
Edmonton, Calgary, CNC plasma cutting machine from 12000$
galleryPlasma gouging is a related process, typically performed on the same equipment as plasma cutting. Instead of cutting the material, plasma gouging uses a different torch configuration (torch nozzles and gas diffusers are usually different), and a longer torch-to-workpiece distance, to blow away metal. Plasma gouging can be used in a variety of applications, including removing a weld for rework. The additional sparks generated by the process requires the operator to wear a leather shield protecting their hand and forearm. Torch leads also can be protected by a leather sheath.
Analog plasma cutters, typically requiring more than 2 kilowatts, use a heavy mains frequency transformer. Inverter plasma cutters rectify the mains voltage into DC, which is fed into either an IGBT or a MOSFET. IGBT transistors operate independently of one another whilst MOSFET transistors need to be paralleled. With paralleled MOSFET transistors if one of the transistors activates prematurely it can lead to a cascading failure of one quarter of the inverter. IGBT transistors do not have this problem as they are independent however are very expensive to manufacture and generally used in high current machines where it is not possible to parallel sufficient MOSFET transistors. The transistors are switched at thousands of Hertz, which greatly reduces the magnetic flux in the step down transformer, and therefore the size of the transformer is reduced accordingly. The switch mode topology is referred to as a dual transistor off-line forward converter.
Plasma cutters use a number of methods to start the pilot arc, depending on the environment the unit is to be used in and its age. Older cutters use a high voltage, high frequency circuit to start the arc. This method has a number of disadvantages, including risk of electrocution, difficulty of repair, sparkgap maintenance, and the large amount of radio frequency emissions. Plasma cutters working near sensitive electronics, such as CNC hardware or computers, use the contact start method. The nozzle and electrode are in contact. The nozzle is the cathode, and the electrode is the anode. When the plasma gas begins to flow, the nozzle is blown forward. A third, less common method is capacitive discharge into the primary circuit via a Silicon Controlled Rectifier.
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