1. Cutting and piercing technology

Any kind of thermal cutting technology, except for a few cases that can start from the edge of the plate, must generally pierce a small hole in the plate. Before, a punch was used to punch a hole on the laser punching compound machine, and then the laser was used to cut from the small hole. There are two basic methods of piercing for laser cutting machines without punching devices:

Blasting perforation - the material is irradiated by a continuous laser to form a pit in the center, and then the molten material is quickly removed by the oxygen flow coaxial with the laser beam to form a hole. The size of general holes is related to the plate thickness, and the average diameter of blasting holes is half of the plate thickness. Therefore, for thicker plates, the blasting holes are larger and not round, so they should not be used on parts with higher processing accuracy requirements, but only on waste materials. In addition, because the oxygen pressure used for perforation is the same as that used for cutting, the spatter is large.

Pulse perforation - use the pulse laser with peak power to melt or vaporize a small amount of materials. Air or nitrogen is often used as the auxiliary gas to reduce the hole expansion due to exothermic oxidation. The gas pressure is lower than the oxygen pressure during cutting. Each pulsed laser only produces a small particle jet, which goes deeper and deeper, so it takes a few seconds for the thick plate to pierce. Once the perforation is completed, replace the auxiliary gas with oxygen for cutting. In this way, the perforation diameter is smaller, and the perforation quality is better than that of blasting perforation. The laser used for this purpose should not only have high output power; What is more important is the temporal and spatial characteristics of the beam, so the general cross flow CO2 laser cutter cannot meet the requirements of laser cutting. In addition, a reliable gas path control system is required for pulse perforation to realize the switching of gas type, gas pressure and control of perforation time.

In the case of pulse piercing, in order to obtain high-quality notch, attention should be paid to the transition technology from pulse piercing when the workpiece is stationary to constant speed continuous cutting of the workpiece. Theoretically, it is usually possible to change the cutting conditions in the acceleration section, such as focal length, nozzle position, gas pressure, etc., but in fact, it is unlikely to change the above conditions due to the short time. In industrial production, it is more realistic to change the average laser power by changing the pulse width; Change the pulse frequency; Change the pulse width and frequency at the same time. The actual results show that the third one is the best.

2. Analysis of deformation of cutting small holes (small diameter and plate thickness) 

This is because the machine tool (only for high-power laser cutting machine) does not adopt the method of blasting perforation when processing small holes, but uses the method of pulse perforation (soft puncture), which makes the laser energy too concentrated in a small area, scorching the non processing area, causing hole deformation and affecting the processing quality. At this time, we should change the pulse perforation (soft puncture) mode to the blasting perforation (ordinary puncture) mode in the processing program to solve the problem. On the contrary, for the laser cutting machine with small power, pulse piercing should be adopted to obtain better surface finish.

3. Solution to burr of workpiece when laser cutting low carbon steel

According to the working and design principle of CO2 laser cutting, the following reasons are analyzed and concluded as the main reasons for burrs of workpieces: the upper and lower positions of laser focus are incorrect, so focus position test is required, and adjustment is made according to the offset of focus; The output power of the laser is not enough. Check whether the laser generator works normally. If it works normally, observe whether the output value of the laser control button is correct and adjust it; The linear speed of cutting is too slow, so it is necessary to increase the linear speed during operation control; The purity of cutting gas is not enough, and high-quality cutting working gas needs to be provided; For laser focus shift, focus position test shall be conducted, and adjustment shall be made according to focus shift; If the machine tool runs for too long and becomes unstable, it needs to be shut down and restarted.

4. Analysis of burrs on workpiece during laser cutting stainless steel and aluminum coated zinc plate

In case of the above situations, the burr factor in cutting low carbon steel shall be considered first, but the cutting speed cannot be simply accelerated, because sometimes the plate will not be cut through when increasing the speed, which is particularly prominent when processing aluminum coated zinc plate. At this time, other factors of the machine tool should be comprehensively considered to solve the problem, such as whether the nozzle should be replaced, and the guide rail motion is unstable.

5. Analysis of incomplete laser cutting

After analysis, it can be found that the following situations are the main ones that cause machining instability: the selection of the laser head nozzle does not match the thickness of the processing plate; The linear speed of laser cutting is too fast, and the linear speed needs to be reduced by operation control; In addition, special attention should be paid to the replacement of 7.5 "focal length laser lenses when cutting carbon steel plates above 5mm.

6. Solution to abnormal sparks when cutting low carbon steel

This situation will affect the machining quality of the cutting section finish of the part. Under the condition that other parameters are normal, the following conditions shall be considered: the nozzle of laser head shall be replaced in time due to NOZZEL loss. In case of no new nozzle replacement, the cutting working gas pressure shall be increased; The thread at the connection between the nozzle and the laser head is loose. At this time, stop cutting immediately, check the connection status of the laser head, and re thread.

7. Selection of puncture point during laser cutting

The working principle of the laser beam during laser cutting is: during the processing, the material is irradiated by the continuous laser to form a pit in the center, and then the molten material is quickly removed by the working air coaxial with the laser beam to form a hole. This hole is similar to the threading hole of wire cutting. The laser beam uses this hole as the starting point for contour cutting. Generally, the line direction of the laser beam in the flight path is perpendicular to the tangent direction of the cutting contour of the part to be processed.

Therefore, from the time when the laser beam starts to penetrate the steel plate to the time when it enters the part contour cutting, its cutting speed will have a great change in the vector direction, that is, the 90 ° rotation of the vector direction will change from the tangent direction perpendicular to the cutting contour to coincide with the tangent of the cutting contour, that is, the included angle with the contour tangent is 0 °. In this way, a relatively rough cutting surface will be left on the cutting section of the material to be processed. This is mainly because in a short time, the vector direction of the laser beam in motion changes quickly. Therefore, attention should be paid to this aspect when using laser cutting to process parts. Generally, when the design part has no roughness requirements for the surface cutting fracture, it can be automatically generated by the control software without manual processing during laser cutting programming; However, when the design has high roughness requirements for the cutting section of the part to be processed, it is necessary to pay attention to this problem. It is usually necessary to manually adjust the starting position of the laser beam when compiling the laser cutting program, that is, manually control the puncture point. It is necessary to move the puncture point originally generated by the laser program to the required reasonable position to meet the requirements for the surface accuracy of the machined parts.

Laser cutting sheet metal parts is an advanced manufacturing and processing technology, which can not only greatly reduce the R&D cycle and mold manufacturing cost, but also improve the quality and production efficiency, which is conducive to improving the technology and equipment innovation in the manufacturing industry. In practical application, we need to constantly accumulate experience, constantly understand and practice, so that this new technology can play its due role in improving our productivity.

About HGTECH: HGTECH is the pioneer and leader of laser industrial application in China, and the authoritative provider of global laser processing solutions. We have comprehensively arranged laser intelligent equipment, measurement and automation production lines, and smart factory construction to provide overall solutions for intelligent manufacturing.