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NITC3 April 2015 Dr. N. RAMACHANDRAN, NITC 2

3 April 2015 Dr. N. RAMACHANDRAN, NITC 3

METAL JOINING Even the simplest object is an assembly of

components

Complex ones - greater number of parts-subassemblies joined to perform the function

METHODS-

WELDING,

BRAZING,

SOLDERING,

ADHESIVE BONDING,

MECHANICAL JOINING

NITC 3 April 2015 Dr. N. RAMACHANDRAN, NITC 4

WHY JOINING?

IMPOSSIBLE TO MAKE AS ONE PIECE

EASINESS AND ECONOMY IN MANUFACTURE

EASY IN REPAIRS AND MAINTENANCE

FUNCTIONAL PROPERTIES DIFFER-

e.g.: Carbide tips of tools,corrosion resistant parts, tungsten carbide tip of pens, brake shoes to metal backing etc

TRANSPORTING SITE/ CUSTOMER

NITC


CLASSIFICATION

According to the STATE of the materials being joined

Extent of external heating- PRESSURE

Use of FILLER materials


Joining Processes

RESISTANCE

MECH.

JOINING

ARCCUTTINGCHEMICAL

CONSUMABLE NON CONSUMABLE

Oxy-fuel

Thermit

LIQUID

SOLID

LIQUID-

SOLID

Spot

Seam

Projection

Flash

Stud

percussion

GTAW

PAW

EBW

LBW

SMAW

SAW

GMAW

FCAW

EGW

ESW

Forge

Cold

Ultrasonic

Friction

Explosion

Diffusion

Brazing

Soldering

Adhesive

Bonding

Fastening

Crimping

Seaming

Stitching

NITC

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Welding


Partial melting and fusion of joint Physical and mechanical changes taking place Can be with application of pressure or by addition of filler material

PARTIAL MELTING

BY 1.CHEMICAL REACTION

2. STRIKING AN ARC

3. MAINTAINING RESISTANCE BETWEEN THE PARTS

Prior to joining, PREPARATION TO BE DONE.

STANDARDS- AWS; ASTM- TYPES OF GROOVES, JOINTS

LIQUID STATE PROCESSES

Slide 2 of 18

WELDING TERMINOLOGY


Standard location of elements of weld symbol

L PS

Specification

process.

No tail-

SMAW

Other side of arrow

Near side of Arrow

Field weld

Weld all around

Size

Length of weld

Unwelded length

G- Grind C- Chip

F-File M-Machine

R- Rolling

Reference line

Finish symbol

Arrow connecting reference

line to arrow side of joint /to

edge prepared /member or

both


ROOT

GROOVE ANGLE

Joint angle

Root Face

Groove face

NITC

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WELDING TECHNIQUES

FOREHAND BACKHAND

THIN

Same direction torch

Heat concentrated away from

bead

Even flow, rippled design

THICK

Opposite direction torch

Heat concentrated on bead

Broad bead3 April 2015 Dr. N. RAMACHANDRAN, NITC 14

WELD POSITIONS WELD MOVEMENTS

FLAT

HORIZONTAL

VERTICAL

OVERHEAD

H

O

C

J

U

ZIGZAG

NITC


WELD POSITIONS

FLAT HORIZONTAL VERTICAL OVERHEAD


ASME Welding PositionsNote the welding progression, (vertically upwards or downwards),

must always be stated and it is an essential variable for both

procedures and performance qualifications.

Welding Positions For Groove welds:-

Welding PositionTest Position ISO and EN

Flat 1G PA

Horizontal 2G PC

Vertical Upwards Progression 3G PF

Vertical Downwards Progression 3G PG

Overhead 4G PE

Pipe Fixed Horizontal 5G PF

Pipe Fixed @ 45 degrees Upwards 6G HL045

Pipe Fixed @ 45 degrees Downwards 6G JL045


G

for Groove

Welds

F

for Fillet

Welds


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Welding Positions For Fillet welds:-

Welding PositionTest Position ISO and EN

Flat (Weld flat joint at 45

degrees)1F PA

Horizontal 2F PB

Horizontal Rotated 2FR PB

Vertical Upwards

Progression3F PF

Vertical Downwards

Progression3F PG

Overhead 4F PD

Pipe Fixed Horizontal 5F PF


G

for Groove

Welds

F

for Fillet

Welds


WELD MOVEMENTS

OZIGZAG

L

ISTRAIGHT

Z


ASME P Material Numbers Explained

ASME has adopted their own designation for welding processes,

which are very different from the ISO definitions adopted by

EN24063.

DesignationDescription

OFW Oxyfuel Gas Welding

SMAW Shielded Metal Arc Welding (MMA)

SAW Submerged Arc Welding

GMAW Gas Metal Arc Welding (MIG/MAG)

FCAW Flux Cored Wire

GTAW Gas Tungsten Arc Welding (TIG)

PAW Plasma Arc Welding

Straight polarity = Electrode -ve

Reverse polarity = Electrode +ve


F Number General Description

1 Heavy rutile coated iron powder electrodes :- A5.1 : E7024

2 Most Rutile consumables such as :- A5.1 : E6013

3 Cellulosic electrodes such as :- A5.1 : E6011

4 Basic coated electrodes such as : A5.1 : E7016 and E7018

5 High alloy austenitic stainless steel and duplex :- A5.4 : E316L-16

6 Any steel solid or cored wire (with flux or metal)

2X Aluminium and its alloys

3X Copper and its alloys

4X Nickel alloys

5X Titanium

6X Zirconium

7X Hard Facing Overlay

ASME F Numbers

Note:- X represents any number 0 to 93 April 2015 Dr. N. RAMACHANDRAN, NITC 24

ASME A Numbers

These refer to the chemical analysis of the deposited weld and not

the parent material. They only apply to welding procedures in

steel materials.

A1Plain unalloyed carbon manganese steels.

A2 to A4 Low alloy steels containing Moly and Chrome Moly

A8 Austenitic stainless steels such as type 316.

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Types of welds and symbols

FILLET, SQUARE BUTT, SINGLE V,

DOUBLE V, SINGLE U, DOUBLE U,

SINGLE BEVEL BUTT, DOUBLE BEVEL BUTT,

SINGLE J BUTT, DOUBLE J BUTT,

STUD, BEAD(EDGE OR SEAL), PLUG,

SPOT, SEAM, MASHED SEAM,

STITCH, PROJECTION,

FLASH, UPSET etc. (REFER sketches supplied)


3 April 2015 Dr. N. RAMACHANDRAN, NITC 27 3 April 2015 Dr. N. RAMACHANDRAN, NITC 28


Multiple-pass layers. Weld layer sequence


Welding Positions

QW431.1 and

QW461.2

Basically there are three

inclinations involved.

Flat, which includes

from 0 to 15 degrees

inclination

15 - 80 degrees

inclination

Vertical, 80 - 90 degrees

For each of these

inclinations the weld

can be rotated from the

flat position to

Horizontal to overhead.

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UNDERWATER WELDING



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Partial melting and fusion of joint Physical and mechanical changes taking place Can be with application of pressure or by addition of filler material

PARTIAL MELTING


2. STRIKING AN ARC

3. MAINTAINING RESISTANCE BETWEEN THE PARTS




Partial melting and fusion of joint

Physical and mechanical changes taking place

Can be with application of pressure or by addition of filler material

PARTIAL MELTING


Oxyacetylene Welding (OAW)

The oxyacetylene welding process

uses a combination of oxygen and

acetylene gas to provide a high

temperature flame.

Oxyacetylene Welding (OAW)

OAW is a manual process in which the

welder must personally control the the torch

movement and filler rod application

The term oxyfuel gas welding outfit refers

to all the equipment needed to weld.

Cylinders contain oxygen and acetylene gas

at extremely high pressure.


OXY ACETYLENE WELDING (OAW)Typical Oxyacetylene Welding

(OAW) Station

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Oxygen Cylinders

Oxygen is stored within cylinders of various sizes and pressures ranging from 2000-2640 psi. (Pounds Per square inch)

Oxygen cylinders are forged from solid armor plate steel. No part of the cylinder may be less than 1/4 thick.

Cylinders are then tested to over 3,300 psi using a (NDE) hydrostatic pressure test.

Oxygen Cylinders

Cylinders are regularly

re-tested using

hydrostatic (NDE) while

in service

Cylinders are regularly

chemically cleaned and

annealed to relieve

jobsite stresses created

by handling .

Cylinder Transportation

Never transport cylinders without the safety

caps in place

Never transport with the regulators in place

Never allow bottles to stand freely. Always

chain them to a secure cart or some other

object that cannot be toppled easily.

Oxygen Cylinders

Oxygen cylinders

incorporate a thin metal

pressure safety disk

made from stainless steel

and are designed to

rupture prior to the

cylinder becoming

damaged by pressure.

The cylinder valve

should always be

handled carefully

Pressure Regulators for

Cylinders

Reduce high storage

cylinder pressure to

lower working

pressure.

Most regulators have

a gauge for cylinder

pressure and

working pressure.

Pressure Regulators for

Cylinders

Regulators are shut off when the adjusting screw is turn out completely.

