High power laser cutting technology is a combination of laser optics, electronics, machinery, technology and materials and other disciplines of advanced manufacturing technology. Laser cutting process is complex and has many influencing factors, including laser output power, cutting speed, defocus volume and cutting material performance. If the process parameters are not selected properly, the quality of cutting will be greatly affected, such as rough cutting surface, notching on the section, and slag sticking on the back.
Cutting speed generally selects a lower value in the upper and lower limits of the speed. Too much speed and too small will affect the quality of cutting, resulting in slag sticking or even cutting.
When the cutting speed is too low, the laser energy density is too large and the heat affected zone will increase, which will lead to the increase of slag and the wide and rough slit. If the cutting speed is too high, the energy density of laser will be small.
Vertical verticality and slag height are most sensitive to velocity parameters, followed by notch width and surface roughness.
It can improve the cutting speed operation including:
Change the beam mode
Reduce the size of the focus spot (such as a short focal lens)
The size of the spot is directly proportional to the length of the lens after the laser beam concentrating. After focusing on the short focal length lens, the light spot size is very small, the power density at the focus is very high and it is very favorable for the cutting of materials. But it is very short, and the adjustment allowance is very small, and it is generally suitable for high speed cutting thin material. For thick workpiece, long focal length lens has wider focal depth, so long as it has enough power density, it is suitable for cutting it. Because of the highest power density at the focal point, in most cases, when cutting, the focus position is just on the surface of the workpiece, or slightly below the surface of the workpiece. To ensure that the relative position of the focus and the workpiece is constant is an important condition for obtaining a stable cutting quality, and sometimes the lens is heated because of bad cooling, which causes the change of the focal length, so the focus position should be adjusted in time.
Laser cutting will produce a lot of heat, so the high heat is concentrated together, which will cause the material to burn at the cutting place, the oxidation reaction, and the deformation of the processed parts. Therefore, some auxiliary gases need to be added. Commonly used oxygen, air and nitrogen are commonly used.
Auxiliary gas and laser beam coaxial spray, protect lens from pollution and blow away slag at the bottom of cutting area, use compressed air or inert gas to remove dissolving and evaporation materials for non metal and partial metal materials, and suppress excessive combustion in cutting zone.
Auxiliary gas pressure
When laser cutting, the laser beam of gas and focus is launched through the nozzle to the cutting material. Thus a stream of airflow is formed. The basic requirement for the air flow is that the gas flow into the incision is large and the speed is high, so that enough oxidation is made to make the incisional material exothermic, and there is enough momentum to blow the molten material out.
Most metal laser cutting uses active gas (oxygen) to form an oxidation exothermic reaction with hot metal, which can increase the cutting speed of 1/3 to 1/2.
When cutting sheet metal at high speed, high gas pressure is required to prevent slag from the back of the incision. When the material thickness or the cutting speed is slow, the gas pressure can be properly reduced.
Laser output power
The size of laser power has great influence on cutting speed, slit width, cutting thickness and cutting quality. The power required by the laser cutting machine depends on the characteristics of the material and the mechanism of cutting. The ideal cutting speed will make the cutting surface present a smooth line, and the lower part of the material will not present the slag. . In practice, the maximum power is often set to obtain high cutting speed or to cut thicker material.