Plasma arc welding (PAW) is a process used in place of gas tungsten arc welding (GTAW). It can be used to weld any metal that can be welded using gas tungsten arc welding, which includes almost all commercially used alloys and metals. Plasma arc welding is considered to be an improvement upon the GTAW process because the arc is more focused.
The electrode of the plasma arc welder is positioned inside the torch body. This allows the plasma arc and the shielding gas to be separated, which distinguishes plasma arc welding from gas tungsten arc welding. The plasma is forced through a copper orifice at very high speeds and temperatures. The plasma arc reaches nearly 36,032 degrees Fahrenheit (about 20,000 degrees Celsius) and reaches speeds nearing that of sound.
The plasma arc is focused by the narrow constriction of the copper orifice. This increased focus gives the process more arc stability and energy concentration than GTAW. In addition, the focused arc used in this method allows the process to be used in automated equipment, thus eliminating the need to place human workers in harm's way for dangerous welding operations.
The process of plasma arc welding can also be varied based on the key components: the electrical current being used to create the arc, the flow rate of the plasma gas and the diameter of the copper orifice. By altering any of these components, different results and modes of plasma arc welding can be achieved. The three most common variations of the plasma arc welding process are micro-plasma, melt-in mode and keyhole mode.
Plasma arc welding requires the flow of at least two types of gas. These gas types are plasma gas and shielding gas. The actual welding process uses plasma gas, and the shielding gas acts as a flux, protecting the weld from the outside atmosphere. A third type of gas, called trailing gas or back-purge, might also be needed when welding certain metals.
Although plasma arc welding is an improvement over gas tungsten arc welding, there are some drawbacks that limit its use. This process is very expensive and complex when compared with the process of gas tungsten arc welding. Plasma arc welding requires routine maintenance of the torch and replacement of the orifice. The equipment used for plasma arc welding also requires a higher level of operator skill than that of gas tungsten arc welding, and this process is less forgiving in terms of fit-up variations and tolerances.