The focus of laser cutting machine is to find out the position of the minimum light point (focus) after the processing lens is focused. The specific method is to use nitrogen as the auxiliary gas to irradiate the low-power laser beam and find out the position with the highest brightness of blue light (blue and white light). The blue brightness of short focal length lens is bright, and the occurrence range is narrow, which is relatively easy to find. The longer the focal length of the lens is, the darker the brightness of the blue light is, and the range of the blue light is relatively wide, so it is difficult to find the focus.
[reason]
Blue light method is a method that only irradiates a high-energy density laser beam on the surface of the material, and determines the focus position by the brightness of the light produced by the material at the moment of evaporation. 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 focus position will be, the brightness of the blue light will also decline, and the search for the focus position will become more difficult. In addition, if the output power setting is an improved setting, the focus depth will increase, the generation range of blue light will also increase, 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, the setting of processing conditions needs to be compensated by increasing the output power. However, because the depth of the focus will become deeper at the same time, that is, the range of the focus will become wider, so the accuracy of the focus position will become worse.
1) In the setting of processing conditions, the average output power should be kept low, and the power of each pulse should be increased, that is, increasing the peak power of the pulse and reducing the pulse frequency can increase the instantaneous energy density and obtain a brighter blue light.
(2) The condition of the auxiliary gas will also affect the brightness. When looking for the focus, try to use low-pressure gas conditions that can be shielded in a wide range. It is recommended to use a large-diameter nozzle.
(3) Pay attention to the surface state of the material used when finding the focus. When there is an oxide layer or oil film on the surface of carbon steel, or the material has been used for focusing for many times, the brightness of blue light will become less obvious. It is recommended to use stainless steel with good surface condition when focusing