Influence of Molecular Structure of POM on Processability Within Metal Injection Molding

TL;DR

This study examines how the molecular structure of polyoxymethylene (POM) affects its performance in metal injection molding processes.

Contribution

The study identifies that POM copolymers with lower viscosity improve processability in metal injection molding compared to homopolymers.

Findings

POM homopolymers degrade more significantly than copolymers under high-temperature processing conditions.

Lower viscosity POM copolymers are preferable for optimizing metal injection molding processability.

Catalytic debinding performance is adequate for all tested POM materials.

Abstract

Metal Injection Molding (MIM) is based on the processing of highly filled polymers via the well established polymer injection molding process. It offers a highly efficient processing route for the indirect manufacturing of especially small and complex metal parts. In this regard, polyoxymethylene (POM) is often used as a primary binder component in MIM feedstocks due to its high debinding rate through a time-saving catalytic debinding process, utilizing the acid-catalyzed degradation of POM for polymer removal. However, thermally induced degradation of POM under processing conditions can also lead to changes in processing behavior, which is particularly important in highly filled polymers due to their already challenging processability. In this context, the present work demonstrates the impact of POM homopolymers (POM-H) and copolymers (POM-C) with varying viscosities on feedstock characteristics, their influence on the thermal processing stability, and their significance for the properties of the green parts. Within the study, the thermal degradation of both material types was assessed by viscosity measurements and thermogravimetry, with POM-H exhibiting more significant degradation compared to the thermally more stable POM-C, especially at higher temperatures. Catalytic debinding performance was found to be adequate for all materials. However, lower viscosity POM-C grades are preferred to optimize processability in MIM.

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