Plasma arc welding.
Plasma arc welding (PAW) is an arc welding process similar to gas tungsten arc welding (GTAW). The electric arc is formed between an electrode (which is usually but not always made of sintered tungsten) and the workpiece. The key difference from GTAW is that in PAW, by positioning the electrode within the body of the torch, the plasma arc can be separated from the shielding gas envelope. The plasma is then forced through a fine-bore copper nozzle which constricts the arc and the plasma exits the orifice at high velocities (approaching the speed of sound) and a temperature approaching 20,000 °C. Plasma arc welding is an advancement over the GTAW process. This process uses a non-consumable tungsten electrode and an arc constricted through a fine-bore copper nozzle. PAW can be used to join all metals that are weldable with GTAW (i.e., most commercial metals and alloys). Several basic PAW process variations are possible by varying the current, plasma gas flow rate, and the orifice diameter, including:
Micro-plasma (< 15 Amperes)
Melt-in mode (15–400 Amperes)
Keyhole mode (>100 Amperes)
Plasma arc welding has a greater energy concentration as compared to GTAW.
A deep, narrow penetration is achievable; reducing distortion and allowing square-butt joints in material up to ½” (12 mm) thick.
Greater arc stability allows a much longer arc length (stand-off), and much greater tolerance to arc length changes.
PAW requires relatively expensive and complex equipment as compared to GTAW; proper torch maintenance is critical
Welding procedures tend to be more complex and less tolerant to variations in fit-up, etc.
Operator skill required is slightly greater than for GTAW.
Orifice replacement is necessary.