Morphology and mechanical properties of micro injection molded polyoxymethylene tensile rods

Publication date: Available online 28 August 2019Source: Polymer TestingAuthor(s): Matthieu Fischer, Pascal Pöhlmann, Ines KühnertAbstractMicro injection molding is a key process in the high-volume production of systems with small-scale parts, as it enables the production of consistent high-quality parts. Depending on the materials used, however, the properties of the parts may be strongly dependent on the processing conditions. Semi-crystalline materials, in particular, exhibit process-dependent structural evolution. To evaluate the impact of processing conditions on the morphology of polyoxymethylene (POM), thin sections of micro-injection-molded tensile rods with total shot weights of around 0.04 g were examined for samples with and without weld lines. Production were set according to an experimental design (DoE), varying injection flow rate, mold temperature, and melt temperature. For the measurement of the crystallinity a DSC analysis was performed. To supplement these results and to improve the understanding of the process-property relationship, tensile tests were performed under light microscopy and a fractographic analysis was done using electron microscopy (SEM). The mechanical behavior of the samples without weld lines was improved by lowering the melt temperature and the injection velocity, which resulted in a thicker skin layer. The elongation at break of the weld line samples was increased by processing at higher mold temperatures, which also resulted in chan...

Source: Polymer Testing - September 4, 2019 Category: Chemistry Source Type: research