The defocusing amount is an important parameter that affects the cutting quality in the laser cutting process. In the non oxidation cutting of stainless steel plates, it is important to blow off the molten metal with auxiliary gas to reduce the slag amount and improve the cutting quality. Therefore, it is necessary to set the focus position inside the steel plate to expand the notch width to increase the flow of auxiliary gas. The actual production experience also proves that in the process of non oxidation cutting of stainless steel plate, setting the focus position to the inside of the steel plate can obtain good processing quality.
The selection of defocusing amount has a great impact on the cutting quality of stainless steel plate:
【1】 When the focus position is appropriate, the slit material will melt, while the material near the cutting edge will not melt, and the slag will be blown away, forming a clean slit without slag.
【2】 When the focus position lags behind, the energy absorbed per unit area of the lower part of the cutting material is reduced, and the cutting energy is weakened, resulting in that the material cannot be completely melted and blown away by the auxiliary gas, so that the incompletely melted material is attached to the lower surface of the cutting plate.
【3】 When the focus position is advanced, the average energy absorbed per unit area in the lower half of the cutting material increases, leading to the melting of the material cut and the material near the cutting edge, and the liquid flow. At this time, because the auxiliary air pressure and cutting speed are unchanged, the melted material adheres to the lower surface of the material in a spherical form, and forms slag.
In actual production, the focus of laser cutting stainless steel plate is required to be selected on or below the material surface. This is because the width of the upper part of the cutting groove is expanded, the fluidity of gas and melt is improved, the smooth range of the section is expanded, and the cutting quality is improved. During the cutting process, there is no definite value for the focus position of steel plates of different thicknesses. When the focus position is taken on or above the surface of the steel plate, slag is easily generated on the lower surface due to low average power density and insufficient energy at the lower part of the steel plate. Therefore, when laser cutting stainless steel plate, the focus position should be selected inside the material. To improve the fluidity of gas and molten metal, ensure that the lower part has sufficient energy density, so that the range of the smooth surface is expanded.
