Influence of tool edge preparation on performance of ceramic tool inserts when hard turning

Coating, as a form of tool edge preparation, changes the properties, geometry and roughness of the active parts of tool inserts. The performance of both uncoated and coated ceramics was tested in machining tests and the results were related to the tool edge and the machined surface as well as cost indices. The presented results show that tool edge preparation by coating does affect forces, tool wear and the machined surface, while friction force from scratch tests and the coating thickness and its hardness have been identified as being relevant to the results of machining tests. The relationship between the thickness of the surface layer and residual stress at the surface due to coating has been evaluated. Though the tool life of coated ceramics is shorter than that of cubic boron nitride, tool edge preparation by coating contributes to the reduction in machining costs due to the application of higher cutting speeds.