Velocity and Strain Distributions in Two-Dimensional Orthogonal Machining

A study has been made of the primary deformation zone and tool-chip interface in two-dimensional (plane strain) orthogonal machining of commercially pure metals. The use of a high-speed, Charge-Coupled Device (CCD) imaging system in conjunction with an optically transparent, sapphire cutting tool, has enabled characteristics of the deformation field such as velocity, strain, and material flow, to be obtained at high spatial and temporal resolution. The velocity distributions in the primary deformation zone and along the tool rake face have been obtained by applying a Particle Image Velocimetry (PIV) technique to sequences of high-speed images of the chip-tool interface taken through the transparent tool, and of the primary deformation zone recorded from a side of the workpiece. A procedure is presented and demonstrated for determining the strain and strain rate distributions in the primary deformation zone. The measurements have provided data about the variations of strain, strain rate and velocity, in and around the cutting edge and primary deformation zone; confirmed the existence of a region of retarded sliding in the region of intimate contact between tool and chip; and highlighted the occurrence of a region of dead metal ahead of the cutting edge when cutting with a negative rake angle tool. The implications of these results to the use of machining as a controlled test for studying very large strain deformation, and for estimating material properties under extreme conditions of deformation are discussed.