Regulators maintain a constant torch pressure although cylinder pressure may vary

Regulator diaphragms are made of stainless steel

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Pressure Regulators Gauges

Using a Bourdon movement

Gas entering the gauge fills a Bourdon tube

As pressure in the semicircular end increases it causes the free end of the tube to move outward.

This movement is transmitted through to a curved rack which engages a pinion gear on the pointer shaft ultimately showing pressure.

Regulator Hoses

Hoses are are fabricated

from rubber

Oxygen hoses are green in

color and have right hand

thread.

Acetylene hoses are red in

color with left hand thread.

Left hand threads can be

identified by a grove in the

body of the nut and it may

have ACET stamped on it

Check Valves &

Flashback Arrestors

Check valves allow gas flow in one direction only

Flashback arrestors are designed to eliminate the possibility of an explosion at the cylinder.

Combination Check/ Flashback Valves can be placed at the torch or

regulator.

Acetylene Gas

Virtually all the acetylene distributed for welding and cutting

use is created by allowing calcium carbide (a man made product)

to react with water.

The nice thing about the calcium carbide method of producing

acetylene is that it can be done on almost any scale desired.

Placed in tightly-sealed cans, calcium carbide keeps indefinitely.

For years, miners lamps produced acetylene by adding water, a

drop at a time, to lumps of carbide.

Before acetylene in cylinders became available in almost every

community of appreciable size produced their own gas from

calcium carbide.

Acetylene Cylinders

Acetylene is stored in cylinders specially designed

for this purpose only.

Acetylene is extremely unstable in its pure form at

pressure above 15 PSI (Pounds per Square Inch)

Acetone is also present within the cylinder to

stabilize the acetylene.

Acetylene cylinders should always be stored in the

upright position to prevent the acetone form

escaping thus causing the acetylene to become

unstable.

Acetylene Cylinders

Cylinders are filled with

a very porous substance

monolithic filler to

help prevent large

pockets of pure acetylene

form forming

Cylinders have safety

(Fuse) plugs in the top

and bottom designed to

melt at 212 F (100 C)

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Acetylene Valves Acetylene cylinder shut

off valves should only

be opened 1/4 to 1/2

turn

This will allow the

cylinder to be closed

quickly in case of fire.

Cylinder valve

wrenches should be left

in place on cylinders

that do not have a hand

wheel.

Oxygen and Acetylene Regulator

Pressure Settings

Regulator pressure may vary with different

torch styles and tip sizes.

PSI (pounds per square inch) is sometimes shown as

PSIG (pounds per square inch -gauge)

Common gauge settings for cutting

1/4 material Oxy 30-35psi Acet 3-9 psi

1/2 material Oxy 55-85psi Acet 6-12 psi

1 material Oxy 110-160psi Acet 7-15 psi

Check the torch manufactures data for

optimum pressure settings

Regulator Pressure Settings

The maximum safe working pressure for

acetylene is 15 PSI !

Typical torch styles A small welding torch, with throttle valves

located at the front end of the handle.

Ideally suited to sheet metal welding. Can

be fitted with cutting

attachment in place of the welding head shown. Welding torches of this general

design are by far the most widely used.

They will handle any oxyacetylene welding

job, can be fitted with multiflame

(Rosebud) heads for heating applications,

and accommodate cutting attachments that

will cut steel 6 in. thick.

A full-size oxygen cutting torch which has all valves located in its rear body. Another

style of cutting torch, with oxygen valves

located at the front end of its handle.

Typical startup procedures

Verify that equipment visually appears safe IE: Hose

condition, visibility of gauges

Clean torch orifices with a tip cleaners (a small wire

gauge file set used to clean slag and dirt form the torch

tip)

Crack (or open) cylinder valves slightly allowing

pressure to enter the regulators slowly

Opening the cylinder valve quickly will Slam the

regulator and will cause failure.


Never stand directly in the path of a regulator

when opening the cylinder

Check for leaks using by listening for Hissing or

by using a soapy Bubble solution

Adjust the regulators to the correct operating

pressure

Slightly open and close the Oxygen and

Acetylene valves at the torch head to purge any

atmosphere from the system.

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Always use a flint and steel spark lighter to light the

oxygen acetylene flame.

Never use a butane lighter to light the flame

Flame Settings

There are three distinct types of oxy-acetylene

flames, usually termed:

Neutral

Carburizing (or excess acetylene)

Oxidizing (or excess oxygen )

The type of flame produced depends upon the

ratio of oxygen to acetylene in the gas mixture

which leaves the torch tip.


TYPES of FLAMES Neutral- with inner cone(30400C-33000C), outer envelope,

(21000C near inner cone, 12600C at tip)- high heating

Reducing- Bright luminous inner cone, acetylene feather,

blue envelope

Low temperature, good for brazing, soldering, flame hardening

Hydrogen, methyl acetylene, propadiene also used as fuel.

Oxidising- pointed inner cone, small and narrow outer

envelope

Harmful for steels, good for Cu- Cu based alloys


OXY ACETYLENE WELDING

(OAW)

Types of Flames

Neutral Reducing Oxidising

high heating low temperature good for Cu- Cu alloys

Pure Acetylene and

Carburizing Flame profiles

Neutral and Oxidizing Flame

Profiles

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Flame definition

The excess acetylene flame (Fig. 2), as its name implies, is created when the proportion of acetylene in the mixture is higher than that required to produce the neutral flame. Used on steel, it will cause an increase in the carbon content of the weld metal.

The neutral flame (Fig. 3) is produced when the ratio of oxygen to acetylene, in the mixture leaving the torch, is almost exactly one-to-one. Its termed neutral because it will usually have no chemical effect on the metal being welded. It will not oxidize the weld metal; it will not cause an increase in the carbon content of the weld metal.

The oxidizing flame (Fig. 4) results from burning a mixture which contains more oxygen than required for a neutral flame. It will oxidize or burn some of the metal being welded.


THERMIT WELDING

LIQUID STATE JOINING PROCESS

PARTIAL MELTING BY CHEMICAL REACTION

USE OF Fine particles of iron oxide, aluminium oxide, iron & aluminium

Termed THERMITE- based on Therm, meaning heat

Involves exothermic reactions between metal oxides and metallic reducing agents

Heat of reaction used for welding.

Reactions are:

(3/4) Fe3 O4 + 2 Al --- (9/4) Fe + Al2O3 + Heat

3 FeO + 2 Al --- 3 Fe + Al2O3 + Heat

Fe2O3 + 2Al --- 2Fe + Al2O3+ Heat

THERMIT WELDING


Slide 13 of 18

THERMIT WELDING


Mixture is non explosive. Produces temperature of 32000 C

within a minute

Practically about 22000- 24000 C. Other materials to impart

special properties added. Applying a Mg fuse of special

compounds of peroxides, chlorates/ chromates.

Welding copper, brasses, bronzes and copper alloys to steel

using oxides of copper, nickel, aluminium, manganese

temperatures of 50000 C obtained


THERMIT WELDING OF RAILS

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Effects of expansion and

contraction


CONTROLLING DISTORTION


HEAT AFFECTED ZONE


SOLID STATE PROCESSES

Joining without fusion of work pieces

No liquid (molten ) phase present in joint

Principle: If two clean surfaces are brought into

atomic contact with each other - made with

sufficient pressure -(in the absence of oxide film

and other contaminents) they form bonds and

produce strong joint

To improve strength, heat and some movement of

mating surfaces by plastic deformation employed.

Eg: USW, Friction Welding (FRW)


FORGE WELDING (FOW)

Both elevated temperature and pressure applied

to form strong bond between members

Components heated and pressed/ hammered

with tools, dies or rollers

Local plastic deformation at interface breaks up

the oxide films improves bond strength.

Not for high load bearing applications.


COLD WELDING (CW)

Pressure applied to work pieces either through dies

or rolls

One (or both) of the mating parts must be ductile

Interface cleaned prior to welding- brushing etc.

Roll

Rolling metal

Bare metal

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EXPLOSIVE WELDING (EXW) Solid state bonding process

Joining by the cohesive force between atoms of two intimate contact surfaces

High pressure waves- thousands of MPa created-

To weld dissimilar metals, thick to thin, high difference in Melting Point metals.

Not a costly process

Extremely large surfaces can be joined (2m X 10 m)

Welding of heat treated metals without affecting the process

No HAZ

Incompatible metals joined(thin foils to heavy plates)

severe deformation needed for joining.3 April 2015 Dr. N. RAMACHANDRAN, NITC 80

Principle:

Explosive Impulse used to produce extremely high

normal pressure and a slight shear or sliding

pressure ( uses a detonator for this)

Two properly laid metal surfaces brought together with high

relative velocity at high pressure

Large amount of plastic interaction between surfaces results.

Two ways


Plastic interaction by positioning explosive charge to deliver shock

waves at an oblique angle to parts to be welded- Less frequently

used.

(1)Contact technique


(2) Impact technique

Two pieces explosively projected towards each other. Impact with high velocity (200 400 m/s)


Severe deformation needed for joining

(minimum 40 to 60%), as welding is by

pressure.


