Plasma cutting is a process that is used to cut steel and other metals using a plasma torch. In this process, an inert gas (or compressed air) is blown at high speed out of a nozzle; while an electrical arc is formed through that gas from the nozzle to the surface being cut, turning some of that gas to plasma.
The HF Contact type typically found in less expensive machines uses a high-frequency, high-voltage spark to ionise the air through the torch head and initiate an arc.
The Pilot Arc type uses a two stage approach to producing plasma. First, a high-voltage, low current circuit is used to initialize a very small high-intensity spark within the torch body, thereby generating a small pocket of plasma gas.
Since Plasma Machines produce a very hot and very localized “cone” to cut with, they are extremely useful for cutting sheet metal in curved or angled shapes.
Analog Plasma Machines, typically requiring more than 2 kilowatts, use a heavy mains-frequency transformer. Inverter Plasma Machines rectify the mains voltage into DC, which is fed into either an IGBT or a MOSFET.
Plasma gouging is a related process, typically performed on the same equipment as plasma cutting. Plasma gouging uses a different torch configuration, and a longer torch-to-workpiece distance, to blow away metal.
Plasma Machines have also been used in CNC (computer numerically controlled) machinery. Manufacturers build CNC cutting tables, some with the cutter built in to the table.
Plasma torches were once quite expensive, usually at least a $1,000. For this reason they were usually only found in professional welding shops and very well-stocked private garages and shops.