3D printed thermoplastic polyurethane with isotropic material properties

Additive Manufacturing (AM) is an emerging field with rapid growth. Fused Deposition Modeling (FDM), as an AM method, is becoming increasingly popular. With the ability to create parts from a wide range of thermoplastics, it is necessary to understand the effects of FDM process on the printed part's mechanical properties for a given material. This paper investigates the mechanical properties of 3D printed TPU parts created by a typical low cost desk-top FDM machine. TPU was first extruded into filament suitable for FDM and printed into samples for tensile tests according to the ASTM 3039 standard. The effects of raster orientation, nozzle temperature, and air gap on the mechanical properties were investigated. The compression-molded samples were used as the baseline. While the printed samples had an overall lower ultimate tensile strength (UTS) compared to the molded samples, the printed samples with a negative air gap showed nearly isotropic material properties, irrespective of raster orientation and nozzle temperature. For samples with a positive air gap, raster orientation had a large influence on the overall UTS. Nozzle temperature did not have much effect on the UTS. When compared to rigid thermoplastics TPU has a much lower glass transition temperature (T-g) at -40 degrees C. This allows for much better interlayer bonding between print lines as TPU is above T-g for the entire printing process.