Detonation velocity approx. 7000 m/s in the detonation front.

Produces pressure at interface 7000 to 70,000 atms. Parts driven at an angle Velocity of impact and angle of collapse selected. Joining as s result of intense plastic flow at the surface called surface jetting

For good joint, surface to be free from contaminants

Pressure sufficient to bring surfaces within interatomic distances of each other

[ In a range of speed and angle of impact, a high velocity metal jet forms. Removes surface contamination.

Speed, angle(10 to 100) of detonation important]

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Bond as strong as the weaker of the two

obtained. 100 % efficient joint, (eg. In sheet

forming in aerospace industries)

At the interface, microhardness slightly

increased. (because of plastic deformation

and strain hardening- a very thin hardness

zone)


Titanium cladding common

Others- Ni, SS(50 mm), tantalum, carbon steels, for heat exchangers, tubes, pressure vessels, etc.

No change in chemical and physical properties of parent metal

But, not for brittle alloys. Metal must possess some ductility.

[Quantity of charge, detonation velocity, and deformation characteristics of flyer plate decide the weld]

Also spot welding by small charge. Handy explosive spot welding sets available (for 10mm to 12 mm spots)


Minus points: :

Severe deformation needed for joining

(minimum 40 to 60/ 50, as welding is by

pressure.



Partial melting and fusion of joint

Physical and mechanical changes taking place

Can be with application of pressure or by addition

of filler material

Prior to joining, PREPARATION TO BE DONE

STANDARDS- AWS; ASTM-

TYPES OF GROOVES, JOINTS

NITC


LIQUID STATE PROCESS

PARTIAL MELTING

BY STRIKING AN ARC

AFTER THE INVENTION OF ELECTRICITY

HOW ARC STRUCK?

ARC COLUMN THEORY

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ANODE +

CATHODE -

ELECTRICAL / IONIC THEORY

IONS FROM ANODE TO CATHODE,

AS METAL IONS ARE +VE CHARGED

DC

ARC COLUMN THEORY

TOUCH AND THEN ESTABLISH A GAPTO BALANCE THE ATOMIC STRUCTURE

IONS COLLIDE WITH GAS MOLECULES

PRODUCES A THERMAL IONISATION LAYER

IONISED GAS COLUMN AS HIGH RESISTANCE CONDUCTOR

ON STRIKING CATHODE, HEAT GENERATEDTERMED AS IONIC THEORY

NOT COMPLETE IN EXPLAINING ARC COLUMN THEORY

THUS, ELECTRON THEORY3 April 2015 Dr. N. RAMACHANDRAN, NITC 92

ANODE +

CATHODE -

ELECTRON THEORY

IONS FROM ANODE TO CATHODE

AS METAL IONS ARE +VE

CHARGED

-VELY CHARGED ELECTRONS

DISSOCIATED FROM CATHODE

MOVE OPPOSITE WITH HIGH

VELOCITY

DC(MASS- 9.1x 10-28 gm)

CAUSES HEAT IN ARC COLUMN

RELEASES HEAT ENERGY IN

STRIKING THE ANODE

CALLED

ELECTRON IMPINGEMENTAND

IONIC BOMBARDMENT

ARC COLUMN THEORY


HIGH HEAT

MEDIUM HEAT

LOW HEAT

ANODE+

CATHODE -

ELECTRON IMPINGEMENT

IONIC BOMBARDMENT


MAGNETIC FLUX THEORY

THE COLUMN NOT FLAIRING

DUE TO THE FLUX LINES AROUND

THE ARC COLUMN.

(Right hand Thumb Rule)

THIS COMPLETES THE ARC COLUMN THEORY


POLARITY

AC

1. Currents higher than those of DCRP can be employed (400A to 500 A for 6 mm electrode)

2. Arc cleaning of the base metal

3. Normal penetration

4. Equal heat distribution at electrode and job

5. Electrode tip is colder as compared to that in DCRP

6. Average arc voltage in argon atmosphere is 16V


DCRP 1. Currents generally less than 125 amps (up to 6 mm dia electrodes) to avoid overheating

2. 2/3rd heat at electrode and 1/3rd at the job

3. Least penetration

4. Average arc voltage on argon atmosphere is 19V

5. Chances of electrode overheating, melting and losses

6. Better arc cleaning action

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DCSP1. Welding currents up to

1000 amps can be

employed for 6 mm

electrodes

2. 33.33% heat is generated

at the electrode and

66.66% at the job.

3. Deep penetration

4. Average arc voltage in an

argon atmosphere is 12 V

5. Electrode runs colder as

compared to AC or DCRP

6. No are cleaning of base

metal

SHIELDED METAL ARC WELDING

(SMAW)


Shielded metal arc welding (SMAW), Also known as Manual Metal Arc (MMA) welding

Informally as stick welding, is a manual arc welding process that uses a

consumable electrode coated in flux to lay the weld.

An electric current, in the form of either alternating current or direct current from a welding power supply, is

used to form an electric arc between the electrode and

the metals to be joined.

As the weld is laid, the flux coating of the electrode disintegrates, giving off vapors that serve as a shielding

gas and providing a layer of slag, both of which protect

the weld area from atmospheric contamination.3 April 2015 Dr. N. RAMACHANDRAN, NITC 100

Because of the versatility of the process and the simplicity of its equipment and operation, shielded metal arc welding is one of the world's most popular welding processes.

It dominates other welding processes in the maintenance and repair industry, used extensively in the construction of steel structures and in industrial fabrication.

The process is used primarily to weld ironand steels (including stainless steel) but aluminum, nickel and copper alloys can also be welded with this method.

Flux-Cored Arc Welding (FCAW) , a modification to SMAW is growing in popularity


SAFETY PRECAUTIONS Uses an open electric arc, so risk of burns to be prevented by protective clothing in the form of heavy leather gloves

and long sleeve jackets.

The brightness of the weld area can lead arc eye, in which ultraviolet light causes

the inflammation of the cornea and can

burn the retinas of the eyes.

Welding helmets with dark face plates to be worn to prevent this exposure

New helmet models have been produced that feature a face plate that self-darkens

upon exposure to high amounts of UV

light.

To protect bystanders, especially in industrial environments, transparent welding curtains often surround the welding area. These are made of a

polyvinyl chloride plastic film, shield nearby workers from exposure to the

UV light from the electric arc, but should not be used to replace the filter

glass used in helmets.

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Arc eye, also known as arc flash or welder's flash or

corneal flash burns, is a painful condition sometimes

experienced by welders who have failed to use adequate

eye protection.

It can also occur due to light from sunbeds, light

reflected from snow (known as snow blindness), water

or sand. The intense ultraviolet light emitted by the arc

causes a superficial and painful keratitis.

Symptoms tend to occur a number of hours

after exposure and typically resolve

spontaneously within 36 hours.

It has been described as having sand poured

into the eyes.

ARC EYE


Signs

Intense lacrimation

Blepharospasm

Photophobia

Fluorescein dye staining will reveal corneal ulcers

under blue light

Management

Instill topical anaesthesia

Inspect the cornea for any foreign body

Patch the worse of the two eyes and prescribe analgesia

Topical antibiotics in the form of eye drops or eye ointment or both should be prescribed for prophylaxis

against infection


EQUIPMENT

3 April 2015 Dr. N. RAMACHANDRAN, NITC 106Various welding electrodes and an electrode holder


PURPOSE OF COATING

Gives out inert or protective gas- shields

Stabilizes the arc- by chemicals

Low rate consumption of electrode- directs arc and molten metal

Removes impurities and oxides as slag

Coatings act as insulators- so narrow grooves welded

Provide means to introduce alloying elements

Bare electrodes - carbon- more conductive- slow consumption in welding


ELECTRODE COATING INGREDIENTS

Slag forming ingredients- silicates of sodium, potassium, Mg, Al, iron oxide, China clay, mica etc.

Gas shielding- cellulose, wood, starch, calcium carbonate

De-oxidising elements- ferro manganese, ferro silicon- to refine molten metal

Arc stabilizing calcium carbonate, potassium silicate, titanates, Mg silicate etc.

.Alloying elements- ferro alloys, Mn, Mo., to impart special properties

Iron powder- to improve arc behaviour, bead appearance

Other elements - to improve penetration, limit spatter, improve metal deposition rates,

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Submerged arc welding

3 April 2015 Dr. N. RAMACHANDRAN, NITC 111CONTROL PANEL 3 April 2015 Dr. N. RAMACHANDRAN, NITC 112

Submerged Arc Welding (SAW)

Is a common arc welding process.

A continuously fed consumable solid or tubular (metal cored) electrode used.

The molten weld and the arc zone are protected from atmospheric contamination by being submerged under a blanket of granular fusible flux.

When molten, the flux becomes conductive, and provides a current path between the electrode and the work


Normally operated in the automatic or mechanized mode.

Semi-automatic (hand-held) SAW guns with pressurized or gravity flux feed delivery are available.

The process is normally limited to the 1F, 1G, or the 2F positions (although 2G position welds have been done with a special arrangement to support the flux). Deposition rates approaching 45 kg/h have been reported this compares to ~5 kg/h (max) for shielded metal arc welding.

