Mechanistic Optimization of Pressure Transmission for Defect Mitigation in Thick‐Walled Aerospace‐Grade Polyetherimide

ABSTRACT High‐performance amorphous thermoplastics such as polyetherimide ( PEI ) are widely used in aerospace applications; however, thick‐walled sections are prone to internal void formation due to volumetric shrinkage and premature gate solidification. In this work, the influence of processing variables on void mitigation in thick‐walled PEI components was investigated using an industrially constrained experimental design. Analysis of variance showed that thermal parameters dominated defect variation, with cooling time and mold temperature contributing 50.4% and 30.15%, respectively. Linear regression identified gate freeze time ( GFT ) as a practical process indicator of pressure‐transmission efficiency, exhibiting a strong negative correlation with the maximum void diameter ( r = −0.964, R 2 = 0.930). A regression‐derived threshold of 5.61 s corresponded to the aerospace specification limit of 0.75 mm, and a conservative production target of 6.5 s was recommended based on the 95% prediction interval analysis. Under optimized conditions (160°C mold temperature, 40 s cooling time), the process achieved a GFT of 8.0 s and produced no ultrasonically detectable voids (maximum void diameter < 0.1 mm). Scrap rates decreased from 18.7% to 1.1%, reducing manufacturing cost per accepted part. These findings establish GFT as a practical mechanistic indicator for process‐window development in thick‐walled high‐performance thermoplastics.