Molds & Tooling
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PC Sink Marks
Fenómeno do problema
Depressions appear on the back of ribs and bosses, appearing as optical distortion spots on transparent parts, obvious on high-gloss surfaces.
Análise das causas
Insufficient shrinkage feeding at locally thick areas; insufficient holding pressure/time or the gate freezing too early, the shrinkage of the thick-wall core pulls the surface inward; an excessive rib thickness ratio is the structural inducement.
Solução
①Rib thickness ≤50%~60% of wall thickness; ②Increase holding pressure and extend holding until gate freeze; ③Arrange the gate near thick walls and enlarge it appropriately; ④Core out and reduce material at thick-wall areas to reduce shrinkage from the source; ⑤Strengthen cooling in the sink mark area.
Conclusão principal
PC sink marks are treated from both ends of 'structural wall thickness and holding feeding': rib thickness and thick walls are the root, holding and freeze are the technique; sink marks on transparent parts are also optical defects, and wall thickness must be controlled from the design stage.
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