Optical Profilometry Replica Metrology Protocol for Mould Cavity Topography
Indirect optical profilometry on elastomeric cavity replicas yields sub-micron texture data while eliminating tool teardown and optical access limits.
Spatial Texture Str
Meaning
A non-dimensional surface texture ratio quantifies spatial isotropy by comparing autocorrelation decay distances in dominant and secondary surface directions. Metrology systems measure spatial texture str to distinguish directional lay patterns from uniform isotropic surface textures on tooling and plastic parts. Values close to one indicate uniform spatial properties in all directions, whereas values approaching zero signal strong directional lay from milling or turning operations.
Part designers specify spatial randomness parameters to control light scattering and liquid flow behavior across functional surfaces.
Isotropy Evaluation
Calculating the autocorrelation function determines how rapidly surface profile patterns lose spatial correlation across distance vectors. Measuring spatial texture str reveals whether surface finishes exhibit uniform texture or distinct linear grooves created by cutter paths. Injection moulded optical diffusers require high spatial isotropy to diffuse light uniformly without creating visual streak artifacts.
Mold cavity polishing processes alter this parameter as manual sanding lines yield to isotropic bead blasting.
Machining Pattern
Parallel tool marks from ball-nose end milling produce low ratio values that indicate strong directional lay. Monitoring spatial texture str allows moldmakers to confirm complete removal of cutter marks during final cavity benching.
Optical Finish
Cosmetic vehicle interior trim components demand uniform anti-glare characteristics without visual grain orientation. Maintaining correct spatial texture str values prevents directional reflectivity variations across complex curved surfaces.