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

fusion #welding

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.

In the fusion welding process, if the atmosphere is in direct contact with the high temperature molten pool, the oxygen in the atmosphere will oxidize the metal and various alloying elements. Nitrogen, water vapor, etc. in the atmosphere enter the molten pool, and also form defects such as pores, slag inclusions, and cracks in the weld during the subsequent cooling process, deteriorating the quality and performance of the weld.

In order to improve the welding quality, various protection methods have been developed. For example, gas shielded arc welding is to use argon, carbon dioxide and other gases to isolate the atmosphere to protect the arc and molten pool rate during welding; another example is when steel is welded, adding titanium-iron powder with high oxygen affinity to the electrode coating for deoxidation. It can protect the beneficial elements such as manganese and silicon in the electrode from oxidation and enter the molten pool, and obtain a high-quality weld after cooling.

pressure welding

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.

A common feature of various pressure #welding methods is the application of pressure without filler material during the welding process. Most pressure welding methods, such as diffusion welding, high frequency welding, cold pressure welding, etc., do not have a melting process, so there is no burning of beneficial alloying elements like fusion welding, and the problem of harmful elements intruding into the weld, thereby simplifying the welding process. Improved welding safety and hygiene conditions. At the same time, because the heating temperature is lower than that of fusion welding and the heating time is shorter, the heat affected zone is small. Many materials that are difficult to weld by fusion welding can often be welded into high-quality joints with the same strength as the base metal by pressure welding.

Brazing

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, and use the liquid solder to wet the workpiece, fill the interface gap, and realize the connection with the workpiece. The interdiffusion of atoms to achieve the method of welding.

The seam formed during welding to connect two connected bodies is called a weld. Both sides of the weld will be subjected to welding heat during #welding, and the structure and properties will change. 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 also reduces the performance of the weldment and deteriorates the weldability. This requires adjustment of welding conditions. Preheating at the interface of the weldment before welding, heat preservation during welding and post-weld heat treatment can improve the welding quality of the weldment.