Cold, Forge and Friction Welding

Cold Welding

Sufficient pressure must be exerted to establish conformance of surfaces. Sliding and deformation accompanied by surface expansion are needed to break up oxides and other adsorbed films. Cold welding processes differ only in the method of providing these conditions. Complex tubular parts such as refrigerator evaporator plates can be made by depositing a parting agent in a pattern to prevent welding; after roll bonding the passages may be inflated.

Forge Welding

As a generic term, it applies to bonding by deformation at hot-working temperatures. Large surface extension in hot-roll bonding creates strong bonds for clading, as in bonding copper-nickel surface layers to a copper core for some US coins (dimes and quarters). For this purpose localised heating of the parts is carried out in high-frequency induction and high-frequency resistance welding. Some melting may take place, but the melt is squeezed out by compression, as in welding tubes from roll-formed strip.

Friction Welding

Heat is produced by friction between a rotating and stationary part; again, some melt may form that is expelled together with oxidized metal. Localization of heat allows welding of dissimilar metals and of very different dimensions (e.g., a thin stem to a large head for an internal combustion engine valve).