Effects of mold temperature on mechanical properties of an injection-molded part with microfeatures

The present study aims to develop a plastic flexspline part for a harmonic gear drive. Due to its high stiffness and strength, polyetheretherketones (PEEK), a semi-crystalline polymer, is used as a molding material. To ensure radial flexibility, the flexspline is designed with a thin-cup shape attached with micro-teeth. This thin-wall molding results in not only filling difficulties in injection molding, but also the deterioration of mechanical properties due to low crystallinity. Among various processing parameters, the effect of mold temperature on crystallinity and relevant mechanical properties is investigated through a tensile test and a Differential Scanning Calorimetric (DSC) test. Use of a composite polymer containing carbon fibers is also discussed for improved stiffness and strength of the product. Induction heating, an efficient way to heat a mold surface, is applied to the injection molding of a flexspline in order to improve moldability and the resulting crystallinity. It is shown that micro-teeth profiles are successfully filled by raising the mold temperature rapidly, and the resulting crystallinity is improved.