Increasing the injection moulding productivity through EDM surface modulation

The productivity of the injection moulding process is considerably deteriorated due to the demoulding issues as a result of increasing part and polymer complexity. An effective method to overcome some of the issues is the application of coatings on mould surface to reduce adhesion and friction during the moulded part ejection. In such solutions, the mould is coated after the machining by methods such as milling and EDM. In fact, die-sinking EDM is widely used to machine moulds with high accuracy, surface quality and aspect ratios. In this research, a novel method is analysed where the texture of the EDM surface is modulated to achieve desirable surface functionality, leading to reduction of part sticking during ejection in injection moulding. The effect of primary parameters of EDM process on the resulting surface is analysed. It is seen that while the surface amplitude parameters such as Ra and Rz remain similar to the standard eroded surface, the spacing parameter RSm and slope measure RΔq can be modulated. The effect of the surface texture during injection moulding is evaluated by measuring the forces during the ejection stage to characterise part sticking. Similar or considerably reduced ejection forces are observed for the modulated EDM texture compared to the polished surfaces, depending on the polymer type and part geometry. The ejection force observations are correlated to the static and dynamic friction coefficient of surface textures against different polymers. The reduction of ejection forces comparable to the coated surfaces places surface texturing as an effective alternative or a supplement to reduce the demoulding issues and thus increasing the injection moulding productivity and part quality