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.
Sdr
Meaning
Topographic surface parameters calculate the additional surface area developed by micro-texture relative to a perfectly flat planar measurement area. Precision moulders specify Sdr to quantify surface area expansion on textured tool steel and injection moulded polymer parts. Flat surfaces return an Sdr value of zero percent, while complex textures increase the area ratio metric.
Datasheet height metrics cannot differentiate between broad rolling waves and sharp micro-peaks of equal amplitude.
Area Calculation
Triangular mesh integration sums localized surface areas across three-dimensional height point arrays. High peak density and steep slope angles increase the total developed area above nominal projected limits. Texturing processes for automotive interior tools adjust Sdr values to optimize tactile feel and scuff resistance.
Polymer melt temperature determines how effectively molten resin replicates micro-area expansion.
Mechanical Interlocking
Developed surface area governs mechanical bond strength in overmoulded multi-material assemblies. Higher area ratios provide expanded contact zones for adhesives and thermal bonding applications. Recycled resin additions alter polymer melt index, causing partial replication of fine surface features.
Tool maintenance tracks parameter reduction to schedule cavity re-texturing before bond strength drops below specification limits.
Control Limit
Optical metrology instruments verify area parameter compliance across large cavity surfaces before production sign-off. High Sdr values increase demoulding friction, requiring higher ejection forces or mould release agents. Production protocols define allowable Sdr ranges to balance aesthetic texture requirements against clean part release.