What is Plasma Arc Welding?
Plasma arc welding is a welding technique that is closely related to gas tungsten arc welding. In plasma arc welding the electric arc is created between an electrode and the metal you are working with. The main difference between plasma arc welding and gas tungsten arc welding is that in plasma welding the welder is able to position the electrode within the body of the torch, this allows for the plasma arc to be separated from the shielding gas. The plasma is then fed through a nozzle which constricts the arc and forces the plasma out at a much higher speed and temperature. The technique of plasma arc welding uses a non-consumable tungsten electrode and an arc that is created by forcing the plasma through a fine-bore nozzle. Plasma arc welding can be successfully applied to any metal that can be welded using the gas tungsten arc welding method.
Picture Credit: Trinity Mechanical Services
In plasma arc welding there are at least two separate flows of gas being used. One is the plasma gas which flows through the nozzle and becomes ionized and the other is a shielding gas. The shielding gas flows through the outer nozzle and shields the weld from the atmosphere. Sometimes a third gas is required, this gas is most commonly a back-purge and trailing gas. This third gas is only required when certain materials and methods are being used. Before beginning work on your piece, it is important to know how many gases will be required for the technique you are using.
The process of plasma arc welding can be used on a multitude of different materials and processes. By varying the current, gas flow, and the size of the nozzle being used, the welder is able to produce a deep, narrow penetration that cannot be achieved with different techniques. Plasma arc welding allows for a much longer arc length and has a greater tolerance to changes in arc length. Although the equipment required for plasma arc welding costs more than standard GTAW equipment, many welders feel that the added expense is worth it to achieve the deeper and high quality welds that are done when using plasma. The process of plasma arc welding does require the welder to have a specialized knowledge of the equipment and the gas, but with little practice in controlling the flow rate there is no doubt that any welder who chooses to embrace plasma arc welding will be the better for it.
When the plasma arc is being used for cutting instead of welding, the flow of the plasma gas should be increased so that it can penetrate the metal deeper. This allows for the plasma to cut through the material and the hot molten metal will be removed as cutting dross. The process of plasma arc cutting is different than that of oxy-fuel cutting in that the plasma technique is accomplished by using the plasma arc to melt the metal. In oxy-fuel cutting the oxygen is used to oxidize the metal and the heat produced from the reaction is used to melt the metal. Plasma arc cutting can be used to cut metals that form refractory oxides when being cut, such as stainless steel, aluminum and cast iron.
Since its introduction in 1954 the uses for plasma arc welding and plasma arc cutting have grown a lot. The techniques can now be used on metals that before were unheard of. With advances and discoveries still occurring in the welding world when it comes to the use of plasma, either as a welding agent or as a method of cutting, I’m sure more uses will be discovered. The world of welding continues to grow as new technology is developed and new materials are invented.
Other Plasma Welding, Cutting Resources
- Overview of Plasma Welding
- The Plasma Arc Welding Process (www.pro-fusiononline.com)
- Plasma Cutting Overview and Tips (www.bakersgas.com)