Influence of Tool Coating, Tool Material, and Cutting Speed on the Machinability of Low-Leaded Brass Alloys in Turning

Abstract

The influence of tool coating and material on the machinability of low-leaded brass alloys (Pb < 0.2%) was analyzed in external turning. Carbide tools with various coatings as well as polycrystalline diamond (PCD) tools were applied. As workpiece materials, three low-leaded brass alloys CuZn38As, CuZn42, and CuZn21Si3P were used. Their machining behavior was compared to the leaded (Pb < 3.32%) brass CuZn39Pb3. CuZn38As showed the worst machinability in terms of process forces, chip formation, and workpiece quality. This is due to the high volume fraction of α-phase with face-centered cubic lattice structure. The machining problems were reduced by the use of tool coatings, in particular by a diamond-like carbon coating. The latter is characterized by high hardness, diamond-like cubic-crystalline lattice structure, and low chemical affinity to brass, which reduced friction in the secondary shear zone. CuZn42 exhibited an improved machinability compared to CuZn38As due to the lower volume fraction of α-phase. The positive influence of the tool coating was similar to CuZn38As. Main machining problem of CuZn21Si3P is tool wear because of the hard silicon-rich κ-phase. In tool life tests, PCD showed higher performance than uncoated and coated carbide tools due to its high abrasive wear resistance and low adhesion tendency.