Molds & Tooling
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ABS brittle cracking——draft angle and insert problems
Fenómeno do problema
The product is difficult to demold and cracks after forced ejection, or products with metal inserts show cracks around the insert.
Análise das causas
The draft angle of the cavity/core is too small, and forced ejection causes the product to crack due to internal stress; ABS has large specific heat and heat storage, and the shrinkage rate difference with metal inserts is large; when the insert is not preheated, great shrinkage stress is generated at the interface, causing cracking around the insert.
Solução
①Ensure a draft angle of 1°~3°, and when demolding is difficult, adjust the corresponding cavity temperature and cooling time; ②minimize metal inserts, and when they must be used, preheat the insert to near the mold temperature; ③ensure sufficient wall thickness around the insert and set rounded corners; ④optimize ejection to avoid forced ejection.
Conclusão principal
ABS's draft angle and insert preheating are often overlooked: insufficient draft angle plus forced ejection = cracking, no insert preheating = interface stress cracking; these two details of structural parts must be fixed at the design stage.
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