1. Using defocus to mark a certain range of contents
Because each focusing mirror has a corresponding depth of focus range, and the method of deviating from the focus will easily lead to a large range of pattern marking, the edge is at the critical point of depth of focus or beyond the depth of focus range, so it is easier to cause the effect of non-uniformity. Therefore, the problem of laser energy should be considered in the method of defocusing calibration.
2. The laser output spot is occluded, that is, the spot of the laser beam passing through the galvanometer and field mirror is defective and not round enough.
When the laser output head, fixture and galvanometer are not adjusted properly, part of the spot is occluded when the laser passes through the galvanometer, and the spot on the doubler is non-circular after focusing through the field mirror, which may also lead to uneven effect.
Another case is that the deflection lens of the galvanometer is damaged, and when the laser beam passes through the damaged area of the lens, it can not reflect out well. Therefore, the laser energy passing through the damaged area of the lens is different from that in the non-damaged area of the lens, and the laser energy acting on the material is also different, so that the marking effect is not uniform.
THERMAL LENS PHENOMENA
When a laser passes through an optical lens (refraction, reflection), it will heat the lens and produce subtle deformation. This deformation will increase the focus and shorten the focal length of the laser. If the machine is fixed and the distance is adjusted to the focal point, after a period of time, the laser energy density acting on the material will change due to the thermal lens phenomenon, resulting in the non-uniform marking effect.
4. The level of the machine is not adjusted, that is, the laser vibration lens or field lens lens is not parallel to the processing table.
Because the two are not level, the distance of laser beam passing through the field mirror to the processed object will not be the same, and the energy density of the laser falling on the processed object will be different eventually, and then the effect will be uneven on the material.
5. Reasons for materials, such as inconsistent film thickness on the surface of materials or changes in physicochemical properties
Materials are sensitive to laser energy response. Usually in the same material, the laser energy reaches the material damage threshold is certain. When the thickness of the coating is not uniform or some other physical and chemical treatment processes are not uniform, the effect of laser marking will also be uneven.