welding process with a deposition rate of up to 100 kg/h.

Due to large molten pools and flux application positional welding is not possible.

When more than one wire

is used in order to obtain a

high deposition rate, arc

interactions occur due to

magnetic arc blow, Fig-

ure 3.34. Therefore, the

selection of the current

type (d.c. or a.c.) and also

sensible phase displace-

ments between the indi-

vidual welding torches are

very important.


+ +

( )_ ( )_

+ _ + ~

__ +( ) ( )_ _

elektrode

arc

workpiece

+ +

Magnetic Interaction of Arcs at SA Tandem Welding

Figure 3.34

4.

TIG Welding and

Plasma Arc Welding

4. TIG Welding and Plasma Arc Welding 49

2005

TIG welding and plasma welding belong to the group of the gas-shielded tungsten arc weld-

ing processes, Figure 4.1. In the gas-shielded tungsten arc welding processes mentioned in

Figure 4.1, the arc burns between a non- consumable tungsten electrode and the work-

piece or, in plasma arc weld-

ing, between the tungsten

electrode and a live copper

electrode inside the torch.

Exclusively inert gases (Ar,

He) are used as shielding

gases.

The potential curve of the

ideal arc, as shown in Figure

4.2, can be divided into

three characteristic sectors:

1.cathode- drop region

2.arc

3. anode-drop region

In the cathode-drop region

almost 50% of the total

voltage drop occurs over a

length of 10-4 mm.

A similarly high voltage drop

occurs in the anode-drop

region, here, however, over

a length of 0.5 mm. The

voltage drop on the remain-

ing arc length is compara-

tively low. Main energy con-

version occurs accordingly

in the anode-drop and cathode-drop region.

Figure 4.3 shows the potential distribution by the example of a real TIG arc under the influ-

ence of different shielding gases. UA and UK have different values, the potential curve in the

© ISF 2002

Classification of Gas-Shielded Arc Welding acc. to DIN ISO 857

br-er4-01e.cdr

Plasma arc welding with

semi-transferred arc

Plasma arc welding

with transferred arc


non-transferred arc

CO welding2 Mixed gas welding

narrow-gap gas-shielded arc welding

plasma metalarc welding

electrogas welding

Metal inert-gas welding

MIG

Metal active gas welding

MAG

Gas-shielded arc welding

Tungsten hydrogen welding

Tungsten plasma welding with

electrode

Tungsten inert-gas welding

TIG

Gas-shielded metal arc welding

GMAW

Gas-shielded arc welding

tungsten

Figure 4.1

© ISF 2002

Arc Potential Curve

br-er4-02e.cdr

U

V

20

10

01 2 3 4 5

10-4

0,5

l

US

lmm

K

L

A

+-

A:

K:

L:

l:

anode spot (up to 4000°C)

cathode spot (approx. 3600°C)

arc column (4500-20000°C)

arc length

arc potential curve(example)

Figure 4.2


2005

arc is not exactly linear. There is no discernible expansion of the cathode-drop and anode-

drop region.

The electrical characteris-

tics of the arc differ, de-

pending on the selected

shielding gas, Figure 4.4. As

the ionisation potential of

helium in comparison with

argon is higher, arc voltage

must necessarily be higher.

The temperature distribu-

tion of a TIG arc is shown in

Figure 4.5.


arc

voltag

e

25

20

15

10

arc

le

ngth

4

2

4

2

helium

argon

weld current

50 100 150 200 250 3500

mmV

A

Figure 4.4

© ISF 2002br-er4--03e.cdr

X

X

0

0

1

1

2

2

3

3

4

4

6

6

20

40

10

20

5

10

U

U

anode

anode

cathode

cathode

U = 6,5 VK

U = 6,5 VK

U = 3,5 VA

U = 6,1 VA

Argon

60 A

Helium

60 AV

V

mm

mm

ARC

ARC

ARC

ARC

Figure 4.3

© ISF 2002

Temperature Distribution in aTIG Arc (at I=100 A)

br-er4-05e.cdr

TIG cathode

10

00

0 K

9 0

00 K

8 0

00 K

x

x

x

x

x

x

x

x

x

x

x

x

x

x

x

x

x

x

x

x

x

x

anodespot

weld pool

2

mm

4

6

8

2

mm

4

6

8 4 3 2 1 0 1 2 mm 4

Figure 4.5


2005

In TIG welding just approximately 30% of the

input electrical energy may be used for

melting the base metal, Figure 4.6. Losses

result from the arc radiation and heat dissipa-

tion in the workpiece and also from the heat

conversion in the tungsten electrode.

Figure 4.7 describes the process principle

of TIG welding.

Figure 4.8 explains by an example the code

for a TIG welding wire, as stipulated in the

drafts of the European Standardisations.

A table with the chemical compositions of the

filler materials is shown in Figure 4.9.

According to Figure 4.10, a conventional

TIG welding installation

consists of a transformer, a

set of rectifiers and a torch.

For most applications an

electrode with a negative

polarity is used. However,

for welding of aluminium,

alternating current must be

used. For arc ignition a

high-frequency high volt-

age is superimposed and

causes ionisation between

electrode and workpiece.

© isf 2002

Tungsten Inert Gas Welding (TIG)

br-er4-07e.cdr

tungsten electrode

electric contact

shielding gas

shielding gas nozzle

filler metal

weld

arc

workpiece

welding powersource

Figure 4.7


melting of wire

welding direction

radiation

R.I2

P = U.I

thermal conductivity [W/m K]

fusion heat [kJ/kg]

specific heat [kJ/kg K]

Figure 4.6


2005

The central part of the

torch for TIG welding is

the tungsten electrode

which is held in a collet

inside the torch body, Fig-

ure 4.11. The hose pack-

age contains the supply

lines for shielding gas and

welding current. The

shielding gas nozzle is

mostly made of ceramic.

Manually operated torches

for TIG welding which are

used for high amperages

as well as machine torches for long duty cycles are water-cooled.

In order to keep the influence of torch distance variations on the current intensity and thus on

the penetration depth as low as possible, power sources used for TIG welding always have

a steeply dropping char-

acteristic, Figure 4.12.

The non-contact reigni-

tion of the A.C. TIG arc

after a voltage zero cross-

over requires ionisation of

the electrode-workpiece

gap by high-frequent

high voltage pulses, Fig-

ure 4.13.

© ISF 2002

Designation of a Tungsten InnertGas Welding Wire to EN 1668

br-er4-08e.cdr

identification of filler rod as an individual product: W2

chemical composition table

rods and wires for tig-welding

minimum impact energy value 47 J at -30°C

minimum weld metal yield point: 460 N/mm2

identification letter for TIG-welding

W 46 3 W2

Figure 4.8

© ISF 2002

Chemical composition offiller rods and wires for TIG-welding

br-er4-09e.cdr

Figure 4.9


2005

When argon is used as a

shielding gas, metals as,

for example, aluminium

and magnesium, which

have low melting points

and also simultaneously

forming tight and high melt-

ing oxide skins, cannot be

welded with a negative po-

larity electrode. With a

positive polarity, however,

a “cleaning effect” takes

place which is caused by

the impact of the positive

charged ions from the shielding gas atmosphere on the negative charged work surface, thus

destroying the oxide skin due to their large cross-section. However, as a positive polarity

© ISF 2002

Principle Structure of a TIG Welding Installation

br-er4-10e.cdr

selector switch

high-frequency choke coilfilte

r capacito

r

transformer

SC: scattering core for adjusting the characteristic curve

main

s

high voltage impulse generator~

O_

O+

rectifier

St

L1L2L3NPE

=

~

Figure 4.10

torch capwith seal

handle of the torch

control switch

control cable

shieldinggas supply

cooling watersupply

cooling waterreturn withwelding currentcable

torch bodywith cooling device

electrode collet

colletcase

tungsten electrode

gas nozzle

br-er4-11e.cdr © ISF 2002

Construction of a Water-CooledT TIG Welding orch for

Figure 4.11

© isf 2002br-er4-12e.cdr

current intensity

longer arc shorter arc

R and U rise R and Udrop

I drops I rises

voltage

U

arc length

long

sh

ort

increasing

increasing

decreasing

decreasingi

Figure 4.12


2005

would cause thermal overload of the electrode, these materials are welded with alternating

current.

However, this has a disturbing side-effect. The electron emission and, consequently, the cur-

rent flow are dependent on the temperature of the cathode.

During the negative phase on the work surface the emission is, due to the lower melting tem-

perature substantially lower than during the negative phase on the tungsten electrode. As a

consequence, a positively connected electrode leads to lower welding current flows than this

would be the case with a negatively connected electrode, Figure 4.14. A filter capacitor in the

welding current circuit fil-

ters out the D.C. compo-

nent which results in equal

half-wave components.

With modern transistorised

power sources which use

alternating current (square

wave) for a faster zero

cross-over, is duration and

height of the phase com-

ponents adjustable. The

electrode thermal stress

and the cleaning effect

may be freely influenced.

Figure 4.15 shows that the

thermal electrode load

can be recognized from the

shape of the electrode tip.

While the normal-load

negative connected elec-

trode end has the shape of

a pointed cone (point angle

approx. 10°), a flattened

electrode tip is the result

© isf 2002

Influence of the Half-Wave Componentsduring A.C. TIG Welding

br-er4-14e.cdr

smaller increasingheat load

of the electrode

cleaning effectlower stronger

ele

ctr

onic

con

tro

led

po

wer

sou

rce

witho

ut filte

rcapacito

r

bala

nce

d h

alf-w

ave c

om

po

nen

ts

ele

ctr

od

e p

ola

rity

time

time-

-

-

-

-

-

+

+

+

+

time- - -

+ +

with filt

er

capacitor

current

a

time

time

+ + +

- - -

+ + +

- - -0

0

time- - -

+ +

current

a

0

weld seam width

Figure 4.14

© ISF 2002

reignition of the arcby voltage impulses

++

- -

time

vo

ltage

Reignition of the A.C. Arc Through Voltage Impulses

Tungsten

br-er4-13e.cdr

A.C.

Figure 4.13


2005

from a.c. welding (higher thermal load by positive half-waves).The tip of a thermally over-

loaded electrode is hemispherical and leads to a stronger spread of the arc and thus to wider

welds with lower penetration.

All fusion weldable materi-

als can be joined using the

TIG process; from the eco-

nomical point of view this

applies especially to plate

thickness of less than

5 mm. The method is,

moreover, predestined for

welding root passes

without backing support,

Figure 4.16.


Applications of TIG Welding

materials:- steels, especially high-alloy steelaluminium and aluminium alloys- copper and copper alloys- nickel and nickel alloys- titanium- circonium- tantalum

workpiece thickness: - 0,5 - 5,0 mm

weld types: - plain butt weld, V-type welds, flanged weld, fillet weld - all positions - surfacing

application examples: - tube to tube sheet welding - orbital welding - root welding

Figure 4.16

Electrode Shapesfor TIG Welding

overloaded electrode

electrode for D.C. welding(direct current)

electrode for A.C. welding(alternating current)

influence of the electrodeshape on penetration profile


Figure 4.15

© ISF 2002

Flow Chart of TIG Orbital Welding

br-er4-17e.cdr

preflow of theshielding gas

postflow of theshielding gas

movement in switch-on position

current decay overlappulsingpreheatingrise ofcurrent

shieldinggas

orbitalmovement

welding current

360 00

Figure 4.17


2005

For circumferential welding of fixed pipes, the TIG orbital welding method is applied. The

welding torch moves orbitrally around the pipe, i.e., the pipe is welded in the positions flat,

vertical down, overhead,

vertical-up and also inter-

pass welding is applied.

Moreover, a defect-free

weld bead overlap must be

achieved. Orbital welding

installations are equipped

with process operational

controls which determine

the appropriate process

parameters, Figure 4.17.

In plasma arc welding

burns the arc between the

tungsten electrode (- pole) and the plasma gas nozzle (+ pole) and is called the “non-

transferred” arc, Figure 4.18. The non-transferred arc is mainly used for metal-spraying and

for the welding of metal-foil strips.

In plasma arc welding with transferred arc burns the arc between the tungsten electrode (-

pole) and the workpiece (+

pole) and is called the

“transferred arc”, Figure

4.19. The plasma gas con-

stricts the arc and leads to a

more concentrated heat in-

put than in TIG welding and

allows thus the exploitation

of the “keyhole effect”.


transferred arc is mainly

used for welding of joints.

© isf 2002

Plasma Arc Welding with Transferred Arc

br-er4-19e.cdr

Ignitiondevice

weldingpowersource

work piece

seam

plasma gas

plasma gas nozzle

transferredarc

shielding gas

contact tube

fillermaterial


tungstenelectrode

Figure 4.19

© isf 2002

Plasma Arc Welding withNon-Transferred Arc

br-er4-18e.cdr

workpiece

surface weld

plasma gas

plasma gas nozzle

non-transferredarc

shielding gas nozzleshielding gas

contact tube tungsten electrode

Ignitiondevice

weldingpowersource

fillermaterial

Figure 4.18


2005


semi-transferred arc is a

combination of the two

methods mentioned above.

This process variant is

used for microplasma

welding, plasma-arc pow-

der surfacing and weld-

joining of aluminium, Fig-

ure 4.20

The plasma welding

equipment includes, be-

sides the water-cooled welding torch, a gas supply for plasma gas (Ar) and shielding gas

(ArH2-mixture, Ar/He mixture or Ar); the gas supply is, in most cases, separated, Figure 4.21.

The copper anode and the additional focusing gas flow constrict the plasma arc which leads,

© ISF 2002

Plasma Arc Welding with Semi-Transferred Arc

br-er4-20e.cdr

surface weld

plasma gas

plasma gas nozzle

non-transferredarc

transferred arc

shielding gas

conveying gas andwelding filler (powder)

contact tube

workpiece


tungstenelectrode

weldingpowersource

ignitiondevice

Figure 4.20


Figure 4.21


Figure 4.22


2005

in comparison with TIG

welding, to a more concen-

trated heat input and thus to

deeper penetration. An arc

that has been generated in

this way burns more stable

and is not easy to deflect,

as, for example, at work-

piece edges, Figure 4.21.

The TIG arc is cone shaped

or bell shaped, respec-

tively, and has an aperture

angle of 45°. The plasma

arc, in comparison, burns highly concentrated with almost parallel flanks, Figure 4.22.

The shielding gas used in plasma arc welding

exerts, due to its thermal conductivity, a deci-

sive influence onto the arc configuration.

The use of a mixture of argon with hydrogen

results in the often desired cylindrical arc

shape, Figure 4.23.

In plasma arc welding of plates thicker than

2.5mm the so-called “keyhole effect” is util-

ised, Figure 4.24. The plasma jet penetrates

the material, forming a weld keyhole. During

welding the plasma jet with the keyhole

moves along the joint edges. Behind the

plasma jet as result of the surface tension and

the vapour pressure in the keyhole, the liquid

metal flows back together and the weld bead

is created.

© ISF 2002

Arc Shapes in Microplasma Weldingwith Different Shielding Gases

br-er4-23e.cdr

Arc shapes of shielding gases:

argon with 6,5% hydrogen

helium

50% argon, 50% helium

argon

plasma gas: argonarc

le

ngth

Figure 4.23


plasma torch

weld (seam)

welding direction

keyhole

weldsurface

root

Figure 4.24


2005

Very thin sheets and metal-foils can be welded using microplasma welding with amperages

between 0.05 and 50 A.

Figures 4.25 and 4.26 show

these application exam-

ples: The circumferential

weld in a diaphragm disk

with a wall thickness of

0.15mm and the joining of

fine metal grids made of Cr-

Ni steel.

© ISF 2002

Microplasma Welding of a Diaphragm Disk Made of CrNi

br-er4-25e.cdr

Figure 4.25


Figure 4.26

5.

Gas– Shielded Metal Arc Welding

5. Gas-Shielded Metal Arc Welding 61

2005

The difference between gas-shielded metal arc welding (GMA) and the gas tungsten arc

welding process is the consumable electrode. Essentially the process is classified as metal

inert gas welding (MIG)

and metal active gas

welding (MAG). Besides,

there are two more process

variants, the electrogas

and the narrow gap weld-

ing and also the gas-

shielded plasma metal arc

welding, a combination of

both plasma welding and

MIG welding, Figure 5.1.

In contrast to TIG welding,

where the electrode is

normally negative in order to avoid the melting

of the tungsten electrode, this effect is ex-

ploited in MIG welding, as the positive pole is

strongly heated than the negative pole, thus

improving the melting characteristics of the

feed wire.

Figure 5.2 shows the principle of a GMA weld-

ing installation. The welding power source is

assembled using the following assembly

groups: The transformer converts the mains

voltage to low voltage which is subsequently

rectified.

Apart from the torch cooling and the shielding

gas control, the process control is the most

important installation component. The process

control ensures that once set welding data are

adhered to.

© ISF 2002

gas-shielded arc welding (SG)

Classification of Gas-ShieldedArc Welding Processes

br-er5-01e.cdr

gas-shielded metal-arc welding (GMAW)

tungsten gas-shielded welding

metal inert gas welding

(MIG)

plasma jetplasma

arcwelding(WPSL)

plasmaarc

welding

(WPL)

Narrow-gap gas-shielded arc

welding (MSGE)

electrogaswelding(MSGG)

plasma gasmetal arcwelding

(MSGP)

gas mixturemetal-arcwelding

(GMMA)

gas metal-arc COwelding

(MAGC)

2

hydrogentungsten arc

welding

(WHG)

plasmajet

welding

(WPS)

metalactive gaswelding

(MAG)

tungsteninert-gaswelding

(TIG)

tungstenplasmawelding

(WP)

consumable electrode non consumable electrode

Figure 5.1

wire feed unit

water cooling

shielding gascontrol device

control switch

cooling watercontrol

rectifier

transformer

welding power source

GMA Welding Installation


Figure 5.2


2005

A selection of common welding installation variants is depicted in Figure 5.3, where the

universal device with a separate wire feed housing is the most frequently used variant in the

industry.

Figure 5.4 shows in detail a manually operated inert-gas shielded torch with the common

swan-neck shape. A machine torch has no handle and its shape is straight or swan-necked.

The hose package contains the wire core and also supply lines for shielding gas, current and

cooling water, the latter for contact tube cooling. The current is transferred to the wire elec-

trode over the contact tube. The shielding gas nozzle is shaped to ensure a steady gas flow

in the arc space, thus protecting arc and molten pool against the atmosphere.

A so-called “Two-Wire-Drive” wire feed system is of the most simple design, as shown in

Figure 5.5. The wire is pulled off a wire reel and fed into the hose package. The wire trans-

port roller, which shows different grooves depending on the used material, is driven by an

electric motor. The counterpressure roller generates the frictional force which is needed for

wire feeding.


Manual Gas-Shielded Arc Welding Torch

1 torch handle 2 torch neck 3 torch trigger 4 hose package 5 shielding gas nozzle 6 contact tube 7 contact tube fixture 8 insulator 9 wire core10 wire guide tube11 wire electrode12 shielding gas supply13 welding current supply

Figure 5.4


Types of Welding Installations

compact device universal device

mini-spool device push-pull device

10, 20 or 30m 5 to 10m

3 to 5m5, 10 or 20m

3 to 5m

Figure 5.3


2005

More complicated but following the same operation principle is the “Four-Wire-Drive”, Fig-

ure 5.6. Here, the second pair of rollers guarantees higher feeding reliability by reducing the

risk of wheel slip. Another design among the wire feed drive systems is the planetary drive,

where the wire is fed in axial direction by the motor. A rectilinear rotation-free wire feed mo-

tion is the outcome of the

motor rotation and the an-

gular offset of the drive

rollers which are firmly

connected to the motor

shaft.

Figure 5.7 depicts the

metal transfer in the short

arc range. During the

burning phase of the arc,

material is molten and ac-


Wire Drives

4-roller drive

1 wire guide tube2 drive rollers3 counter pressure rollers4 wire guide tube

3 4 3

3

3

1

1

1

2 2

2

1 wire guide tube2 roller holding device3 drive rollers

planetary drive

direction of rotation

Figure 5.6


Wire Feed System

1

2

4 2

F

65

1 wire reel

2 wire guide tube

5 wire feed roll with a V-groove for steel electrodes

6 wire feed roll with a rounded groove for aluminium

3 wire transport roll

4 counter pressure roll

4 4 3

Figure 5.5

© ISF 2002

Short-Circuiting Arc Metal Transfer

br-er5-07e.cdr

1 ms

1 mm

time

time

weld

ing c

urr

ent

weld

ing v

oltage

Figure 5.7


2005

cumulates at the electrode end. The voltage drops slowly while the arc shortens. Electrode

and workpiece make contact and a short-circuit occurs. In the short-circuit phase is the liquid

electrode material drawn as

result of surface tension into

the molten pool. The nar-

rowing liquid root and the

rising current lead to a very

high current density that

causes a sudden evapora-

tion of the remaining root.

The arc is reignited. The

short-arc technique is par-

ticularly suitable for out-of-

position and root passes

welding.

© ISF 2002

Choke Effect

br-er5-08e.cdr

timetime

weld

ing

cu

rre

nt

weld

ing

cu

rre

nt

choke effectlow medium

Figure 5.8


Long Arc

we

ldin

g v

olta

ge

weld

ing

cu

rre

nt

time

time

Figure 5.9


Spray Arc

weld

ing v

olta

ge

weld

ing c

urr

ent

time

time

Figure 5.10


2005

The limitation of the rate of the current rise during the short-circuit phase with a choke

leads to a pointed burn-off process which is smoother and clearly shows less spatter forma-

tion, Figures 5.8

In shielding gases with a

high CO2 proportion a

long arc is formed in the

upper power range, Figure

5.9. Material transfer is

undefined and occurs as

illustrated in Figures 5.13

and 5.14. Short-circuits

with very strong spatter

formation are caused by

the formation of very large

droplets at the electrode

end.

If the inert gas content of the shielding gas

exceeds 80%, a spray arc forms in the upper

power range, Figure 5.10. The spray arc is

characterised by a non-short-circuiting and

spray-like material transfer. For its high deposi-

tion rate the spray arc is used for welding filler

and cover passes in the flat position.

Connections between welding parameters,

shielding gas and arc type are shown in Fig-

ure 5.11. When the shielding gas M23 is used,

the spray arc may already be produced with an

amperage of 260 A. With the decreasing argon

proportion the amperage has to be increased

in order to remain in the spray arc range. When

pure carbon dioxide is applied, the spray arc

© ISF 2002

Welding Parameters in Dependence on the Shielding Gas Mixture (SG 2, Ø1,2 mm)

br-er5-11e.cdr

weld

ing v

oltage

150 200 250 300A

15

20

25

V

35

contact tube distance: approx. 15 mm

spray arc

long arc

short arc

contact tube distance: approx. 19 mm

mixedcircuiting arc

C1

M21

M23

welding current

wire feed 5,53,5 4,5 7,0 8,0 10,5m/min

shielding gas composition:C1: CO

M21: 82% Ar, 18% CO

M23: 92% Ar, 8% O

2

2

2

Figure 5.11


argon helium

argon

helium

temperature

therm

al co

nd

uctivity

hydrogen

nitrogen

CO2

CO282%Ar+18%CO2

Figure 5.12


2005

cannot be produced. Figure 5.11 shows, moreover, that with the increasing CO2 content the

welding voltage must also be increased in order to achieve the same deposition rate.

The different thermal conductivity of the

shielding gases has a considerable influence

on the arc configuration and weld geometry,

Figure 5.12. Caused by the low thermal con-

ductivity of the argon the arc core becomes

very hot – this results in a deep penetration in

the weld centre, the so-called “argon finger-

type penetration”. Weld reinforcement is

strongly pronounced. Application of CO2 and

helium leads, due to the better thermal conduc-

tivity of these shielding gases, to a wide and

deep penetration.

A recombination (endothermic break of the linkage in the arc space – exothermal reaction

2CO + O2 ->2CO2 in the workpiece proximity) intensifies this effect when CO2 is used.

In argon, the current-carrying arc core is wider and envelops the wire electrode end, Figure

5.13. This generates electromagnetic forces which bring about the detachment of the liquid

electrode material. This so-called “pinch effect” causes a metal transfer in small drops, Fig-

ure 5.14.


wire elektrodes

current-carryingarc core

argon carbon dioxide

Figure 5.14

Figure 5.13

© ISF 2006

Influence of Shielding Gason Forces in the Arc Space

br-er5-13e.cdr

current-carryingarc core

argon carbon dioxider

argon carbon dioxide

r

tem

pe

ratu

re

Fr

FaF

Fa F

Fr


2005

The pointed shape of the arc attachment in

carbon dioxide produces a reverse-direction

force component, i.e., the molten metal is

pushed up until gravity has overcome that

force component and material transfer in the

form of very coarse drops appear.

Besides the pinch effect, the inertia and the

gravitational force, other forces, shown in Fig-

ure 5.15, are active inside the arc space;

however these forces are of less importance.

If the welding voltage and the wire feed speed

are further increased, a rotating arc occurs

after an undefined transition zone, Figure

5.16. High-efficiency MAG welding has

been applied since the beginning of the nine-

ties; the deposition rate, when this process is

used, is twice the size as, in comparison, to spray arc welding. Apart from a multicomponent

gas with a helium proportion, also a high-rating power source and a precisely controlled wire

feed system for high wire feed speeds are necessary.

Figure 5.17 depicts the

deposition rates over the

wire feed speed, as achiev-

able with modern high-

efficiency MAG welding

processes.

During the transition from

the short to the spray arc

the drop frequency rate in-

creases erratically while the

drop volume decreases at


Forces in Arc Space

work piece

electrostaticforces

surfacetension S

acceleration due to gravity

wire electrode

viscosity

droplets necking down

inertia

suction forces, plasma flowinduced

electromagnetic force F(pinch effect)

L

backlash forces fof the evaporating material

r

Figure 5.15

Figure 5.16

Rotating Arc



2005

the same degree. With an

increasing CO2-content,

this “critical current

range” moves up to higher

power ranges and is, with

inert gas constituents of

lower than 80%, hardly

achievable thereafter. This

effect facilitates the

pulsed-arc welding tech-

nique, Figure 5.18.

In pulsed-arc welding, a

change-over occurs be-

tween a low, subcritical background current and a high, supercritical pulsed current. During

the background phase which corresponds with the short arc range, the arc length is ionised

Setting parameters:

- background current I

- pulse voltage U

- impulse time t

- background time

t or frequency f with

f = 1 / ( t + t ), resp.

- wire feed speed v

G

P

P

G

G P

D

300 300

time

200

I G I m I krit

400 600

t Gt P

200 200

100 100

0 00

dro

p v

olu

me

num

ber

of

dro

ple

ts 1/s 10 cm-4 3

critical currentrange

A


Pulsed Arc

Figure 5.18


500

time

arc

volta

ge

150 5 10 20 300

50

100

150

200

250

300

350

400

5

10

15

20

25

35

A

V

we

ldin

g c

urr

ent

ms

Um

Im

IEff

UEff

Figure 5.19

© ISF 2002

Deposition Rate

br-er5-17e.cdr

conventionalGMA

Ø 0,8 mm

Ø 1,0 mm

Ø 1,2 mm

wire feed speed

de

po

sitio

n r

ate

m/min

kg/hhigh performanceGMA welding

25

20

15

10

5

00 5 10 15 20 25 30 35 40 45

Figure 5.17


2005

and wire electrode and work

surface are preheated. Dur-

ing the pulsed phase the

material is molten and, as in

spray arc welding, super-

seded by the magnetic

forces. Figure 5.20.

Figure 5.19 shows an ex-

ample of pulsed arc real

current path and voltage

time curve. The formula for

mean current is:

∫=

T

0

midt

T

1I

for energy per unit length of weld is:

∫=

T

0

2eff dti

T

1I

By a sensible selection of welding parameters, the GMA welding technique allows a selection

of different arc types which

are distinguished by their

metal transfer way. Figure

5.21 shows the setting

range for a good welding

process in the field of con-

ventional GMA welding.

Figure 5.22 shows the ex-

tended setting range for the

high-efficiency MAGM weld-

ing process with a rotating

arc.

© ISF 2002

Parameter Setting Range in GMA Welding

br-er5-21e.cdr

optimal settinglower limitupper limit

working range welding current / arc voltage

400325

50

10

15

20

25

30

35

40

45

50 75 100 125 150 175 200 225 250 275 300 350 375

spray arc

transition arc

short arcshielding gas: 82%Ar, 18%CO2

wire diameter: 1,2 mmwire type: SG 2

vo

ltag

e [

v]

welding current

Figure 5.21

we

ldin

g c

urr

en

t

pulsed current intensity

Non-short-circuiting metal tranfer range

backround current intensity

time

Pulsed Metal Transfer

br-er5-20e.cdr © isf 2002

Figure 5.20


2005

Some typical applications of the different arc types are depicted in Figure 5.23. The rotating

arc, (not mentioned in the figure), is applied in just the same way as the spray arc, however,

it is not used for the welding of copper and aluminium.

The arc length within the

working range is linearly

dependent on the set weld-

ing voltage, Figure 5.24.

The weld seam shape is

considerably influenced by

the arc length. A long arc

produces a wide flat weld

seam and, in the case of

fillet welds, generally under-

cuts. A short arc produces a

narrow, banked weld bead.

On the other hand, the arc length is inversely proportional to the wire feed speed, Figure

5.25. This has influence on the current over the internal adjustment with a slightly dropping

power source characteristic. This again is of considerable importance for the deposition rate,

i.e., a low wire feed speed leads to a low deposition rate, the result is flat penetration and low

base metal fusion. At a constant weld speed and a high wire feed speed a deep penetration

can be obtained.

At equal arc lengths, the

current intensity is de-

pendent on the contact

tube distance, Figure 5.26.

With a large contact tube

distance, the wire stickout is

longer and is therefore

characterised by a higher

ohmic resistance which

leads to a decreased current

© ISF 2002

Applications of Different Arc Types

br-er5-23e.cdr

arc types

ap

plic

atio

ns

spray arc long arc short arc pulsed arc

MIG

MA

GM

MA

GC

weld

ing m

eth

ods

seam

type, po

sitio

ns

work

pie

ce thic

kness

aluminiumcopper

aluminiumcopper

aluminium(s < 1,5 mm)

steel unalloyed, low-alloy, high-alloy

steel unalloyed, low-alloy

steel unalloyed, low-alloy

steel unalloyed,low-alloy

steel unalloyed, low-alloy,high-alloy

steel low-alloy, high-alloy

-

-

-

fillet welds or butt welds at thin sheets, all positions

root layers of butt welds

all positions

inner passes and cover passes of fillet or butt welds in position PC, PD, PE, PF, PG (out-of-position)

at medium-thick or thickcomponents,

fillet welds or innerpasses and cover passes of thin and medium-thick components, all positions

root layer welds only conditionally possible

fillet welds or inner passes and cover passes of butt welds at medium-thick or thickcomponents in positionPA, PB

fillet welds or inner passes and cover passes of butt welds at medium-thick or thickcomponents in positionPA, PB

welding of root layers in position PA

Figure 5.23

Setting Range or Welding Parameters in Dependence on Arc Type

br-er5-22e.cdr Quelle: Linde, ISF2002

10

20

30

50

Vvo

lta

ge

high-efficiency spray arc

rotating arc

transition zones

short arc

high-efficiency short arc

100 200 300 400 600A

filler metal: SG2 -1,2 mmshielding gas: Ar/He/CO /O -65/26,5/8/0,52 2

welding current

spray arc

Figure 5.22


2005

intensity. For the adjustment of the contact

tube distance, as a thumb rule, ten to twelve

times the size of the wire diameter should be

considered.

