The influence and control of CNC fine plasma cutting precision

The influence and control of CNC fine plasma cutting precision

Fine Plasma cutting is divided into four processes: arc ignition, transfer, perforation, and cutting. Generally, it is equipped with a robot system or a CNC system and a gantry frame as the basic component of cutting. Both processes are widely used in the manufacturing industry and have their own advantages; The repeat accuracy of the general robot body is ≤0.08mm. For plasma, its mechanical accuracy has little effect on the cutting accuracy; the gantry type CNC fine plasma cutting machine has relatively more mechanical accuracy control elements, and its cutting quality is affected by the structure of the door frame and Restricted factors such as precision, plasma power cutting quality, cutting environment factors, etc., the improvement of the overall cutting accuracy have strict requirements for machine design, manufacturing, debugging and use.

Track accuracy control

It is recommended to use a dual-drive gantry structure for the gantry air fine plasma cutting machine. The straightness of the main rail should be controlled within ±0.2mm/10m, and the longitudinal horizontality should be ±0.2mm/m. The straightness of the second rail can be appropriately relaxed, but the main and parallelism of the second guide rail are less than ±2mm, so the first requirement for the track is that the height of the overall track is as small as possible. It is recommended to use concrete to pour the overall track foundation during the on-site construction process. Even if there is a large settlement around the foundation, there will be no excessive settlement errors at the four endpoints of the overall foundation, and regular inspection and leveling must be performed within 2 years after the foundation is completed to provide a stable foundation environment for the plasma.

Mast precision control

The rigidity and structure of the gantry may also affect the cutting accuracy. In the manufacturing process of many low-power machines, the cutting power supply is directly applied to the gantry beam. Even now, many devices need to be fixed on the gantry beam. If the foundation settlement is too large for a long time, the mast will be deformed or twisted, and jitter will occur during the cutting process, which will affect the cutting quality; if the deformation is too large, it will affect the normal operation of the torch assembly slider.

Precision control of cutting torch assembly

In the manufacturing process of fine air plasma machines, the precision control of the installation method of the cutting torch assembly and the slider. To reduce the load of the beam, the overall slider can be considered to use aluminum alloy as the base material, and the fine plasma cutting torch assembly The integrated design of water, electricity, gas, control unit, anti-collision structure, etc., its fixing method must be firm and stable, and the verticality of the cutting torch must be ensured. It is recommended to increase the guide rail automatic lubrication device as a slider for the operation of the slider assembly Provide lubrication guarantee and require interlocking control with the front end limit. The dust removal equipment adds collision, rotating barrel, or other devices to prevent the hidden danger of combustible ignition of the filter cartridge.

Electrical system control

Figure 1

In the old-fashioned air plasma cutting process, the arc starting point, including the intermediate point, requires manual intervention to control the lifting of the cutting torch. The fine plasma generally uses mainstream brand control systems with high-precision arc voltage control and proportional valves to cut during arc starting and cutting. The vertical distance between the torch and the sheet is different (as shown in Figure 1). Different materials and thicknesses will be automatically adjusted and matched according to the database information in the control system, which reduces the manual intervention process, and is more stable and better than manual intervention control. Through the database and cutting compensation to simplify the manual process of setting theoretical cutting parameters according to materials and consumables, as long as the upper and lower slopes and the slag of the cutting parts are appropriately reduced after the first piece is cut, the arc voltage is increased (such as Figure 2) The parameter setting of the same specifications can be completed; the transmission error caused by the control system and servo has little effect on the cutting accuracy.

Figure 2

Platform accuracy control

The working platform is an indispensable part of cutting, which has a great impact on the cutting quality. The fine plasma is controlled more accurately due to the arc voltage and arc density during the cutting process. If the material drop error is too large, the cutting quality will decrease, and the working platform Air duct isolation and slag accumulation also have a great impact on cutting; generally, when making and adjusting the plane error, try to control it within 5MM. According to the site construction experience, the use of a zigzag grid will reduce the adhesion of slag, and due to the large separation space The influence of the grille on the plasma arc is reduced, and the cutting quality is more excellent; the influence of the air duct is mainly the vibration of the suction port and the vibration of the door frame caused by the wind resistance (the design of the suction port and the pipe is critical to the air volume of the dust removal equipment). The space reserved between the middle suction port and the platform air duct should be appropriate, and the non-cutting area of ​​the platform should be properly covered with idle plates during use, which will reduce the accuracy impact of suction to a certain extent.

