Molds & Tooling
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PP Part Shrinkage Exceeding Design
Problem Phenomenon
After cutting the mold with conventional shrinkage, PP parts are overall too small or have large local deviations, requiring repeated mold corrections after trials.
Cause Analysis
PP actual shrinkage is greatly affected by wall thickness, holding pressure, mold temperature, and orientation; actual shrinkage at thick walls can reach the upper limit—if design values are improper or areas are not distinguished, overall or local dimensional deviations occur.
Solution
①Record measured shrinkage for different wall thicknesses during trials and correct the mold differentially by wall thickness; ②optimize holding pressure to compensate shrinkage; ③reserve mold correction margin for critical fit dimensions; ④unify measurement aging and temperature; ⑤if necessary, use CAE to predict shrinkage and guide mold design.
Key Takeaway
PP shrinkage cannot use one fixed value 'one-size-fits-all': measure by wall thickness, compensate by zones, and reserve mold correction margin for critical dimensions to control dimensions of high-shrinkage materials.
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