How Plasma Cutters Work2012-5-13
Plasma cutters cut metal using a plasma torch. For it work, plasma (the fourth state of matter) has to be created. Plasma is a super-heated (15,000 degrees Celsius) substance that is a gas and a liquid at the same time. Two things are required to create plasma, a gas and a heat source.
Plasma cutters use inert gases (often compressed air) and electricity to create plasma. The plasma cutting equipment is set up so that it creates an electric circuit with the metal that is being cut. When the end of the torch is touched to the metal, the circuit is created and a spark flashes through the nozzle of the plasma torch. This spark travels to the negative electrode in the torch handle and meets with the rapidly flowing inert gas. When the gas comes into contact with the electricity it is heated to around 15,000 degrees Celsius and becomes plasma. The plasma surges out of the tiny nozzle and onto the surface that you want to cut. The tiny opening in the nozzle focuses the plasma flow and causes it to speed up. It is the speed, temperature and focus of the plasma that enables it to cut metal almost as well as a laser.
As long as everything is set up properly, the cuts can be very clean with little noticeable affect on the rest of the work piece.
Since a plasma cutter's function requires an electric circuit they can cut pretty much anything that conducts electricity including copper, aluminum and stainless steel.
There are two methods used to create the plasma for plasma cutting.
HF (High Frequency) Contact. This method is generally used in low budget equipment since it cannot be used for CNC (Computer Numeric Control) Plasma Cutting operations. To generate plasma, this method uses a high frequency, high voltage spark. When the plasma torch touches the material to be cut, thereby closing the circuit, the spark fires into the torch head and plasma is created.
Pilot Arc. This method is a little more involved since it produces plasma in two cycles. Cycle one: inside the body of the torch a low current, high voltage circuit creates a high intensity spark. This spark creates a small volume of plasma (the pilot arc). Cycle two: the pilot arc remains static until the torch head is touched to the metal at which point a trigger allows the pilot arc to light the main flow of gas and plasma cutting begins.
The old versions of plasma cutters (plasma cutting was invented during World War II) started the arc with high frequency, high voltage circuits. This means that the operator risked electrocution if they were not careful. Also, these old machines are difficult to repair and maintain.
A plasma cutter can cut metals of different thicknesses. The size of the machine is what determines the sever cut. "Sever cut" is the standard used to define the thickest possible cutting potential for a given plasma cutter. The thicker the metal to be cut the easier it is for a CNC plasma cutter to operate. You have to watch out though, the closer the metal thickness comes to the sever cut rating of a plasma cutter the messier the cut may be. This means you may have to clean up the edges after you are finished cutting.
Since CNC plasma cutters are computer controlled they are very precise. For very repetitive projects or industrial applications a CNC plasma cutter is must. These machines can do the same thing over and over and over all day long.
When you are using plasma cutters please make sure that you follow safety guidelines.
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