TW Applications
• Joining of railroad rails
• Repair of cracks in large steel castings and forgings
• Weld surface is often smooth enough that no finishing is required
๖. Solid State Welding (SSW)
• Coalescence of part surfaces is achieved by:
▫ Pressure alone, or
▫ Heat and pressure
If both heat and pressure are used, heat is not enough to melt work surfaces
▫ For some SSW processes, time is also a factor
• No filler metal is added
• Each SSW process has its own way of creating a bond at the faying surfaces
Success Factors in SSW
• Essential factors for a successful solid state weld are that the two faying surfaces must
be:
▫ Very clean
▫ In very close physical contact with each other to permit atomic bonding
๗๓
SSW Advantages over FW Processes
• If no melting, then no heat affected zone, so metal around joint retains original
properties
• Many SSW processes produce welded joints that bond the entire contact interface
between two parts rather than at distinct spots or seams
• Some SSW processes can be used to bond dissimilar metals, without concerns about
relative melting points, thermal expansions, and other problems that arise in FW
Solid State Welding Processes
• Forge welding
• Cold welding
• Roll welding
• Hot pressure welding
• Diffusion welding
• Explosion welding
• Friction welding
• Ultrasonic welding
Forge Welding
Welding process in which components to be joined are heated to hot working temperature
range and then forged together by hammering or similar means
• Historic significance in development of manufacturing technology
▫ Process dates from about 1000 B.C., when blacksmiths learned to weld two
pieces of metal
• Of minor commercial importance today except for its variants
๗๔
Cold Welding (CW)
SSW process done by applying high pressure between clean contacting surfaces at room
temperature
• Cleaning usually done by degreasing and wire brushing immediately before joining
• No heat is applied, but deformation raises work temperature
• At least one of the metals, preferably both, must be very ductile
▫ Soft aluminum and copper suited to CW
• Applications: making electrical connections
Roll Welding (ROW)
SSW process in which pressure sufficient to cause coalescence is applied by means of rolls,
either with or without external heat
• Variation of either forge welding or cold welding, depending on whether heating of
workparts is done prior to process
▫ If no external heat, called cold roll welding
▫ If heat is supplied, hot roll welding