Arc: a strong and persistent gas discharge phenomenon. There is a certain voltage between the positive and negative electrodes, and the gas medium between the two electrodes should be. It is in the state of ionization. When igniting welding arc, usually two electrodes (one pole is workpiece, another pole is filler wire or electrode). Through the power supply, it contacts and separations rapidly, and the two poles are short circuited when they contact each other, forming an arc. This way is called contact arc. electric After the arc is formed, as long as the power supply keeps a certain potential difference between the poles, the combustion of the arc can be maintained. Arc characteristics: low voltage, high current, high temperature, high energy density, good mobility, etc., generally 20 to 30V voltage can maintain electricity. The steady combustion of the arc, and the current in the arc can range from tens of amperes to thousands of amperes to meet the welding requirements of different workpieces. The degree is more than 5000K, which can melt all kinds of metals. The arc consists of three parts: cathode area, anode area and arc column area. Arc welding power source: the power used for welding arc is called arc welding power source. It can be generally divided into four main categories: AC arc welding power and DC arc welding power. Source, pulse arc welding power supply and inverter arc welding power supply. DC Direct Connection: DC welding machine is used when the workpiece is connected to the anode and the electrode is connected to the cathode. Welding thick large workpiece; DC reverse connection: when the workpiece is connected to the cathode and the electrode is connected with the anode, it is called DC reverse connection. At this time, the workpiece is less heated and suitable for welding Bo Xiaogong. Piece. When alternating current welder is used for welding, the polarity of the two poles alternates alternately, so there is no problem of positive connection or reverse connection.