Welding: Usually refers to the welding of metal. It is a forming method by heating or pressurizing, or using both at the same time, so that two separated objects generate interatomic bonding force and join into one.

Classification: According to the heating degree and process characteristics of the welding process, the welding method can be divided into three categories.

(1) Fusion welding. The workpiece is partially heated to a molten state at the welding point to form a molten pool (usually with filler metal), which is cooled and crystallized to form a weld, which is combined into an inseparable whole by the welder. Common fusion welding methods are gas welding, arc welding, electroslag welding, plasma arc welding, electron beam welding, laser welding and so on.

(2) pressure welding. In the welding process, regardless of heating or not, pressure welding method is required. Common pressure welding is resistance welding, friction welding, cold pressure welding, diffusion welding, explosive welding and so on.

(3) Brazing. The filler metal (filler metal) with a melting point lower than the welded metal is melted, and the joint gap is filled and diffused with the welded metal to realize the connection. The welded parts do not melt during brazing, and there is generally no plastic deformation.

Characteristics of welding production:

(1) Save metal materials, light structural weight.

(2) To small, large, small, manufacturing heavy, complex machine parts, simplify casting, forging and cutting processing technology, to obtain the best technical and economic results.

(3) The welded joint has good mechanical properties and tightness.

(4) Can manufacture bimetallic structure, so that the performance of the material can be fully utilized.

Application: Welding technology is widely used in machine manufacturing, shipbuilding industry, construction engineering, power equipment production, aviation and aerospace industry.

Shortcomings: Welding technology also has some shortcomings, such as the welding structure is not removable, which brings inconvenience to maintenance; There will be welding stress and deformation in the welding structure. The microstructure and properties of welded joints are often uneven, and welding defects will occur.