MACHINING OF CERAMIC Si3N4-TiN SCAFFOLDS USING MICRO-EDM

Advanced engineering ceramics display excellent mechanical properties such as high hardness, high compressive strength, chemical stability, wear and thermal shock resistance. Due to their superior performance over other materials, the use of ceramics in a range of different applications is increasing year by year. Bio-ceramics, such as alumina, zirconia, titania, Si3N4-TiN, just to mention a few, have been of interest for many years for orthopaedic and dental applications. However, a number of challenges in their application still remain, including improvements in the material properties (mechanical and 'bio-compatible' feasibilities) and in the manufacturing process chain toward the final product. Electrical Discharge Machining (EDM) can be successfully employed to machine complex 3D geometries also on hard materials exhibiting a brittle behaviour, such as ceramics, on the condition that the limit of their low electrical resistivity is overcome. To this aim, some ceramic composites are synthesized using second electroconductive phases comprising Titanium, resulting in ZrO2-TiN, Si3N4-TiN, B4C-TiB2. Moreover, when ceramic-based scaffolds and prostheses are fabricated, this additional phase seems to have a good physiological impact on cell growth and proliferation. In this paper, micro-EDM manufacturing of different micro-textures for scaffold realization made on Si3N4-TiN is presented and discussed. Different experiments have been performed in order to define optimal micro- EDM electrical parameters in terms of material removal rate (MRR) and tool wear ratio (TWR). Micro-electrodes with different diameters are used for different machining regimes, roughing, semi-finishing and finishing, with the goal of identifying minimum geometrical limits on micro-pins textures machining and also taking into account that high averaged surface roughness is required for this application.