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Chapter 32
Resistance Welding and Solid‐State Welding
MET 33800 Manufacturing Processes
Materials Processing
Chapters 15-17
Chapters 20-27
Chapters 30-33
Chapters 11-13
Chapter 31 - 2
Classification of Processes
Figure 30-1 Classification of common welding processes along with their AWS designations.
Chapter 32 - 3
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Resistance Welding
Uses both heat and pressure to induce coalescence.
Heat is generated through electrical resistance of welding circuit.
Pressure is applied to control contact resistance at the interface and then induce coalescence after melting has occurred.
Chapter 32 - 4
Heat GenerationHeat is generated through resistance:
H = I2 R t where: H = total heat (joules)
I = current (amperes)
R = resistance (ohms)
t = time (seconds)
Figure 32-1 The basic resistance welding circuit.
Chapter 32 - 5
Creating ResistanceResistance (R) comes from three sources:
Bulk Resistance – Includes materials and electrodes. Material’s resistance determined by conductivity and thickness. Electrode resistance is usually low.
Contact Resistance – Resistance between electrodes and workpiece which is controlled by electrode shape, size, material, and pressure.
Faying Surface Resistance – Resistance of surfaces to be joined. Should be the highest resistance to generate the highest temperature concentration. Function of surface finish, contaminants, pressure, & contact area.
Chapter 32 - 6
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Heat Generation Heat is generated at the point of maximum resistance.
Critical to keep unwanted resistances small as possible.
Essential to keep bulk resistance and contact resistance as low as possible. These take away from the process and can create negative effects.
Faying Surface Resistance is the one used to create enough heat for coalescence between the materials.
Chapter 32 - 7
Heat Generation
Figure 32-2 The desired temperature distribution across the electrodes and workpiece during resistance welding.
Chapter 32 - 8
Faying Surface Resistance Faying surface resistance must be controlled to produce
quality welds.
This resistance is a function of the several factors:
Quality of the surfaces – surface finish and/or roughness.
Presence of non-conductive scale, dirt and other contaminants.
Pressure
Contact area
Chapter 32 - 9
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Pressure Because the pressure induces a forging action,
resistance welds can be produced at lower temperatures than other welding processes.
If too little pressure is applied, contact resistance will be high and surface burning and pitting will occur.
If too much pressure is applied, molten or softened metal may be expelled from between the faying surfaces.
Chapter 32 - 10
Current Temperature is primarily dependent on current, both
magnitude and duration.
Production resistance welders programmed to follow specific cycle of pressure and current.
Figure 32-3 A typical current and pressure cycle for resistance welding. This cycle includes forging and post-heating operations..
Chapter 32 - 11
Power Supply
Example of programmable resistance welder controller.
Chapter 32 - 12
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Power Supply Since overall resistance is usually low, high currents are
required. Remember H = I2Rt.
Power transformers convert line high voltage and low current into low voltage and high current for welding:
Voltage: 0.5 to 10 vdc
Current: up to 100,000 A
Chapter 32 - 13
Resistance Welding Processes Resistance Spot Welding (RSW) is used extensively in
the automotive industry.
Each automobile may contain anywhere from 2000 –5000 spot welds
Typical weld size: - inch dia.
Primarily used on thin sheets of steel.
Chapter 32 - 14
Profile of a Spot Weld Quality spot welds will look like a
nugget.
There will be little or no indentation of the metal surfaces.
Upon tensile test or tear test, metal immediately surrounding weld should be first to fail.
Chapter 32 - 15
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Profile of a Spot Weld
Figure 32-5 A spot-weld nugget between two sheets of aluminum alloy.
Figure 32-6 Tear test of a satisfactory spot weld, showing how failure occurs outside of the weld.
Chapter 32 - 16
Equipment Different variations of RSW equipment can be purchased
to meet the production requirements.
Light-duty uses RSW uses a rocker-arm machine.
Larger equipment used in auto industry may be able to produce up to 200 simultaneous welds in less than 60 seconds.
Portable spot welding equipment is available to extend application of the process where it was originally limited.
Transguns integrate the transformer/power supply into the welding gun.
Chapter 32 - 17
Equipment
Examples of spot-welding equipment.
Chapter 32 - 18
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Equipment Electrodes must:
Reach area to be welded
Conduct current
Apply pressure
Help dissipate heat
Resistance Welder Manufacturers Alliance (RWMA/AWS), has standardized electrodes geometries and materials.
