1. Cutting and piercing technology
Any kind of thermal cutting technology, except for a few cases where it can be started from the edge of the plate, generally has to punch a small hole in the plate. Previously, a hole was punched with a punch on the laser stamping 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 stamping devices:
Blasting perforation - after the material is irradiated by continuous laser, a pit is formed in the center, and then the molten material is quickly removed by the oxygen flow coaxial with the laser beam to form a hole. Generally, the size of the hole is related to the thickness of the plate. The average diameter of the blasting hole is half of the thickness of the plate. Therefore, the blasting hole diameter of the thicker plate is large and non-circular. It is not suitable for use on parts with high processing accuracy, but only on waste materials. In addition, since the oxygen pressure used for piercing is the same as that used for cutting, the spatter is large.
Pulse piercing - a small amount of material is melted or vaporized by pulse laser with high peak power. Air or nitrogen is often used as auxiliary gas to reduce hole expansion due to exothermic oxidation. The gas pressure is lower than the oxygen pressure during cutting. Each pulse laser only produces a small particle jet, which goes deeper step by step, so the piercing time of thick plates needs a few seconds. Once the perforation is completed, the auxiliary gas is immediately replaced with oxygen for cutting. The diameter of the hole is smaller and the quality of the hole is better than that of the blasting hole. The laser used for this purpose should not only have a high output power; What is more important is the temporal and spatial characteristics of the beam, so the general transverse flow CO2 laser can not meet the requirements of laser cutting. In addition, pulse piercing must also have a more reliable gas path control system to realize the switching of gas type, gas pressure and the control of piercing time.
In the case of pulse piercing, in order to obtain high-quality cuts, 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, the cutting conditions of the acceleration section, such as focal length, nozzle position, gas pressure, etc., can be changed, but in practice, it is unlikely to change the above conditions due to the short time. In industrial production, it is more realistic to change the average power of laser. The specific method is to change the pulse width; Change the pulse frequency; While changing the pulse width and frequency. The practical results show that the third method has the best effect.
2. Analysis of deformation of small holes (small diameter and plate thickness) during cutting
This is because the machine tool (only for high-power laser cutting machine) uses pulse piercing (soft piercing) instead of blasting piercing when processing small holes, which makes the laser energy too concentrated in a very small area, scorching the non processing area, causing hole deformation and affecting the processing quality. At this time, we should change the pulse piercing (soft piercing) mode to the blasting piercing (ordinary piercing) mode in the processing program to solve the problem. On the contrary, for the laser cutting machine with lower power, pulse piercing should be adopted to obtain better surface finish when machining small holes.
3. Solution for burr on workpiece during laser cutting of low carbon steel
According to the work and design principle of CO2 laser cutting, the following reasons are the main reasons for burr of machined parts: the up and down positions of the laser focus are incorrect, and the focus position needs to be tested and adjusted according to the offset of the focus; The output power of the laser is insufficient. It is necessary to 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; If the laser focus shifts, the focus position needs to be tested and adjusted according to the shift of the focus; Instability occurs when the machine tool runs for a long time. At this time, it needs to be shut down and restarted.
4. Analysis of burrs on the workpiece during laser cutting of stainless steel and aluminum coated zinc plate
In the above situation, the burr factor when cutting low carbon steel should be considered first, but the cutting speed can not be simply accelerated, because sometimes the plate will not be cut through when the speed is increased, which is particularly prominent when processing aluminum zinc coated plate. At this time, other factors of the machine tool should be considered comprehensively to solve the problem, such as whether the nozzle needs to be replaced or not, and the movement of the guide rail is unstable.
5. Analysis of incomplete laser cutting
After analysis, it can be found that the following conditions are the main conditions that cause machining instability: the selection of the nozzle of the laser head does not match the thickness of the machined plate; The linear speed of laser cutting is too fast, which requires operation control to reduce the linear speed; The nozzle sensing is not accurate and the laser focus position error is too large. It is necessary to re detect the nozzle sensing data, especially when cutting aluminum materials.
6. Solutions for abnormal spark during cutting low carbon steel
This situation will affect the cutting surface finish and processing quality of parts. At this time, when other parameters are normal, the following conditions should be considered: loss of nozzle nozzel of laser head should be replaced in time. In case of no new nozzle replacement, increase the cutting working gas pressure; The thread at the connection between the nozzle and the laser head is loose. At this time, immediately stop cutting, check the connection state of the laser head, and re thread.