TABLE OF CONTENTS Resistance welding is a joining process belonging to the pressure welding sector. With its locally applied heat and pressure it has an obvious relationship with the forge welding technique practised by blacksmiths when joining metal. The resistance welding process was invented in 1877 by Professor E. Thomson of Philadelphia, USA, when an accidental short circuit gave him the idea for what was originally termed short circuit welding. From the beginning of the twentieth century it was used on a small scale in industry, but it was only after the Second World War that resistance spot welding had its real beginning in the automobile industry. It has since grown to be the most important method of welding used in the construction and mass production of vehicle bodies.
Resistance welding is extensively used for the mass production assembly of the all-steel body and its component sheet metal parts (see Figure 10.1). Its wide adoption has been brought about by its technical advantages and the reductions in cost. Most mass produced car bodies are assembled entirely by welding steel pressings together to produce an integral rigid chassis and body structure. Low-carbon steel thicknesses used in this unitary construction range from 0.8 1 mm for skin or floor panels to 3 mm for major structural pressings such as suspension brackets. Intermediate gauges such as 1.2 mm are used for hinge reinforcements, 1.6 mm for chassis structural members, and 1.8 mm to 2.5 mm for suspension and steering members.