The torch position has considerable influ-

ence on weld formation and welding proc-

ess, Figure 5.27. When welding with the torch

pointed in forward direction of the weld, a part

of the weld pool is moved in front of the arc.

This results in process instability. However, it

ha s the advantage of a flat smooth weld sur-

face with good gap bridging. When welding

with the torch pointed in reversing direction of

the weld, the weld process is more stable and

the penetration deeper, as base metal fusion


Welding Voltage

weld appearancebutt weld

weld appearancefillet weld

operating point:welding voltage:arc length:

highlong

mediummedium

lowshort

arc length:longmediumshort

U

v , ID

AL

AM

AK

AL AM AK

Figure 5.24


Wire Feed Speed

operating point:

wire feed speed:

arc length:

welding current:

deposition efficiency:

low

long

low

low

AL

medium

medium

medium

medium

high

short

high

high

AM AK

weld appearance:

arc length:

long

medium

short

v , ID

U

ALAM

AK

Figure 5.25


Contact Tube-to-Work Distance

lk1 lk2 lk3

wire electrode:

shielding gas:

arc voltage:

wire feed speed:

welding speed:

1,2 mm diameter

82% Ar + 18% CO

29 V

8,8 m/min

58 cm/min

2

conta

ct

tub

e-t

o-w

ork

dis

tance l

k

mm

current

30

20

10

0200 250 A300 350

3

2

1

operating rule:

l = 10 to 12 dk D

Figure 5.26


2005

by the arc is better, although the weld bead

surface is irregular and banked.

Figure 5.28 shows a selection of different ap-

plication areas for the GMA technique and the

appropriate shielding gases.

The welding current may be produced by dif-

ferent welding power sources. In d.c. welding

the transformer must be equipped with down-

stream rectifier assemblies, Figure 5.29. An

additional ripple-filter choke suppresses the

residual ripple of the rectified current and has

also a process-stabilising effect.

With the development of efficient transistors

the design of transistor analogue power

sources became possible, Figure 5.29. The

operating principle of a transistor analogue

power source follows the principle of an audio frequency amplifier which amplifies a low-level

to a high level input signal, possibly distortion-free. The transistor power source is, as con-

ventional power sources, also equipped with a three-phase transformer, with generally only

one secondary tap. The secondary voltage is rectified by silicon diodes into full wave opera-

tion, smoothed by capacitors

and fed to the arc through a

transistor cascade. The

welding voltage is steplessly

adjustable until no-load volt-

age is reached. The differ-

ence between source volt-

age and welding voltage

reduces at the transistor

cascade and produces a

comparatively high stray

power which, in general,


Torch Position

penetration:

gap bridging:

arc stability:

spatter formation:

weld width:

weld appearance:

shallow average

average

average

average

average

average

bad

bad

good

good

low

smooth rippled

narrowwide

deep

strong

advance direction

Figure 5.27

© ISF 2002

Fields of Application ofDifferent Shielding Gases

br-er5-28e.cdr

Arg

on 4

.6

Arg

on 4

.8

Heliu

m 4

.6

Ar/

He-m

ixtu

re

Ar

+ 5

% H

or

7,5

% H

99%

Ar

+ 1

% O

or

97%

Ar

+ 3

% O

97,5

%A

r +

2,5

% C

O

83%

Ar

+ 1

5%

He +

2%

CO

90%

Ar

+ 5

% O

+ 5

% C

O

80%

Ar

+ 5

% O

+ 1

5%

CO

92%

Ar

+ 8

% O

88%

Ar

+ 1

2%

O

82%

Ar

+ 1

8%

CO

92%

Ar

+ 8

% C

O

form

ing g

as (

N-H

-mix

ture

)

22

2 2

2

2

22

22

2

2

2

2

22

autoclaves, vessels, mixers, cylinderspanelling, window frames, gates, gridsstainless steel pipes, flanges, bendsspherical holders, bridges, vehicles, dump bodiesreactors, fuel rods, control devicesrocket, launch platforms, satellitesvalves, sliders, control systemsstator packages, transformer boxespassenger cars, trucksradiators, shock absorbers, exhaustscranes, conveyor roads, excavators (crawlers)shelves (chains), switch boxesbraces, railings, stock boxesmud guards, side parts, tops, engine bonnetsattachments to flame nozzles, blast pipes, rollersvessels, tanks, containers, pipe linesstanchions, stands, frames, cagesbeams, bracings, cranewaysharvester-threshers, tractors, narrows, ploughswaggons, locomotives, lorries

chemical-apparatus engineeringshopwindow constructionpipe productionaluminium-working industrynuclear engineeringaerospace engineeringfittings productionelectrical engineering industryautomotive industrymotor car accessoriesmaterials-handling technologysheet metal workingcraftsmotor car repairsteel productionboiler and tank constructionmachine engineeringstructural steel engineeringagricultural machine industryrail car production

industrial sections shie

ldin

g g

ases

application examples

Figure 5.28


2005

makes water-cooling necessary. The efficiency factor is between 50 and 75%. This disad-

vantage is, however, accepted as those power sources are characterised by very short reac-

tion times (30 to 50 µs). Along with the development of transistor analogue power sources,

the consequent separation

of the power section (trans-

former and rectifier) and

electronic control took

place. The analogue or

digital control sets the ref-

erence values and also

controls the welding proc-

ess. The power section

operates exclusively as an

amplifier for the signals

coming from the control.

The output stage may also

be carried out by clocked cycle. A secondary clocked transistor power source features just

as the analogue power sources, a transformer and a rectifier, Figure 5.30. The transistor unit

functions as an on-off switch. By varying the on-off period, i.e., of the pulse duty factor, the

average voltage at the output of the transistor stage may be varied. The arc voltage achieves

small ripples, which are of a limited amplitude, in the switching frequency of, in general, 20

kHz; whereas the welding

current shows to be strongly

smoothed during the high

pulse frequencies caused by

inductivities. As the transis-

tor unit has only a switching

function, the stray power is

lower than that of analogue

sources. The efficiency

factor is approx. 75 – 95%.

The reaction times of these

clocked units are within of

© isf 2002

GMA Welding Power Source,Electronically Controlled, Analogue

br-er5-29e.cdr

welding currentmainssupply

uist

u . . u1 n iist

three-phasetransformer

reference inputvalues

signal processor(analog-to-digital)

current pickup

transistorpower section

energystore

fully-controlledthree-phase

bridge rectifier

Figure 5.29

© ISF 2002

GMA Welding Power Source,Electronically Controlled, Secondary Chopped

br-er5-30e.cdr

weldingcurrent

mains supply

Uist

Iist

3-phasetransformer

reference inputvalues


currentpickup

transistorswitch

protectivereactor

energy store

3-phasebridgerectifier

U . . U1 n

Figure 5.30


2005

300 – 500 µs clearly longer

than those of analogue

power sources.

Series regulator power

sources, the so-called “in-

verter power sources”, dif-

fer widely from the afore-

mentioned welding ma-

chines, Figure 5.31. The

alternating voltage coming

from the mains (50 Hz) is

initially rectified, smoothed

and converted into a me-

dium frequency alternating voltage (approx. 25-50 kHz) with the help of controllable transistor

and thyristor switches. The alternating voltage is then transformer reduced to welding voltage

levels and fed into the welding process through a secondary rectifier, where the alternating

voltage also shows switching frequency related ripples. The advantage of inverter power

sources is their low weight. A transformer that transforms voltage with frequency of 20 kHz,

has, compared with a 50 Hz transformer, considerably lower magnetic losses, that is to say,

its size may accordingly be smaller and its weight is just 10% of that of a 50 Hz transformer.

Reaction time and effi-

ciency factor are compa-

rable to the corresponding

values of switching-type

power sources.

All welding power sources

are fitted with a rating

plate, Figure 5.32. Here

the performance capability

and the properties of the

power source are listed.

© ISF 2002

GMA Welding Power Source, ElectronicallyControlled, Primary Chopped, Inverter

br-er5-31e.cdr

weldingcurrent

mainssupply

Uist

Iist

filter

reference input values


current pickup

transistorinverter

energystorage

3-phasebridgerectifier rectifier

U . . U1 n

mediumfrequency

transformer

Figure 5.31

© ISF 2002

Rating Plate

br-er5-32e.cdr

Spower range

power capacity

in dependence

of current flow

power supply

manufacturer

rotary current welding rectifier

VDE 0542

typeproduction

numberswitchgearnumber

protective system

DIN 40 050

F F

IP21

35A/13V - 220A/25V

220

25

60%

15380

26

6,6 0,72

220 17

10

100%

15 - 38 23

170

insulations class

cooling type

~_

X

I2

U2

I1U1

U1

U1

U1

I1

I1

I1

U0 V

EDED

A

A A

AV

V

V

V

A

A A

A A

A

V V

welding

MIG/MAG

input

3~50Hz

kVA (DB) cos�

min. and max. no-load voltage

Figure 5.32


2005

The S in capital letter (for-

mer K) in the middle shows

that the power source is

suitable for welding opera-

tions under hazardous

situations, i.e., the secon-

dary no-load voltage is

lower than 48 Volt and

therefore not dangerous to

the welder.

Besides the familiar solid

wires also filler wires are

used for gas-shielded

metal arc welding. They consist of a metallic tube and a flux core filling. Figure 5.33 depicts

common cross-sectional shapes.

Filler wires contain arc stabilisators, slag-forming and also alloying elements which support a

stable welding process, help to protect the solidifying weld from the atmosphere and, more

often than not, guarantee

very good mechanical

properties.

An important distinctive

criteria is the type of the

filling. The influence of the

filling is very similar to that

of the electrode covering in

manual electrode welding

(see chapter 2). Figure

5.34 shows a list of the

different types of filler wire.

© ISF 2002

Cross-Sections of Flux-Cored Wire Electrodes

br-er5-33e.cdr

a b c

form-enclosed flux-cored wire electrode

seamless flux-coredwire electrode

Figure 5.33

© ISF 2002

Type Symbols of Flux-Cored Wire Electrodes According to DIN EN 12535

br-er5-34e.cdr

symbol slag characteristicscustomary application* shielding gas **

R rutile base, slowly soldifying slag

S and M C and M2

P S and M C and M2

B basic S and M C and M2

M filling: metal powder S and M C and M2

V rutile- or fluoride-basic S without

W fluoride basic, slowly slagsoldifying

S and M without

S and M withoutY

S other types

*) S: single pass welding - M: multi pass welding**) C: CO - M2: mixed gas M2 according to DIN EN 4392

rutile base, rapidly soldifying slag

fluoride basic, slowly slagsoldifying

Figure 5.34

6.

Narrow Gap Welding,

Electrogas - and

Electroslag Welding

6. Narrow Gap Welding, Electrogas- and Electroslag Welding 77

2005

Up to this day, there is no universal agreement about the definition of the term “Narrow

Gap Welding” although the term is actually self-explanatory. In the international technical

literature, the process

characteristics mentioned

in the upper part of Figure

6.1 are frequently con-

nected with the definition

for narrow gap welding. In

spite of these “definition

difficulties” all questions

about the universally valid

advantages and disadvan-

tages of the narrow gap

welding method can be

clearly answered.

The numerous variations of narrow gap welding are, in general, a further development of the

conventional welding technologies. Figure 6.2 shows a classification with emphasis on sev-

eral important process characteristics. Narrow gap TIG welding with cold or hot wire addi-

tion is mainly applied as

an orbital process method

or for the joining of high-

alloy as well as non-

ferrous metals. This

method is, however, hardly

applied in the practice.

The other processes are

more widely spread and

are explained in detail in

the following.

© ISF 2002

Narrow Gap Welding

br-er6-01e.cdr

Process characteristics:

- narrow, almost parallel weld edges. The small preparation angle has the function to compensate the distortion of the joining members

- multipass technique where the weld build-up is a constant 1 or 2 beads per pass- usually very small heat affected zone (HAZ) caused by low energy input

Advantages:

- profitable through low consumption quantities of filler material, gas and/ or powder due to the narrow gaps

- excellent quality values of the weld metal and the HAZ due to low heat input

- decreased tendency to shrink

- higher apparatus expenditure, espacially for the control of the weld head and the wire feed device

- increased risk of imperfections at large wall thicknesses due to more difficult accessibility during process control

- repair possibilities more difficult

Disadvantages

Figure 6.1

Figure 6.2

© ISF 2006

Survey of Narrow Gap Welding TechniquesBased on Conventional Technologies

br-er6-02e.cdr

process withstraightened

wire electrode(1P/L, 2P/L, 3P/L)

process withoscillating

wire electrode(1P/L)

process withtwin electrode(1P/L, 2P/L)

process withlengthwisepositioned

strip electrode(2P/L)

process withlinearly oscillating

filler wire

process withstripshaped

filler andfusing feed

electrogasprocess with

linearlyoscillating

wire electrode

electrogasprocess with

bent,longitudinally

positionedstrip electrode

MIG/MAG-processes

(1P/L,2P/L,3P/L)

process with hotwire addition(1P/L, 2P/L)

process with coldwire addition(1P/L, 2P/L)

submerged arcnarrow gap welding

electroslag narrowgap welding

gas-shielded metal arcnarrow gap welding

tungsten innertgas-shielded

narrow gap welding

flat position vertical up position all welding positions


2005

In Figure 6.3, a systematic subdivision of the

various GMA narrow gap technologies is

shown. In accordance with this, the fundamen-

tal distinguishing feature of the methods is

whether the process is carried out with or with-

out wire deformation. Overlaps in the structure

result from the application of methods where a

single or several additional wires are used.

While most methods are suitable for single

pass per layer welding, other methods require

a weld build-up with at least two passes per

layer. A further subdivision is made in accor-

dance with the different types of arc move-

ment.

In the following, some of the GMA narrow gap

technologies are explained:

Using the turning tube method, Figure 6.4, side

wall fusion is achieved by the turning of the contact tube; the contact tip angles are set in de-

grees of between 3° and 15° towards the torch axis. With an electronic stepper motor control,

arbitrary transverse-arc oscillating motions with defined dwell periods of oscillation and oscil-

lation frequencies can be realised - independent of the filler wire properties. In contrast, when

the corrugated wire

method with mechanical

oscillator is applied, arc

oscillation is produced by

the plastic, wavy deforma-

tion of the wire electrode.

The deformation is ob-

tained by a continuously

swinging oscillator which is

fixed above the wire feed

rollers. Amplitude and fre-

quency of the wave motion

Figure 6.3

Figure 6.4

Principle of GMANarrow Gap Welding

br-er 6-04e.cdr

corrugated wire method with mech. oscillator

1 - wire reel2 - drive rollers3 - wire mechanism for wire guidance4 - inert gas shroud5 - wire guide tube and shielding gas tube6 - contact tip

1 - wire reel2 -

3 - 4 - inert gas shroud5 - wire feed nozzle and shielding gas tube6 - contact tip

mechanical oscillator for wire deformation

drive rollers

12 -

14

8 -

10

1 1

22

33

4 4

5 5

6 6

© ISF 2006

Survey and Structure of the Variations of Gas-Shielded Metal Arc Narrow Gap Welding

br-er6-03e.cdr

D

A

C

B

long-wire method(1 P/L, 2 P/L)

thick-wire method(1 P/L, 2 P/L)

twin-wire method(1 P/L)

tandem-wire method(1 P/L, 2 P/L, 3 P/L)

twisted wire method(1 P/L)

coiled-wire method(1 P/L)

rotation method(1 P/L)

corrugated wire methodwith mechanical oscillator

(1 P/L)

corrugated wire methodwith oscillating rollers

(1 P/L)

corrugated wire methodwith contour roll (1 P/L)

zigzag wire method(1 P/L)

wire loop method(1 P/L)

GMA narrow gap weldingno wire-deformation

GMA narrow gap weldingwire-deformation

explanation:P/L:Pass/Layer

A: method without forced arc movementB: method with rotating arc movementC: method with oscillating arc movementD: method with two or more filler wires


2005

can be varied over the total amplitude of oscil-

lation and the speed of the mechanical oscil-

lator or, also, over the wire feed speed. As the

contact tube remains stationary, very narrow

gaps with widths from 9 to 12 mm with plate

thicknesses of up to 300 mm can be welded.

Figure 6.5 shows the macro section of a

GMA narrow gap welded joint with plates

(thickness: 300 mm) which has been pro-

duced by the mechanical oscillator method in

approx. 70 passes. A highly regular weld

build-up and an almost straight fusion line

with an extremely narrow heat affected zone

can be noticed. Thanks to the correct setting

of the oscillation parameters and the precise,

centred torch manipulation no sidewall fusion

defects occurred, in spite of the low sidewall

penetration depth. A further advantage of the weave-bead technique is the high crystal re-

structuring rate in the weld metal and in the basemetal adjacent to the fusion line – an advan-

tage that gains good toughness properties.

Two narrow-gap welding

variations with a rotating

arc movement are shown in

Figure 6.6. When the rota-

tion method is applied, the

arc movement is produced

by an eccentrically protrud-

ing wire electrode (1.2 mm)

from a contact tube nozzle

which is rotating with fre-

quencies between 100 and

150 Hz. When the wave


plate thickness:gap preparation:

elctrode diameter:amperage:pulse frequency:arc voltage:welding speed:wire oscillation:oscillation width:shielding gas:primery gas flow:secondary gas flow:number of passes:

300 mmsquare-butt joint, 9 mmflame cut1.2 mm260 A120 HZ30 V22 cm/min80 min4 mm80% Ar/ 20% Co

25 l/min50 l/minapprox. 70

-1

2

Figure 6.5

Figure 6.6

Principle ofGMA Narrow Gap Welding

br-er 6-06e.cdr

rotation method spiral wire method

1 - wire reel2 - drive rollers3 - mechanism for nozzle rotation4 - inert gas shroud5 - shielding gas nozzle6 - wire guiding tube

1 - wire reel2 - wire mechanism for wire deformation3 - drive rollers4 - wire feed nozzle and shielding gas supply5 - contact piece

13 -

14

1 1

2

2

3

3

4 4

5

6 5

9 -

12


2005

wire method is used, the 1.2 mm solid wire is being spiralwise deformed. This happens be-

fore it enters the rotating 3 roll wire feed device. With a turning speed of 120 to 150 revs per

minute the welding wire is deformed. The effect of this is such that after leaving the contact

piece the deformed wire creates a spiral diameter of 2.5 to 3.0 mm in the gap – adequate

enough to weld plates with thicknesses of up to 200 mm at gap widths between 9 and 12 mm

with a good sidewall fusion.

Figure 6.7 explains two

GMA narrow gap welding

methods which are oper-

ated without forced arc

movement, where a reli-

able sidewall fusion is ob-

tained either by the wire

deflection through constant

deformation (tandem wire

method) or by forced wire

deflection with the contact

tip (twin-wire method). In

both cases, two wire elec-

trodes with thicknesses

between 0.8 and 1.2 mm are used. When the tandem technique is applied, these electrodes

are transported to the two weld heads which are arranged inside the gap in tandem and

which are indeFigure pendently selectable.

When the twin-wire method is applied, two parallel switched electrodes are transported by a

common wire feed unit, and, subsequently, adjusted in a common sword-type torch at an in-

cline towards the weld edges at small spaces behind each other (approx. 8 mm) and molten.

In place of the SA narrow gap welding methods, mentioned in Figure 6.2, the method with

a lengthwise positioned strip electrode as well as the twin-wire method are explained in more

detail, Figure 6.8. SA narrow gap welding with strip electrode is carried out in the multi-

pass layer technique, where the strip electrode is deflected at an angle of approx. 5° towards

the edge in order to avoid collisions. After completing the first fillet weld and slag removal the

opposite fillet is made. Solid wire as well as cored-strip electrodes with widths between 10

Principle of GMANarrow Gap Welding

br-er 6-07e.cdr

tandem method

1 - wire reel2 - deflection rollers3 - drive rollers4 - inert gas shroud5 - shielding gas nozzle6 - wire feed nozzle and contact tip

1

2

3

4

5

6

9 -

12

350

twin-wire method

1 - wire reel2 - drive rollers3 - inert gas shroud4 - wire feed nozzle and shielding gas supply5 - contact tips

1

2

3

4

5

15 -

18

Figure 6.7


2005

and 25 mm are used. The gap width is, de-

pending on the number of passes per layer,

between 20 and 25 mm. SA twin-wire weld-

ing is, in general, carried out using two elec-

trodes (1.2 to 1.6 mm) where one electrode is

deflected towards one weld edge and the

other towards the bottom of the groove or to-

wards the opposite weld edge. Either a single

pass layer or a two pass layer technique are

applied. Dependent on the electrode diameter

and also on the type of welding powder, is the

gap width between 12 and 13 mm.

Figure 6.9 shows a comparison of groove

shapes in relation to plate thickness for SA

welding (DIN 8551 part 4) with those for GMA

welding (EN 29692) and the unstandardised,

mainly used, narrow gap welding. Depending

on the plate thickness, significant differences in

the weld cross-sectional dimensions occur

which may lead to substantial saving of mate-

rial and energy during welding. For example,

when welding thicknesses of 120 mm to 200

mm with the narrow gap welding technique,

66% up to 75% of the weld metal weight are

saved, compared to the SA square edge weld.

The practical application of SA narrow gap

welding for the production of a flanged calotte

joint for a reactor pressure vessel cover is de-

picted in Figure 6.10. The inner diameter of the

pressure vessel is more than 5,000 mm with

br-er6-09e.cdr

Comparison of theWeld Groove Shape

8

8

s

10°

s

16

7°

8°

6

3 s s

3

10

double-U butt weldSA-DU weld preparation

(8UP DIN 8551)

square-edge butt weldSA-SE weld preparation

(3UP DIN 8551)

double-U butt weldGMA-DU weld preparation

(Indexno. 2.7.7 DIN EN 29692)

narrow gap weldGMA-NG weld preparation

(not standardised)

Figure 6.9

br-er6-08e.cdr

Submerged ArcNarrow Gap Welding

strip electrode

twin-wire electrode

α

s

xa

so

h

h

w

w

f

p

H

a

z

vw

s

v weld speed

a electrode deflectionH stick out z distance torch - flank

s gap widthh bead heightw bead widthp penetration depth

w

SO stick out

s gap widtha electrode deflectionx distance of strip tip to flank

twisting angle

h bead hightw bead width

α

Figure 6.8


2005

wall thicknesses of 400 mm and with a height of 40,000 mm. The total weight is 3,000 tons.

The weld depth at the joint was 670 mm, so it had been necessary to select a gap width of at

least 35 mm and to work in the three pass layer technique.

Electrogas welding (EG) is characterised by a vertical groove which is bound by two water-

cooled copper shoes. In the groove, a filler wire electrode which is fed through a copper noz-

zle, is melted by a shielded arc, Figure 6.11. During this process, are groove edges fused. In

relation with the ascending rate of the weld pool volume, the welding nozzle and the copper

shoes are pulled upwards. In order to avoid poor fusion at the beginning of the welding, the

process has to be started on a run-up plate which closes the bottom end of the groove. The

shrinkholes forming at the weld end are transferred onto the run-off plate. If possible, any

interruptions of the welding process should be avoided. Suitable power sources are rectifiers

with a slightly dropping static characteristic. The electrode has a positive polarity.

© ISF 2002br-er6-10e_sw.cdr

Figure 6.10

br-er6-11e.cdr

Electrogas Welding

+-

weld advance

workpiecewire guide

electrode

shielding gas

arc

weld pool

Cu-shoe

weld metal water

designation:position:plate thickness:

materials:gap width:electrodes:

amperage:voltage:weld speed:shielding gas:

gas-shielded metal arc welding (GMAW acc. DIN 1910 T.4)vertical (width deviations of up to 45°)6 - 30 mm square-butt joint or V weld seam 30 mm double-V weld seamunalloyed, lowalloy and highalloy steels8 - 20 mmonly 1 (flux-cored wire, for slag formation betweencopper shoe and weld surface) Ø 1.6 - 3.2 mm350 - 650 A28 - 45 V2 - 12 m/hunalloyed and lowalloy steelsCO or mixed gas (Ar 60% and 40% Co )highalloy steels: argon or helium

2 2

Figure 6.11


2005

The application of electrogas welding for low-

alloyed steels is – more often than not - limited,

as the toughness of the heat affected zone with

the complex coarse grain formation does not

meet sophisticated demands. Long-time expo-

sure to temperatures of more than 1500°C and

low crystallisation rates are responsible for this.

The same applies to the weld metal. For a

more wide-spread application of electrogas

welding, the High-Speed Electrogas Welding

Method has been developed in the ISF. In this

process, the gap cross-section is reduced and

additional metal powder is added to increase

the deposition rate. By the increase of the

welding speed, the dwell times of weld-

adjacent regions above critical temperatures

and thus the brittleness effects are significantly

reduced.

Figure 6.12 shows the process principle of Electroslag Welding. Heating and melting of the

groove faces occurs in a slag bath. The temperature of the slag bath must always exceed the

melting temperature of the metal. The Joule effect, produced when the current is transferred

through the conducting

bath, keeps the slag bath

temperature constant. The

welding current is fed over

one or more endless wire

electrodes which melt in

the highly heated slag

bath. Molten pool and slag

bath which both form the

weld pool are, sideways

retained by the groove

faces and, in general, by

br-er6-12e.cdr

Electroslag Welding

1

2

3

4

5

6

7

8

9

1. base metal2. welding boom3. filler metal4. slag pool5. metal pool

6. copper shoe7. water cooling8. weld seam9. Run-up plate

designation:position:plate thickness:gap width:materials:electrodes:

amperage:voltage:welding speed:slag hight:

resistance fusion weldingvertical (and deviation of up to 45°) 30 mm (up to 2,000 mm)24 - 28 mmunalloyed, lowalloy and highalloy steels1 or more solid or cored wires Ø 2.0 - 3.2 mmplate thickness range per electrode: fixed 30 - 50 mmoscillated: up to 150 mm550 - 800 A per electrode35 - 52 V0.5 - 2 m/h30 - 50 mm

Figure 6.12

© ISF 2002

Process Phases During ES Welding

br-er6-13e.cdr

~

ignition with arc powder fusion

start of welding welding end of welding

powder

slag

weld metal

molten pool

slag

Figure 6.13


2005

water-cooled copper shoes which are, with the complete welding unit, and in relation with the

welding speed, moved progressively upwards. To avoid the inevitable welding defects at the

beginning of the welding process (insufficient penetration, inclusion of unmolten powder) and

at the end of the welding (shrinkholes, slag inclusions), run-up and run-off plates are used.

The electroslag welding process can be divided into four process phases, Figure 6.13. At

the beginning of the welding process, in the so-called “ignition phase”, the arc is ignited for

a short period and liquefies the non-conductive welding flux powder into conductive slag. The

arc is extinguished as the electrical conductivity of the arc length exceeds that of the conduc-

tive slag. When the desired slag bath level is reached, the lower ignition parameters (current

and voltage) are, during the so-called “Data-Increase-Phase”, raised to the values of the

stationary welding process. This occurs on the run-up plate. The subsequent actual welding

process starts, the process phase. At the end of the weld, the switch-off phase is initiated

in the run-off plate. The solidifying slag bath is located on the run-off plate which is subse-

quently removed.

The electroslag welding with consumable feed wire (channel-slot welding) proved to be

very useful for shorter welds.

The copper sliding shoes are replaced by fixed Cu cooling bars and the welding nozzle by a

steel tube, Figure 6.14. The length of the sheathed steel tube, in general, corresponds with

the weld seam length (mainly shorter than 2.500 mm) and the steel tube melts during welding

in the ascending slag bath. Dependent on the plate thickness, welding can be carried out with

one single or with several

wire and strip electrodes. A

feature of this process

variation is the handiness

of the welding device and

the easier welding area

preparation. Also curved

seams can be welded with

a bent consumable elec-

trode. As the groove width

can be significantly re-

duced when comparing Electroslag Welding withFusing Wire Feed Nozzle

br-er 6-14e.cdr

=~

drive motorwire or stripelectrode

run-off plate

welding cable

workpiece workpiece

fusingfeed nozzle

workpiece cable run-up plate

copper shoes

workpieceworkpiece

copper shoes

Electroslag fusingnozzle process (channel welding)

position: verticalplate thickness: 15 mmmaterials: unalloyed, lowalloy and highalloy steels

welding consumables:

wire electrodes: Ø 2.5 - 4 mmstrip electrodes: 60 x 0.5 mmplate electrodes: 80 x60 up to 10 x 120 mmfusingfeed nozzle: Ø 10 - 15 mm welding powder: slag formation with high electrical conductivity

Figure 6.14


2005

with conventional processes, and a strip shaped filler material with a consumable guide piece

is used, this welding process is rightly placed under the group of narrow gap welding tech-

niques.

Likewise in electrogas welding, the electroslag welding process is also characterised by a

large molten pool with a – simultaneously - low heating and cooling rate. Due to the low cool-

ing rate good degassing and thus almost porefree hardening of the slag bath is possible.

Disadvantageous, however, is the formation of a coarse-grain structure. There are, however,

possibilities to improve

the weld properties, Fig-

ure 6.15.

To avoid postweld heat

treatment the electroslag

welding process with lo-

cal continuous normali-

sation has been devel-

oped for plate thicknesses

of up to approx. 60 mm,

Figure 6.16. The welding

temperature in the weld

region drops below the Ar1-

temperature and is subse-

quently heated to the nor-

malising temperature

(>Ac3). The specially de-

signed torches follow the

copper shoes along the

weld seam. By reason of

the residual heat in the

workpiece the necessary

temperature can be

reached in a short time.

