Reduction of Sink Mark Defects in Injection Molding of Polyoxymethylene (POM) Through Thermal Modeling and Process Parameter Optimization

Abdussalam Topandi; Khadijah S. Nisa; Herlin Arina; Subhan Rizki Fadilah; Diva Pahlevi Putra Aumee; Pranata

doi:10.31572/inotera.Vol11.Iss1.2026.ID579

Abdussalam Topandi Polymer Chemical Engineering, Polytechnic STMI Jakarta
Khadijah S. Nisa Polymer Chemical Engineering, Polytechnic STMI Jakarta
Herlin Arina Polymer Chemical Engineering, Polytechnic STMI Jakarta
Subhan Rizki Fadilah Polymer Chemical Engineering, Polytechnic STMI Jakarta
Diva Pahlevi Putra Aumee Polymer Chemical Engineering, Polytechnic STMI Jakarta
Pranata Kementerian Perindustrian Republik Indonesia

DOI: https://doi.org/10.31572/inotera.Vol11.Iss1.2026.ID579

Keywords: Injection molding, sink mark, thermal modelling, POM, Tait equation

Abstract

This study aims to minimize sink-mark defects in polyoxymethylene (POM) injection-moulded products through thermal modelling and process parameter optimization. The end-of-packing temperature (T_EOP) was estimated using a one-dimensional transient cooling model. At the same time, the specific volume at the end of packing (v_EOP) was calculated using the Two-Domain Tait Equation of State. Volumetric (S_V) and linear shrinkage (S_L) were derived following Chen’s shrinkage framework. Results showed that v_EOP ranged from 0.1640 to 0.1764 m³/kg, S_V ranged from 13.30 to 19.40%, and S_L ranged from 4.64 to 6.94%. Higher T_EOP correlated with increased v_EOP and higher shrinkage, indicating ineffective packing. Optimization revealed that a melt temperature of 203.41 °C, combined with T_EOP of 145.02 °C and a cooling temperature of 16 °C, produced zero shrinkage in the model. These findings provide a quantitative basis for defining process control limits for melt temperature, coolant stability, and packing conditions to reduce sink marks and improve dimensional consistency of POM products.

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