• 한국정밀공학회지
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• 제13권10호
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• pp.105-111
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• 1996

This paper suggests the scheme to simultaneously accomplish prediction of fracture initiation and geomeytical configuration of deformation in metal forming processes using the artificial neural network. A three-layer neural network is used and a back propagation algorithm is adapted to train the network. The Cookcroft-Lathjam criterion is used to estimate whether fracture occurs during the deformation process. The geometrical configuration and the value of ductile fracture are measured by finite element method. The predictions of neural network and numerical results of simple upsetting are compared. The proposed scheme has successfully predicted the geometrical configuration and fracture initiation.

• 한국정밀공학회지
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• 제12권3호
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• pp.32-41
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• 1995

In the analysis of metal forming processes by the finite element method, there are many numerical instabilities such as element locking, hourglass mode and shear locking. These instabilities may have a bad effect upon accuracy and convergence. The present work is concerned with improvement of stability and efficiency in two-dimensional rigid-plastic finite element method using various type of elemenmts and numerical intergration schemes. As metal forming examples, upsetting and backward extrusion are taken for comparison among the methods: various element types and numerical integration schemes. Comparison is made in terms of stability and efficiency in element behavior and computational efficiency and a new scheme of adaptive directional reduced integration is introduced. As a result, the finite element computation has been stabilized from the viewpoint of computational time, convergency, and numerical instability.

• 한국소성가공학회:학술대회논문집
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• 한국소성가공학회 1994년도 춘계학술대회 논문집
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• pp.47-54
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• 1994

The study is concerned with the coupled analysis of heat transfer and thermoelastoplastic deformation. The thermoelastoplastic model is very useful for the analysis of residual stress and the analysis of thermal stress as well as the analysis of metal forming. Heat of deformation, phase transformation and contact heat transfer boundary are considered. The contact heat transfer boundary is treated by the interpolation of shape function. The analysis of deformation and the analysis of heat transfer are carried out for the could upsetting and the hot rolling. The computed results are found to be in good agreement with the experimental results.

• 한국소성가공학회:학술대회논문집
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• 한국소성가공학회 2003년도 The 8th Asian Symposium on Precision Forging ASPF
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• pp.31-35
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• 2003

Friction in cold forging with mist lubrication is measured with the ring compression test. Small quantity of mist lubricant is sprayed onto the surfaces of cemented tungsten carbide (WC) tools polished to mirror surfaces, and the specimens of pure aluminum are compressed. It is found that spraying small quantity of lubricant $(0.5\;g/m^2)$ is effective to reduce the friction in comparison with the dry condition. The mist particles stick to the tool surface as separated dots, and the behavior of the trapped mist lubricant between the tool and specimen during upsetting is discussed.

• 한국정밀공학회:학술대회논문집
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• 한국정밀공학회 1996년도 춘계학술대회 논문집
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• pp.201-205
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• 1996

This paper suggests the scheme to simultaneously accomplish prediction of fracture initation and geometrical configuration of deformation in metal forming processes using the artificial neural network. A three-layer neural network is used and a back propagation algorithm is adapted to train the network. The Cockcroft-Latham criterion is used to estimate whether fracture occurs during the deformation process. The geometrical configuration and the value of ductile fracture are measured by finite element method. The prediction of network and numerical results of simple upsetting are compared. The proposed scheme has successfully predicted the geometrical configuration and fracture initiation.

• 한국정밀공학회지
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• 제22권8호
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• pp.100-107
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• 2005

The objective of the study is to improve the quality of wheel bearing hub by the rigid-plastic finite element analysis and the response surface methodology. The rigid-plastic finite element codes, AFDEX-2D and DEFORM-3D, were used to analyze the two-dimensional and three-dimensional forging processes, respectively. The response surface analysis is used to find the minimum underfill by the variation of design variables such as the height of billet after upsetting and punch angles of blocker dies. The metal flow of forged product shows good agreement with the results from 2D and 3D analysis. Also, the quality of the wheel bearing hub has been improved by the optimization of design variables and the machining time has been reduced by the machining allowance.

• 한국정밀공학회지
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• 제15권5호
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• pp.167-175
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• 1998

A mathematical formulation is presented to model anisotropy from the deformation textures developed in a forming process. In this work, a micro-mechanical-based polycrystalline analysis is implemented into a consistent finite element method for the anisotropic, viscoplastic deformation of polycrystalline metals. As suggested by Taylor, the deformation of each grain in an aggregate is assumed to be same as the macroscopic deformation of an aggregate or a macro-continuum point. Algorithms are developed to represent the plastic anisotropy, such as the anisotropic yield surface and R-value, from the predicted deformation texture. As applications, the evolution of texture in rolling, upsetting and drawing/extrusion processes are simulated and the corresponding changes of mechanical properties such as yield surface and R-value are predicted.

• 한국정밀공학회:학술대회논문집
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• 한국정밀공학회 1997년도 춘계학술대회 논문집
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• pp.777-781
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• 1997

In this study, the effect of strain-rate and inital solid fraction on the deformation behaviour of semi-solid material is investigated, when semi-solid forging is performed by the process of closed-die compression using A356 alloy of which the above results can be practically applied for industrical purpose. In order to simulate densification in the deformation of semi-solid material, the semi-solid material is assumed to be composed of solid region following rigid visco-plastic material, the liquid region following Darcy's law for the liquid flow saturated in the interstitial space. Simulation results of closed-die compression and simple upsetting under different strain-rate and initial solid fraction are compared.

• 한국정밀공학회:학술대회논문집
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• 한국정밀공학회 2003년도 춘계학술대회 논문집
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• pp.1513-1516
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• 2003

A crank throw, which is one of the crankshaft part for a large diesel engine is manufactured by closed die forging or open die forging. For the purpose of improvement of productivity the open die forging is usually adopted these days. However it has disadvantage of low yield ratio compare to closed die forging. To overcome this problem, the material properties for hot top and bottom zones of ingot are investigated to utilize them to the product and a modified forging process to reduce the material loss of ingot body through forging analysis according to forging factors(a , R, Ø$\sub$B/, Ø$\sub$D/) is suggested.

• 한국소성가공학회:학술대회논문집
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• 한국소성가공학회 1999년도 춘계학술대회논문집
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• pp.98-101
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• 1999

The plastic instable flow phenomenon happens in practical forming process I. e. upsetting backward extrusion piercing indentation. And also it is difficult to control precisely the shape and dimensions of forming process. It is found that instabilities of the process are mainly connected with imperfection in the lubrication billet eccentricity inclined punch alignment. In view of the direct relationship between instable material flow and quality defects of the products and it is for better control of forming operation we should necessarily find out their phenomena. In this study we used the friction disturbance due to inclined punch angle and introduced the method considering kinematic hardening effect Analysis of upset forging is carried out using the rigid plastic FEM and slab method with eccentricity.