• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2000.04a
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• pp.40-43
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• 2000

A process optimal design methodology applicable to steady-state forming with a strain-hardening material is presented. in this approach the optimal design problem is formulated on the basis of a rigid-viscoplastic finite element process model and a derivative based approach is adopted as an optimization technique The process model the schemes for the evaluation of the design sensitivity considering the effect of strain-hardening and an iterative procedure for design optimization are described. the validity of the proposed approach is demonstrated through application to die shape optimal design in extrusion.

• Transactions of the Korean Society of Mechanical Engineers
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• v.16 no.3
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• pp.443-452
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• 1992

본 연구에서는 소성가공 공정의 최적설계를 위한 새로운 접근 방법이 소개 된다.이방법은 소성가공 공정의 유한요소해석 기술과 기계시스템의 최적설계 기술 에 바탕을 두고 있다. 벌칙 강소성유한요소법, 정상 상태의 소성가공 공정(steady -state metal forming process)을 위한 최적설계 문제의 수식화, 설계민감도의 해석 방법, 설계민감도의 정확성에 관한 고찰, 구배투영법(gradient projection emthod)등 이 본 논문에서 상세하게 소개된다.

• Journal of the Korean Society for Precision Engineering
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• v.2 no.2
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• pp.31-42
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• 1985

The metal flow and the strain distribution is investigated for the steady state and non-steady state bulk deformation processes by using an improved visioplasticity method which includes the effective smoothing scheme. The comparison of various smoothing schemes leads to the selection of the five- point least square smoothing method which is employed to reduce the measurement errors. As a steady state forming process experiments are carried out for axisy- mmetric forward extrusion through conical and curved dies of various area reduc- tions using Aluminum and steel billets. Axisymmetric backward extrusion is chosen for a nonsteady state forming process. In axisymmetric forward extrusion the results from visioplasticity show that the curved die of a fourth-order polynomial renders more uniform distribution of strain rates and strains. Higher reduction leads to greater strain rates at the outer side of the billet. The visioplastic observation for axisymmetric backward extrusion as a non-steady state deformation process shows the concentration of higher strain at the inner wall of the extruded product. The visioplastic results in forward extrusion are in agreement with the computed results by the finite element method. It is thus shown that the visio- plasticity combined with a smoothing technique is an effective method to determine the pattern and the distribution of strain rates and strains.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 1997.03a
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• pp.113-118
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• 1997

A new approach to process optimal design in non-isothermal, non-steady state metal forming is presented. In this approach, the optimal design problem is formulated on the basis of the integrated thermo-mechanical finite element process model so as to cover a wide range of the objective functions and design variables, and the derivative based approach is adopted for conducting optimization by design iteration. The process model, the formulation for process optimal design, and the procedures for the evaluation of the design sensitivity and for design iteration for optimization are described.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 1994.03a
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• pp.37-46
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• 1994

In metal forming, there ar problems with recurrent geometric characteristics and without explicitly prescribed boundary conditions. In such problems, so-called recurrent boundary conditions must be introduced. The present study deals with nonsteady-state three-dimensional finite element analysis for extrusion of a trocoidal helical gear through a curved die. The boundary-directed remeshing scheme based on the modular remeshing technique is developed to reduce the errors arising in fitting old and new mesh systems. The computed extrusion pressure in reaching the near steady-state loading stage is compared with the results of the experiment and the steady-state analysis. The three-dimensional deformed pattern involving warping at the extruded end due to torsional deformation mode is demonstrated.

• Proceedings of the KSME Conference
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• 2000.04b
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• pp.252-257
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• 2000

An efficient method is developed for mold thermal cycle analysis in repeated forming process, which is well suited to the analysis in TV glass production. plunger, which is a mold to press-form the glass, undergoes temperature fluctuation during a cycle due to the repeated contact and separation from the glass, which attains a cyclic steady state in the end. If analyzed straightforwardly of this problem, it leads to more than 80 cycles to get reasonable solution, and it is yet hard to setup stopping creteria due to extremely slow convergence. An exponential fitting method is proposed to solve the problem, where an exponential function is found to best approximate temperature values of 3 consecutive cycles, and new cycle is restarted with the function value at infinite time. From numerical implementation, it is found that the method reduces the number of cycles dramatically to only $6{\sim}15$ cycles to reach accurate solution within $1^{\circ}$ error. A system for the analysis is contructed, in which the thermal analysis is performed by commercial software ANSYS, and the fitting of the result is done by IMSL library.

• Transactions of Materials Processing
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• v.5 no.4
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• pp.297-304
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• 1996

A process model is formulated considering the effect of crystallographic texture developed in forming process. The deformation induced plastic anisotropy can be predicted by capturing the evolution of texture during large deformation in the polycrystalline aggregate. The anisotropic stiffness matrix for the aggregate is derived and implemented in Eulerian finite element code using a Consistent Penalty method. As an application the evolution of texture in rolling drawing and extrusion processes are simulated. The numerical results show good agreements with report-ed experimental textures.

• Transactions of the Korean Society of Mechanical Engineers
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• v.16 no.3
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• pp.453-458
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• 1992

본 연구에서는 유한요소법에 바탕을 둔 최적공정설계법을 이용하여 압출 금형 형상의 최적설계를 실시하였다.설계의 결과를 참고문헌에서 발췌한 이론해와 비교 하였으며, 축대칭 압출공정에서 압하율, 마찰, 재료특성 등이 금형의 최적형상에 미치 는 영향에 대하여 조사하였다.

• Journal of the Korean Society for Precision Engineering
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• v.21 no.7
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• pp.53-61
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• 2004

Condenser tube which is used for a cooling system of automobiles is mainly manufactured by conform extrusion. However, direct extrusion using porthole die in comparison with conform extrusion has many advantages such as improvement of productivity, reduction of production cost etc. In general, the porthole die extrusion process is useful for manufacturing long tubes with hollow sections and consists of three stages(dividing, welding and forming stages). Especially, Porthole die for producing condenser tube is very complex. Thus, in order to obtain the detailed mechanics, to assist in the design of proper die shapes and sizes, and to improve the quality of products, porthole die extrusion should be analyzed in as non-steady state as possible. This paper describes FE analysis of non-steady state porthole die extrusion for producing condenser tube with multi-hole through 3D simulation in the non-steady state during the entire process to evaluate detailed metal flow, temperature distribution, welding pressure and extrusion load. Also to validate FE simulation of porthole die extrusion, a comparison of simulation and experiment results was presented in this paper.

• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
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• 2010.10a
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• pp.295-298
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• 2010

To find out moving and dissipation patterns of laid floating object estuary this paper has focused on forming, changing and variation of the wind forced river plume. In steady state(without external force), river can be form a bulge and downcoast alongshore current on gently sloped continental shelf. Under the downwelling wind and downcoast meanflow those river plume's patterns are similar with the steady state case except enhancement of downcoast transportation. Under the upwelling wind condition bulge linearly move to the northwest with 45 angle due to Ekman transport. It's moving speed are linear with the strength of the wind stress but moving paths are independent of that. So, in this case, floating object will be dissipate to outside as move to the upcoast.