ES Welding with LocalContinuous Normalisation

br-er 6-16e.cdr

1. filler wire

2. copper shoes

3. slag pool

4. metal pool

5. water cooling

6. slag layer

7. weld seam

8. distance plate

9. postheating torch

10. side plate

11. heat treated zone

temperature °C

2000

1500

900

500

950

1

2

3

4

5

6

7

8

9

10

2

7

8

9

11

10

Figure 6.16

Possibilities to ImproveWeld Seam Properties

br-er 6-15e.cdr

technological measures metallurgical measures

increase of purity

application of suitablebase and filler metals

addition of suitable alloyand micro-alloy elements(nucleus formation)

reduction ofS-, P-, H -, N -and O - contentsand otherunfavourabletrace elements

2 2

2

C-content limitsMn, Si, Mo, Cr, Ni,Cu, Nb, V, Zr, Ti

post weld heattreatment

decrease of peak temperatureand dwell times at hightemperatures

increase of welding speed

reduction of energy perunit length

continuousnormalisationfurnacenormalisation

increase of deposit rate

decrease of groove volume

application ofseveral wireelectrodes,metal powderaddition

V, double-V buttjoints, multi-passtechnique

Figure 6.15


2005

In order to circumvent an expensive postheat weld treatment which is often unrealistic for use

on-site, the electroslag high-speed welding process with multilayer technique has been

developed. Similar to electrogas welding, the weld cross-section is reduced and, by applica-

tion of a twin-wire electrode in tandem arrangement and addition of metal powder, the weld

speed is increased, as in contrast to the conventional technique. In the heat affected zones

toughness values are determined which correspond with those of the unaffected base metal.

The slag bath and the molten pool of the first layer are retained by a sliding shoe, Fig-

ure 6.17. The weld preparation is a double-V butt weld with a gap of approx. 15 mm, so the

carried along sliding shoe seals the slag and the metal bath. Plate preparation is, as in con-

ventional electroslag welding, exclusively done by flame cutting. Thus, the advantage of eas-

ier weld preparation can be maintained.

For larger plate thicknesses (70 to 100 mm), the three passes layer technique has been

developed. When welding the first pass with a double-V-groove preparation (root width: 20

to 30 mm; gap width: approx. 15 mm) two sliding shoes which are adjusted to the weld


1 magnetic screening

2 metal powder addition

3 tandem electrode

4 water cooling

5 copper shoe (water cooled)

6 slag pool

7 molten pool

8 solidified slag

9 welding powder addition

10 weld seam

ES-welding in 2 passes with sliding shoe

1

2

3

4

9

5

6

7

8

4

10

Figure 6.17

© ISF 2002br-er6-18e.cdrES-welding of the outer passes

1

11

2

3

4

9

5

6

7

8

4

10

12

1 magnetic screening

2 metal powder supply

3 three-wire electrode

4 water cooling

5 copper shoe (water cooled)

6 slag pool

7 molten pool

8 solidified slag

9 welding powder supply

10 weld seam

11 first pass

12 second pass

Figure 6.18


2005

groove are used. The first layer is welded using the conventional technique, with one wire

electrode without metal powder addition.

When welding the outer passes flat Cu shoes are again used, Figure 6.18. Three wire elec-

trodes, arranged in a triangular formation, are used. Thus, one electrode is positioned close

to the root and on the plate outer sides two electrodes in parallel arrangement are fed into the

bath. The single as well as the parallel wire electrodes are fed with different metal powder

quantities which as outcome permit a welding speed 5 times higher than the speed of the

single layer conventional technique and also leads to strong increase of toughness in all

zones of the welded joint.

If wall thicknesses of more than 100 mm are to be welded, several twin-wire electrodes with

metal powder addition have to be used to reach deposition rates of approx. 200 kg/h. The

electroslag welding process is limited by the possible crack formation in the centre of the

weld metal. Reasons for this are the concentration of elements such as sulphur and phos-

phor in the weld centre as well as too fast a cooling of the molten pool in the proximity of the

weld seam edges.

7.

Pressure Welding


2005

Figure 7.1 shows a survey of the pressure welding processes for joining of metals in ac-

cordance with DIN 1910.

In gas pressure welding a distinction is made between open square and closed square gas

pressure welding, Figure 7.2.

Both methods use efficient gas torches to bring the workpiece ends up to the welding tem-

perature. When the welding temperature is reached, both joining members are butt-welded

by the application of axial force when a flash edge forms. The long preheating time leads to

the formation of a coarse-

grained structure in the

joining area, therefore the

welds are of low toughness

values. As the process is

operated mains-

independently and the

process equipment is low in

weight and also easy to

handle, the main applica-

tion areas of gas pressure

welding are the welding of

reinforcement steels and of

pipes in the building trade.

In pressure butt welding,

the input of the necessary

welding heat is produced

by resistance heating. The

necessary axial force is

applied by copper clamping

jaws which also receive the

current supply, Figure 7.3.

The current circuit is closed

over the abutting surfaces

Classification of WeldingProcesses acc. to DIN 1910

br-er7-01e.cdr

pressure welding

welding

fusion welding

conductive pressurewelding

gas pressurewelding

resistance pressurewelding

friction welding

induction pressurewelding

resistance spotwelding

projectionwelding

roll seamwelding

pressure buttwelding

flash buttwelding

Figure 7.1

Open Square and Closed SquareGas Pressure Welding

br-er7-02e.cdr

initial state: gap closed initial state: gap opened(for special cases)

stationary mobile

ring-shaped burner(sectional view)

closed gap

working cycles:

2. welding by pressing

1. heating

gas flame torch in the open gap

workpiece

1. heating

2. torch positioning

3. welding by rapid pressing

completed weld seam

pressure

Figure 7.2


2005

of the two joining members where, by the increased interface resistance, the highest heat

generation is obtained. After the welding temperature - which is lower than the melting

temperature of the weld

metal – is reached, upset

pressure is applied and the

current circuit is opened.

This produces a thick flash-

free upset seam which is

typical for this method. In

order to guarantee the uni-

form heating of the abutting

faces, they must be con-

formable in their cross-

sectional sizes and shapes

with each other and they

must have parallel faces.

As no molten metal develops during pressure upset butt welding, the joining surfaces must

be free from contaminations and from oxides. Suitable for welding are unalloyed and low-

alloy steels. The welding of

aluminium and copper ma-

terial is, because of the

tendency towards oxidation

and good conductivity,

possible only up to a point.

For the most part, smaller

cross-sections with sur-

faces of up to 100 mm² are

welded. Areas of applica-

tions are chain manufactur-

ing and also extensions of

wires in a wire drawing

shop.

Process Principle ofPressure Butt Welding

br-er7-03e.cdr

before upset forcehas been applied

water-cooled clampingchucks (Cu electrodes)

upset force

~_bulging at the endof the weld

Figure 7.3

Schematic Structure of a FlashButt Welding Equipment

br-er7-04e.cdr

secondary side

fixed clamping chuck mobile clamping chuck

clamping force

steel chuck

copper shoe

a+b

b2

a

welding transformer

primary side

a = flashing lengthb = upset loss

Figure 7.4


2005

A flash butt welding equipment is, in its principal structure, similar to the pressure butt

welding device, Figure 7.4.

While in pressure upset butt welding the joining members are always strongly pressed to-

gether, in flash butt welding only “fusing contact” is made during the heating phase. During

the welding process, the workpiece ends are progressively advanced towards each other

until they make contact at several points and the current circuit is over these contact bridges

closed. As the local current density at these points is high, the heating also develops very

fast. The metal is liquified and, partly, evaporated. The metal vapour pressure causes the

liquified metal to be thrown out of the gap. At the same time, the metal vapour is generating a

shielding gas atmosphere; that is to say, with the exception of pipe welds, welding can be

carried out without the use of shielding gas.

The constant creation and destruction of

the contact bridges causes the abutting

faces to “burn”, starting from the contact

points, with heavy spray-type ejection. Along

with the occurrence of material loss, the parts

are progressively advanced towards each

other again. New contact bridges are created

again and again. When the entire abutting face

is uniformly fused, the two workpiece ends

are, through a high axial force, abruptly

pressed together and the welding current is

switched off. This way, a narrow, sharp and, in

contrast to friction welding, irregular weld

edge is produced during the upsetting pro-

gress, which, if necessary, can be easy me-

chanically removed while the weld is still

warm, Figure 7.5.

In flash butt welding, a fundamental distinction is made between two different working

techniques. During hot flash butt welding a preheating operation precedes the actual

flashing process, Figure 7.6. The preceding resistance heating is carried out by “reversing”,

i.e., by the changing short-circuiting and pressing of the joining surfaces and by the mechani-


Figure 7.5


2005

cal separation in the reversed motion. When the joint ends are sufficiently heated, is the

flashing process is initialised automatically and the following process is similar to cold flash

butt welding. In contrast to cold flash butt welding, the advantage of hot flash butt welding is

that, on one hand, sections of 20 times the size can be welded with the same machine effi-

ciency and, on the other hand, a smaller temperature drop and with that a lower cooling rate

in the workpiece can be obtained. This is of importance, especially with steels which because

of their chemical composition have a tendency to harden. The cooling rate may also be re-

duced by conductive re-

heating inside the machine.

A smooth and clean sur-

face is not necessary with

hot flash butt welding. If the

abutting faces differ greatly

from the desired plane-

parallelism, an additional

flashing process (a short

flashing period with low

speed and high energy)

may be carried out first.

The welding area of the

structure of a flash butt

weld shows a zone which

is reduced in carbon and

other alloying elements,

Figure 7.7. Moreover, all

flash butt welded joints

have a pronounced coarse

grain zone, whereby the

toughness properties of the

welded joint are lower than

of the base metal. By the

impact normalizing effect in

Figure 7.6

Flashing Travel, Upset Travel, Upset Forceand Welding Current in Timely Order

br-er7-06e.cdr

hot flash welding cold flash welding

upset travel

flashing travel

upset force

amperage

time time

preheating flashing flashing

Secondary StructureAlong a Flash Butt Weld

br-er7-07e.cdr

heat affected zone

10 mm

0,1 mm

material: C60 E

weld coarse grain zone fine grain zone soft-annealing zone base metal

Figure 7.7


2005

the machine successive to the actual welding process, can the toughness properties be con-

siderably increased. By one or several current impulses the weld temperatures are increased

by up to approximately 50° over the austeniting temperature of the metal.

Steels, aluminium, nickel and copper alloys can be welded economically with the flash butt

welding process. Supported by the axial force, shrinkage in flash butt welding is so insignifi-

cant that only very low residual stresses occur. It is, therefore, possible to weld also steels

with a higher carbon content.

Profiles of all kind are butt welded with this method. The method is used for large-scale

manufacture and with components of equal dimensions. The weldable cross-sections may

reach dimensions of up to 120,000 mm². Areas of application are the welding of rails, the

manufacture of car axles, wheel rims and shafts, the welding of chain links and also the

manufacture of tools and endless strips for pipe production.

Friction welding is a pressure welding method where the necessary heat for joining is pro-

duced by mechanical friction. The friction is, as a rule, generated by a relative motion be-


n

n

F friction force1

F upset force2

Figure 7.8

br-er7-09e_sw.cdr

Phases of Friction Welding Process

Figure 7.9


2005

tween a rotating and a stationary workpiece

while axial force is being applied at the same

time, Figure 7.8.

After the joint surfaces are adequately heated,

the relative motion is discontinued and the

friction force is increased to upsetting force.

An even, lip-shaped bead is produced which

may be removed in the welding machine by

an additional accessory unit. The bead is of-

ten considered as the first quality criterion.

Figure 7.9 shows all phases of the friction

welding process. In most cases this method

is used for rotation-symmetrical parts. It is,

nowadays, also possible to accurately join

rectangular and polygonal cross-sections.

The most common variant of friction weld-

ing is friction welding with a continuous drive and friction welding with a flywheel drive, Fig-

ure 7.10. In friction welding with continuous drive, the clamped-on part to be joined is

kept at a constant nominal speed by a drive, while the workpiece in the sliding chuck is

pressed with a defined friction force. The nominal speed is maintained until the demanded

temperature profile has

been achieved. Then the

motor is declutched and

the relative motion is neu-

tralised by external braking.

In general, the friction force

is raised to upsetting force

after the rotation movement

has been discontinued.

During flywheel friction

welding, the inertia mass

is raised to nominal speed,


conventional friction welding

clutch

driving motor

brakeclamping tool clamping tool

workpiece pressure elementfor axial pressure

flywheel friction welding

clamping tool clamping tool

workpiecepressure elementfor axial pressure

flywheel

Figure 7.10

Comparison of the Welding Processes forConventional and Flywheel Friction Welding

br-er7-11e.cdr

conventional friction welding flywheel friction welding

number ofrevolutions

axialpressure

torque

20...100 Nmm-2

40...280

Nmm-2

time

friction welding time1...100s

friction welding time0,125...2s

braking0,1...0,5s

1800...

5400 min-1

900...

5400min-1

40...280

Nmm-2

Figure 7.11


2005

the drive motor is declutched and the stationary workpiece is, with a defined axial force,

pressed against the rotating workpiece. Welding is finished when the total kinetic energy -

stored in the flywheel – has been consumed by the friction processes. This is the so-called

self-breaking effect of the system. The method is used when, based on metallurgical proc-

esses, extremely short welding times may be realised. Further process variants are radial

friction welding, orbital friction welding, oscillation friction welding and friction surfacing. How-

ever, these process variants are until today still in the experimental stage. Recently, new de-

velopments in the field of friction stud welding – studs on plates – have been introduced.

Figure 7.11 depicts the variation in time of the most important process parameters in

friction welding with continuous drive and flywheel friction welding. The occuring moments’

maxima may be interpreted as follows: The first maximum, at the start of the frictional con-

tact, is explained by the formation of local fusion zones and their shearing off in the lower

temperature range.

The torque decreases as a result of the risen temperature - which again is a consequence

of the increased plasticity - and of the lowered deformation resistance. The second maximum

is generated during the braking phase which precedes the spindle standstill. The second

maximum is explained by

the increased deformation

resistance at dropping

temperatures. The tem-

perature drop in the joining

zone is explained by the

lowered energy input – due

to the rotation-speed de-

crease – and also by the

augmented radial dis-

placement of the highly

heated material into the

weld upset.

In friction welding with a continuous drive, the process variation “combined friction weld-

ing” allows the free and independent from each other selection of the braking and upsetting

moments, Fig. 7.12.

© ISF 2002

Combined Friction Welding

br-er7-12e.cdr

time

number of revolutions

friction force

reduction

upset force

Figure 7.12


2005

In this case, the rotation-energy which has been stored in the drive motor, the spindle and

also in the clamping chuck, may be totally or partially converted by self-breaking. Here, the

breaking phase matches the breaking phase in flywheel welding. The use of this process

variant allows the welding structures to influence each other in a positive way when many

welding tasks are to be carried out. Moreover, the torque range may be accurately predeter-

mined by the microcontroller of the braking initiator which prevents the slip-through of the

workpieces in the clamping chuck.

The universal friction weld-

ing machine is in its struc-

ture similar to a turning

lathe, however, for the

transmission of the high

axial forces, the machine

structure must be consid-

erably more rigid.

Basically, there are three

types of friction welding: a)

friction welding with a rotat-

ing workpiece and a trans-

lational motion of the other

workpiece; b) friction weld-

ing with rotation and trans-

lational motion of one

workpiece facing a station-

ary other workpiece, c)

rotation and translation of

two workpieces against a

stationary intermediate

piece. The remaining varia-

tions, shown in Fig-

ure 7.13, also find applica-

tions when both work-

pieces have to rotate in

© ISF 2002

Types of Friction Welding Processes

br-er7-13e.cdr

a) b)

c) d)

e) f)

P

P

P P

P

P

PP

P

Figure 7.13

© ISF 2002

Joint Types Obtainedby Friction Welding

br-er7-14e.cdr

beforewelding

afterwelding

beforewelding

afterwelding

8. pipe with plate, without preparation

7. round material with plate, without preparation

6. pipe with plate

5. round material with plate

g/d 0,25...0,3»

4. pipe with pipe1. a)round stock with round stock

b) round stock with round stock, chamfered

2. a)round stock with round stock (different cross-sections, partially machined)

b) round stock with round stock (different cross-sections, bevelled)

3. round stock with pipe

d=0,75D

dD

0,75d

d

d D

d 0,6D»

1..2°

(1/6)d

d

g

Figure 7.14


2005

opposite direction to each other. For example, when a low diameter and, in connection with

this, the low relative speeds demand the necessary heat quantity.

A survey of possible joint shapes achievable with friction welding is given in Figure 7.14.

The specimen preparation of the joining members should, if possible, be carried out in a way

that the heat input and the heat dissipation is equal for both members. Depending on the

combination of materials can this provision facilitate the joining task considerably. The abut-

ting surfaces should be smooth, angular and of equal dimensions. A simple saw cut is, for

many applications, sufficient.

The method of heat generation causes a

comparatively low joining temperature – lower

than the melting temperature of the metals.

This is the main reason why friction welding is

the suitable method for metals and material

combinations which are difficult to weld. It is

also possible to weld material combinations

(e.g. Cu/Al or Al/steel) which cannot be joined

using other welding processes otherwise only

with increased expenditure. Figure 7.15

shows a survey of possible material combi-

nations. Many combinations have, however,

not yet been tested on their suitability to fric-

tion welding. Metallurgical reasons which may

reduce the friction weldability are:

1. the quantity and distribution of non-metal inclusions,

2. formation of low-melting or intermetallic phases,

3. embrittlement by gas absorption (as a rule, the costly, inert gas shielding can be dis-

pensed with, even when welding titanium),

4. softening of hardened or precipitataly-hardened materials and

5. hardening caused by too high a cooling rate.


aluminiumaluminium alloysaluminium, sinteredleadcast iron (GGG, GT)hard metal, sinteredcobaltcoppermagnesiumbrassmolybdenumnickelnickel alloysniobiumsilversteel, unalloyedsteel, alloyed steel, high alloyedsteel, austenticcast steelfree cutting steelstellitetantalumtitaniumvanadiumtungstencirkon

cir

kon

tung

ste

nva

nadiu

mtita

niu

mta

nta

lum

ste

llite

free c

utt

ing

ste

el

ca

st ste

el

ste

el, a

uste

ntic

ste

el, h

igh a

lloyed

ste

el, a

lloyed

ste

el, u

nallo

yed

silv

er

nio

biu

mnic

kel allo

ys

nic

kel

moly

bde

num

bra

ss

mag

ne

siu

mco

pper

co

balt

hard

meta

l, s

inte

red

ca

st iron

(G

GG

, G

T)

lea

dalu

min

ium

, sin

tere

dalu

min

ium

allo

ys

alu

min

ium

friction weldable

restricted friction weldable

not friction weldable

not tested

Figure 7.15


2005

Secondary StructureAlong a Friction Weld

br-er7-16e.cdr

10 µm

1 mm

10 mm

metal: S235JRp = 30 N/mmt = 6 st = 250 N/mmn = 1500 U/min

2

2

St

structures on parallels with a 5 mm distance from the sample axis

base metal heat affected zone transition heat affected zone - weld metal

weld metal

Figure 7.16

By the adjustment of the welding parameters in respect toweld joints, can in most cases

joints with good mechano-technological properties be obtained.

The secondary structure

along the friction-welded

joint is depicted in Fig-

ure 7.16. An extremely

fine-grained structure

(forge structure) develops

in the joining zone region.

This structure which is

typical of a friction-welded

joint is characterised by

high strength and tough-

ness properties.

Figure 7.17 shows a comparison between a flash butt-welded and a friction-welded car-

dan shaft. The two welds are distinguished by the size of their heat affected zone and the

development of the weld upset. While in fric-

tion welding a regular, lip-shaped upset is pro-

duced, the weld flash formation in flash butt

welding is narrower and sharper and also con-

siderably more irregular. Besides, the heat

affected zone during friction welding is sub-

stantially smaller than during flash butt weld-

ing.

Friction welding machines are fully

mechanized and may well be integrated into

production lines. Loading and unloading

equipment, turning attachments for the prepa-

ration of the abutting surfaces and for upset

removal and also storage units for

complete welding programs make these ma-

chines well adaptable to automation. The ma-

chines may furthermore be equipped with


flash butt welding

friction welding

Figure 7.17


2005

parameter supervisory systems. During weld-

ing are parameters: welding path, pressure,

rotational speed, and time are governed by

the desired value/actual value comparison.

This allows an indirect quality control. A fur-

ther complement to the retension of parame-

ters is the torque control, however this method

is costly and it cannot be used for all applica-

tions because of its structural dimensions.

Friction welding machines are mainly used in

the series production and industrial mass

production.

Nevertheless, these machines are also al-

ways applied when metals and material com-


1 2

3 4

1,2 joint ring 3 loading device

4 unloading grippersmaterial combination:Cf53/ Ck45


1 cardan shaft, AIZn 4,5 Mg 1

2 cardan shaft, retracted tube

3 cardan shaft, flattening test specimen

4 crown wheel, 16MnCr5/ 42Cr4

5 bimetal valve, X45CrSi9-3/ NiCr20 TiAl



1 pump shaft

2 shaft C22E/ E295

3 press cylinder S185/9S 20K

4 hydraulic cylinder S235J3G2/ C60E or S235JR/ C15

5 cylinder case S235JR/ S355J2G3

6 piston rod 42Cr4

7 connecting rod 100Cr6/ S235JR

8 stud S235J2G3/ X5CrNi18-10

9 knotter hook 15CrNi6

Figure 7.20


2005

binations which are difficult to weld have to be joined in a reliable and cost-effective way.

With the machines that are presently used in Germany, it is possible to weld massive work-

pieces in the diameter

range of 0.6 up to 250 mm

For steel pipes, the maxi-

mum weldable diameter is

at present approximately

900 mm, the wall thick-

nesses are approx. 6 mm.

Figures 7.18 to 7.20 show

a selection of examples for

the application of friction

welding.

Figure 7.21 shows a com-

parison of the cost expenditure for the manufacture of a cardan shaft, carried out by

forging and by friction welding, respectively.

It shows that the application of the friction

welding method may save approx. 20% of the

production costs. This comparison is, however,

not an universally valid statement as for each

component a profitability evaluation must be

carried out separately. The comparison is just

to show that, in many applications, consider-

able savings can be made if the matter of the

joining technology by “friction welding” could

be circulated to a wider audience of design

and production engineers.

Figure 7.22 shows in brief the important ad-

vantages and disadvantages of friction

welding in comparison with the competitive

method of flash butt welding.

Cost Comparison of Forging/ FrictionWelding in a Case of a Cardan Shaft

br-er7-21e.cdr

forged piece

motor shaft € 20,-

€ 20,-

friction-welded piece

material costs shaftØ30 und 40 mm

€

€

€

€

7,50

4,25

3,-

14,75

2x friction weldsincl. upset removal

flange,forged

160 m

m

Ø40 m

m

Ø30 mm

friction welds

940 mm

Figure 7.21


Advantages and disadvantages of friction weldingin comparison with the competitive flash butt welding

advantages:

disadvantages:

- clean and well controllable bulging- low heat influence on joining members- better control of heat input- low phase seperation phenomena in the bond zone- hot forming causes permanent recovery and recrystallisation processes in the welding area thus forming a very fine-grained structure with good toughness and strength properties (forged structure)- low susceptibility to defects, extremely good reproducibility within a wide parameter range- frequently shorter welding times- more choice in the selection of weldable materials and material combinations

- torque-safe clamping necessary- machine-determined smaller maximum weldable cross-sections- susceptibility to non-metal inclusions- high expenditure requested because of high manufacturing tolerances- high capital investment for the machine

Figure 7.22


2005

Pressure welding with magnetically impelled arc, “Magnetarc Welding”, is an arc pres-

sure welding method for the joining of closed structural tubular shapes, Figure 7.23. The

weldable wall thickness

range is between 0.7 and

5 mm, the weldable diame-

ter range between 5 and

300 mm. In “Magnetarc

Welding” an arc burns be-

tween the joining surfaces

and is rotated by external

magnetic forces. This is

achieved by a magnet coil

system that produces a

magnetic field.

The combined action of this magnetic field and the arc’s own magnetic field effects a tangen-

tial force to act upon the arc. The rotation of the arc heats and melts the joint surfaces. After

an adequate heating operation, the two work-

piece members are pressed and fused to-

gether. A regular weld upset develops which is

normally not removed. The welding operation

takes place under shielding gas (mainly CO2).

The shielding gas’ function is not the protec-

tion of the weld from the surrounding atmos-

phere but rather a contribution towards the

stabilisation of the arc. The reproducibility of

the arc ignition and motion behaviour and the

regularity of the weld bead are therefore im-

proved.

The prerequisite for the application of a mate-

rial in “Magnetarc Welding” is its electrical

conductivity and melting behaviour. Fig-

Diagrammatic Representationof Magnetic Arc Welding

br-er7-23e.cdr

1. starting position

2. starting of welding

3. heating

4. completion of welding

a) both workpieces are brought into contactb) welding current and magnetic field are switched on

a) both workpieces are seperated until a defined gap width is reached (retracting movement) - the arc ignites

a) the arc rotatesb) the joint surfaces are melting

a) both workpieces are broght into contact again and upsetb) welding current and magnetic field are switched off

Figure 7.23


steel, unalloyed

steel, lowalloyed

free cutting steel

cast steel

malleable

ste

el, u

nallo

yed

ste

el, low

allo

yed

free c

uttin

g s

teel

cast ste

el

ma

llea

blematerials

suitable for

magnetic arc

welding

not tested

Figure 7.24


2005

ure 7.24 gives a survey of

the material combinations

which are nowadays al-

ready weldable under in-

dustrial conditions.

As reason is the symmetric

heat input, the subsequent

upsetting of the liquid

phase and the cooling off

under pressure. The

cracking sensitivity of the

welds is, in general, rela-

tively low. This has a posi-

tive effect, particulary when

steels with a high carbon content or machining steels are welded. The joining faces of the

workpieces must be free from contamination, such as rust or scale.

To obtain a defect-free weld, normally a sim-

ple saw cut is a sufficient preparation of the

abutting surfaces. If special demands are put

on the dimensional accuracy of the joints, the

prefabrication tolerances have to be adjusted

accordingly. This applies also to friction weld-

ing.

Figures 7.25 and 7.26 show several applica-

tion examples of pressure welding with mag-

netically impelled arc.

Figure 7.27 shows a summary of the most

important advantages and disadvantages of

this method in comparison with the competi-

tive methods of friction welding and flash butt

welding.

© ISF 2002

Applications for Magnetic Arc Welding

br-er7-25e_sw.cdr

Figure 7.25


Figure 7.26


2005

In friction-stir welding a cylindrical, mandrel-

like tool carries out rotating self-movements

between two plates which are knocked and

clamped onto a fixed backing. The resulting

friction heat softens the base metal, although

the melting point is not reached. The plastified

material is displaced by the mandrel and

transported behind the tool where a longitudi-

nal seam develops.

The advantages of this method which is

mainly used for welding of aluminium alloys is

the low thermal stress of the component

which allows joining with a minimum of distor-

tion and shrinkage. Welding fumes do not de-

velop and the addition of filler metal or shield-

ing gases is not required.


Advantages and disadvantages of magnetic arc welding in

comparison with flash butt welding and/ or friction welding

advantages:

- lower energy demands

- material savings through lower loss of length

- better dimensional accuracy in joining especially for small

wall thicknesses

- in comparison with friction welding less moving parts

(only axial movement of one joining member during upsetting)

- no restrictions to the free clamping length

- smaller and more regular welding edge

- no spatter formation

disadvantages:

- suitable for small wall thicknesses only

(maximum wall thickness: 4 - 5 mm)

- welding parameters must be kept within narrow limits

- only magnetizing steels are weldable without any difficulties

Figure 7.27

Friction-Stir Welding

br-er7-28e.cdr

tool collar

fixed backing

contoured pin

workpiece

Figure 7.28

8.

Resistance Spot Welding,

Resistance Projection Welding

and Resistance Seam Welding

8. Resistance Spot-, Resistance Projection- and Resistance Seam Welding 105

2005

Figure 8.1 shows an extract from the classification of the welding methods according to DIN

1910 with a detailed account of the conductive resistance pressure welding.

In the case of resistance pressure welding, the heating occurs at the welding point as a con-

sequence of Joule resistance heating caused by current flow through an electrical conductor,

Figure 8.2. In spot and pro-

jection welding, the plates

to be welded in overlap.

Current supply is carried

out through spherical or

flat electrodes, respec-

tively. In roller seam weld-

ing, two driven roller elec-

trodes are applied. The

plates to be welded are

mainly overlapped. The

heat input rate Qinput is

generated by resistance

heating in a current-

carrying conductor, Figure

8.3. However, only the ef-

fective heat quantity Qeff is

instrumental in the forma-

tion of the weld nugget.

Qeff is composed of the

input heat minus the dissi-

pation heat. The heat loss

arises from the heat dissi-

pation into the electrodes

and the plates and also

from thermal radiation.

© ISF 2002

Classification of WeldingAccording to DIN 1910

br-er8-01e.cdr

resistance spotwelding

roller seam welding

projectionwelding

resistance buttwelding

flash buttwelding

resistance pressurewelding

induction pressurewelding

Conduction pressurewelding

pressurewelding

cold pressurewelding

friction welding

fusionwelding

welding

Figure 8.1

br-er8-02e.cdr

4 loaded area

roller seam welding

workpiece usually in general overlap

driven roller electrode spot rows (stitch weld,

roller spots)

�

�

�

1

3

4

2

1

5 projection

projection welding

workpieces with elevations (concentration of electicity)

workpieces overlap pad electrode several joints in a single weld weld nugget joint

�

�

�

�

�

1 3

5

2

1

spot welding

�

�

�

workpieces overlap electrode weld nugget

1 electrode force2 elektrodes3 production part

1 32

1

Figure 8.2


2005

The resistance during resistance heating is composed of the contact resistances on the two

plates and of their material resistance. The reduction of the electrode force down to 90% in-

creases the heat input rate by 105%, the reduction of the welding current down to 90% de-

creases the heat rate to 80% and a welding time reduction to 90% decreases the heat rate to

92%.

The time progression of the resistance is shown in Figure 8.4. The contact resistance is

composed of the interface resistances between the electrode and the plate (electrode/plate)

and between the plates

(plate/plate). The resis-

tance height is greatly de-

pendent on the applied

electrode force. The higher

this force is set, the larger

are the conductive cross-

sections at the contact

points and smaller the re-

sistances. The contact sur-

faces, which are rapidly

increasing at the start of

welding, effect a rapid re-

duction of interface resis-

tances.

With the formation of the

weld nugget the interface

resistances between the

plates disappear. During

the progress of the weld

the material resistance in-

creases from a low value

(surrounding temperatures)

to a maximum value above

the melting temperature.

br-er8-04e.cdr

theoretical contact area100% metallic conduction contact

proportion at room temperature

proportion after firstmilliseconds welding time

low electrode forcehigh resistance

high electrode forcelow resistance

surface resistance is collapsed,a3 is highly extended

A1: area out-of-contactA2: contact area with high resistanceA3: contact area completely conductive

welding time

5 10 periods

resis

tance

mOhm

total resistance

sum of contact resistances

sum of material resistance

Figure 8.4


Heat Balance in Spot Welding

Qeff

Q2

Q2

Q4

Q4

Q4

Fel

Fel

Q4

Q3

Q3

Q = Q - Qeff input 1l

Q = Q + Q + Q1 2 3 4

R(t) = R (t) + R (t)material c

Q = C I (t) R(t) dtinput

2

t=tS

t=0

F :

Q :

Q :

I:

Q :

Q :

Q :

Q :

R(t):

R (t):

R (t):

el

eff

input

1

2

3

4

material

c

electrode force

effective heat

total heat input

current (time dependence)

heat losses

losses into the electrodes

losses into the sheet metal

losses by heat radiation

total resistance

material resistance

contact resistance

Figure 8.3


2005

Figure 8.5 shows dia-

grammatically the different

resistances during the spot

welding process with act-

ing electrode force, but

without welding current.

