Effects of injection molding parameters and cooling conditions on the dimensional stability and mechanical properties of polypropylene boxes for automotive batteries

This study investigates the influence of injection molding parameters, including temperature, cooling duration, and coolant flow conditions, on the dimensional stability and mechanical properties of automotive battery boxes made from polypropylene impact copolymer (PPIC). PPICs are widely used materials for battery boxes because of their strength, toughness, chemical resistance, and low cost. Disruption of coolant flow during molding, simulating a real-world manufacturing anomaly, was shown to cause localized warpage. The lower injection temperature, 220 °C, indicated greater robustness to coolant anomalies than 250 °C, maintaining dimensional stability despite cooling disturbances. Mechanical testing of tensile bars extracted from the molded boxes suggested orientation-dependent behavior in a limited sample set, with longitudinal samples tending to exhibit greater elongation than transverse samples. Notched tensile bar observations were consistent with rate sensitivity; however, the small number of specimens and deviations from ISO 527 limit statistical inference. An exploratory random forest model was trained on the available data to illustrate how the process parameters could be related to elongation; within the observed input space, the model suggested that injection temperatures of 220–234 °C and cooling times of 38–47 s may be associated with higher elongation. These preliminary indications may inform future process tuning aimed at minimizing warpage and improving toughness, contingent on validation with expanded testing under ISO-compliant conditions. It could be possible to improve the robustness and reliability of automotive-grade PPIC parts by adjusting the injection temperature and maintaining stable cooling. Future work should also explore additional variables such as mold design and polymer formulation to further refine processing strategies.