Welding method

Welding technology is mainly used on metal base materials. Commonly used ones include 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 metal welding methods, which are mainly divided into three categories: fusion welding, pressure welding and brazing.

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 applying pressure. During welding, the heat source rapidly heats and melts the interface between the two workpieces to be welded, forming 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 body.

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

Brazing is to use a metal material with a lower melting point than the workpiece as the filler metal. The workpiece and the filler metal are heated to a temperature higher than the melting point of the filler metal and lower than the melting point of the workpiece. The liquid filler metal is used to moisten the workpiece, fill the interface gap, and realize the connection with the workpiece. The mutual diffusion between atoms realizes the welding method.

The seam formed during welding that connects two connected bodies is called a weld. Both sides of the weld will be affected by the welding heat during welding, resulting in changes in structure and properties. This area is called the heat-affected zone. During welding, due to different workpiece materials, welding materials, welding current, etc., overheating, embrittlement, hardening or softening may occur in the weld and heat-affected zone after welding, which will also reduce the performance of the weldment and worsen the weldability. This requires adjusting the welding conditions. Preheating the interface of the weldment before welding, insulation during welding and post-weld heat treatment can improve the welding quality of the weldment.

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