Knowledgeable designers recognize such cost-saving and quality-improvement methods and specify them in the manufacturing process. The consistency attainable with such methods surpasses that of sophisticated jigs and fixtures but the greatest value is the cost efficiency. Additionally, these techniques can be used for fillet welding applications, and mechanical assemblies. A refinement of resistance spot welding is resistance projection welding (RPW). It makes use of projections previously formed on the workpiece to reduce the power required to make a resistance weld. Consequently, multiple welds can be made more easily at the same time, and thicker sections can be joined more readily than in RSW. Other advantages include reduced shunting effects, closer weld-to-weld spacing and welding of workpieces with smaller flanges.
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.
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. See more details at Tecna Spot Welder.
What type of sheets can be welded? Rust-free, non-painted sheets of the same or different metals can be welded provided they are compatible alloys with a very similar melting point. Metals such as stainless steel, aluminium, steel alloys and galvanized steels can be spot welded, subject to operating adjustments (current, welding time, intensity of compression). Note that the coating on galvanized metals tends to clog the electrodes – which must be cleaned regularly!