Avaliação da integridade superficial de insertos retificados da liga WC-Co para ferramentas de corte

Abstract

Cutting tools produced from cobalt tungsten carbide alloy (WC-Co), compared to conventional cutting tools, provide lower cost of machining, with increasing productivity and acceptable combination of hardness and fracture toughness. Due to the high value of hardness, the finished product after sintering is obtained by grinding process, which produces high thermal and mechanical loads. However, this process may change the surface characteristics, which affect the cutting insert performance during the application in the machining process. In this context, the present work evaluates the influence of the grinding process variables on the surface integrity of carbide inserts and, consequently, on the tool life in service, in this case, the orthogonal turning of a nodular cast iron. The effects of different conditions of the grinding process were observed (cutting and axial feed speeds, dressing axial speed, diamond grinding wheel of different grain size and bonding material) on the surface roughness (Rz) and edge roughness (∆r), variation in hardness in relation to that of the base material (∆HK) and residual stress in the perpendicular direction to the grinding (σ) of the cemented tungsten carbide cutting inserts. As main results, it was verified that the use of the grinding wheel with smaller grain size (D15) and the use of resinoid binder improved the achievement of lower values of Rz and ∆r, with the consequent generation of more regular surfaces and edges. Higher compressive residual stress and higher hardness in the surface were found after grinding with a vitrified binder wheel and larger grain size (D46). The compressive residual stress e high hardness contributed to increase of the insert ́s life in turning experiments, due to the formation of crack by mechanical effort determining factor for the end of tool life.