Welding is a process and connection method that produces atomic bonding between two workpieces of the same sex or opposite sex by heating, pressurizing, or using both. Welding has a wide range of applications, both for metals and for non-metals.

Welding technology is mainly used on metal base materials, commonly used arc welding, argon arc welding, CO2 shielded welding, oxygen-acetylene welding, laser welding, electroslag pressure welding, etc. Non-metallic materials such as plastics can also be welded.​​

There are more than 40 kinds of metal #welding methods, mainly divided into three categories: fusion #welding, pressure welding and brazing.

1. Fusion welding is a method in which the workpiece interface is heated to a molten state during the welding process, and the welding is completed without pressure. During fusion welding, the heat source rapidly heats and melts the interface of the two workpieces to be welded to form a molten pool. The molten pool moves forward with the heat source, and after cooling, a continuous weld is formed to connect the two workpieces into one.

2. Pressure welding is to achieve atomic bonding between two workpieces in a solid state under pressure, also known as solid state welding. The commonly used pressure welding process is resistance butt welding. When the current passes through the connecting end of the two workpieces, the temperature of the place rises due to the large resistance. When heated to a plastic state, the connection becomes one under the action of axial pressure.

3. Brazing is to use a metal material with a lower melting point than the workpiece as the solder, heat the workpiece and the solder to a temperature higher than the melting point of the solder and lower than the melting point of the workpiece, use the liquid solder to wet the workpiece, fill the interface gap and connect with the workpiece. The workpiece realizes the mutual diffusion between atoms, thereby realizing the welding method.