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.
Start off by drilling 7.5mm holes in the front sheet of metal at a spacing of normally 25mm to 40mm (or whatever the original spot weld spacing was). Then clamp this sheet onto the back sheet. 7.5mm is a reasonably good hole size for 0.8 or 1.0mm sheet. Thicker sheet might require a slightly larger hole size. Try a little test piece out like this one before welding a whole sill onto a car and check the weld has penetrated through both sheets.
Although aluminium has a thermal conductivity and electrical resistance close to that of copper, the melting point for aluminium is lower, which means welding is possible. However, due to its low resistance, very high levels of current need to be used when welding aluminium (in the order of two to three times higher than for steel of equivalent thickness). In addition, aluminium degrades the surface of copper electrodes within a very small number of welds, meaning that stable high quality welding is very hard to achieve. For this reason, only specialist applications of aluminium spot welding are currently found in industry. Various new technology developments are emerging to help enable stable high quality spot welding in aluminium. Read more info at Tecna Spot Welder.
Stationary spot welders are mounted on a column with a jack and mobile arms. The frame is heavy and bulky and the machine has a welding capacity of 0.5–10mm. The body of the machine often equipped with a 380V generator and two arms with a mechanical, pneumatic or hydraulic jack to adjust operating height, as well as heat-resistant electrodes made of copper or copper-chromium alloy. No electric arc is produced, and the arms are water-cooled in closed circuit. The arms and electrodes are interchangeable to vary spot size and form across different types of weld.