FEM modeling and simulation of cutting process in single point diamond turning

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FEM modeling and simulation of cutting process in single point diamond turning

 

Author: Wu, Hongyu
Title: FEM modeling and simulation of cutting process in single point diamond turning
Degree: M.Phil.
Year: 2006
Subject: Hong Kong Polytechnic University -- Dissertations.
Diamond cutting -- Mathematical models.
Finite element method.
Department: Dept. of Industrial and Systems Engineering
Pages: xii, 143, [7] leaves : ill. (some col.) ; 30 cm.
Language: English
InnoPac Record: http://library.polyu.edu.hk/record=b1973647
URI: http://theses.lib.polyu.edu.hk/handle/200/1684
Abstract: Ultra-precision machining technology has advanced rapidly and has become one of the most important processes in the manufacture of high-technology products with excellent surface quality. Single point diamond turning (SPDT), which is categorized as an ultra-precision machining technology, is capable of producing components possessing nanometric edge sharpness, form reproducibility, and wear resistance. The process of SPDT has attracted a lot of research interest and many of the works are based on physical cutting experiments, which are very expensive and time-consuming. This study focuses on the development of finite element method (FEM) models for the simulation of the cutting process in SPDT. The FEM models developed can be regarded as the "virtual prototype" of physical cutting and are taking advantage of the current computing power available. Based on the captioned FEM models, a comprehensive parametric study of the SPDT process via a series of FEM simulation experiments has been carried out to explore the effects of various parameters of cutting conditions. The historical reviews of metal cutting have been outlined and compared with the SPDT. In particular, the characteristics of the single point diamond turning are highlighted such as the effects of the cutting tool edge radius and the phenomenon of "size effect." The chip formation in SPDT is based on the 2D orthogonal cutting model (plain strain problem). Essentially the chip formation is a highly nonlinear problem in terms of both geometry and material and it also involves complex contact throughout the cutting process. In the present study, the chip formation in SPDT cutting is modeled and simulated as a quasi-static process. The FEM models are concentrated to handle the large deformation, plasticity material behaviour, contact and friction, mesh distortion problems and cutting tool edge geometrical model taking account of the fact that the cutting tool edge is not perfectly sharp. The FEM models of SPDT are developed by using the commercial FEM software ABAQUS as the computational platform. The finite element formulation is described using an Arbitrary Lagrangian-Eulerian approach, which combines the strength of both Lagrangian and Eulerian formulations. Since the problem is a highly nonlinear quasi-static problem with complex contact problems involved, the explicit procedure is considered more suitable than the implicit method, therefore, is used in solving the FEM equations. The models are built by employing an adaptive meshing approach as well as a pure deformation technique, which addresses the mesh distortion problem due to the large deformation existing in the chip formation process of cutting. In modeling the chip formation, the pure deformation technique employed addresses the deficiency of the conventional FEM model based on chip separation criterion. This method not only eliminates the need for the use of the chip separation criterion and a pre-defined parting line, but also achieves a more realistic and physically based chip formation. Since the tool edge radius has comparable size to the uncut chip thickness in SPDT, the proposed FEM model makes use of a round edge cutting tool model instead of the perfect sharp tool edge model that has been adopted in most previous research work. The proposed FEM models of SPDT are implemented and run for the simulations for workpiece materials, aluminum and copper respectively in ABAQUS platform. The FEM simulations yield the chip formation and distribution of strain/stress field. The morphological features of the chip formation are revealed, which agree well with previous studies. A thermal-coupled FEM cutting model taking account of the adiabatic heating effect has been implemented and executed for calculating the temperature distribution in the vicinity of chip-tool interaction. The current 2D FEM model also has been successfully upgraded to a 3D FEM model. The implementation of the thermal and the 3D models reflects the expandability of the current models. Therefore it makes sense to build further FEM models of SPDT cutting, in addition to the present models. A further parametric study on SPDT has been carried out by performing a series of FEM simulation experiments. The designated numerical simulation experimentation focuses on studying the effects of the depth of cut, rake angle, and friction conditions as well as the tool edge radius during the process of SPDT. The numerical experimental results show that the chip formation morphology, stress/strain fields and forces of interest vary with the variation of those parameters. The results reveal the partial contributions of variation of depth of cut and tool edge radius to the "size effect" in the cutting of SPDT (i.e., they are critical factors accounting for size effect.) The counterpart physical SPDT cutting experiments are usually either very difficult or expensive to perform, (e.g., the different friction conditions and a series of tools with a variety of tool edge radii.) The simulation results show that the present FEM models are successful "virtual prototype" for SPDT, while FEM numerical experimentation has the potential to be an economical substitute for the physical SPDT cutting in the real world. Furthermore, the present FEM models can be a solid foundation for the future development of such models and the simulation of the SPDT cutting process. Some recommendations for future study have been given, which can advance the methodology based on the current FEM models.

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