High-power laser cutting technology is an advanced manufacturing technology combining laser optics, electronics, machinery, technology, and materials. The laser cutting process is complicated, and there are many influencing factors, including laser output power, cutting speed, defocusing amount, and cutting material performance. If you don’t select the right laser cutting machine, the cutting quality will be affected, such as rough cutting surface, the notch on the section, or adhesion and slag on the back.
The cutting speed is generally in the upper and lower limits of the speed to choose a lower value, too high and too small speed will affect the cutting quality.
When the cutting speed is too low, the laser energy density is too high and the heat affected area becomes larger, which will lead to the increase of hanging slag and the width and roughness of the cutting seam. When the cutting speed is too high, the laser energy density is small and may not cut through.
Notch verticality and slag height are the most sensitive to velocity parameters, followed by notch width and surface roughness.
Operations to increase cutting speed include:
- Increased power
- Change the beam mode
- Reduce the focusing spot size (e.g. a short focal length lens)
The spot size of the laser beam is proportional to the length of the lens. When the beam is focused by a short focal length lens, and the spot size is small and the power density is high, which is good for material cutting. But its disadvantage is that the focal depth is short, the adjustment margin is small, generally more suitable for high speed cutting thin material. For a thick workpiece, as the telephoto lens has a wider focal depth, as long as it has enough power density, it is more suitable for cutting it. Because the power density is highest at the focal point, in most cases the focal point position is just above or just below the surface of the workpiece when cutting. To ensure the constant relative position of the focus and the workpiece is an important condition for obtaining a stable cutting quality. Sometimes the lens is heated due to improper cooling, which causes the change of focal length. Therefore, it is necessary to timely adjust the focus position.
Laser cutting will produce a lot of heat, so high heat concentration, will make the cutting material combustion, oxidation reaction, but also easy to make the workpiece deformation. Therefore, some auxiliary gases need to be added. The commonly used ones are oxygen, air, and nitrogen.
The auxiliary gas is a coaxial spray with the laser beam to protect the lens from pollution and blow away the dissolved slag at the bottom of the cutting area. For non-metallic and some metallic materials, compressed air or inert gas is used to remove the dissolved and evaporated materials, while restraining the excessive combustion in the cutting area.
Auxiliary Gas Pressure
In laser cutting, the gas and focused laser beam are directed through the nozzle to the material to be cut. This creates a stream of air. The basic requirement for airflow is that the flow rate into the incision should be large and the velocity should be high, to allow sufficient oxidation for the exothermic reaction of the incision material and at the same time have enough momentum to jet the molten material out.
Most metal laser cutting USES an active gas (oxygen) to form an oxidative exothermic reaction with the glowing metal. This additional heat increases the cutting speed by a third to a half.
High gas pressure is required to prevent slagging on the back of the cut when cutting thin plates at high speed. When the material thickness or cutting speed is slow, the gas pressure could be reduced appropriately.
Laser Output Power
The size of laser power has a considerable impact on the cutting speed, slit width, cutting thickness, and cutting quality. The required power of the laser cutting machine is determined by the cutting material and the cutting mechanism. The ideal cutting speed will make the cutting surface show relatively smooth lines, and the lower part of the material will not show slag. In practice, the maximum power is set to achieve high cutting speed or to cut thicker materials.
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