How a Plasma Cutter Works

What is plasma?

To properly explain how a plasma cutter works, we must begin by answering the basic question “What is plasma?  In its simplest terms, plasma is the fourth state of matter.  We commonly think of matter having three states: a solid, a liquid, and a gas.  Matter changes from one state to the other through the introduction of energy, such as heat.  For example, water will change from a solid (ice) to its liquid state when a certain amount of heat is applied.  If the heat levels are increased, it will change again from a liquid to a gas (steam).  Now, if the heat levels increase again, the gases that make up the 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 cleaner, faster cutting process than with oxyfuel. 

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 work piece and blowing away the molten material. 

Plasma system components

• Power supply -- The plasma power supply converts single or three phase AC line voltage into a smooth, constant DC voltage ranging from 200 to 400VDC.   This DC voltage is responsible for maintaining the plasma arc throughout the cut.  It also regulates the current output required based on the material type and thickness being processed.
• Arc Starting Console – The ASC circuit produces an AC voltage of approximately 5,000 VAC at 2 MHz which produces the spark inside of the plasma torch to create the plasma arc.
• Plasma torch – The function of the plasma torch is to provide proper alignment and cooling of the consumables.  The main consumable parts required for plasma arc generation are the electrode, swirl ring, and nozzle.  An additional shielding cap may be used to further improve cut quality, and all the parts are held together by inner and outer retaining caps.

The vast majority of plasma cutting systems today can be grouped into either conventional or precision categories.