To meet the large demand for irregular sheet metal in mass production processes of contemporary industrial machinery enterprises, laser cutting machines are widely used due to their advantages such as fast cutting speeds and smooth cutting surfaces when cutting irregular sheet metal below 30mm.
There are many factors that affect the quality of laser cutting, including the type and purity of the cutting gas, cutting parameters, the rationality of the layout process, the comprehensive technical ability of the operator, and the degree of understanding of the equipment.
This article focuses on the technical problems that need special attention, including the cutting program settings, layout, cutting speed, laser output power, and auxiliary gas.
2. Characteristics of CNC laser cutting
Laser cutting refers to the use of a focusing mirror to focus the laser beam on the surface of the material, melting or vaporizing it as a whole, and blowing away the melted material with compressed gas that is coaxial with the laser beam.
The laser beam and material move relative to each other along a certain trajectory to cut the material into a predetermined shape.
With the development of modern industry, the demand for cutting technology in product processing is getting higher and higher.
Compared with traditional cutting methods, laser cutting has the advantages of faster cutting speed, higher accuracy, smaller kerf, and wider cutting range. Therefore, it has been widely used in modern machinery processing.
3. Factors affecting the quality of CNC laser cutting machines
1. The condition of the raw material during the operation of the CNC laser cutting machine is an important factor affecting the quality of laser cutting.
The state of the material affects its absorption of the laser beam, especially the roughness and oxide layer of the material, which can greatly influence the absorption rate of the laser beam.
Additionally, if the material surface is corroded or has a thick layer of oil, it can not only affect the cutting speed but also cause incomplete cutting or rough/serrated cut surfaces with excessive burrs.
Therefore, in the process of using laser cutting raw materials, it is necessary to ensure that the material surface is free of rust and oil, and to follow the principle of cutting parts from the larger to smaller sizes according to the reasonable utilization of the material.
2. The processing environment temperature will also affect the cutting quality of the laser cutting machine, especially in the hot summer season.
For equipment that is not sealed, such as the entire bed body of the laser cutting machine, water cooling units can only work normally at temperatures of 18-21 ℃.
With the workshop temperature as high as 32-33 ℃ in summer, the temperature of the water cooling unit is difficult to drop, which may cause the laser cutting machine to have low energy and insufficient laser beam.
3. In the layout process, the spacing between sheets with thickness below 20mm should be kept at 10mm, but in the case of narrow and long-size sheets (length over 3 meters), the spacing of the long sides should be adjusted according to the actual situation.
4. The function of cutting two parts with a shared edge can improve the utilization of materials and reduce cutting gaps to some extent.
Therefore, the shared edge cutting should be selected as much as possible in the processing of sheet metal.
5. In the layout process, suitable size sheet metal should be chosen according to the size and shape of the parts to be laid out, and the material saving should also be considered.
6. It is also necessary to pay attention to the spacing between gear racks on the laser cutting machine.
For parts smaller than the distance between gear racks, they should be placed perpendicular to the direction of the gear racks during the layout process to avoid dropping under the worktable after cutting, which is not convenient for material picking.
For parts with dimensions smaller than the distance between the gear racks, micro-connections can be used for processing.
7. The problems of burrs and slag are caused by factors such as the cutting speed being too fast or too slow, and the burning and aging of the cutting nozzle of the laser device. These factors can cause burrs and slag to form around the edge of the parts during the laser cutting process.
8. The main reasons for errors in laser cutting parts are as follows:
- (1) Thermal deformation of the raw material;
- (2) Errors in the straightness and parallelism of the equipment guide rails;
- (3) Errors in the parallelism between the support surface of the raw material and the equipment guide rails;
- (4) Errors in the perpendicularity between the cutting nozzle and the surface of the raw material;
- (5) Human factors. The diagonal deviation of the parts is a common cutting defect in laser cutting, mainly caused by the driving and traveling mechanism of the equipment itself. As the equipment runs for a long time, the transmission parts wear out, and the side gears become loose or misaligned, resulting in unreasonable gaps during the installation process.
