Plasma arc cutting is a machining method that uses the heat of a high-temperature plasma arc to partially melt (and evaporate) the metal at the cutting edge of a workpiece, and uses the momentum of high-speed plasma to remove the molten metal to form a cutting edge. Plasma arc cutting machine is a mechanical device that uses plasma cutting technology to process metal materials.

1、 Industrial use

The CNC plasma cutting machine, when combined with different working gases, can cut various metals that are difficult to cut with oxygen acetylene cutting, especially for non-ferrous metals (stainless steel, aluminum, copper, titanium, nickel). Its main advantage is that when cutting metals with small thickness, the ion cutting speed is fast, especially when cutting ordinary carbon steel thin plates, the speed can reach 5-6 times that of oxygen acetylene cutting method, the cutting surface is smooth, the thermal deformation is small, and the heat affected zone is less.

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

2、 Working gas

The development of plasma cutting to the present day has a significant impact on the cutting characteristics, cutting quality, and speed of plasma arc using the working gas (which is the conductive medium and heat carrier of the plasma arc, while also excluding the molten metal in the incision). The commonly used plasma arc working gases include argon, hydrogen, nitrogen, oxygen, air, water vapor, and certain mixed gases.

3、 Cutting specifications

Various plasma arc cutting process parameters directly affect the stability, cutting quality, and effectiveness of the cutting process. The main cutting specifications are briefly described as follows:

1. No load voltage and arc column voltage

The plasma cutting power supply must have a sufficiently high no-load voltage in order to easily initiate the arc and ensure stable combustion of the plasma arc. The no-load voltage is generally between 120-600V, while the arc column voltage is generally half of the no-load voltage. Increasing the arc column voltage can significantly increase the power of the plasma arc, thereby improving cutting speed and cutting thicker metal sheets. The arc column voltage is often achieved by adjusting the gas flow rate and increasing the electrode contraction, but the arc column voltage cannot exceed 65% of the no-load voltage, otherwise it will make the plasma arc unstable.

2. Cutting current

Increasing the cutting current can also increase the power of the plasma arc, but it is limited by the maximum allowable current, otherwise it will cause the plasma arc column to become thicker, the slit width to increase, and the electrode life to decrease.

3. Gas flow rate

Increasing the gas flow rate can not only increase the arc column voltage, but also enhance the compression effect on the arc column, making the plasma arc energy more concentrated and the jet force stronger, thus improving the cutting speed and quality. However, excessive gas flow can actually shorten the arc column, increase heat loss, weaken cutting ability, and ultimately prevent the cutting process from proceeding normally.

4. Electrode shrinkage

The so-called internal contraction refers to the distance between the electrode and the cutting nozzle end face. A suitable distance can enable the arc to be well compressed inside the cutting nozzle, resulting in energy concentration and high temperature plasma arc for effective cutting. If the distance is too large or too small, it will cause severe electrode burnout, nozzle burnout, and reduced cutting ability. The internal shrinkage is generally taken as 8-11mm.

5. Cutting mouth height

The cutting nozzle height refers to the distance from the cutting nozzle end face to the surface of the workpiece being cut. The distance is generally 4-10mm. It is the same as the electrode shrinkage, and the distance needs to be appropriate to fully utilize the cutting efficiency of the plasma arc. Otherwise, it will reduce the cutting efficiency and quality or burn out the cutting nozzle.

6. Cutting speed

The above factors directly affect the compression effect of plasma arc, that is, the temperature and energy density of plasma arc. The high temperature and high energy of plasma arc determine the cutting speed, so all the above factors are related to the cutting speed. On the premise of ensuring cutting quality, the cutting speed should be increased as much as possible. This not only improves productivity, but also reduces the deformation of the cut parts and the heat affected area of the cutting seam. If the cutting speed is not appropriate, the effect will be opposite, and it will increase slag adhesion and decrease cutting quality.

4、 Cutting method

In addition to the general form, plasma cutting methods have also derived forms such as water compression plasma cutting. *The commonly used methods are general plasma cutting and air plasma cutting.

Conventional plasma cutting does not require protective gas, as the working gas and cutting gas are sprayed from the same nozzle. During arc initiation, a small stream of ionized gas is ejected as the ionization medium; When cutting, atmospheric gas is simultaneously sprayed to remove molten metal.

Air plasma cutting generally uses compressed air as the ion gas, which has low cutting cost and convenient gas source. Compressed air heats, decomposes, and ionizes in an arc, generating oxygen that cuts metal and produces a chemical exothermic reaction, accelerating the cutting speed. The fully ionized air plasma has a high enthalpy value, resulting in a high energy of the arc and fast cutting speed.

5、 Cutting equipment

The plasma cutting system mainly consists of gas supply device, water device, power supply, and cutting gun. The water-cooled gun also needs a cooling circulating water device.

1. Gas supply device: The main equipment of the gas supply device for air plasma arc cutting is an air compressor with a power greater than 1.5kW, and the gas pressure required for cutting is 0.3-0.6MPa. If other gases are used, bottled gas can be used for cutting after decompression.

2. Power supply: Plasma cutting uses a DC power supply with steep drop or constant current characteristics. To achieve satisfactory arc initiation and stabilization effects, the no-load voltage of the power supply is generally twice the arc voltage. The commonly used cutting power supply has an unloaded voltage of 350-400V.

3. Cutting gun: The specific form of the cutting gun depends on the current level of the cutting gun. Generally, cutting guns below 60A use air-cooled structures; Cutting guns above 60A often use water-cooled structures. The electrodes in the cutting gun can be made of pure tungsten, thorium tungsten, tungsten rods, or embedded electrodes. Tungsten casting is preferred as the electrode material.

Plasma cutting has the advantages of large cutting thickness, flexible cutting, simple workpiece clamping, and the ability to cut curves. It can be widely applied to the cutting of all metal materials and non metal chip materials.

6、 Security protection

1. A water tank should be set up at the bottom of plasma cutting, and the cutting part should be placed underwater during the cutting process to avoid the toxicity of smoke to the human body.

2. During the plasma arc cutting process, avoid direct visual inspection of the plasma arc and wear professional protective goggles and face shields to prevent eye and skin burns caused by the arc light.

During the plasma arc cutting process, a large amount of toxic gases will be generated, requiring ventilation and wearing multi-layer filtered dust masks.

4. During the plasma arc cutting process, it is necessary to wear protective equipment such as towels, gloves, and foot shields to prevent skin burns from splashing sparks.

5. The high frequency and electromagnetic radiation generated by the high-frequency oscillator during plasma arc cutting can cause damage to the body, and some long-term practitioners may even experience infertility symptoms. Although there is currently no consensus in the medical and industry fields, protective measures still need to be taken.