Electrode materials typically copper-based alloys, refractory materials and refractory-metal composites.
Chapter 32 - 19
Unique Characteristic of RSW One distinct advantage of resistance spot welding is the
ability to join dissimilar metals.
Most other welding processes require the parent or base materials to be the same.
RSW can also join metals of varying thickness. Electrode size and/or conductivity used to control temperature and insure even fusion.
Table 32.1 (next slide) shows the joining capabilities of dissimilar metals.
Chapter 32 - 20
Metal Combinations
Chapter 32 - 21
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Seam Welds (RSEW)Resistance Seam Welding (RSEW) is similar to spot welding. Variations:
By overlapping the spot welds, the resulting series of welds can be used to form a seam. Used to produce gas or liquid-tight vessels.
Also can be used to create butt welds by rolling plate into tube and joining ends. Used extensively in production of pipe and tubing.
Chapter 32 - 22
Seam Welds (RSEW)
Schematic representation of the seam-welding process.
Figure 32-8 Seam welds made with overlapping spots of varied spacing.
Chapter 32 - 23
Seam Welds (RSEW)
Examples of resistance seam welding (RSEW) equipment.
Chapter 32 - 24
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Seam Welds (RSEW)Figure 32-10 Using high-frequency AC current to produce a resistance seam weld in butt-welded tubing. Arrows from the contacts indicate the path of the high-frequency current.
Chapter 32 - 25
Projection Welding (RPW) For mass production operations, two major limitations to
spot welding are present:
Small electrodes require frequent attention.
Process is only designed to create 1 weld at a time (at each electrode).
Projection welding can be used to overcome these limitations.
Projection welding can also be used to attach hardware such as bolts and nuts to other metal parts.
Chapter 32 - 26
Projection Welding Dimples are embossed into the workpiece wherever
welds are desired:
Different sizes and shapes can be employed.
Multiple weld spots can be produced simultaneously.
Electrodes are then replaced by larger area electrodes in the press machine:
Eliminates the need for single, small-size electrodes capable of producing only one weld at a time.
Chapter 32 - 27
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Projection Welding
Figure 32-11 Principle of projection welding (a) prior to application of current and pressure and (b) after formation of the welds.
Chapter 32 - 28
Projection WeldingExamples of the
projection welding process and equipment.
Examples of fasteners used in projection welding. Note the
dimples.
Chapter 32 - 29
RW Advantages Very rapid.
Equipment can be fully automated.
Conserve material (no filler, shielding gases, flux).
Minimal distortion of welded parts.
Skilled operators (welders) not needed.
Dissimilar metals can be joined.
High degree of reliability and reproducibility can be achieved.
Chapter 32 - 30
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RW Disadvantages Equipment has high initial cost.
Limitations to the thickness of materials that can be joined (generally less than ¼ in.).
Skilled maintenance personnel needed to service and maintain equipment.
Some materials and/or surfaces will require special preparation prior to welding.
Chapter 32 - 31
RW Process Summary
Chapter 32 - 32
Example of a Transgun
Classification of Processes
Figure 30-1 Classification of common welding processes along with their AWS designations.
Chapter 32 - 33
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Solid-State Welding Processes Forge welding
Forge seam welding
Cold welding
Roll welding or roll bonding
Friction or inertia welding
Friction stir welding
Ultrasonic welding
Diffusion welding
Explosive welding
Chapter 32 - 34
Solid-State Welding Processes Forge welding (FOW)
Forge seam welding
Cold welding
Roll welding or roll bonding
Friction or inertia welding
Friction stir welding
Ultrasonic welding
Diffusion welding
Explosive welding
Chapter 32 - 35
Forge Welding (FOW) Most ancient of the welding processes.
Has historic and practical value.
Helps us to understand how and why modern welding processes were developed.
Key historic examples:
Armor makers
Blacksmiths
Chapter 32 - 36
13
Forge Welding (FOW)Very crude processes:
Uncertainty of heat source
No way to measure temperature
Judged by color
Difficult to maintain metal cleanliness
Great amount of skill required
Results were highly variable
Chapter 32 - 37
Solid-State Welding Processes Forge welding
Forge seam welding (FOW)
Cold welding
Roll welding or roll bonding
Friction or inertia welding
Friction stir welding
Ultrasonic welding
Diffusion welding
Explosive welding
Chapter 32 - 38
Forge Seam Welding (FOW) Heated strips of steel are formed
into a cylinder and then edges are pressed into either a lap or butt configuration.
