Coherence Scanning Calibration Procedures for High Aspect Ratio Tool Steel Sidewalls
Calibrating optical coherence scanners on tool steel sidewalls requires specular tilt mapping, transfer function correction, and noise floor subtractive adjustment.
Tilt Artifact
Meaning
Misalignment between the optical axis of a profiler and the surface normal of a measured part introduces geometric distortions in the height map. A tilt artifact arises when the residual slope is not fully subtracted from the measurement data, leading to a skewed representation of the surface texture. This distortion interferes with the evaluation of fine features on molded polymer parts.
Geometric Distortion
The presence of a tilt artifact superimposes a linear height gradient across the measurement area, which inflates the calculated amplitude parameters such as arithmetic mean roughness. This tilt can mask high-frequency surface features, such as machining marks or polishing scratches. In severe cases, the slope can distort the calculated form of aspherical or cylindrical lenses.
Removal Technique
Metrologists eliminate the tilt artifact by applying a software-based leveling procedure, which fits a mathematical reference plane to the measured data using least-squares estimation and subtracts it. This digital leveling process restores the true horizontal orientation of the surface profile relative to the coordinate system of the profiler. Care must be taken to exclude high-relief or asymmetric features from the plane-fitting region to prevent the algorithm from introducing secondary, artificial shape distortions into the corrected dataset.
Molding Inspection
In injection molding quality control, accurate leveling is necessary to verify the flatness of sealing surfaces and housing joints. A failure to remove the slope artifact can lead to the false rejection of parts that are actually within specification. Reliable leveling procedures ensure that decisions are based on the true geometry of the molded product.