Wall Section Changes That Arrive after the Steel Is Cut
Post-cut wall section increases require steel removal that permanently alters cooling dynamics, cycle time, and dimensional stack-ups.
Sink Mark Index
Meaning
Analytical value predicting the likelihood of surface indentations forming due to uneven local cooling in thickened sections of a part. Calculating the sink mark index during the design phase identifies where heavy ribs or bosses will cause visible depressions on the A-side surface. It quantifies the risk that a cosmetic feature will fail the final quality inspection.
Geometry Optimization
Adjusting wall thickness ratios remains the most effective way to lower a high value in this category. When the sink mark index suggests high risk, engineers specify coring out thick areas to make cooling more uniform across the geometry. This allows for faster cycles because the heat trapped in thick sections no longer dictates the entire cooling time.
Mould Packing
Increase of injection pressure during the hold stage helps offset the local volume reduction that causes the mark. Even when a sink mark index is borderline, careful pressure control can maintain part aesthetics in the short term. However, excessive pack pressure may lead to high internal stress and part warping.
Aesthetic Outcome
Perception of quality suffers when customers see slight dips in smooth plastic surfaces. Utilizing the sink mark index before metal is cut for the tool avoids costly re-works or part revisions after initial sampling. This predictive tool ensures that hidden structural features do not detract from the premium look of an assembly.