Plasma Cutting (PAC)
Plasma Cutting (PAC) is an electric arc cutting process that severs metal by melting a localized area with a constricted arc of super heated gas, which melts the base material at high velocity. The plasma torch has a recessed electrode which uses electrical energy to heat the gas which may be air, nitrogen or oxygen. The gas is delivered to the torch at high pressure (100 psi) and is forced through a constricting orifice held in close proximity to the base material being cut.
Plasma Cutting is ideal for many industrial applications because it can cut any electrically conductive metal if its thickness and shape permit full penetration by the plasma jet. Plasma Cutting can cut nonferrous materials and is faster than oxy-fuel cutting for ferrous materials that are less than two inches thick.
Among the available process variations are:
- Conventional plasma cutting where the arc is constricted by the nozzle only and no shielding gas is added, nitrogen or air serves as the cutting gas; (Air systems are very popular with manual PAC)
- Oxygen plasma arc cutting, which requires the use of special consumables that are made to operate in an oxidizing atmosphere, is widely used for mechanized cutting of steel since the additional oxygen to the cut zone can boost the cutting speeds by approximately 25%;
- Water injection cutting, which utilizes water introduced inside the nozzle to provide additional arc constriction to improve cut surface quality and increase cutting speeds.
A recent process variation is precision plasma where arc constriction is increased dramatically to provide a high energy density for improved cut squareness and cut quality. Most Plasma Cutting equipment for conventional cutting utilizes only an orifice gas, generally nitrogen or air. Argon or nitrogen can also be used in some applications. Nitrogen/hydrogen and argon/hydrogen are used in special cutting applications, particularly for stainless steel, aluminum and with plasma arc gouging.
Why Plasma Cutting?
- High quality cutting of both ferrous and non-ferrous materials, particularly useful for cutting aluminum, copper and stainless steel
- “Instant” cutting starts with no preheat required
- Process is readily mechanized for high volume, high speed cutting applications
- Equipment is available for cutting a wide range of material thicknesses
- Precision plasma can produce laser-quality cuts in some applications for significantly lower equipment costs
Plasma Cutting Limitations
- Cut squareness is affected by plate thickness and material type; more material tends to be removed from the top of the kerf rather than the lower
- With manual cutting, high levels of noise and fume are generated which require the operator to wear protective equipment
- Equipment is more costly than oxy-fuel cutting
- For some materials, grinding of the cut surface must be done to remove chemically altered material before subsequent welding operations are conducted. High operating voltages present the danger of electric shock.