1. Chapter 32: Resistance and Solid-State Welding Processes
DeGarmo’s Materials and Processes in Manufacturing

2. 32.1 Introduction Electrical resistance heating to form the joint.
Create joints without any melting of the workpiece or filler material, know as solid –state welding process.

3. 32.2 Theory of Resistance Welding
Both heat and pressure are used to induce coalescence.
Electrodes contact the material, and electrical resistance heating is used to raise the temperature of the workpiece and the interface between them.
H=I2Rt
H = total heat input in joules
I = current in amperes
R = electrical resistance in ohms
t = time in seconds

4. Basic Resistance Welding
FIGURE 32-1 The basic resistance welding circuit.
Total resistance:
The bulk resistance of the electrode and workpieces.
The contact resistance between the electrode and the workpieces.
The resistance between the surfaces to be joined, known as the faying surfaces.

5. Resistance Welding Temperature Distribution
FIGURE 32-2 The desired
temperature distribution across
the electrodes and workpieces
during resistance welding.
Water cooling is usually used to keep the electrode temperature low and thereby extend their useful life.

6. Current and Pressure for Resistance Welding
FIGURE 32-3 A typical current and pressure cycle for resistance welding. This cycle includes forging and postheating operations.
Applying pressure promotes a forging action, so resistance welds can be produced at lower temperatures than welds made by other processes.

7. 32.3 Resistance Welding Processes
Resistance spot welding
Resistance seam welding
Projection welding
Mass production

8. Schematic of Resistance Spot Welding (RSW)
FIGURE 32-4 The
arrangement of the electrodes
and workpieces in resistance
spot welding.

9. Microstructure of a Resistance Weld
FIGURE 32-5 A spot-weld nugget between two sheets of 1.3-mm (0.05-in.) aluminum alloy. The nugget is not symmetrical because the radius of the upper electrode is greater than that of the lower electrode. (Courtesy Lockheed Martin Corporation, Bethesda, MD.)

10. Tear Test FIGURE 32-6 Tear test of a satisfactory spot
weld, showing how failure occurs outside of
the weld.

11. Spot-Welding Equipment
FIGURE 32-7 Single-phase,
air-operated, press-type
resistance welder with
microprocessor control.
(Courtesy Sciaky Inc., Chicago, IL.)
Rocker-arm machine: for light-production work where complex current-pressure cycles are not required.
Press-type welder: for larger spot welds used at high production rates.

12. Spot Welding Application
Monel: Alloy of Nickel, Copper, Iron and Manganese, with antacidity

13. Resistance Seam Welding (RSEW)
FIGURE 32-8 Seam welds
made with overlapping spots
of varied spacing. (Courtesy
Taylor-Winfield Corporation,
Brookfield, OH.)
Gas- or liquid-tight welding
Resistance butt welding

14. Schematic of Seam Welding
FIGURE 32-9 Schematic
representation of the
seam-welding process.
those

15. Tube Welding FIGURE 32-10 Using high-Squeeze roll
frequency AC current to produce
a resistance seam weld in buttwelded
tubing. Arrows from the
contacts indicate the path of the
high-frequency current

16. Projection Welding
FIGURE Principle of
projection welding (a) prior to
application of current and
pressure and (b) after formation
of the welds.
For mass-production operation, not only one spot weld at a time.

17. 32.4 Advantages and Limitations of Resistance Welding
Rapid
Fully automated
Conserve material, no filler metal, shielding gases, or flux
Minimal distortion
Skilled operation are not required
Dissimilar metals can be easily joined
High degree of reliability and reproducibility

18. 32.4 Advantages and Limitations of Resistance Welding (continued)
High initial cost
Limitation to thickness of material (less than 6mm)
Both sides of the joint require to apply the proper electrode force or pressure
Skilled maintenance on servicing the equipment
Some materials need special preparation prior to welding

19. Process Summary for RW

20. 32.5 Solid-State Welding Processes
Forge welding
Forge-seam welding
Cold welding
Roll welding or roll bonding
Friction welding and inertia welding
Friction stir welding
Ultrasonic welding
Diffusion welding
Explosive welding

21. Forge Welding (FOW) The most ancient of the welding process
Using a charcoal forge, the blacksmith heated the pieces to be welded to a practical forging temperature (by color) and then prepared the ends by hammering (hammer and anvil) so that they could be properly fitted together.