Currents ranging from 200 to 1500 A are commonly used; currents of up to 5000 A have been used (multiple arcs).


Single or multiple (2 to 5) electrode wire variations of the process exist

SAW strip-cladding utilizes a flat strip electrode (e.g. 60 mm wide x 0.5 mm thick).

DC or AC power can be utilized, and combinations of DC and AC are common on multiple electrode systems.

Constant Voltage welding power suppliesare most commonly used, however Constant Current systems in combination with a voltage sensing wire-feeder are available.

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Material applications

Carbon steels (structural and vessel construction);

Low alloy steels;

Stainless Steels;

Nickel-based alloys;

Surfacing applications (wearfacing, build-up, and corrosion resistant overlay of

steels).


Advantages of SAW

High deposition rates (over45 kg/h) have been reported;

High operating factors in mechanized applications;

Deep weld penetration; Sound welds are readily made (with good

process design and control);

High speed welding of thin sheet steels at over 2.5 m/min is possible;

Minimal welding fume or arc light is emitted.


Limitations of SAW

Limited to ferrous (steel or stainless steels) and some nickel based alloys;

Normally limited to the 1F, 1G, and 2F positions; Normally limited to long straight seams or

rotated pipes or vessels;

Requires relatively troublesome flux handling systems;

Flux and slag residue can present a health & safety issue;

Requires inter-pass and post weld slag removal.


Key SAW process variables

Wire Feed Speed (main factor in welding current control); Arc Voltage; Travel Speed; Electrical Stick-Out (ESO) or Contact Tip to Work (CTTW); Polarity and Current Type (AC or DC).

Other factors

Flux depth/width; Flux and electrode classification and type; Electrode wire diameter; Multiple electrode configurations.

GAS TUNGSTEN ARC WELDING (GTAW)


Gas tungsten arc welding

4/3/2015

21


GTAW Fusion Welding Process

Arc Between Non-Consumable Tungsten Rod And Work

Arc & Weld Pool Shielded By Argon/Gas

Filler Wire Separately Added To Weld Pool

Welding Torch & Tungsten Rod Cooled by Flow OF Argon / Cooling Water


GAS TUNGSTEN ARC WELDING (GTAW)

ELECTRODE NOT CONSUMED

TUNGSTEN ELECTRODES USED

ARGON- HEAVIER FOR NARROW AND LIMITED

EXPANSION,WIDER, DEEPER PUDDLE

HELIUM FOR EVEN EXPANSIONLIMITED

STRESS BUILDUP

MORE He, MORE HEAT IN ARC

Ar-He MIX FOR AUTOMATIC GTAW

Ar- CO2 FOR CARBON STEELS, ECONIMICAL,

INCREASES WETTING ACTION

GTAW TORCH- WATER OR AIR COOLED

CONSTANT CURRENT SOURCE.(IIIr TO SMAW)


GTAW Equipment &

Accessories

Power Source Inverter, Thyrister, Rectifier, Generator

High Frequency Unit

Water Cooling System

Welding Torch- (Ceramic Cup, Tungsten Rod, Collet, Gas-lens)

Pedal Switch

Argon Gas Cylinder

Pressure Gauge, Regulator, Flow Meter

Earthing Cable With Clamp


Equipment & Accessories

+

Argon Gas In

Flow Meter

Welding Cable & Cooling

Water In Tube

HF Unit &

Water Cooling

System

Argon Cylinder

Pressure Regulator

Cooling Water In

Cooling Water OutArgon Shielding

Tungsten Rod

Power Source

Work

Arc

+High Frequency

Connection

Solenoid

Valve

Ceramic Cup

Pedal Switch

Gas Lens


Equipment

GTAW torch, disassembledGTAW torch with various

electrodes, cups, collets and gas

diffusers


Gas tungsten arc welding (GTAW),

commonly known as Tungsten Inert Gas

(TIG) welding Is an arc welding process that uses a

nonconsumable tungsten electrode to produce the weld.

The weld area is protected from atmospheric contamination by a shielding gas (usually an inert gas such as argon), and a filler metal is normally used, though some welds, known as autogenous welds, do not require it.

A constant current welding power supplyproduces energy which is conducted across the arc through a column of highly ionized gas and metal vapors known as a plasma.

4/3/2015

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Most commonly used to weld thin sections of stainless steel and light metals such as aluminum, magnesium, and copper alloys.

The process grants the operator greater control over the weld than competing procedures such as shielded metal arc welding and gas metal arc welding, allowing for stronger, higher quality welds.

GTAW is comparatively more complex and difficult to master, and furthermore, it is significantly slower than most other welding techniques.

A related process, plasma arc welding, uses a slightly different welding torch to create a more focused welding arc and as a result is often automated.


GTAW system setup


Applications

Aerospace industry is one of the primary users of gas tungsten arc welding, the process is used in a number of other areas.

Many industries use GTAW for welding thin workpieces, especially nonferrous metals.

It is used extensively in the manufacture of space vehicles, and is also frequently employed to weld small-diameter, thin-wall tubing.

Is often used to make root or first pass welds for piping of various sizes.

In maintenance and repair work, the process is commonly used to repair tools and dies, especially components made of aluminum and magnesium.

Because the welds it produces are highly resistant to corrosion and cracking over long time periods, GTAW is the welding procedure of choice for critical welding operations like sealing spent nuclear fuel canisters before burial.


ABOUT THE POWER SOURCE

DCRP, DCSP, ACHF USED

ELECTRODES OF 0.25 mm TO 6.4 mm FOR

DIFFERENT APPLICATIONS

ELECTRODES CODED, WITH COLOR STRIPS

BEST FOR ALUMINIUM, SINCE OXIDE FILM BREAKS

BY PENETRATION

Frequent cleaning and shaping of electrode tip to be done


QualityGTAW ranks the highest in terms of the

quality of weld produced.

Operation must be with free from oil,

moisture, dirt and other impurities, as

these cause weld porosity and

consequently a decrease in weld

strength and quality.

To remove oil & grease, alcohol or

similar commercial solvents used, while

a stainless steel wire brush or chemical

process remove oxides from the

surfaces of metals like aluminum.

Rust on steels removed by first grit

blasting the surface and then using a

wire brush to remove imbedded grit.

These steps important when DCEN

used, because this provides no cleaning

during the welding process, unlike

DCEPor AC.

To maintain a clean weld pool during welding, the shielding gas flow should be

sufficient and consistent so that the gas covers the weld and blocks impurities in

the atmosphere. GTA welding in windy or drafty environments increases the

amount of shielding gas necessary to protect the weld, increasing the cost and

making the process unpopular outdoors.

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Because of GTAW's relative difficulty and the importance of proper technique, skilled operators are employed for important applications.

Low heat input, caused by low welding current or high welding speed, can limit penetration and cause the weld bead to lift away from the surface being welded.

If there is too much heat input, the weld bead grows in width while the likelihood of excessive penetration and spatter increase.

If the welder holds the welding torch too far from the workpiece, shielding gas is wasted and the appearance of the weld worsens.


If the amount of current used exceeds the capability of the electrode, tungsten inclusions in the weld may result. Known as tungsten spitting, it can be identified with radiography and prevented by changing the type of electrode or increasing the electrode diameter.

If the electrode is not well protected by the gas shield or the operator accidentally allows it to contact the molten metal, it can become dirty or contaminated. This often causes the welding arc to become unstable, requiring that electrode be ground with a diamond abrasive to remove the impurity.


GTAW welding torches designed for either automatic or manual operation and are equipped with cooling systems using air or water. The automatic and manual torches are similar in construction, but the manual torch has a handle while the automatic torch normally comes with a mounting rack.

The angle between the centerline of the handle and the centerline of the tungsten electrode, known as the head angle, can be varied on some manual torches according to the preference of the operator.

Air cooling systems are most often used for low-current operations (up to about 200 A), while water cooling is required for high-current welding (up to about 600 A).

The torches are connected with cables to the power supply and with hoses to the shielding gas source and where used, the water supply.


The internal metal parts of a torch are made of hard alloys of copper or brass in order to transmit current and heat effectively.

The tungsten electrode must be held firmly in the center of the torch with an appropriately sized collet, and ports around the electrode provide a constant flow of shielding gas.

The body of the torch is made of heat-resistant, insulating plastics covering the metal components, providing insulation from heat and electricity to protect the welder.


GTAW TORCH

Tungsten Rod

Ceramic Cup

Arc

Argon Gas Inlet

Cooling Water Outlet

Cooling Water Inlet Tube with cable

Base Metal

Torch HandleCap with collet For

Holding Tungsten

Argon Shielding Gas

Earthing Cable


The size of the welding torch nozzle depends on the size of the desired welding arc, and

the inside diameter of the nozzle is normally

at least three times the diameter of the

electrode.

The nozzle must be heat resistant and thus is normally made of alumina or a ceramic

material, but fused quartz, a glass-like

substance, offers greater visibility.

Devices can be inserted into the nozzle for special applications, such as gas lenses or

valves to control shielding gas flow and

switches to control welding current.

