Wyniki wyszukiwania - Biblioteka Nauki

1

Finite element investigations of friction condition in equal channel angular extrusion

100%

Son I. H. , Jin Y. G. , Im Y. T.

Journal of Achievements in Materials and Manufacturing Engineering

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2006

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tom Vol. 17, nr 1-2

285--288

EN

Purpose: This study concentrates on the investigation of contact phenomenon at the interface between dies and the workpiece in terms of material flow and forming load requirement. Design/methodology/approach: The numerical simulations of an equal channel angular extrusion (ECAE) with a CP-Ti Gr-1 cylindrical specimen were carried out by applying the mixed finite element formulation with tetrahedral elements under the non-isothermal condition. Compression test was used for determination of the material data. The change of contact conditions during remeshing was also investigated in terms of variation of load requirements and volume losses after remeshing. In order to validate the numerical algorithm proposed, simulation results were compared with the experimental data. Findings: It was found that the forming load simulated was very sensitive to the contact condition of the workpiece with the channel. The current investigation clearly showed the importance of proper handling of boundary conditions to improve the solution accuracy. Research limitations/implications: Further applications of the proposed scheme are required. Practical implications: The new numerical scheme will be beneficial in better understanding the deformation mechanics of the ECAE. Originality/value: New contact algorithm to solve ECAE was developed to reduce the volume loss and load requirement after remeshing.

2

Application of element deletion method for numerical analyses of cracking

100%

Lee H. C. , Choi J. S. , Jung K. H. , Im Y. T.

Journal of Achievements in Materials and Manufacturing Engineering

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2009

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tom Vol. 35, nr 2

154-161

EN

Purpose: To develop a numerical algorithm to simulate cracking and its evolution for machining, shearing and multi-pass hot bar rolling processes. Design/methodology/approach: Element deletion method was adopted for developing a numerical algorithm and implemented to a rigid-viscoplastic finite element program. Cockcroft-Latham and specific plastic work criteria were incorporated in the present investigation for simulating cracking and shearing processes. An instability condition for the tension was assumed to be valid to determine a critical damage factor for initiation of possible cracking. Findings: The developed element deletion algorithm was simple to be applied for simulating cracking and shearing patterns for the processes applied. Cockcroft-Latham and specific plastic work fracture criteria were reasonable in predicting the internal and external crack, respectively. Research limitations/implications: The research finding can be utilized for investigating occurrence of external and internal cracking involved with metal forming processes such as Chevron cracking in extrusion. Practical implications: By expanding the current approach to determine a processing map for extrusion the processing condition to prevent Chevron cracking can be determined easily and utilized in industry. Also, the current investigation can be easily expanded to other process design and control. Originality/value: Numerical algorithm based on the element deletion method was developed and implemented to the existing finite element program to examine the processes including cracking phenomenon. The applicability to utilize a critical damage factor for the fracture criteria based on the instability was evaluated.

3

Research activities of computer-aided materials processing laboratory

75%

Im Y. T. , Lee H. W. , Lee H. C. , Awais M. , Jin Y. G. , Jung K. H. , Jung K. H.

Journal of Achievements in Materials and Manufacturing Engineering

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2007

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tom Vol. 24, nr 1

219-229

EN

Purpose: of this paper is to review the research works carried out at the national research laboratory for computer-aided materials processing at the department of mechanical engineering at KAIST. Design/methodology/approach: The research papers published so far from the laboratory were carefully reviewed and highlights for developing simulation tools for mesh generation, 2D or 3D finite element analyses for forging, shape rolling, solidification, semi-solid forging, compression molding of thermoset composites, injection molding without or with short fibers, and expert system for multi-stage axi-symmetric cold forging, extrusion, and multi-pass shape rolling are recaptured. Findings: According to this survey, the important issues involved with program developments and their industrial applications were revisited. Research limitations/implications: Understanding of material behaviour at various processing conditions and characterization of proper boundary conditions in terms of friction and temperature should be carefully made. Handling of complex geometry and computational efficiency for such geometry should be improved as well. Further development of three dimensional design systems should be necessary. Practical implications: Proper usage of the simulation tools and interface such tools with the automatic design system with the help of artificial intelligence will be very useful at the design stage of new manufacturing products and processes. In addition, proper understanding of deformation mechanics is of importance to properly utilize such numerical tools. Originality/value: Various aspects of limitations involved with program developments and their usage are identified and some important industrial applications demonstrated.

4

Sustainability issues of research and development of forging

63%

Im Y. T. , Hwang S. K. , Kim D. K. , Baek H. M. , Park W. Y. , Lee J. W. , Joo H. S. , Kim J. M.

Journal of Achievements in Materials and Manufacturing Engineering

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2012

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tom Vol. 54, nr 2

147--158

EN

Purpose: of this paper is to review recent research activities of the Computer Aided Materials Processing Laboratory to improve sustainability of the material and manufacturing process in forging. Design/methodology/approach: Empirically obtained non-dimensional equation to determine friction factor was introduced by employing tip test results. Equal channel angular processing (ECAP) and hybrid process consisting of pinch rolling, ECAP, and drawing were newly designed to make the process continuous and improve the strength of the material. The numerical program based on cellular automata and crystal plasticity was developed to predict microstructure and texture evolution during recrystallization. Findings: The friction factors at the punch or die interfaces during cold forging can be determined separately as a function of the hardness and surface roughness of the material and punch or dies, initial yield strength of the material, viscosity of the lubricant, and die velocity. Severe plastic deformation was applied in a continuous manner and strength increase of the material was obtained as a result. The microstructure and texture evolution during recrystallization can be predicted numerically by the developed program. Research limitations/implications: The proposed results should be compared with the practical results to further the applicability and solution accuracy. Practical implications: The present approach can be used as an example to tackle the sustainability of the material and manufacturing process. Originality/value: The current approach is practically easy to apply and the simulation tool developed can replace the laborious and expensive experiments.