Optimal Layout and Sizing of Ejector Pins for Injection Mold Design
Abstract Injection molding is the most prevalent technology used for processing thermoplastic polymers. At the end of the injection molding cycle, the plastic molded part should be ejected when the injection mold opens. Complex moldings with bosses, ribs, or other features are generally ejected by ejector pins because they are economical and easy to be installed. However, the ejector pins can cause high local stresses and strains in the molding at the stage of ejection leading to the part deformation and damage. This paper proposes a method to determine the layout and size of the ejector pins required to eject thermoplastic moldings with minimizing the part deformation and damage. The proposed method calculates the distribution of the necessary ejecting forces to overcome the friction between the part and its mold. Then, it transforms the ejecting forces into a certain number of representative forces by the wavelet transform. Finally, we can get the location and size of the ejector pins corresponding to the discrete ejecting forces with the help of a rule-based system. The proposed method helps an injection mold designer to systematically obtain an optimum ejector design.