1、 Mark a certain range of content with offset focus
Because each focusing lens has a corresponding depth of focus range, the method of deviation from the focus will easily lead to the edge being at the critical point of depth of focus or beyond the depth of focus range when marking a pattern in a large range, which is more likely to cause non-uniformity of the effect. Therefore, the problem of laser energy must be considered in the method of offset marking.
2、 The output spot of the laser is blocked, that is, the spot of the laser beam after passing through the galvanometer and field mirror is incomplete and not round enough
The laser output head, fixed fixture and galvanometer are not adjusted properly, which results in partial light spot being blocked when the laser passes through the galvanometer. The light spot on the frequency multiplier after focusing by the field mirror is non-circular, which may also lead to uneven effect.
Another case is that the galvanometer deflection lens is damaged. When the laser beam passes through the damaged area of the lens, it cannot be reflected well. Therefore, the laser energy of the laser beam passing through the damaged area of the lens is different from that of 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.
3、 Thermal lensing phenomenon
When the laser passes through the optical lens (refraction, reflection), it will cause the lens to heat up and produce slight deformation. This deformation will cause the laser focus to rise and the focal length to become shorter. If the machine is fixed, when the distance is adjusted to the focus, the laser energy density acting on the material will change due to the thermal lens phenomenon after turning on the laser for a period of time, resulting in uneven marking effect.
4、 The machine level is not adjusted properly, that is, the laser galvanometer or field lens is not parallel to the processing table
Because the two are not horizontal, the distance between the laser beam and the processed object after passing through the field mirror will be inconsistent, and the energy of the laser falling on the processed object will have inconsistent energy density, and then the effect will be uneven on the material.
5、 The reason of the material, such as the film thickness of the material surface is inconsistent or the physical and chemical properties change
Materials are sensitive to laser energy response. Generally, under the same material, it is certain that the laser energy reaches the material damage threshold. When the coating thickness of the material is different, or there are some other physical and chemical treatment processes that are not uniform, the effect after laser marking will also be uneven.