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.
Steel Cavity Topography
Meaning
Geometric layout of the interior mould faces includes the micro roughness left by milling and subsequent hand finishing. Monitoring steel cavity topography ensures that the metal surface will create the intended plastic finish without causing part ejection problems. The peaks and valleys of the steel act as the master template for every part produced during the life of the tool.
Wear Tracking
Repeated contact with abrasive resins like glass filled nylon alters the surface over time. Measuring steel cavity topography identifies when the original finish has been rounded off or scratched beyond repair. This preventative check avoids mass rejects during production restarts.
Ejection Force
Deep features in the topography increase the grip the plastic holds on the metal once it cools. Polishing the steel cavity topography along the direction of draw helps the part slide out without stress marks. Rough profiles require higher clamp and kick out forces.
Refurbishment Decision
Comparisons against the original CAD file show how much metal has been lost to corrosion or erosion. When steel cavity topography deviates too far from specification, the tool must be removed for welding or re texturing. Accuracy in these scans saves money by targeting only the worn areas.