Comprises welding energy equipment, a welding machine head and a welding control system. ① Welding energy equipment: used to provide the energy needed for welding. Commonly used are various arc welding power sources, also known as electric welding machines. Its no-load voltage is 60 ~100V, its working voltage is 25 ~ 45V, and its output current is 50 ~1000A. During manual arc welding, the arc length often changes, which leads to the change of welding voltage. In order to stabilize the welding current, the external characteristics of the arc welding power supply used should be steep, that is, with the change of output voltage, the change of output current should be very small. The flat characteristic power supply can be used for GMAW and SAW, and its output voltage changes little when the current changes. Arc welding power supply generally includes arc welding transformer, DC arc welding generator and arc welding rectifier. Arc welding transformer provides alternating current, which is widely used. DC arc welding generator provides DC power supply, which is more complicated to manufacture, more consumables and lower in efficiency, and tends to be gradually replaced by arc welding rectifier. Arc welding rectifier is a DC arc welding power source developed in 1950s. It uses silicon diode or silicon controlled rectifier as rectifier. Transistor arc welding power supply composed of high-power transistors appeared in 1960s, which can achieve high control accuracy and excellent performance, but the cost is high. Resistance welding transformer is a simple welding energy equipment, with no-load voltage ranging from 1 to 36 volts and current ranging from thousands to tens of thousands. The welding machine equipped with this welding energy equipment is called AC resistance welding machine. Others include low frequency resistance welding machine, DC pulse resistance welding machine, capacitor energy storage resistance welding machine and secondary rectifier resistance welding machine.

(2) welding machine head: its function is to convert the energy output by welding energy equipment into welding heat, and continuously feed welding materials, and at the same time, the head itself moves forward to realize welding. The electrode holder used for manual arc welding, with the melting of covered electrode, must be continuously manually sent down to covered electrode and moved forward to form a weld. The automatic welding machine has an automatic wire feeding mechanism and an organic head walking mechanism to move the head forward. There are two kinds in common use: trolley type and suspension type. The welding head of resistance spot welding and projection welding is the electrode and its pressurizing mechanism, which is used to apply pressure and current to the workpiece. There is also a transmission mechanism for seam welding to drive the workpiece to move. When butt welding, there should be not only static and dynamic jigs and fixture clamping mechanisms, but also mobile jigs and upsetting mechanisms.

③ Welding control system: Its function is to control the whole welding process, including controlling welding procedures and welding specification parameters. General AC arc welding machine has no control system. Electronic circuit, digital circuit and microprocessor control of high efficiency or precision welding machine.