What are the principles and characteristics of plasma welding?

Principle: Plasma arc cutting is a common cutting process for metal and nonmetal materials. It uses high-speed, high-temperature and high-energy plasma airflow to heat and melt the cut material, and uses internal or external high-speed airflow or water flow to discharge the melted material until the plasma airflow penetrates the back to form a cut.

Features:

(1) Micro-plasma arc welding can weld foil and thin plate.

(2) It has pinhole effect, and can realize single-sided welding and double-sided free forming.

(3) The plasma arc has high energy density, high arc column temperature and strong penetration ability, and can realize the groove-free welding of steel with the thickness of 10 ~ 12 mm, and can be formed by one-time penetration on both sides, with high welding speed, high productivity and small stress deformation.

(4) The equipment is complex, the gas consumption is high, and the assembly clearance and the cleanliness of the workpiece are strict, so it is only suitable for indoor welding.

Extended data:

Plasma arc welding is a high quality welding method. The depth-width ratio of weld is large, the heat affected zone is narrow, the deformation of workpiece is small, and there are many kinds of weldable materials. Especially with the development of pulsed current plasma arc welding and melting electrode plasma arc welding, the application range of plasma arc welding has been expanded.

Plasma arc welding is very similar to TIG welding, and their arc is formed between the pointed tungsten electrode and the workpiece. However, by arranging electrodes in the welding torch, the plasma arc can be separated from the airbag of protective gas, and then the plasma can be pushed to a copper nozzle with good hole shape to compress the arc.

According to the different connection modes of power supply, plasma arc has three forms: non-transfer type, transfer type and combined type.

(1) The tungsten electrode of non-transfer plasma arc is connected to the negative terminal of power supply, and the nozzle is connected to the positive terminal of power supply. A plasma arc is generated between the tungsten electrode and the nozzle. Under the pressure of plasma gas, the arc column is ejected from the nozzle to form a plasma flame.

(2) The tungsten electrode transferring the plasma arc is connected to the negative end of the current, and the weldment is connected to the positive end of the current, so that a plasma arc is generated between the tungsten electrode and the weldment. Because transfer arc can transfer more heat to weldments, almost all metal welding and cutting adopt transfer plasma arc.

(3) When the combined plasma arc works, the non-transfer arc and the transfer arc coexist at the same time, so it is called the combined plasma arc. Non-transfer arc plays the role of arc stabilization and supplementary heating, and transfer arc directly heats the weldment to melt it for welding. Mainly used for micro-beam plasma arc welding and powder surfacing.

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