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Learn welding knowledge: MIG welding (MIG welding)

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Metal arc welding (MIG welding)

(1) Principles and characteristics

TIG welding using a molten electrode is called TIG welding, or MIG welding for short. The welding wire is transported by the wire feed roller to the welding area, generates an arc with the base metal. And melts the welding wire and the base metal to form a molten pool. Argon gas flows out of the nozzle for protection, and the weld is formed after the welding gun moves. Since the electrode is a welding wire, the welding current can be greatly increased and the heat is concentrated, so it can be used to weld thick plates. At the same time, it is easy to mechanize and automate the welding process.

The transfer form of molten arc welding droplets usually adopts spray transfer. Spray transfer occurs at higher arc voltage and larger current density. The welding current when spray transfer occurs is called the critical current, which is related to the diameter of the welding wire and the type of protective gas.

(2) Welding process parameters

Since melting arc welding has higher requirements for the protection of the molten pool, if the protection is poor, the surface of the weld will wrinkle. So the nozzle diameter and gas flow rate are correspondingly larger than those of tungsten arc welding. Usually the nozzle diameter is About 20mm, the argon flow rate is within the range of 30~60L/min.

(3) Welding equipment

1) In order to achieve spray transition and reduce spatter. The welding power supply uses DC power supply for argon arc welding and is connected in reverse. When using fine welding wire, use a constant velocity wire feeding system and balance the external characteristic power supply. When using thick welding wire, use a uniformly adjusted wire feeding system and balance the external characteristic power supply.

2) Wire feeding mechanism. The wire feeding mechanism of fusion electrode argon arc welding is the same as that of CO2 gas shielded welding, and is also divided into push wire type, drawing type and push-pull wire type.

3) Gas supply system. The gas supply system for melting electrode argon arc welding includes gas bottles, pressure reducers, flow meters and solenoid gas valves.

4) The function of the welding gun is to hold the electrode, conduct the welding current and transport the protective gas. The welding gun handle is equipped with start and stop buttons. Welding guns are available in water-cooled or air-cooled types. The welding current used by air-cooled welding guns is less than 150A; the welding current used by water-cooled welding guns is greater than 150A.

5) Control system

(A) Pre-supply the shielding gas before arc ignition, and delay shutting off the gas when welding stops.

(B) Wire feed control and speed adjustment include feeding, retracting and stopping of the welding wire, and evenly adjusting the wire feed speed.

(C) Control the main circuit on and off. When starting the arc, you can turn on the power before or at the same time as wire feeding; when welding stops, you should stop the wire first and then turn off the power, so that the arc crater can be filled and the welding wire and welding wire can be avoided. The pieces stick firmly.

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