9. In the laser layout process, the default cutting direction is clockwise.
Therefore, the layout should be arranged according to the principle of not causing deformation of the parts, and the perforation point position should be selected reasonably.
At the same time, it should minimize the cutting gaps and maximize the efficiency of the laser device. It is necessary to strictly follow the established requirements for layout and pay attention to the location of the perforation points and the cutting sequence of the parts to avoid deformation.
10. The cutting entry point should be placed as much as possible on the corner and weld surface of the part to ensure the external appearance quality of the part.
11. Due to certain deficiencies in existing software in terms of perforation, it is necessary to check the perforation points after the layout is completed to avoid irregular perforation inside the part or not meeting the required process of the drawing.
12. In the part sorting process, the principle of ordering from large to small, from outside to inside, and from front to back should be followed to minimize the cutting gap and improve work efficiency.
13. The bending of parts and the assembly of welds should be organically combined with the cutting process. When the adjacent sides of the parts are bent, the bending fillet should be left. When the welds are spliced using tenons, positioning holes and pins should be reserved on the cut parts.
Although laser cutting has many advantages in operation, it also needs to consider some of the above-mentioned issues during use in order to improve production efficiency, increase steel utilization rate, and reduce labor intensity.
However, the laser cutting machine also has some disadvantages, such as strong arc light, high noise, and the production of harmful gases and smoke, which may pollute the working environment to some extent.
Additionally, environmental temperature, cutting gas flow rate, and cutting speed all affect the quality of the parts.
If these factors are not well mastered, the cutting quality may not be ideal compared to flame cutting, which is simpler and has lower costs.
Generally, for thin plate cutting, the surface quality of the part is better than flame cutting, and there are fewer burrs and slag. However, with the advancement of technology, the above-mentioned shortcomings are gradually being solved by engineering technicians.
14. Cutting Speed: When the laser power and the auxiliary gas pressure are constant, the cutting speed has a non-linear inverse proportion relationship with the cutting width. As the cutting speed increases, the cutting width decreases. Conversely, when the cutting speed decreases, the cutting width will increase. The cutting speed has a parabolic relationship with the roughness of the cutting section surface.
As the cutting speed decreases, the surface roughness of the section increases. As the cutting speed increases, the surface roughness improves. When the optimal cutting speed is reached, the roughness of the cutting section surface is the minimum. When the cutting speed increases to a certain value, it becomes impossible to cut through the plate.
15. Laser Output Power: The size of the laser power greatly affects the cutting thickness, cutting speed, cutting width, and cutting quality. Generally speaking, the larger the laser power, the thicker the plate that can be cut, and the cutting speed can be improved. At a certain plate thickness and cutting speed, there is an optimal range of laser power. Within this range, the roughness of the cutting surface is the smallest. Deviation from this range will increase the roughness. Further increasing or decreasing the power will produce overburn or slag defects.
16. The effect of cutting auxiliary gas on cutting quality: The cutting auxiliary gas includes oxygen, nitrogen, and compressed air.
Oxygen is mainly used for cutting low carbon steel plates. The higher the purity of the oxygen, the brighter the cutting surface. If water and impurities are present in the oxygen, it will seriously affect the roughness of the cutting surface.
For better cutting quality in thick plate cutting, oxygen with a purity above 99.999% is recommended, and the oxygen pressure used for cutting carbon steel plates increases with the thickness of the plate.
Nitrogen is mainly used for cutting stainless steel and aluminum alloy materials. The higher the pressure of nitrogen used, the thicker the plate that can be cut. Nitrogen with lower purity will cause the cutting surface to become yellow and the brightness to decrease.
Compressed air is mainly used for cutting thin plates below 3mm. It is difficult to achieve good cutting quality for medium-thick plates.
In conclusion, the above situations explored some technical issues related to laser program settings, layout, cutting speed, laser output power, and cutting auxiliary gas.
Due to the limitation of the author’s theoretical and practical experience, there may be some errors and insufficient analysis of the technical problems associated with the use of laser cutting machines.
Therefore, readers and colleagues are invited to provide valuable suggestions.