ISO 25178 Areal Surface Texture Parameters for Optical Inspection
ISO 25178 defines 3D areal surface parameters like Sa and Sdr, replacing 2D profiles to qualify optical non-contact inspection on textured tool steel and mouldings.
Cavity Tool Signoff
Meaning
Final tool validation marks the formal boundary between steel manufacturing and production injection moulding. During this phase, metrology inspectors verify cavity dimensions against nominal CAD geometry while processing trials establish baseline melt temperature, clamping tonnage, and injection velocity. Shrinkage compensation rates fixed inside the mould steel must align with actual volumetric contraction observed during initial shot sampling.
Once cavity tool signoff occurs, responsibility for dimensional compliance shifts from the toolmaker to the production plant, locking the tooling geometry against further unauthorized alterations.
Tooling Acceptance
Dimensional qualification requires coordinate measuring machine data collected across multiple moulded samples produced under stable processing conditions. Toolmakers achieve acceptance only when all critical features fall inside narrow tolerance bands without requiring secondary machining operations. Processing windows established during trials demonstrate whether the mould can hold required tolerances across extended production runs without thermal drift.
Any deviation exceeding specified limits halts the release sequence until technicians rework the steel or adjust cooling channel layouts.
Shrinkage Variance
Volumetric contraction rates dictate final part dimensions far more than nominal steel sizing alone. Crystallinity differences between amorphous polymers and semi-crystalline resins alter final part dimensions significantly during cooling phases. Regrind ratios introduced into the feed throat change melt flow behaviour, shifting shrinkage patterns away from values established with virgin material.
Processing technicians compensate for these variables by adjusting packing pressure profiles inside the injection unit rather than relying solely on initial tool dimensions.
Economic Risk
Uncontrolled dimensional drift during production leads directly to high scrap rates and costly tool modifications. Mould modifications executed after final tool acceptance incur severe financial penalties and extend equipment downtime. Production plants absorb these costs when tooling validation protocols fail to detect thermal instability prior to full-scale manufacturing.
Establishing rigorous verification standards prevents premature deployment of unproven moulds into active production schedules.