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Power supply GTAW uses a constant

current power source,

meaning that the current (and

thus the heat) remains

relatively constant, even if

the arc distance and voltage

change.

This is important because most applications of GTAW

are manual or semiautomatic,

requiring that an operator

hold the torch.

Maintaining a suitably steady arc distance is difficult if a

constant voltage power

source is used instead, since

it can cause dramatic heat

variations and make welding

more difficult.3 April 2015 Dr. N. RAMACHANDRAN, NITC 140

The preferred polarity of the GTAW system depends largely on the type of metal being welded.

DCEN is often employed when welding steels, nickel, titanium, and other metals. It can also be used in automatic GTA welding of aluminum or magnesium when helium is used as a shielding gas. The negatively charged electrode generates heat by emitting electrons which travel across the arc, causing thermal ionization of the shielding gas and increasing the temperature of the base material. The ionized shielding gas flows toward the electrode, not the base material, and this can allow oxides to build on the surface of the weld.

DCEP is less common, and is used primarily for shallow welds since less heat is generated in the base material. Instead of flowing from the electrode to the base material, as in DCEN, electrons go the other direction, causing the electrode to reach very high temperatures. To help it maintain its shape and prevent softening, a larger electrode is often used. As the electrons flow toward the electrode, ionized shielding gas flows back toward the base material, cleaning the weld by removing oxides and other impurities and thereby improving its quality and appearance.


AC commonly used when welding aluminum and magnesium manually or semi-automatically, combines the two direct currents by making the electrode and base material alternate between positive and negative charge. This causes the electron flow to switch directions constantly, preventing the tungsten electrode from overheating while maintaining the heat in the base material. This makes the ionized shielding gas constantly switch its direction of flow, causing impurities to be removed during a portion of the cycle.

Some power supplies enable operators to use an unbalanced alternating current wave by modifying the exact percentage of time that the current spends in each state of polarity, giving them more control over the amount of heat and cleaning action supplied by the power source.

In addition, operators must be wary of rectification, in which the arc fails to reignite as it passes from straight polarity (negative electrode) to reverse polarity (positive electrode).

To remedy the problem, a square wave power supply can be used, as can high frequency voltage to encourage ignition. 3 April 2015 Dr. N. RAMACHANDRAN, NITC 142

Tungsten Rod

Non Consumable Electrode.

Maintains Stable Arc

Tip to be Ground to a cone Shape of 60 to 30 angle

Thoriated Tungsten for General Application, Zerconiated Tungsten for Aluminium Welding

Sizes :- 2, 2.4 & 3 mm

Tungsten Rod

Ground to

50 angle


ISO

ClassISO Color AWS Class

AWS

ColorAlloy [18]

WP Green EWP Green None

WC20 Gray EWCe-2 Orange ~2% CeO2

WL10 Black EWLa-1 Black ~1% LaO2

WL15 Gold EWLa-1.5 Gold ~1.5% LaO2

WL20 Sky-blue EWLa-2 Blue ~2% LaO2

WT10 Yellow EWTh-1 Yellow ~1% ThO2

WT20 Red EWTh-2 Red ~2% ThO2

WT30 Violet ~3% ThO2

WT40 Orange ~4% ThO2

WY20 Blue ~2% Y2O3

WZ3 Brown EWZr-1 Brown ~0.3% ZrO2

WZ8 White ~0.8% ZrO2

The electrode used in GTAW is made of tungsten or a tungsten alloy,

because tungsten has the highest

melting temperature among metals,

at 3422 C.

The electrode is not consumed during welding, though some erosion

(called burn-off) can occur.

Electrodes can have either a clean finish or a ground finishclean finish electrodes have been chemically

cleaned, while ground finish

electrodes have been ground to a

uniform size and have a polished

surface, making them optimal for

heat conduction.

The diameter of the electrode can vary between 0.5 mm and 6.4 mm,

and their length can range from 75 to

610 mm . 3 April 2015 Dr. N. RAMACHANDRAN, NITC 144

A number of tungsten alloys have been standardized by the International Organization for Standardization and the American Welding Society in ISO 6848 and AWS A5.12, respectively, for use in GTAW electrodes- refer table

Pure tungsten electrodes (classified as WP or EWP) are general purpose and low cost electrodes. Cerium oxide (or ceria) as an alloying element improves arc stability and ease of starting while decreasing burn-off. Using an alloy of lanthanum oxide (or lanthana) has a similar effect. Thorium oxide (or thoria) alloy electrodes were designed for DC applications and can withstand somewhat higher temperatures while providing many of the benefits of other alloys.

However, it is somewhat radioactive, and as a replacement, electrodes with larger concentrations of lanthanum oxide can be used. Electrodes containing zirconium oxide (or zirconia) increase the current capacity while improving arc stability and starting and increasing electrode life.

Electrode manufacturers may create alternative tungsten alloys with specified metal additions, and these are designated with the classification EWG under the AWS system.

Filler metals are also used in nearly all applications of GTAW, the major exception being the welding of thin materials. Filler metals are available with different diameters and are made of a variety of materials. In most cases, the filler metal in the form of a rod is added to the weld pool manually, but some applications call for an automatically fed filler metal, which is fed from rolls.

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shielding gases Necessary in GTAW to protect the welding area from atmospheric

gases such as nitrogen and oxygen, which can cause fusion defects, porosity, and weld metal embrittlement if they come in contact with the electrode, the arc, or the welding metal. The gas also transfers heat from the tungsten electrode to the metal, and it helps start and maintain a stable arc.

The selection of a shielding gas depends on several factors, including the type of material being welded, joint design, and desired final weld appearance.

Argon is the most commonly used shielding gas for GTAW, since it helps prevent defects due to a varying arc length. When used with alternating current, the use of argon results in high weld quality and good appearance.

Another common shielding gas, helium, is most often used to increase the weld penetration in a joint, to increase the welding speed, and to weld conductive metals like copper and aluminum.

A significant disadvantage is the difficulty of striking an arc with helium gas, and the decreased weld quality associated with a varying arc length.


Shielding Gas Inert Gas - Argon , Helium

Common Shielding Gas Argon

When Helium Is Used Called Heli Arc Welding

When Argon Is Used Called Argon Arc Welding

Inert Gas Prevents Contamination Of Molten Metal

It Prevents Oxidation Of Tungsten Rod

It Ionizes Air Gap and Stabilizes Arc

It Cools Welding Torch & Tungsten Rod


Shielding Gas

Argon - Purity 99.95%

Impure Argon Results In Porosities

Purity Verified by Fusing BQ CS plate

Leakage of Argon in Torch Results in

Porosity.

Check Leakage by Closing the Ceramic Cup

With Thump


Argon Gas Cylinder

Light Blue In Colour

Full Cylinder Pressure: 1800 psi ( 130 Kgs / cm2 )

Volume Of Argon In Full Cylinder: 7.3 M3

Commercial Argon (99.99%) Cost: Rs 70/- Per M3

High Purity Argon (99.999) Cost: Rs 87/- Per M3


Back Purging

Purging Gas Commercial Argon or

Nitrogen

Applicable to Single

Sided full penetration

Prevents oxidation of

root pass from opposite

side of weld

Essential for high alloy

steels, nonferrous

metals and alloys

Desirable For All

Material

Welding Torch

Root Pass

Purging Gas InPurging

Gas Out

Purging

chamber

Filler Wire


Argon-helium mixtures are also frequently utilized in GTAW, since they can increase control of the heat input while maintaining the benefits of using argon. Normally, the mixtures are made with primarily helium (often about 75% or higher) and a balance of argon. These mixtures increase the speed and quality of the AC welding of aluminum, and also make it easier to strike an arc.

Argon-hydrogen, is used in the mechanized welding of light gauge stainless steel, but because hydrogen can cause porosity, its uses are limited.

Nitrogen can sometimes be added to argon to help stabilize the austenite in austentitic stainless steels and increase penetration when welding copper. Due to porosity problems in ferritic steels and limited benefits, however, it is not a popular shielding gas additive.

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Materials Most commonly used to weld stainless steel

and nonferrous materials, such as aluminum and magnesium, but it can be applied to nearly all metals, with notable exceptions being lead and zinc.

Its applications involving carbon steels are limited not because of process restrictions, but because of the existence of more economical steel welding techniques, such as gas metal arc welding and shielded metal arc welding.

GTAW can be performed in a variety of other-than-flat positions, depending on the skill of the welder and the materials being welded.


A TIG weld showing an

accentuated AC etched zone

Closeup view of an

aluminium TIG weld AC etch zone


Aluminum and magnesium are most often welded using alternating current, but the use of direct current is also possible, depending on the properties desired. Before welding, the work area should be cleaned and may be preheated to 175-200 C for aluminum or to a maximum of 150 C for thick magnesium workpieces to improve penetration and increase travel speed.

AC current can provide a self-cleaning effect, removing the thin, refractory aluminium oxide (sapphire) layer that forms on aluminium metal within minutes of exposure to air. This oxide layer must be removed for welding to occur. When alternating current is used, pure tungsten electrodes or zirconiated tungsten electrodes are preferred over thoriated electrodes, as the latter are more likely to "spit" electrode particles across the welding arc into the weld.

