Combining Injection Molding and 3D Printing for Tailoring Polymer Material Properties

Modern polymer-based technical components not only have to fulfill demanding mechanical-structural properties but need to integrate different functions to yield hybrid systems for complex operations. Typically, neither materials nor processing technologies are fully compatible with each other. The aim of the work is to combine the advantages of seemingly incompatible manufacturing processes such as high-volume injection molding (IM) and precision additive manufacturing to produce functional and customized hybrid materials. IM is widely used for polymer processing but stands against high investment costs for tailor-made molds with high-resolution features. They focus on overprinting of injection-molded parts made of thermoplastic polyurethane (TPU) with microstructures via projection-microstereolithography (PµSL) to generate hybrid polymer materials with spatially tailored stiffness, enabling selective reinforcement, resulting in an E modulus increase of 195% compared to mere IM-processed TPU. With that, the hybridization of processing methods is showcased to extend the product properties of polymer materials obtained via either IM or PµSL printing that have, prospectively, a maximum degree of individualization as well as a multitude of structural and functional features at the same time. To achieve optimum interfacial adhesion, the influence of surface roughness is studied, and reinforcement effects of different overprinted microstructure types are evaluated.