At the beginning of the 20th century, with the outbreak of World War I and World War II, there was a great demand for cheap and reliable connection methods for military equipment, which promoted the development of welding technology. Nowadays, welding robots are widely used in industrial applications, researchers are still deeply studying the essence of welding and continuing to develop new welding methods to further improve welding quality.
In the welding process, the workpiece and solder melt to form a melting zone, and the molten pool cools and solidifies to form a connection between materials. In this process, pressure is usually needed. There are many sources of welding energy, including gas flame, arc, laser, electron beam, friction and ultrasound.
Before the end of 19, the only welding process was the metal forging welding that blacksmiths had used for hundreds of years. The earliest modern welding technology appeared at the end of 19, including arc welding and oxygen welding, and then resistance welding.