Experimental determination of friction coefficients between thermoplastics and rapid tooled injection mold materials

摘要

Purpose - To determine static friction coefficients between rapid tooled materials and thermoplastic materials to better understand ejection force requirements for the injection molding process using rapid-tooled mold inserts. Design/methodology/approach - Static coefficients of friction were determined for semi-crystalline high-density polyethylene (HDPE) and amorphous high-impact polystyrene (HIPS) against two rapid tooling materials, sintered steel with bronze (LaserForm ST-100) and stereolithography resin (SL5170), and against P-20 mold steel. Friction tests, using the ASTM D 1894 standard, were run for all material pairs at room temperature, at typical part ejection temperatures, and at ejection temperatures preceded by processing temperatures. The tests at high temperature were designed to simulate injection molding process conditions. Findings - The friction coefficients for HDPE were similar on P-20 Steel, LaserForm ST-100, and SL5170 Resin at all temperature conditions. The HIPS coefficients, however, varied significantly among tooling materials in heated tests. Both polymers showed highest coefficients on SL5170 Resin at all temperature conditions. Friction coefficients were especially high for HIPS on the SL5170 Resin tooling material. Research limitations/implications - Applications of these findings must consider that elevated temperature tests more closely simulated the injection-molding environment, but did not exactly duplicate it. Practical implications - The data obtained from these tests allow for more accurate determination of friction conditions and ejection forces, which can improve future design of injection molds using rapid tooling technologies. Originality/value - This work provides previously unavailable friction data for two common thermoplastics against two rapid tooling materials and one steel tooling material, and under conditions that more closely simulate the injection-molding environment.