Common equipment and operation of Additive Manufacturing (AM) of titanium is usually cost intensive due to advanced machines and high maintenance costs. Fused Filament Fabrication (FFF) offers the fabrication of titanium implants, for instance hip endoprostheses or dental implants, adapted to the patient with a high level of detail at low costs. This can be achieved by the low waste of titanium powder and by using cost-effective, commercial FFF printers. These printers are fed with feedstocks containing titanium powder and thermoplastic polymers (binders), which enable the mixture to be shaped at moderate temperatures. After shaping, the binder must be removed by dissolving in water and subsequently pyrolyzing. A final sintering step densifies the metal and controls its structure and mechanical properties. With respect to the requirements of the printing process, we established and optimized the process chain to fabricate dense and defect-free Ti6Al4V implants by FFF.
At first, new feedstock systems with various polymeric components were developed and subsequently characterized by shear and oscillation rheology. The second step involved the extrusion of flexible filaments and their characterization using dynamic mechanical thermal analysis (DMTA). Green parts were then printed. A matter of interest were the printing parameters, such as the printing temperature or the infill pattern, and their influence on the properties of the green parts. At last, the debinding behavior of the green parts in water and the sintering parameters (temperature, time, and atmosphere) were investigated and optimized.
After sintering, a density of 96.5 % of theory could be achieved, an additional hot isostatic pressing delivered density values better than 99.9 % of theory. Tensile tests showed comparable mechanical properties to conventional manufacturing methods. In addition, the low contamination with oxygen and carbon complies with the ASTM F2885-17 standard for surgical implants, thus validating the process chain. Furthermore, the knowledge gained about binder systems could be transferred to other implant materials such as CoCrMo or ZrO₂.