• Transactions of the Korean Society of Mechanical Engineers
• /
• v.16 no.2
• /
• pp.207-225
• /
• 1992

The study is concerned with the thermo-viscoplastic finite element analysis of axisymmetric forward hot extrusion through square dies. The problem is treated as a nonsteady state problem because the distribution of temperature and material properties are continuously changing with the punch travel. In square die extrusion, difficulties arise from the severe distortion and die interference of elements at the aperture rim of the die even with a small punch travel. And finite element computation is impossible without intermittent remeshing. Accordingly, an automatic remeshing technique is proposed by employing specially designed mesh structure near the aperture rim. The analysis of temperature distribution includes heat conduction through material interfaces, heat convection and radiation to the atmosphere and is carried out by decoupling the heat analysis from the analysis of the deformation. The extrusion load and the distributions of strain rate and temperature are computed for the given cases rendering reasonable results. Computed grid distortions are found to be in good agreement with the experimental results. It has been thus shown that the proposed method of analysis can be effectively applied to the axisymmetric hot extrusion through square dies.

• Proceedings of the Korean Society for Technology of Plasticity Conference
• /
• 2003.10a
• /
• pp.159-162
• /
• 2003

The remeshing algorithm using the constrained Delaunay method adapted to the mesh density map is developed. In the finite element simulation of forging process, the numerical error increases as the process goes on. However, it is not desirable to use a uniformly fine mesh in the whole domain. Therefore, it is necessary to reduce the analysis error by constructing locally fine mesh at the region where the error is concentrated such as die corner. In this paper, the point insertion algorithm is used and mesh size is controlled by using a mesh density map constructed with a posteriori error estimation. And an optimized smoothing technique is adapted to have smooth distribution and improve the quality of the mesh.

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

• Transactions of Materials Processing
• /
• v.28 no.3
• /
• pp.115-122
• /
• 2019

In this paper, finite element analysis of an automatic five-stage precision cold forging process of a yoke, a steering part of a passenger's car, is conducted with emphasis on spring back analysis at the yoke-forming stage and its experimental verification is subsequently made. An elastoplastic finite element method with MINI-element technique employed for the analysis of the entire process is explained. There is emphasis that the thin film of material formed between the punch and die in the stage may result to some errors especially in elastoplastic finite element analysis of spring back due to frequent remeshing. The numerical robustness of the spring back analysis in regards to remeshing is hence shown first through investigation into its effect on the predicted spring back. Experimental measurement of displacement due to spring back is carried out for comparison with the predicted results, and they are in a qualitative agreement with each other.

• Transactions of Materials Processing
• /
• v.4 no.3
• /
• pp.204-213
• /
• 1995

A finite element program is developed to analyze the flow phenomena in SMC compression molding as a viscoplastic model. The calculation of temperature distribution is also carried out by uncoupling the thermal analysis from the flow analysis. SMC molding processes with a flat plate substructure and the one with a T-shaped rib are considered in numerical simulation. The numerical results provide deformed shapes, temperature distribution in a SMC charge, and the forming load. The simulation of compression molding of a flat plate with a T-shaped rib requires a remeshing technique for the whole process.

• International Journal of Naval Architecture and Ocean Engineering
• /
• v.4 no.3
• /
• pp.228-240
• /
• 2012

Morphing is a geometric interpolation technique that is often used by the animation industry to transform one form into another seemingly seamlessly. It does this by producing a large number of 'intermediate' forms between the two 'extreme' or 'parent' forms. It has already been shown that morphing technique can be a powerful tool for form design and as such can be a useful addition to the armoury of product designers. Morphing procedure itself is simple and consists of straightforward linear interpolation. However, establishing the correspondence between vertices of the parent models is one of the most difficult and important tasks during a morphing process. This paper discusses the mesh-merging method employed for this process as against the already established mesh-regularising method. It has been found that the merging method minimises the need for manual manipulation, allowing automation to a large extent.

• The Journal of the Korea Contents Association
• /
• v.9 no.5
• /
• pp.76-83
• /
• 2009

This paper presents a compression method for animated meshes or mesh sequences which have a shared connectivity and geometry streams. Our approach is based on static semi-regular mesh compression algorithm introduced by Khodakovky et al. Our encoding algorithm consists of two stages. First, the proposed technique creates a semi-regular mesh sequence from an input irregular mesh sequence. For semi-regular remeshing of irregular mesh sequences, this paper adapts the MAPS algorithm. However, MAPS cannot directly be performed to the input irregular mesh sequence. Thus, the proposed remesh algorithm revises the MAPS remesher using the clustering information, which classify coherent parts during the animation. The second stage uses wavelet transformation and clustering information to compress geometries of mesh sequences efficiently. The proposed compression algorithm predicts the vertex trajectories using the clustering information and the cluster transformation during the animation and compress the difference other frames from the reference frame in order to reduce the range of 3D position values.

• Proceedings of the Computational Structural Engineering Institute Conference
• /
• 2004.04a
• /
• pp.341-348
• /
• 2004

This paper presents a modeling technique of cracks by combined extended and superposed finite element method (XSFEM) which is a combination of the extended finite element method (XFEM) and the mesh superposition method (sversion FEM). In the proposed method, the near-tip field is modeled by a superimposed patch consisting of quarter point elements and the rest of the discontinuity is treated by the XFEM. The actual crack opening in this method is measured by the sum of the crack openings of XFEM and SFEM in transition region. This method retains the strong point of the XFEM so it can avoid remeshing in crack evolution and trace the crack growth by translation or rotation of the overlaid mesh and the update of the nodes to be enriched by step functions. Moreover, the quadrature of the Galerkin weak form becomes simpler. Numerical experiments are provided to demonstrate the effectiveness and robustness of the proposed method.

• Structural Engineering and Mechanics
• /
• v.2 no.2
• /
• pp.173-184
• /
• 1994

The objective of this study was to develop a simple and efficient numerical modeling technique for dynamic crack propagation using the finite element method. The study focused on the analysis of a rapidly propagation crack in an elastic body. As already known, discrete crack tip advance with the stationary node procedure results in spurious oscillation in the calculated energy terms. To reduce the spurious oscillation, a simple and efficient moving node procedure is proposed. The procedure does require neither remeshing the discretization nor distorting the original mesh. Two different central difference schemes are also evaluated and compared for dynamic crack propagation problem.

• Transactions of the Korean Society of Mechanical Engineers
• /
• v.13 no.6
• /
• pp.1070-1081
• /
• 1989

본 논문의 목적은 일반적인 곡면을 갖는 냉간단조 공정을 컴퓨터 시뮬레이션 을 통해 해석하고자 강소성 유한요소법의 프로그램을 개발하고, 이를 축대칭 및 평면 변형 단조성형에 적용하고자 한다. 축대칭 문제로는 산업적으로 이용이 많은 치차 블랭크(gear blank) 형태의 예제를 선택하였고 평면변형으 경우 정밀 단조품의 하나인 터어빈 블레이드(turbine blade)를 평면변형 문제로 보아 해석하였다. 한편 심한 변형을 하는 후방압출과 같은 문제의 수렴성을 향상시키고 공정을 계속적으로 해석하 기 위하여 격자 재구성기법을 도입함으로서 냉간단조 문제의 일반적인 해석을 하도록 한다.