Plasma cutters are actually a very simple, economical technique to cut a variety of shapes in metals very accurately. The introduction of these cutters or torches has revolutionized the speed, accuracy and types of cuts made in all types of metals as long as these metals are capable of conducting electricity. Plasma cutting is a process that severs metals by using a constricted arc to melt a small area of work. Plasma cutters only require a low skill level and due to their effectiveness, plasma cutters are beginning to threaten to obsolete a large number of conventional metalworking tools.
Plasma is the result of a gas boosted to an extremely high temperature, causing the energy to break apart the gas molecules and the atoms begin to split. Normal atoms contain protons and neutrons in the nucleus, surrounded by a cloud of electrons, but with plasma, the electrons separate from the nucleus.
Once the energy of heat releases the electrons from the atom, the electrons begin to move around quickly. The electrons are negatively charged, and they leave behind their positively charged nuclei, known as ions. The quickly moving electrons collide with other electrons and ions, releasing vast amounts of energy, creating a plasma with its unique status and unbelievable cutting power.
Plasma cutters work very similarly to the explanation above. Plasma cutters send pressurized gas, such as nitrogen, argon, or oxygen through a small channel that contains a negatively charged electrode in the center. When power is applied to the negatively charged electrode and the tip of the nozzle is touched to the metal a circuit is created, generating a powerful spark between the electrode and the metal.
Inert gas passes through the channel and the spark heats the gas until the plasma is created, reducing metal to molten slag. This plasma conducts electrical current and the cycle of creating the arc is continuous as long as power is supplied to the electrode and the plasma stays in contact with the metal that is being cut.
The plasma cutter nozzle has a second set of channels that are important because this channel ensures the contact, protects the cut from oxidation and regulates the unpredictable nature of plasma. The second set of channels in the cutter nozzle also releases a constant flow of high-speed gas that shields the cut. The pressure of this gas flow controls the radius of the plasma beam.
A plasma cutter set-up consists of a power supply, ground clamp, and a hand torch. The power supply is necessary to convert the AC line voltage into a user-adjustable regulated DC current. The hand torch contains a trigger for controlling the cutting and a nozzle for allowing compressed air to blow through along with an electrode mounted inside the hand torch, directly behind the nozzle.
Many of today’s better plasma cutters contain a pilot arc found between this electrode and the nozzle. This pilot arc is used to ionize the gas and initially generate the plasma prior to the arc transfer.