Ultrasonic Detection of Unstable Plastic Flow in Metal Cutting

Abstract

Recently developed metal-cutting tools, made from such materials as ceramics and polycrystalline cubic boron nitride (PCBN), allow turning and milling operations to be applied to heat-treated steels in the hardened (50–65 Rockwell C) state. Understanding the linkage between controllable machining parameters and the associated mechanical phenomena is difficult because of the extreme complexity of the environment of the tool and workpiece. For most reasonable machining conditions, the flow of material is unstable, leading to oscillations in tool-workpiece stresses, local chip velocities, and temperatures. In precision hard turning, with chip dimensions on the order of tens of μm, the oscillation frequencies may approach a few hundred kHz. The goal of this work is to investigate ultrasonic measurement techniques suitable for characterization of material flow during machining, as an aid to understanding the effect of material flow on important process variables and product quality.