Thermoplastic material extrusion additive manufacturing with in-situ milling: A novel approach for shaping of ceramics

A notable disadvantage of thermoplastic material extrusion additive manufacturing is the prevalence of printing defects within the structures. This phenomenon results in a reduction in the mechanical strength of the structures in comparison to pressed parts. In this study, we evaluated the combination of additive and subtractive manufacturing processes to achieve defect-free structural ceramic parts. Zirconia discs were fabricated with and without contour and surface milling between the printing processes. For this purpose, the ceramic injection molding (CIM) feedstock based on zirconia and a 3D printer equipped with a milling head were employed. To assess mechanical performance, biaxial mechanical analyses were conducted using ring-on-ring and a ball-on-three balls setup to investigate the flexural strength of the sintered disks. This hybrid printing method yielded significantly improved mechanical properties, with flexural strength enhanced by a factor of 1.6. The milling process and its effect on the surface also led to a substantial improvement in the Weibull modulus. Additionally, contour milling resulted in a defect-free interface between the outline shell and the internal printed regions, although this did not further influence the mechanical strength. The ball-on-three balls test provided higher mechanical values, with biaxial bending strength reaching 627 MPa and a Weibull modulus of 9.6.