Additive manufacturing and mechanical analysis of multi-material polymer parts combining thermosets and thermoplastics

Multi-material additive manufacturing (AM) represents one of the most promising solutions to target the contemporary demand for complex products with high individuality and inherent functionalities. Besides continuous advances in machinery and the available material spectrum, a substantial aspect of multi-material AM is still underrepresented: the simultaneous combination of thermosets and thermoplastic within a single AM process. A promising technology in this regard is the newly developed Fusion Jetting (FJ) process. This investigation focuses on the combination of acrylate-based photopolymers (thermoset) and thermoplastic polyurethane (TPU) with FJ. Tensile specimens are built with strategic variations of the process parameters and experimentally analyzed to derive beneficial processing conditions. A proof of concept is delivered by demonstrating a significant increase in Young’s modulus of TPU specimens from approximately 65 to 160 MPa through integration of photopolymer reinforcements. Further experiments regarding variable layer heights and laser powers identify an optimum layer height of 100 µm along with a tolerable laser power of 15 W for maximum mechanical properties. An overall challenging aspect of the FJ process is the presence of unwanted delamination between reinforced and non-reinforced layers. The failure mode is observed during tensile testing on multiple multi-material specimens of this investigation. The origin of delamination can be correlated to the deviation of integrated reinforcements from their originally intended dimensions as well as the unwanted crystallization within reinforced layers. First, countermeasures to minimize delamination are identified, such as decreasing the rotational increment of the laser hatch orientation from 90 to 10° per layer.