Cutting Force Variation Due to Wear of Multi-Layer Ceramic Coated Tools

Abstract

Cutting forces were measured during turning AISI 4340 steel with uncoated, two-layer coated (TiC/Al2 O3 ), and three-layer coated (TiC/Al2 O3 /TiN) cemented WC-Co inserts possessing chip-breaker grooves in order to investigate the progression of tool wear. The variations of cutting force signals are interpreted in light of predominant wear mechanisms. A characteristic feature of wearing coated tools is shown to be the rapid increase of the radial and axial cutting forces when the tool life is reached. This behavior is associated with both the increase of the real contact area on the nose and the flank face due to coating delamination and the relatively less severe wear on the rake face. Normalizing the cutting forces by those of unworn tools yields a single curve for each cutting force. The instant at which either the radial or the axial force deviates from these curves determines the wear life of coated tools. The good agreement between results for the wear life of coated tools obtained from cutting force and nose wear measurements suggests that the wear life of multilayer ceramic coated tools can be accurately determined by monitoring the cutting force response.