Elastic-plastic finite element analysis for oblique cutting with a discontinuous chip of 6-4 brass

Abstract

If the workpiece material experiences tremendous strain during the chip formation process or brittle material undergoes fracture in the primary deformation zone when the chip is only partly formed, the segmented chip formed under the above conditions is called a discontinuous chip. With the introduction of the tool inclination angle geometry, an elastic-plastic finite element model is developed for oblique cutting of discontinuous chip. The tool is P20 while the workpiece is made of 6-4 brass. The initial crack location, the direction of crack growth and variations of discrete chips are examined under the condition of a low cutting speed. These predictions are made possible by application of the strain energy density theory. The initial crack was formed in the (dW/dV)^max_min region (i.e. the maximum region among many of the strain energy density minima) of the chip surface and grew progressively along the stationary values of the strain energy density function. The direction of crack growth was based on the maximum strain energy density curve along the surface. The fracture process on the other chip layers was identical with that on the chip surface and occurred in sequence until it reached the chip free surface. The plastic deformation and friction result in a high equivalent stress on the chip surface above the tool tip, especially at the place of crack formation. As more residual stress is present after cutting, degradation of the workpiece prevails and should be accounted for.