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Note CNC plasma cutting

Source: Time:2016-03-10 08:39:12 views:

Note CNC plasma cutting
Effect of CNC plasma cutting machine process parameters choice of cutting quality, cutting speed and cutting efficiency effects is essential. Proper use of CNC plasma cutting machine for fast high-quality, cutting process parameters must deeply understand and master.
First, the arc voltage: generally believed that normal power supply output voltage is cut voltage. Plasma arc cutting machine usually has a higher load voltage and the operating voltage, the use of high gas ionization energy, such as when nitrogen, hydrogen, or air, stable plasma arc voltage required will be higher. When the current is constant, the ability to enhance and improve the cutting arc voltage increase means that the enthalpy values. If the increase in enthalpy while reducing the diameter of the jet and increase the gas flow rate can often get better faster cutting speed and cut quality.
Second, cutting current: it is the most important parameters of the cutting process, and directly determines the thickness of the cutting speed, the cutting ability.
Impact: 1, cutting current increases, the arc energy is increased to improve the cutting ability, the cutting speed increases; 2, cutting current increases, increasing the diameter of the arc, the arc such that the cut thicker widened; 3, cutting current is too large heat load increases so that the nozzle, the nozzle prematurely damage, cutting quality decline naturally, can not even be properly cut. So before cutting to the correct selection of cutting current and the corresponding nozzles according to the thickness of the material.
Three, cutting speed: optimum cutting speed range is selected in accordance with the device instructions or determined experimentally, since the thickness of the material, different materials, and low melting point, thermal conductivity, and the size of the melted surface tension and other factors, the cutting speed accordingly. Mainly:
1, the cutting speed can improve moderately improve the quality of the cut, which is slightly narrower cut, the cut surface is smooth, and can reduce the deformation.
2, the cutting speed is too fast so that the wire is cut below the desired energy value, cut the cracks can not quickly melt jet cutting melt blown off immediately after the formation of a large amount of drag, along with the dross cut, cut surface quality.
3, when the cutting speed is too low, due to the cutting of the plasma arc anode in order to maintain the arc itself stable anode spots or anode region is bound to find the conduction current place in the vicinity from the arc nearest the slit, and will to the jet radial transfer more heat, thus making wider incision, the incision on both sides of the molten material in the bottom edge aggregation and coagulation, formation of dross is not easy to clean up, and the upper edge of the cut due to excessive heating and melting to form a fillet.
4, when the speed is very low, since the incision is too wide, or even extinguish the arc. Thus, good cutting quality and cutting speed are inseparable. Fourth, the working gas flow: working gas include cutting gas and auxiliary gas, some devices also require arcing gas, usually to select the appropriate operating gas depending on the type, thickness, and cutting method of cutting material. Cutting gas is necessary to ensure the formation of the plasma jet, but also to ensure the removal of the cut of the molten metal and oxide. Excessive gas flow will take away more heat from the arc, so that the jet of shorter length, resulting in a reduced ability to cut and arc instability; too small gas flow makes plasma arc lose their straightness leaving the cut shallow depth, but also prone to dross; therefore gas flow must be a good fit with the current and the cutting speed. Now plasma arc cutting machine mostly by gas pressure to control flow, because when the gun aperture is fixed, the control of the gas pressure will control traffic. Cutting the gas pressure of a certain thickness of the material used are usually handled in accordance with the equipment manufacturer selection data, if when other special applications, the gas pressure needs to be determined by the actual cutting tests. The most commonly used working gases: argon, nitrogen, oxygen, air and H35 is, argon - nitrogen mixed gas.
1, hydrogen gas is usually used as an auxiliary role in mixing with other gases, such as the famous gas H35 (hydrogen volume fraction of 35%, the remainder being argon) and so is one of the strongest plasma arc cutting gases, largely thanks to hydrogen . Because hydrogen can significantly increase the arc voltage, the hydrogen plasma jet has a high enthalpy, when mixed with argon gas use, the plasma jet cutting ability is greatly improved. 70MM thickness generally more metallic materials, commonly used as a cutting gas argon + hydrogen. If you use water jet argon and hydrogen plasma arc further compression, but also to obtain higher cutting efficiency.
2, argon reaction hardly occurs with any metal at high temperature argon plasma arc is very stable. And the electrode and the nozzle used has a higher service life. However argon plasma arc voltage is low, a high enthalpy value is not limited cutting capacity, as compared with the thickness of the cutting air is reduced to approximately a cutting 25%. In addition, in argon environment, molten metal surface tension greater than in a nitrogen atmosphere up to about 30%, so there will be more dross problems. Even with argon and other gases mixed gas cut will have a tendency sticky residue. So, now rarely used alone pure argon plasma cutting.
