1. Cutting and perforating technology


Any thermal cutting technique, except in a few cases, can start from the edge of the board, generally a small hole must be punched in the board. Previously, on the laser stamping compound machine, a punch was used to punch a hole, and then a laser was used to start cutting 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 a flow of oxygen 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 perforation is half of the thickness of the plate. Therefore, the diameter of the blasting perforation for thicker plates is larger and not round. It should not be used on parts with high machining accuracy requirements. on waste. In addition, because the oxygen pressure used for perforation is the same as that for cutting, the splash is larger.


Pulse perforation - a pulsed laser with high peak power is used to melt or vaporize a small amount of material. Air or nitrogen is often used as an auxiliary gas to reduce the expansion of the hole due to exothermic oxidation. The gas pressure is lower than the oxygen pressure during cutting. Each pulsed laser produces only a small jet of particles, which gradually penetrate deeper, so the perforation time for thick plates takes a few seconds. Once the perforation is complete, immediately change the assist gas to oxygen for cutting. In this way, the diameter of the perforation 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; more importantly, the time and space characteristics of the beam, so the general cross-flow CO2 laser can not meet the requirements of laser cutting. In addition, pulse perforation also needs a more reliable gas circuit control system to realize the switching of gas type, gas pressure and the control of perforation time.


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


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


This is because the machine tool (only for high-power laser cutting machines) does not use blasting perforation when processing small holes, but pulse perforation (soft perforation), which makes the laser energy too concentrated in a small area, The non-processed area is also charred, causing the deformation of the hole and affecting the processing quality. At this time, we should change the pulse perforation (soft perforation) method to the blast perforation (ordinary perforation) method in the processing program to solve it. For the laser cutting machine with lower power, it is just the opposite. When processing small holes, pulse perforation should be adopted to obtain better surface finish.


3. The solution to the burr on the workpiece when laser cutting mild steel


According to the working and design principle of CO2 laser cutting, it is concluded that the following reasons are the main reasons for the burr of the workpiece: the upper and lower positions of the laser focus are not correct, and it is necessary to do a focus position test and adjust according to the offset of the focus; If the output power of the laser is not enough, it is necessary to check whether the laser generator is working normally. If it is normal, observe whether the output value of the laser control button is correct and adjust it; the cutting line speed is too slow, and it is necessary to increase the line speed during operation control; If the purity of the cutting gas is not enough, it is necessary to provide high-quality cutting working gas; if the laser focus is shifted, it is necessary to do a focus position test and adjust it according to the offset of the focus; if the machine tool runs for too long, it needs to be turned off at this time. Restart.


4. Analysis of burrs on workpieces when laser cutting stainless steel and aluminum-zinc-coated sheets


When the above situation occurs, first consider the factor of burrs when cutting low carbon steel, but the cutting speed cannot be simply accelerated, because sometimes the plate cannot be cut through when the speed is increased, which is particularly prominent when processing aluminum-zinc plates. . At this time, other factors of the machine tool should be considered comprehensively, such as whether the nozzle needs to be replaced, and the movement of the guide rail is unstable.


5. Analysis of laser incomplete cutting through state


After analysis, it can be found that the following situations are the main reasons for unstable processing: the selection of the laser head nozzle does not match the thickness of the processed plate; the laser cutting line speed is too fast, and the operation control is required to reduce the line speed; the nozzle induction is not accurate If the error of the laser focus position is too large, it is necessary to re-detect the nozzle sensing data, especially when cutting aluminum.


6. Solutions to abnormal sparks when cutting mild steel


This situation will affect the machining quality of the cut section finish of the part. At this time, when other parameters are normal, the following conditions should be considered: the loss of the laser head nozzle NOZZEL, the nozzle should be replaced in time. In the case of no new nozzle replacement, the cutting working gas pressure should be increased; the thread at the connection between the nozzle and the laser head is loose. At this time, the cutting should be suspended immediately, the connection status of the laser head should be checked, and the threads should be re-threaded.