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.
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).
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. See extra details at Tecna Spot Welder Price.
As is often the case with machine tools, there are two types: portable (for ease of use but with limited performance); and stationary (better suited to intensive work and thicker metal sheet).