Generation of the Plasma Arc (2 Ways):

Plasma cutters produce the plasma in one of two ways: High-Frequency (HF) Contact or Pilot Arcs. Which one your plasma cutter uses depends on how old it is; the new high tech equipments use pilot arcs. The major dissimilarity is that HF Contact models have to close a circuit with a work piece that conducts electrical energy in order to cut while the pilot arc models can cut anything. They work in very different ways.

HF contact method of generating plasma is still found in low financial plan plasma cutters and in older plasma cutters. How it works is the plasma cutting component is connected to the work piece by a clamp and wire and when you touch the nozzle of the torch to the work piece an electric circuit is created. An electric arc zips from the work piece threw the plasma torch nozzle to the negative electrode inside the torch head. At the same time, pressurized inert gas runs in the opposite way, from the torch head out onto the work piece. As the gas surges past the zapping electric arc it is heated to around 50,000 degrees Celsius. At that heat the gas becomes plasma which is a form of matter that is a liquid and a gas at the same time. It is this super hot, super fast moving plasma that cuts the metal. The HF contact technique is said to contain one cycle since the major plasma flow is created in one step.

The Pilot Arc technique is a two cycle procedure. First, a high power, low amperage circuit is used to make a small, high intensity flash in the body of the torch which creates a small pocket of plasma in the torch head (note that the plasma is previously produced in the torch without the required to touch the work piece, this is what eliminates the require for a conducting work piece). Now, you can use a trigger to ignite the main plasma arc that will be used for cutting whatever it is you desire to cut. Pilot Arc is the technique used in CNC plasma cutting applications.