[Phenomenon] Focusing of laser cutting machine is to find out the position of the smallest light point (focus) after the processing lens is focused. The specific method is to use nitrogen as the auxiliary gas and find the position with the highest brightness of blue light (blue white bright light) while illuminating the low power laser beam. The blue light brightness of the short focus lens is bright, and the occurrence range is narrow, which is easier to find. The longer the focal length of the lens, the darker the brightness of blue light, and the wider the production range, so it is difficult to find the focus.
[Reason]
The blue light method is a method to irradiate the high energy density laser beam only on the surface of the material, and determine the focus position by the brightness of the light generated at the moment of evaporation of the material. The longer the focal length of the lens is, the larger the diameter of the light spot will be, the lower the energy density at or near the focal position will be, the lower the brightness of blue light will also be, and it will become more difficult to find the focal position. In addition, if the output power is set to an improved setting, the focus depth will become larger, the blue light generation range will also become larger, and it is not easy to find the focus position with high accuracy.
Solution
Because the focal point diameter of the lens with long focal length is large and the energy density is low, it is necessary to increase the output power to compensate for the setting of processing conditions. However, because the focus depth will become deeper at the same time, that is, the focus range will become wider, so the accuracy of the focus position will become worse.
1) In the setting of processing conditions, it is necessary to keep the average output power low and increase the power of each pulse, that is, increase the peak power of the pulse and reduce the pulse frequency, so that the instantaneous energy density can be increased and the blue light with greater brightness can be obtained.
(2) The conditions of the auxiliary gas also affect the brightness. When focusing, try to use low pressure gas conditions that can shield a large range, and it is recommended to use a large diameter nozzle.
(3) Pay attention to the surface state of the materials used when focusing. When there is an oxide layer or oil film on the surface of the carbon steel material, or the material has been used for focusing for many times, the brightness of the blue light will become less obvious. It is recommended to use stainless steel with good surface condition when focusing.