Blunt electrode tips are preferred, and pure argon shielding gas should be employed for thin workpieces. Introducing helium allows for greater penetration in thicker workpieces, but can make arc starting difficult.


Direct current of either polarity, positive or negative, can be used to weld aluminum and magnesium as well.

DCEN allows for high penetration, and is most commonly used on joints with butting surfaces, such as square groove joints. Short arc length (generally less than 2 mm or 0.07 in) gives the best results, making the process better suited for automatic operation than manual operation. Shielding gases with high helium contents are most commonly used with DCEN, and thoriated electrodes are suitable.

DCEP is used primarily for shallow welds, especially those with a joint thickness of less than 1.6 mm. While still important, cleaning is less essential for DCEP than DCEN, since the electron flow from the workpiece to the electrode helps maintain a clean weld. A large, thoriated tungsten electrode is commonly used, along with a pure argon shielding gas.


Steels For GTA welding of carbon and stainless steels, the

selection of a filler material is important to prevent excessive porosity. Oxides on the filler material and workpieces must be removed before welding to prevent contamination, and immediately prior to welding, alcohol or acetone should be used to clean the surface.

Preheating is generally not necessary for mild steels less than one inch thick, but low alloy steels may require preheating to slow the cooling process and prevent the formation of martensite in the heat-affected zone.

Tool steels should also be preheated to prevent cracking in the heat-affected zone. Austenitic stainless steels do not require preheating, but martensitic and ferritic chromium stainless steels do. A DCEN power source is normally used, and thoriated electrodes, tapered to a sharp point, are recommended. Pure argon is used for thin workpieces, but helium can be introduced as thickness increases.


Dissimilar metals

Welding dissimilar metals often introduces new difficulties to GTA welding, because most materials do not easily fuse to form a strong bond. Welds of dissimilar materials have numerous applications in manufacturing, repair work, and the prevention of corrosion and oxidation. In some joints, a compatible filler metal is chosen to help form the bond, and this filler metal can be the same as one of the base materials (eg:, using a stainless steel filler metal stainless steel and carbon steel as base materials), or a different metal (such as the use of a nickel filler metal for joining steel and cast iron). Very different materials may be coated or "buttered" with a material compatible with a particular filler metal, and then welded. In addition, GTAW can be used in cladding or overlaying dissimilar materials.

When welding dissimilar metals, the joint must have an accurate fit, with proper gap dimensions and bevel angles. Care should be taken to avoid melting excessive base material. Pulsed current is particularly useful for these applications, as it helps limit the heat input. The filler metal should be added quickly, and a large weld pool should be avoided to prevent dilution of the base materials.

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Process variations

Pulsed-current

In the pulsed-current mode, the welding current rapidly alternates between two levels.

The higher current state is known as the pulse current,while the lower current level is called the background current.

During the period of pulse current, the weld area is heated and fusion occurs. Upon dropping to the background current, the weld area is allowed to cool and solidify.

Pulsed-current GTAW has a number of advantages, including lower heat input and consequently a reduction in distortion and warpage in thin workpieces. In addition, it allows for greater control of the weld pool, and can increase weld penetration, welding speed, and quality. A similar method, manual programmed GTAW, allows the operator to program a specific rate and magnitude of current variations, making it useful for specialized applications.


Dabber

The Dabber variation is used to precisely place weld metal on thin edges. The automatic

process replicates the motions of manual

welding by feeding a cold filler wire into the weld

area and dabbing (or oscillating) it into the

welding arc. It can be used in conjunction with

pulsed current, and is used to weld a variety of

alloys, including titanium, nickel, and tool steels.

Common applications include rebuilding seals in

jet engines and building up saw blades, milling

cutters, drill bits, and mower blades


Heat-affected zone

The cross-section of a welded butt joint, with the

darkest gray representing the weld or fusion zone,

the medium gray the heat affected zone, and

the lightest gray the base material.


The heat-affected zone (HAZ) is the area of base material, either a metal or a thermoplastic, which has had its microstructure and properties altered by welding. The heat from the welding process and subsequent re-cooling causes this change in the area surrounding the weld. The extent and magnitude of property change depends primarily on the base material, the weld filler metal, and the amount and concentration of heat input by the welding process.

The thermal diffusivity of the base material plays a large role if the diffusivity is high, the material cooling rate is high and the HAZ is relatively small. Alternatively, a low diffusivity leads to slower cooling and a larger HAZ. The amount of heat inputted by the welding process plays an important role as well, as processes like oxyfuel weldinguse high heat input and increase the size of the HAZ. Processes like laser beam welding give a highly concentrated, limited amount of heat, resulting in a small HAZ. Arc welding falls between these two extremes, with the individual processes varying somewhat in heat input


To calculate the heat input for arc welding procedures, the formula used is:

where Q = heat input (kJ/mm), V = voltage (V), I =

current (A), and S = welding speed (mm/min). The

efficiency is dependent on the welding process used,

with shielded metal arc welding having a value of

0.75, gas metal arc welding and submerged arc

welding, 0.9, and gas tungsten arc welding, 0.8.


Types Of GTAW Power Source

Inverter- DC

Thyrister DC

Motor Generator DC

Rectifier DC

Transformer AC (For Aluminium Welding Only)

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Power Source

Provides Electric Energy Arc Heat

Drooping Characteristic

OCV Approx. 90V,

Current Range 40 A to 300 A ( Capacity Of M/s)

Arc Voltage 18V to 26V


Characteristic Of GTAW

Power Source

A

Vertical

Curve

V1

V2

A1 A2

Drooping Constant Current

V


High Frequency Unit

Provides High Voltage Electric Energy With Very high Frequency 10000 Cycles / Sec.

Initiates low energy Arc / Spark & Ionize Air Gap.

Electrically charges Air Gap For welding Current to Jump Across the Tungsten Tip & BM to Form An Arc.

HF Gets Cut Off, Once Welding Arc Struck.


Water Cooling System

Provides Cooling Water To Welding Torch.

Cools Tungsten Rod, Torch handle & Welding

Cable.

Cooling Water Returns through Flexible Tube

Which Carries welding cable within.


Pedal Switch

Switches system

on And off in sequence

When Pedal Pressed

Solenoid valve opens, Argon gas flows

High Frequency current jumps from tungsten rod generating sparks

Welding current flows generating an arc across tungsten rod and work.

High frequency gets cut off from the system & welding continues.

When Pedal Released

1 Current gets cut off, Arc extinguishes

2 Gas flow remains for few more seconds before it stops.


Argon Gas Cylinder- Pressure Regulator +

Flow Meter

Cylinder Stores Argon At

High Pressure

Regulator Regulates

Cylinder Pressure to

Working Pressure

Flow Meter Controls

Flow Rate

Argon Cylinder

Flow Meter

Pressure Regulator

Flow Regulator

Pressure gauges

Cylinder Valve

Connection To Torch

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Tools For GTAW

Head Screen

Hand gloves

Chipping Hammer

Wire Brush

Spanner Set


Filler Wire

Added Separately to the weld pool.

Compatible to base metal

Used in cut length for manual welding.

Used from layer wound spool for automatic welding.

Sizes :- 0.8, 1, 1.2, 1.6, 2, 2.4 & 3 mm


ASME Classification Of Filler Wire

SS Filler Wire:

SFA-5.9, ER 308, 308L, 316, 316L, 347, 309

LAS Filler Wire:

SFA 5.28, ER 70S A1, ER 80S B2, ER90S D2,

ER 80S Ni2

CS Filler Wire:

SFA- 5.18 , ER 70S2

C = 0.07%, Mn = 0.9% 1.4%, Si = 0.4 0.7%, P = 0.025%, S = 0.035%


Dos & Don'ts In GTAW

Always Connect

Electrode Ve

Keep Always Flow

Meter Vertical

Check & Confirm

Argon Purity

Clean Groove & Filler

wire With Acetone

Grind Tungsten Tip to

Point

Dont Strike Arc With

Electrode + Ve

Dont strike Arc Without

Argon Flow

Dont Strike Arc By

touching Tungsten Rod

Dont Touch Weld Pool

With Tungsten Rod

Dont Lift and break Arc

Dos Donts



Break The Arc Only By

Pedal Switch

Lift The Torch only After

5 Sec Of Arc Break.

Ensure Pre Purging &

Post Purging of 5Sec

Ensure Argon Flow &

Water Circulation To

Torch

When Arc is Stopped Dont

Lift Torch immediately.

Dont Weld With Blend

Tungsten Rod

Dont Weld With Argon

Leaking Torch

Dont Weld Without Water

Circulation

Dos Donts



Provide Back Purging For

Single Sided Full

Penetration Welds

Use N2 or Argon as Back

Purging Gas For CS &

LAS

Use Argon As Back

Purging Gas For SS &

Non Ferrous Alloys

Dont Weld Single Sided

Full Penetration Welds

Without Back Purging

Dont Use N2 As Back

Purging Gas For Non

Ferrous Alloys

Dont Empty Ag Cylinders

Fully.

