Plasma cutting essentially makes use of a plasma jet to cut metals. Plasma is basically the 4th state of matter. Matter changes from one state to another and when steam is heated to a very high temperature, then the gases in steam become ionised and electrically conductive and turn into plasma. This plasma is used by a plasma cutter to transfer electric energy from a power supply to a conductive material and cuts it. Plasma cutting is a faster and a cleaner cutting process compared to oxyfuel cutting.
When any gas such as nitrogen, oxygen, argon or even shop air is passed via a small hole in a nozzle, a plasma arc is formed. When an electric arc from a power source is introduced to this high-pressure gas flow, a plasma jet is formed which reaches a very high temperature of up to 40,000oF that pierces through the workpiece and blows away the molten material.
Components of the Plasma Cutting System
The torch provides proper cooling and alignment of the torch consumables i.e. the swirl ring, nozzle, electrode, shield cap and inner and outer retaining caps.
The power supply converts the AC current into a smooth DC voltage which helps to maintain the plasma arc constant through the entire process of cutting. The DC voltage also helps to regulate the output on basis of the type and thickness of the material being cut.
Arc Starting Console (ASC)
The ASC produces an AC current of around 5000 VAC at 2 MHz that produces a spark inside the torch in order to produce the plasma arc.
Types of Plasma Cutting Systems
Most plasma cutters are classified as conventional plasma systems or precision systems.
Conventional Plasma Cutting Systems
These essentially make use of shop air as the plasma gas and the plasma arc shape is defined by the nozzle’s orifice. This kind of plasma arc usually has an amperage of around 12-20 Kamps/square inch. All handheld plasma cutters make use of conventional plasma systems and it is used in certain mechanised jobs where the part tolerances are more tolerant.
Precision Plasma Cutting Systems
These are high current density systems which are designed to produce the highest quality and sharpest cuts that are possible with plasma cutting. The design of the plasma cutting torch and the consumables are more complex and more pieces are added to shape and constrict the plasma arc. The amperage of a precision plasma arc ranges between 40-50 Kamps/square inch and multiple gases like nitrogen, oxygen, air of high purity or a nitrogen/argon/hydrogen mixture are used as plasma gas for best cutting results on varied conductive materials.
Today, the plasma cutting process is extremely versatile and has become a very popular way of cutting that is used by several types of fabrication operations, both big and small.