• 대한기계학회논문집A
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• 제26권11호
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• pp.2245-2252
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• 2002

Design sensitivity analysis scheme is proposed in an elasto -plastic finite element method with explicit time integration using a direct differentiation method. The direct differentiation is concerned with large deformation, the elasto-plastic constitutive relation, shell elements with reduced integration and the contact scheme. The design sensitivities with respect to the process parameter are calculated with the direct analytical differentiation of the governing equation. The sensitivity results obtained from the present theory are compared with that obtained by the finite difference method in a class of sheet metal forming problems such as hemi-spherical stretching and cylindrical cup deep-drawing. The result shows good agreement with the finite difference method and demonstrates that the preposed sensitivity calculation scheme is a pplicable in the complicated sheet metal forming analysis and design.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2004년도 추계학술대회
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• pp.643-648
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• 2004

This paper is dedicated to the thermoelastic modeling and dynamic response of the rotating blades made of functionally graded ceramic-metal based materials. The blades modeled as non-uniform thin walled beams fixed at the hub with various selected values of setting angles and pre-twisted angles. In this study, the blade is rotating with a constant angular velocity and exposed to a steady temperature field as well as external excitation. Moreover, the effect of the temperature gradient through the blade thickness is considered. Material properties are graded in the thickness direction of the blade according to the volume fraction power law distribution. The numerical results highlight the effects of the volume fraction, temperature gradient, taper ratio, setting angle and pre-twisted angle on the dynamic response of bending-bending coupled beam characteristics are provided for the case of a biconvex cross section and pertinent conclusions are outlined.

• 한국기계가공학회지
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• 제15권1호
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• pp.95-102
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• 2016

Wrinkle, spring-back, and fracture are major defects frequently found in the sheet metal forming process, and the reduction of such defects is difficult as they are affected by uncontrollable factors, such as variations in properties of the incoming material and process parameters. Without any countermeasures against these issues, attempts to reduce defects through optimal design methods often lead to failure. In this research, a new multi-attribute robust design methodology, based on the Mahalanobis Taguchi System (MTS), is presented for reducing the possibilities of wrinkle, spring-back, and fracture. MTS performs experimentation, based on the orthogonal array under various noise conditions, uses the SN ratio of the Mahalanobis distance as a performance metric. The proposed method is illustrated through a robust design of the sheet metal forming process of a cross member of automotive body.

• 한국생산제조학회지
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• 제22권1호
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• pp.162-167
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• 2013

The most important factor in an aircraft manufacturing is stability and weight reduction. Most of aircraft components are designed with thin plate type to satisfy weight reduction needs. The thin plate is difficult to be machined because it is apt to be vibrated by dynamic force generated in milling process. The most critical factor in machining of aluminum thin plate is width and thickness between stiffeners. So we tested many cases to find out the machinable minimum thickness at different width between stiffeners. And with the data obtained from many tests, this papers suggested the standard width thickness relation that is machinable without vacuum fixture. Machinist will be able to reduce the cost of aircraft thin plate parts by reducing the number of vacuum fixture used by the help of this standard.

• 대한기계학회논문집A
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• 제26권11호
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• pp.2466-2473
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• 2002

In twin roll strip casting process, the design of casting roll is the most important equipment for producing strip. Analyses of heat transfer and deformation for the casting roll are carried out by using the finite element program, ANSYS. Both the elastic deformation and the elasto-plastic deformation under a thermal load are considered in the analysis. Optimization to minimize the volume of roll is performed under the various thermal loads such as the heat flux and the roll speed. Design variables are defined by diameters and positions of the cooling hole in the roll , Although the thermal load remarkably varies, the design variables and objective function are found to be consistent.

• 대한기계학회논문집A
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• 제26권11호
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• pp.2262-2269
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• 2002

Process optimization is carried out to determine process parameters which satisfy the given design requirement and constraint conditions in sheet metal forming processes. Sensitivity -based-approach is utilized for the optimum searching of process parameters in sheet metal forming precesses. The scheme incorporates an elasto-plastic finite element method with shell elements . Sensitivities of state variables are calculated from the direct differentiation of the governing equation for the finite element analysis. The algorithm developed is applied to design of the variablc blank holding force in deep drawing processes. Results show that determination of process parameters is well performed to control the major strain for preventing fracture by tearing or to decrease the amount of springback for improving the shape accuracy. Results demonstrate that design of process parameters with the present approach is applicable to real sheet metal forming processes.

• 한국정밀공학회지
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• 제23권1호
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• pp.152-158
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• 2006

The AutoForm previously used the membrane element and it accomplished sheet metal forming analysis. The membrane analysis has been widely applied to various sheet metal forming processes because of its time effectiveness. However, it is well-known that the membrane analysis can not provide correct information for the processes which have considerable bending effects. In this research experimental results were compared with the analysis results obtained by using the shell element which is applied newly in the AutoForm commercial software. The shell element is a compromise element between continuum element and membrane element. The Finite element method by using shell element is the most efficient numerical method. From this research, it is known that FEA by using shell element can predict accurately the problems happened in actual experimental auto-body panel.

• 한국정밀공학회지
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• 제19권11호
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• pp.200-210
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• 2002

In twin roll strip casting process, coupled analyses of heat transfer and deformation for the cast roll are carried out by using the finite element program MARC to examine the thermal crown. Shrink fit effect and plastic deformation are considered. The results shows that the thermal crown is greatly influenced by shrink ft and that the thermal crown for POSCO Pilot Caster 2 Copper Roll has “M” shape. The effects of several factors on thermal crown are also investigated. The amount of thermal crown increases as heat flux, casting speed, steeve thickness and casting roll width increase and decreases as the casting roll diameter increases.

• 한국정밀공학회지
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• 제33권4호
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• pp.247-255
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• 2016

Sheet metal-forming processes such as stamping, deep drawing, bending, shearing, hydroforming, hydromechanical deep drawing, rubber forming, and incremental forming have been widely used in the automotive, aircraft, and ship-building industries. With the expansion of the automotive industry, research on these processes has been remarkably developed in Korea since the 1980s. Here, we review the history of this research as well as recent trends in sheet metal-forming processes. This overview focuses specifically on the results of research in Korea and on the works of Professor D.Y. Yang, in honor of his retirement.

• 소성∙가공
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• 제7권1호
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• pp.12-22
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• 1998

An expert drawbead model is developed for the finite element analysis of stamping processes. The expert model calculates drawbead restraining forces and bead-exit thinnings with the forming condi-tions and drawbead size. The drawbead restraining forces and bead-exit thinnings of a circular draw-bead and stepped drawbead are computed by mathematical models and corrected by the multiple lin-ear regression method based on experimental measurements. The squared drawbead preventing the sheet from drawing-in inside die cavity is assumed to have a very huge drawbead restraining force and no pre-strain just after drawbead. The combined beads are considered as a combination of basic draw-beads such as circular a drawbead stepped drawbead and squared drawbead so that the drawbead restraining forces and bead-exit thinnigs are basically sum of those of basic drawbeads.