Brief Analysis of Causes for Uneven Marking Effects in Fiber Laser Marking Machines

I. Marking Content Over a Specific Range Using Defocused Focusing

Since each focusing lens has a corresponding depth of field range, employing a defocused approach can easily cause the edges of large-area marked patterns to fall at the depth of field boundary or beyond its range. This often results in uneven marking effects. Therefore, the defocused marking method must consider laser energy issues.

II. Laser output spot obstruction, resulting in an incomplete or non-circular spot after passing through the galvanometer and field lens

Improper alignment of the laser output head, fixture, or galvanometer may cause partial obstruction of the laser spot as it passes through the galvanometer lens. After focusing by the field lens, this produces a non-circular spot on the frequency-doubling crystal, potentially causing uneven results.

Another scenario involves damage to the galvanometer's deflection mirror. When the laser beam passes through the damaged area of the mirror, it cannot be reflected effectively. Consequently, the laser energy passing through the damaged region differs from that passing through the undamaged region. This results in inconsistent laser energy ultimately applied to the material, leading to uneven marking effects.

III. Thermal Lens Effect

When laser light passes through optical lenses (via refraction or reflection), it causes the lenses to heat up and undergo minute deformation. This deformation shifts the laser's focal point upward, shortening the focal length. If the machine is fixed and the distance is adjusted to the focal point, the laser energy density applied to the material will change after operating for a period due to the thermal lens effect, resulting in uneven marking.

IV. Improper Machine Leveling (Laser Vibration or Field Lens Non-Parallelism with Work Surface)

Non-parallel alignment between the laser head and field lens causes inconsistent distances traveled by the beam after passing through the field lens. This results in uneven energy density distribution on the workpiece, manifesting as inconsistent marking effects on the material.

V. Material-related factors, such as inconsistent coating thickness or variations in physical/chemical properties

Materials exhibit high sensitivity to laser energy. Typically, for identical materials, the laser energy required to reach the material's damage threshold is constant. However, when coating thicknesses vary or other physical/chemical treatment processes are uneven, this can also cause inconsistent laser marking results.