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

注塑模具的制造目标是使功能表面尽可能光滑，以实现均匀填充，同时保持低流动阻力。流体力学领域的研究和初步实验表明，微观结构的模具表面可以降低剪切速率和流动阻力，并扩大流道长度。基本上，减少注射成型可以有两个后果：首先，在恒定注射压力下更快的填充时间可以帮助减少注射成型的周期时间。更快的注射速度可以进一步改善可实现的流动长度，因为更少的冷却以及腔内更均匀的温度分布，从而提高了零件的质量。其次，减少流动路径上的压力损失可以减少所需浇口的数量，此外，对于恒定的注射速度，它可以帮助减少塑料熔体的剪切，从而减少热应力。较低注射压力的另一个直接优势是所需的夹紧力减少，这也降低了注射成型过程中的能耗，并可以使用更小的注塑机。由于机械负荷和压力引起的注塑模具的维护，因此可以减少停机时间，从而进一步提高注塑成型过程的可靠性。此外，关于微结构模具表面对塑性流动行为影响的基本知识可以帮助未来确定地优化工艺。在这个项目中，将全面分析电火花加工（EDM）模具表面对热塑性材料流动行为的影响。电火花加工是模具制造中经常使用的一种工艺，可以对表面进行详细的剪裁。作为第一步，我们将实验研究电火花加工的放电能量依赖结构，根据不同的粗糙度制度，这些粗糙度制度内在地与模具制造过程中热改变的边缘区域的相应扩展相关联。为了对表面结构进行建模和仿真，验证其对塑料流动的影响，电火花加工表面完整性对模具壁传热系数（HTC）的影响将成为实验和仿真的重点。这是WZL独特的研究点。此外，创建的模具表面的耐久性将通过长期测试（WZL和IKV）进行监测。进一步的研究将基于计算流体动力学（CFD）与传热系数（HTC）模拟作为表面结构的耦合以及注塑过程中的验证实验和测量，这是IKV的核心研究。

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.