The method of welding copper is gas welding, manual carbon arc welding, manual arc welding and manual argon arc welding. Large structure can also be welded by automatic welding. (1) copper gas welding. The most commonly used butt joints for welded copper are lap joints and T-joints. Two kinds of wire can be used in gas welding, one kind of wire containing deoxidizing element, such as silk 201 and 202, another kind of copper wire and material cutting strip, and gas agent 301 as the flux. Neutral flame should be used when welding copper. (2) the hand arc welding edge of copper. When the thickness of the weldment is greater than 4 mm, it must be preheated before welding, and the preheating temperature is generally around 400-500 C. When welding with copper 107 electrode, DC power should be adopted. Short arc should be used when welding, and the electrode should not be swinging horizontally. The welding line can be improved by reciprocating straight movement. The step back welding method should be adopted for long weld. The welding speed should be as fast as possible. Interlayer slag must be thoroughly removed during multi-layer welding. Welding should be carried out in a well ventilated place to prevent copper poisoning. After welding, use flat head hammer to strike weld, eliminate stress and improve weld quality. (3) manual argon arc welding of copper. When the manual argon arc welding of copper was made, the wire 201 (special copper wire) and the wire 202 were used, and the copper wire, such as T2, was also used. Before welding, the welding edge of the workpiece and the oxide film, oil and other dirt on the surface of the welding wire must be cleaned up so as to avoid blowholes and slag inclusion. Cleaning methods include mechanical cleaning and chemical cleaning. When the thickness of the butt joint plate is less than 3 mm, it does not open the groove; when the thickness is 3~10 mm, the V groove is opened and the angle of the groove is 60-70. When the plate thickness is more than 10 mm, the X groove is opened and the angle of the slope is 60-70. According to the plate thickness and groove size, the butt joint assembly clearance is selected in the range of 0.5-1.5 mm. The manual argon arc welding of copper is usually made by direct current connection, that is, tungsten electrode is connected to the negative electrode. In order to eliminate porosity and ensure reliable fusion and penetration at the root of weld, it is necessary to increase welding speed, reduce argon consumption and preheat the weldment. When the thickness of the plate is less than 3 mm, the preheating temperature is 150-300 C; when the thickness is more than 3 mm, the preheating temperature is 350-500 C. The preheating temperature should not be too high, otherwise the mechanical properties of the welded joint will be reduced. There are also copper carbon arc welding. Carbon arc welding uses electrodes with carbon electrodes and graphite electrodes. The welding wire used for carbon arc welding of copper is also the same as that used for gas welding. It can also be used as cutting bar for parent material, such as gas welding copper flux, such as gas agent 301.