Recommended spacing between welds and distances from a spot weld to component edges and other part features should be followed to obtain optimum weld quality and strength. Weld-to-weld spacing should be a minimum of 10 material thicknesses. For 0.060 sheet steel, that’s about 0.6 in. (15 mm). Ideally, 20 times material thickness is recommended to reduce shunting effects with a minimum spacing of 1/2 in. (13 mm). See Table I for minimum and recommended weld spacing for various material thickness of aluminum, carbon and stainless steel. Weld-to-edge distance should also conform to a minimum dimension that is a function of the weld diameter. Generally, the center of a spot weld (its location point) is positioned one to two diameters away from the edge of the part being welded or from a feature in the part being welded depending on thickness of material.
One alternative to plug welding is “MIG spot welding”. It is similar to plug welding, although a hole is not drilled in the front sheet of metal. Instead the power of the MIG is relied upon to fully melt the top sheet and penetrate into the back sheet. This technique would require less preparation work than plug welding, but the two sheets need to be in tight contact and high amps used to complete the weld or else the weld could be very weak. Plug welding is a much more suitable technique for all but the most experienced welders.
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. See more info on Tecna Spot Welder Parts.
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.