22. Forge-Seam Welding
Still used in the manufacture of pipe – a heated strip of steel is first formed into a cylinder, and the edges are simply pressed together in either a lap or a butt configuration.
Welding is the result of pressure and deformation.

23. Cold Welding
FIGURE Small parts joined by cold welding. (Courtesy of Koldweld Corporation, Willoughby, OH.)
A variation of forge welding uses no heating but produces metallurgical bonds by means of room-temperature plastic deformation.

24. Roll Welding or Roll-Bonding (ROW)
Two or more sheets or plates of metal are joined by passing them simultaneously through a rolling mill.
Perform either hot or cold and can be used to join either similar or dissimilar metals.
FIGURE Examples of
roll-bonded refrigerator freezer
evaporators. Note the raised
channels that have been
formed between the roll-bonded
sheets. (Courtesy Olin Brass,
East Alton, IL.)

25. Friction Welding (FRW)
FIGURE Sequence for making a friction weld. (a) Components with square 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 the pressure is increased rapidly, creating a forged joint with external flash.

26. Schematic for Friction Welding
FIGURE Schematic diagram of the equipment used for friction welding. (Courtesy of Materials Engineering.)

27. Inertia Welding FIGURE 32-16 Schematic representation of the various
steps in inertia welding. The
rotating part is now attached
to a large flywheel.

28. Examples of Friction Welding
FIGURE Some typical
friction-welded parts. (Top)
Impeller made by joining a
chrome–moly steel shaft to a
nickel–steel casting. (Center)
Stud plate with two mild steel
studs joined to a square plate.
(Bottom) Tube component
where a turned segment is
joined to medium-carbon steel
tubing. (Courtesy of Newcor Bay
City, Division of Newcor, Inc.,
Royal Oak, MI.)

29. Friction-Stir Welding (FSW)
First performed by the Welding Institute of Great Britain in 1991
A nonconsumable welding tool (shoulder + protruding cylindrical or tapered probe or pin) is rotated at several hundred revolutions per minute.
Most common application is the formation of butt welds, usually between plates of the lower-point metals (both wrought and cast alloys) or thermoplastic polymers.

30. Schematic of Friction-Stir Welding
FIGURE 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. (Note: To provide additional forging
action and confine the softened material, the tool may be tilted so the
trailing edge is lower than the leading segment.)

31. Example of Friction-Stir Welding
FIGURE (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 and
has retracted at the right of the
photo. (b) Metallurgical cross
section through an alloy 356
aluminum casting that has been
modified by friction-stir
processing.

32. Features of Friction-Stir Welding

33. Ultrasonic Welding (USW)
Coalescence is produced by the localized application of high-frequency (10,000 to 200,000 Hz) shear vibrations to surfaces that are held together under rather light normal pressure.
Some heating is existed at the faying surfaces, but the temperature at the interface is rarely exceeds one-half of the melting point of the material.

34. Schematic of Ultrasonic Welding
FIGURE Diagram of the
equipment used in ultrasonic
welding

35. Application of Ultrasonic Welding

36. Diffusion Welding (DFW)
Joining surfaces are maintained in contact under sufficient pressure and time at elevated temperature.
Frequently used to join dissimilar metals and composite materials.

37. Explosive Welding (EXW)
FIGURE (Left) Schematic of the explosive welding process. (Right) Explosive weld between mild steel and stainless steel, showing the characteristic wavy interface.

38. Reference Problems
Review Questions
4, 5, 9, 12, 21, 28, 32, 34, 37