Molds & Tooling
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COC Shrinkage Rate Estimation Deviation
Problem Phenomenon
Molds for COC precision parts were designed with empirical shrinkage rates, dimensions were out of tolerance after mold trials, and shrinkage differences among different grades and wall thicknesses caused repeated mold repairs.
Cause Analysis
The COC shrinkage rate is 0.1~0.7% and varies with grade, wall thickness and process; although the shrinkage of amorphous materials is small, directionality and process sensitivity still exist; applying empirical values causes large errors.
Solution
①Set the shrinkage rate according to the specific grade manual data; ②use mold flow analysis to assist prediction; ③leave mold repair allowance for critical dimensions; ④correct by actual measurement after mold trial and fix the process window.
Key Takeaway
COC low shrinkage is an advantage, but accurate values still depend on grade data; precision part molds should leave compensation allowance; the process sensitivity of amorphous materials cannot be ignored.
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