1. A few definitions

Welding is a practice that has been in use since the earliest days of metalworking. In fact, metallurgical expertise carried out on archaeological metal objects dating from before our era shows the execution of welds in the current sense of the term, i.e. the assembly of several elementary parts executed separately, with the aim of creating a macroscopic, finished object, complex in form and/or nature, whose different parts have been united on an atomic scale. Today, such welds are only used by skilled blacksmiths. This joining technique, which unambiguously meets today's definition of welding, remained the only one really practised until the end of the 19th century, i.e. until the discovery of acetylene and the oxyacetylene flashlight, although there were a few attempts to use electrical processes in the 19th century (resistance...