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.
Material Ratio Curve
Meaning
A topographic representation describes the distribution of surface heights across a sampled area by mapping the percentage of contact length relative to the assessment length. This material ratio curve characterizes the load bearing potential of an injection moulded polymer part by identifying the peaks and valleys formed during the replication of tool textures. The measurement functions as a statistical distribution of material versus void volume within a specific cross section of the part surface.
It applies to quality control protocols for high precision optical or functional housings where surface uniformity dictates assembly performance.
Production Analysis
Precise mould cavity preparation influences the topographical outcome measured at the final part gate or runner position. This material ratio curve remains dependent on the cooling rate of the resin against the tool steel and the shrinkage characteristics inherent to the selected grade. Higher cooling rates usually compress the crests of the surface features, whereas slow cooling permits larger depth variations that shift the distribution downward.
Virgin material often maintains a stable rheology during injection but regrind percentages fluctuate, altering the viscosity that dictates how the melt fills intricate micro features on the tool wall. A moulder maintains a target value across production runs by adjusting the holding pressure and the barrel temperature to manage how the polymer skin develops against the metal interface. Mismatch between the specification of the tool and the resulting part indicates a deviation in the thermal stability or the shear profile within the hot runner system.
Surface Calibration
Tooling experts compare the profile against a specific reference length to identify wear patterns that emerge after several thousand cycles. This material ratio curve quantifies the degradation of textured surfaces by showing how the bearing area shifts as peaks erode due to friction from the ejection mechanism or the abrasive nature of glass filled additives. Engineers distinguish the datasheet properties provided by a resin supplier from the actual surface geometry created on the factory floor.
While the datasheet indicates the mechanical strength of the bulk material, the measured curve verifies that the surface replicates the grain pattern intended for aesthetic or functional grip. Variations in this curve across a cavity signify that the polymer filling pattern lacks symmetry or that the thermal mass of the tool steel varies across the parting line.
Process Validation
Monitoring these geometric trends prevents dimensional failures during the assembly of mating components in high tolerance housings. This material ratio curve confirms that the surface possesses the topography required to support local stress without deformation or premature wear during the operation of the part. Parts with irregular surface distributions fail under concentrated mechanical loads if the peaks collapse or if the valleys create stress concentrations that lead to brittle fracture.
Constant observation of the distribution helps determine the end of life for specific moulds before the finished product deviates from the tolerance limits required for a press fit. The shape of the distribution remains an objective standard for verifying that the moulding process replicates the intended physical texture of the tool face.