Laser cutting machine is an advanced equipment that can greatly increase labor productivity in the processing of sheet metal parts. It has the advantages of high precision of machined parts, short processing cycle, and the ability to process arbitrary complex parts without the need for traditional stamping die replacement during processing. Many switchgear manufacturers use it.
Laser cutting uses a focusing lens to focus the laser beam on the surface of the material to melt the material. At the same time, the compressed gas coaxial to the laser beam is used to blow away the melted material and make the laser beam and the material move relative to each other along a certain path, thus forming a certain Shaped slits. Laser cutting technology has developed rapidly and has become more widely used. It is an advanced processing method and is particularly suitable for cutting steel plates.
The obvious advantages of laser cutting technology over other methods are:
(1) The cutting quality is good. The width of the incision is narrow (usually 0.1~0.5mm), the precision is high (normal hole center distance error 0.1~0.4mm, contour size error 0.1~0.5mm), and the incision surface roughness is good (usually 12.5~ 25μm), slits generally do not need to be processed to weld.
(2) Fast cutting speed For example, with 2kW laser power, 8mm thick carbon steel cutting speed is 1.6m/min; 2mm thick stainless steel cutting speed is 3.5m/min, heat affected zone is small, deformation is minimal.
(3) Clean, safe, and free from pollution.
(4) Metal sheet metal parts that are not suitable for making molds from a technical and economic point of view, especially with complex contours and small batches, generally have a low carbon steel thickness of less than 12 mm and stainless steel thickness of less than 6 mm to save the cost and cycle time of manufacturing molds.
Common problems in cutting and treatment methods
1. Cutting and piercing
Any kind of thermal cutting technology, except that it can start from the edge of the board in a few cases, generally must wear a small hole in the board. Previously in the laser stamping compound machine, a hole was punched out first with a punch, and then laser cutting was started from the small hole. For laser cutting machines without a stamping device there are two basic methods for perforating:
Blasting perforations - The material forms a pit in the center after being irradiated by a continuous laser, and then the molten material is quickly removed by the oxygen flow coaxial with the laser beam to form a hole. The size of the general hole is related to the thickness of the plate. The average diameter of the blasting perforation is half of the plate thickness. Therefore, the thicker blasting perforation of the plate has a large hole diameter and is not round. It is not suitable for use on parts with high machining accuracy. On scrap. In addition, since the oxygen pressure used for the perforation is the same as when cutting, the spatter is large.
Pulse piercing - using high-peak-power pulsed lasers to melt or vaporize small amounts of material, commonly used air or nitrogen as an auxiliary gas, in order to reduce the hole expansion due to exothermal oxidation, the gas pressure is less than the oxygen pressure when cutting. Each pulsed laser produces only a small particle spray, which is progressively deeper, so that the thick plate piercing time takes several seconds. Once piercing is complete, the auxiliary gas is immediately replaced with oxygen for cutting. In this way, the diameter of the perforation is smaller, and the perforation quality is better than the perforation. The laser used for this purpose should not only have a higher output power; more importantly, the temporal and spatial characteristics of the beam, so the general cross-flow CO2 laser cannot adapt to the requirements of laser cutting. In addition, the pulse perforation also requires a more reliable pneumatic control system to achieve gas type, gas pressure switching and perforation time control.
In the case of pulse piercing, in order to obtain high-quality cuts, transition techniques from pulse piercing when the workpiece is at rest to constant speed continuous cutting of the workpiece should be taken into account. Theoretically speaking, cutting conditions of the acceleration section, such as focal length, nozzle position, and gas pressure, may be changed. However, it is actually unlikely that the above conditions will be changed due to the short time. In industrial production, the main method to change the laser average power is more realistic. The specific method is to change the pulse width; change the pulse frequency; and simultaneously change the pulse width and frequency. The actual results show that the third kind of effect is the best.
2. Analysis of the deformation of small holes (small diameter and thickness) during cutting
This is because the machine tool (only for high-power laser cutting machines) does not adopt the method of blasting perforation when processing small holes, but uses pulse piercing (soft piercing), which makes the laser energy concentrated in a very small area. The non-processed area is also charred, resulting in hole deformation, affecting the quality of processing. At this time, we should change the way of pulse piercing (soft piercing) to blast piercing (ordinary piercing) in the machining program. For the smaller power laser cutting machine, the opposite is true. In the processing of small holes, pulse perforation should be used to achieve a good surface finish.
