Welding technology, also known as connection engineering, is an important material processing technology. The definition of welding is as follows: the material of the workpiece to be welded (same or different), by heating or pressurizing or both, and with or without filling materials, the material of the workpiece can be bonded between atoms to form a permanent connection. The project is called welding .

Theoretically speaking, for two separate materials, we put the surfaces that need to be connected together. If the surfaces that need to be connected are close enough (the so-called close enough is to make the two separated surfaces, the distance between them can be It is close to the distance of an atom, that is, 0.4 to 0.5 nanometers.) In this case, the material can be connected together according to its physical nature to form a connected building block. But in fact, under normal temperature, we can't do it under normal circumstances, why? Because even after finishing the two surfaces to be combined, we use a microscope. From a microscopic point of view, the surface is still uneven, especially because the material is chemically affected by the oxygen in the atmosphere. In the air, within a few seconds, an oxide film will be formed on the surface. This oxide film will continue to thicken as time goes by. At the same time, it is difficult to avoid other impurities on the surface of the material, such as Moisture, impurities, and oil form additional layers. This oxide film and additional layers greatly hinder the connection of materials.

Therefore, the basic principle of welding is to apply external energy to promote the proximity of the atoms of the separated material to form an atomic bond bond, while removing all surface films and adsorption layers that hinder the atomic bond bond to form a high-quality welded joint In fact, in the welding technology, the methods that we often use to apply external energy are: 1. Heating, heating the material to a molten state, or heating the material to a plastic state; 

2. Pressing, to make the material produce plastic flow.

In order to realize welding, additional energy is required. At present, heat energy is one of the main forms of applying external energy. We call the heat source provided for the welding process as welding.

Connect the heat source. The invention and development of welding heat sources often give birth to new welding methods and technological changes and advancements. The invention of electric arc at the end of the 19th century brought the welding technology into the era of fusion welding. At the beginning of this century, with the in-depth study of frictional heat sources, the friction stir welding method was invented, which played an important role for the welding technology to enter a new development period. At present, the energy sources used as welding heat sources include arc heat, resistance heat, electron beam, laser beam, chemical reaction heat, high frequency heat source and friction heat. The requirements for welding heat sources are increasingly pursuing a high concentration of energy density, rapid completion of the welding process, and high-quality welds and heat-affected zones. Conventional welding methods include gas welding, electrode arc welding, metal inert gas shielded welding, metal active gas shielded welding, tungsten inert gas shielded welding and other methods.