Plasma cutting came into existence since World War II. Since then plasma cutting technology has evolved and today it is the most popular cutting process to cut metals such as stainless steel, carbon steel, or aluminium. You can use plasma cutting for precision cutting on gauge material which is even 6” in thickness and it can also be used in conjunction with waterjet and oxyfuel cutting. In this two-part guide, we take a look at some of the basics of plasma cutting.
The plasma that is used in plasma cutting is a heated gas stream that is electrically charged and becomes ionized as it is heated to very high temperatures. A plasma torch makes use of a copper nozzle to compress the ionized gas and focus its energy onto a small section. The gas that flows through the nozzle melts the molten metal that is heated by the gas.
The swirling gas helps the cutting process in many ways. The swirling action increases cooling. This cool barrier protects the copper nozzle from the intense heat of the plasma arc. As the amperage increases, the ionization also increases and the cooling decreases and this reduces the nozzle life. If the plasma gas is stationary and is not swirled, a bevel occurs on either side of the cut. The swirling of the gas ensures that the arc falls along the one portion of the cut uniformly.
Creating a Plasma Arc
The torch body contains three components: the electrode, swirl or gas baffle, and the nozzle. The negative side of the power supply is connected to the electrode while the positive terminal is connected to the nozzle.
When the plasma cutter is given an electrical input, a high negative voltage is applied to the electrode. The baffle swirls the gas which then flows to the torch. The circuit of the nozzle closes and provides a path to the positive terminal of the power supply. A small spark is produced that jumps between the electrode and the nozzle that ionizes a conduit through the gas.
A bigger DC arc starts flowing between the electrode and the nozzle, known as the pilot arc. This pilot arc shoots out from the nozzle propelled by the gas flow and makes contact the workpiece. When the pilot arc moves to the workpiece, the main arc is formed. The nozzle is removed from the circuit when the relay of the nozzle opens. After the relay of the nozzle is opened, the main arc increases to amperage suitable for cutting.
The concludes part one of the two-part guide to the basics of plasma cutting. Check back on our blog for the second part of this series.