Electric resistance welding is the use of current through resistor between the workpiece and the welding heat generated by the contact surface, the plastic is heated to a weldment or partial melting state, then apply pressure welding method of forming a welded joint. There are four main resistance welding method that spot, seam welding, projection welding, butt welding. Resistance welding is the workpiece at a certain electrode resistance heat and pressure generated by the current through the workpiece when the workpiece contacting surface between the two melting the welding connection method. Usually large current in order to prevent arcing contact surface and to forging weld metal during welding pressure to be applied consistently. 

Electric resistance welding has two notable features: first, the welding heat is heat resistance, so called resistance welding; second, the need to exert pressure welding, so vigorous in bonding. 

Advantages of electric resistance welding
1, nugget form, has always been surrounded by a plastic ring, molten metal and air separation, metallurgical process is simple. 
2, the heating time is short, heat is concentrated, so a small heat-affected zone, deformation and stress are small, usually having to arrange correction after welding and heat treatment processes. 
3, no wires, rods and other filler metals, as well as oxygen, acetylene, hydrogen and other welding materials, welding low cost. 
4, simple operation, easy to implement mechanization and automation, improved working conditions. 
5, high productivity, and no noise and harmful gases, in mass production, and other manufacturing processes can be compiled together to the assembly line. However, due to flash butt welding sparks splash, requiring isolation. 

Disadvantages of resistance resistance welding
1, there is a lack of reliable non-destructive testing methods, the quality of welding processes rely on destructive test specimens and artifacts to examine, as well as by a variety of monitoring techniques to ensure that. 
2, the point, not only the lap joint seam welding increases the weight member, and because the two plates form an angle around the weld nugget, resulting in tensile strength and fatigue strength of the joints were low. 
3, the device power, high mechanization, automation, so that the higher cost of equipment, maintenance more difficult, and the commonly used high-power single-phase AC welder is not conducive to balanced operation of the grid.