Plasma Arc Welding: Working Principle, Advantages, Disadvantages and Applications

What is Plasma Arc Welding?

Plasma arc welding (PAW) is a welding process in which the electric arc is formed between an electrode and the workpiece. The electrode used in the plasma arc welding is usually but not always made of sintered tungsten. The process of plasma arc welding was discovered by Robert Merrell Gage in 1957.

By positioning the electrode within the body of the welding torch, the plasma arc can be separated from the shielding gas envelope. Then, the plasma is forced through a fine-bore copper nozzle which constricts the arc and the plasma exits the nozzle orifice at high velocities and a temperature approaching 2000 °C.

Plasma arc welding uses a non-consumable tungsten electrode and an electric arc is constricted through a fine-bore copper nozzle. Most commercial metals and alloys can be welded by the plasma arc welding.

By changing the welding current, plasma gas flow rate and the diameter of the nozzle orifice, several variations can be done in the plasma arc welding process, such as −

• Micro Plasma (when welding current is less than 15 A)

• Melt-in Mode (for welding current 15 to 400 A)

• Keyhole Mode (for welding current more than 100 A)

Working Principle of Plasma Arc Welding

Plasma arc welding is a welding process in which a coalescence is generated with the temperature which is developed from a setup between a tungsten alloy electrode and the workpiece.

In case of plasma arc welding, there are three types of gas supplies used, viz. −

• Plasma Gas - The plasma gas supplies throughout the nozzle turn into ionized.

• Shielding Gas - The shielding gas supplies throughout the external nozzle and protects the weld from the atmospheric contamination

• Back Purge Gas - The back purge gas is mainly used when some particular materials are being welded.

Equipment Used in Plasma Arc Welding

The schematic diagram of plasma arc welding is shown in the figure. The equipment used in the plasma arc welding are given as follows −

• Power Supply - The power supply used in the plasma arc welding is a DC power source of the voltage value ranging from 30 V to 250 V.

• A high frequency generator and current limiting resistors are used for the arc ignition.

• The welding torch having an electrode as well as water-cooling arrangement for saving the nozzle and the electrode’s life span from dissolving due to extreme heat generated while welding.

Advantages of Plasma Arc Welding

The chief advantages of the plasma arc welding are given as follows −

• The plasma arc welding has a greater energy concentration as compared to other arc welding processes.

• With the plasma arc welding, a deep and narrow penetration is achieved, with a maximum depth of 12 to 18 mm depending upon the material.

• Plasma arc welding has greater arc stability that allows a much longer arc length and much greater tolerance to arc length changes.

• Power consumed by the plasma arc welding is also low.

• Welding speed high with the plasma arc welding.

Disadvantages of Plasma Arc Welding

The disadvantages of the plasma arc welding are given as follows −

• The plasma arc welding process is noisy.

• It requires highly skilled welders.

• The plasma arc welding requires the replacement of orifice.

• The equipment used for the plasma arc welding is expensive and complex.

• It produces more radiation.

• With the plasma arc welding, the welding procedures tend to be more complex and less tolerant to variations in fit-up, etc.

Applications of Plasma Arc Welding

Some of the applications of the plasma arc welding are given as follows −

• Plasma arc welding process is mainly used to tools, die and mold, etc.

• The plasma arc welding is used in various industries like aerospace, marine industry, etc.

• Plasma arc welding is also used to weld stainless tubes and pipes.

• It is used for welding of the turbine blades.

• Plasma arc welding is also applicable for electronic industries.