Dos Donts

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Defects In GTAW

1. Cracks 2. Lack Of Fusion

3. Porosity 4. Undercut

5.Lack Of Penetration 6. Excess Penetration

7.Overlap 8. Suck Back

9. Under Flush 10. Burn Through

11. Tungsten Inclusion 11.Stray Arcing


Crack

Cause Remedy

1) Wrong Consumable

2) Wrong Procedure

3) Improper Preheat

4) Inadequate Thickness

In Root Pass

1) Use Right Filler Wire

2) Qualify Procedure

3) Preheat Uniformly

4) Add More Filler Wire

in root Pass

crack


Lack Of Fusion

Cause Remedy

1) Inadequate Current

2) Wrong Torch angle

3) Improper bead placement

1) Use Right Current

2) Train /Qualify welder

3) Train/Qualify Welder

Lack Of Fusion


PorosityCause Remedy

1) Impure Argon Gas

2) Argon Leak Within Torch

3) Defective Filler Wire

4) Wet surface of BM

5) Rusted / Pitted Filler wire

6) Improper Flow Of Argon

1) Replace Argon Cylinder

2) Replace Leaking Torch

3) Replace Filler Wire

4) Clean & Warm BM

5) Clean Filler Wire

6) Provide Gas lens

Porosity . .


Undercut

Cause Remedy

1) Excess Current

2) Excess Voltage

3) Improper Torch angle

1) Reduce the Current

2) Reduce Arc length

3) Train & Qualify the Welder

Under cut


Lack Of Penetration*

Cause Remedy

1) Excess Root Face

2) Inadequate Root opening

3) Over size Filler Wire

4) Wrong Direction of Arc


6) Improper weaving technique

1) Reduce Root Face

2) Increase Root Opening

3) Reduce Filler Wire size

4) Train / Qualify Welder


6) Train & Qualify Welder

LOP

* Applicable to SSFPW

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Excess Penetration*Cause Remedy

1)Excess root opening

2) Excess Current

3) Inadequate root face

4) Excess Weaving

5) Wrong Direction Of Arc

1) Reduce root gap

2) Reduce Current

3) Increase Root face

4) Train Welder

5) Train Welder

Excess Penetration



Overlap

Cause Remedy

1) Wrong Direction Of Arc


3) Excess Filler Wire

1) Train & Qualify Welder

2) Increase Current

3) Reduce Filler Metal

Overlap


Suck Back*

Cause Remedy

1) Excess weaving in root

2) Excess Current

3) Inadequate root face

4) Wrong Electrode angle

1) Reduce weaving

2) Reduce Current

3) Increase root face


Suck Back

* Applicable to SSFPW in 4G, 3G & 2G


Under flushCause Remedy

1) Inadequate weld beads in

final layer

2) Inadequate understanding on

weld reinforcement

3) Wrong selection of filler wire

size

1) Weld some more beads

in final layer

2) Train / Qualify welder


Under flush


Burn through*

Cause Remedy

1) Excess Current

2) Excess Root opening

3) Inadequate Root face

4) Improper weaving


2) Reduce root opening



Burn trough

*Applicable to root pass


Tungsten InclusionCause Remedy

1) Ineffective HF

2) Improper Starting of Arc

3) Tungsten Tip Comes in

Contact With Weld

1) Rectify HF Unit

2) Never Touch Weld

With Tungsten Rod


Tungsten Inclusion

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Stray Arcing

Cause Remedy

1) HF Not In Operation

2) Inadequate Skill of Welder

1) Rectify HF Unit

2) Train the Welder

Arc Strikes


What Is GMAW ?

A Fusion Welding Process Semi Automatic

Arc Between Consumable Electrode &Work

Arc Generated by Electric Energy From a Rectifier / Thyrester / Inverter

Filler Metal As Electrode Continuously fed From Layer Wound Spool.

Filler Wire Driven to Arc By Wire Feeder through Welding Torch

Arc & Molten Pool Shielded by Inert Gas through Torch / Nozzle

Gas Metal Arc Welding

MIG Shielding Gas Ar / Ar + O2 / Ar + Co2

MAG Shielding Gas Co2

FCAW Shielding Gas Co2 With Flux cored

Wire

Note:- Addition of 1 5% of O2 or 5 10% of Co2 in Ar.

increases wetting action of molten metal

Power Source For MIG / MAG

Inverter- DC

Thyrister DC

Motor Generator DC

Rectifier DC

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Characteristic Of GMAW Power

Source

Constant V / Linear Characteristic

Appx. Horizontal

Curve

V1V2

A1 A2A

V

Current & Polarity

DC- Electrode +Ve

Stable Arc

Smooth Metal Transfer

Relatively Low Spatter

Good Weld Bead Characteristics

DC- Electrode Ve, Seldom Used

AC- Commercially Not In use

Accessories Of GMAW

Power Source

Wire Feed Unit

Shielding Gas Cylinder, Pressure gauges/

Regulator, Flow meter (Heater For Co2 )

Welding Torch

Water Cooling System (For Water cooled Torch)


Tools For GMAW

Head Screen With DIN 13 / 14 Dark Glass

Hand Wire Brush / Grinder With Wire Wheel

Cutting Pliers

Hand Gloves

Chipping Hammer / Chisel & hammer

Spanner Set

Cylinder Key

Anti-spatter Spray


GMAW Torch

Torch HandleSpring Conduit

Job

Arc

Gas Cup

Shielding Gas

Filler Wire - ElectrodeNozzle Tip

On / Off Switch

Equipment & Accessories

+

Wire Inside Spring Lining

Flow Meter

Welding Torch Wire Feeder

Shielding Gas

Cylinder

Pressure Regulator

Argon / Co2Shielding

Power Source

With Inductance

Work

Arc

Solenoid

Valve

Copper Cup

Wire

SpoolElectrode /

Wire

Shielding GasHeater

(Only For

Co2)

Contact Tip

Switch

Torch With Cable Max. 3Mtr

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34

Types Of Wire Feeding In

GMAW

Push Type Wire fed in to The torch by Pushing through Flexible

Conduit From A Remote Spool

Pull Type Feed Rollers Mounted on The Torch Handle Pulls the

Wire From A Remote spool

Self Contained Wire Feeder & The Spool On the Torch

Function Of Shielding Gas In

GMAW

Prevents Air contamination of weld Pool

Prevents Contamination During Metal Transfer

Increases fluidity of molten metal

Minimizes the spatter generation

Helps in even & uniform bead finish

Shielding Gases For GMAW

MIG: Argon Or Helium

For SS, CS, LAS & Non-ferrous Mt & Al

MIG: Ar + 1 to 2 % O2, Wire With Add. Mn & Si


MIG: Ar + 5 to 20 % Co2 Wire With Add. Mn & Si


MAG: Co2 With Solid Wire

For CS & LAS

FCAW: Co2 With Flux Cored Wire

For CS, LAS & SS Overlay

ASME Classification For CS

GMAW Wire

SFA 5.18 : - CS Solid Wire

ER 70 S 2, ER 70 S 3

ER 70 S 6, ER 70 S 7

SFA 5.20 :- CS Flux Cored Wire

E 71 T-1, E 71 T-2 ( Co2 Gas )

E 71 T-1M, E 71 T-2M ( Ar + Co2 Mix)

GMAW CS Wire

Generally Copper Coated

Prevents Oxidation / rusting in Storage

Promotes Electric Conductivity in Arcing

Available In Solid & Flux Cored

Size in mm 0.8, 1, 1.2, 1.6, 2, 2.4, 3

Manganese & Silicon ( Mn 1 2 %, Si Max 1%)

Act As Deoxidizing Agents

Eliminate Porosity

Increase Wetting Of Molten Pool

Metal Transfer In MIG

Short-Circuiting / Dip Transfer

Globular Transfer

Spray Transfer

4/3/2015

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GAS METAL ARC WELDING (GMAW)ALMOST REPLACING SMAW, FASTER, INTRODUCED IN 1940S,

DCRP GENERALLY EMPLOYED, CONTINUOUS WIRE FEEDING

MODES OF METAL TRANSFER

1

SPRAY

2

SHORT

CIRCUIT

3

GLOBULAR

4

BURIED ARC

5

PULSED

ARC

HIGH

VOLTAGE

HIGH

AMPERAGE

(WIRE FEED)

VERY LOW

VOLTAGE

MODERATE

WIRE FEED

BETWEEN 1&2

UNIQUE IN

GMAW,

HIGHER WIRE

FEED

PULSING

BETWEEN

MODES

DROPLETS-

DEEP Penet.

FOR THICK

COOLEST

MODE,

LEAST

Penetration.

FOR CARBON

STEELS, 6 TO

12 MM

HIGH SPPED,

LOW SPATTER,

DEEP Penet.,

FOR MS AND SS

NO GUN

OSCILLATI

ON

ARGON ST.

