Integration of soft tooling by additive manufacturing and multiphysics simulation in polymer profile extrusion process chain

The die design process in polymer extrusion has traditionally relied on a trial-and-error approach, resulting in significant costs in tooling development. Additive manufacturing (AM) offers significant flexibility and design freedom, allowing the production of optimized extrusion dies with complex and free-form geometry. Furthermore, polymer-based AM has advanced in the printing of durable polymers and composite materials, leading to the opportunity for the application of
soft tooling through AM in the polymer extrusion process chain. Simulation has the potential to revolutionize die design by offering optimized solutions and reducing the need for test iterations when making design changes. Therefore, this Ph.D. project aims to explore the integration of soft tooling by AM and multiphysics simulation in the polymer extrusion process chain to facilitate the production of small batches and highly customized products.

The state-of-the-art in polymer extrusion highlights the importance of extrusion dies and calibration slides to influence the dimension and surface quality of extrudates as the final products of polymer extrusion. Furthermore, Fused Filament Fabrication (FFF) and Masked Stereolithography (MSLA) were the AM processes selected to manufacture the extrusion dies and calibration slides. A single piece streamlined die design with free-form geometry was implemented for three
die profiles, namely MEK01, MEK02, and MEK03. Extrusion pilot production with soft tooling by AM was performed, indicating that the AM carbon fiber- polyether ether ketone (CF-PEEK) die withstands the demanding process conditions of polymer extrusion.

Simulation enables the prediction of melt flow rate and pressure drop, which is critical in the die design process. Flow simulation for polymer extrusion was established using non-isothermal flow conditions and incorporating extruded material properties and boundary conditions derived from actual rheology and extrusion tests. The simulation was then experimentally validated with the extrusion die profile MEK02 and the extruded materials of polypropylene (PP) and acrylonitrile butadiene styrene (ABS). Furthermore, the experimentally validated simulation was implemented in the semi-streamlined die design for the conventional die profile MEK01. In addition, profile MEK03 resulted in an unbalanced flow due to its non-uniform wall thickness. Flow optimization was performed by implementing the flow restrictor to address the issue.

Dimensional evaluation and surface characterization were performed to identify the repeatability and precision of AM parts and the effect of AM extrusion die and AM calibration slides on the final products of polymer extrusion. The AM CF-PEEK die manufactured by FFF has surface topography with high peaks and notably deep valleys. Furthermore, the surface roughness of the extrudates is significantly lower than that of the AM CF-PEEK die. It was observed that the peak areas of the die surfaces have a greater influence on the surface roughness of the extrudates. The dimensional evaluation of the AM CF-PEEK die was performed before and after the experimental tests, indicating thermal expansion in the outside diameter of the die. Finally, a fluid-structure interaction (FSI) simulation was developed to evaluate the wear of soft tooling in polymer extrusion, including the polymer melt domain, the die domain, and its interaction.

In conclusion, the investigations present a promising result in the integration of soft tooling by AM and multiphysics simulation in the polymer profile extrusion process chain. Extensive dimensional and surface characterization indicates that AM soft tooling is capable of producing extrudates comparable to that of the commercial profile. Streamlined die design with free-form transition geometry has a lower pressure drop, which is beneficial for the lifetime of soft tooling. Finally, it is feasible to evaluate the wear of the soft tooling, as the main challenge in the application of soft tooling, through the FSI simulation.