| Scope and methodology of study. Hardened AISI 4340 steel is one of the difficult-to-machine materials. As the cutting speed increases, the chip morphology changes from discontinuous chip, to continuous chip, to shear-localized chip. At speeds above this, the shear-localized chips continue to form except that instead of continuous series of segments in the chips, the segments get isolated. As the hardness of the workmaterial increases, these transitions occur at much lower speeds. To understand the mechanism of chip formation in high-speed machining of AISI 4340 steel, finite element analysis is used. It is a Lagrangian explicit finite element code available commercially (AdvantEdge(TM)). To overcome the problems associated with extensive element distortion, adaptive meshing and remeshing are used. Johnson-Cook's material model that is capable of giving flow stresses at various strains, strain rates, and temperature is used along with Recht's catastrophic shear failure criterion. A user-subroutine (UMAT) is developed to incorporate Johnson-Cook's material model and Recht's catastrophic shear failure criterion in the finite element code. Effects of workmaterial hardness, cutting speed, tool rake angle, and contact length on the chip morphology, temperature, strains, forces, and power are investigated. (Abstract shortened by UMI.)... |
