Laser cutting machine is considered to be the most mature technology in laser applications, so in recent years, people put laser application research hotspot into laser welding, heat treatment, marking, rapid prototyping, and laser cutting research is relatively small. However, with the overall development of the automotive industry, as well as fine cutting and good welding performance needs, we must further improve and control the quality of cutting. The quality of laser cutting refers to the cutting dimension precision and cutting surface quality, cutting surface quality is generally measured by the following 4 indicators:
① incision width and surface roughness of incision;
② the width of the heat affected zone;
③ incision section of the ripple;
There is no slag hanging on the ④ incision section or the lower surface.
The main factors affecting the surface quality of laser cutting are analyzed below.
1. Laser for cutting, laser should have high beam quality. Laser cutting is based on the thermal effect of the processing, in order to get high power density and fine incision, focusing spot diameter is small, at the same time, in order to ensure the consistency of the quality of cutting in different directions, the laser beam should have a good rotation around the optical axis symmetry and the circular polarization and high launch direction stability, to ensure that the focus spot position stability. Modern lasers should also have fast switching functions of continuous and high repetitive outputs to ensure high quality cutting of complex contours.
2. Focus lens and plate thickness, lens focal length according to the thickness of the cut material selected, taking into account the focus spot diameter and focal depth, material thickness, focal length should be large, on the contrary, the focal length should be small. The focus spot position should be close to the workpiece surface, which generally causes the focus to fall on the surface of the plate about 1/3 thick.
3. Airflow and nozzle, the laser cutting machine in the air flow has blown the melting material, protect the focus lens and even provide some cutting energy. Gas pressure, flow is an important factor affecting the quality of cutting, the pressure is too low, blowing the incision at the melting material; too high, easy to form Eddy current on the workpiece surface, but weaken the effect of air flow to remove molten material. It has been proved by practice that different structure nozzles have different effects on cutting.
4. Laser cutting machine cutting speed, cutting speed depends on the power density of laser and the thermal properties of the material and its thickness. For certain cutting conditions, there is a reasonable cutting speed range, cutting speed is too high, the incision slag is not enough, or even cut, cutting speed is too low, the material has been burned, incision width and heat affected area.
5. Cutting trajectory, for the complex contour or inflection point of the cutting parts, due to the change in acceleration, easy to make the inflection point of overheating melting and formation of collapse angle, so reasonable cutting trajectory is one of the effective ways to avoid this phenomenon.