Projection welding can be used on low-carbon, low-alloy and stainless steels, as well as on aluminum. Typically, thicknesses up to 0.125 in. (3.18 mm) can be joined. Thin workpieces–from 0.010 in. (0.25 mm) up to 0.022 in. (0.56 mm)–may require special equipment. Below 0.010 in. (0.25 mm), resistance spot welding is recommended, because on this thin material the projections would collapse before the fusion temperature is reached. While projection welding can be less expensive than resistance spot welding, workpiece alignment is more critical, and heights of projections with simultaneous welds need to be closely controlled– typically, within 0.003 in. (0.08 mm) of each other.
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.
The welding heat is generated by the electric current, which is transferred to the workpiece through copper alloy electrodes. Copper is used for the electrodes as it has a high thermal conductivity and low electrical resistance compared to most other metals, ensuring that the heat is generated preferentially in the work pieces rather than the electrodes. The amount of heat depends on the thermal conductivity and electrical resistance of the metal as well as the amount of time the current is applied. Other materials commonly spot welded include stainless steels (in particular austenitic and ferritic grades), nickel alloys and titanium. Read extra info at 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.