(FOR

NARROW)

75 % Ar +

25% CO2

90%Ar + 7.5%

CO2 +2.5% He

FOR

THICK TO

THIN, DISSIMILAR

Metal Transfer In MIG

Dip/Short Circuiting Globular Spray

CS Solid Wire 1.2 mm

Above230A

24 35 V

120 to 250A

16 24 V

Up to 120A

14 22V

Co2 or Ar Co2 or Ar Only Ar / Ar+O2

Short-Circuiting / Dip Transfer Wire In Contact With Molten Pool 20 to 200 times per

Second

Operates in Low Amps & Volts Less Deposition

Best Suitable for Out of Position Welding

Suitable for Welding Thin Sheets

Relatively Large opening of Root Can be Welded

Less Distortion

Best Suitable for Tacking in Set up

Prone to Get Lack of Fusion in Between Beads

Globular Transfer

Metal transferred in droplets of Size grater than

wire diameter

Operates in Moderate Amps & Volts Better

Deposition

Common in Co2 Flux Cored and Solid Wire

Suitable for General purpose Welding

Spray Transfer

Metal transferred in multiples of small droplets

100 to 1000 Droplets per Second

Metal Spray Axially Directed

Electrode Tip Remains pointed

Applicable Only With Inert Gas Shielding Not With Co2

Operates in Higher Amps & Volts Higher Deposition Rate

Not Suitable for Welding in Out of Position.

Suitable for Welding Deep Grooves

Pulsed Spray Welding

Power Source Provides Two different Current LevelsBackground and Peakat regular interval

Background & Peak are above and below the Average Current

Best Suitable for Full Penetration Open Root Pass Welding

Good Control on Bead Shape and Finish

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Synergic Pulse GMAW

Parameters of Pulsed Current (Frequency, Amplitude, Duration, Background Current) Related to Wire feed Rate

One Droplet detaches with each pulse

An Electronic Control unit synchronizes wire feed Rate with Pulse Parameters

Best Suitable for Most Critical Full Penetration Open Root Pass Welding

Good Control on Open Root penetration, Bead Shape and Finish


GASES PUROPOSE-

1.TO SHIELD MOLTEN PUDDLE FROM CONTAMINATION

2.CREATE A SMOOTH ELECTRICAL CONDUCTION

PATH FOR ELECTRONS IN ARC

SOME GASES (ARGON)MAKE SMOOTH PATH, BUT SOME RESISTS (CO2) PATH.

STRAIGHT ARGON FOR NARROW BEADS

98% Ar+ 2 OXYGEN FOR SPRAY,

He FOR COPPER, THICK Al (WITH Ar).

75 % Ar + 25% CO2 FOR SHORT CIRCUIT.,

STRAIGHT CO2 ECONOMICAL, BUT SPATTERING. 90%Ar + 7.5% CO2 +2.5% He FOR BURIED ARC, SS.

90% Ar + 10% He FOR AUTOMATIC V, WIRE FEED SYSTEMS

A CONSTANT VOLTAGE POWER SOURCE USED.


+ POINTS OF GMAW HIGH WELDING SPEED

NO NEED TO CHANGE ELECTRODES (ONLY WIRE SPOOL IN GMAW)

HAZ SMALL

VERY LITTLE SMOKE AND VERY LIGHT SiO2 SLAG(CALLED GLASS SLAG)

LEAST DISTORTION

EASE OF OPERATION (QUICK LEARNING)

GUN MANIPULATION EASIER

MOST FLEXIBLE PROCESS- VERSATILE

VERY FEW MACHINE ADJUSTMENTS FOR THICK TO THIN CHANGE

MS, MCS, TOOL STEEL GRADES, SS, COPPER, Al, Mg WELDED

FCAW, SAW, ESW- OTER FORMS OF GMAW

GMAW Process Variables Current

Voltage

Travel Speed

Stick Out / Electrode Extension

Electrode Inclination

Electrode Size

Shielding Gas & Flow Rate

Welding Position

Parameter For 1.2 FC Wire

Current 200 to 240 A

Voltage 22-24

Travel Speed 150 to 250 mm / min

Stick Out / Electrode Extension 15 to 20 mm

Electrode Inclination Back Hand Technique

Shielding Gas Co2, 12 L/Min

Parameter For 1.2 Solid Wire

Current 180 to 220 A

Voltage 20-22

Travel Speed 150 to 200 mm / min

Stick Out / Electrode Extension 10 to 20 mm

Electrode Inclination Back Hand Technique

Shielding Gas Co2 12 L/Min

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Results In Change Of Parameters

Increase In Current

More deposition, More Penetration, More BM Fusion

Increase In Voltage

More Weld Bead Width, Less Penetration, Less Reinforcement, Excess Spatter

Increase In Travel Speed

Decrease in Penetration, Decrease in Bead Width,

Decrease In Gas Flow rate

Results In porosity

Long Stick Out / Electrode Extension

Excess Weld Deposit With Less Arc intensity, Poor Bead Finish, Shallow Penetration

Common Defects In GMAW

1. Porosity 2. Spatters

3. Lack Of Fusion 4. Under Cut

5. Over Lap 6. Slag

7. Crack 8. Lack Of Penetration

9. Burn Through 10. Convex Bead

11. Unstable Arc 12. Wire Stubbing

Porosity

Cause Remedy

1) Less Mn & Si In Wire

2) Rusted / Unclean BM / Groove

3) Rusted wire

4) Inadequate Shielding Gas

1) Use High Mn & Si Wire

2) Clean & warm the BM

3) Replace the Wire

4) Check & Correct Flow Rate

Porosity . .

Spatters

Cause Remedy

1) Low Voltage

2) Inadequate Inductance

3) Rusted BM surface

4) Rusted Core wire

5) Quality Of Gas

1) Increase Voltage

2) Increase Inductance

3) Clean BM surface

4) Replace By Rust Free wire

5) Change Over To Ar + Co2

Spatters

Lack Of Fusion

Cause Remedy


2) Inadequate Voltage

3) Wrong Polarity

4) Slow Travel Speed

5) Excessive Oxide On Joint


2) Use Right Voltage

3) Connect Ele. + Ve

4) Increase Travel speed

5) Clean Weld Joint

Lack Of Fusion

Undercut

Cause Remedy

1) Excess Voltage

2) Excess Current

3) Improper Torch angle

4) Excess Travel Speed

1) Reduce Voltage

2) Reduce Current

3) Train & Qualify the Welder

4) Reduce Travel Speed

Under cut

4/3/2015

38

Overlap

Cause Remedy

1) Too Long Stick Out

2) Inadequate Voltage

1) Reduce Stick Out

2) Increase the Voltage

Overlap

Slag

Cause Remedy

1) Inadequate Cleaning




1) Clean each bead




Slag

Crack

Cause Remedy

1) Incorrect Wire Chemistry

2) Too Small Weld Bead

3) Improper Preheat

4) Excessive Restrain

1) Use Right Wire

2) Increase wire Feed

3) Preheat Uniformly

4) Post heating or ISR

crack

Lack Of Penetration*

Cause Remedy

1) Too Narrow Groove Angle

2) Inadequate Root opening

3) Too Low Welding current


5) Puddle Roll In Front Of Arc

6) Long Stick Out

1) Widen The Groove

2) Increase Root Opening

3) Increase Current


5) Correct Torch Angle

6) Reduce Stick Out

LOP


Burn through*

Cause Remedy

1) Excess Current

2) Excess Root opening

3) Inadequate Root face

4) Too Low Travel Speed

5) Quality Of Gas


2) Reduce root opening


4) Increase Speed

5) Use Ar + Co2

Burn trough*Applicable to root pass

Convex Bead FinishCause Remedy

1) Low Current

2) Low Voltage

3) Low Travel Speed

4) Low Inductance

5) Too Narrow Groove

1) Increase Current

2) Increase Voltage

3) Increase Travel Speed

4) Increase Inductance

5) Increase Groove Width

Uneven bead finish

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Unstable arc

Cause Remedy

1) Improper Wire Feed

2) Improper Gas Flow

3) Twisted Torch Conduit

1) Check Wire Feeder

2) Check Flow Meter

3) Straighten Torch Cab

Wire Stubbing

Cause Remedy

1) Too Low Voltage

2) Too High Inductance

3) Excess Slope

4) Too Long Stick Out

1) Increase Voltage

2) Reduce Inductance

3) Adjust Slope

4) Reduce Stick Out

Important Terminology used in

Critical Welding

Preheating

Post Heating or Dehydrogenation

Intermediate Stress leaving

Inter pass Temperature

Post Weld Heat Treatment

Preheating

Heating the base metal along the weld joint to a predetermined minimum temperature immediately before starting the weld.

Heating by Oxy fuel flame or electric resistant coil

Heating from opposite side of welding wherever possible

Temperature to be verified by thermo chalks prior to starting the weld

Why Preheating?

Preheating eliminates possible cracking of weld and HAZ

Applicable to

Hardenable low alloy steels of all thickness

Carbon steels of thickness above 25 mm.

Restrained welds of all thickness

Preheating temperature vary from 75C to 200C

depending on hardenabi

10 MJfirst.pdf

Documents

nitc 7welding3

welding progression

g pahorizontal

g pfvertical

g pepipe

g pgoverhead

g pfpipe

g hl045pipe