Spot welding is often selected for joining sheet metal fabrications, stampings and assemblies because it is fast, reliable and economical. However, numerous design considerations can affect the quality and cost of the weld, among them: size of the spot weld, accessibility, positioning, materials and thicknesses being joined, and the number of spots needed to attain the desired strength. This section will focus primarily on resistance spot welding (RSW) and resistance projection welding (RPW) since these processes are most commonly used due to their speed and flexibility. See Figure 1, for schematics of RSW and RPW.
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).
How Does Spot Welding Work? A form of resistance welding, spot welding is one of the oldest welding processes whereby two or more sheets of metal are welded together without the use of any filler material. The process involves applying pressure and heat to the weld area using shaped alloy copper electrodes which convey an electrical current through the weld pieces. The material melts, fusing the parts together at which point the current is turned off, pressure from the electrodes is maintained and the molten “nugget” solidifies to form the joint. Read extra details at https://www.weldingsuppliesdirect.co.uk/welding-equipment/spot-welding.html.
Portable spot welders are compact, lightweight and handy for difficult-to-access joints. As such, they are most commonly used in coachbuilding. They have an average welding capacity of 2 + 2mm and are relatively inefficient due to the fact that the electrodes aren’t cooled between cycles. Automatic adjustment makes it easier to adjust the spot parameters according to the thickness of sheet and welding head used.
