Layout and sizing of ejector pins for injection mould desian using the wavelet transform

Abstract

Injection moulding is one of the most prevalent technologies used in processing thermoplastic polymers. At the end of the injection moulding cycle, the plastic moulded part should be ejected when the injection mould opens. To eject complex mouldings with bosses, ribs and other features, ejector pins are generally used because they are economical and easy to install. However, the ejector pins can cause high local stresses and strains in the moulding at the stage of ejection, leading to part deformation and damage. Thus, the proper layout of ejector pins is very important in mould design. A method is proposed for determining the layout and size of the ejector pins required to eject thermoplastic mouldings, minimizing part deformation and damage. The proposed method computes the distribution of the necessary ejecting forces to overcome the friction between the part and its mould. Then, it transforms the ejecting forces into a certain number of representative forces by the wavelet transform. Finally, the location and size of the ejector pins that correspond to the discrete ejecting forces are obtained. The proposed method will help injection mould designers systematically to obtain ejector designs.