Mostly been replaced by other welding processes.
Used primarily in the manufacture of pipe.
Discussed in detail in chapter 17.
Chapter 32 - 39
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Solid-State Welding Processes Forge welding
Forge seam welding
Cold welding (CW)
Roll welding or roll bonding
Friction or inertia welding
Friction stir welding
Ultrasonic welding
Diffusion welding
Explosive welding
Figure 32-12 Small parts joined by cold welding.
Chapter 32 - 40
Cold Welding (CW) Variation of forge welding except uses no heat.
Produces metallurgical bonds by means of cold plastic deformation:
Surfaces must be cleaned and placed in contact
Placed in localized pressure sufficient to cause 30 –50% plastic deformation
Process is generally confined to joining small parts from highly ductile materials:
Example: crimping of electrical connectors.
Chapter 32 - 41
Solid-State Welding Processes Forge welding
Forge seam welding
Cold welding (CW)
Roll welding or roll bonding (ROW)
Friction or inertia welding
Friction stir welding
Ultrasonic welding
Diffusion welding
Explosive welding
Figure 32-13 Examples of roll-bondedrefrigerator freezer evaporators. Note the raised channels that have been formed between the roll-bonded sheets.
Chapter 32 - 42
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Roll Welding or Roll Bonding Used to join two or more sheets or plates of metal.
Surfaces must be clean and contaminant free for welding to occur.
Accomplished by passing sheets simultaneously through rolling mill.
Can be performed hot or cold.
Chapter 32 - 43
Roll Welding or Roll Bonding Examples of roll welding include:
Alclad – corrosion resistance aluminum bonded to high-strength aluminum.
Steel w/stainless steel cladding.
U.S. coins.
Variation used to create refrigerator freezer panels:
Uses special coating that prevents bonding
Where coating is used, bonding does not occur
These regions can then be used to flow coolant
Chapter 32 - 44
Solid-State Welding Processes Forge welding
Forge seam welding
Cold welding (CW)
Roll welding or roll bonding
Friction and inertia welding (FRW)
Friction stir welding
Ultrasonic welding
Diffusion welding
Explosive welding
Chapter 32 - 45
16
Friction & Inertia Welding (FRW) Heat required to produce the joint is generated by friction
heating at the interfaces.
Surfaces are square-cut, smooth.
One piece is held stationary.
Second piece is mounted in motor-driven chuck and rotated at high speed.
Pieces brought in contact and pressure applied.
Contact friction quickly generates elevated temperatures.
Softened metal is squeezed out to form flash.
Oxides and contaminants are also expelled in the flash.
Chapter 32 - 46
Friction & Inertia Welding (FRW) Ideal for joining dissimilar metals.
Good for metals with very different melting points.
Inertia welding is variation:
Part is attached to rotating flywheel.
Motor is used to bring part up to desired speed and then detached from motor.
Pressure is applied between parts and kinetic energy is used to create friction and weld.
Weld is completed with pressure continuing to be applied after rotation has stopped.
Chapter 32 - 47
Friction & Inertia Welding (FRW)
Figure 32-14 Sequence for making a friction weld.
(a) Components with squares surfaces are inserted into a machine where one part is rotated and the other is held stationary.
(b) The components are pushed together with a low axial pressure to clean and prepare the surfaces.
(c) The pressure is increased, causing an increase in temperature, softening, and possibly some melting.
(d) Rotation is stopped and pressure is increased rapidly, creating a forged joint with external flash.
Chapter 32 - 48
17
Friction & Inertia Welding (FRW)
Figure 32-15 Schematic diagram of the equipment used for friction welding.
Figure 32-16 Schematic representation of the various steps in inertia welding. The rotating part is now attached to a large flywheel.
Chapter 32 - 49
Solid-State Welding Processes Forge welding
Forge seam welding
Cold welding (CW)
Roll welding or roll bonding
Friction and inertia welding
Friction stir welding (FSW)
Ultrasonic welding
Diffusion welding
Explosive welding
Chapter 32 - 50
Friction Stir Welding (FSW) Used to make butt welds between plates of lower
melting-point metals as well as thermoplastic polymers.
Relatively new process – 1991.
No filler metal or shielding gas needed.
Total heat input and distortion are low.
Can be performed in any position.
Requires access to only one side of the plate.
