Applications include attachment of reinforcing braces and stiffeners, functional brackets, hinges and other parts. Often, spot welding is the method of choice for assembly of entire enclosures, cabinets and multipart assemblies. Thickness of the majority of parts joined by spot welding ranges up to 1/8 in. (3 mm) for each member, although parts up to 1/4 in. (6 mm) thick have been successfully spot welded. Based on the experience of stampers and fabricators, certain general recommendations can facilitate spot welding of a sheet metal design, no matter what metalforming process is used to make it. It is always useful to consult with the metalformer in the design stage when questions arise regarding the part design, application of spot welding or, control of spot welding cost for a particular design.
Plug welding is an alternative to spot welding used by vehicle manufacturers where there is insufficient access for a spot welder. For DIY car restoration it’s generally used instead of spot welding on panels flanges that would have originally been spot welded. Plug welds when done properly tend to be stronger than the original spot welds. Rally car builders often use the technique, and it is acceptable in a UK MOT test as an alternative to spot welds where repairing older cars (it would not be suitable for modern high tensile steels).
Copper and its alloys can also be joined by resistance spot welding, although spot welding copper cannot be easily achieved with conventional copper alloy spot welding electrodes, as heat generation in the electrodes and work piece are very similar. The solution to welding copper is to use an electrode made of an alloy with a high electrical resistance and a melting temperature far in excess of the melting point of copper (much greater than 1080°C). Electrode materials typically used for spot welding copper include molybdenum and tungsten. Read more details on Tecna Spot Welder.
To make sure your welding settings are correct, you should carry out a test run using metal offcuts, followed by a destructive test where you separate the welded parts with a hammer and a forked chisel. After separation, a hole must be made in one of the two conjoined sheets – a process known as “unbuttoning” in metalworking jargon – as proof that the settings are right for the metals and thicknesses involved. Apologies for the abstruse technical term! When welding radiators, make sure you also carry out a leak test.