Application of a new, severe-condition friction test method to understand the machining characteristics of Cu-Zn alloys using coated cutting tools

Friction between copper-zinc (brass) alloys and uncoated as well as differently coated carbide tools was investigated by using a recently developed friction test, characterized by high contact forces, temperatures, and relative velocities. The major aim was to analyze the ability of various tool-brass combinations for reducing friction, adhesion and thus tool wear in cutting operations and to understand the existent mechanisms of action. In the first part of the study, the friction conditions between low-leaded brass alloys with varying chemical composition (CuZn38As, CuZn42 and CuZn21Si3P) and uncoated as well as TiB2 and DLC (ta-C) coated carbide tools were analyzed and compared to the high-leaded free-cutting brass CuZn39Pb3. In a second step, materials with almost the same chemical composition were used (CuZn41.5). Hereby, the influence of low lead contents ranging from Pb=0.003-0.19% on friction was analyzed and compared to a high lead content of Pb=1.9%. It can be summarized that significant differences in frictional behavior were determined depending on the material's chemical composition, microstructure, mechanical properties, lead content, tool coating and relative velocity. Regarding the applied tools, the lowest coefficients of friction and process temperatures were detected when using a DLC (ta-C) coating.