ISO 25178 Surface Parameters for Injection Moulding Optical Components
ISO 25178 areal parameters define 3D optical surface texture to control stray light and guide injection moulding process windows for precision lenses.
Mean Square Surface Slope Sdq
Meaning
A hybrid surface parameter quantifies the root mean square of local slopes across a defined sample area. The mean square surface slope Sdq evaluates the average steepness of surface features, which correlates with light scattering and tactile quality. In the context of polymer processing, this parameter dictates how a molded part interacts with adhesives and coatings.
Angle Evaluation
Determination of the surface slope involves calculating the local gradient at every point across the measurement area. High values for Sdq indicate steep-sided asperities that increase the surface area available for mechanical interlocking. Polymer components molded from virgin resins replicate these fine features more accurately than those produced from highly degraded regrind.
Tooling Wear
Steel replication in injection molding gradually degrades as repeated thermal cycles and polymer flow wear down the sharp micro-textures of the mold. Monitoring the mean square surface slope Sdq over a production run reveals the onset of tool erosion. When the slope decreases, the molded parts lose their satin or matte finish, turning shiny and failing aesthetic specifications.
This decline signal tells the operator to schedule maintenance.
Adhesion Assessment
Insufficient surface slope reduces the bond strength of post-molding coatings. The mean square surface slope Sdq verifies that the molded texture matches the specification required for paint or plating. Parts with low slope values exhibit poor paint retention, leading to peeling and warranty claims.