3, the nitrogen is a common working gas at a higher supply voltage conditions, nitrogen plasma arc has good stability and higher energy than the argon jet, even if the viscosity of the liquid metal cutting material such as when stainless steel and nickel-based alloys, slag hanging edge of the incision is very small. Nitrogen may be used alone may also be used mixed with other gases, such as nitrogen or automation often use air as working gas during the cutting, the two gases has become a standard gas high-speed cutting of carbon steel. Sometimes nitrogen is also used as an oxygen plasma arc cutting the arc gas.
4, the air contains a volume fraction of about 78% nitrogen, so the use of dross case of air cutting formed with very imagination with nitrogen cutting; air also contains a volume fraction of about 21% oxygen, because the presence of oxygen, air the low-carbon steel cutting speed is also very high; at the same time the air is the most economical working gas. However, when used alone air cutting, dross, and the cut will be oxidized by nitrogen and other issues, and the lower electrode and the nozzle life will affect the efficiency and cutting costs.
5, oxygen can increase the speed of cutting mild steel material. When using oxygen cutting, cutting mode and flame cutting is to imagine, the high temperature high-energy plasma arc so that the cutting is faster, but it must be used in conjunction with an electrode high-temperature oxidation, while the electrodes are anti-shock arcing time protection to extend electrode life.
Fifth, cutting power density: In order to obtain a high compression of the plasma arc cutting arc, cutting nozzles are used in smaller nozzle diameter, the longer the channel length and to enhance the cooling effect, so it can make the current effective cross section through the nozzle increases , i.e., arc power density increases. But also so that the power loss of the arc compression increased, therefore, the actual effective energy for cutting to smaller than the power supply output, the loss rate is generally between 25% to 50%, some compression methods such as water plasma arc cutting the rate of energy loss will be even greater, you should consider this issue during the cutting process design parameters or cut costs when economic accounting.
Example: Most of the thickness of the metal used in the industry is 50MM or less in thickness within the range of a conventional plasma arc cutting tends to form on the big small cut mouth, cut mouth and upper edges of the cut will result in dimensional accuracy decline and subsequent increase in processing volume. When oxygen and nitrogen plasma arc cutting carbon steel, aluminum and stainless steel, while the thickness in the range of 10 ~ 25MM, usually thicker material, the better the end edge of the vertical angle of the cutting edge of the error in 1 degrees to 4 degrees. When the thickness is less than 1MM, with reduced thickness, cut the angle error from 3 degrees to 4 degrees to 15 degrees to 25 degrees.
Generally it believed that the cause of this phenomenon is due to the hot plasma jet cutting notch surfaces due to unbalanced inputs, that cut the upper part of the mouth of the plasma arc energy release than the lower portion. This release of energy imbalance, is closely related to many parameters, such as plasma arc compression, cutting speed and distance from the nozzle to the workpiece and the like. The degree of compression increases arc temperature plasma jet can be extended to form a more uniform temperature region, while increasing the velocity of the jet, you can reduce the width of the vertical incision difference. However, the conventional nozzle excessive compression often lead to double arcing, the arc will not only double the consumable electrode and the nozzle, the cutting process can not be carried out, but also lead to a decline in the quality of the cut. In addition, the cutting speed is too large and too large nozzle height can cause an increase in the difference between the width of the vertical incision.
Six, nozzle height: refers to the end of the jet from the cutting surface which forms part of the entire arc length. Due to the general use of plasma arc cutting or sudden drop constant external power characteristics after the nozzle height increases, the current change is small, but will increase the arc length and the arc voltage result in increases, so that the arc power is increased; however, it will also make exposed to the environment of the arc length increase, the energy loss of arc column increases. In the case of the combined effect of the two factors, the role of the former is often completely offset by the latter, but will make the effective cutting energy decreases, resulting in cutting ability. Typically exhibit a cutting jet blow weakened, increased residual slag notch lower part of the upper edge of the melt through the emergence of fillets. In addition, the plasma jet from the viewpoint of the shape, the diameter of the jet after leaving the muzzle is expanded outward, increasing the height of the nozzle would inevitably lead to increased kerf width. Therefore, the choice of nozzle height as small as possible to improve the cutting speed and cutting quality are beneficial, but may cause double arcing nozzle height is too low. Ceramic outer nozzle nozzle height can be set to zero, that is in direct contact with the end face of the spout is cut surfaces can be obtained very good results.
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