Influence of Different Powder Conditioning Strategies on Metal Binder Jetting with Ti-6Al-4V.

Metal binder jetting shows great potential for medical technology. This potential can be exploited by integrating binder jetting into existing process routes known from metal injection molding. The biggest challenge here is the flowability and packing behavior of the powders used, due to their low size distributions. This paper investigates different powder-drying strategies to improve flowability using a statistical experimental design. Because of its relevance for medical applications, spherical Ti-6Al-4V powder with a size distribution under 25 µm is dried under various parameters using vacuum and gas purging. The investigated parameters, time and temperature, are selected in a central-composite-circumscribed test plan with eleven tests and three center points. The target parameters-water content, flowability and impurity levels (oxygen, nitrogen)-of the powder are analyzed. For validation, practical test trials are carried out on an industrial binder jetting system with unconditioned powder and conditioning with optimized parameters, comparing the manufactured parts and the powder bed. An optimized drying cycle with a duration of 6 h at 200 °C was determined for the investigated powder. Significant improvements in the dimensional accuracy (from ±1.5 to 0.3%) of the components and the visual impression of the powder bed are demonstrated.

Piston-Based Material Extrusion of Ti-6Al-4V Feedstock for Complementary Use in Metal Injection Molding.

Piston-based material extrusion enables cost savings for metal injection molding users when it is utilized as a complementary shaping process for green parts in small batch sizes. This, however, requires the use of series feedstock and the production of sufficiently dense green parts in order to ensure metal injection molding-like material properties. In this paper, a methodological approach is presented to identify material-specific process parameters for an industrially used Ti-6Al-4V metal injection molding feedstock based on the extrusion force. It was found that for an optimum extrusion temperature of 95 °C and printing speed of 8 mm/s an extrusion force of 1300 N ensures high-density green parts without under-extrusion. The resulting sintered part properties exhibit values comparable to metal injection molding in terms of part density (max. 99.1%) and tensile properties (max. yield strength: 933 MPa, max. ultimate tensile strength: 1000 MPa, max. elongation at break: 18.5%) depending on the selected build orientation. Thus, a complementary use could be demonstrated in principle for the Ti-6Al-4V feedstock.