Welding: also known as welding and melting, is a manufacturing process and technology to connect other thermoplastic materials such as metals or plastics by heating, high temperature or high pressure. Welding can achieve the purpose of connection in the following three ways:
1, heating the workpiece to be connected to partially melt it to form a molten pool, and connecting the molten pool after cooling and solidification, and adding filler for assistance if necessary;
2. The low melting point solder is heated separately, and the workpiece is connected through the capillary action of the solder (such as soldering and brazing) without melting the workpiece itself;
3. At the temperature equal to or lower than the melting point of the workpiece, the two workpieces are infiltrated by high pressure, overlapping extrusion or vibration (such as forging welding and solid welding).
According to the specific welding process, welding can be subdivided into special welding such as gas welding, resistance welding, arc welding, induction welding and laser welding.
There are many sources of welding energy, including gas flame, arc, laser, electron beam, friction and ultrasound. Besides being used in factories, welding can also be carried out in various environments, such as outdoor, underwater and space. No matter where, welding may bring danger to operators, so appropriate protective measures must be taken during welding. Welding may cause harm to human body, including burns, electric shock, visual impairment, inhalation of toxic gases, excessive ultraviolet radiation, etc.
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, the two rivers civilization began to use welding technology. In the first 340 years, people used welding technology when making iron columns weighing 5.4 tons in Delhi, India.
Blacksmiths in the Middle Ages forged hot metals to connect them. This process is called forging welding. Forging and welding techniques are described in The First Secretary of Flamology published by Vinezhong Billinger Theo in 1540. Artisans in the Renaissance had mastered forging and welding well, and in the following centuries, forging and welding techniques were constantly 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.
Resistance welding was developed in the last decade of19th century. The first patent on resistance welding was applied by Elihu Thomson in 1885, and he constantly improved this technology in the following 15 years. Thermite welding and combustible gas welding were invented by 1893. Edmund David discovered acetylene at 1836. At around 1900, combustible gas welding began to be widely used due to the appearance of new air guns. Because of its low cost and good fluidity, combustible gas welding has become one of the most popular welding technologies from the beginning. However, with the continuous improvement of the metal coating technology on the electrode surface by engineers in the mid-20th century (that is, the development of flux), the new electrode can provide a more stable arc and effectively isolate the base metal from impurities, so arc welding can gradually replace combustible gas welding and become the most widely used industrial welding technology.
The first world war made the welding demand surge, and all countries are actively studying new welding technology. Arc welding is mainly used in Britain, and they built the first all-welded ship, Frago. During World War II, arc welding was also first applied to aircraft manufacturing. For example, the fuselage of many German planes is made in this way. It is also worth noting that the world's first all-welded highway bridge was built in 1929 in S? The bridge was built on the udwia Maurzyce River by Stefan Blerring of Warsaw Institute of Technology. A) designed in 1927.
1920s, welding technology made a major breakthrough. Automatic welding appeared in 1920, and automatic wire feeding device ensured the continuity of arc. During this period, more and more attention has been paid to protective gas. Because in the welding process, the metal at high temperature will react chemically with oxygen and nitrogen in the atmosphere, the bubbles and compounds produced will affect the strength of the joint. The solution is to use hydrogen, argon and helium to isolate the molten pool from the atmosphere. In the next 10 year, the further development of welding technology enabled active metals such as aluminum and magnesium to be welded. 1930 During World War II, the introduction of automatic welding, alternating current and active agent greatly promoted the development of arc welding.
In the mid-20th century, scientists and engineers invented many new welding technologies. The stud welding (nail welding) invented in 1930 was soon widely used in shipbuilding and construction industry. Submerged arc welding invented in the same year is still very popular today. After decades of development, tungsten gas shielded welding was finally perfected in 194 1. Then in 1948, MIG arc welding made it possible to weld nonferrous metals quickly, but this technology required a lot of expensive shielding gas. Manual arc welding using consumable electrode as electrode developed in 1950' s and quickly became the most popular metal arc welding technology. 1957 flux-cored wire arc welding first appeared, and its self-protecting wire electrode can be used for automatic welding, which greatly improved the welding speed. In the same year, plasma arc welding was invented. Electroslag welding was invented in 1958 and gas welding in 196 1.
The development of welding technology in recent years includes: 1958 electron beam welding can heat a small area, making it possible to weld deep and narrow workpieces. Later 1960 invented laser welding. In the following decades, it proved to be the most effective high-speed automatic welding technology. However, the application of electron beam welding and laser welding is limited because of their high equipment cost.