Standard ISO 25178 Parameters for Optical Profilometry Inspection
ISO 25178 areal optical profilometry replaces subjective 2D stylus traces with quantitative 3D parameters that accurately govern tool wear and part demoulding.
Topography Metrology
Meaning
Optical surface evaluation methodology establishes quantitative height profiles across polymer components and injection tooling. Industrial topography metrology maps microstructural variations on cavity walls to verify that textured surfaces transfer precisely onto molded thermoplastics. This discipline measures parameters such as roughness average and maximum profile height using white light interferometry or focus variation microscopy.
Moulders apply these measurements during tool qualification to separate raw steel variations from polymer shrinkage effects that distort finished geometry. Analysis stops at the boundary where internal molecular orientation begins, leaving bulk mechanical testing to other procedures.
Tooling Variance
Cavity wall finish directly dictates how molten polymer flows and cools against steel inserts during high pressure injection. Tooling topography metrology identifies microscopic machining marks left by high speed milling or electrical discharge machining before production runs begin. Unverified tool surfaces trap polymer melt and cause localized demolding drag that tears thin walls during ejection.
Toolmakers use interferometric scans to verify that polishing removes microscopic peaks without altering draft angles specified in the engineering drawing.
Resin Shrinkage
Semicrystalline polymers contract significantly during solidification, transferring tool surface textures with varying fidelity depending on local cooling rates. Topography metrology tracks how volumetric contraction alters surface roughness across thick structural ribs and thin hinge sections. Virgin polyethylene yields predictable surface replication, whereas regrind batches introduce melt flow index shifts that alter final part texture depth.
Technicians compare molded plaques against master CAD models to calculate specific shrinkage compensation factors for each resin grade.
Defect Cost
Surface irregularities trap particulate contaminants and create stress concentration points that cause premature mechanical failure under load. Inadequate topography metrology lets defective cavity finishes pass into production, leading to high scrap rates and costly tool rework. Part specifications demand precise microgeometry to ensure proper sealing performance and aesthetic uniformity across commercial product assemblies.
Tooling modifications required after initial sampling delay commercial launches and increase total program expenditure.