Several precautions for arc cutting of CNC plasma cutting machine

Several precautions for arc cutting of CNC plasma cutting machine

Plasma arc cutting is a processing method that uses the heat of a high-temperature plasma arc to melt (and evaporate) the metal part or part of the incision of the workpiece, and remove the molten metal by the momentum of high-speed plasma to form an incision. A plasma arc cutting machine is a machine that processes metal materials with the help of plasma cutting technology.

1. Industrial use

The CNC plasma cutting machine can cut various metals that are difficult to cut by oxygen-acetylene cutting with different working gases, especially for non-ferrous metals (stainless steel, aluminum, copper, titanium, nickel), the cutting effect is better, and its main advantage is that the cutting thickness is different. When cutting large metals, the plasma cutting speed is fast, especially when cutting ordinary carbon steel sheets, the speed can reach 5 to 6 times that of the 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 automobiles, locomotives, pressure vessels, chemical machinery, nuclear industry, general machinery, construction machinery, steel structures, ships and other industries.

2. Working gas

The development of plasma cutting to the present, the available working gas (the working gas is the conductive medium of the plasma arc, but also the heat-carrying body, and at the same time removes the molten metal in the incision) has the cutting characteristics, cutting quality and speed of the plasma arc. obvious impact. Commonly used plasma arc working gases are argon, hydrogen, nitrogen, oxygen, air, water vapor and some mixed gases.

3. Cutting Specifications

Various plasma arc cutting process parameters directly affect the stability, cutting quality and effect 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 high enough no-load voltage to easily start the arc and make the plasma arc burn stably. The no-load voltage is generally 120-600V, and 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 increasing the cutting speed and cutting metal sheets with larger thicknesses. The arc column voltage is often achieved by adjusting the gas flow and increasing the retraction of the electrode, but the arc column voltage cannot exceed 65% of the no-load voltage, otherwise the plasma arc will be 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 the plasma arc column will become thicker, the slit width will increase, and the electrode life will decrease.

3. Gas flow

Increasing the gas flow can not only increase the arc column voltage, but also enhance the compression effect on the arc column, so that the plasma arc energy is more concentrated and the jetting force is stronger, so the cutting speed and quality can be improved. However, if the gas flow is too large, the arc column will be shortened, the heat loss will increase, and the cutting ability will be weakened until the cutting process cannot be carried out normally.

4. Electrode retraction

The so-called retraction refers to the distance from the electrode to the end face of the cutting nozzle. A suitable distance can make the arc well compressed in the cutting nozzle and obtain a plasma arc with concentrated energy and high temperature for effective cutting. If the distance is too large or too small, the electrode will be seriously burned, the cutting tip will be burned out and the cutting ability will be reduced. The amount of shrinkage is generally 8 to 11mm.

5. Cutting nozzle height

The height of the cutting tip refers to the distance from the end face of the cutting tip to the surface of the workpiece being cut. The distance is generally 4 to 10 mm. It is the same as the retraction of the electrode, and the distance must be appropriate to give full play to the cutting efficiency of the plasma arc, otherwise the cutting efficiency and cutting quality will be reduced or the cutting nozzle will be burned out.

6. Cutting speed

The above factors directly affect the compression effect of the plasma arc, that is, the temperature and energy density of the plasma arc, and the high temperature and high energy of the plasma arc determine the cutting speed, so the above factors are related to the cutting speed. On the premise of ensuring the cutting quality, the cutting speed should be increased as much as possible. This not only increases productivity, but also reduces the amount of deformation of the part being cut and the heat-affected zone in the kerf area. If the cutting speed is not suitable, the effect will be opposite, and it will increase the slag and reduce the cutting quality.

Four, cutting method

In addition to the general form of the plasma cutting method, there are also derived forms such as water compression plasma cutting. The most common methods are general plasma cutting and air plasma cutting.

General plasma cutting does not need shielding gas, and the working gas and cutting gas are sprayed from the same nozzle. When striking the arc, a small gas flow of ion gas is sprayed out as an ionization medium; when cutting, a large flow of gas is sprayed out at the same time to remove the molten metal.

Air plasma cutting generally uses compressed air as the ionized gas. This method has low cutting cost and convenient gas source. The compressed air is heated, decomposed and ionized in the arc, and the oxygen produced cuts the metal to produce a chemical exothermic reaction that speeds up the cutting speed. The fully ionized air plasma has a high enthalpy value, so the energy of the arc is large and the cutting speed is fast.

5. Cutting equipment

The plasma cutting system is mainly composed of air supply device, water device, power supply and cutting torch. The water cooling gun also needs a cooling circulating water device.

1. Air supply device: The main equipment of the air supply device for air plasma arc cutting is an air compressor larger 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 adopts DC power supply with steep drop or constant current external characteristics. In order to obtain satisfactory arc ignition and arc stabilization effects, the no-load voltage of the power supply is generally twice the arc voltage. The no-load voltage of the commonly used cutting power supply is 350-400V.

3. Cutting torch: The specific form of the cutting torch depends on the current level of the cutting torch. Generally, the cutting torch below 60A adopts an air-cooled structure; while the cutting torch above 60A adopts a water-cooled structure. The electrodes in the torch can be pure tungsten, thoriated tungsten, tungsten rods, or inlaid electrodes. The electrode material is preferably cast tungsten.

Plasma cutting has the advantages of large cutting thickness, flexible cutting, simple clamping of workpieces and the ability to cut curves. It can be widely used in the cutting of all metal materials and non-gold chips.

6. Safety protection

1. The lower part of the plasma cutting should be set with a water tank, and the cutting part should be placed under water for cutting during the cutting process to avoid the poisoning of the human body by the generation of smoke.

2. Avoid looking directly at the plasma arc during the plasma arc cutting process, and wear professional protective glasses and face shields to avoid burns to the eyes and skin by the arc light.

3. During the plasma arc cutting process, a large amount of poisonous gas will be generated, which requires ventilation and multi-layer filtering dust masks.

4. During the plasma arc cutting process, it is necessary to wear protective equipment such as towels, gloves, foot guards, etc. to prevent the skin from being burned by the splashing sparks.

5. The high frequency and electromagnetic radiation generated by the high-frequency oscillator during the plasma arc cutting process will cause damage to the body, and some long-term practitioners may even experience symptoms of infertility. Good protection work.

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