This study focuses on addressing the severe plastic deformation (SPD) behavior and the effects o f machining parameters on microstructure alternations in machined surface cre ated from high-speed machining. A finite element (FE) model is proposed to predict the orthogonal machining of A16061-T6 alloys at high speeds. By extracting strains, strain rates, stresses, and temperatures from this model, a dislocation density-based model is incorporated into it as a user-defined subroutine to predict dislocation densities and grain sizes in machined surface. The predicted results show that dislocation densities decrease with the depths below the machined surface, but grain sizes present an opposite tendency. Higher cutting speeds are associated with thinner plastic deformation layers. Dislocation densities decrease with cutting speeds, but grain sizes increase with cutting speeds in machined surface. Dislocation densities decrease initially and then increase with feed rates. There exists a critical feed rate to generate the maximum SPD layer in machined surface. Tool rake angle has a great impact on the depth o f plastic deformation layer. Thus, it affects the distributions of dislocation densities and grain sizes. A large negative rake angle can induce an increased dislocation density in machined surface. The predicted chip thicknesses, cutting forces, distributions of dislocation densities, and grain sizes within the range of machining parameters have good agreement with experi ments in terms of chip morphology, cutting forces, microstructure, and microhardness in chip and machined surface.

A new method called submersed gas-jetting EDM was proposed, in which the high-pressure gas working as the dielectric medium, is blown throughout the inner hole of a tubular electrode, and machining liquid around the gas plays significant roles of helping cooling and debris evacuation but doesn’t involve in the discharge directly. Experiments were conducted to investigate the influence of polarity, pulse duration, peak current, gas pressure and different gas/machining liquid combination. The comparison of submersed gas-jetting EDM and dry EDM indicated that this new method revealed higher material removal rate (MRR), better surface quality and equivalently minute electrode wear.

Machining process usually induces Severe Plastic Deformation (SPD) in the chip and machined surface, which will further lead to rapid increase of dislocation density and alteration of grain size in micro-scale. This paper presents a novel FE model to simulate the dislocation density and grain size evolution in the machined surface and subsurface generated from the orthogonal cutting process of Al6061-T6. A dislocation density model of microstructure evolution is implemented in the FE model as a user-defined subroutine written in FORTRAN. The model can predict the microstructure characteristic in a machined surface. The predicted chip thicknesses, cutting forces, distributions of dislocation density and grain size are verified by the experimental tests of the chip, forces, microstructure and micro-hardness. The predicted results show that the dislocation density decreases along the depths of machined surface; whereas the grain size shows an opposite tendency. Dislocation density in machined surface decreases and grain size increases when cutting speed increases. Higher cutting speeds are associated with thinner deformation layers. Dislocation density in a machined surface decreases initially and then increases with feed rates. Dislocation density increases significantly when cutting tool has a larger negative rake angle. The bigger negative rake angles further lead to the thicker deformation layers in machined surface.