Modeling of cutting forces in near dry machining under tool wear effect

Abstract

A predictive model for the cutting forces in near dry machining, in which only a small amount of cutting fluid is used, is developed based on considerations of both the lubricating effect and the cooling effect. For the lubricating effect, with the material properties, lubricating parameters, and cutting conditions, the friction coefficient in near dry machining is calculated based on the boundary lubrication model for use in a modified Oxley's approach to determine the cutting forces. For the cooling effect in near dry machining, a moving heat source method is pursued to quantify the primary-zone shear deformation heating, the secondary-zone friction heating, and flank face air–oil mixture cooling. These two effects are considered collectively to estimate cutting forces under the condition of sharp tools. The predicted variables of flow stress, contact length, and shear angle obtained from the model are used to predict the cutting forces due to the tool flank wear effect based on Waldorf's model. Comparisons are made between predicted and experimental cutting forces for sharp tools and worn tools in the cutting of AISI 1045 with uncoated carbide tools. The results show that the proposed model provides average prediction errors of 14% in the tangential cutting force direction, 21% in the axial directions, and 30% in the radial directions within the experimental test condition range (cutting speeds of 45.75–137.25 m/min, feeds 0.0508–0.1016 mm/rev, and depth of cuts 0.508–1.016 mm). It is also found that the cutting forces in near dry machining are generally lower than those under dry machining condition. Under cutting speeds of 91.5 and 137.25 m/min, the deviations of the predicted forces between near dry machining and dry machining range from 5% to 39% for axial cutting forces, 3% to 36% for radial cutting forces, and 1% to 32% for tangential cutting forces. It suggests that the lubricating mechanism has a stronger effect on cutting forces than the cooling mechanism when cutting AISI 1045 with uncoated carbide tools.