For centuries, the only method man had for metallurgically joining metals was forge welding, a crude and cumbersome blacksmith-type operation in which heated metals were pounded or rammed together until they bonded. No one knows when man first learned to use make welding, but by the time of the Renaissance, craftsmen were highly skilled in forge welding. Parts to be joined were shaped and then heated in a make or furnace before being destroyed, rolled or pressed together.
For some centuries thereafter, ordinary fire remained the principle source of heat for welding. The traveling tinker carried with him a small charcoal heater for heating his irons. During this era, tinsmiths and other workers within metal often used the heat associated with burning gases to braze plus solder.
Within the span of a couple of years prior to 1900, three new procedures came into existence, arc welding, resistance welded and oxyacetylene welding.
Arc Welded is done when two high-voltage electric terminals are brought near one another causing an arc. This arch, which casts a bright light, and provides off considerable heat, can be hit and maintained at will. Its size and intensity can be varied inside limits determined by the circuit volts and by the type of terminals used.
Level of resistance Welding refers to a group of welding processes such as spot and seam welding that produces coalescence of faying surfaces where heat to form the weld is generated by the resistance of the welding current through the work pieces. Small pools of smelted metal are formed at the stage of most electrical resistance (the linking surfaces) as a high current is usually passed through the metal. In general, resistance-welding methods are efficient and trigger little pollution, but their applications are limited to relatively thin material.
The Oxyacetylene Welding process is built on two fundamental principles: first, that acetylene burned with oxygen generates a flame so intensely warm that it can be used to melt and fuse even the most refractory metals; second, that a stream of oxygen directed against a pieced of iron or steel that has been heated in order to its kindling temperature causes the particular metal to burn away and so may be used to cu or shape it since desired. In principle, oxy-acetylene welding is fairly simple. Two pieces of metallic are brought together and the sides in contact are melted by the oxy-acetylene flame, with or without the addition of molten steel from a welding rod. The molten edges will flow together till each is completely fused with the other. After the metal has cooled, there is a single continuous piece with no seam.