Molds & Tooling
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ASA thick wall sink mark
Problem Phenomenon
ASA product thick-wall areas and rib backs show depressed sink marks, surface defects unacceptable for automotive exterior parts, flash appears at edges after increasing holding pressure.
Cause Analysis
Thick-wall area cools unevenly and outer layer solidifies first, internal shrinkage with insufficient feeding forms depression; ASA shrinkage rate 0.4~0.7% is low, but local thick-wall shrinkage concentration still exceeds appearance tolerance; holding pressure transmission is limited by gate freezing.
Solution
①Increase holding pressure and time to compensate thick-wall shrinkage; ②design rib wall thickness at 50~60% of main wall; ③move gate near thick-wall area; ④solve the balance between holding pressure and flash with multi-stage holding pressure.
Key Takeaway
ASA sink mark governance emphasizes both holding pressure and structural design; rib thickness ratio is a design red line; multi-stage holding pressure resolves the contradiction between sink mark and flash.; After confirming effectiveness, fix the parameters and practices into the work instruction to prevent recurrence
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