Brazing refers to a welding method in which the solder below the melting point of the weldment and the weldment are heated to the melting temperature of the solder at the same time, and then the gaps in the solid workpiece are filled with liquid solder to connect the metals. When brazing, the oxide film and oil stain on the contact surface of the base metal should be removed first, so as to facilitate the function of the capillary after the solder is melted, and increase the wettability and capillary fluidity of the solder. According to the melting point of solder, brazing is divided into hard brazing and soft brazing.