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.
Peak Extreme Height Sxp
Meaning
An areal surface parameter measures the height difference between specific material ratio points to characterize the peaks of a texture. The peak extreme height Sxp represents the height of the surface between the zero percent material ratio and a defined reference ratio, typically fifty percent. In injection molding, this metric quantifies the tallest features on the textured surface of a part that could affect tactile feel and part ejection.
Height Evaluation
Mathematical calculation of Sxp utilizes the areal material ratio curve to isolate the upper peak zone from the core roughness. This makes the parameter highly sensitive to transient anomalies like high asperities or microscopic burrs on molded surfaces. In contrast, standard roughness measurements often average these peaks out, missing critical defects.
Demolding Behavior
Demolding a plastic part from a textured tool requires that the part surfaces release cleanly without tearing or scratching. The peak extreme height Sxp of the tool surface determines the mechanical resistance during the ejection phase. When the peaks are excessively high, they lock into the shrinking polymer, increasing the force needed to push the part out.
This leads to drag marks, stress whitening, or structural deformation of the molded component.
Wear Assessment
Tool wear over extended molding runs alters the peak profiles of the cavity texture. Measuring the peak extreme height Sxp at regular production intervals tracks the flattening of these peak structures. A significant decrease in this value indicates that the tool requires re-texturing to maintain the specified matte finish.