3. Workpiece burr solution when laser cutting low carbon steel
According to the work and design principle of CO2 laser cutting, the following reasons are the main reasons for the burr produced in the workpiece: the laser's focus position is not correct. The focus position must be tested and adjusted according to the offset of the focal point. The laser output power is not enough, you need to check the laser generator is working properly, if it is normal, then observe the laser control button output value is correct, to adjust; cut the line speed is too slow, need to increase the line speed in the operation and control; The purity of cutting gas is not enough, and it is necessary to provide high-quality cutting working gas; laser focus shifting, focus position testing needs to be done, and adjustment is performed according to the offset of the focal point; instability occurs when the machine running time is too long, and it needs to be turned off at this time. Restart.
4. Analysis of workpieces with burrs when laser cutting stainless steel and aluminum zinc plate
The occurrence of the above situation, first consider the burr when cutting low-carbon steel, but can not simply accelerate the cutting speed, because the increase in speed sometimes there will be sheet cutting does not wear, this situation is particularly prominent in the processing of aluminum-zinc sheet . At this time, other factors of the machine tool should be considered comprehensively to solve, such as whether the nozzle should be replaced, and the guide rail movement is not stable.
5. Analysis of laser incompletely cut-through state
After analysis, it can be found that the following conditions are the main conditions for processing instability: the selection of the laser head nozzle does not match the processing board thickness; the laser cutting line speed is too fast and requires the operation control to reduce the line speed; in addition, special needs are also needed. Note that the 7.5′′ focal length laser lens needs to be replaced when the L3030 laser cutting machine cuts carbon steel plates above 5mm.
6. Solution for abnormal sparks when cutting mild steel
This condition will affect the quality of the cut surface finish of the part. At this point in the case of other parameters are normal, the following conditions should be considered: Loss of laser head nozzle NOZZEL, the nozzle should be replaced. In the case of no new nozzle replacement, the pressure of the cutting working gas should be increased; the threads of the nozzle and the laser head are loosened. At this time, the cutting should be suspended immediately, check the laser head connection status, and re-apply the thread.
7. Selection of puncture points during laser cutting
The working principle of the laser beam during laser cutting is that during the processing, the material forms a pit in the center after being irradiated with a continuous laser, and then the molten material is quickly removed from the molten material to form a hole by the working airflow coaxial with the laser beam. The hole is similar to the thread cutting thread hole. The laser beam is used for the contour cutting of the starting point of the processing. Usually, the direction of the laser beam of the flying light path is perpendicular to the tangential direction of the cut contour of the processed part.
Therefore, during the period from the start of the penetration of the steel plate to the cut of the part, the cutting speed of the laser beam will have a large change in the vector direction, that is, a 90° rotation in the vector direction, and a tangent line perpendicular to the cutting profile. The direction is changed to coincide with the tangent of the cutting contour, ie, the angle with the tangent of the contour is 0°. In this way, a relatively rough cutting surface will flow on the cut surface of the material to be processed. This is mainly because the direction of the vector of the laser beam during the movement changes very quickly in a short time. Therefore, we must pay attention to this situation when laser cutting parts. In general, when the design part does not have a roughness requirement on the surface cutting fracture, manual processing may be omitted during the laser cutting programming so that the control software automatically generates a puncture point; however, when the design has a high roughness on the cut section of the part to be processed. When this is required, it is necessary to notice this problem. It is usually necessary to manually adjust the starting position of the laser beam during the laser cutting program, that is, to manually control the puncture point. The puncture point originally generated by the laser program needs to be moved to a desired and reasonable position in order to achieve the required surface precision of the machined part.
figure 1
As shown in Figure 1 above, if the part has arc accuracy, we must set the cutting start point (puncture point) in A and C, and not in B and D. If the part is only required for the accuracy of the straight edge, then when we program the laser cutting program, the cutting start point must be set at B and D, but not at A and C.
figure 2
Similarly, as shown in Fig. 2, if the shape design of this part has an accuracy requirement for the arc, we can only set the cutting start point (puncture point) at D when programming the laser cutting program, and if this part is only for the straight edge Accuracy requirements, then we in the preparation of laser cutting procedures, the cutting start point (puncture point) can choose any point except D point.
Laser cutting sheet metal parts is an advanced manufacturing and processing technology, which can not only greatly reduce the research and development cycle, mold manufacturing costs, but also improve the quality and production efficiency, help to improve the technology and equipment innovation in the manufacturing industry. In practical applications, we need to constantly accumulate experience, constantly understand and practice, and let this new technology play its due contribution to our productivity enhancement.
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