Simulative Evaluation Of The Optimization Potential Of Additively Manufactured Static Mixing Elements For Extrusion

In plastics extrusion, the homogeneity of the melt is an essential pre-requisite for uniform product quality. Static mixing elements for the extrusion of plastics serve to homogenize the melt by splitting and recombining the flow of polymer melt, thus removing e.g. hot streaks in the melt. However, the geometric complexity of static mixers, which typically consist of crossed bars of metal joined together, makes both the design and the manufacture of specialized mixer geometries difficult. Against this background, both simulation of melt flow in static mixers and additive manufacturing of static mixers by means of Selective Laser Melting are investigated. In order to accurately model the flow through the multitude of small gaps between the bars, the open-source CFD software OpenFOAM is employed. While OpenFOAM already supports very high resolution meshes and parallel computing, the interaction between melt temperature and melt viscosity and the effect of viscous heating are added to the simulation model. By means of the new simulation model, thermal mixing occurring during flow of a highly viscous HPDE through a reference static mixer is evaluated numerically. Selective Laser Melting not only allows an economic production of small and very small lots, but also offers design freedoms that have not been available before. This allows the production of static mixer geometries that cannot be manufactured with conventional processes. A framework for the exploitation of this advantage is shown. As an example, the potential thermal benefits of tempering channels located within each bar of the static mixer are explored.