Friction in metal machining—Mechanical aspects

Abstract

A review is presented concerning the mechanical aspects of friction at the land and rake faces of a cutting tool when machining under orthogonal conditions. Methods are described for determining the mean frictional and normal forces on these faces and calculating the mean coefficients of friction. Considerable confusion exists concerning the nature of the frictional conditions in the region of the tool land to the point where definitive conclusions cannot be drawn. However, it is suggested that sliding and subsurface plastic deformation may occur simultaneously. When machining under dry, unlubricated conditions regions of sticking friction where the frictional stress is constant and sliding friction where the coefficient of friction is constant can exist simultaneously on the tool rake face. Theories which predict a linear relationship of the form ( φ) = A − B ( β− α) between the angle parameters used to describe the geometry of the cutting process cannot be used to interpret much of the available experimental data. The apparent linear relationships observed in some previous experimental work are thought to be due partly to the method of presentation of the results. It is suggested that a more significant combination of the angle parameters is the difference between the shear angle φ and rake angle a, that is (φ−α). Two parameters which can be used to describe the frictional conditions at the tool rake face are the mean frictional stress and mean normal stress which can vary independently of each other. It is concluded that the mean angle of friction β is insufficient in itself to describe the frictional conditions on the tool rake face. The effects of changes in cutting conditions on the mean coefficient of friction at the tool rake face are examined and the results interpreted in terms of the associated changes in the mean normal and mean frictional stresses in that region. The lubricating action of cutting fluids is discussed briefly.