The effect of rapid prototype tooling on final product properties

Rapid tooling has allowed manufacturers to produce plastic injection-molded prototypes quickly and inexpensively. However, the mechanical properties of parts differ between rapid and conventional tools. The tensile and flexural properties of injection-molded parts produced in geometrically identical steel and composite molds were compared using atactic and syndiotactic polystyrene. When molded in the composite mold, both isomers exhibited an average of 17% lower ultimate tensile strength, similar Young's modulus, and 20% lower ultimate elongation than parts produced in the steel mold. The tensile stress-strain data for both isomers were found to be correlated. In flexural testing, both isomers molded in the composite mold exhibited an average of 19% higher flexural strength, 39% higher flexural modulus, and 27% lower ultimate flexural elongation than parts produced in the steel mold.