Metal cutting and plasticity theory

Abstract

A fundamental approach to the mechanics of metal cutting inevitably necessitates correlating the data obtained from cutting with plasticity theory. To make this correlation it is necessary to determine the geometric configuration of the deformed zone and to obtain the material flow behaviour at the large strain and high strain rates encountered in cutting. To date a satisfactory correlation has not been obtained as it has not been possible to reproduce the conditions of cutting in any other mechanical test. A fresh experimental approach to the problem was attempted by carrying out cutting tests at an extremely low temperature (−196 °C) in order to minimize the effects of the strain rate and the shear zone temperature. This has enabled the cutting data to be correlated with the stress-strain curve obtained at the same low temperature by means of a conventional low strain rate compression test. Comparative tests were carried out at room temperature and at an intermediate temperature (−76 °C). The tool-chip interface conditions were maintained invariant by using a geometrically controlled tool-chip contact length and dry cutting. The experimental results confirmed that the effect of strain rate is frozen at low temperatures so that the cutting data obtained at these temperatures could be satisfactorily correlated with the results of a low strain rate compression test. Under the large strains and high strain rates reached in cutting, the material behaves as a perfectly plastic solid.