Cutting consumables control

Figure 3

Fine plasma power supply cutting different base materials requires different cutting gases. Commonly used gases are compressed air, oxygen, nitrogen, and argon-hydrogen. The quality of compressed air requires dry, oil-free, and impurity-free, pressure ≮0.7MPa, oxygen purity ≮99.95 %, nitrogen purity ≮99.995%, argon-hydrogen is a dual gas system used to improve cutting quality. It has the advantages of large energy, a small cutting torch, and a good finish. It performs well when cutting 9mm-50mm stainless steel, but the cutting cost Higher: Generally, oxygen is used as the plasma gas for cutting mild steel, which has a good cutting finish, small slagging, and small cutting thickness. Set the current to 10 times the thickness of the plate for quality cutting. Aluminum and other materials generally use nitrogen as the cutting gas.
Choose appropriate consumables according to the thickness and quality of the cutting material. The quality and specifications of the consumables will also affect the cutting effect of the product to a certain extent (Figure 3). Electrodes, nozzles, and swirl rings are common consumables, and their quality affects the cutting quality Larger; electrode materials are copper alloy and silver alloy, there are also two types of vortex ring materials, one is engineering plastic parts, the other is ceramic parts. Engineering plastics are used for small currents and ceramics are used for large currents. According to its opening direction, clockwise is CW, counterclockwise is CCW, vortex ring is usually CW, so pay attention to the cutting direction when nesting and cutting, otherwise it will affect the verticality.

Process influence

The cutting process is very important in CNC plasma cutting. Cutting torch, consumable status, gas, cutting height, current, and speed are all process factors. In addition to hardware, many software on the market can provide good nesting and cutting processes. Output, but some details still require manual intervention. In the plasma cutting process, the arc starting is generally performed on non-material parts, but the arc extinguishing point is generally at the combination of the two. It is difficult to avoid the arc extinguishing point. When arcing, the requirements for machine arc change are stricter and the slagging phenomenon is difficult to deal with, and it can only be optimized at present; the last is the verticality of the cutting surface. Generally, the verticality of fine plasma cutting can be controlled to ≤3°, and high-precision plasma ≤2° Several aspects are the elements to improve the plasma cutting process. The influence can be appropriately reduced by adjusting parameters (speed, arc voltage, current), changing the air pressure and the position of the arc starting and stopping points, setting the lead wire, and setting the time parameters.

Comprehensive mechanical accuracy

In addition to the above-mentioned accuracy, the mechanical accuracy also has the guiding and transmission accuracy. In the case of the gantry running in an empty state, the mechanical accuracy is 1m. The comprehensive test pattern requires side length, diagonal line, intersection offset <0.5mm, return to the origin, forward and reverse linear deviation <0.2mm, the whole machine runs without jitter or abnormal noise in the whole track length. Compared with the ordinary plasma cutting machine, the precision plasma cutting machine has obvious differences in the use of transmission and guide components. The selection of the transmission mechanism servo system and the drive motor is more reliable. Track transmission is convenient. It is recommended to abandon the old structure and change to helical gear transmission, rollers, and guide bearings. There is also a correction function. The horizontal guide mechanism is changed to a linear guide rail to increase the running accuracy of the overall machine. The whole machine has a zero mark, and the machine returns to zero after the construction is completed.

With the continuous update of the technology, through the power supply technology update and product positioning analysis of major mainstream companies in recent years, the plasma power supply will continue to develop towards high-precision and intelligent development, forming a differentiated competition with the laser industry, and forming a competition for independent brand plasma power supplies. Overwhelming advantages; in terms of guns and consumables, due to intellectual property restrictions and early technical accumulation issues; the upgrade of the CNC system is an extension of the plasma power supply, cutting torch, and lifting control unit technology. It is basically synchronized with the technical update of its components. The data processing is more accurate and the cutting effect is better.

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