Plasma Cutter History

The plasma-arc process had its origin almost 50 years ago, during the height of World War II. In an effort to improve the joining of aircraft materials, a method of welding was developed that used a protective barrier of inert gas around an electric arc to protect the weld from oxidation.

Over the course of the next couple of decades, it was discovered that by restricting the opening through which the inert gas passed, the heat produced by the process was greatly increased. At the same time, the smaller opening caused the flow of gas to speed up dramatically, ultimately blowing out a channel in the work.

The plasma-arc cutting process started seeing commercial use in the first few years of the sixties. It was an extremely expensive process to undertake, and most cutting was performed by large burning services that used their systems continuously to help amortize the equipment.

In the ensuing years, various manufacturers have realized the enormous benefit even small shop owners could derive from being able to burn both ferous and non-ferrous metals. Today, dozens of manufacturers offer portable plasma cutters -- some so light they can be carried with little effort. Units are starting to appear with built-in air compressors that make the whole operation fully mobile.

Most, if not all, of the light portable plasma cutters are 110 volt machines that are suited primarily for cutting sheetmetal and other light work. The next level up are the 220 volt machines with 50 to 80 amp output current. These are portable from the standpoint that one person can put it on a truck and take it to the job.

Plasma Cutters

HOW A
PLASMA CUTTER WORKS

Plasma cutter work by sending an electric arc through a gas that is passing through a constricted opening. The gas can be shop air, nitrogen, argon, oxygen. etc.

This elevates the temperature of the gas to the point that it enters a 4th state of matter. We all are familiar with the first three: i.e., solid, liquid, and gas. Scientists call this additional state plasma. As the metal being cut is part of the circuit, the electrical conductivity of the plasma causes the arc to transfer to the work.

The restricted opening (nozzle) the gas passes through causes it to sqeeze by at a high speed, like air passing through a venturi in a carburetor. This high speed gas cuts through the molten metal. The gas is also directed around the perimeter of the cutting area to shield the cut.

In many of today's better plasma cutters, a pilot arc between the electrode and nozzle is used to ionize the gas and initially generate the plasma prior to the arc transfer.

Other methods that have been used are touching the torch tip to the work to create a spark, and the use of a high-frequency starting circuit (like a spark plug). Neither of these latter two methods is compatible with CNC (automated) cutting.

The photo at right shows consumables from a Hypertherm Powermax 900 plasma cutter. The electrode is at the center, and the nozzle just below it. The orange piece above the electrode is the swirl ring, which causes the plasma to turn rapidly as it passes.

While these parts are all referred to as consumables, it is the electrode and nozzle that wear and require periodic replacement.