Laser cutting equipment is mainly composed of laser, light guide system, numerical control motion system, automatic height-adjusting cutting head, working platform and high-pressure gas blowing system. The main parameters of laser cutting are:
Fundamental mode, also known as Gaussian mode, is the most ideal mode for cutting, and it mainly appears in low-power lasers with power less than 1kW. The low-order mode, which is relatively close to the fundamental mode, mainly appears in 1-2kW medium-power lasers. Multimode, which is a mixture of higher-order modes, occurs in high-power lasers with powers greater than 3kW.
Under the same power, multi-mode lasers have poor focus and low cutting ability, and the cutting ability and cutting quality of single-mode lasers are better than multi-mode lasers.
The laser power required for laser cutting mainly depends on the cutting material, material thickness and cutting speed requirements. Laser power has a great influence on cutting thickness, cutting speed, kerf width, etc. Generally, as the laser power increases, the thickness of the material that can be cut is also increased, the cutting speed is accelerated, and the incision width is also increased.
The focus position has a great influence on the incision width. Generally, the focus of selection is located at about 1/3 of the plate thickness below the surface of the material, where the cutting depth is the largest and the mouth width is the smallest.
When cutting thicker steel plates, a beam with a longer focal moment should be used to obtain a cutting surface with good verticality. The larger the depth of focus, the larger the diameter of the spot, the lower the power density, and the lower the cutting speed. To maintain a certain cutting speed needs to increase the laser power. It is better to use a beam with a smaller focal length for cutting thin plates, so that the spot diameter is small, the power density is high, and the cutting speed is fast.
When cutting low-carbon steel, oxygen is often used as the cutting gas to promote the cutting process by using the iron-oxygen combustion reaction heat, and the cutting speed is fast, the incision quality is good, and the incision without dross can be obtained. The pressure increases, the kinetic energy increases, and the slag discharge capacity increases; the cutting air pressure is determined according to the material, plate thickness, cutting speed and cutting surface quality factors. In addition, the purity of oxygen has a certain influence on the cutting speed. For example, if the oxygen purity is reduced by 2%, the cutting speed will be reduced by 50%.
The structural shape of the nozzle and the size of the light outlet also affect the quality and efficiency of laser cutting. Different cutting requirements use different nozzles. Commonly used nozzle shapes are: cylindrical, conical, square and other shapes. Laser cutting generally adopts the coaxial (airflow and optical axis concentric) air blowing method. If the airflow is not in the same axis as the optical axis, it is easy to generate a lot of spatter during cutting. In order to ensure the stability of the cutting process, it is usually necessary to control the distance between the end face of the nozzle and the surface of the workpiece, generally 0.5-2.0mm, so that the cutting can proceed smoothly. The process parameters of laser cutting of commonly used metal materials are shown in Figure 3.