Some Observations on the Shearing Process in Metal Cutting

Abstract

It was found that shearing forces on the shear plane were linear functions of the area on which they acted. This was observed for all materials investigated; for SAE 1112 steel, 2024-T4, and 6061-T6 aluminum alloys, and alpha-brass, and also is in agreement with data taken from the literature. Furthermore, all data examined showed that the straight line of shear force Fs versus area As intercepted the ordinate at a positive force value. This was interpreted to mean that the intercept part of the shearing force was used up in overcoming workpiece deformation or friction at the flank of the tool and was not available for chip deformation. Accepting this concept, it can then be shown that the average shearing stress on the shear plane for SAE 1112 is constant and is independent of normal stress, cutting speed, or strain rate, extent of deformation or finite strain, and extent of prior deformation. The shearing stresses for the other materials tested or examined were also constant for the limited range of variables available. In contrast to the shearing stress, the normal stress on the shear plane was not constant and appears to be a yet unknown function of the mechanism of friction on the tool face. The shearing stresses calculated from the metal-cutting data showed good correlation with flow stresses at the same finite strains which were obtained from static compression tests. The reason for the uniqueness of the finite strains at which correlation is achieved is not as yet clear.

Severe Plastic Deformation by Machining Characterized by Finite Element Simulation

“…Similar conclusions have been arrived at in prior studies using quick-stop and related observations. [12,13] Furthermore, the PIV analysis has shown that the cumulative strain imposed in the chip varies for different materials at the same tool rake angle. These observations highlight the need for modeling of the chip formation process to relate machining parameters (e.g., rake angle, velocity, and friction) to deformation parameters (e.g., strain, strain rate, and temperature) ( Figure 1).…”

“…[11][12][13] Although the chip length increases proportional to the length of cut, the deformed chip thickness, precut (undeformed) thickness, and cutting velocity all remain constant after deformation has reached steady state. Therefore the deformation zone should maintain a constant size and shape after a certain amount of incipient deformation.…”

“…[10,11] Chip formation occurs by concentrated shear within a narrow deformation zone often idealized as a ''shear plane.'' [11][12][13] Grain refinement occurs as a direct consequence of the large shear strains imposed within this zone. [8,9] In the shear plane model of machining, the resultant deformation is uniquely determined by the tool rake angle (a) and shear plane angle (/); in fact, this model is an upper bound model for machining.…”

Large strain deformation field in machining

“…[5] Chip formation occurs by concentrated shear within a narrow, primary deformation zone often idealized as the ''shear plane.'' [5,6,7] The microstructure changes associated with the formation of UFG chips have been attributed to the large shear strains imposed within this deformation zone. [8] In the shear plane model of plane-strain machining, the deformation field is uniquely determined by the tool rake angle (a) and the shear angle (f).…”

“…In practice, the primary deformation zone is not a plane but a fan-shaped zone of finite width and thickness, [6,7] and the shear strain within this zone may or may not be uniform over its volume. While the deformation field in this zone has been the subject of intensive numerical study using theoretical or computational analysis, [10,11,12] there have been few experimental determinations of the strain distribution in and around this zone.…”