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. At the beginning of the 20th century, there was a great demand for military equipment in World War I and World War II, and the corresponding cheap and reliable metal connection technology was paid attention to, which promoted the development of welding technology. After the war, several modern welding technologies appeared successively, including the most popular manual arc welding, and automatic or semi-automatic welding technologies such as gas shielded arc welding, submerged arc welding, flux-cored arc welding and electroslag welding. In the second half of the 20th century, with the rapid development of welding technology, laser welding and electron beam welding have been developed. Nowadays, welding robots have been widely used in industrial production. Researchers are still deeply studying the essence of welding, and continue to develop new welding methods to further improve the welding quality. The history of metal connection can be traced back thousands of years. Early welding techniques can be found in Europe and the Middle East in the Bronze Age and the Iron Age. Thousands of years ago, Babylonian civilization in Cuba began to use welding technology. In 340 BC, people used welding technology when making iron columns weighing 5.4 tons in Delhi, ancient India. Blacksmiths in the Middle Ages forged hot metals to connect them, a process called forging welding. Forging and welding techniques are described in The First Secretary of Flamology published by Vinezhong Billinger Theo in 1540. European Renaissance craftsmen mastered forging and welding well, and in the next few centuries, forging and welding technology has been continuously improved. In the19th century, the development of welding technology has advanced by leaps and bounds, and the style has also been greatly improved. 1800, Sir humphry davy discovered the electric arc; Later, the metal electrode invented by Russian scientist Nikolai Slavyanov and American scientist C·L· Coffin promoted the formation of arc welding process. Arc welding and later developed carbon arc welding with carbon electrode are widely used in industrial production. Around 1900, A. P. Stroganov developed a metal-coated carbon electrode in Britain, which can provide a more stable arc. In 19 19, C J Holslag used alternating current for welding for the first time, but this technology was not widely used until ten years later.