How Does a Plasma Cutting Machine Work?

Plasma cutters can be used with different working gases to cut all metals that are difficult to cut by oxygen. It should be noted that non-ferrous metals (stainless steel, aluminum, copper, titanium, nickel) cut better.

Its advantage lies in the cutting thickness for small metals, and the plasma cutting speed is fast. When cutting ordinary carbon steel sheets, the speed can reach 5-6 times that of the oxygen cutting method. The cutting surface is bright, the thermal deformation is small, and there is almost no heat affected zone.

Plasma cutting machines are widely used in various industries such as automobiles, locomotives, pressure vessels, chemical machinery, nuclear industry, general machinery, construction machinery and steel structures.

Ⅰ. The working principle and process of plasma cutting machine

1. After the compressed air enters the torch, it is distributed by the gas chamber to form plasma gas and auxiliary gas. The plasma arc has the effect of melting the metal, while the assist gas cools the various parts of the torch and blows away the molten metal.

2. The cut-off power supply consists of two parts: the main circuit and the control circuit.

3. Electrical principle: The main circuit consists of a contactor, a three-phase power transformer with high leakage reactance, a three-phase bridge rectifier, a high-frequency arc ignition coil and maintenance components.

Due to the high leakage reactance, the external characteristics of the power supply are steep. The control circuit completes the entire cutting process through the button switch on the torch: pre-exhaust - main circuit power supply - high frequency arc ignition - cutting process - arc off - stop. The main loop power is controlled by the contactor; the gas flow is controlled by the solenoid valve; the high frequency oscillator is controlled by the control circuit to ignite the arc and stop the high frequency operation after the arc is established.

Various plasma cutting machine arc cutting process parameters directly affect the stability of the cutting process, cutting quality and effect.

Ⅱ. The main incision standards of the plasma cutting machine are briefly described as follows:

1. No-load voltage and arc column voltage. The plasma cutting power supply needs to have a high no-load voltage to facilitate arc starting and make the plasma arc burn stably. The no-load voltage is usually 120-600V, and the arc column voltage is usually half of the no-load voltage. Increasing the arc column voltage can significantly increase the power of the plasma arc, thus increasing the cutting speed and cutting greater thicknesses of sheet metal.

The arc column voltage cannot usually be achieved by adjusting the gas flow and increasing the internal shrinkage of the electrode, but the arc column voltage cannot exceed 65% of the no-load voltage, otherwise the plasma arc will become unstable.

2. The cut-in current of the plasma cutting machine is increased. The cut-in current can also increase the power of the plasma arc, but is limited by the allowable current, which would otherwise thicken the plasma arc column, increase the gap width, and reduce electrode life.

3. The airflow increases. The airflow can not only increase the arc column voltage, but also improve the compaction effect of the arc column, make the plasma arc energy more concentrated, and the eruption force is stronger, which can improve the cutting effect, speed and quality. However, if the gas flow is too high, the arc tower will be shortened, the additional heat will be lost, and the cutting ability will be impaired until the cutting process cannot be performed properly.

4. The electrode shrinks. The so-called shrinkage refers to the distance between the electrode and the end face of the cutting nozzle. Proper spacing allows the arc to be compact in the cutting nozzle and obtain a plasma arc with concentrated energy and high temperature for useful cutting. If the interval is too large or too small, the electrode will burn out badly, the cutting tip will burn out, and the cutting ability will be reduced. The shrinkage rate is generally 8-11mm.

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