Weld nugget formation

must therefore start in the

joining zone because of

the existing high contact

resistance there.

Figure 8.6 shows directly

cooled electrodes for resis-

tance welding. The coolant

is normally water. In the

cooling tube, the cooling

water is transported to the

electrode base. The dia-

gram shows the tempera-

ture distribution in the elec-

trodes and in the plates.

The maximum temperature

is reached in the centre of

the weld nugget and de-

creases strongly in the

electrode direction.

Sequence of a resistance spot welding process, Figure 8.7:

1->2 Lowering of the top electrode

2->3 Application of the adjusted electrode force Set-up time tpre, sequence

3->4 Switching-on of the adjusted welding current for the period of the welding time tw. For-

mation of the weld nugget in the joining zone of both workpieces.

br-er8-05e.cdr

electrode force resistance rate

~_

R1

R3

R6

R7

R4

R2

0 100 200

R4

R7

R5

R6

R3

R [µOhm]

R5

Figure 8.5


Electrode Cooling

cooling tube

cooling drill-hole

slope

10 -

20

2-5

6-8

°C

Figure 8.6


2005

An example shows the macrosection of a weld nugget after the welding time has

ended.

4->5 Maintaining the electrode force for the period of the set post-weld holding time th.

5->6 Switching-off the force generating system and lifting the electrodes off the workpiece.

The functions of the set-up time and the post-weld holding time are listed in Figure 8.8. De-

pendent on the welding task different force and current programs can be set in the weld-

ing machines, Figure 8.9. In the top the simplest possible welding program sequence is

shown: The application of the electrode force, the set-up time sequence tpre, the switching-on

of the welding current and the sequence of the welding time tw, the sequence of the post-

weld holding time th and the switching-off of the force generating system. The diagram in the

centre is almost identical to the one just described.

Merely in the welding current range, welding is carried out using an adjustable current rise (7)

and current decay (8). The diagram below depicts a more sophisticated current program. In

addition, welding is carried out with a variable electrode force (2) and with preheating (4) and

post-heating current (6). Dependent on the control system, the process can be influenced by

adjustment.


Time Sequence ofResistance Spot Welding

Fel Iw

electrode force Fel

welding current Iw

time t

top electrode

workpiece

weld nuggetlower electrode

tpre tw th

insufficiently melted weld nugget totally melted weld nugget

Figure 8.7


Functions of Pre- and Postwelding

set-up time

postweld-holding time

- compressing the workpiece - build-up of electrode force to preset value - setting-up of reproducible resistance before welding - electrode resting after bounce - preventing resting of electrode on workpiece under electricle voltage

- holding time of workpiece during cooling of molten metal - prevention of pore formation in the welding nugget - prevention of lifting the electrode under voltage

The postweld-holding time hasinfluence on the weld point hardeningwithin certain limits.

Figure 8.8


2005

A controlled variable may be, for instance, the electrode path, the resistance progress, the

welding current or the welding voltage.

Figure 8.10 shows the principle structure of a resistance spot welding machine. The

main components are: the machine frame, the welding transformer with secondary lines, the

electrode pressure system and the control system. This principle design applies to spot, pro-

jection and roller seam welding machines. Differences are to be found merely in the type of

electrode fittings and in the electrode shapes.

Figure 8.11 depicts the possible process variations of resistance spot welding. These are

distinguished by the number of plates to be welded and by the arrangement of the electrodes

or, respectively, of the transformers. It has to be noted that with a corresponding arrange-

ment also plates can be welded where one of the two plates has a non-conductive surface

(as, for example, plastics).


Schematic Assembly of Spot Welding Machine

1 electrode force cylinder 2 pneumatic equipment 3 machine tool frame 4 welding transformer 5 power control unit 6 current conductor 7 lower arm 8 foot switch 9 top arm10 electrical power supply cable11 water cooled electrode holder12 electrode

1

2

3

4

5

6

7

8

9

10

11 12



Course of Force and Current

t = pre-weld time

t = welding time

t = holding time

t = pressure time

pre

w

h

pres

tpres

ele

ctr

od

e f

orc

e

we

ldin

g c

urr

en

t

5 Iw

tpre tw th

Fel

time

ele

ctr

od

e f

orc

e

we

ldin

g c

urr

en

t

57 8

Iw

Fel

time

ele

ctr

od

e f

orc

e

weld

ing

cu

rre

nt

52

1

7 864

3

Iw

Fel

time

1 - initial force2 - welding pressure force3 - post pressure force4 - preheating current5 - welding current6 - postheating current7 - ascending current8 - descending current


2005

Figure 8.12 shows the current types which are normally used for resistance welding.

Alternating current has the

simplest structure (Figure

8.13) and is most price ef-

fective, unavoidable are,

however, the disadvan-

tages of current zeros and

weld nugget cooling. In

relation to the average cur-

rent values, peak loads

occur and, with that, in-

creased electrode wear.

These extreme peak loads

do not occur with direct

current.

The structural design of a d.c. supply unit is, however, more complicated and, therefore,

more expensive than an a.c. supply unit.

As conventional welding machines operate with a 50 Hz primary current supply, the welding

current can be controlled only in 20 ms units (1 period). When the inverter-direct current

technique or, respectively, the medium-frequency technique is used, a finer setting of the cur-

rent-on period and a more

precise control of the weld-

ing current is possible.

In order to realise higher

currents and shorter weld-

ing times, the impulse ca-

pacitor resistance welding

technique is applied. The

rectified primary current is

stored in capacitors and,

through a high-voltage

transformer, converted to


Variants of Spot Welding

~~

two-sided single-shearsingle-spot welding

one-sided duplex spot weldingwith conductive base

two-sided two-shearspot welding (stack welding)

~

one-sided single-spot weldingwith contact electrode

two-sided duplex spotwelding

~

+

~

+

~

+

one-sided multi-spot weldingwith conductive base

~

+ +

Figur 8.11

Figur 8.12


Current Types

impulse capacitor current

45

40

35

30

25

20

15

10

5

0

0.00 0.02 0.04 0.06 0.08 0.10 0.12 0.14 0.16

alternating current

welding time [s]

20

15

10

5

0

-5

-10

-15

-20

0.00 0.02 0.04 0.07 0.09 0.11 0.13 0.16

curr

en

t [k

A]

12

10

8

6

4

2

0

medium frequency direct current

0.00 0.02 0.04 0.06 0.08 0.10 0.12 0.14 0.16

welding time [s]

curr

ent [k

A]

"conventional" direct current

18

16

14

12

10

8

6

4

2

0

0.00 0.02 0.04 0.06 0.08 0.10 0.12 0.14 0.16

welding time [s] welding time [s]

curr

ent [k

A]

curr

ent [k

A]


2005

high welding currents. The

advantages of this tech-

nique are low heat input

and high reproducibility.

Because of the high energy

density, materials with

good conductivity can be

welded and also multiple-

projection welds can be

carried out. A disadvantage

of this method is, apart

from the high equipment

costs, the difficult regula-

tion of the welding current.

Electrodes for spot resistance welding have the property of transferring the electrode force

and the welding current. They are wearing parts and, therefore, easily replaceable.

br-er8-15e.cdr

Electrode Materials

requirements

- good electrical conductivity- good thermal conductivity- high high-temperature strength- high temperature stability- high softening temperature- little tendency to alloying with workpiece material- easy options in machining

Cu - ETP

Cu Cdl

Cu Crl

Cu Crl Zr

Cu CO2 Be

Cu Ni2 Si

Cu Ni1 P

Cu Be2 Co Ni

Cu Ag6

CuAl10NiFe5Ni5

ISO 5182

A

1

2

3

4

1

2

1

2

1

2

1

2

3

4

Group Type No.

Key

W75 Cu

W78 Cu

WC70 Cu

Mo

W

W65 Ag

ISO 5182

B

10

11

12

13

14

15

Group Type No.

Key

Figure 8.15

br-er8-13e.cdr

3-phase direct current

static-inverter direct current

capacitor impulse discharge

single-phasealternating current

Figure 8.13

Figure 8.14


Electrodes,Electrode Caps and Holders

electrodes

electrode caps

electrode holders

form A form B

form Fform E form G

form Dform C


2005

Depending on the shape and type of electrode, solid electrodes or electrode caps, must

be either remachined or recycled. Figure 8.14 depicts various types of electrodes, electrode

caps and holders.

Dependent upon the electrode application, different alloyed electrode materials are used,

Figure 8.15. The added alloying elements influence the red hardness, the tempering resis-

tance, the conductivity, the fusion temperature, the electrode alloying tendency, and, finally,

the machinability of the electrode material. When beryllium is used as an alloying element,

the admissible MAC values must be strictly adhered to during remachining or dressing of the

electrodes.

Already during the design phase of the components to be welded, importance must be at-

tached to a good accessibility of the welding point. Moreover, the electrode force which is

imperative to the process must be applied in a way that no damage is done to the workpiece.

In the ideal case, the welding point is accessible from the top and from below, Figure 8.16.


Accessibility for SpotWelding Electrode

poor good

Figure 8.16


Contact Area forSpot Welding Electrodes

poor good

Figure 8.17


2005

In order to avoid the displacement of the elec-

trodes, the electrode working surface must

be flat. Also during the design phase space

must be provided for an adequately large

clearing zone around the working point, in

order to guarantee the unimpeded electrode

approach to the working point, Figure 8.17.

Dependent on the joining job, the process

variation, or the resistance welding method, a

so-called “shunt current/effect” may be no-

ticed. This current component, as a rule, does

not contribute to the formation of the weld

nugget; under certain circumstances it might

even prevent a reliable welding process. In

the example, shown in Figure 8.18, the shunt

current leads to undesired fusing contacts

and, because of the lacking electrode force at

this point, also to damages to the plate sur-

face.

If unsuitable welding parameters have been

set, weld spatter formation may occur, Fig-

ure 8.19. Liquid molten metal forms on the

plate surface or in the joining zone. The rea-

sons for this kind of process disturbance are,

for example, too low an electrode force with

regard to the set welding current or welding

time, too high an energy input with regard to

the plate thickness or too small an edge dis-

tance of the welding point.

Figure 8.18

br-er8-18e.cdr

Shunting

spot welding

roller seam welding

indirect weldingone side

A

coppercurrent path

shunt connection current

br-er8-19e.cdr

Welding Spatter

Welding spatter:Discharge of molten material between two steelsheets or from the surface of steel sheets.

Reason here is high welding current, (fig. 1) or too-small edge distance (fig. 2)

fig. 1 fig. 2

porosity in the joint causedby welding spatter

discharge of moltenmaterial at the joint plane

Figure 8.19


2005

Figure 8.20 shows a list of

a large number of possible

disturbances in resistance

spot welding. Welding cur-

rent changes are caused

by: shunt, electrode wear,

cable wear, mains voltage

variations, secondary im-

pedance.

Different welding condi-

tions are caused by weld-

ing machine wear, different

heat dissipation. Non-

uniform conditions by alterations to components are: different plate thicknesses, plate quality,

number of plates, plate surfaces, edge distances. Electrode force changes are caused by:

pressure fluctuations and -changes, plate bouncing.

The resistance spot welding method allows

welding of a large number of materials. A list

of the various materials is shown in Figure

8.21. The alloying elements which are used

for steels have a varying influence on the suit-

ability for resistance spot welding. The values

which are indicated in the table are valid only

when the stated element is the sole alloying

constituent of the steel material.

Figure 8.22 shows a comparison between

resistance spot and resistance projection

welding. The fundamental difference between

the two methods lies in the definition of the

current transition point.

Figure 8.20

br-er8-20e.cdr

Qeff

Q = Q - Qeff input losses

welding current changes

modification of the unit

alt

era

tio

n t

o f

orc

e

weld

ing

equ

ipm

ent

shuntconnection

platethickness

alteration

of

pressure

wear

platediversion

heat

wear ofelectrodes

qualityof plates

wear ofcable

numberof plates

mains voltagefluctuation

platesurface

secondaryelectrical

impedance

edgedistance

br-er8-21e.cdr

Weldable Materials

weldable materials

materials weld-ability

aluminium

iron

gold

cobalt

copper

magnesium

molybdenum

nickel

platinum

silver

tantalum

titanium

tungsten

satisfactory

very good

satisfactory

very good

poor

good

satisfactory

very good

very good

very good

very good

very good

satisfactory

alloyingelements

goodweldability

sufficientweldability

maximum content [%]

C

C + Cr

C + Mo

C + V

C + Mn

C + Ni

Si

Cu

P + S

C+Cr+Mo+V

0,25

0,35

0,50

0,40

1,40

3,00

0,40

0,60

0,10

0,60

0,40

1,60

0,70

0,60

1,60

4,00

1,00

0,60

0,10

1,60

influence ofalloying elements(steel materials)

Figure 8.21


2005

The differences between both methods are illustrated in Figure 8.23. The short life of the

electrodes used for resistance spot welding is explained by the higher thermal load and the

larger pressing area caused by the smaller electrode contact areas. The term “electrode life”

stands for the number of welds that can be carried out with one pair of electrodes without

further rework and without

exceeding the tolerances

for quality criteria of the

weld.

Depending on the de-

mands on the joint strength

or on the projection rigidity,

different projection shapes

are applied. These are an-

nular, circular or longitudi-

nal projections. The weld-

ing projections are, accord-

br-er8-22e.cdr

before welding after welding

projection

elektrode

follow-updistance

Figure 8.22


Differences Between ResistanceSpot and Projection Welding

spotwelding

projectionwelding

elektrodes:

diameter

tip face

electrode life

up to 20 mm

convex

less

> 20 mm

flat

longer

elektrodes projections

place wherethe nuggetoriginates

no

no

yes

yes

problems:

current distribution

force distribution

number ofwelding nuggets

one several

follow-up distance small big

Figure 8.23

br-er8-24e.cdr

Customary Projection Shapes

circular

longitudinal

annular

interrupted annular

circular

longitudinal

annular

spot

contact

line

contact

embossedprojection shape

solidprojection shape

naturalprojection shape

pressed

mould pressed

struck

machined

cut

pushed

crossed wires

bolt-pipe

Longitudinal wire-platecut

Circular

weld nut

pushed Annular

Figure 8.24


2005

ing to their size, adapted to the used plate

thickness and may, therefore, appear as dif-

ferent types in the workpiece: embossed pro-

jections, solid projections and natural projec-

tions. The survey is shown in Figure 8.24.

In Figure 8.25 the production of embossed

projections in different shapes is shown. The

shape is embossed onto the plate surface by

appropriate die plates, dies and, if necessary,

counter dies.

Various problems occur in projection weld-

ing caused by the welding of several joints in

a single working cycle. Due to different current

paths - when using direct current - and a cur-

rent displacement - when using alternating

current -, welding nuggets with differing quali-


Problem of Current DistributionDuring Projection Welding

direct current distribution intensity of current decreases from the center tothe outer area caused by the longer current path

alternating current intensity of current increases from the center tothe outer area caused by current displacement

distribution

Figure 8.26


Problems of Force DistributionDuring Projection Welding

force distribution of a C-frame projection presswelder during bending of machine tool frame

force distribution of a C-frame projection welder with non-parallel positioning tables

press

Figure 8.27


Production ofEmbossed Projection Shapes

embossed projection ring projection

longitudinal projection

l

mould plate plate

die

b

d1

d1

die

plate

mould plate

die

plate

mould plate

counter-die

Figure 8.25


2005

ties are produced when no preventive remedies are taken, Figure 8.26.

A varying force distribution,

as shown by the example

in Figure 8.27, also leads

to differing qualities of the

produced weld nuggets.

In Figure 8.28 several ex-

amples of application using

projection welding are de-

picted. In this example, the

shapes are of the em-

bossed type.

Figures 8.29 and 8.30 show several process variations of roller seam welding. Seam welding

is actually a continuous spot welding process, but with the application of roller electrodes. In

contrast to resistance spot welding the electrodes remain in contact and turn continuously

after the first weld spot has been produced. At the points where a welding spot is to be pro-

duced again current flow is

initiated. Dependent on the

electrode feed rate and on

the welding current fre-

quency, spot welds or seal

welds with overlapping

weld nuggets are pro-

duced. The application of

d.c. current also produces

seal welds. © ISF 2002br-er8-28e.cdr

Roller Seam Welding

lap joint lap joint withwire electrode

lap jointwith foil

squash seamweld

butt weldwith foil

beforewelding

afterwelding

Figure 8.29


Application of Projection WeldingExamples

Figure 8.28


2005


Weld Types for Roller Seam Welding

interrupted-current roller seam weld

overlap seal weld

continuous D.C. seal weld

Figure 8.30

9.

Electron Beam Welding


2005

The application of highly accelerated elec-

trons as a tool for material processing in the

fusion, drilling and welding process and also

for surface treatment has been known since

the Fifties. Ever since, the electron beam

welding process has been developed from the

laboratory stage for particular applications. In

this cases, this materials could not have been

joined by any industrially applied high-

production joining method.

The electron beam welding machine is made

up of three main components:

beam generation, beam manipulation and

forming and working chamber. These compo-

nents may also have separate vacuum sys-

tems, Figure 9.1.

A tungsten cathode which has been heated

under vacuum emits electrons by thermal

emission. The heating of the tungsten cathode

may be carried out directly - by filament cur-

rent - or indirectly - as, for example, by coiled

filaments. The electrons are accelerated by

high voltage between the cathode and the

pierced anode. A modulating electrode, the so-

called “Wehnelt cylinder”, which is positioned

between anode and cathode, regulates the

electron flow. Dependent on the height of the

cut-off voltage between the cathode and the

modulating electrode, is a barrier field which

may pass only a certain quantity of electrons.

This happens during an electron excess in

front of the cathode where it culminates in


Schematic Representation of anElectron Beam Welding Machine

high voltage supply

cathode

control elektrode

anode

focussing coil

stigmator

adjustment coil

defelction coil

viewing optics

valve

bea

m g

en

era

tion

beam

form

ing a

nd g

uid

ance

wo

rkin

g c

ha

mbe

r

workpiece

chamber door

workpiecehandling

to vacuum pump

to vacuum pump

Figure 9.1

© ISF 2002br-er9-02e_f.cdr

All-Purpose EBWMachine and Equipment

chamber evacuationsystem

valve

evacuationsystem for gun

EB-gun

power supply

control cabinet

workpiece receiving platform

workpiece handling

working chamber

control desk

control panel

Figure 9.2


2005

form of an electron cloud. Due to its particular shape which can be compared to a concave

mirror as used in light optic, the Wehnelt cylinder also effects, besides the beam current ad-

justment, the electrostatic focussing of the electron beam. The electron beam which diverges

after having passed the pierced anode, however, obtains the power density which is neces-

sary for welding only after having passed the adjacent alignment and focussing system. One

or several electromagnetic focussing lenses bundle the beam onto the workpiece inside the

vacuum chamber. A deflection coil assists in maintaining the electron beam oscillating mo-

tion. An additional stigmator coil may help to correct aberrations of the lenses. A viewing op-

tic or a video system allows the exact positioning of the electron beam onto the weld groove.

The core piece of the electron beam welding machine is the electron beam gun where the

electron beam is generated under high vacuum. The tightly focussed electron beam diverges

rapidly under atmospheric pressure caused by scattering and ionisation development with air.

As it would, here, loose power density and efficiency, the welding process is, as a rule, car-

ried out under medium or high vacuum. The necessary vacuum is generated in separate

vacuum pumps for working chamber and beam gun. A shut-off valve which is positioned be-

tween electron gun and working chamber serves to maintain the gun vacuum while the work-

ing chamber is flooded. In universal machines, Figure 9.2, the workpiece manipulator as-

sembly inside the vacuum chamber is a slide with working table positioned over NC-

controlled stepper motors. For workpiece removal, the slide is moved from the vacuum

chamber onto the workpiece platform. A distinction is made between electron beam ma-

chines with vertical and horizontal beam manipulation systems.

The energy conversion in

the workpiece, which is

schematically shown in

Figure 9.3, indicates that

the kinetic energy of the

highly accelerated elec-

trons is, at the operational

point, not only converted

into the heat necessary for

welding, but is also re-

leased by heat radiation


Energy Transformation Inside Workpiece

z

y

xconvection

thermal radiation

heat conduction

x-ray

secondary electrons

back-scattered electrons

Figure 9.3


2005

and heat dissipation. Furthermore, a part of the incident electrons (primary electrons) is sub-

ject to backscatter and by secondary processes the secondary electrons are emitted from the

workpiece thus generating X-rays.

The impact of the electrons, which are tightly focussed into a corpuscular beam, onto the

workpiece surface stops the electrons; their penetration depth into the workpiece is very low,

just a few µm. Most of the kinetic energy is released in the form of heat. The high energy

density at the impact point causes the metal to evaporate thus allowing the following elec-

trons a deeper penetration.

This finally leads to a metal

vapour cavity which is sur-

rounded by a shell of fluid

metal, covering the entire

weld depth, Figure 9.4. This

deep-weld effect allows

nowadays penetration

depths into steel materials

of up to 300 mm, when

modern high vacuum-high

voltage machines are used.

The diameter of the cavity

corresponds approximately

with the beam diameter. By

a relative motion in the di-

rection of the weld groove

between workpiece and

electron beam the cavity

penetrates through the ma-

terial, Figure 9.5. At the

front side of the cavity new

material is molten which, to

some extent, evaporates,

but for the most part flows


Condition in Capillary

F1 : force resulting from vapour pressure

F2 : force resulting from surface tension

F3 : force resulting from hydrostatic pressure

motion of the molten metalgroove

vapour capillary

groovefront side

electron beam

solidifiedzone

moltenzone

melting pool

welding direction

F2

F3

F1

F1

keyhole

Figure 9.5


Principle of Deep Penetration Welding

a) b) c) d)

Figure 9.4


2005

around the cavity and rapidly solidifies at the backside. In order to maintain the welding cavity

open, the vapour pressure must press the molten metal round the vapour column against the

cavity walls, by counteracting its hydrostatic pressure and the surface tension.

However, this equilibrium of

forces is unstable. The tran-

sient pressure and tempera-

ture conditions inside the

cavity as well as their re-

spective, momentary diame-

ters are subject to dynamic

changes. Under the influ-

ence of the resulting, dy-

namically changing geome-

try of the vapour cavity and

with an unfavourable selec-

tion of the welding parameters, metal fume

bubbles may be included which on cooling

turn into shrinkholes, Figure 9.6.

The unstable pressure exposes the molten

backside of the vapour cavity to strong and

irregular changes in shape (case II). Pressure

variations interfere with the regular flow at the

cavity backside, act upon the molten metal

and, in the most unfavourable case, press the

unevenly distributed molten metal into differ-

ent zones of the molten cavity backside, thus

forming the so-called vapour pockets. The

cavities are not always filling with molten

metal, they collapse sporadically and remain

as hollow spaces after solidification (case Ill).

The angle ß (case I) increases with the rising


Model of Shrinkage Cavity Formation

workpiece movement

IIIIIβ

I

Figure 9.6


Comparison of EB, GMAW and SAW-Narrow Gap and Conventional SAW

EBW MSG(narrow gap)

UP(narrow gap)

UP(conventional)

150

EBW MSG(narrow gap)

UP(narrow gap)

UP

welding current 0,27 A 260 A 650 A 510 A

welding voltage 150.000 V 30 V 30 V 28 V

groove area 896 mm2

2098 mm2

4905 mm2

5966 mm2

number of passes 1 35 81 143

filler metal 0 23 kg 54 kg 66 kg

melting efficiency 7,7 kg/h 5 kg/h 13 kg/h 9 kg/h

energy input 64·10 kJ3

128·10 kJ3 293·10 kJ

3 377·10 kJ

3

welding time 27 min 4 h 35 min 4 h 11 min 7 h 20 min

(conventional)

Figure 9.7


2005

weld speed and this is defined as a turbulent process. Flaws such as a constantly open va-

pour cavity and subsequent continuous weld solidification could be avoided by selection of

job-suitable welding parameter combination and in particular of beam oscillation characteris-

tics, it has to be seen to a constantly of the molten metal, in order to avoid the above-

mentioned defects. Customary beam oscillation types are: circular, sine, double parabola or

triangular functions.

Thick plate welding accentuates the process-specific advantage of the deep-weld effect and,

with that, the possibility to join in a single working cycle with high weld speed and low heat

input quantity. A comparison with the submerged-arc and the gas metal-arc welding proc-

esses illustrates the depth-to-width ratio which is obtainable with the electron beam technol-

ogy, Figure 9.7. Electron beam welding of thick plates offers thereby decisive advantages.

With modern equipment, wall thicknesses of up to 300 mm with length-to-width ratios of up to

50 : 1 and consisting of low and high-alloy materials can be welded fast and precisely in one

pass and without adding any filler metal. A corresponding quantification shows the advantage

in regard of the applied filler metal and of the primary energy demand.

Compared with the gas-shielded narrow gap

welding process, the production time can be

reduced by the factor of approx. 20 to 50.

Numerous specific advantages speak in fa-

vour of the increased application of this high

productivity process in the manufacturing

practice, Figure 9.8. Pointing to series produc-

tion, the high profitability of this process is

dominant. This process depends on highly

energetic efficiency together with a sparing

use of resources during fabrication.


Advantages of EBW

in vacuum

at atmosphere

thin and thick plate welding (0,1 mm bis 300 mm)

extremely narrow seams (t:b = 50:1)

low overall heat input => low distortion => welding of completely processed components

high welding speed possible

no shielding gas required

high process and plant efficiency

very high welding velocity

gap bridging

no problems with reflection during energy entry into workpiece

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material dependence, often the only welding method

good

Figure 9.8


2005

Considering the above-mentioned advan-

tages, there are also disadvantages which

emerge from the process. These are, in par-

ticular, the high cooling rate, the high equip-

ment costs and the size of the chamber, Fig-

ure 9.9.

In accordance with DIN 32511 (terms for

methods and equipment applied in electron

and laser beam welding), the specific desig-

nations, shown in Figure 9.10, have been

standardised for electron beam welding.

Electron beam units are not only distinguished

by their working vacuum quality or the unit

concept but also by the acceleration voltage

level, Figure 9.11. The latter exerts a consid-

erable influence onto the obtainable welding

results. With the increasing acceleration voltage, the achievable weld depth and the depth-to-

width ratio of the weld geometry are also increasing. A disadvantage of the increasing accel-

erating voltage is, however, the exponential increase of X-rays and, also, the likewise in-

creased sensitivity to flash-over voltages. In correspondence with the size of the workpiece to

be welded and the size of

the chamber volume, high-

voltage beam generators

(150 - 200 kV) with powers

of up to 200 kW are applied

in industrial production,

while the low-voltage tech-

nology (max. 60 kV) is a

good alternative for smaller

units and weld thicknesses.

The design of the unit for the

low-voltage technique is

upper bead

lower bead

molten area

blind bead

end cratergroove

length of seam

length of seam

width of seam

weld

rein

forc

em

ent

roo

t re

info

rce

me

nt

unapproachable gap

weld

p

ene

tra

tio

nd

ep

th

root weld

Na

htd

icke

weld

thic

kne

ss


Basic Definitions

Figure 9.10


Disadvantages of EBW

in vacuum

at atmosphere

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electrical conductivity of materials is required

high cooling rates => hardening => cracks

high precision of seam preparation

beam may be deflected by magnetism

X-ray formation

size of workpiece limited by chamber size

high investment

X-ray formation

limited sheet thickness (max. 10 mm)

high investment

small working distance�

Figure 9.9


2005

simpler as, due to the lower acceleration voltage, a separate complete lead covering of the

unit is not necessary.

While during the beam generation, the vacuum (p = 10-5 mbar) for the insulation of the beam

generation compartment and the prevention of cathode oxidation is imperative, the possible

working pressures inside the vacuum chamber vary between a high vacuum (p = 10-4 mbar)

and atmospheric pressure. A collision of the electrodes with the residual gas molecules and

the scattering of the electron beam which is connected to this is, naturally, lowest in high vac-

uum.

The beam diameter is minimal in high vacuum and the beam power density is maximum in

high vacuum, Figure 9.12. The reasons for the application of a high vacuum unit are, among

others, special demands on the weld (narrow, deep welds with a minimum energy input) or

the choice of the materials to be welded (materials with a high oxygen affinity). The applica-

tion of the electron beam welding process also entails advantages as far as the structural

design of the components is concerned.

br-er9-20e.cdr

Classification of EBW Machines

by accelerating voltage:

by pressure:

by machine concept:

high voltage machine (U =150 kV)

low

high vacuum machine

fine vacuum machine

atmospheric machine (NV-EB welding)

conveyor machine

clock system

all-purpose EBW machine

local vacuum machine

mobile vacuum machine

micro and fine welding machine

B

voltage machine (U =60 kV)B

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Figure 9.11

br-er9-09e_f.cdr

EB-Welding in High Vacuum

< 5 x 10 mbar-4

< 1 x 10 mbar-6

Figure 9.12


2005

With a low risk of oxidation and reduced demands on the welds, the so-called “medium-

vacuum units” (p = 10-2 mbar) are applied. This is mainly because of economic considera-

tions, as, for instance, the reduction of cycle times, Figure 9.13. Areas of application are in

the automotive industry (pistons, valves, torque converters, gear parts) and also in the metal-

working industry (fittings, gauge heads, accumulators).

Under extreme demands on the welding time, reduced requirements to the weld geometry,

distortion and in case of full material compatibility with air or shielding gas, out-of-vacuum

welding units are applied, Figure 9.14. Their advantages are the continuous welding time

and/or short cycle times. Areas of application are in the metal-working industry (precision

tubes, bimetal strips) and in the automotive industry (converters, pinion cages, socket joints

and module holders).

br-er9-10e_f.cdr

EB-Welding in Fine Vacuum

< 5 x 10 mbar-2

< 1 x 10 mbar-6

Figure 9.13

br-er9-11e_f.cdr

Atmospheric Welding (NV-EBW)

< 1x 10 mbar-4

~ 10 mbar-1

~ 1 mbar

Figure 9.14


2005

A further distinction criterion is the adjustment of the vacuum chambers to the different joining

tasks. Universal machines are characterised by their simply designed working chamber, Fig-

ure 9.15. They are equipped with vertically or horizontally positioned and, in most cases,

travelling beam generators. Here, several workpieces can be welded in subsequence during

an evacuation cycle. The largest, presently existing working chamber has a volume of 265

m³.

