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Ale simulation of chip formation in orthogonal metal cutting process Movahhedy, Mohammad R.

Abstract

This thesis deals with the application of the Arbitrary Lagrangian-Eulerian (ALE) finite element analysis in simulation of chip formation in orthogonal metal cutting process. A critical review of the literature in this field shows that due to the very complex set of conditions present in a cutting process, the application of conventional Lagrangian and Eulerian methods for this problem is inefficient and entails numerical difficulties. In particular, the pertinent problems in the node separation technique or the remeshing approach are discussed. In contrast, the adaptivity of the mesh in an ALE analysis provides the possibility of combining the strengths of both Lagrangian and Eulerian methods in a single analysis. In this approach, the chip formation occurs as a result of plastic flow of the work material around the tool edge on the one hand, and unconstrained flow of the material on free surfaces of the chip, on the other. Due to high deformation speed, strain rate and temperature play a significant role in the chip formation process. In this work, the ALE formulation originally proposed by Wang and Gadala [72] is extended to include rate and thermal effects. A heat transfer module is included that updates the temperature field in the cutting zone at each step of the analysis. Contact algorithms are developed which are able to detect emerging contact conditions and apply contact constraints at interfaces between flexible-flexible or rigid-flexible pairs. An efficient ALE mesh motion is designed that prevents element distortion in the deformation zone and at the same time facilitates the evolution of the chip size at free boundaries. Furthermore, General guidelines for designing a mesh motion strategy are presented, an algorithm for mesh sliding on free boundaries is introduced, and transfinite and isoparametric mapping techniques are adopted for moving the mesh in the interior of the body, so that the mesh remains optimal throughout the analysis The large deformation, rate-dependent, thermo-mechanical ALE finite element code is used to simulate chip formation in orthogonal metal cutting processes. The results of simulation of cutting low carbon steel with a carbide tool are presented as a benchmark problem, and a parametric study is conducted to investigate the influence of cutting conditions on the chip formation process. The results of these studies are verified through comparison with available experimental data. The fairly good qualitative and quantitative agreement between predicted and experimental results confirms that ALE simulation provides a realistic representation of the actual process. Finally, the influence of cutting edge geometry on the chip formation process is investigated through simulation of high speed cutting of hardened steel alloys with chamfered or worn tools of carbide or CBN type. This study shows that changing the chamfer angle does not affect the chip significantly, because the dead metal zone that is formed under the chamfer acts as the main cutting edge of the tool. However, cutting and thrust forces increase with increase in the chamfer angle. The predictions on the effects of chamfer angle are in agreement with experimental observations. A study of the influence of cutting speed on the deformation process for chamfered CBN tools shows that at higher cutting speeds, the maximum temperature on the rake face increases substantially, signifying the importance of diffusion wear at such speeds.

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