Feasibility study on piston-based feedstock fabrication with Ti-6Al-4V metal injection molding feedstock

The use of feedstocks from metal injection molding (MIM) for the additive manufacturing (AM) of green parts, which are then debound and sintered in a process called shaping, debinding, and sintering (SDS), is promising in terms of production costs of metallic parts. However, in order to use the cost-efficient AM technique fused filament fabrication (FFF) for SDS, powder-binder mixtures known for MIM feedstocks must be adapted to filament requirements resulting in adjustments to debinding and sintering. In contrast to FFF, screw-based material extrusion is capable of processing already available MIM feedstocks, but machine costs are high due to complex print heads. In this work, a new process called piston-based feedstock fabrication (PFF) is developed for processing already available MIM feedstocks at comparable costs to FFF. First, the state of the art is reviewed highlighting the potential of piston-based material extrusion for its usage in SDS. Based on the review, an extruder module is developed which is integrated into a kinematic system. Experimental studies are performed to validate the developed PFF printer. As material, a Ti-6Al-4V MIM feedstock is used. Thresholds for piston speed (0.175 mm/min), extrusion temperature (80 degrees C), and nozzle diameter (0.4 mm) are determined to ensure a viscosity that allows to control the extrusion process via steps per mm. With these thresholds it is found that a constant extrusion process can be established in a filling range of the cylinder up to 155 mm. Finally, the performance of the PFF system is evaluated in terms of nozzle geometry, print speed, and reproducibility showing that reproducible green part properties are achieved at a maximum speed of 8.18 mm/s while using a tapered FFF nozzle.