Experimental investigation of coatings efficiency in micro-ball-end milling of pre-sintered 5Y-TZP ceramic

This study deals with micro-ball-end milling of a pre-sintered yttria tetragonal zirconia polycrystal. The aim is to underline the reliability of different coatings while machining this material regularly used in dental and luxury industries. Micro-ball-end mills are often used to machine partially sintered ceramics in dry conditions. This process is identified as critical by tool manufacturers and users in terms of wear and machining accuracy. The purpose is then to analyse the capacity of different tool/coating couples to ensure stable micro-machining of such ceramics. Cutting forces, tool reliability and surface integrity data are obtained from green machining tests of a 5Y-TZP (tetragonal zirconia polycrystal stabilised by 5%mol of yttrium) with 1-mm-diameter tungsten carbide micro-tools coated with two PVD coatings and one CVD coating (respectively AlCrN, DLC and diamond). The results highlight that the choice of an appropriate coating is mandatory for this type of abrasive ceramics, even if they are partially sintered. Material flow, tool wear and machined surface quality are discussed and correlated.