Elliptical Vibration Assisted Machining with Single Crystal Diamond Tools

Abstract

Optical quality surfaces on non-ferrous materials are commonly produced with single crystal diamond tools and precision turning machines. To add ferrous and brittle materials to the list of diamond turnable materials, a process know as elliptical vibration assisted machining (EVAM) has been developed. EVAM combines a small, less than 50 &#181m size, oscillatory tool path to the linear motion of standard orthogonal cutting. EVAM reduces cutting forces and tool wear by reducing chip thickness and bringing the tool tip out of contact with the workpiece 75% of the time. These characteristics may increase tool life and work piece material compatibility with single crystal diamond tools. A non-resonant piezo electric stack driven tool actuator was designed and built for a large range of operating frequencies (0-5KHz) and tool path dimensional flexibility (ellipse motion up to 50 x 9 µm). The diamond tool is mounted to a kinematic linkage. Finite element analysis (FEA) was used to aid the design of a light weight, high stiffness tool holder/kinematic linkage for high frequency operation. The effects of heat generation caused by high voltage, high frequency operation of piezo stacks were simulated using FEA and finite difference programs. These simulations were used to design and develop an efficient active cooling system. Tool path geometry and its effects on sliding distance, chip geometry, and surface finish were modeled with Maple software. Calculated chip geometry was successfully used to predict cutting and thrust forces. Force predictions were compared with measured forces for 6061 aluminum. A method generated for precision contour grinding was implemented to accurately predict theoretical surface roughness for EVAM machined surfaces. EVAM machining tests with brittle workpiece materials, such as silicon carbide, produced optical quality surfaces.