Numerical control CNC plasma cutting machine arc cutting several matters needing attention

Plasma arc cutting is a kind of processing method using the heat of high temperature plasma arc to make the metal part or local melting (and evaporation) of the workpiece incision, and by the momentum of high speed plasma to eliminate the molten metal to form the incision.Plasma arc cutting machine is the use of CNC plasma cutting machine  technology to metal material processing machinery.

First, industrial use

CNC plasma cutting machine cooperate with different gases can cut all kinds of oxygen - acetylene cutting hard cutting metal, especially for non-ferrous metal (stainless steel, aluminum, copper, titanium, nickel) cutting effect is better, its main advantage is that small thickness of metal cutting, plasma cutting speed, especially when cutting ordinary carbon steel sheet,The speed can reach 5~6 times of oxy-acetylene cutting method, the cutting surface is smooth, the thermal deformation is small, the heat affected zone is less.

Plasma cutting machine is widely used in automobiles, locomotives, pressure vessels, chemical machinery, nuclear industry, general machinery, engineering machinery, steel structure, ships and other industries.

Two, working gas

Plasma cutting development to the current, can be used in the working gas (working gas is the conductive medium of the plasma arc, and the heat carrier, but also to eliminate the incision of the molten metal) on the cutting characteristics of the plasma arc and cutting quality, speed have a significant impact.Common plasma arc working gases include argon, hydrogen, nitrogen, oxygen, air, water vapor and some mixed gases.

Three, cutting specifications

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

1. No-load voltage and arc column voltage

Plasma cutting power supply, must have high enough no-load voltage, in order to easily start the arc and make the plasma arc stable combustion.No-load voltage is generally 120~600V, and arc column voltage is generally half of no-load voltage.Increasing the voltage of the arc column can obviously increase the power of the plasma arc, so it can improve the cutting speed and the cutting thickness of the metal plate.The arc column voltage is usually achieved by adjusting the gas flow rate and increasing the electrode shrinkage, but the arc column voltage should not 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 rate can not only improve 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 jet force is stronger, so that the cutting speed and quality can be improved.But the gas flow is too large, but will make the arc column shorter, increase the heat loss, so that the cutting ability is weakened, until the cutting process can not be carried out normally.

4. Internal shrinkage of electrode

The so-called shrinkage refers to the distance between the electrode and the end face of the cutting nozzles. The appropriate distance can make the arc compress well in the cutting nozzles and obtain the plasma arc with energy concentration and high temperature for effective cutting.If the distance is too large or too small, the electrode will be seriously burned, the cutting nozzle will be burned out and the cutting ability will be reduced.The inner shrinkage is generally 8~11mm.

5. Height of cutting nozzle

The height of the cutting mouth refers to the distance between the end face of the cutting mouth and the surface of the workpiece to be cut.The distance is generally 4~10mm.It is the same as the electrode shrinkage, the distance should be appropriate to give full play to the cutting efficiency of the plasma arc, otherwise it will reduce the cutting efficiency and cutting quality or make the cutting nozzle burn 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.Under the premise of ensuring the cutting quality, the cutting speed should be improved as far as possible.This not only improves productivity, but also reduces the amount of deformation of the cut parts and the heat-affected area in the slit area.If the cutting speed is not appropriate, the effect is opposite, and it will increase the viscosity of slag, cutting quality decline.

Four, cutting method

Plasma cutting method in addition to the general form, derived form and water compression plasma cutting, etc.The most commonly used methods are general plasma cutting and air plasma cutting.

General plasma cutting without protective gas, working gas and cutting gas ejected from the same nozzle.When the arc is initiated, a small airstream of ionized gas is ejected as the ionization medium.When cutting, a large air stream is ejected at the same time to exclude the molten metal.

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

Five, cutting equipment

Plasma cutting system is mainly composed of gas supply device, water device, power supply and cutting gun.The water cooling gun shall also have a cooling circulating water device.

1. Air supply device: the main equipment of air supply device of air plasma arc cutting is an air compressor of greater than L. 5KW, and the gas pressure required for cutting is 0.3~ 0.6Mpa.If other gases are used, bottled gas can be decompressed and used for cutting.

2 power supply: plasma cutting with a steep drop or constant current external characteristics of the DC power supply.In order to obtain satisfactory effect of arc initiation and arc stabilization, the no-load voltage of the power supply is usually twice of the arc voltage.The no-load voltage of commonly used cutting power supply is 350~400V.

3. Cutting gun: the specific form of the cutting gun depends on the current level of the cutting gun. Generally, the cutting gun below 60A mostly adopts air-cooled structure;And more than 60A cutting guns adopt water cooling structure.The electrode in the cutting gun can use pure tungsten, thorium tungsten, bell tungsten rod, also can use inlay type electrode.Cast tungsten is preferred as electrode material.

Plasma cutting has the advantages of large cutting thickness, flexible cutting, simple clamping workpiece and cutting curves, which can be widely used in the cutting of all metal materials and non-gold materials.

6. Safety protection

1. The lower part of the plasma cutting should be set up a water tank, and the cutting part should be cut underwater in the cutting process to avoid the poisoning of the smoke to the human body.

2. In the process of plasma arc cutting, direct visual plasma arc should be avoided. Professional protective glasses and facial cover should be worn to avoid the burning of eyes and skin caused by arc light.

3. A large number of toxic gases will be produced in the process of plasma arc cutting, so it is necessary to ventilate and wear a multi-layer filter dust mask.

4. In the process of plasma arc cutting, it is necessary to wear towels, gloves, foot protector and other protective equipment to prevent the burning of the skin from the splash of Mars.

5. In the process of plasma arc cutting, the high frequency and electromagnetic radiation produced by the high frequency oscillator will cause damage to the body, and some long-term practitioners even have the symptoms of infertility. Although the medical community and the industry have not yet concluded for the time being, it is still necessary to do a good job of protection.