Spot welding creates overlapping seams which, when immersed in electroplating solutions, trap solution residues through capillary action. This creates two problems. First, the residue often leaves plating salt deposits which are unsightly and which, in extreme cases, may require touch up or manual removal at increased cost. Second, the metal in the seam is unprotected and can corrode severely in harsh environments. When designing spot welded assemblies for electroplating, consideration must be given to plating drainage, enclosed seams and pockets, overlapping seams and other areas where solutions may be trapped or where special cleaning or processing techniques may be required. When these operations are combined, early consultation with an experienced supplier is crucial.
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.
Spot welding is a resistance welding process that is used primarily for welding two or more metal sheets together by applying pressure and heat to the weld area. It works by contacting copper alloy electrodes to the sheet surfaces, whereby pressure and electric current are applied and heat is generated by the passage of current through resistive materials such as low carbon steels. Read more details on https://www.weldingsuppliesdirect.co.uk/welding-equipment/spot-welding.html.
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.