Machining of Hard Materials

Summary This paper deals with the machining of ferrous materials in their hardened condition (hardness: 50 to 70 Rc). Work materials considered include high-speed tool steels, die steels, bearing steels, alloy steels, case-hardened steels, white cast iron, and alloy cast iron. Prerequisites for the successful machining of hardened ferrous alloys include: • Use of an extremely rigid, high-precision machine tool system with adequate power and proper sensors and control for monitoring the cutting process • Very hard(> HV 1800) and tough (KIC > 6 MP m1/2) tool material • Negative rake (≥−10°) tool geometry with a high wedge angle (> 90°), strong shape (e.g., round), and in some cases appropriate chamfer or radius, honed at the cutting edge • Tool holders with high stiffness • Appropriate cutting conditions Submicron-grain cemented carbide with a low binder content (≅3%) can be used to machine ferrous alloys of hardness up to ≈Rc 58, ceramic tools for up to ≈Rc63, and cubic boron nitride tools up to ≈Rc70. In many applications, the machining of ferrous materials in their hardened condition can replace grinding to give significant savings in cost and increase in productivity. Fewer machine tools and fewer processing operations are needed as a result. Machining steels in their hardened condition is thus both techologically and economically feasible.