Basic analysis and optimization of the flow behavior of thermoplastics by adjusting the surface of electrical discharge machined injection molds (EDSIMP)

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Manufacturing of injection molds aims at functional surfaces being as smooth as possible in order to achieve uniform filling and maintaining low flow resistance at the same time. Studies in the field of fluid mechanics as well as preliminary experiments have shown that micro structured mold surfaces can reduce shear rate and flow resistance as well as enlarge flow path lengths.Basically, the reduction can have two consequences for injection molding: First, faster filling times for constant injection pressures can help reducing the cycle time of injection molding. Faster injection speeds can further lead to improved achievable flow lengths due to less cooling as well as a more homogeneous temperature distribution within the cavity, which improves the quality of the part. Second, decreased pressure loss over the flow path could reduce the amount of required gates and furthermore, for constant injection velocities, it could help to reduce shear of plastic melt and therefore thermal stress. Another direct advantage of lower injection pressure is the reduction of the required clamping force, which also decreases the energy consumption in the injection molding process and can enable the use of smaller injection molding machines. The reliability of the injection molding process can furthermore be increased due to less downtime because of maintenance of the injection mold caused by mechanical load and pressures. In addition, fundamental knowledge on the influence of microstructured mold surfaces on the plastic flow behavior can help to deterministically optimize the process in future.In this project, the influence of the electrical discharge machined (EDM) mold surfaces on the flow behavior of thermoplastic materials will be comprehensively analyzed. EDM is a frequently used process for mold manufacturing and allows for detailed tailoring of surfaces. As a first step, the discharge energy dependent structures of sinking EDM will be experimentally investigated in terms of different roughness regimes which are inherently connected to an according extend of a thermally altered rim zone during mold manufacture. For modelling and simulation of surface structures and the validation of their influence on plastics flow, the impact of the EDM surface integrity on the heat transfer coefficient (HTC) at the molds wall will be in experimental and simulation focus. This represents the distinct research point of WZL. In addition, the durability of created mold surfaces will be monitored by long term testing (WZL and IKV). The further investigations will be based on the coupling of Computational Fluid Dynamics (CFD) with heat transfer coefficient (HTC) simulations as function of the surface structure along with validation experiments and measurements during injection molding, representing the core research of IKV.