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The demand for inert bioceramics is always increasing in the dental field. Yttrium oxide tetragonal zirconia polycrystals (Y-TZP) are oxide ceramics which are currently used because of their interesting mechanical properties due to a toughening transformation. Industrially speaking, machining of the ceramic before sintering (green body) is very common because it allows a better productivity and it reduces crack probability during the sintering process. The goal of this paper is to determine the behavior of green ceramic during the machining operation. This study is carried out on several blanks with different binder percentages. The specific cutting energy (SCE) and the surface quality (Ra and Rz) are determined for several cutting speeds. The SCE follows a logarithmic evolution when the cutting speed increases. Despite this increase, the Ra are relatively stable whatever the cutting speed and the binder percentage. At a low cutting speed, a higher Rz value is observed caused by pullout of material. The increase of cutting speed allows to stabilize the Rz value whatever the binder percentage. This study shows that the green ceramic has a pseudo-plastic behavior whose machinability depends mainly on the interaction between the material and the cutting edge of the tool, so unlike pre-sintered ceramic or metallic part cutting speed has a low influence on the quality of the machined part.

Standards enabling the objective tolerancing and evaluation of dimensional and geometrical performances of additive manufacturing (AM) printers are still missing. The design, printing and measurements of geometrical benchmark test artefacts (GBTA) is the current solution proposed in literature. However, the current GBTA with fixed dimensions cannot cover most of the available printing area of printers with large building platform dimensions. This article proposes to solve this problem by developing an adaptive GBTA design whose main dimensions can be adapted to any common 3D printer. Moreover, an innovative design is implemented to decrease the risk of warping. The adaptive GBTA will then be used to characterise the performances of two different architecture material extrusion printers (Ultimaker 2+ and Pollen AM Series MC). Dimensional and geometrical accuracy, as well as top surface topography, were evaluated. The Ultimaker printer could reproduce features with maximum deviations below the tolerance interval (IT) 13 of the ISO 286-1, while the Pollen machine achieved a higher IT of 15 or 16. The highest geometrical deviations were observed for the coaxiality of cylinders oriented along the build direction (Ultimaker: 0.250 mm and Pollen: 0.497 mm). Top surface topography exhibited higher Ra values for Pollen (13.7 µm) than for Ultimaker 2+ (4.9 µm). The performances of the Pollen printer were lower than the Ultimaker machine in terms of surface topography, dimensional and geometrical accuracy. The proposed adaptive GBTA design covers most of the printing areas exhibited by Pollen and Ultimaker printers and offers flexibility to test other printers even with larger or smaller dimensions.

Manufacturing of advanced ceramic parts exhibiting complex geometries is laborious and expensive. Traditionally, the machining is carried out on a so-called ‘green ceramic’: a compact composed of ceramic powder held with the help of a binder. This difficulty is due not only to the composition of the material, but also to the lack of methods that determine optimal machining parameters. The goal of this paper is to apply the method based on ductile material behavior to determine a feed rate working range to ensure a machining quality. Indeed, a previous study demonstrated the limits of this method in determining cutting speed. In this case, two material removal mechanisms are observed: a mechanism dominated by pulling of the material and a proper machining mechanism. This demonstrates that the specific cutting energy is a reliable indicator for machining quality assessment. In the studied case, the recommended machining parameters to ensure quality machining of Y-TZP green ceramic with a 3 mm diameter cylindrical tool are: a cutting speed of 250 m/min, a feed per tooth of 0.037 mm/tooth, an axial depth of cut of 0.7 mm, and a radial depth of cut of 3 mm.