Optical Coherence Measurement Fundamentals for Deep Tooling Cavities
Optical coherence measurement uses broad-bandwidth infrared interference to capture deep cavity topographies without mechanical probe contact or lens clipping.
Draft Angle Reflection
Meaning
Visual shifts in the appearance of a moulded plastic surface caused by the angular tilt of cavity walls relative to the light source define the primary aesthetic challenge of part geometry. This draft angle reflection alters how light bounces off the textured or polished faces of the component. Part designers must account for these changes to prevent unwanted highlights or shadows on visible cosmetic surfaces.
When the angle is incorrect, the part appears warped or uneven even if its dimensions are perfect.
Optical Deviation
Textured moulds scatter light in multiple directions to produce a matte finish on the polymer surface. If draft angle reflection is uneven, the grain of the texture appears stretched or flattened along the direction of part ejection. This discrepancy is particularly noticeable on large automotive interior panels.
The surface finishes must be adjusted to compensate for these geometry-driven highlights.
Tooling Layout
Tool designers locate the parting line to distribute the draft angles symmetrically across the visible face of the part. Because each side of the parting line must taper away to allow release, draft angle reflection can create a sharp transition in the surface lustre. Correcting this requires a gradual blending of the draft on the tool.
Visual Inspection
Automated camera systems monitor the surface quality of moulded housings by detecting inconsistencies in the returned light. Any deviation in draft angle reflection can trigger false failures during cosmetic inspection. Process stability minimizes the frequency of these inspection errors.