<p>Orthopedic implants are widely used for treating bone tumors and trauma defects in patients. They enable restoring the functionality and aesthetics of the original bone through reconstruction surgeries. These implants are generally available in standard shapes and sizes, which are mass-produced using casting, forming and machining processes. Such standard implants may not be suitable in complex cases of tumors or fractures due to their topology mismatch with the implantation site. Such cases require patient-specific implants (PSI), which can be produced using a combination of recent developments in the fields of medical imaging, computer-aided design (CAD) and additive manufacturing (AM). These implants are specifically made to meet patients’ requirements, using their own medical imaging data, leading to higher success rates compared to standard implants. The complex and organic geometry of PSI coupled with single order quantity make it suitable for production within a short lead time using AM. There is considerable technical literature on PSI manufacture using laser-beam powder bed fusion technologies, such as selective laser sintering (SLS), selective laser melting (SLM) and direct metal laser sintering (DMLS). However, the choice of optimal process parameters to obtain the required quality considering various international quality standards for implants does not appear to have been published so far.</p><p>This experimental work considers the minimum requirements of various mechanical properties suggested by ASTM standards, in determining the optimal AM process parameters for PSI manufacture. The biocompatible metallic alloy Titanium–6Aluminum–4Vanadium Extra-Low-Interstitial (Ti6Al4V ELI), which is among the most widely used orthopedic implant materials, is considered for this study. The test samples were fabricated using a DMLS system and annealed in a vacuum furnace. The three most important printing parameters, namely, laser power, laser velocity and hatch distance, were varied in three levels using the Taguchi approach. Properties such as tensile yield strength, ultimate tensile strength, percentage elongation and part density were considered for comparing the process parameter combinations. Multi criteria decision making techniques were employed, such as the technique for order preference by similarity to the ideal solution (TOPSIS), Grey relational analysis (GRA) and simple additive weighting (SAW) method. The results show that a combination of medium power, high velocity and low hatch distance values produce implants with superior mechanical properties. The proposed methodology and results are expected to help researchers and manufacturers in choosing the initial process parameters for PSI fabrication. Later, depending upon the results obtained by a specific system, the parameter values can be fine-tuned to achieve more precise physio-mechanical requirements.</p>

Additive Manufacturing Process Parameter Optimization for Titanium-Alloy Orthopedic Implants

Paper Proceedings: https://asmedigitalcollection.asme.org/IMECE/IMECE2021/volume/85543

ASME 2021 International Mechanical Engineering Congress and Exposition (IMECE2021)

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