1. Cutting perforation techniques
Any kind of thermal cutting technology, except for a few cases can start from the edge of the board, generally must be perforated in the board a small hole. Previously on laser stamping compound machines a hole was punched out with a punch and then cut with a laser starting from the small hole. For laser cutting machines without a punch there are two basic methods of perforation.
Blast perforation – the material is irradiated by a continuous laser to form a crater in the centre and then a hole is quickly formed by the oxygen flow coaxially with the laser beam to remove the molten material. The size of the hole is generally related to the thickness of the plate, the average diameter of the blast perforation is half the thickness of the plate, so for thicker plates blast perforation hole diameter is larger, and not round, not suitable for use in the processing of parts requiring high precision, only for scrap. In addition, as the oxygen pressure used for perforation is the same as for cutting, the spatter is greater.
Pulsed piercing – using high peak power pulsed laser to melt or vaporise a small amount of material, often using air or nitrogen as an auxiliary gas to reduce the expansion of the hole due to exothermic oxidation, the gas pressure is less than the oxygen pressure used for cutting. Each pulse of the laser produces only small jets of particles that penetrate progressively deeper, so that the perforation of thick plates takes a few seconds. Once the piercing is complete, the auxiliary gas is immediately replaced by oxygen for cutting. This results in smaller hole diameters and a better quality of piercing than blast piercing. The laser used for this purpose should not only have a high output power; more importantly, the temporal and spatial characteristics of the beam, so the general cross-flow CO2 laser cannot be adapted to the requirements of laser cutting. In addition, pulse perforation requires a reliable gas control system to realise the gas type, gas pressure switching and control of the perforation time.
In the case of pulse perforation, the transition from pulse perforation of the workpiece at rest to continuous cutting at the same speed as the workpiece should be taken into account in order to obtain a high quality kerf. 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 practice it is not possible to change these conditions because the time is too short. In industrial production, the main method of changing the average laser power is more realistic, the specific method is to change the pulse width; change the pulse frequency; change the pulse width and frequency at the same time. The actual results show that the third kind of effect is the best.
2. cutting processing small holes (small diameter and plate thickness) the analysis of the deformation situation
This is because the machine tool (only for high-power laser cutting machine) in the processing of small holes is not to take the way of blasting perforation, but with pulse perforation (soft piercing), which makes the laser energy in a very small area is too concentrated, will not process the area also scorched, resulting in hole deformation, affecting the quality of processing. At this point we should change the pulse piercing (soft piercing) method to blast piercing (ordinary piercing) method in the processing program to solve. For smaller power laser cutting machine is the opposite, in the small hole processing should be taken pulse perforation in order to achieve a better surface finish.
3. laser cutting of mild steel, the workpiece burr solution
According to the working and design principle of CO2 laser cutting, the following reasons are analyzed as the main reasons for the burr of the processed parts: the upper and lower position of the laser focal point is not correct, the focal point position test needs to be done and adjusted according to the offset of the focal point; the output power of the laser is not enough, the laser generator needs to be checked to see if it is working normally, if it is normal, the output value of the laser control button is observed to see if it is correct The cutting line speed is too slow, you need to increase the line speed in the operation control; cutting gas purity is not enough, you need to provide high quality cutting gas; laser focus offset, you need to do the focus position test, according to the amount of focus offset to adjust; machine running too long instability, you need to shut down the machine to restart.
4. laser cutting processing of stainless steel and aluminum zinc plate, the workpiece has burrs generated analysis
The above situation, the first consideration of cutting mild steel burr factors, but not simply to speed up the cutting speed, because the increase in speed will sometimes appear in the plate cutting does not wear the situation, this situation is particularly prominent in the processing of aluminum zinc plate. This should be a comprehensive consideration of other factors of the machine to solve, such as whether the nozzle to be replaced, guide movement is not stable, etc.. 5.
5. The laser does not completely cut through the state of analysis
Analysis can be found in the following situations is the main case of processing instability: laser head nozzle selection and processing plate thickness does not match; laser cutting line speed is too fast, the need for operational control to reduce the line speed; in addition, special attention should be paid to the L3030 laser cutting machine cutting more than 5mm carbon steel plate when the need to replace the 7.5″ focal length of the laser lens.
6. The solution to abnormal sparks when cutting mild steel
This situation will affect the quality of the cut section finish of the part processing. In this case, with all other parameters normal, the following should be considered: loss of the laser head nozzle NOZZEL, the nozzle should be replaced in time. In the absence of a new nozzle replacement, should increase the cutting work gas pressure; nozzle and laser head connection at the thread is loose. In this case, the cutting should be suspended immediately, check the state of the laser head connection and rethread it.
7. Selection of the piercing point during laser cutting processing
The working principle of the laser beam during laser cutting is that during the process, the material is irradiated by a continuous laser beam and a crater is formed in the centre, which is then quickly removed by the working gas stream coaxial to the laser beam to form a hole. This hole is similar to a wire-cutting hole, from which the laser beam starts to cut the contour.
Therefore, when the laser beam starts to penetrate the steel plate to enter the part contour cutting period, its cutting speed in the vector direction will have a great change, that is, the vector direction of 90 ° rotation, from perpendicular to the cutting contour of the tangent direction to the cutting contour of the tangent line coincident, that is, with the contour of the tangent angle of 0 °. This results in a relatively rough cut surface flowing down the cut section of the material being processed, which is mainly due to the rapid change in the vector direction of the laser beam during its movement in a short period of time. Therefore, attention should be paid to this aspect when using laser cutting to process parts. In general, when the design of the part does not have roughness requirements for the surface cutting section, you can do no manual processing when programming the laser cutting, so that the control software automatically generates the puncture point; however, when the design of the part to be processed has high roughness requirements for the cutting section, we need to pay attention to this problem, usually need to do manual adjustment of the laser beam start position when programming the laser cutting, i.e. manual for the puncture point control. The original puncture point of the laser programme needs to be moved to a reasonable position in order to achieve the required surface accuracy of the machined part.