Optimize the process to improve the effect of fiber laser cutting

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Fiber laser cutting machine has many advantages, such as high cutting accuracy, narrow cutting slit, smooth cutting surface and high efficiency. At the same time, the use of fiber laser cutting machine has significant advantages in safety and environmental protection. In the future development trend, fiber laser cutting machine will occupy the position of mainstream equipment. The following describes several directions of fiber laser cutting process optimization.

 

• Cutting speed

Fast cutting speed is one of the advantages of laser cutting, but the faster the cutting speed is not the better. Under the condition of a certain laser power, it is necessary to select an appropriate cutting speed according to the cutting plate to make the cutting surface texture beautiful and obtain high-quality cutting workpieces. The following methods can be used to determine whether the cutting speed is appropriate and then adjust the cutting speed:

（1）Observe the cutting spark

When the cutting speed is appropriate, the cutting spark is evenly diffused from top to bottom; When the cutting speed is too fast, the cutting spark will incline; When the cutting speed is too slow, the cutting sparks are gathered together, non diffused and less.

（2）Observe the cutting plate

When the cutting speed is appropriate, the cutting surface presents a relatively smooth line, and there is no slag in the lower half. When the cutting speed is too fast, it may not be able to cut through and sparks may be sprayed out; Some areas can be cut through, and some areas cannot be cut through; The cutting section is inclined, and slag is generated in the lower half. When the cutting speed is too slow, it will cause over melting, the cutting section will be rough, and the cutting seam will become wider.

 

• Nozzle and nozzle height

As the beam and auxiliary gas channel, the shape, aperture and height of the nozzle will affect the cutting effect.

The nozzle mainly controls the gas diffusion area and size, so as to control the cutting quality; Prevent slag and other sundries from bouncing upward, passing through the nozzle and polluting the lens. Generally speaking, when cutting thin plates, the defocusing amount is small and small-diameter nozzles are selected; When cutting thick plates, large slit and light spot are required, and large-diameter nozzles are selected.

The nozzle is divided into single layer and double layer. The single layer laser nozzle is used for melting and cutting, that is, nitrogen is used as auxiliary gas to cut stainless steel and aluminum plate; Double layer laser nozzle is generally used for oxidation cutting, that is, oxygen is used as auxiliary gas for cutting carbon steel.

The nozzle height is the distance between the nozzle outlet and the workpiece surface. During cutting, this height is generally set at 0.3mm-0.8mm. If it is too low, the nozzle will easily collide with the workpiece surface. If it is too high, the concentration and pressure of auxiliary gas will be reduced, resulting in the reduction of cutting quality. During perforation, the height of the nozzle can be appropriately raised to prevent the generated slag from being reflected on the lens.

 

• Focal position

After checking the actual zero focal point of cutting in the previous article, we need to set the appropriate focal point position in the actual cutting process to obtain a cutting workpiece with better cutting surface effect:

（1）Zero focal length

The focus is on the surface of the workpiece, suitable for cutting thin plates.

（2）Negative focal length

The focus is under the surface of the workpiece, generally at 1 / 2-2 / 3 of the thickness of the workpiece, so the range of the smooth surface is large, and the slit will be wider than the zero focal length.

（3）Positive focal length

The focus is on the upper surface of the workpiece, which is generally applicable to the cutting of thick plate carbon steel (thick plate needs a large cutting seam, and the negative focus will cause carbon steel overburning).

 

• Protective gas pressure

The size of the auxiliary gas pressure also has an impact on the cutting effect of the fiber laser cutting machine. Adjusting the gas pressure can also improve the cutting effect:

（1） Insufficient air pressure

When the gas pressure is insufficient, the slag generated by cutting cannot be removed, and it is not easy to penetrate, resulting in slag generated on the cutting surface; The cutting speed cannot be increased, which affects the cutting efficiency. In general, when cutting thin plates at high speed, high air pressure is required to prevent slag from being attached to the back of the cutting seam; When the material is thick or the cutting speed is slow, the air pressure can be appropriately reduced.

（2）The air pressure is too high

Increasing the gas pressure can improve the cutting speed to a certain extent, but excessive gas pressure will reduce the cutting speed. It is because under high pressure, too fast gas flow rate will enhance the cooling effect and even interfere with the focusing of beam energy, resulting in the reduction of cutting quality and efficiency. At the same time, when the air pressure is too high, the cutting surface will be thicker and the cutting slit will be wider.

 

Summary

Excellent cutting equipment was selected and pre cutting inspection was done. The process parameters during laser cutting must be adjusted according to the actual situation during cutting, and the most appropriate cutting parameters shall be selected according to the situation in specific application. In production, every time we optimize the cutting process is also an important means to maintain long-term stability and leadership.