Clock system machines, in contrast, are equipped with several small vacuum chambers

which are adapted to the workpiece shape and they are, therefore, characterised by short

evacuation times, Figure 9.16. Just immediately before the welding starts, is the beam gun

coupled to the vacuum chamber which has been evacuated during the preceding evacuation

cycle, while, at the same time, the next vacuum chamber may be flooded and

charged/loaded.

br-er9-14e_f.cdr

Machine Concept - Conventional Plant

Figure 9.15

br-er9-15e_f.cdr

EBW Clock System Machine

Figure 9.16


2005

Conveyor machines allow the continuous production of welded joints, as, for example, bi-

metal semi finished products such as saw blades or thermostatic bimetals, Figure 9.17. In the

main chamber of these units is a gradually raising pressure system as partial vacuum pre

and post activated, to serve as a vacuum lock.

Systems which are operating with a mobile and local vacuum are characterised by shorter

evacuation times with a simultaneous maintenance of the vacuum by decreasing the pump-

ing volume. In the “local vacuum systems”, with the use of suitable sealing, is the vacuum

produced only in the welding area. In “mobile vacuum systems” welding is carried out in a

small vacuum chamber which is restricted to the welding area but is travelling along the

welded seam. In this case, a sufficient sealing between workpiece and vacuum chamber is

more difficult.

With these types of machine design, electron beam welding may be carried out with compo-

nents which, due to their sizes, can not be loaded into a stationary vacuum chamber (e.g.

vessel skins, components for particle accelerators and nuclear fusion plants).

br-er9-16e_f.cdr

EBW Conveyor Machine

endproduct

semi-finished material

Figure 9.17


Seam Appearancefor EB-Welding in Vacuum

butt weld

T-joint/ fillet weld

a) b)

T-joint butt welded lap weld

Figure 9.18


2005

In general the workpiece is moved during electron beam welding, while the beam remains

stationary and is directed onto the workpiece in the horizontal or the vertical position. De-

pending on the control systems of the working table and similar to conventional welding are

different welding positions possible. The weld type preferred in electron beam welding is the

plain butt weld. Frequently, also centring allowance for centralising tasks and machining is

made. For the execution of axial welds, slightly oversized parts (press fit) should be selected

during weld preparation, as a transverse shrinkage sets in at the beginning of the weld and

may lead to a considerable increase of the gap width in the opposite groove area. In some

cases also T-welds may be carried out; the T-joint with a plain butt weld should, however, be

chosen only when the demands on the

strength of the joints are low, Figure 9.18. As

the beam spread is large under atmosphere,

odd seam formations have to be considered

during Non-Vacuum Electron Beam Welding,

Figure 9.19.

In order to receive uniform and reproducible

results with electron beam welding, an exact

knowledge about the beam geometry is nec-

essary and a prerequisite for:

- tests on the interactions between

beam and substance

- applicability of welding parameters to

other welding machines

- development of beam generation

systems.

The objective of many tests is therefore the exact measurement of the beam and the investi-

gation of the effects of different beam geometries on the welding result.

For the exact measurement of the electron beam, a microprocessor-controlled measuring

system has been developed in the ISF. The electron beam is linearly scanned at a high

speed by means of a point probe, which, with a diameter of 20 µm is much smaller than the

beam diameter in the focus, Figure 9.20. When the electron beam is deflected through the

aperture diaphragm located inside the sensor, the electrons flowing through the diaphragm


Seam Appearence at Atmospheric Welding (NV-EBW)

Figure 9.19


2005

are picked up by a Faraday shield and diverted over a precision resistor. The time progres-

sion of the signal, intercepted at the resistor, corresponds with the intensity distribution of the

electron beam in the scanning path. In order to receive an overall picture of the power density

distribution inside the electron beam, the beam is line scanned over the slit sensor (60 lines).

An evaluation program creates a perspective view of the power density distribution in the

beam and also a two-dimensional representation of lines with the same power density.

An example for a measured electron beam is shown in Figure 9.21. It can be seen clearly

that the cathode had not been heated up sufficiently. Therefore, the electrons are sucked off

directly from the cathode surface during saturation and unsaturated beams, which may lead

to impaired welding results, develop. During the space charge mode of a generator, the elec-

tron cloud is sufficiently large, i.e., there are always enough electrons which can be sucked

off. In the ideal case, the developed power density is rotationally symmetrical and in accor-

dance with the Gaussian distribution curve.

The electron signals are used for the automatic seam tracking. These may be either primary

or secondary electrons or passing-through current or the developing X-rays. When backscat-

tered primary electrons are used, the electron beam is scanned transversely to the groove. A

br-er9-21e.cdr

Two Principles ofElectron Beam Measuring

hole with aperturediaphragm Faradaycup (20 µm)

cross sectionof the beam

track ofthe beam

measurementfield

vo

ltag

e

slit withFaraday cup

cross sectionof the beam

beam deflection

slit sensor

hole sensor

Figure 9.20


Energy Concentration and Development in Electron Beam

FILENAME: R I N G S T R

Accel. voltage: 150 kV

Beam current: 600 mA

Prefocus current: 700 mA

Main focus current: 1500 mA

Cath. heat current: 500 mm

Max. Density: 26,456 kW/mm

Ref. Density: 26,456 kW/mm

2

2

Figure 9.21


2005

computer may determine the position of the groove relative to the beam by the signals from

the reflected electrons. In correspondence with the deflection the beam is guided by electro-

magnetic deflection coils or by moving the working table.

This kind of seam tracking system may be used either on-line or off-line.

The broad variation range of the weldable ma-

terials and also material thicknesses offer this

joining method a large range of application,

Figure 9.22. Besides the fine and micro weld-

ing carried out by the electronics industry

where in particular the low heat input and the

precisely programmable control is of impor-

tance, electron beam welding is also particu-

larly suited for the joining of large cross-

sections.

br-er9-20e.cdr

EBW Fields of Application

industrial areas:

material:

automotive industries

aircraft and space industries

mechanical engineering

tool construction

nuclear power industries

power plants

fine mechanics and electrical

industries

job shop

almost all steels

aluminium and its alloys

magnesium alloys

copper and its alloys

titanium

tungsten

gold

material combinations

(e.g. Cu-steel, bronze-steel)

ceramics (electrically conductive)

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Figure 9.22

10.

Laser Beam Welding


2005

The term laser is the abbreviation for ,,Light Amplification by Stimulated Emission of Radia-

tion”. The laser is the further development of the maser (m=microwave), Figure 10.1. Al-

though the principle of the stimulated emis-

sion and the quantum-mechanical fundamen-

tals have already been postulated by Einstein

in the beginning of the 20th century, the first

laser - a ruby laser - was not implemented

until 1960 in the Hughes Research Laborato-

ries. Until then numerous tests on materials

had to be carried out in order to gain a more

precise knowledge about the atomic structure.

The following years had been characterised

by a fast development of the laser technology.

Already since the beginning of the Seventies

and, increasingly since the Eighties when the

first high-performance lasers were available,

CO2 and solid state lasers have been used

for production metal working.

The number of the annual

sales of laser beam sources

has constantly increased in

the course of the last few

years, Figure 10.2.

The application areas for the

laser beam sources sold in

1994 are shown in Figure

10.3. The main application

areas of the laser in the field

of production metal working

are joining and cutting jobs.

br-er10-01e.cdr

History of the Laser

1917 postulate of stimulated emission by Einstein

1950 physical basics and realisation of a maser (Microwave Amplification by Stimulated Emission of Radiation) by Towens, Prokhorov, Basov

1954 construction of the first maser

1960 construction of the first ruby laser (Light Amplification by Stimulated Emission of Radiation)

1961 manufacturing of the first HeNe lasers and Nd: glass lasers

1962 development of the first semiconductor lasers

1964 nobel price for Towens, Prokhorov and Basov for their works in the field of masers construction of the first Nd:YAG solid state lasers and CO gas lasers

1966 established laser emission on organic dyes

since increased application of CO and solid state laser

1970 technologies in industry

1975 first applications of laser beam cutting in sheet fabrication industry

1983 introduction into the market of 1-kW-CO lasers

1984 first applications of laser beam welding in industrial serial production

work out of

2

2

2

Figure 10.1

br-er10-02e.cdr

3

10 €

2

1.5

1

0.5

0

9

Japan and South East AsiaNorth AmericaWest Europe

1986 1988 1990 1992 1994 1996 1998 2000

Figure 10.2


2005

The availability of more efficient laser beam sources opens up new application possibilities

and - guided by financial considerations - makes the use of the laser also more attractive,

Figure 10.4.


characteristic properties

of the laser beam. By rea-

son of the induced or

stimulated emission the

radiation is coherent and

monochromatic. As the

divergence is only 1/10

mrad, long transmission

paths without significant

beam divergences are

possible.

Inside the resonator, Fig-

ure 10.6, the laser-active medium (gas molecules, ions) is excited to a higher energy level

(“pumping”) by energy input (electrical gas discharge, flash lamps).

During retreat to a lower

level, the energy is re-

leased in the form of a light

quantum (photon). The

wave length depends on

the energy difference be-

tween both excited states

and is thus a characteris-

tic for the respective la-

ser-active medium.

br-er10-03e.cdr

inscribe20,5%

microelectronics

5,4%

welding18,7%

drilling1,8%

others9,3%

cutting44,3%

Figure 10.3

br-er10-04e.cdr

lase

r po

we

r

CO2

Nd:YAG

diode laser0

1

2

3

4

5

10

20

kW

40

19

70

19

75

19

80

19

85

19

95

19

90

20

00

Figure 10.4


2005

A distinction is made be-

tween spontaneous and

induced transition. While

the spontaneous emission

is non-directional and in

coherent (e.g. in fluores-

cent tubes) is a laser beam

generated by induced

emission when a particle

with a higher energy level

is hit by a photon. The re-

sulting photon has the

same properties (fre-

quency, direction, phase)

as the exciting photon (“coherence”). In order to maintain the ratio of the desired induced

emission I spontaneous emission as high as possible, the upper energy level must be con-

stantly overcrowded, in comparison with the lower one, the so-called “laser-inversion”. As

result, a stationary light wave is formed between the mirrors of the resonator (one of which is

semi-reflecting) causing parts of the excited laser-active medium to emit light.

In the field of production metal working, and particularly in welding, especially CO2 and

Nd:YAG lasers are applied for their high power outputs. At present, the development of diode

lasers is so far advanced

that their sporadic use in the

field of material processing

is also possible. The indus-

trial standard powers for

CO2 lasers are, nowadays,

approximately 5 - 20 kW,

lasers with powers of up to

40 kW are available. In the

field of solid state lasers

average output powers of

up to 4 kW are nowadays

obtainable.


Characteristics of Laser Beams

light bulb Laser

E2

E1 exitedstate

groundstate

polychromatic

incoherent

large divergence

(multiple wave length)

(not in phase)

0,46"

0,94"

monochromatic

coherent

small divergence

(in phase)

induced emission

Figure 10.5


Laser Principle

energy source

energy source

resonator

fully reflecting mirror

R = 100%

partially reflectingmirrorR < 100%

las

er

be

am

active laser medium

Figure 10.6


2005

In the case of the CO2 laser, Figure 10.7, where the resonator is filled with a N2-C02-He gas

mixture, pumping is carried out over the vibrational excitation of nitrogen molecules which

again, with thrusts of the

second type, transfer their

vibrational energy to the

carbon dioxide. During the

transition to the lower en-

ergy level, CO2 molecules

emit a radiation with a

wavelength of 10.6 µm.

The helium atoms, finally,

lead the CO2 molecules

back to their energy level.

The efficiency of up to

15%, which is achievable with CO2 high performance lasers, is, in comparison with other la-

ser systems, relatively high. The high dissipation component is the heat which must be dis-

charged from the resonator. This is achieved by means of the constant gas mixture circula-

tion and cooling by heat exchangers. In

dependence of the type of

gas transport, laser sys-

tems are classified into

longitudinal-flow and trans-

verse-flow laser systems,

Figures 10.8 and 10.9.

br-er10-08e.cdr

radio frequency high voltage exitaion

laser beam

cooling water cooling water

laser gas

gas circulation pump

vakuum pump

laser gas:CO : 5 l/h

He: 100 l/hN : 45 l/h

2

2

Figure 10.8


Energy Diagram of CO Laser2

0,6

eV

0,4

0,3

0,2

0,1

0

en

erg

y

0,288 eV

2

1 001 0,290 eV

100

002

LASER = 10,6 µmλ

transmission ofvibration energy

thrust of second type

thrust of first type

∆E = 0,002 eV

transition withoutemission

discharge through thrust with helium

N2 CO2

0000

Figure 10.7


2005

With transverse-flow laser systems of a compact design can the multiple folding ability of

the beam reach higher output powers than those achievable with longitudinal-flow sys-

tems, the beam quality, however, is worse. In d.c.-excited systems (high voltage), the elec-

trodes are positioned inside the resonator. The interaction between the electrode material

and the gas molecules causes electrode burn-off.

In addition to the wear of the electrodes, the burn-off also entails a contamination of the laser

gas. Parts of the gas mixture must be therefore exchanged permanently. In high-frequency

a.c.-excited systems the electrodes are positioned outside the gas discharge tube where

the electrical energy is ca-

pacitively coupled. High

electrode lives and high

achievable pulse frequen-

cies characterise this kind

of excitation principle. In

diffusion-cooled CO2 sys-

tems beams of a high qual-

ity are generated in a mini-

mum of space. Moreover,

gas exchange is hardly

ever necessary.

The intensity distribution is

not constant across the la-

ser beam. The intensity dis-

tribution in the case of the

ideal beam is described by

TEM modes (transversal

electronic-magnetic). In the

Gaussian or basic mode

TEM00 is the peak energy in

the centre of the beam

weakening towards its pe-

riphery, similar to the Gaus-

sian normal distribution. In


Laser Beam Qualitiy

0<K<1

with d d. d. =c.σ σ 0.

0 F FΘ = Θ = Θ

ΘF

d0

unfocussed beam focussed beam

f2,57"

dF

K = .

2 1 λ

π dσ σΘ

Figure 10.10

br-er10-09e.cdr

Cooling water

cooling water

laser gas:CO : 11 l/h

He: 142 l/hN : 130 l/h

2

2

laser gasend mirror

turningmirrors

gas circulationpump

mirror(partially reflecting)

gas discharge

laser beam

Figure 10.9


2005

practice, the quality of a laser beam is, in accordance with DIN EN 11146, distinguished by

the non-dimensional beam quality factor (or propagation factor) K (0...1), Figure 10.10.

The factor describes the ratio of the distance field divergence of a beam in the basic mode to

that of a real beam and is

therefore a measure of a

beam focus strength. By

means of the beam quality

factor, different beam

sources may be compared

objectively and quanti-

taively.

The CO2 laser beam is

guided from the resonator

over a beam reflection mir-

ror system to one or sev-

eral processing stations,

Figures 10.11 and 10.12.

The low divergence allows

long transmission paths. At

the processing station is

the beam, with the help of

the focussing optics,

formed according to the

working task. The relative

motion between beam and

workpiece may be realised

in different ways:

- moving workpiece, fixed optics

- moving (“flying”) optics

- moving workpiece and moving optics (two handling facilities).

br-er10-11e.cdr

resonator

LASER

work piece manipulator

absorber

partiallyreflecting

mirror

shutter

work piece

endmirror

beam creationfocussing system

beam divergence mirror

beam transmissiontube

Figure 10.11

Figure 10.12


CO Laser Beam Welding Station2


2005

In the case of the CO2 laser,

beam focussing is normally

carried out with mirror op-

tics, Figure 10.13. Lenses

may heat up, due to ab-

sorption, especially with

high powers or contamina-

tions. As the heat may be

dissipated only over the

holders, there is a risk of

deformation (alteration of

the focal length) or destruc-

tion through thermal over-

loading.

In the case of solid state laser, the normally cylindrical rod serves only the purpose to pick

up the laser-active ions (in the case of the Nd:YAG laser with yttrium-aluminium-garnet

crystals dosed with Nd3+ ions), Figure 10.14. The excitation is, for the most part, carried out

using flash or arc lamps, which for the optimal utilisation of the excitation energy are ar-

ranged as a double ellipsoid; the rod is positioned in their common focal point. The achieved

efficiency is below 4%. In the meantime, also diode-pumped solid state lasers have been in-

troduced to the market.

The possibility to guide the

solid-state laser beam over

flexible fibre optics makes

these systems destined for

the robot application,

whereas the CO2 laser ap-

plication is restricted, as its

necessary complex mirror

systems may cause radia-

tion losses, Figure 10.15. © ISF 2002br-er10-14e.cdr

Principle Layout of Solid State Laser

laser rod

laser beam

partially reflectingmirror (R < 100%)

flash lamps

end mirror (r = 100%)

Figure 10.14


Focussing Optics

reflective90°-mirror optic

α

Figure 10.13


2005

Some types of optical fibres allow, with fibre diameters of ≤ 1 mm bending radii of up to 100

mm. With optical switches a multiple utilisation of the solid state laser source is possible; with

beam splitters (mostly with a fixed splitting proportion) simultaneous welding at several proc-

essing stations is possible. The disadvantage of this type of beam projection is the impaired

beam quality on account of multiple reflection.

The semiconductor or

diode lasers are charac-

terised by their mechanical

robustness, high efficiency

and compact design, Fig-

ure 10.16. High perform-

ance diode lasers allow the

welding of metals, although

no deep penetration effect

is achieved. In material

processing they are there-

fore particularly suitable for

welding thin sheets.

Energy input into the workpiece is carried out over the absorption of the laser beam. The

absorption coefficient is,

apart from the surface qual-

ity, also dependent on the

wave length and the mate-

rial. The problem is that a

large part of the radiation is

reflected and that, for ex-

ample, steel which is ex-

posed to wave lengths of

10.6 µm reflects only 10%

of the impinging radiation,

Figure 10.17. As copper is

a highly reflective metal


Diode Laser

Figure 10.16

© ISF 2002

Nd:YAG Laser Beam Welding Station

br-er10-15e_f.cdr

Figure 10.15


2005

with also a good heat conductivity, it is frequently used as mirror material.

Intensity adjustment at the

working surface by the fo-

cal position with a simulta-

neous variation of the

working speed make the

laser a flexible and contact-

less tool, Figure 10.18. The

methods of welding and

cutting demand high inten-

sities in the focal point,

which means the distance

between focussing optics

and workpiece surface must

be maintained within close

tolerances. At the same

time, highest accuracy and

quality demands are set on

all machine components

(handling, optics, resonator,

beam manipulation, etc.).

Steel materials with treated

surfaces reflect the laser

beam to a degree of up to

95%, Figures 10.19 - 10.22.

When metals are welded with a low-intensity laser beam (I ≤ 105 W/cm2), just the workpiece

surfaces and/or edges are melted and thus thermal-conduction welding with a low deep-

penetration effect is possible. Above the threshold intensity value (I ≤ 106 W/cm2) a phase

transition occurs and laser-induced plasma develops. The plasma, whose absorption char-

acteristics depend on the beam intensity and the vapour density, absorbs an increased

quantity of radiation.

Figure 10.18

br-er10-18e.cdr

10 10 10 10 s 10-8 -6 -4 -2 0

10

W/cm

10

10

10

10

10

10

10

2

8

7

6

5

4

3

po

wer

de

ns

ity

acting time

energy density [J/cm²]

drilling102

100

104

106

remeltingcoating

glaze

shock hardening

weldingcutting

martensitic hardening

Figure 10.17


Wave Length Absorption Dependent of Various Materials

absorp

tion A

0,30

0,25

0,20

0,15

0,10

0,05

0

wave length λ0,1 0,2 0,3 0,5 0,8 1 2 4 5 8 10 µm 20

Al

Cu

Ag

Mo

Fe

Stahl

Nd:YAG-laser

CO -

laser2


2005

A vapour cavity forms and

allows the laser beam to

penetrate deep into the

material (energy input

deep beyond the work-

piece surface); this effect is

called the “deep penetra-

tion effect”. The cavity

which is moved though the

joining zone and is pre-

vented to close due to the

vapour pressure is sur-

rounded by the largest part

of the molten metal. The residual material vaporises and condenses either on the cavity side

walls or flows off in an ionised form. With suitable parameter selection, an almost complete

energy input into the workpiece can be obtained.

Figure 10.20


Principle of Laser Beam Welding

heat conductingwelding

deep penetrationwelding

laser beam

molten pool

soldifiedweld metal

laser beam

keyhole(vapour-/plasma cavity)

metal vapourblowing away

laser-inducedplasma

molten pool

soldifiedweld metal

Figure 10.19


Calculated Intensity Threshold forProducing a Laser-Induced Plasma

10 10 10 s 10-10 -8 -6 -2

las

er

inte

ns

ity

I

radiation time t

10

W/cm

10

10

10

10

10

2

8

7

6

5

steel

r = 100 µm

= 10.6 µmF

l

A = 0,1

A = 1

working zone

plasma threshold

plasma shielding

Figure 10.21


Reflection and Penetration Depthin Dependence on Intensity

10 10 W/cm 105 6 2 7

laser intesity I

pen

etr

ati

on

de

pth

tre

fle

cti

on

R

100

%

60

40

20

0

4

mm

2

1

0

material: steel

wave length 10,6 µmlaser power: 2 kWwelding speed: 10 mm/sworking gas: helium

λ:


2005

However, in dependence of the electron density in the plasma and of the radiated beam in-

tensity, plasma may detach from the workpiece surface and screen off the working zone. The

plasma is heated to such a high degree that only a fraction of the beam radiation reaches the

workpiece. This is the rea-

son why, in laser beam

welding, gases are applied

for plasma control. The

gases’ ionisation potential

should be as high as pos-

sible, since also the forma-

tion of “shielding gas plas-

mas” is possible which

again decreases the en-

ergy input.

Only a part of the beam energy from the reso-

nator is used up for the actual welding process,

Figure 10.23. Another part is absorbed by the

optics in the beam manipulation system, an-

other part is lost by reflection or transmission

(beam penetration through the vapour cavity).

Other parts flow over thermal conductance into

the workpiece.

Figure 10.24 shows the most important advan-

tages and disadvantages of the laser beam

welding method.


Interaction Between Laser Beam and Material

Transformation of electromagnetic energy into thermal energywithin nm range at the surface of the work piece by

stimulation of atoms to resonant oscillations

"normal" absorption: "abormal" absorption:

−

−

−

−

−

−

−

depandent on laser beam intensity:

I < 10 W/cm²

dependent on wave length

dependent on temperature

dependent on material

absorption at solid or liquid surface: A < 30%

formation of a molten bath with low

penetration depth

6 −

−

−

−

dependent on laser intesity:

I 10 W/cm²

heating up to temperature of evaporation and formation of a metal

vapour plasma

almost complete energy entry through absorption by plasma: A > 90%

formation of a vapour cavity

≥6

heat conducting welding deep penetration welding

Figure 10.22

br-er10-23e.cdr

Scheme of Energy Flow

beam energy

diagnostics

beam transmissionfocussing system

reflection

transmission

heat convectionheat conductionmetal vapourplasma

recombination

work piece

fusion energy

0-2,5%

2,5-12,5%

ca. 5%

ca. 10%

ca. 40%

85-95%

10-15%ca. 30%

Figure 10.23


2005

Penetration depths in dependence of the beam power and welding speed which are

achievable in laser beam welding are depicted in Figure 10.25. Further relevant influential

factors are, among others,

the material (thermal con-

ductivity), the design of

the resonator (beam qual-

ity), the focal position and

the applied optics (focal

length; focus diameter).

Figure 10.26 shows several

joint shapes which are typi-

cal for car body production

and which can be welded

by laser beam application.

The high cooling rate during laser beam

welding leads, when transforming steel mate-

rials are used, to significantly increased

hardness values in comparison with other

welding methods, Figure 10.27. These are a

sign for the increased strength at a lower

toughness and they are particularly critical in

circumstances of dynamic loads.

The small beam diameter demands the very

precise manipulation and positioning of the

workpiece or of the beam and an exact weld

preparation, Figure 10.28. Otherwise, as re-

sult, lack of fusion, sagged welds or concave

root surfaces are possible weld defects.


Advantages and Disadvantagesof Laser Beam Welding

advantages disadvantages

process

work piece

installation

- high power density- small beam diameter- high welding speed- non-contact toolwelding possibleatmosphere

- high reflection at metallic surfaces- restricted penetration depth ( 25 mm)

- minimum thermal stress- little distortion- completely processed components- welding at positions difficult to access- different materials weldable

- expensive edge preparation- exact positioning required- danger of increased hardness- danger of cracks- Al, Cu difficult to weld

- expensive beam transmission and forming- power losses at optical devices- laser radiation protection required- high investment cost- low efficency (CO -Laser: < 20%, Nd:YAG: < 5%)2

- short cycle times- operation at several stations possible- installation availability > 90%- well suitable to automatic function

Figure 10.24

br-er10-25e.cdr

Penetration Depths

pene

tra

tion

de

pth

pe

netr

atio

n d

ep

th

welding speed

welding speed

28

mm

20

16

12

8

4

0

15

mm

5

0

0 0,6 1,2 1,8 m/min 3,0

0 1 2 3 4 5 6 7 m/min 9

laser power:

0,2% C-steelCO -laser2

(cross flow)

X 5 CrNi 18 10CO -laser2

(axial flow)

laser power:

15 kW

8 kW

1,5 kW

6 kW4 kW

6 kW4 kW2 kW

1 kW

10 kW

Figure 10.25


2005


Welding Defects

edge preparation misalignment

gap mispositioning

(e 0,1 x plate thickness)≤

(a 0,1 x plate thickness)≤

beam

br-er10-27e_f.cdr

laser beam weld

submerged arc weld

hard

ne

ss

distance from the weld centre

weld submerged arc weld

MAZ

MAZ MAZ

MAZWMA

0 12

500

HV 0,4

Figure 10.27

Figure 10.28

br-er10-26e.cdr

butt weld

lap weld at overlap joint

fillet weld at overlap joint

flanged weld at overlap joint

Figure 10.26


2005

br-er10-30e.cdr

backward wire feedingforward wire feeding

welding direction

filler wire filler wirelaser beam laser beam

gas gas

plasma plasma

work piece work pieceweld metal weld metal

molten pool molten poolkeyhole keyhole

Figure 10.30

Caused by the high cooling rate and, in connection with this, the insufficient degassing of the

molten metal, pore formation may occur during laser beam welding of, in particular, thick

plates (very deep welds) or while carrying out welding-in works (insufficient degassing over

the root), Figure 10.29.

However, too low a weld speed may also cause pore formation when the molten metal picks

up gases from the root side.

The materials that may be

welded with the laser reach

from unalloyed and low-

alloy steels up to high qual-

ity titanium and nickel

based alloys. The high

carbon content of the

transforming steel materials

is, due to the high cooling

rate, to be considered a

critical influential factor

where contents of C >

0.22% may be stipulated as

the limiting reference value.

Aluminium and copper

properties cause problems

during energy input and

process stability. Highly

reactive materials demand,

also during laser beam

welding, sufficient gas

shielding beyond the solidi-

fication of the weld seam.

The sole application of

working gases is, as a rule,

not adequate.


Porosity

v = 0,7 m/minw v = 0,9 m/minw v = 1,5 m/minw

material: P460N (StE460), s = 20 mm, P = 15 kw

Figure 10.29


2005

br-er10-31e.cdr

without filler wire with filler wire

filler wire: Sg2d = 0,8 mmw

gap: 0 mmv = 1,6 m/minw

gap: 0,5 mmwire: SG-Ni Cr21 Fe18 Mo

v = 1,0 m/min

d = 1,2 mmw

w

weld zoneweld zone

increase of gapbridging ability

material:

gap:

S380N (StE 380)0,5 mm

P = 8,3 kW

V = 3 m/min

E = 166 J/mins = 4 mm

L

W

S

Possibility ofmetallurgical influence

material combination:

10CrMo9-10/ X6CrNiTi18-10P = 5,0 kWL

Figure 10.31

The application of laser beam welding may be extended by process variants. One is laser

beam welding with filler wire, Figures 10.30 and 10.31 which offers the following advantages:

- influence on the me-

chanic-technological prop-

erties of the weld and fu-

sion zone (e.g. strength,

toughness, corrosion, wear

resistance) over the metal-

lurgical composition of the

filler wire

- reduction of the demands

on the accuracy of the weld

preparation in regard to

edge misalignment, edge

preparation and beam mis-

alignment, due to larger

molten pools

- “filling” of non-ideal, for example, V-shaped groove geometries

- a realisation of a defined weld reinforcement on the beam entry and beam exit side.

The exact positioning of the

filler wire is a prerequisite

for a high weld quality and a

sufficient dilution of the mol-

ten pool through which filler

wire of different composition

as the base can reach right

to the root. Therefore, the

use of sensor systems is

indispensable for industrial

application, Figure 10.32.

The sensor systems are to

take over the tasks of

- process control,

br-er10-32e.cdr

0.1 mm 0.2 mm 0.3 mm 0.4 mm 0.5 mm 0.6 mm

with sensing device; fill factor 120 %

without sensing device; wire speed v = 4 m/min constantD

KB 4620/1220:1

10/92

Probe OS1-6A

KB 4621/720:1

10/92

Probe OS1-1B

KB 4621/1520:1

10/92

Probe OS1-4C

KB 4620/1720:110/92

Probe OS1-5C

KB 4621/920:1

10/92

Probe OS1-2B

KB 4621/1220:1

10/92

Probe OS1-3B

KB 4620/920:1

10/92

Probe MS1-6C

KB 4620/620:110/92

Probe MS1-5A

KB 4620/3820:1

10/92

Probe MS1-1C

KB 4620/420:1

10/92

Probe MS1-4C

KB 4620/020:1

10/92

Probe MS1-3A

KB 4620/4120:1

10/92

Probe MS1-2B

1 mm

Figure 10.32


2005

- weld quality as surance

- beam positioning and joint tracking, respectively.

The present state-of-the-art is the further development of systems for industrial applications

which until now have been tested in the laboratory.

Welding by means of solid state lasers has, in the past, mainly been applied by manufactur-

ers from the fields of precision mechanics and microelectronics. Ever since solid state lasers

with higher powers are available on the market, they are applied in the car industry to an ever

increasing degree. This is due to their more variable beam manipulation possibilities when

comparing with CO2 la-

sers. The CO2 laser is

mostly used by the car in-

dustry and by their ancil-

lary industry for welding

rotation-symmetrical mass-

produced parts or sheets.

Figure 10.33 shows some

typical application exam-

ples for laser beam weld-

ing.

