Laser was originally called "Lesser" in China, which is the translation of English "Laser". As early as 1964, according to the suggestion of Academician Qian Xuesen, the beam exciter was renamed as "laser" or "laser". The laser is composed of inert gas high-purity helium, CO2 and high-purity nitrogen mixed in the gas mixing unit. The laser is generated by the laser generator, and then the cutting gas, such as N 2 or O2, is added to irradiate the processed object. Its energy is highly concentrated in a short time, making the material melt and vaporize instantaneously. Cutting with this method can solve the processing difficulties of hard, brittle and refractory materials, and it has high speed, high precision and small deformation. It is especially suitable for the processing of precision parts and micro parts.
In the process of laser processing, there are many factors that affect the quality of laser cutting. The main factors include cutting speed, focus position, auxiliary gas pressure, laser output power and other process parameters. In addition to the above four most important variables, the factors that may affect the cutting quality also include external light path, workpiece characteristics (material surface reflectivity, material surface state), cutting torch, nozzle, plate clamping, etc.
The above factors that affect the quality of laser cutting are particularly prominent in the processing of stainless steel sheet, which are as follows: there are large accumulation and burr on the reverse side of the workpiece; When the hole diameter on the workpiece reaches 1~1.5 times the plate thickness, it obviously fails to meet the roundness requirements, and the straight line at the corner is obviously not straight; These problems are also a headache for the sheet metal industry in laser processing.
Small hole roundness problem
During the cutting process of laser cutting machine, holes close to 1~1.5 times the plate thickness are not easy to process with high quality, especially round holes. Laser processing needs to perforate, lead, and then turn to cut, and the intermediate parameters need to be exchanged, which will cause instant exchange time difference. This will lead to the phenomenon that the round hole on the processed workpiece is not round. For this reason, we adjusted the time of piercing and lead to cutting, and adjusted the piercing method to make it consistent with the cutting method, so that there would be no obvious parameter conversion process.
Corner straightness
In laser processing, several parameters (acceleration factor, acceleration, deceleration factor, deceleration, corner dwell time) that are not within the conventional adjustment range are key parameters in sheet metal processing. Because there are frequent corners in the processing of sheet metal with complex shape. Slow down every time you reach the corner; After the corner, it accelerates again. These parameters determine the pause time of the laser beam at some point:
(1) If the acceleration value is too large and the deceleration value is too small, the laser beam will not penetrate the plate well at the corner, resulting in the phenomenon of impermeability (causing the increase of workpiece scrap rate).
(2) If the acceleration value is too small and the deceleration value is too large, the laser beam has penetrated the plate at the corner, but the acceleration value is too small, so the laser beam stays at the point of acceleration and deceleration exchange for too long, and the penetrated plate is continuously melted and vaporized by the continuous laser beam, It will cause the straightness at the corner (laser power, gas pressure, workpiece fixation and other factors that affect the cutting quality will not be considered here).
(3) When processing the thin plate workpiece, the cutting power shall be reduced as far as possible without affecting the cutting quality, so that the surface of the workpiece will not have obvious color difference caused by laser cutting.
(4) The cutting gas pressure shall be reduced as much as possible, which can greatly reduce the local micro jitter of the plate under strong air pressure.
Through the above analysis, what value should we set to be the appropriate acceleration and deceleration value? Is there a certain proportional relationship between acceleration value and deceleration value to follow?
For this reason, technicians constantly adjust the acceleration and deceleration values, mark each piece cut out, and record the adjustment parameters. After repeatedly comparing the sample and carefully studying the change of parameters, it is finally found that when cutting stainless steel within the range of 0.5~1.5mm, the acceleration value is 0.7~1.4g, the deceleration value is 0.3~0.6g, and the acceleration value=deceleration value × About 2 is better. This rule is also applicable to cold rolled sheet with similar plate thickness (for aluminum sheet with similar plate thickness, the value must be adjusted accordingly).