This is a kind of welding method that takes resistance heat as energy source, including electric slag welding with slag resistance heat as energy source and resistance welding with solid resistance heat as energy source. Resistance welding is usually a welding method to connect the contact surface between two pieces of the workpiece under the action of a certain electrode pressure and the resistance heat generated by the current through the workpiece. A large current is usually used. In order to prevent the arc from occurring on the contact surface and to weld the weld metal, pressure is always applied during welding. In this type of resistance welding, the surface quality of weldment is of primary importance for achieving stable welding quality. Therefore, the contact surface between electrode and workpiece and workpiece and workpiece must be cleaned before welding. Advantage: 1) when the nugget is formed, it is surrounded by plastic rings. The molten metal is isolated from the air and the metallurgical process is simple. 2) the heating time is short, the heat concentration is concentrated, so the heat affected zone is small, and the deformation and stress are also small. Usually, there is no need to arrange correction and heat treatment after welding. 3) do not need filler metal such as welding wire and electrode, and welding materials such as oxygen, acetylene and argon. 4) simple operation, easy realization of mechanization and automation, and improvement of labor conditions. 5) high productivity, and noiseless and harmful gases. In mass production, it can be combined with other manufacturing processes on the assembly line. But flash butt welding needs to be isolated because of spark splashing. Shortcomings: 1) there is still a lack of reliable nondestructive testing methods at present. The welding quality can only be checked by the destructive test of the process sample and the workpiece, and it is guaranteed by various monitoring techniques. 2) the lap joint of point and seam welds not only increases the weight of the component, but also forms the angle between the two plates, which leads to the lower tensile strength and fatigue strength of the joint. 3) the equipment is of high power and high degree of automation, which makes the equipment cost higher and the maintenance more difficult. The commonly used high-power single-phase AC welder is not conducive to the normal operation of the power grid. Scope of application: widely used in automobile, aircraft, equipment, electrical appliances, building steel, and other industries. It is widely used, but the resistance welding of oxidizing metals is poor. It is mainly used for welding thin plate components with thickness less than 3mm. All kinds of steel, aluminum, magnesium and other non-ferrous metals and their alloys, stainless steel and so on can be welded.