Practical Application Fields


plant and apparatus engineering- seal welds at housings

- measurement probes

aerospace industry

- engine components

- instrument casesautomotive industry

- gear parts

- body-making

- engine components

(cog-wheels, planet gears)

(bottom plates, skins)

(tappet housings, diesel engine

precombustion chambers)

medical industry

- heart pacemaker cases

- artificial hip joints

electronic industry

- PCBs

- accumulator cases

- transformer plates

- CRTs

steel industry

- pipe production

- vehicle superstructures

- continuous metal strips

- tins

Figure 10.33

11.

Surfacing

and Shape Welding


2005

DIN 1910 (“Welding”) clas-

sifies the welding process

according to its applica-

tions: welding of joints

and surfacing. According

to DIN 1910 surfacing is

the coating of a workpiece

by means of welding.

Dependent on the applied

filler material a further

classification may be

made: deposition repair

welding and surfacing for

the production of a composite material with certain functions. Surfacing carried out with wear-

resistant materials in preference to the base metal material is called hardfacing; but when

mainly chemically stable filler materials are

used, the method is called cladding. In the

case of buffering, surfacing layers are pro-

duced which allow the appropriate-to-the-

type-of-duty joining of dissimilar materials

and/or of materials with differing properties,

Figure 11.1.

A buffering, for instance, is an intermediate

layer made from a relatively tough material

between two layers with strongly differing

thermal expansion coefficients.

Figure 11.2 shows different kinds of stresses

which demand the surfacing of components.

Furthermore surfacing may be used for pri-

mary forming as well as for joining by primary

forming.

br-er11-01e.cdr

base metal/ surfacing metal

similar

for repair welding�

dissimilar

hardfacing (wear protection)

cladding (corrosion prevention)

buffering (production of an appropriate-to-the-type-of-duty joint of dissimilar materials)

�

�

�

Figure 11.1

br-er11-02e.cdr

Components -Kinds of Stress

� wear caused by very high impact and compressive stress

wear by friction (metal against metal) during high impact and compression stress

strong sanding or grinding wear

very strong wear caused by grinding during low impact stress

cold forming tools

hot forming tools

cavitation

wear parts (plastics industry)

corrosion

temperature stresses

�

�

�

�

�

�

�

�

�

Figure 11.2


2005

In case of surfacing - as for all fabrication processes - certain limiting conditions have to be

observed. For example, hard and wear-resistant weld filler metals cannot be drawn into solid

wires. Here, another form has to be selected (filler wire, continuously cast rods, powder).

Process materials, as for example SA welding flux demand a certain welding position which

in terms limits the method of welding.

The coating material must be selected with view to the type of duty and, moreover, must be

compatible with the base metal, Figure 11.3.

For all surfacing tasks a large product line of welding filler metals is available. In depend-

ence on the welding method as well as on the selected materials, filler metals in the form of

wires, filler wires, strips, cored strips, rods or powder are applied, Figure 11.4.

The filler/base metal dilution is rather important, as the desired high-quality properties of the

surfacing layer deteriorate with the increasing degree of dilution.

br-er11-03e.cdr

Boundary Conditions in Surfacing

component(material)

coating

coatingmaterial(filler)

surfacingmethod

stresscompatibility

manufacturingconditionsavailability

consumable

Figure 11.3

br-er11-04e.cdr

Materials for Surfacing

wearing protection (armouring)

corrosion prevention

hard facing on

cobalt base

nickel base

iron base

ferritic to martensitic chromium steel alloys

soft martensitic chromium-nickel steel alloys

austenitic-ferritic chromium-nickel steel alloys

austenitic chromium-nickel steel alloys

�

�

�

�

�

�

�

Figure 11.4


2005

A weld parameter optimisation has the objective to optimise the degree of dilution in order to

guarantee a sufficient adherence of the layer with the minimum metal dissimilation. A

planimetric determination

of the surfacing and pene-

tration areas will roughly

assess the proportion of

filler to base metal. When

the analysis of base and

filler metal is known, a

more precise calculation is

possible by the determina-

tion of the content of a cer-

tain element in the surfac-

ing layer as well as in the

base metal, Figure 11.5.

Figure 11.6 shows record charts of an electron

beam microprobe analysis for the elements

nickel and chromium. It is evident that - after

passing a narrow transition zone between

base metal and layer — the analysis inside

the layer is quasi constant.

As depicted in Figure 11.7 almost all arc weld-

ing methods are not only suitable for joining

but also for surfacing.

Definition of Dilution


surface built up by welding FB

penetration area F P

base metal

(X-content - X-content ) [% in weight]

(X-content - X-content ) [% in weight]surfacing layer FM

base metal FM

FP

F + FP B

A = x 100%

A = x 100%

D

D

FM: weld filler metal A : dilutionD

Figure 11.5

br-er11-06e.cdr

Microprobe Analyses

10

0

20

30

%

Cr

pe

rce

nta

ge

s b

y m

ass

µm0 100 200

distance

300 500

10

%

0

20

30

Ni p

erc

en

tag

es b

y m

ass

µm0 100 200 300 500

distance

Figure 11.6


2005

In the case of the strip-electrode submerged-arc surfacing process normally strips

(widths: 20 - 120mm) are used. These strips allow high cladding rates. Solid wire electrodes

as well as flux-cored strip electrodes are used. The flux-cored strip electrodes contain certain

alloying elements. The strip is continuously fed into the process via feed rollers. Current con-

tact is normally carried out

via copper contact jaws

which in some cases are

protected against wear by

hard metal inserts. The

slag-forming flux is sup-

plied onto the workpiece in

front of the strip electrode

by means of a flux support.

The non-molten flux can be

extracted and returned to

the flux circuit.

Should the slag developed

on top of the welding bead

not detach itself, it will

have to be removed me-

chanically in order to avoid

slag inclusions during

overwelding. The arc wan-

ders along the lower edge

of the strip. Thus the strip

is melted consistently, Fig-

ure 11.8.

br-er11-07e.cdr

inert gas-shielded arc weldingmetal-arc welding submerged arc welding

arc spraying

plasma spraying

electroslag welding

- stick electrode- filler wire

- MIG / MAG- MIG cold wire- filler wire

TIG welding

- TIG cold wire

plasma welding

- plasma powder- plasma hot wire

- wire electrode- strip electrode

arc welding with self-shieldedcored wire electrode

- filler wire

- powder- wire

- wire electrode

Figure 11.7

br-er11-08e.cdr

flux support

filler metal

slag

surfacing bead

drive rolls + -

flux application

base metal

power source

Figure 11.8


2005


cladding of a roll barrel.

The coating is deposited

helically while the work-

piece is rotating. The weld

head is moved axially over

the workpiece.

The macro-section and

possible weld defects of a

strip-electrode submerged-

arc surfacing process are

depicted in Figure 11.10.

Electroslag surfacing us-

ing a strip electrode is

similar to strip-electrode SA

surfacing, Figure 11.11.

The difference is that the

weld filler metal is not

melted in the arc but in liq-

uefied welding flux — the

liquid slag – as a result of

Joule resistance heating.

The slag is held by a slight

inclination of the plate and

the flux mound to prevent it

from running off.

br-er11-10e.cdr

coarse grain zone lack of fusion mirco slag inclusions sagged weld

crack formationin these areas of

the coarse grain zoneundercutsgusset

base metal

Figure 11.10

br-er11-09e.cdr

Figure 11.9


2005

TIG weld surfacing is a suitable surfacing method for small and complicated contours and/or

low quantities (e.g. repair work) with normally relatively low deposition rates. The process

principle has already been shown when the TIG joint welding process was explained, Figure

11.12. The arc is burning

between a gas-backed non-

consumable tungsten elec-

trode and the workpiece.

The arc melts the base

metal and the wire or rod-

shaped weld filler metal

which is fed either continu-

ously or intermittently. Thus

a fusion welded joint devel-

ops between base metal

and surfacing bead.

In the case of MIG/MAG surfacing proc-

esses the arc burns between a consumable

wire electrode and the workpiece. This

method allows higher deposition rates. Filler

as well as solid wires are used. The wire elec-

trode has a positive, while the workpiece to be

surfaced has a negative polarity, Figure

11.13.


Process Principle ofTIG Weld Surfacing

rod/ wire-shapedfiller metal

arc


base metal(+ / ~) surfacing bead

tungsten electrode(- / ~)

Figure 11.12

br-er11-11e.cdr

molten pool

Figure 11.11


2005

A further development of

the TIG welding process is

plasma welding. While the

TIG arc develops freely, the

plasma welding arc is me-

chanically and thermally

constricted by a water-

cooled copper nozzle. Thus

the arc obtains a higher

energy density.

In the case of plasma arc

powder surfacing this

constricting nozzle has a

positive, the tungsten electrode has a negative polarity, Figure 11.14. Through a pilot arc

power supply a non-transferred arc (pilot arc) develops inside the torch. A second, separate

power source feeds the transferred arc between electrode and workpiece. The non-

transferred arc ionises the centrally fed plasma gas (inert gases, as, e.g., Ar or He) thus

causing a plasma jet of high energy to emerge from the nozzle. This plasma jet serves to

produce and to stabilise the arc striking ability of the transferred arc gap. The surfacing filler

metal powder added by a feeding gas flow is melted in the plasma jet. The partly liquefied

weld filler metal meets the

by transferred arc molten

base metal and forms the

surfacing bead. A third gas

flow, the shielding gas, pro-

tects the surfacing bead

and the adjacent high-

temperature zone from the

surrounding influence. The

applied gases are mainly

inert gases, as, for exam-

ple, Ar and He and/or Ar-

/He mixtures.

br-er11-13e.cdr

workpiece

+-

oscillation

feed direction

shielding gas

arc

surfacing bead


contact tube

weld filler metal power source

wire feed deviceshielding gas

Figure 11.13

br-er11-14e.cdr

power sources

HIG

U

workpiece oscillation

surfacing bead

pilot arc

welding arc

filler metal

shielding gas

conveying gas

plasma gas

tungsten electrode

TA

UNTA

Figure 11.14


2005

The method is applied for surfacing small and medium-sized parts (car exhaust valves, ex-

truder spirals). Figure 11.15 shows a cross-section of armour plating of a car exhaust valve

seat. The fusion line, i.e.,

the region between surfac-

ing and base metal, is

shown enlarged on the

right side of Figure 11.15

(blow-up). It shows

hardfacing with cobalt

which is high-temperature

and hot gas corrosion

resistant.

In plasma arc hot wire

surfacing the base metal

is melted by an oscillating

plasma torch, Figure 11.16.

The weld filler metal in the form of two parallel wires is added to the base metal quite inde-

pendently. The arc between the tips of the two parallel wires is generated through the appli-

cation of a separate power

source. The plasma arc

with a length of approx. 20

mm is oscillating (oscilla-

tion width between 20 to 50

mm). The two wires are fed

in a V-formation at an an-

gle of approx. 30° and melt

in the high-temperature

region in the trailing zone

of the plasma torch.

br-er11-16e.cdr

workpiece

wires from spool

plasma powersource

shieldinggas

arc

plasma gas

tungstenelectrode

=

~

surfacingbead

hot wire power source

weld pool

Figure 11.16

br-er11-15e.cdr

section A

GW

ZW

Figure 11.15


2005

For surfacing purposes,

besides the arc-welding

methods, the beam weld-

ing methods laser beam

and electron beam welding

may also be applied. Fig-

ure 11.17 shows the proc-

ess principle of laser sur-

facing. The powder filler

metal is added to the laser

beam via a powder nozzle

and the powder gas flow

is, in addition, constricted

by shielding gas flow.

Friction surfacing is, in principle, similar to friction welding for the production of joints which

due to the different materials are difficult to produce with fusion welding, Figure 11.18.

The filler metal is “advanced” over the workpiece with high pressure and rotation. By the

pressure and the relative movement frictional heat develops and puts the weld filler end into

a pasty condition. The advance motion causes an adherent, “spreaded” layer on the base

metal. This method is not applied frequently and is mainly used for materials which show

strong differences in their melting and oxidation behaviours.

A comparison of the differ-

ent surfacing methods

shows that the application

fields are limited - de-

pendent on the welding

method. A specific

method, for example, is

the low filler/base metal

dilution. These methods

are applied where high-

quality filler metals are

br-er11-18e.cdr

rotation

bulge

force

surfacing layer

base metal

filler metal

advance

Figure 11.18

Figure 11.17


2005

welded. Another criterion for the selection of a surfacing method is the deposition rate. In the

case of cladding large sur-

faces a method with a high

deposition rate is chosen,

this with regard to profit-

ability.

In thermal spraying the

filler metal is melted inside

the torch and then, with a

high kinetic energy, dis-

charged onto the unfused

but preheated workpiece

surface.

There is no fusion of base and filler metal but rather adhesive binding and mechanical inter-

locking of the spray deposit with the base material. These mechanisms are effective only

when the workpiece surface is coarse (pre-treatment by sandblasting) and free of oxides.

The filler and base materials are metallic and non-metallic. Plastics may be sprayed as well.

The utilisation of filler metals in thermal spraying is relatively low.

The most important methods of thermal spraying are: plasma arc spraying, flame spraying

and arc spraying.

In powder flame spraying

an oxyacetylene flame pro-

vides the heating source

where the centrally fed filler

metal is melted, Figure

11.19. The kinetic energy for

the acceleration and atomi-

sation of the filler metal is

produced by compressed

gas (air).

br-er11-19e.cdr

spraying materialcompressedair

workpiece

flame conefuel gas-oxygenmixture

spray deposit

Figure 11.19

br-er11-20e.cdr

compressed air

gas mixture

adjustable wirefeed device

spraying wire spray deposit

spraying jet non-bindingsprayed particles(loss in spraying)

fusingwire tip

Figure 11.20


2005

In contrast to powder flame

spraying, is for flame

spraying a wire filler metal

fed mechanically into the

centre cone, melted, atom-

ised and accelerated in

direction of the substrate,

Figure 11.20.

In plasma arc spraying an

internal, high-energy arc is

ignited between the tung-

sten cathode and the an-

ode, Figure 11.21. This arc

ionises the plasma gas (argon, 50 - 100 l/min). The plasma emerges from the torch with a

high kinetic and thermal energy and carries the side-fed powder along with it which then

meets the workpiece surface in a semi-fluid state with the necessary kinetic energy. In the

case of shape welding, steel shapes with larger dimensions and higher weights are pro-

duced from molten weld metal only. In comparison to cast parts this method brings about es-

sentially more favourable mechano-technological material properties, especially a better

toughness characteristic. The reason for this lies mainly in the high purity and the homogene-

ity of the steel which is helped by the repeated melting process and the resulting slag reac-

tions. These properties are

also put down to the fa-

vourable fine-grained struc-

ture formation which is

achieved by the repeated

subsequent thermal treat-

ment with the multi-pass

technique. Also in contrast

with the shapes produced

by forging, the workpieces

produced by shape welding

show quality advantages,

Plasma Powder Spraying Unit


powder injector

jet of particles

copper anode

plasmagas

coolingwater cooling water tungsten cathode arc

anodecarrier

middleframe

gasdistributor

isolationring

backframe

Figure 11.21

Shape Welding - Integration


shape welding

forming(forging)

joining(welding)

primary forming(casting)

Figure 11.22


2005

br-er11-23e.cdr

Shape Welded Goblet (1936)

Figure 11.23

especially in the isotropy and the regularity of their toughness and strength properties as far

as larger workpiece thicknesses are concerned. In Europe, due to the lack of expensive forg-

ing equipment, very high individual weights

may not be produced as forged parts.

Therefore, shape welding is, for certain appli-

cations, a sensible technological and eco-

nomical alternative to the methods of primary

forming, forming or joining, Figure 11.22.

Figure 11.23 shows an early application which

is related to the field of arts.

The higher tooling costs in forging make the

shape welding method less expensive; this

applies to parts with certain increasing com-

plexity. This comparison is, however, related

to relatively low numbers of pieces, where the

tooling costs per part are accordingly higher,

Figure 11.24.

br-er11-24e.cdr

sh

afts

boile

r she

ll rings

bra

ces

sp

heri

cal ca

ps

pip

e b

end

s

forged products

shape-weldedproducts

complexity of the parts

€/kg

Figure 11.24


2005

br-er11-26e.cdr

tractionmechanism

joistturntable

phase 1

phase 3

phase 5

phase 2

phase 4

phase 6

phase 7

Figure 11.26


Shape Welding Procedures

+ several weld heads possible+ no interruption during weld head failure

- core made of foreign material necessary

applications:shafts, large boiler shell rings, flanges

+ free rotationally-symmetrical shapes+ several weld heads possible+ weld head manipulation not necessary+ each head capable to weld a specific layer+ small diameters possible

- component movement must correspond with the contour- number of weld heads limited when smaller diameters are welded

applications:spherical caps, pipe bends, braces

+ transportable unit

- limited welding efficiency

applications:welding-on of connection pieces

Baumkuchenmethode

Töpfermethode

Klammeraffe

Figure 11.25

Figure 11.25 shows the principal procedure for

the production of typical shape-welded parts.

Cylindrical containers are produced with the

“Baumkuchenmethode” method: the filler metal

is welded by submerged-arc with helical mo-

vement in multiple passes into a tube which

has the function of a traction mechanism (for

the most part mechanically removed later).

This brings about the possibility to produce

seamless containers with bottom and flange in

one working cycle.

Elbows are mainly manufactured with the

Töpfer method. On the traction mechanism a

rotationally symmetrical part with a semicircle

cross-section is produced which is later sepa-

rated and welded to an elbow, Figures 11.26

and 11.27. The Klammeraffe method serves

the purpose to weld exter-

nal connection pieces onto

pipes. A portable unit

which is connected with the

pipe welds the connection

pipe in a similar manner to

the Töpfer method.


2005

In the case of electron beam surfacing the

filler metal is added to the process in the form

of a film, Figure 11.28.

© ISF 1998

feed direction

metal foil

metal foil feeding

electron beam

surface layer

base material

workpiece

Process PrincipleElectron Beam Surface Welding

ka11-18.cdr

Figure 11.28

br-er11-27e.cdr

Production of a Pipe Bendby Shape Welding

testing

1. welding of the half-torus2. stress relief annealing3. mechanical treatment4. seperating/ halving5. folding6. welding togehter7. stress relief annealing8. testing

Figure 11.27

12.

Thermal Cutting


2005

Thermal cutting processes

are applied in different

fields of mechanical engi-

neering, shipbuilding and

process technology for the

production of components

and for the preparation of

welding edges. The ther-

mal cutting processes are

classified into different

categories according to DIN

2310, Figure 12.1.

Figure 12.2 shows the clas-

sification according to the physics of the cutting process:

- flame cutting – the material is mainly oxidised (burnt)

- fusion cutting – the material is mainly fused

- sublimation cutting – the material is mainly evaporat

The gas jet and/or evaporation expansion is in all processes responsible for the ejection of

molten material or emerging reaction products such as slag.

The different energy carriers for the thermal cutting are depicted in Figure 12.3:

- gas,

- electrical gas discharge

and

- beams.

Electron beams for ther-

mal cutting are listed in the

DIN-Standard, they pro-

duce, however, only very

small boreholes. Cutting

is impossible.

Classification of Thermal CuttingProcesses acc. to DIN 2310-6

Classification of thermal cutting processes

- physics of the cutting process

- degree of mechanisation

- type of energy source

- arrangement of water bath

br-er12-01e.cdr

Figure 12.1

Classification of Processes bythe Physics of Cutting

Flame cutting

Fusion cutting

Sublimation cutting

The material is mainly oxidised;the products

are blown out by an oxygen jet.

The material is mainly fused and blown out

by a high-speed gas jet.

The material is mainly evaporated.

It is transported out of the cutting groove by

the created expansion or by additional gas.

br-er12-02e.cdr

Figure 12.2


2005

Figure 12.4 depicts the different methods of thermal cutting with gas according to DIN

8580. These are:

- flame cutting

- metal powder

flame cutting

- metal powder

fusion cutting

- flame planing

-oxygen-lance cutting

- flame gouging or scarf-

ing

-flame cleaning

In flame cutting (principle

is depicted in Figure 12.5)

the material is brought to

the ignition temperature by

a heating flame and is then

burnt in the oxygen stream.

During the process the igni-

tion temperature is main-

tained on the plate top side

by the heating flame and

below the plate top side by

thermal conduction and

convection.

However, this process is

suited for automation and is, also easy to apply on site. Figure 12.6. shows a commercial

torch which combines a welding with a cutting torch. By means of different nozzle shapes

the process may be adapted to varying materials and plate thicknesses. Hand-held torches

or machine-type torches are equipped with different cutting nozzles: Standard or block-

type nozzles (cutting-oxygen pressure 5 bar) are used for hand-held torches and for torches

which are fixed to guide carriages.

Classification of Thermal Cutting Processes acc. to DIN 2310-6

-

- - sparks - arc - plasma

- - laser beam (light) - electron beam - ion beam

gas

electrical gas discharge

beams

thermal cutting by:

br-er12-03e.cdr

Figure 1.3

Thermal Cutting Processes Using Gas

thermal cutting processes using gas:

� metal powder

flame cutting

� oxygen cutting � metal powder

fusion cutting

� flame planing �

�

�

oxygen-lance cutting

flame gouging

scarfing

� flame cleaning

br-er12-04e.cdr

Figure 1.4


2005

The high-speed cutting nozzle (cutting-oxygen pressure 8 bar) allows higher cutting

speeds with increased cutting-oxygen pressure. The heavy-duty cutting nozzle (cutting-

oxygen pressure 11 bar) is

mainly applied for eco-

nomic cutting with flame-

cutting machines. A further

development of the heavy-

duty nozzle is the oxygen-

shrouded nozzle which

allows even faster and

more economic cutting of

plates within certain thick-

ness ranges. Gas mixing is

either carried out in the

torch handle, the cutting

attachment, the torch head

or in the nozzle (gas mix-

ing nozzle); in special

cases also outside the

torch – in front of the noz-

zle. As the design of cutting

torches is not yet subject to

standardisation, many

types and systems exist on

the market.

Principle of Oxygen Cutting

cutting oxygenheating oxygengas fuel

cutting jet

heating flame

workpiece

br-er12-05e.cdr

Figure 12.5

Cutting Torch and Nozzle Shapes

block-typenozze

gas mixingnozzle

manual cutting equipmentas a cutting and weldingtorch combination

cutting oxygen

mixing chamber

gas fuel

heating oxygen

br-er12-06e.cdr

Figure 12.6


2005

The selection of a torch or

nozzles important and de-

pends mainly on the cutting

thickness, the desired cut-

ting quality, and/or the ge-

ometry of the cutting edge.

Figure 12.7 gives a survey

of the definitions of flame-

cutting.

In flame cutting, the ther-

mal conductivity of the ma-

terial must be low enough

to constantly maintain

the ignition temperature,

Figure 12.8. Moreover, the

material must neither

melt during the oxidation

nor form high-melting

oxides, as these would

produce difficult cutting

surfaces. In accordance,

only steel or titanium mate-

rials fulfill the conditions for

oxygen cutting., Figure

12.9

Function of the Flame During Flame Cutting

The heating flame has to perform the following tasks:

- rapid heating of the material (about 1200°C)

- substitution of losses due to heat conduction

in order to maintain a positive heat balance

- preheating of cutting oxygen

- stabilisation of the cutting oxygen jet; formation

of a cylindrical geometry over a extensive length

and protection against nitrogen of the surrounding air

br-er12-08e.cdr

Figure 12.8

Flame Cutting Terms

cut lengthcutting length

end of the cut

cut

thic

kne

ss

start

kerf

kerf width

heating and cutting nozzle

torch

cutting jet

nozzle

-to

-wo

rkd

ista

nce

br-er12-07e.cdr

Figure 12.7


2005

Steel materials with a C-content of up to approx. 0.45% may be flame-cut without preheating,

with a C-content of approx. 1.6% flame-cutting is carried out with preheating, because an

increased C-content demands more heat. Carbon accumulates at the cutting surface, so a

very high degree of hardness is to be expected. Should the carbon content exceed 0.45%

and should the material not have been subject to prior heat treatment, hardening cracks on

the cutting surface are re-

garded as likely.

Some alloying elements

form high-melting oxides

which impair the slag ex-

pulsion and influence the

thermal conductivity.

The iron-carbon equilibrium

diagram illustrates the car-

bon content-temperature

interrelation, Figure 12.10.

As the carbon content

increases, the melting

temperature is lowered.

That means: from a certain

carbon content upwards,

the ignition temperature is

higher than the melting

temperature, i.e., this

would be the first violation

to the basic requirement in

flame cutting.

Conditions of Flame Cutting

The material has to fulfill the following requirements:

- the ignition temperature has to be lower than the

melting temperature

- the melting temperature of the oxides has to be lower

than the melting temperature of the material itself

- the ignition temperature has to be permanently maintained;

i. e. the sum of the supplied energy and heat losses due to

heat conduction has to result in a positive heat balance

br-er12-09e.cdr

Figure 12.9

Ignition Temperature in theIron-Carbon-Equilibrium Diagram

liquid

Liquidus

Solidus

solid

solid

pasty

steel cast iron

tem

pera

ture

[°C

]

1500

1000

ignition curve

2,0 carbon content [%]

br-er12-10e.cdr

Figure 12.10


2005

Steel compositions may

influence flame cuttability

substantially - the individual

alloying elements may

show reciprocate effects

(reinforcing/weakening),

Figure 12.11. The content

limits of the alloying con-

stituents are therefore only

reference values for the

evaluation of the flame cut-

tability of steels, as the cut-

ting quality is substantially

deteriorating, as a rule al-

ready with lower alloy con-

tents.

By an arrangement of one

or several nozzles already

during the cutting phase a

weld preparation may be

carried out and certain

welding grooves be pro-

duced. Figure 12.12 shows

torch arrangements for

- the square butt weld,

- the single V butt weld,

- the single V butt weld with root face,

- the double V butt weld and

- the double V butt weld with root face.

Flame Cutting Suitability in Dependance of Alloy-Elements

Maximum allowable contents of alloy-elements:

carbon: up to 1,6 %

silicon: up to 2,5 % with max. 0,2 %C

manganese: up to 13 % and 1,3 % C

chromium: up to 1,5 %

tungsten: up to 10 % and 5 % Cr, 0,2 % Ni, 0,8 % C

nickel: up to 7,0 % and/or up to 35 % with min. 0,3 % C

copper: up to 0,7 %

molybdenum: up to 0,8 %, with higher proportions of W, Cr and C

not suitable for cutting

br-er12-11e.cdr

Figure 12.11

Weld-Groove Preparation by Oxygen Cutting

square butt weld single-V butt weld single-V butt weldwith rootface

double-V butt weld double-V butt weldwith root face

br-er12-12e.cdr

Figure 12.12


2005

Possible Flame Cutting Defects

edge defect:

cut face defects:

edge rounding chain of fused globules edge overhang

kerf constriction or extension angular deviation step at lower edge of the cut excessive depth of cutting grooves

cratering:

adherent slag:

cracks:

sporadic craterings connected craterings cratering areas

slag adhearing to bottom cut edge

face cracks cracks below the cut face

br-er12-13e.cdr

Figure 12.13

It has to be considered that, particularly in cases where flame cutting is applied for weld

preparations, flame cutting-related defects may lead to increased weld dressing work. Slag

adhesion or chains of molten globules have to be removed in order to guarantee process

safety and part accuracy for the subsequent processes. Figure 12.13 gives a survey of pos-

sible defects in flame cutting.

In order to improve the

flame-cutting capacity

and/or cutting of materials

which are normally not to

be flame-cut the powder

flame cutting process may

be applied.

Here, in addition to the cut-

ting oxygen, iron powder is

blown into the cutting gap.

In the flame, the iron pow-

der oxidises very fast and

adds further energy to the

process. Through the addi-

tional energy input the

high-melting oxides of

the high-alloy materials

are molten. Figure 12.14

shows a diagrammatic rep-

resentation of a metal

powder cutting arrange-

ment.

Metal Powder Flame Cutting

waterseperator

powderdispenser

acetylene

oxygencompressed

air

br-er12-14e.cdr

Figure 12.14


2005


principle of flame gouging

and scarfing. Both meth-

ods are suited for the weld

preparation; material is re-

moved but not cut. This

way, root passes may be

grooved out or fillets for

welding may be produced

later.


methods of thermal cut-

ting processes by electri-

cal gas discharge:

- plasma cutting with non-transferred arc

- plasma cutting with transferred arc

- plasma cutting with transferred arc and secondary gas flow

- plasma cutting with transferred arc and water injection

- arc air gouging (represented diagrammatically)

- arc oxygen cutting (represented diagrammatically)

Flame Gouging and Scarfing

flame gouging scarfing

gougingoxygen scarfing

oxygen

gas-heatoxygen mixture gas-heat

oxygen mixture

br-er12-15e.cdr

Figure 12.15

Thermal Cutting Processesby Electrical Gas Discharge

Thermal cutting processes by electrical gas discharge:

arc air gouging arc oxygen cuttingplasma cutting

- with non-transferred arc

- with transferred arc -with secondary gas flow -with water injection

carbonelectrode

compressedair =

tube

electrodecoating

cuttingoxygen

arc

br-er2-16e.cdr

Figure 12.16


2005

In plasma cutting the en-

tire workpiece must be

heated to the melting tem-

perature by the plasma jet.

The nozzle forms the

plasma jet only in a re-

stricted way and limits thus

the cutting ability of plate to

a thickness of approx.

150 mm, Figure 12.17.

Characteristic for the

plasma cut are the cone-

shaped formation of the

kerf and the rounded

edges in the plasma jet entry zone which were caused by the hot gas shield that envelops

the plasma jet. These process-specific disadvantages may be significantly reduced or limited

to just one side of the plate (high quality or scrap side), respectively, by the inclination of the

torch and/or water addition. With the plasma cutting process, all electrically conductive ma-

terials may be separated. Nonconductive materials, or similar materials, may be separated by

the emerging plasma flame, but only with limited ability.

In order to cool and to re-

duce the emissions,

plasma torches may be

surrounded by additional

gas or water curtains

which also serve as arc

constriction, Figure 12.18.

In dry plasma cutting

where Ar/H2, N2, or air are

used, harmful substances

always develop which not

only have to be sucked off

very carefully but which

Water Injection Plasma Cutting

electrodeplasma gas

nozzle

workpiece

water curtain

cone of water

cutting waterswirl chamber

water bath

br-er12-18e.cdr

Figure 12.18

Plasma Cutting

R

HFpowersource

-

+

electrodeplasma gas

nozzle

workpiece

coolingwater

br-er12-17e.cdr

Figure 12.17


2005

also must be disposed of.

In water-induced plasma

cutting (plasma arc cutting

in water or under water)

gases, dust, also the noise,

and the UV radiation are,

for the most part, held back

by the water. A further,

positive effect is the cooling

of the cutting surface, Fig-

ure 12.18. Careful disposal

of the residues is here in-

evitable.

Figure 12.19 gives a survey

of the different cutting meth-

ods using a water bath.

