Many factors affect the cutting quality of a CNC plasma cutter. In addition to the design parameters of the cutting machine, it is also related to operation control and cutting technology. The main criteria for evaluating the quality of CNC plasma cutting are the inclination of the cutting surface, the depth of the cut pattern of the slit, and the amount of dross. The inclination of a high-quality cutting surface should be below 3°, the cutting depth should be below 0.15mm, and there is less dross and easy to remove.
To minimize the cutting deformation, it is necessary to ensure the accurate and reliable positioning of the metal sheet before cutting. If conditions permit, use a multi-point contact electromagnetic platform for proper leveling to eliminate the uneven residual internal stress of the metal sheet. Improve the flatness of the board.
1. Starting point selection
Under normal circumstances, the arc starting point of the cut piece should be at the edge of the sheet metal, or in the middle of the cut seam of the cut piece. When the distance is too large, there will be no arc or broken arc, so that the processed parts cannot be cut through, resulting in product waste or scrap. When the distance is too small, it is easy to short-circuit between the nozzle and the workpiece, which will burn the nozzle and destroy the normal cutting process. The practice has proved that the distance between the nozzle and the workpiece is generally 6-8mm, and the nozzle height for air plasma cutting and water recompression plasma arc cutting can be slightly less than 6-8mm.
2. Cutting direction selection
The correct cutting direction should ensure that the last cutting edge is mostly separated from the motherboard. If it is separated from most of the motherboard prematurely, the surrounding corner frames will not be able to resist the thermal deformation stress that occurs during the cutting process, causing the cutting piece to shift during the cutting process, and the size will be out of tolerance.
3. Cutting speed selection
The cutting speed of the plasma cutter is the relative movement speed between the cutting torch and the workpiece during the cutting process. Appropriate cutting speed is an important condition for a straight cut surface. The cutting speed is determined by the material thickness, cutting current, gas type and flow rate, nozzle structure, and appropriate drag amount. Under the same power, increasing the cutting speed will cause the incision to become oblique. The cutting torch should be perpendicular to the surface of the workpiece when cutting, but to facilitate the removal of slag, it can be with a certain backward inclination angle (in general, the inclination angle is not more than 3°), so to improve productivity, it should be done under the premise of ensuring the penetration It is possible to choose a large cutting speed.
4. Influence of cutting order
The cutting sequence refers to the sequence of cutting several nested parts on the steel plate. Generally, the principle of "inside and out, small and large" should be followed: that is, the inner contour of the processed part (or the parts nested in the inner contour) is cut first, and then the outer contour; the small area is cut first, then the Large size parts. Otherwise, deformation will occur when the inner contour or other small parts are cut on the sheet metal, resulting in scrapping of the processed parts.
5. Cutting current
Increasing the cutting current can also increase the power of the plasma arc, but it is limited by the maximum current, which will make the plasma arc column thicker, increase the slit width, and decrease the electrode life. The arc column voltage is often 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, it will cause chaos in the plasma arc. If the interval is too large or too small, the electrode will be severe. Burnout, burnout of cutting nozzle, and reduced cutting ability. The interval is generally 4~10mm. It is the same as the internal shrinkage of the electrode. The interval must be appropriate to fully display the cutting efficiency of the plasma arc, otherwise, it will reduce the cutting efficiency and cutting quality or burn the cutting nozzle.
6. Gas flow
Increasing the gas flow can not only enhance the arc column voltage but also enhance the compression of the arc column, so that the plasma arc energy is more concentrated and the jet force is stronger, thus improving the cutting speed and quality.
7. No-load voltage and arc column voltage
The plasma cutter must have a high enough no-load voltage to easily hit the arc and ensure that the plasma arc burns stably. The open-circuit voltage is usually 120 to 600V, and the arc column voltage is usually half of the open-circuit voltage. Increasing the arc column voltage can greatly increase the power of the plasma arc, thereby increasing the cutting speed and cutting thicker metal plates. By adjusting the gas flow and increasing the electrode contraction rate, the arc column voltage cannot usually be reached, but the arc column voltage cannot exceed 65% of the no-load voltage, otherwise, the plasma arc will become unstable.
8. The electrode shrinks
Electrode contraction refers to the distance between the electrode and the end surface of the cutting nozzle. The proper distance can make the arc well compressed in the cutting nozzle, to realize the plasma arc with high energy concentration and high temperature, to realize efficient cutting. If the distance is too large or too small, the electrode will be severely burned, the cutting nozzle will go out, and the cutting ability will be reduced. The amount of shrinkage is usually 8-11 mm.
9. Cutting nozzle height
The height of the cutting nozzle refers to the distance between the end surface of the cutting nozzle and the surface of the workpiece. The distance is usually 4 to 10 mm. It is the same as the amount of contraction in the electrode. The distance must 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 burn the cutting nozzle.