Principles for determining the deformed state of the surface layer and precision of machine parts in cutting

Abstract

645 The existing theory of cutting and the specification of the cutting conditions corresponding to the required surfacelayer properties and precision rely on experimental data and mathematical models obtained by regression analysis. Consequently, the results can� not be extrapolated to an expanded range of cutting parameters. Accordingly, there is a need for additional experiments to improve the existing mathematical models, especially as the shaping kinematics become ever more complex in the machining of metals. In modern equipment, shaping is undertaken by multi� coordinate machine tools equipped with a cutting tool of complex geometry, with sharp increase in the fluc� tuation of the margin and corresponding decrease in precision of the calculations. Physically, the operational properties in the surface layer depend on two basic factors: (1) cold working by residual compressive stress, with increase in wear resis� tance of the surface layer as machining continues; (2) heating of the surface layer as a result of plastic deformation, with partial tempering of the surface layer and the formation of tensile stress. As yet, there has been no reliable analytical calculation of the resid� ual compressive stress, and hence reliable prediction of the time required for runningin of the surfaces is impossible. Such analytical solutions would permit sharp reduction in the time for runningin of the sur� faces and thereby extend the period of steady wear. They would also significantly reduce the costs of pre� paring plant standards and permit improvement in the