Figure 12.20 shows a torch

which is equipped with an

additional gas supply, the

so-called secondary gas.

The secondary gas shields

the plasma jet and in-

creases the transition resis-

tance at the nozzle front.

The so-called “double and/or parasite arcs” are avoided and nozzle life is increased.

Types of Water Bath Plasma Cutting

cutting with water bath

plasma cutting with workpieceon water surface

underwater plasma cutting

water injection plasma cuttingwith water curtain

br-er12-19e.cdr

Figure 12.19

Plasma Cutting With Secondary Gas Flow

electrodeplasma gas

nozzle

workpiece

secondary gas

br-er12-20e.cdr

Figure 12.20


2005

Thanks to new electrode

materials, compressed air

and even pure oxygen

may be applied as plasma

gas – therefore, in flame

cutting, the burning of unal-

loyed steel may be used for

increased capacity and

quality. The selection of the

plasma forming gases

depends on the require-

ments of the cutting proc-

ess. Plasma forming media

are argon, helium, hydro-

gen, nitrogen, air, oxygen or water.

The advantage of the use of oxygen as plasma gas is in the achievable cutting speeds

within the plate thickness range of approx. 3 – 12 mm (400 A, WIPC). In the steel plate thick-

ness range of approx. 1 – 10 mm the application of 40 A-compressed air units is recom-

mended. In comparison with 400 A WIPC systems, these allow vertical and significantly nar-

rower cutting kerfs, but with

lower cutting speeds. Fig-

ure 12.21 shows different

cutting speeds for different

units and plasma gases.

In the thermal cutting

processes with beams

only the laser is used as

the jet generator for cutting,

Figure 12.22.

Cutting Speeds of Different PlasmaCutting Equipment for Steel Plates

cuttin

g s

peed [m

/min

]

plate thickness [mm]

5 10 15 20

2

4

8

6

machine type and plasma medium1 WIPC, 400 A, O

2 WIPC, 400 A, N

3 200 A, s < 8 mm: N

4 40 A, compressed air

2

2

2

1

2

3

4

s > 8 mm: Ar/H2

br-er12-21e.cdr

Figure 12.21

Thermal Cutting With Beams

Thermal cutting processes

by laser beam

- laser beam combustion cutting

- laser beam fusion cutting

- laser beam sublimation cutting

br-er12-22e.cdr

Figure 12.22


2005

Variations of the laser beam cutting process:

- laser beam combustion cutting, Figure 12.25

- laser beam fusion cutting, Figure 12.26

- laser beam sublimation cutting, Figure 12.27.

The process sequence in laser beam combustion cutting is comparable to oxygen cut-

ting. The material is heated to the ignition temperature and subsequently burnt in the oxy-

gen stream, Figure 12.23. Due to the concentrated energy input almost all metals in the

plate thickness range of up to approx. 2 mm may be cut. In addition, it is possible to achieve

very good bur-free cutting

qualities for stainless steels

(thickness of up to approx.

8 mm) and for structural

steels (thickness of up to

12 mm). Very narrow and

parallel cutting kerfs are

characteristic for laser

beam cutting of structural

steels.

In laser beam cutting, ei-

ther oxygen (additional en-

ergy contribution for oxidis-

ing materials) or an inactive

cutting gas may be applied

depending on the cutting

job. Besides, the very high

beam powers

(pulsed/superpulsed mode

of operation) allow a direct

evaporation of the material

(sublimation). In laser

beam combustion cutting

and laser beam sublima-

Laser Beam Cutting

cutting oxygen

lens

workpiece

slag jet

laser focus

thin layer of cristallisedmolten metal

br-er12-23e.cdr

Figure 12.23

Qualitative Temperature Dependencyon Absorption Ability

melting point Tm boiling point Tb

temperature

λ =µ

1,06 m (Nd:YAG-laser)

λ =µ

10,06 m (CO -laser)2

he

atin

g-u

p

me

ltin

g

evap

ora

tin

g

20

40

60

80

absorp

tion

facto

r

br-er12-24e.cdr

Figure 12.24


2005

tion cutting the reflexion of the laser beam of more than 90 % on the workpiece surface de-

creases unevenly when the process starts. In laser beam fusion cutting remains the reflex-

ion on the molten material, however, at more than 90%! Figure 12.24 shows the absorption

factor of the laser light in

dependence on the tem-

perature. This factor mainly

depends on the wave

length of the used laser

light. When the melting

point of the material has

been reached, the absorp-

tion factor increases un-

evenly and reaches values

of more than 80%.

During laser beam combus-

tion cutting of structural

steel high cutting speeds are achieved due to the exothermal energy input and the low laser

beam powers, Figure 12.25. In the above-mentioned case (dependent on beam quality, fo-

cussing, etc.), above a

beam power of approx.

3,3 kW, spontaneous

evaporation of the material

takes place and allows

sublimation cutting. Signifi-

cantly higher laser powers

are necessary to fuse the

material and blow it out

with an inert gas, as the

reflexion loss remains con-

stant.

Characteristics of the LaserBeam Cutting Processes I

laser cutting (with oxygen jet)

- the laser beam is focused on the workpiece surface and the material burns in the oxygen jet starting from the heated surface

materials: - steel aluminium alloys, titanium alloys

cutting gas: - O N Ar

criteria: - high cutting speed, cut faces with oxide skin

2, 2,

br-er12-25e.cdr

Figure 12.25

laser fusion cutting:

- the laser beam melts the entire plate thickness (optimum focus point 1/3 below plate surface) - high reflection losses (>90%)

materials: - metals, glasses, polymers

cutting gas: - N , Ar, He

criterions: - cutting speed is only 10-15% in comparison to cutting with oxygen jet, characteristics melting drag lines

2

Characteristics of the LaserBeam Cutting Processes II

br-er12-26e.cdr

Figure 12.26


2005

Important influence quantities for the cutting speed and quality in laser beam cutting are

the focus intensity, the position of the focus point in relation to the plate surface and the

formation of the cutting gas flow. A prerequisite for a high intensity in the focus is the high

beam quality (Gaussian intensity distribution in the beam) with a high beam power and suit-

able focussing optics.

Laser beam cutting of contours, especially of pointed corners and narrow root faces, requires

adaptation of the beam power in order to avoid heat accumulation and burning of the mate-

rial. In such a case the

beam power might be re-

duced in the continuous

wave (CW) operating

mode. With a decreasing

beam efficiency decreases

the cuttable plate thickness

as well. Better suited is the

switching of the laser to

pulse mode (standard

equipment of HF-excited

lasers) where pulse height

can be selected right up to

the height of the continuous

wave. A super pulse

equipment (increased exci-

tation) allows significantly

higher pulse efficiencies to

be selected than those

achieved with CW. Further

fields of application for the

pulse and super pulse op-

eration mode are punching

and laser beam sublimation

cutting.

Characteristics of the LaserBeam Cutting Processes III

laser evaporation cutting:

- spontaneous evaporation of the material starting from 10 W/cmwith high absorption rate and deep-penetration effect

- metallic vapour is pressed from the cavity by own vapour pressure and by a supporting gas flow

materials: - metals, wood, paper, ceramic, polymer

cutting gas: - N , Ar, He (lens protection)

criteria: - low cutting speed, smooth cut edges, minimum heat input

5 2

2

br-er12-27e.cdr

Figure 12.27

Fields of Application of Cutting Processes

laser 600 W 1500 W 600 W 1500 W 1500 W

plasma 50 A 5 kW 250 A 25 kW 500 A 150 kW

oxy-flame

10 100 10001

steel

Cr-Ni-steel

aluminium

steelCr-Ni-steelaluminium

StahlCr-Ni-Stahl


br-er12-28e.cdr

Figure 12.28


2005

Laser beam cutting of aluminium plates thicker than appx. 2 mm does not produce bur-free

results due to a high reflex-

ion property, high heat

conductivity and large

temperature differences

between Al and Al2O3. The

addition of iron powder al-

lows the flame cutting of

stainless steels (energy

input and improvement of

the molten-metal viscosity).

The cutting quality, how-

ever, does not meet high

standards.

Figure 12.28 shows a comparison of the different plate thicknesses which were cut using

different processes. For the plate thickness range of up to 12 mm (steel plate), laser beam

cutting is the approved precision cutting process. Plasma cutting of plates > 3 mm allows

higher cutting speeds, in comparison to laser beam cutting, the cutting quality, however, is

significantly lower. Flame cutting is used for cutting plates > 3 mm, the cutting speeds are, in

comparison to plasma cutting, significantly lower. With an increasing plate thickness the dif-

ference in the cutting

speed is reduced. Plates

with a thickness of more

than 40 mm may be cut

even faster using the flame

cutting process.


cutting speeds of some

thermal cutting processes.

Cutting Speeds of Thermal Cutting Processes

cutt

ig s

peed

s

[m/m

in]

10

10

1001

1

0,1


oxygen cutting(Vadura 1210-A)

plasma cutting(WIPC, 300-600 A)

CO2-laser(1500 W)

br-er12-29e.cdr

Figure 12.29

Thermal Cutting Costs - Steal

costs

[D

M/m

cu

t le

ngth

]


5 10 15 20 25 30 35 40

1

2

3

4

5

6

laser

plasmaflame cuttingwith 3 torches

total costs

machine costs

br-er12-30e.cdr

Figure 12.30


2005

Apart from technological aspects, financial considerations as well determine the application

of a certain cutting method. Figures 12.30 and 12.31 show a comparison of the costs of

flame cutting, plasma arc

and laser beam cutting –

the costs per m/cutting

length and the costs per

operating hour. The high

investment costs for a laser

beam cutting equipment

might be a deterrent to ex-

ploit the high cutting quali-

ties obtainable with this

process. Cost Comparison of Cutting Processes

plasma cutting(plasma 300A)

flame cutting(6-8 torches)

laser beam cutting(laser 1500W)

investment total(replacement value)

170,000.00€

€/h

€/h

€/h

€/h

220,000.00 500,000.00

1 shift, 1600h/year, 80% availability, utilisation time 1280h/year

calculation for a 6-year-accounting depreciation 23.50 29.00 65.00

maintenance costs 3.50 4.00 10.00

production cost unit ratecosts/1 operating hour 65.00 75.00 130.00

energy costs 1.00 2.50 2.50

extract from a costing acc. to VDI 3258

br-er12-31e.cdr

Figure 12.31

13.

Special Processes


2005

Apart from the welding processes explained earlier there is also a multitude of special weld-

ing processes. One of them is stud welding. Figure 13.1 depicts different stud shapes. De-

pending on the application, the studs are equipped with either internal or external screw

threads; also studs with pointed tips or with corrugated shanks are used.

In arc stud welding, a dis-

tinction is basically made

between three process

variations. Figure 13.2.

depicts the three variations

– the differences lie in the

kind of arc ignition and in

the cycle of motions during

the welding process.

The switching arrange-

ment of an arc stud weld-

ing unit is shown in Fig-

ure 13.3. Besides a power

source which produces

high currents for a short-

time, a control as well as a

lifting device are necessary.

Figure 13.1

rammed flange

br-er13-01e.cdr

Figure 13.2

drawn-arcstud welding

capacitor-discharge studwelding withtip ignition

drawn-arc studwelding withferrule ignition

ceramic ferrulecold-upsettip ignition

ignitionring

br-er13-02e.cdr


2005

In drawn-arc stud welding the stud is first mounted onto the plate, Figure 13.4. The arc is

ignited by lifting the stud and melts the entire stud diameter in a short time. When stud and

base plate are fused, the stud is dipped into the molten weld pool while the ceramic ferrule is

forming the weld. After the solidification of the liquid weld pool the ceramic ferrule is knocked

off.

Figure 13.5 illustrates tip

ignition stud welding.

The tip melts away imme-

diately after touching the

plate and allows the arc to

be ignited. The lifting of the

stud is dispensed with.

When the stud base is mol-

ten, the stud is positioned

onto the partly molten

workpiece.

Studs with diameters of up

to 22 mm can be used.

Welding currents of more

than 1000 A are necessary.

The arc stud welding proc-

ess allows to join different

materials, see Figure 13.6.

Problematic are the differ-

ent melting points and the

heat dissipation of the indi-

vidual materials. Aluminium

studs, for example, may

not be welded onto steel.

Figure 13.3

A

V

liftingdevice

stud holdingdevice

stud

ceramicferrule

workpiece

welding timeadjustment

control device

power source

br-er13-03e.cdr

Figure 13.4

stu

d m

ove

me

nt

cu

rren

t

start lifting dipping end

L

L

(L + P)>projection

P

0 1 2 3 4

time

time

PP

L

br-er13-04e.cdr


2005

The relatively high welding currents in the arc

stud welding process cause the somewhat

troublesome side-effects of the arc blow. Fig-

ure 13.7 depicts different arrangements of cur-

rent contact points and cable runs and illus-

trates the developing arc deflection (B,C,E). A,

D and F show possible countermeasures.

In high-frequency welding of pipes the en-

ergy input into the workpiece may be carried

out via sliding contacts, as shown in Fig-

ure 13.8, or via rollers, as shown in Fig-

ure 13.9. Only the high-frequency technique

allows a safe current transfer in spite of the

scale or oxide layers. Through the skin effect

the current flows only conditionally at the sur-

face. Therefore no thorough fusion of thick-

wall pipes may be achieved.

Figure 13.6

unalloyed sructuralsteel S235J0 and/orcomparable steels

otherunalloyed

steels

stainlesssteels acc.

DIN EN 17440

heat resistingsteels acc.SEW 470

aluminium andaluminium

alloys

unalloyed structural steel S235J0,S355J0 and/or comparable steels

(acc. DIN EN 10 025)

other unalloyed steels

stainless steelsacc. DIN EN 17440

heat resisting steelsacc. SEW 470

aluminium andaluminium alloys

explanation of the weldability classification numbers:

1 = well suitable (transmission of energy)2 = suitable (transmission of energy possible with restriction)

3 =

0 = not possible

suitable only up to a point (not for transmission of energy

1 2 3 2 0

2 2 3 2 0

3 3 1 3 0

2 2 2 2 0

0 0 0 0 2

base meatl

stud material

br-er13-06e.cdr

Figure 13.5

a b

c d© ISF 2002br-er13-05e.cdr

Phases of Capacitor-DischargeStud Welding With Tip Ignition


2005

Only welding of small wall

thicknesses is profitable –

as the weld speed must be

greatly reduced with in-

creasing wall thicknesses,

Figure 13.10.

Figure 13.8

moving directionof the pipe

pressurerollers

sliding contacts(fixed)

interstagetransformer

HF-valvegenerator

∼


High-Frequency Weldingof Pipes

Figure 13.7

A B

C Dbr-er13-07e.cdr

~

rotary transformer

Isolation

copper electrode wheel(water-cooled)

slot pipe

pressure rollers

counterpressure rollers


Rotary TransformerResistance Welding

Figure 13.9


2005

In induction welding – a process which is

used frequently nowadays – the energy input

is received contactless, Figure 13.11. Varying

magnetic fields produce eddy currents inside

the workpiece, which again cause resistance

heating in the slotted tube. A distinction is

made between coil inductors (left) and line

inductors (right).

Also in case of induction welding flows the

current flows only close to the surface areas

of the pipe. Only the current part which

reaches the joining zone and causes to fill the

gap may be utilised. Figure 13.12 illustrates

two current paths. On the left side: the useful

current path, on the right side: the useless

current path which does not contribute to the

fusion of the edges.


effective depth during the

inductive heating for differ-

ent materials, in depend-

ence on the frequency. As

soon as the Curie tempera-

ture point is reached, the

effective depth for ferritic

steels increases.

Figure 13.10

weld

ing s

pee

d

wall thickness

0

20

40

80

0 2 4 6 8 10 12 16mm

m/min

1

2

3

4 56

1:2:3:4:5:6:

36 kA;57 kA;75 kA;

125 kA;150 kA;200 kA;

100 kVA;200 kVA;300 kVA;500 kVA;

1200 kVA;1850 kVA;

60 Hz60 Hz60 Hz60 Hz

120 Hz120 Hz

© ISF 2002Br-er13-10e.cdr

Welding Speeds inHF-Resistance Welding

Figure 13.11



pressurerollers

pressurerollers

line inductorcoil inductor

br-er13-11e.cdr


2005

The application of the in-

duction welding method

allows high welding speeds

of more than 100m/min,

Figure 13.14.

Figure 13.13

0,04

0,02

0,060,080,10

0,2

0,4

0,60,81,0

2

4

68

10mm20

1 4 10 100 200 kHz 1000frequency f

effe

ctive

dep

th δ

3

1

2

45

6

7

1

23456

7

steel (ferriticsteel (austenitic)brassaluminium copperbrasscopperaluminiumsteel (ferritic)

800°C20....1400°C800°C600°C850°C20°C20°C20°C20°C


Standard Values of the EffectiveDepths During Inductive Heating

Figure 13.14

we

ld s

pee

d

wall thickness

0

20

40

80

0 2 4 6 8 10 12 16 mm

m/min

60

100

120

160

14 20

0 50 100 200mm

100

%

0

pipe diameter

corr

ective

facto

r

high frequency200 - 450 kW

600 kW

200 kW

300 kW

450 kW

60 kW 100 kW 150 kW


Welding Speeds in Induction Welding

Figure 13.12

l

b b

d

s

δ2

δ1

δ1

width of the heating inductorwall thickness of the pipecurrent penetration depthon pipe backside

bsδ1

δ2

d

current penetration depthat the strip edgesoutside diameter of the pipedistance inductor- welding pointl

br-er13-12e.cdr


2005

Aluminothermic fusion

welding or cast welding is

mainly used for joining

railway tracks on site. A

crucible is filled with a mix-

ture consisting of alumin-

ium powder and iron ox-

ide. An exothermal reac-

tion is initiated by an igniter

– the aluminium oxidises

and the iron oxide is re-

duced to iron, Fig-

ure 13.15. The molten iron

flows into a ceramic mould

which matches the contour of the track. After the melt has cooled, the mould is knocked off.

Figure 13.16 shows the process assembly.

Explosion welding or ex-

plosion cladding is fre-

quently used for joining

dissimilar materials, as,

for example, unalloyed

steel/alloyed steel, cop-

per/aluminium or

steel/aluminium. The mate-

rials which are to be joined

are pressed together by a

shock wave. Wavy transi-

tions develop in the joining

area, Figures 13.17 and

13.18.

Figure 13.16

weld cross-section

slag mould

workpiece

mould

riser

blow-holeorifice

riser

runnergate

workpiece

cast-aroundbulge

thermit slag

thermit steel

channel betweenriser and runnergate

runner gate

blow-holeorifice

iron or sand plug

foundry sand

thermit crucible

slag mould

riser

thermit bulge

thickness of thecast b

riser

workpiece

runner gate

preheating

air

gas fuel

A

B

b

bc

cut A-B

br-er13-16e.cdr

Figure 13.15

3FeO + 2Al Al O + 3Fe - 783 kJ2 3

Fe O + 2Al Al O + 2Fe - 758 kJ2 3 2 3

3Fe O + 8Al 4Al O + 9Fe - 3012 kJ3 4 2 3

br-er13-15e.cdr


2005

The determined cladding

speed must be strictly

adhered to during the

welding process. If the

welding speed is too low,

lack of fusion is the result.

If the welding speed is

exceeded, the develop-

ment of the waves in the

joining zone is erratic.


critical cladding speeds

for different material com-

binations.

Figure 13.20 shows a diagrammatic representation of a diffusion welding unit. Diffusion

welding, like ultrasonic welding, is welding in the solid state. The surfaces which are to be

joined are cleaned, polished and then joined in a vacuum with pressure and temperature.

After a certain time (minutes, right up to several days) joining is achieved by diffusion proc-

esses.

The advantage of this costly welding method lies in the possibility of joining dissimilar materi-

als without taking the risk

of structural transformation

due to the heat input. Fig-

ure 13.21 shows several

possible material combina-

tions. The joining of two

extremely different materi-

als, as, e.g. austenite and a

zirconium alloy, may be

obtained by several inter-

mediate layers.

Figure 13.18

Br-er13-18e.cdr

Figure 13.17

a) b)

Amboßanvil

explosive charge explosive chargebuffer buffer

flyer plate flyer plate

parent plate parent plate

igniter

anvil

igniter

d

vd

A

A'

KvK

B

B'

vP

tvF β

vd

AA'

KvK

B

B'

vP

t

v Fα β

K vK

B

B'

vP

v F

β

αβ90 - + /2

α /290 -

K v = vK D

B

B'

vPvF

β

br-er13-17e.cdr


2005

Figure 13.22 shows the structure of a joint

where nickel, copper and vanadium had been

used as intermediate layers. As the diffusion

of the individual components takes place only

in the region close to the surface, very thin

layers may be realised.

Figure 13.19

materialsflyer plate/parent plate

critical speed [m s ]-1

vk1 vk2 vk3

aluminium/aluminium

copper/copper

steel/steel

copper/aluminium

aluminium/steel

cooper/steel

aluminium/zinc

copper/zinc

600

1200

2100

1000

1200

1400

500

800 1400

1000

2400

1600

1400

2700

1600

1000

3300

3000

>4000

>3600

>3900


Critical Cladding Speedsin Explosive Cladding

Figure 13.20

HF-generator

working pressure1,33 mPa

workpieces

loading device

recorderp,T = f(t)

hydraulic aggregate unit

pumpingstation

measuring amplifier

P


Schematic Representationof a Diffusion Welding Unit

Figure 13.21

niobium

zirconium

tungsten

molybdenum

titanium

nickel

copper

aluminium

stainless steel

tool steel

structural steel

cast iron

ca

st ir

on

str

uctu

ral ste

el

too

l ste

el

sta

inle

ss s

tee

l

alu

min

ium

co

pp

er

nic

kel

tita

niu

m

mo

lyb

den

um

tun

gste

n

zir

con

ium

nio

biu

m

tan

talu

m

tantalum

material

very good weld quality

good weld quality

bad weld quality

not tested/results not reported


Possible Material Combinationsfor Diffusion Welding


2005

In cold pressure welding -

in contrast to diffusion weld-

ing - a deformation is pro-

duced by the high contact

pressure in the bonding

plane, Figure 13.23. The

joint surfaces are moved

very close towards each

other, i.e., to the atomic

distance. Through transpo-

sition processes as well as

through adhesion forces

can joining of similar and

dissimilar materials be real-

ised.

Ultrasonic welding is used as a microwelding method. The process principle is shown in

Figure 13.24. The surface layers of overlap arranged plates are destroyed by applying me-

chanical vibrator energy. At this instance are joining surfaces deformed by very short local-

ised warming up and point-interspersed connected. The joining members are welded under

pressure, where one part small amplitudes (up to 50 µm) relative to the other is moved with

with ultrasonic frequency.

As far as metals are con-

cerned, the vibratory vector

is in the joining zone, in

contrast to ultrasonic weld-

ing of plastics. The ultra-

sonics which have been

produced by a magne-

tostrictive transducer and

transmitted by a sonotrode

lie in the frequency range

of 20 up to 60 Hz.

Figure 13.23

dies

guideand buffer

specimen A

specimen B

d2

d1

br-er13-23e.cdr

Figure 13.22

X10CrNiTi18 9 Ni Cu V Zr2Sn

br-er13-22e.cdr


2005

Figure 13.25 shows possible material combinations for ultrasonic welding.

Further microwelding proc-

esses are methods which

are also called heated ele-

ment welding methods, as,

for example, nailhead

bonding and wedge bond-

ing. These methods are

applied in the electronics

industry for joining very fine

wires, as, for example, gold

wires from microchips with

aluminium strip conductors.

In wedge bonding a wire

is positioned onto the contact point via a feeding nozzle. The welding wedge is lowered and

the wire is welded with the aluminium thin foil,

Figure 13.26. The wire is cut with a cutting

tool.

In nailhead bonding, the wire which emerges

from the feeding nozzle may have diameters

from 12 to 100 µm. By a reducing hydrogen

flame its end is molten to a globule, Fig-

ure 13.27. The nozzle then presses this glob-

ule onto the part aimed at and shapes it into a

nail head.

Figure 13.28 depicts this type of weld.

A further method related to welding is solder-

ing. The process principle of soldering is

briefly explained in Figure 13.29.

Figure 13.25

copper, Cu-Zn-alloy

beryllium+alloy

germanium

gold

ironmagnesium+alloy

molybdenum+alloy

nickel+alloy

palladium+alloy

platin+alloy

siliconsilver+alloy

tantalium+alloy

tintitanium+alloy

tungsten+alloy

zirconium+alloy

aluminium+alloy

copper, C

u-Z

n-a

lloy

bery

lliu

m+

allo

y

germ

aniu

m

gold

iron

magnesiu

m+

allo

y

moly

bden

um

+allo

y

nic

kel+

allo

y

palla

diu

m+

allo

y

pla

tin+

allo

y

sili

con

silv

er+

allo

y

tanta

lium

+allo

y

tin

tita

niu

m+

allo

y

tungste

n+

allo

y

zirconiu

m+

allo

y

alu

min

ium

+allo

y


Possible Material Combinations for Ultrasonic Welding

Figure 13.24

HF-generator

process observationoptics

sonotrode

pressure force

workpiece

anvil

ultrasonic vibrator

sonotrode tip

br-er13-24e.cdr


2005

Figure 13.28

br-er13-28e.cdr

Figure 13.27

heated wedge

(tungsten-carbide)

wedge bonding Al-strip conductor nailhead

gold wire5-50 mm

H -flame2

br-er13-27e.cdr

Figure 13.26

heated wedge

(tungsten-carbide)

wedge bonding Al-strip conductor cutting toolgold wire

5-50 mµ

br-er13-26e.cdr


2005

The individual soldering methods are classified into different mechanisms depending on the

type of heating, Figure 13.30. There are two basic distinctions: soft soldering (melting tem-

perature of the solder is approx. up to 450°C) and brazing (melting temperature of the braz-

ing solder is approx. up to 1100°C. For high-temperature soldering solders with high melt-

ing points (melting temperature is approx. up to 1200°C) are used. This process is frequently

subject to automation.

Figure 13.29


Soldering - Definitionand Process Principle

In soldering, atomar forces of attraction are effective.

Similar and dissimilar metals are joined by addition of

a solder with a low melting point. In the boundary area

transposition processes occur between solder and

base metal. This is called a “two-dimensional”diffusion.

In the subsequent diffusion glowing phase

(high-temperature soldering) the solder may be

completely absorbed by the base metal.

A distinction is made between soft soldering (melting

temperature of the solder is below 450°C) and brazing

(melting temperature of the solder is 450°C up to 1100°C)

as well as high-temperature soldering (melting

temperature of the solder is up to 1200°C). Heating of

the component for melting the solder may be effected in

various ways.

Figure 13.30


Classification of Soldering Methods

classification accordingto the type of heating:

- flame brazing

- iron soldering

- block brazing

- furnace soldering

- salt bath brazing

- dip soldering

- wave soldering

- resistance soldering

- induction brazing

14.

Mechanisation

and Welding Fixture


2005

As the production costs of the metal-working industry are nowadays mainly determined by

the costs of labour, many

factories are compelled to

rationalise their manufac-

turing methods by partially

and fully mechanised pro-

duction processes. In the

field of welding engineering

where a consistently good

quality with a maximum

productivity is a must,

automation aspects are

conse-quently taken into

account.

The levels of mechanisation in welding are

stipulated in DIN 1910, part 1. Distinctions are

made with regard to the type of torch control

and to filler addition and to the type of process

sequence, as, e.g., the transport of parts to

the welding point. Figure 14.1 explains the

four levels of mechanisation.

Figure 14.2. shows manual welding, in this

case: manual electrode welding. The control

of the electrode and/or the arc is carried out

manually. The filler metal (the consumable

electrode) is also fed manually to the welding

point.

Designationexamples

gas-shielded arc weldingTIG GMAW

movement/ working cycles

manual welding

m

partiallymechanised

weldingt

fully mechanisedwelding

v

automaticwelding

a

mechanically

mechanicallymechanically mechanically

mechanicallymechanically

manually manually

manually

manually

manually

manually

torch-/workpiece

control

workpiecehandling

filler wirefeeding

br-er14-01e.cdr

Figure 14.1


Manual Welding(Manual Electrode Welding)

Figure 14.2


2005

In partially mechanised

welding, e.g. gas-shielded

metal-arc welding, the arc

manipulation is carried out

manually, the filler metal

addition, however, is exe-

cuted mechanically by

means of a wire feed mo-

tor, Figure 14.3.

In fully mechanised weld-

ing, Figure 14.4, an auto-

matic equipment

mechanism carries out the welding advance and thus the torch control. Wire feeding is re-

alised by means of wire feed units. The workpieces must be positioned manually in accor-

dance with the direction of the moving machine support.

In automatic welding, be-

sides the process se-

quences described above,

the work-pieces are me-

chanically positioned at

the welding point and,

after welding, auto-

matically trans-ported to

the next working station.

Figure14. 5 shows an ex-

ample of automatic welding

(assembly line in the car

industry).

br-er14-03e.cdr

Partially Mechanised Welding(Gas-Shielded Metal-Arc Welding)

Figure 14.3

br-er14-04e.cdr

Fully Mechanised Welding(Gas-Shielded Metal-Arc Welding)

Figure 14.4


2005

Apart from the actual weld-

ing device, that is, the

welding power source, the

filler metal feeding unit and

the simple torch control

units, there is a variety of

auxiliary devices available

which facilitate or make the

welding process at all pos-

sible. Figure 14.6 shows a

survey of the most impor-

tant assisting devices.

Before welding, the parts

are normally aligned and

then tack-welded. Fig-

ure 14.7 depicts a simple

tack-welding jig for pipe

clamping. The lower part of

the device has the shape

of a prism. This allows to

clamp pipes with different

diameters.

Devices, however, may be

significantly more complex.

Figure 14.8 shows an example of an assembly equipment used in car body manufacturing.

This type of device allows to fix complex parts at several points. Thus a defined position of

any weld seam is reproducible.

br-er14-05e.cdr

Automatic Welding (Assembly Line)

Figure 14.5

br-er14-06e.cdr

assembly line

welding robot

machine carrier

linear travelling mechanism

track-mounted welding robots

spindle / sliding head turntable

turn-/ tilt table

dollies

assembly devices

Figure 14.6


2005

In apparatus engineering

and tank construction it is

often necessary to rotate

the components, e.g.,

when welding circumferen-

tial seams. The equipment

should be as versatile as

possible and suit several

tank diameters. Figure 14.9

shows three types of turn-

ing rolls which fulfil the

demands. Figure top: the

rollers are adjustable;

Figure middle: the rollers

automatically adapt to the

tank diameter; Figure bot-

tom: the roller spacing may

be varied by a scissor-like

arrangement.

In general, dollies are mo-

tor-driven. This provides

also an effortless move-

ment of heavy compo-

nents, Figure 14.10.

