Plasma cutting is the process that is used to cut steel and other metals of different thicknesses using a plasma torch. An inert gas or compressed air is blown at high speed out of a nozzle and at the same time an electric arc is formed through the gas from the nozzle to the surface being cut, turning part of that gas to plasma. The plasma generated is hot enough to melt the metal being cut and moving very fast, thus blowing molten metal away from the cut. A high-frequency, high-voltage spark is needed to ionize the gas through the torch head and initiate the arc. This style of plasma cutter requires the torch to be in contact with the job material when starting, and is not suitable for CNC (automatic) cutting.
Pilot Arc Plasma Cutters
Pilot Arc style plasma cutters use a two cycle system to produce the plasma, avoiding the need for any initial torch tip contact. A high voltage, low current circuit is used to establish a very small high-intensity spark in the torch body, that creates a small pocket of plasma gas, or pilot arc. The pilot arc operates until it is brought into the designed range of the workpiece, and then ignites the main plasma cutting arc. Plasma arcs are extremely hot and are in the range of 25,000° C (45,000° F).
Plasma cutting is a cost effective and versatile way of cutting thin and thick materials alike. Hand-held torches can cut up to 2 inches (48 mm) thick steel plate, and automated / computer-controlled torches can cut steel up to 6 inches (150 mm) thick. Plasma cutters produce a very hot and localized arc to cut with, and they are extremely useful for cutting sheet metal in curved or angled shapes.
Inverter Plasma Cutters
Inverter plasma cutters rectify (convert) the AC main supply to DC, which is then fed into a high-frequency transistor inverter, allowing its size and weight to be reduced, lowering cost to the consumer.
New Technology
In the past decade, new models with a smaller nozzle and a thinner plasma arc now allow close to laser precision cuts. A lot of manufacturers have combined precision CNC control with today's torches, enabling fabricators to produce parts that require little or no finishing. Plasma torches were quite expensive, and they were usually only found in professional welding shops or very well-stocked private garages or shops. However, today modern plasma cutting torches are considerably cheaper, and within the price range of many hobbyists. Older units were very heavy, but still portable. Newer plasma cutters with inverter technology weigh a lot less, and equal or exceed the capability of the older machines.
Safety
Proper eye protection such as welding goggles and face shields are needed to prevent eye damage, called arc-eye or flash burn, as well as injury from debris.
Tips
- Plasma cutting outfits eliminate the need of storing and transporting awkward, expensive, and explosive specialty gases.
- The artistic welder, hobbyist, hobby farm owner, etc, is faced with a wide variety of metals, and a plasma cutting machine is a cost effective solution.
Written by Brian Chalmers
