Saturday, August 20, 2011

Plasma cutting

Plasma cutting uses a focused stream of ionized gas, or plasma, to cut through sheet metal. The plasma flows at extremely high temperatures and high velocity and is directed toward the cutting location by a nozzle. When the plasma contacts the surface below, the metal melts into a molten state. The molten metal is then blown away from the cut by the flow of ionized gas from the nozzle. The position of the plasma stream relative to the sheet is precisely controlled to follow the desired cutting path.

Plasma cutting is performed with a plasma torch that may be hand held or, more commonly, computer controlled. CNC (computer numerically controlled) plasma cutting machines enable complex and precision cuts to made. In either type of plasma torch, the flow of plasma is created by first blowing an inert gas at high speed though a nozzle pointed at the cutting surface. An electrical arc, formed through the flow of gas, ionizes the gas into plasma. The nozzle then focuses the flow of plasma onto the cut location. As with laser cutting, this process does not require any physical tooling which reduces initial costs and allows for cost effective low volume production.

The capabilities of plasma cutting vary slightly from laser cutting. While both processes are able to cut nearly any 2D shape out of sheet metal, plasma cutting cannot achieve the same level of precision and finish. Edges may be rough, especially with thicker sheets, and the surface of the material will have an oxide layer that can be removed with secondary processes. However, plasma cutting is capable of cutting through far thicker sheets than laser cutting and is often used for workpieces beyond sheet metal.

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