A work piece positioner, e.g. a turn-tilt-table, is part of the standard equipment of a robot

working station. Figure 14.11 shows a diagrammatic representation of a turn-tilt-table. Rota-

tions around the tilting axis of approx. 135° are possible while the turn-table can be turned by

365°. Those types of turn-tables are designed for working parts with weights of just a few

kilograms right up to several hundred tons.

br-er14-07e.cdr

Simple Tack Welding Jig forWelding Circumferential Welds

Figure 14.7

br-er14-08e.cdr

1 portal with 2 industrial robots IR 400, equipped with tool change system2 resting transformer welding tongs3 depot of welding tongs4 clamping tool5 copper back-up bar for car roof welding6 transformer welding tongs for car roof welding7 driverless transport system8 component support frame9 swivelled support for component support frames10 resting transformer welding tongs for car boot

Figure 17.8


2005

A turn-tilt table with hydrau-

lic adjustment of the tilting

and vertical motion as well

as chucking grooves for the

part fixture is depicted in

Figure 14.12.

br-er14-09e.cdr

Turning Rolls

set of rollers 1 set of rollers 2

Figure 14.9

br-er14-10e.cdr

Turning Rolls

Figure 14.10

Figure 14.11

br-er14-11e.cdr

support

tilting axis

table support

gear segmenttable top

rotational axis


2005

Turn-Tilt-Tables


single-column turn-tilt-table orbital turn-tilt-table

table top table top

rotational axisrotational axis

tilting axis tilting axis

support

table support table support

support

Figure 14.13

In robot technology the

types of turn-tilt-tables - as

shown in Figure 14.13 - are

gaining importance. Posi-

tioners with orbital de-

sign have a decisive

advantage because the

component, when turning

around the tilting axis, re-

mains approx. equally dis-

tant to the welding robot.

Other types of workpiece

positioners are shown in

Figure 14.14 – the double

column turn-tilt-table and

the spindle and sliding

holder turn-tilt-table.

Those types of positioners

are used for special com-

ponent geometries and

allow welding of any seam

in the flat and in the hori-

zontal position.

In the field of welding, spe-

cial units are designed for

special tasks. Figure 14.16 shows a pipe-flange-welding machine. This machine allows the

welding of flanges to a pipe. The weld head has to be guided to follow the seam contour.

br-er14-12e.cdr

Turn-Tilt-Table With Hydraulic Adjustment

Figure 14.12


2005

br-er14-16e.cdr

Figure 14.16

Figure 14.15 Spindle / Sliding Holder Turntable


bed way

spindle holder

table tops

sliding holder

Double-Column Turn-Tilt-Table


table support

rotational axis

table top

tilting axis

support

Figure 14.14


2005

br-er14-17e.cdr

Figure 14.17

Plain plates or rounded

tanks are clamped by

means of longitudinal jigs

for the welding of a longi-

tudinal seam, Figure 14.17.

The design and the grip-

ping power are very de-

pendent of the thickness of

the plates to be welded.

A simple example of a

special welding machine is

the tractor travelling car-

riage for submerged-arc

welding, Figure 14.18. This device is de-

signed for the application on-site and pro-

vides, besides the supply of the filler metal,

also the welding speed as well as the feeding

and suction of the welding flux.

For the guidance of a welding head and/or

welding device, machine supports may be

used. Figure 14.19 shows different types of

machine supports for welding and cutting.

Apart from the translatory and rotary principal

axes they are often also equipped with addi-

tional axes to allow precise positioning.

br-er14-18e.cdr

Tractor for Submerged-Arc Welding

Figure 14.18


2005

To increase levels of

mechanisation of welding

processes robots are fre-

quently applied. Robots are

handling devices which are

equipped with more than

three user-programmable

axes. Figure 14.20 de-

scribes kinematic chains

which can be realised by

different combinations of

translatory and rotary axes.

The most common design

of a track-mounted weld-

ing robot is shown in Fig-

ure 14.21. The robot

depicted here is a hinged-

arm robot with six axes. The

axes are divided into three

principal and three addi-

tional axes or hand axes.

The wire feed unit and the

spool carriers for the wire

electrodes are often fixed on

the robot. This allows a

compact welding design.

br-er14-19e.cdr

boom

pillar

travelling mechanism

a b c

d e

main piloting system case cross pilotingsystem case

auxiliary piloting system case

auxiliary piloting system case

Figure 14.19

Kinematic Chains


designation

arrangement

kinematicschedule

operatingspace

cartesianrobot

cylindercoordinated

robot

sphericalcoordinated

robot

horizontalknuckle arm

robot

verticalknuckle arm

robot

x

y

zz

z

C

C

CC

B

BR R D

A

Figure 14.20


2005

Varying lever lengths permit the design of robots with different operating ranges. Fig-

ure 14.22 shows the operating range of a robot. In the unrestricted operating range the

component may be reached with the torch in

any position. The restricted operating range

allows the torch to reach the component only

certain positions. In the case of a suspended

arrangement the robot fixing device is short-

ened thus allowing a compact design.

For the completion of a robot welding station

workpiece positioners are necessary. Fig-

ure 14.23 shows positioner devices where

also several axes may be combined. These

axes may either turn to certain defined posi-

tions or be guided by the robot control and

moved synchronically with the internal axes.

The complexity and versatility of the axis posi-

tions increases with the number of axes which

participate in the movement.

br-er14-22e.cdr

Figure 14.22

br-er14-21e.cdr

Robot Motions

Figure 14.21


2005

Movement by means of a

linear travelling mecha-

nism increases the operat-

ing range of the robot,

Figure 14.24. This may be

done in ease of stationary

as well as suspended ar-

rangement, where there is

a possibility to move to

fixed end positions or to

stay in a synchronised mo-

tion with the other move-

ment axes.

br-er14-24e.cdr

Figure 14.24

br-er14-23e.cdr

Figure 14.23

15.

Welding Robots


2005

Increased quality requirements for products and the trend to automate production processes

along with increased profitability result in the use of industrial robots in modern manufactur-

ing, Figures 15.1 – 15.2. Since robots have been introduced in industry in the 70s, their most

frequently fields of application ranged from installation jobs up to spot welding, and seam

welding.

The definition says that an

industrial robot for gas

welding is an universal

movement automaton with

more than three axes

which are user-

programmable and may be

sensor-controlled. It is

equipped with a welding

torch and carries out weld-

ing jobs.

Core of a modern robot welding cell are one or more seam welding robots of swan neck type.

Normally, they have six user-programmable axes; so they can access any point within the

working range at any orientation of the welding torch. To extend their working range, robots

may be installed in over-

head position. A further

extension of the working

range can be achieved by

installation of the robot

onto a linear carriage with

Cartesian axes. Such 'ex-

ternal' axes are also user-

programmable, Figure

15.3.

Figure 15.1

Inernational Distribution of InstalledWelding Robots (1990 -2002)

br-er15-01e.cdr

1990

1992

1994

1996

1998

2000

2002

0

1000

2000

3000

4000

5000

6000

7000

8000

Europa

Amerika

Japan

Europe

America

Japan

Figure 15.2

br-er15-02e.cdr

research andtraining2.656

other workpiecemanipulators8.214

metal cuttingmachine tools6022

diecasting andinjection moulding4.681

pressingand forging2.064

commissioningand palletising3.234

measurement1.251others

1.562assembly10.229

machining1.767

seam welding8.749

spot welding12.349 applying bonding

and sealing agents1.485

surfacing2.337


2005

To turn the workpiece in the welding-favourable downhand position and to ensure accessibil-

ity to any joints, workpiece positioners are used as external axes which are steered by the

robot control. Multi-station

cycle tables are often used

to increase profitability of

the complete system instal-

lation. The operator feeds

and removes the welded

workpiece on one side,

while the robot is welding

on the other side.

The robot control is the

centre of an industrial robot

system for arc welding,

Figure 15.4. It provides and processes all information for robot mechanics, positioner, weld-

ing unit, safety equipment, and external sensors. The robot program transforms information

into signals for control of robot- and positioner-mechanics as well as welding power source.

Communication with external systems is possible by a host or master computer.

Modern industrial robot controls are build as multi-processor controls due to the multitude of

parallel calculations and control functions. Figure 15.5 shows the internal structure of such a

control. Individual assem-

blies which are designed

for special jobs and

equipped with an own mi-

cro-processor are linked

with the host computer via

the system bus. The host

controls and coordinates

the actions of the compo-

nents based on the operat-

ing system and the robot

program. Examples of

Figure 15.3

Examples for Robot Arrangements

br-er15-03e.cdr

Figure 15.4

Industrial Robot Systemfor Arc Welding

industrialrobot

control

robotmechanics

powersource

weldinginstallation

weldinggun

positioner

tools

sensors

host-computer

safetydevice

linkto

SPS

offlineCAD

expert

MDR

br-er15-04e.cdr


2005

such assemblies, which are mostly installed on individual printed boards, are e.g. the axes

computers. They are responsible for calculation of movement and for control of power units

of the individual axes. To control the drive motors, two interconnected control loops per axis

are available which control speed and position of each axis.

Further assemblies control the display screen, the manual programming unit (PHG); these

assemblies are responsible for communication with the welding power source, external sen-

sors, and peripheral units via digital and analogue in- and outputs and field bus systems. Or

they complete the data transmission with external control systems. To reduce downtimes in

the case of malfunction,

some robot controls can

be connected via internet

with telediagnosis sys-

tems of the robot manu-

facturer to support service

personnel during trouble-

shooting and commission-

ing.

Programming of welding

robots can be carried out

in different ways which are

distinguished in On-Line

(programming at the ro-

bot) and Off-Line (pro-

gramming out of the robot

cell), Figure 15.6.

The robot is manually

guided along the later

track with decoupled

drives during Play-Back

programming. The path of

the track is recorded and

transformed into a corre-Figure 15.6

Programming Procedures forWelding Robots

X

Y

Z

A

B

C

+

-

-

-

+

+

+

-

- +

+

+

-

- +

+

-+

-

-+

+

NOT-AUS

+

X

Y

Z

A

B

C

+

-

-

-

+

+

+

-

- +

+

+

-

- +

+

-+

-

-+

+

NOT-AUS

direct programming

(online)

mixed proced.(online/ offline)

indirect programming

(off-line)

play-backprogramming

teach-inprogramming

sensor supportedprogramming

textualprogramming,teach-in points

macropro-gramming,teach-in points chains

textualprogramming

with point coordinates

knowledge-basedprogramming

with expert systems

graphical programmingwith CAD data

movement oriented

movement oriented

function oriented

function oriented

br-er15-06e.cdr

Figure 15.5

Industrial Robot Control

digitalI/0

memoryassembly

mastercomputer

analogI/0

compilercomputer

axses-computer

welding unit

screen

keyboard

bulk memory

printer

PHG

sensors

welding unit

host Computer

chaining

offline programm

expert system

MDRbrakemotor

encodertacho

programminterface

Internet

telediagnosis

fieldbus

positioner

sensors

tools

welding unit

br-er15-05e.cdr

po

sitio

n c

ontr

ol lo

ops

pe

ed

con

tro

llo

op


2005

sponding robot control pro-

gram. This procedure is

preferably used for painting

jobs.

A common technique to

program a robot is the

Teach-In procedure. During

Teach-In programming,

with the help of the manual

programming unit, the

welding torch is moved to

notable points of the

groove to be welded which

are stored with information about position and orientation. In addition, track parameters must

be entered, like e.g. type of movement and speed or welding parameter sets.

During sensor supported Teach-In programming, the path progress through some typical

points is only roughly indicated. Then the accurate path is picked-up by sensors and auto-

matically calculated in the robot steering control. Afterwards the movement program is sup-

plemented by additional information about e.g. welding parameter sets.

Textual programming be-

longs to mixed procedures.

The sequence program in

form of a text file is created

on an external computer

and is then transmitted to

the robot steering control,

Figure 15.7. The recording

of the position of points is

carried out in the same way

as with Teach-In program-

ming: moving into position

and recording.

Figure 15.7

TEA1PTP

23 4

5 6

7

8

$ 1

$ 2

$ 1

point filepointno.

CP/PTP

OV/SPD

AUSG1 2 3 4

XEXT1

YEXT2

ZEXT3

BETAEXT5

ALPHAEXT4

GAMMAEXT6

1

2

3

4

5

6

7

8

PTP

PTP

PTP

PTP

PTP

PTP

PTP

PTP

100

100

100

100

100

100

100

100

0000

0000

1100

1100

1100

1100

0000

0000

10560

10700

10700

10700

10700

10700

10700

10700

1

1128

1513

2420

3190

3852

4510

4510

1317

1344

1344

1344

1344

1344

1344

1344

17204

15164

14220

14229

13294

14448

15520

15520

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0 LIST1=(20,0,0,50,60,75,15,12,0,0)

1 LIST2=(30,0,0,55,70,0,0,0,0,0)

2 MAIN

3 $(1)

4 GP(1-3)

5 GC (4,$2,5,$1,6)

6 GP(7,8,1)

7 END

definition ofwelding parameters

selection of weldingparameter set1move to point 1-3in PTP operationwelding with changewelding parameters

br-er15-07e.cdr

Figure 15.8

geometric macro welding macro

= TCP

= torch angel

- welding parameters

= TCP

- torch angel

- welding parameters

- welding programme (ignition,

welding, crater filling)

Length macro

Profile macro

br-er15-08e.cdr


2005

Macro-programming is also regarded as a mixed method which shortens programming time

at the robot, Figure 15.8. Macros are structured processing sequences which are created

online to fulfil working functions and which can be repeated for further similar working func-

tions. Geometry macros

contain information about

torch guidance to produce

certain joints or joint sec-

tions. Welding technology

parameters for individual

welding situations are

summarised in welding

macros. This applies for

torch positioning, torch in-

clination, relative position of

beads to root and welding

parameters.

Using a collection (can be created online or offline) of such macros, the programming time

can be shortened for workpieces with often repeated welding jobs, e.g. steel construction

when welding stiffeners and head plates

Using offline programming practice, the programming work is shifted out from the producing

robot cell. This avoids unproductive stoppages and allows for economic-viable, limited num-

ber of pieces to be reduced.

During textual program-

ming, the 3-dimensional

point coordinates and torch

orientations are entered into

an external computer in a

manufacturer-specific pro-

gram language. To achieve

a complete program se-

quence, each instruction

must be entered individu-

ally.

Figure 15.9

Quelle:Cloos, Kuka 2002

Graphical Simulation ofRobot Movement

br-er15-09e.cdr

Figure 15.10

movementinstructions

program sequenceinstructions

arithmetical andlogical functions

special functions

−

−

−

−

synchronical PTP pro-cedure (point to point)

linear interpolation, CP (continious path)

cicule and graduated cicule interpolation

continuously program-mable tool speed

−

−

−

−

−

−

sub program techni-que

jump instruction

conditional instruc-tions

repeated loops

inquiry of entries

programmed stop

−

−

−

+, -, *, :

boolean operations

etc.

−

−

−

−

−

3D online and offline transformation of pro-gram parts

mirroring of program parts

processing variables

communication with sensors

communication with external computers

br-er15-10e.cdr


2005

The graphical offline programming uses CAD data for modelling the complete robot working

cell and parts to be welded. Planning of the path is carried out with CAD functions directly at

the workpiece which is dis-

played on a screen. In

most cases, the program-

ming systems provide a

graphical simulation of the

movement, e.g. to check

for collisions between torch

and workpiece, Figure

15.9. For the following

transformation of the pro-

gram into the robot control,

a calibration between

model and physical robot

working cell is required.

In the case of knowledge-

based offline program-

ming, the operator is sup-

ported by integrated

expert systems when it

comes to creation of robot

welding programs, e.g. for

determination of job-

specific welding parame-

ters. However, checking

and adapting the program

must be carried out by the

operator.

Modern robot controls provide the programmer with some functions for movement control

and for modification of program sequence, Figure 15.10. PTP movement (point to point)

serves to move the robot in the space. All axes are controlled in such a way that they reach

Figure 15.11

TEA EDI

1

2

3

4

50 LIST1=(20,0,0,50,60,75,15,12,0,0)

1 MAIN

2 $(1)

3 GP(1-3)

4 GC(4)

5 GP(5,1)

definition of welding parameters

selection of welding parameters set 1

move to dots 1-3 in PTP mode

move to dot 4 in CP mode

move to dot 5 and 1 in PTP mode

6 END

br-er15-11e.cdr

Figure 15.12

TEA EDI

120°

10°

1

2

34

5

6 7

8

9

10

11

0 LIST1=(20,0,0,50,60,75,15,12,0,0)

1 LIST2=(30,0,0,55,70,0,0,0,0,0)

2 MAIN

3 $(1)

4 GP(1-3)

5 CIRO(1)

6 Cir(3,4,5,50)

7 GP(6-8)

8 $(2)

9 CIRO(0)

10 CIR(8,9,10,0)

11 GP(11,1)

12 END

definition of welding parameters

selection of welding parameter set 1

move to dot 1-3 in PTP mode

with rotating the 6 axis

circle instruction

selection of welding parameter set 2

lock 6 axis

th

th

br-er15-12e.cdr


2005

their set-point at the same time. Thereby the actual path of the torch depends on kinematics

of the robot and on current position of the axes.

A linear interpolation (CP procedure, continuous Path), Figure 15.11, is used for accurate

movement along a straight line, e.g. movement to weld start point or welding. The active

point of the tool 'arc' (Tool-Centre-Point, TCP) is moved along a straight line between two

programmed points, adapting torch angle and torch inclination between the two points.

Circles and graduated circles are entered by means of circle interpolation programs, Figure

15.12. Then the orientation of the torch can be adapted through turning the knuckle axis or

6th axis of the robot and the value of spill-weld at the end of the seam can be indicated.

Speed of the torch is user-programmable and, if required, can be superimposed by an

oscillation. To control the program run, commands are available for: repeated loops,

conditional and unconditional program jumps, waiting periods, waiting for inputs, and working

with sub-programs.

The software of modern seam welding robots contains – as special functions – 3-dimansional

transfor-mations and mir-

roring of programs and

partial programs, palletis-

ing functions, processing

sensor data and com-

mands for communication

with other robot controls

(Master/Slave operation)

as well as with external

computers, Figure 15.13.

Figure 15.13

x

x

y

y

z

z

x

y

z

offsetx

y

z

br-er15-13e.cdr

16.

Sensors

16. Sensors 217

2005

The welding process is ex-

posed to disturbances like

misalignment of workpiece,

inaccurate preparation, ma-

chine and device

tolerances, and proess dis-

turbances, Figure 16.1.

The manual welder notices

them by eyesight and cor-

rects them manually

according to strategies

learned and gained by ex-

perience. To record process

irregularities and path deviations, a fully mechanised welding plant requires sensors provid-

ing control signals which are then used in accordance with implemented rules. Using

corresponding control elements, the control loop is closed for the welding process.

Scopes of duty of the sensors is finding the weld start point and seam tracking. In addition,

with the help of information about joint geometry, process parameters can be adapted online

and offline. The ideal sensor for a robot application should measure the welding point (avoid-

ance of tracking misalignment), detect in advance (finding the start point of the seam,

recognising corners, avoid-

ing collisions) and should

be as small as possible (no

restriction in accessibility).

The ideal sensor which

combines all three re-

quirements, does not yet

exist, therefore one must

select a sensor which is

suitable for the individual

welding job. Figure 16.2

shows different sensor

Figure 16.1

© ISF 2002

Adaptive Process Control Manually - Fully Mechanised

br-er16-01e.cdr

process disturbances

weldingprocess

brain

eye hand control

strategy

sensor

Figure 16.2

Sensors for Arc WeldingSystems Survey

br-er16-02e.cdr

16. Sensors 218

2005

principles used in welding engineering. The most frequently used systems in practice are tac-

tile, optical, and arc based

sensor systems with me-

chanical arc adjustment.

With tactile scanning sys-

tems, the simplest type of

scanning is a mechanical

sensor. Pins, rollers, balls,

or similar devices may be

used as sensors.

Such scanning systems

show a long distance be-

tween sensor and torch, the

application range is limited. Only grooves with large dimensions and relatively straight seam

path can be scanned with these systems. Figure 16.3 shows some examples of different

groove geometries.

Tactile sensors can recognise 3-dimensional

offsets of the workpiece. Through scanning of

three levels the 3-dimensional point of inter-

section can be calculated and the robot

program for correcting the deviation can be

shifted accordingly thus finding the start point

of the weld. In this case, the gas nozzle of the

torch serves as a sensor, Figure 16.4, which

is charged with electrical tension. As soon as

the torch touches the workpiece, a current

flows, which is then taken by the robot control

as a signal for obtaining the level to be

scanned.

Inductive sensors are graded as non-contact

measurement systems. Due to their function

Figure 16.4


A A'

B'C'

B

Figure 16.3

Scanning Principles With Tactile Sensors

br-er16-03e.cdr

V, X Y seam with ball-probe

I seam with blanc-probe

fillet seam with ball-probe

overlapp seam with ball-probe

multilayer seam with ball-probe

edge seam with edge-probe

16. Sensors 219

2005

principle, they can be applied for metallic and electrically conductive materials. The simplest

type is a ring coil. If alternating current flows though the coil, ,a magnetic field is generated

close to the workpiece.

When the coil approaches

the workpiece surface, the

magnetic field weakens.

Figure 16.5 shows the dis-

tance-dependent electrical

signal. Such simple sen-

sors are used to recognise

the workpiece position.

Using several distance

sensors, also a welding

groove can be scanned.

With multi-coil arrangements in one sensor, the position of the welding groove, the angle be-

tween sensor and workpiece surface and the distance can be recorded. Figure 16.6 shows a

principle arrangement. A transmitter coil generates an magnetically alternating field which

induces alternating currents in the two receiver coils. In the undisturbed case, these currents

are phase-shifted by 180° and neutralise each other. If the sensor is moved crosswise to the

groove, magnetical asymmetries will occur in the scanning area, which will show in the pre-

sented signal shape. The

output signal will be zero, if

the coils are positioned ex-

actly above the centre of

the groove.

The radar sensor in Fig-

ure 16.6 uses Doppler's

effect to generate a signal.

Here the phase difference

between transmitter signal

and receiving signal is

evaluated.

A mathematical process

Figure 16.5

© ISF 2002

Principle of an Inductive Sensor (Single Coil and Multicoil Arrangement)

br-er16-05e.cdr

A B

sensor signals

groove position

distance

coil arrangement for groove position

coil arrangement fordistance measurement

transmitter coil

reception coil

Figure 16.6

© ISF 2002

Functional Principle of a Radar Sensor

br-er16-06e.cdr

radar sensor

oscillation

workpiece

signal path

work pieceradar sensor

transmitting wave

receiving wave

phase difference

functional principle of continuous wavedoppler’s radar

16. Sensors 220

2005

transforms such signals into distance values. To record the position and the depth of the

groove, the sensor must be continuously moved along the seam. Radar sensors form a so

called radar baton, which is focussed onto a measurement spot of about 0,7 mm diameter for

this application. Figure 16.6 shows the sensor signal, which represents the relative move-

ment along the workpiece. At the moment, the characteristic values of the weld groove can

be determined with a resolution in the range of 1/10 mm.

Arc sensors evaluate the continuous change of the welding current with a change of the con-

tact tip-to-work distance,

Figure 16.7. A signal for

side control of the torch is

determined by measure-

ment and subtraction of the

currents on the flanks of a

groove. A comparison be-

tween actual welding

current and programmed

rated current provides a

signal for distance control

of the welding torch.

To let this sensor method

work, a divergence of the

arc or the use of a second

arc is required.

To realise this principle,

there are numerous possi-

bili-ties. Figure 16.8 shows

some variants of signal re-

cording. The most

frequently used method is a

mechanical oscillation of

the welding torch, which is

carried out by a rotor

Figure 16.7

© ISF 2002

Arc Sensor

br-er16-07e.cdr

I O

l 2

l 1

∆l

U

II

l2 l0 I1

side correction

l = 0∆

∆

l 1,2

height correction

= 2 x IΣI Soll

Figure 16.8

© ISF 2002

Arc Sensor- Signal Detection -

br-er16-08e.cdr

mechanical oscillation twin wire welding

magnetical oscillation rotating wire

16. Sensors 221

2005

movement with an oscillation frequency up to 5 Hz.

The second method is mainly used with submerged arc welding. Both wires are aligned

crossways to welding direction and the difference of the two currents is evaluated.

Magnetic fields can diverge only the arc itself. The advantage of this method is a high diver-

gence frequency of about 15 Hz. A disadvantage is the size of the electromagnets and the

limited accessibility to the workpiece.

The last variant of an arc sensor incorporates a mechanical rotation of the welding wire. In

this case, the divergence frequency of the arc can reach up to 30 Hz.

The signal recording is continuous during the movement. In this way, information about orien-

tation of the torch and groove width is also provided. The arc sensor principle is limited to

groove shapes with clear flanks. Together with the tactile torch gas nozzle sensor, it provides

a frequently used combination for seam finding and seam tracking during robot welding.

Optical sensors can be used for a great number of jobs. The easiest method is the recogni-

tion of the radiation intensity, which is reflected during welding.

E.g. with laser beam welding, this is carried out through recording the reflected laser radiation

with simple sensors for control of penetration depth, Figure 16.9.

The procedure is based on the line-up between the degree of reflection and shaft relation

(penetration depth/focus position) of the capillary. The amount of back-reflection of the laser

beam power is measured,

which due to multi-

reflection is not absorbed

by the workpiece. Changes

of penetration depth due to

modified laser power or a

shifted focus position can

be identified by the signal

of reflected laser power

and can be used for control

of the penetration depth.

Figure 16.9

© ISF 2002

Back Reflection Procedure forLaser Beam Welding

br-er16-09e.cdr

NdYAG-Laser CO -Laser2

16. Sensors 222

2005

However, optical sensors can also be used for measuring geometrical values. Such informa-

tion may be used for finding the start point of a seam, for seam tracking, and for identification

of groove profile. The two last mentioned functions provide the possibility to use the informa-

tion for filling rate control and/or quality control.

Geometry-measuring optical sensors are normally external systems, which are positioned in

front of the torch as a leading element. It is practical to equip the sensor with additional axes,

because both, torch and sensor, must be moved along the groove. Without additional axes, a

robot would be limited in its accessibility to the workpiece and in its working range. Another

problem is the tremendous effort to introduce the control-technical integration into the robot

control. Among other things, information must be exchanged in real time.

Most of geometry-measuring sensors use the triangulation principle or a variant of this meas-

urement procedure. The triangulation measurement procedure provides information about

the distance to the workpiece surface. A light spot is projected onto the workpiece surface

and displayed to a line-type receiver element

under a certain angle. With distance changes

emerge corresponding positions on the re-

ceiver element, Figure 16.10. Sensors which

use this triangulation principle are applied for

recognition of workpiece position and for off-

line seam finding.

Both, the laser scanner and the light-section

procedure are based on the triangulation

measurement principle. With the laser scan-

ner, Figure 16.11, this principle is

complemen-ted by an oscillating axis in paral-

lel to the groove axis. The measurement of a

sequence of distances along a line becomes

possible and provides a 2-dimensional record

and evaluation of the groove contours.

Figure 16.10


Triangulation Principle

laser beam

depth measurementrange

laser

CCD camera

lens

16. Sensors 223

2005

Sensors as part of the light-section procedure, also provide information about the 2-

dimensional position of the groove. As a function of this system, one or more light lines are

projected onto the workpiece surface and displayed to a CCD matrix under a certain angle,

Figure 16.12. In contrast to scanning, information about the groove profile is provided by tak-

ing a picture scene. Using sensors, it is pssible to obtain additional 3-dimensional information

through evaluation of more, in succession taken, while the camera moves over the grooves.

Systems, which generate their information through a projection of several light lines, provide

additional information about the path of the seam and the orientation of the sensor related to

the workpiece surface.

Both, scanning systems

and sensors based on the

light section procedure, can

be used for recognition of

the welded seam to make

an automised quality control

of the outer weld character-

istics possible.

Another optical measure-

ment principle uses, similar

to human sight, the stereo

procedure to record ge-

ometry information across

the weld groove. Two inde-

pendent optics photograph

the interesting groove area

and displays them onto two

image converter elements

(CCD-lines or CCD-matrix).

Based on the correspond-

ing image points in both

picture scenes, the 3-

dimensional position of ob-

ject points is evaluated.

Figure 16.12

© ISF 2002

Principle of Light-Section Procedure

br-er16-12e.cdr

2-D DetektorDioden-

Laser

laser ligthing

workpiece

CCD camera

line projection

diode laser

2-D detector

Figure 16.11

© ISF 2002

Laser Scanner Principle

br-er15-20e.cdr

CCD camera

lens

mirror

laser

focusing lensmotor

angle transmitter

beam deflection mirror

workpiece

oscillation

16. Sensors 224

2005

Figure 16.13 shows the measurement principle, which uses CCD lines as image converter

elements, and idealised signals for generating information. The grey scale drop in the signal

is ideally used as corresponding image area, which occurs with butt welds due to different

reflection intensity between

workpiece surface and gap.

Both, the lateral position of

the groove and the dis-

tance to the sensor can be

determined by evaluating

the centre positions of both

signal drops. The width of

the groove is taken from

the width of the signal drop.

Optical sensors may also

be used for geometrical

recognition of the weld pool, to adapt process parame-ters in the case of possible deviations.

Figure 16.14 depicts such a system for use with laser beam welding. The welding process is

monitored by a CCD camera through a filter system. An optical filter allows to observe the

weld pool surface without disturbing effects of the plasma in the near infrared spectrum. Pic-

ture data are transferred to an image processing computer which measures the geometry of

the weld pool. Geometry

data contain information

which is used online for

control of the welding proc-

ess. Among others,

penetration depth and fo-

cus position can be

controlled. The system also

provides the recognition of

protrusion-welded joints

and welding defects like

e.g. molten pool ejections.

Figure 16.14

© ISF 2002

Weld Pool Recognition

br-er16-14e.cdr

Figure 16.13

© ISF 2002

Principle of Stereo Measurement Procedure

br-er16-13e.cdr

CCD lines

light line projection

workpiece

displaylevels

laserside position :

distance :

groove width :

left signal right signal

signal drop

stereo measurement principle stereo measurement principle

16. Sensors 225

2005

During electron beam welding, the beam is in combination with a detector used for both, to

carry out a seam tracking and a monitoring of the welded seam. For this, the beam can be

diverged as well as bent, Figure 16.15. Backscattered electrons are recognised by a special

detector and converted into grey values. The line or area surface scanning by the spotted

electron beam provides a

progressive series of greys

across the scanned line or

area. During electron beam

welding, these signals can

be used for seam tracking

by scanning an edge which

is parallel to the groove.

The area-type scanning

provides the possibility for

observing the welded seam

or the focus position.

Figure 16.15

Sensor Principle of Electron Beam Welding

functional principle(evaluation of back-scattered electrons)

seam tracking

monitoring

br-er16-15e.cdr

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