A rough cut surface is a common quality issue in laser cutting operations, directly impacting both the aesthetic appeal of the workpiece and subsequent processing steps. Roughness typically manifests as prominent striations, severe slag adhesion, or even jagged edges.

I. Four Primary Causes of Rough Cut Surfaces

1. Improper Focus Position (Most Common)

When the focal point deviates from its optimal position, the energy distribution within the laser spot becomes uneven. This results in inconsistent kerf widths (wider at the top or bottom), preventing molten material from being smoothly expelled and leading to the formation of rough striations. If the focal point is positioned too high, the upper section of the material undergoes excessive melting; conversely, if positioned too low, severe slag adhesion occurs at the bottom.

2. Auxiliary Gas Issues

If the gas pressure is too low, molten slag cannot be effectively blown away; conversely, if the pressure is too high, it may induce turbulence that causes ripples on the cut surface. Insufficient gas purity (e.g., oxygen containing impurities) exacerbates oxidation reactions, resulting in a blackened and rough cut surface. It is recommended to use process gases with a purity level of 99.95% or higher.

3. Mismatched Cutting Parameters

Cutting at an excessive speed causes the material to be pulled apart before it has fully melted, resulting in a torn or ragged appearance on the cut surface. Conversely, cutting too slowly leads to heat accumulation and an excess of molten material, resulting in slag adhesion. Insufficient laser power can also cause the cut surface to exhibit a "wire-drawing" phenomenon (elongated streaks).

4. Contamination of the Optical System

When protective lenses or focusing lenses become contaminated, laser transmittance decreases and the laser spot becomes distorted, leading to irregular patterns on the cut surface. Studies indicate that a mere 5% reduction in lens transmittance can double the roughness of the cut surface.

II. Rapid Improvement Measures

*   **Calibrate Focus:** Use the "ramp test" or "dot-marking method" to identify the optimal focal position.

*   **Check Gas Supply:** Verify that the gas pressure (typically 0.8–1.2 MPa) and purity meet the specific process requirements.

*   **Optimize Parameters:** Adjust the cutting speed and laser power matching curve based on the thickness of the material being cut.

*   **Clean Lenses:** Inspect and clean optical lenses daily; replace protective lenses on a quarterly basis.

III. Preventive Recommendations

Establish a comprehensive database of process parameters, recording the optimal parameter combinations for various materials and thicknesses. After replacing the nozzle or lenses, always re-verify the quality of the cut surface to ensure consistency in processing results.