Welding technology is mainly used in metal base material, commonly used arc welding, argon arc welding, CO2 protection welding, oxygen - acetylene welding, laser welding, electro-slag pressure welding and other non-metallic materials such as plastics can also be welded. There are more than 40 metal welding methods, mainly divided into welding, welding and brazing three categories.
Welding is in the welding process will be heated to the workpiece interface melting state, without pressure to complete the welding method. Fusion welding, the heat source to be welded two workpiece interface quickly heated to melt, forming a pool. The molten pool moves forward with the heat source, forming a continuous weld after cooling and connecting the two workpieces together.
In the welding process, if the atmosphere is in direct contact with the molten pool of high temperature, the oxygen in the atmosphere oxidizes the metal and various alloying elements. Atmospheric nitrogen, water vapor, etc. into the pool, but also in the subsequent cooling process in the formation of porosity, slag, cracks and other defects, deterioration of weld quality and performance.
Pressure welding is under pressure, so that the two work pieces in the solid state to achieve atomic bonding, also known as solid state welding. Commonly used in the welding process is resistance butt welding, when the current through the two ends of the workpiece, where the resistance due to a large temperature rise, when heated to plastic state, under the action of axial pressure connected to become one.
A common feature of various press-welding methods is the application of pressure during the welding process without filler material. Most compression welding methods such as diffusion welding, high frequency welding, cold welding, etc. are not melting process, and therefore not as beneficial as the melting of the alloy element burning, and harmful elements invade the weld problem, thus simplifying the welding process, but also Improved welding safety and hygiene conditions. At the same time as the heating temperature is lower than the welding, heating time is short, so heat-affected zone is small. Many materials that are difficult to weld by fusion welding can often be welded to high quality joints of the same strength as the base metal.
Brazing is the use of metal materials than the melting point of the workpiece as a brazing filler metal, the workpiece and the brazing filler metal is heated to a temperature higher than the melting point of the brazing filler metal, lower than the melting temperature of the workpiece, wetting the workpiece with liquid brazing filler metal, Inter-atomic diffusion between, in order to achieve the welding method.
The seam formed by welding that connects two connected bodies is called the weld seam. Welds on both sides of the weld are subjected to heat of welding and structural and property changes occur. This area is called the heat affected zone. Welding due to the workpiece material welding materials, welding current, etc., after welding in the weld and heat affected zone may have overheating, embrittlement, hardening or softening phenomenon, but also to weld performance degradation, deterioration of weldability. This requires the adjustment of welding conditions, pre-weld weldment interface at the pre-weld heat preservation and post-weld heat treatment can improve the welding quality of weldment.