EXPERIMENTAL OPTIMIZATION OF POLYMER JETTING ADDITIVE MANUFACTURING PROCESS USING TAGUCHI DESIGN

摘要

Polymer jet printing (PJP) is a direct-write additive manufacturing process, emerging as a rapid high-resolution method particularly in the medical field for the fabrication of a wide spectrum of products, e.g., anatomical models, tissue scaffolds, implants, and prosthetics. PJP allows for non-contact multi-material deposition of functional polymer inks. The PJP process centers on simultaneous deposition of build and support photopolymer materials on a free surface, which are immediately cured in situ using a UV light source, allowing for solid-freeform fabrication. The PJP process is inherently complex, governed by a multitude of parameters as well as material-machine-process interactions, which collectively affect the functional properties of a fabricated structure. Consequently, physics-based characterization and optimization of the PJP process would be inevitable. In this study, a new test standard was forwarded for the characterization of the mechanical properties of PJP-fabricated bone structures; the standard was designed on the basis of an X-ray μ-CT scan of a femur bone in addition to the ASTM D638-14 standard. Furthermore, the Taguchi L_8 orthogonal array design was utilized to investigate the effects of influential PJP process parameters on the mechanical properties of the bone structures, including Young's modulus of elasticity, tensile strength, breaking strength, and ductility. The selected process parameters (each at two levels) were: (ⅰ) print direction, (ⅱ) resolution factor, ( ⅲ) UV light intensity, and (ⅳ) deposition head temperature. The mechanical properties of the femur bone structures were measured using a tensile testing machine. The UV light intensity appeared as the most significant factor, influencing all the aforementioned mechanical properties, while the resolution factor was identified as an inconsequential factor. In addition, it was observed that the print direction and the head temperature significantly affected the breaking strength and the ductility, respectively. Overall, the results of this study pave the way for further investigation of the effects of the PJP parameters toward optimal fabrication of complex bone tissue scaffolds and implants with long-lasting functional characteristics.