Module 1 - Processes Review. Process Review Lesson Objectives When you finish this lesson you will understand: The basic principles of the most common.

Module 1 - Processes Review

Process Review

Lesson ObjectivesWhen you finish this lesson you will understand:• The basic principles of the most common resistance welding processes

Learning Activities1. Review the contents

of WE6022. Look up Keywords3. View Slides; 4. Read Notes, 5. Listen to lecture6. Do on-line

workbook

KeywordsResistance Spot Weld, Resistance Projection Weld, Resistance Seam Weld, Flash Weld, Upset Butt Weld, Electric Resistance Weld, High Frequency Weld, Electro-Brazing

Introduction to Resistance Spot Welding

Top ElectrodeWater

WeldNugget

Bottom Electrode

Resistance

Dis

tan

ce

Typical Equipment of Resistance Spot Welding

(a) (b)[Reference: Welding Process Slides, The Welding Institute]

Process Operation of Resistance Spot Welding

[Reference: Welding Process Slides, The Welding Institute]

Advantages of Resistance Spot Welding

Adaptability for Automation in High-Rate

Production of Sheet Metal Assemblies

High Speed

Economical

Dimensional Accuracy

Limitations of Resistance Spot Welding

Difficulty for maintenance or repair Adds weight and material cost to the product, compared with

a butt joint

Generally have higher cost than most arc welding equipment

Produces unfavorable line power demands

Low tensile and fatigue strength The full strength of the sheet cannot prevail across a spot

welded joint

Eccentric loading condition

Turn to the person sitting next to you and discuss (1 min.):• The heating in resistance spot welding is related to the resistance by the equation H=I2Rt. The resistance can be both bulk and surface resistance. If we change from welding steel to welding aluminum what changes in resistance do you expect?

Introduction to Projection Welding

(a) (b) (c) (d)

[Reference: Welding Handbook, Volume 2, p.566, AWS]

Advantages of Projection Welding

• A number of welds can be made simultaneously in one welding cycle of the machine

• Less overlap and closer weld spacing are possible• 1 < Thickness ratio < 6• Smaller in size than spot welding• Better appearance on the side without projection• Less electrode wear than spot welding• Oil, rust, scale, and coatings are less of a problem

than spot welding

Limitations of Projection Welding

• Require an additional operation to form projections

• With multiple welds, require accurate control of projection height and precise alignment of the welding dies

• Thickness limitation for sheet metals

• Require higher capacity equipment than spot welding

Examples of Various Projection Designs

(a)(b)

(c) (d) (e)

[Reference: Welding Handbook, Volume 2, p.562, AWS]

Examples of Various Projection Designs (CONT.)

(f) (g) (h)

(i) (j)[Reference: Welding Handbook, Volume 2, p.562, AWS]

Turn to the person sitting next to you and discuss (1 min.):• As projections collapse, the welding electrode and head must move rapidly to keep up with the projection collapse. What things might hinder the heads rapid movement? What would you do to design a more rapid moving head?

Introduction to Resistance Seam Welding

Upper Electrode Wheel

Workpiece

Lower Electrode Wheel

Throat

Knurl or FrictionDrive Wheel

Roll Spot Weld

Overlapping SeamWeld

Continuous SeamWeld

[Reference: Welding Handbook, Volume 2, p.553, AWS]

Mash Seam WeldSlightly LappedSheets Wide, Flat

Electrodes

Weld Nuggets

Before welding After Welding

[Reference: Welding Handbook, Volume 2, p.554, AWS]

Introduction to Flash Welding

[Reference: Welding Process Slides, The Welding Institute]

Basic Steps in Flash Welding

(a) (c)

(b) (d)

Electrodes

[Reference: Welding Handbook, Volume 2, p.583, AWS]

Position and Clamp the Parts

Apply Flashing Voltageand Start Platen Motion

Flash

Upset and Terminate Current

Equipment Example of Flash Welding

[Reference: Welding Process Slides, The Welding Institute]

Advantages of Flash Welding

• Flexible cross sectioned shapes

• Flexible positioning for similar cross section parts

• Impurities can be removed during upset acts• Faying surface preparation is not critical except for large

parts

• Can weld rings of various cross sections

• Narrower heat-affected zones than those of upset welds

Limitations of Flash Welding

• Produce unbalance on three-phase primary power lines

• The ejected molten metal particles present a fire hazard

• Require special equipment for removal of flash metal• Difficult alignment for workpieces with small cross

sections

• Require almost identical cross section parts

Common Types of Flash Welds

Cross Section After Welding

Transformer

Fixed Platen Movable Platen

Dies

Axially Aligned Weld

[Reference: Welding Handbook, Volume 2, p.589, AWS]

Common Types of Flash Welds (CONT.)

Cross Section After WeldingFixed Platen Movable Platen

Transformer

Miter Weld

[Reference: Welding Handbook, Volume 2, p.589, AWS]

Common Types of Flash Welds (CONT.)

Cross Section After WeldingFixed Platen Movable Platen

Transformer

Ring Weld

[Reference: Welding Handbook, Volume 2, p.589, AWS]

Turn to the person sitting next to you and discuss (1 min.):• In flash welding of steel, the iron burns to iron oxide during flashing and removes oxygen from the flashing interface. The free energy of formation of iron oxides at 1500K are about –40 kcal/gram-atom of oxygen. The free energy of formation of titanium oxides at 1500K is about –90 kcal/gram-atom oxygen. What effect do you suppose this would have on the flash welding operation?

Introduction to Upset Welding

Finished Upset Weld

Heated Zone

To Welding Transformer

Clamping Die

UpsettingForce

Movable Part

Clamping Die

Stationary Part

[Reference: Welding Handbook, Volume 2, p.598, AWS]

Typical Mill Forms and Products of Upset Welding

[Reference: Welding Handbook, Volume 2, p.600, AWS]

Resistance Tube Welding (ERW)

W. Stanley, Resistance WeldingMcGraw-Hill, 1950

High Frequency Welding Applications

[Reference: Welding Handbook, Volume 2, p.653, AWS]

Tube Butt Seam Tube Butt Seam Tube Mash Seam

HF

HF

HFInduction Coil

High Frequency Welding Applications (CONT.)

Strip Butt T-Joint

Spiral Tube

Spiral Tube Fin

HFHF

HFHF

[Reference: Welding Handbook, Volume 2, p.653, AWS]

High Frequency Welding Applications (CONT.)

Projection Seam

Pipe Butt Bar Butt

HF

HF

HF

InductionCoil

[Reference: Welding Handbook, Volume 2, p.653, AWS]

Advantages of High-Frequency Welding

• Produce welds with very narrow heat-affected zones

• High welding speed and low-power consumption

• Able to weld very thin wall tubes

• Adaptable to many metals

• Minimize oxidation and discoloration as well as

distortion

• High efficiency

Limitations of High-Frequency Welding

• Special care must be taken to avoid radiation interference

in the plant’s vicinity

• Uneconomical for products required in small quantities

• Need the proper fit-up

• Hazards of high-frequency current

Some Products of High-Frequency Welding

[Reference: Welding Handbook, Volume 2, p.665, AWS]

Turn to the person sitting next to you and discuss (1 min.):• If you were going to make tubing or pipe materials what might be the criteria when you would select ERW over High Frequency Welding?

Electro-brazing

W. Stanley, Resistance WeldingMcGraw-Hill, 1950