Resistance welding processes

The present magnetic force resistance welding process appears to be basically most satisfactory, but it has limits of application to thin cladding. Some developments of the process are in hand at the present time aimed at extending its use and at detailed improvements in weld design. 

The resistance welding process can be performed at either constant power or constant temperature. In eonstant power processing, a particular voltage and eurrent is set for the entire weld, and welding oeeurs for a specified time. This process is not isothermal, and peak temperatures are difficult to predict. In constant temperature resistance welding, sensors, sueh as thermocouples, are used to monitor the welding process in order to adjust current and voltage as neees-sary. The constant temperature process provides more thermal uniformity but is not commonly used. ... 

Resistance welding has been successfully appHed to copper alloys in all of its various spot, seam, or butt joining modes. Because the process depends on ohmic (l R) heating at the interface to be joined, the abiHty to resistance weld is inversely related to electrical conductivity of the alloys being welded. 

The effect of the welding process on the severity of weld decay varies according to the process and the plate thickness so that no single recommendation is possible for every thickness of plate if resistance to attack is essential. The severity of weld decay correlates quite well with sensitisation times as calculated from recorded weld heating cycles. 

The surface preparation method must be carefully considered, especially if the completed weldbond is to have long-term durability to hostile environments. The surface preparation should provide an optimal surface for both adhesion and welding. Thus, the choice of surface treatment is crucial, and there can be a conflict of requirements. The spot welding process requires a low electrical surface resistance, and many adhesive surface preparation processes provide a high surface resistance because of oxide layer buildup. When it is impossible to harmonize on a surface treatment, current practice tends to favor treatments that yield good weld nuggets at the expense of the adhesive bond. 

Large parts can require considerable power requirements. Resistance welding has been applied to complex joints in automotive applications, including vehicle bumpers and panels, and joints in plastic pipe, and in medical devices. Resistance wire welding is not restricted to flat surfaces. If access to the heating element is possible, repair of badly bonded joints is possible, and joints can be disassembled in a reverse process to which they were made. 

Electric resistance weld pipe manufacturing process.114... 

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