FOCUS ON PLASMA CUTTING
THE PLASMA PRINCIPLE
We outline the principles of plasma cutting as well as process variations , key components and variables .
Electrically conductive , ionized gas is called plasma . The plasma cutting process , used in the cutting of electrically conductive metals , utilises this electrically conductive gas to transfer energy from an electrical power source through a plasma cutting torch to the material being cut .
Plasma cutting has long proved to be a flexible and cost-effective method of processing parts . The plasma process can cut aluminium , mild steel , stainless steel and the toughest wear-resistant materials from as little as 1mm thick through to 60mm . Plasma cutting can really shine in some niche applications , such as cutting expanded metal .
It differs from the oxy-fuel process in that the plasma process operates by using the arc to melt the metal whereas in the oxy-fuel process , the oxygen oxidises the metal and the heat from the exothermic reaction melts
“ While the plasma unit is central to the cutting process , it is the sum of the complementary parts which control , hold and move the plasma cutting torch that will ultimately define cut quality .”
the metal . Therefore , unlike the oxy-fuel process , the plasma process can be applied to cutting metals which form refractory oxides such as stainless steel , aluminium , cast iron and non-ferrous alloys .
The plasma cutting process
If heat levels are increased , the gases that make up steam will become ionized and electrically conductive , becoming plasma . A plasma cutter will use this electrically conductive gas to transfer energy from a power supply to any conductive material , resulting in a relatively clean , rapid cutting process .
The plasma arc formation begins when a gas such as oxygen , nitrogen , argon or even shop air is forced through a small nozzle orifice inside the torch . An electric arc generated from the external power supply is then introduced to this high-pressured gas flow , resulting in what is commonly referred to as a plasma jet . The plasma jet immediately reaches temperatures up to 40,000 ° F , quickly piercing through the workpiece and blowing away the molten material .
Precision plasma systems ( high current density ) are designed and engineered to produce the sharpest , highest quality cuts achievable with plasma . The torch and consumable designs are more complex , and additional pieces are included to further constrict and shape the arc . Multiple gases ( such as oxygen , high purity air , nitrogen , and a hydrogen / argon / nitrogen mixture ) are used as the plasma gas for strong results on a multitude of conductive materials .
Key plasma cutting components
The basic plasma arc cutting system consists of a power supply , an arc starting circuit and a torch . These system components provide the electrical energy , ionization capability and process control that is necessary to produce high-quality , highly
16 | sheetmetalplus . com | ISMR July / August 2021