Chapter 32 Resistance Welding and Solid

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Chapter 32 Resistance Welding and Solid
MET 33800 Manufacturing Processes
Chapter 32
Resistance Welding and Solid‐
State Welding
 Before you begin: Turn on the sound on your computer. There is audio to accompany this presentation.
Materials Processing
Chapters 11-13
Chapters 20-27
Chapters 15-17
Chapters 30-33
Chapter 31 - 2
Classification of Processes
Figure 30-1 Classification of common welding processes
along with their AWS designations.
Chapter 32 - 3
1
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 Generation
Heat 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 Resistance
Resistance (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
2
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
3
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 postheating operations..
Chapter 32 - 11
Power Supply
Example of programmable resistance welder controller.
Chapter 32 - 12
4
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
5
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
6
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
7
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)
Figure 32-8 Seam welds made
with overlapping spots of varied
spacing.
Schematic representation of
the seam-welding process.
Chapter 32 - 23
Seam Welds (RSEW)
Examples of resistance seam
welding (RSEW) equipment.
Chapter 32 - 24
8
Seam Welds (RSEW)
Figure 32-10 Using highfrequency AC current to produce a
resistance seam weld in buttwelded 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
9
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 Welding
Examples 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
10
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
Example of a Transgun
Chapter 32 - 32
Classification of Processes
Figure 30-1 Classification of common welding processes
along with their AWS designations.
Chapter 32 - 33
11
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
12
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
13
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-bonded
refrigerator freezer evaporators. Note the
raised channels that have been formed
between the roll-bonded sheets.
Chapter 32 - 42
14
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
15
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
16
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
17
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 frictionstir 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 frictionstir 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
18
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
19
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
20
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
21
Diffusion Welding (DFW)

Process is slow and applications are limited to lowvolume 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
22
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
The End – See Oncourse for Videos
Chapter 32 - 69
23

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