Weld speed is slower than most fusion processes.
Chapter 32 - 51
18
Friction Stir Welding (FSW) Frictional heat is generated by non-consumable probe
rotated at high speed between butting edges of rigidly clamped plates.
Plasticized region is created, softened material flows to the back of the advancing probe and coalesces to form solid-state bond.
Used in aircraft industry.
Plates up to 2 in. have been welded from a single-side.
Chapter 32 - 52
Friction Stir Welding (FSW)Figure 32-18 Schematic of the friction-stir welding process. The rotating probe generates frictional heat, while the shoulder provides additional friction heating and prevents expulsion of the softened material from the joint.
Chapter 32 - 53
Friction Stir Welding (FSW)
Figure 32-19 (a) Top surface of a friction-stir weld joining 1.5 mm and 1.65 mm thick aluminum sheets with 1500 rpm pin rotation. The welding tool has traversed left-to-right of the photo. (b) Metallurgical cross section through an alloy 356 aluminum casting that has been modified by friction-stir processing.
Chapter 32 - 54
19
Friction Stir Welding (FSW)
Chapter 32 - 55
Solid-State Welding Processes Forge welding
Forge seam welding
Cold welding (CW)
Roll welding or roll bonding
Friction and inertia welding
Friction stir welding
Ultrasonic welding (USW)
Diffusion welding
Explosive welding
Chapter 32 - 56
Ultrasonic Welding (USW) Coalescence is produced by localized application of high
frequency shear vibrations (10k – 200K Hz).
Surfaces are held together under light pressure.
Some increase in temperature, but does not exceed ½ the melting point (on absolute scale).
Chapter 32 - 57
20
Ultrasonic Welding (USW) Process is restricted to lap joint welding of thin materials
(sheet, foil, wire).
Maximum thickness is 0.100 in for aluminum or 0.040 in. for harder materials.
Particularly valuable for joining dissimilar metals (table 32-4).
Can also be used to join metals with some non-metals and with plastics.
Chapter 32 - 58
Ultrasonic Welding (USW)
Chapter 32 - 59
Ultrasonic Welding (USW)
Figure 32-20 Diagram of the equipment used in ultrasonic welding.
Chapter 32 - 60
21
Solid-State Welding Processes Forge welding
Forge seam welding
Cold welding (CW)
Roll welding or roll bonding
Friction and inertia welding
Friction stir welding
Ultrasonic welding (USW)
Diffusion welding (DFW)
Explosive welding
Chapter 32 - 61
Diffusion Welding (DFW) Occurs when properly prepared surfaces are maintained
in contact under sufficient pressure, temperature, and time.
Primary bonding mechanism is atomic diffusion.
Used to join dissimilar materials and composite materials.
Furnaces with protective or inert atmospheres can be used to join reactive materials such as titanium, beryllium, and zirconium.
Chapter 32 - 62
Diffusion Welding (DFW)Quality of weld depends on:
Temperature.
Time at temperature.
Pressure.
Surface condition of the material.
Possible use of intermediate material layers which can either promote diffusion or prevent the formation of undesirable intermetallic compounds.
Chapter 32 - 63
22
Diffusion Welding (DFW) Process is slow and applications are limited to low-
volume applications.
Practical example: permanent joining of gage blocks (no heat necessary in this case).
Example of a diffusion welded part.
Chapter 32 - 64
Solid-State Welding Processes Forge welding
Forge seam welding
Cold welding (CW)
Roll welding or roll bonding
Friction and inertia welding
Friction stir welding
Ultrasonic welding (USW)
Diffusion welding
Explosive welding (EXW)
Chapter 32 - 65
Explosive Welding (EXW) Primarily used to bond sheets of corrosion-resistant
metal to heavier plates of base metal (cladding operation).
Particular use when large areas are involved.
Base metal is positioned on rigid base.
Top sheet is inclined to it with small open angle.
Explosive material is placed on top of two layers.
Detonation takes place in progressive wave beginning where materials touch.
Chapter 32 - 66
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Explosive Welding (EXW) Bond strength is high.
Plates can be subsequently processes (i.e. rolling).
Dissimilar metals can be joined.
Figure 32-21 (Left) Schematic of the explosive welding process. (Right) Explosive weld between mild steel and stainless showing the characteristic wavy interface.
Chapter 32 - 67
Explosive Welding (EXW)
Chapter 32 - 68
Chapter 32 - 69
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