Injection Molding
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Large and Unstable Dimensional Shrinkage in PE '2079851475616104452
Problem Phenomenon
The overall dimensions of PE parts are too small and out of tolerance, or dimensions fluctuate greatly between batches, causing poor assembly.
Cause Analysis
PE has a high shrinkage rate (1.5%~4%) that varies greatly with wall thickness, holding pressure, and mold temperature; HDPE shrinks more than LDPE; excessive or insufficient holding pressure, mold temperature drift, and inconsistent measurement timing all cause deviation.
Solution
①Correct the mold according to measured shrinkage, with differentiated compensation in thick-wall areas; ②Optimize the holding pressure curve; ③Control mold temperature constant; ④Unify measurement timing and temperature (crystallization continues); ⑤Leave mold correction allowance for critical dimensions and monitor with SPC.
Key Takeaway
PE dimensions = 'high shrinkage + aging': correct the mold based on actual measurement by wall thickness, unify the measurement time point, and use holding pressure to compensate shrinkage; HDPE 'shrinks more' than LDPE, so the shrinkage difference must be factored in when selecting the material.
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