The project achieved a significant industrial upgrade of the ARBURG Freeformer for the production of metallic components. The main technical goal was to reduce wear of the discharge unit and to obtain a consistent volume output through an optimized control system. In the first phase a comprehensive requirement analysis was carried out, which led to the qualification of a suitable feedstock based on stainless steel 316L. The feedstock was formulated with a binder system adapted to the specific surface area and density of the powder, allowing the production of green 316L parts with a standard layer thickness of 0.2 mm. The process parameters that proved effective were a discharge frequency of 85 % at a form factor of 1.45, a build‑room temperature of 40 °C and a nozzle temperature of 160 °C.
To extend the service life of the discharge unit, the geometry of the nozzle and the closing needle was modified. The wear analysis followed the VDI 3822 guideline, starting with damage description, hypothesis formulation and verification by destructive and non‑destructive testing. A metallographic investigation revealed abrasion and cold‑welding between the needle tip and the sealing seat, caused by the abrasive feedstock. The needle was tested with the 316L feedstock at 150 Hz for 4.5 million opening‑closing cycles, after which significant damage and loss of sealing performance were observed. The study identified the needle‑to‑nozzle interface as the critical wear mechanism and guided the design of a more wear‑resistant geometry.
Fluid dynamics of the melt in the discharge unit were investigated with ANSYS Fluent. The standard geometry and several variants were compared. Mesh refinement in the ring‑gap region and dynamic mesh generation during needle motion ensured sufficient quality. For a discharge frequency of 200 Hz the pressure at the needle’s starting position was higher than the ring‑gap pressure and decreased to ambient pressure at the outlet. During needle descent the pressure and volumetric flow increased, while the flow velocity rose after the ring‑gap. The simulations showed that a larger nozzle‑wall angle reduced melt velocity and volume flow, whereas a 120° peak angle produced the highest mass pressure and wall shear stress. These results guided the redesign of the discharge unit to balance flow rate and wear.
An optimized control system was designed in MATLAB Simulink. The controller dynamically regulates the mass‑pressure generation in the discharge unit to achieve a robust volume flow. High‑frequency pressure measurement inside the nozzle was enabled by optical pressure sensors, which were integrated into the control loop. The controller was validated through life‑cycle tests on improved prototypes of the discharge unit, and complex demonstrators were fabricated using the optimized manufacturing parameters.
The project was funded by the German Research Foundation (DFG) and carried out in collaboration with ARBURG GmbH & Co. KG, which supplied the Freeformer and provided technical expertise on the discharge unit; Heidelberger Druckmaschinen AG, which facilitated industrial transfer and the use of stainless‑steel feedstock; and CeWOTeC, which performed material characterization and spectroscopic analysis. The research period spanned from 2021 to 2023, during which the team developed a new feedstock, redesigned the discharge unit, implemented a high‑performance control system, and demonstrated the feasibility of industrial‑grade production of 316L metallic parts with the ARBURG Freeformer.