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A straightforward approach integrating a visco-plastic self-consistent (VPSC) model with a phenomenological dynamic recrystallization (DRX) criterion is proposed for coupling simulation of hot deformation and accompanying DRX. The phenomenological DRX nucleation and growth criteria are embedded into VPSC through a dislocation density based hardening model. The approach is validated and demonstrated by simulating compression of polycrystal copper at various conditions. The key characteristics of DRX during hot deformation of copper, in terms of mechanical response and microstructure evolution, are well reproduced and illustrated with the VPSC-DDRX coupling simulation approach. Furthermore, a series of numerical studies on the hot deformation behaviors corresponding to different loading paths and initial textures are carried out to explore their effects on dynamic recrystallization and further demonstrate the capability of the proposed method. The innovation of current work is establishing a relatively simple crystal plasticity based DRX simulation method that incorporates crystal information, deformation modes and grain population, and realizes integrated computation of deformation, texture and DRX process. [ABSTRACT FROM AUTHOR]

The accuracy of machine tools is significantly affected by the geometric defect and thermal deformation of the mechanical components. This paper intends to provide a comprehensive compensation method for the integrated geometric and thermal errors of machine tools. Firstly, a synthesized volumetric model is established with homogeneous transformation matrix method, considering both the geometric and thermal effects. Then, in order to improve the modeling accuracy and efficiency of the geometric error components, an automatic modeling algorithm is proposed with the Chebyshev polynomial-based orthogonal least squares regression. Also, to improve the robustness of the thermal error models for the feed axes and the spindle system, the thermal effects caused by external ambient variation and internal heat sources are identified and modeled separately. Finally, an intelligent virtual compensation system is developed for machine tools based on the function of external machine original coordinate shift and fast Ethernet data interaction technique, and compensation tests on a vertical machining center showed that the position accuracy of the machine tool could be significantly improved after compensation. [ABSTRACT FROM AUTHOR]

Thermal expansion of ball screw systems affects the machining accuracy of machine tools significantly. This paper intends to provide a comprehensive error compensation method for the time-varying positioning error of machine tools. To confirm the thermal deformation mechanism of ball screw systems, experiments have been designed to study the thermal behaviors of a ball screw system under varying temperature conditions. An exponential algorithm is proposed to predict the temperature variation pattern of the ball screw based on finite element analysis, and the actual thermal boundary conditions of the ball screw system are exactly defined according to the proposed algorithm and the experimental results. Then, a comprehensive compensation model is established based on the decomposition of the initial geometric error and thermal error components. Finally, a real-time error compensation system is developed for machine tools based on the function of external machine original coordinate shift and fast Ethernet data interaction, and satisfactory results have been achieved for the compensation experiments on a machining center. [ABSTRACT FROM AUTHOR]

Microchannel tube (MCT) is widely employed in industry due to its excellent efficiency in heat transfer. An MCT is commonly produced through extrusion within a porthole die, where severe plastic deformation is inevitably involved. Moreover, the plastic deformation, which dramatically affects the final property of the MCT, varies significantly from location to location. In order to understand the development of the microstructure and its effect on the final property of the MCT, the viscoplastic self-consistent (VPSC) model, together with the finite element analysis and the flow line model, is employed in the current study. The flow line model is used to reproduce the local velocity gradient within the complex porthole die, while VPSC model is employed to predict the evolution of the microstructure accordingly. In addition, electron backscatter diffraction (EBSD) measurement and mechanical tests are used to characterize the evolution of the microstructure and the property of the MCT. The simulation results agree well with the corresponding experimental ones. The influence of the material's flow line on the evolution of the orientation and morphology of the grains, and the property of the produced MCT are discussed in detail. [ABSTRACT FROM AUTHOR]