• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 1997.10a
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• pp.76-79
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• 1997

In this study, an elasto-plastic finite element code, ESFORM, was developed to analyze sheet stamping processes. A formulation of 4-node degenerated shell element was implemented in the code. Workpiece materials were assumed to have planar anisotropy, and governed by associated flow rule. Explicit time integration method was employed to save computation time and reduce the required computer memory. Penalty method was used to describe interface behavior between workpiece and rigid die. Deep drawing of square cup and front finder stamping processes were simulated by ESFORM>

• Transactions of the Korean Society of Mechanical Engineers
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• v.16 no.8
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• pp.1468-1484
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• 1992

In the present paper forward projection is proposed as a new approach to determine the preform shape in rib-web type forging. In the forward projection technique an optimal billet is determined by applying some mathematical relationship between geometrical trials in the initial billet shape and the final products. In forward projection a volume difference between the desired product shape and the final computed shape obtained by the rigid-plastic finite element method is used as a measure of incomplete filling of working material in the die. At first linear inter-/extrapolation is employed to find a proper trial shape for the initial billet and the method is successfully applied to some cases of different aspect ratios of the initial billet. However, when the initial guesses are not sufficiently near the optimal value linear inter-/extrapolation does not render complete die filling. For more general application, a fuzzy system is used in the forward projection technique in order to determine the initial billet shape for rib-web type forging. It has been thus shown that the fuzzy system is more reliable for the preform design in the rib-web type forging process.

• Clinical and Molecular Hepatology
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• v.24 no.4
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• pp.358-366
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• 2018

Severe acute alcoholic liver disease (SAAH) unresponsive to medical therapy shows one-year-mortality rates of up to 90%. Most transplant centers request six months of alcohol abstinence prior to transplantation, the so-called "6-month rule." This regulation is not based on strong evidence, repeatedly making it a topic of controversial debates. The majority of patients with SAAH will die before fulfilling the 6-month rule. Therefore, liver transplantation (LT) protocols are becoming more flexible towards the rigid abstinence regulation, especially concerning SAAH patients. We conducted a literature review regarding LT in SAAH and its outcomes, including post-transplant mortality and recidivism. We studied available data on PubMed from 2011 and onwards whilst including articles dealing with genetic components, medical therapy and historic snapshots of alcoholism. Emerging studies recommend LT in SAAH not responding to medical therapies even without realizing the required abstinence period, since the majority of these patients would die within 6 months. SAAH without response to medical therapy has one-year-mortality rates of up to 90%. The 6-month rule is not based on strong evidence and is repeatedly a topic of controversial debates. There is genetic linkage to alcoholism and medical therapy is not as effective as estimated, yet. The 6-months-regulation has not shown to evidently decrease the risk of recidivism post-LT, which is a lifesaving treatment in SAAH patients. Insisting on rigid sobriety rules results in excluding patients with a low risk of recidivism from being transplanted. Moreover, the genetic linkage of alcoholism must be recognized.

• Transactions of Materials Processing
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• v.16 no.8
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• pp.603-613
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• 2007

This paper is concerned with joining of thin metal sheets by single stroke clinching process. This method has been used in sheet metal work as it is a simple process and offers the possibility of joining similar-dissimilar thin sheet metals. Clinching generates a joint by overlapping metal sheets deforming plastically by punching and squeezing sequence. AA 5754 aluminum alloy of 0.5 mm thick sheets have been selected as a modal material and the process has been simulated under different process conditions and the results have been analyzed in terms of the quality of clinch joints which are influenced mainly by tool geometries. The rigid-plastic finite element method is applied to analyses in this paper. Analysis is focused mainly on investigation of deformation and material flow patterns influenced by major geometrical parameters such as die diameter, die depth, groove width, and groove corner radius, respectively. To evaluate the quality of clinch joints, four controlling or evaluation parameters have been chosen and they are bottom, neck thickness of bottom and top sheets, and undercut thickness, respectively. It has been concluded from the simulation results that the die geometries such as die depth and diameters are the most decisive process parameters influencing on the quality of clinch joints, and the bottom thickness is the most important evaluation parameter to determine if the quality of clinch joints satisfies the demand for industrial application.

• Transactions of Materials Processing
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• v.9 no.3
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• pp.233-241
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• 2000

It is well known that the quality and efficiency of the design of metal forming processes can be significantly improved with the aid of effective numerical simulations. In the present study, a two-and three-dimensional finite element simulation system, CAMP form, was developed for the analysis of metal forming processes in the PC environment. It is composed of a solver based on the thermo-rigid-viscoplastic approach and graphic user interface (GUI) based pre-and post-processors to be used for the effective description of forming conditions and graphic display of simulation results, respectively. In particular, in the case of CAMPform 2D (two-dimensional), as the solver contains an automatic remeshing module which determines the deformation step when remeshing is required and reconstructs the new mesh system, it is possible to carry out simulations automatically without any user intervention. Also, the forming analysis considers ductile fracture of the workpiece and wear of dies for better usage of the system. In the case of CAMPform 3D, general three-dimensional problems that involve complex die geometries and require remeshing can be analyzed, but full automation of simulations has yet to be achieved. In this paper, the overall structure and computational background of CAMPform will be briefly explained and analysis results of several forming processes will be shown. From the current results, it is construed that CAMPform can be used in providing useful information to assist the design of forming processes.

• Journal of the Korean Society for Precision Engineering
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• v.22 no.3 s.168
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• pp.86-92
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• 2005

In this paper a forward-backward can extrusion process are analyzed by using rigid-plastic FEM simulation. FEM simulation is conducted to investigate forming characteristics such as deformation modes fur different process parameters. Design parameters such as thickness ratio, punch angle, friction factor and diameter ratio are selected to study the effect of them on the pattern of material flow. The analysis is focused mainly on the influences of the design factors on deformation pattern in terms of forming load, extruded length ratio and volume ratio. It is known for the simulation that the forming load, the length ratio and the volume ratio increase as the thickness ratio (TR), the wall thickness in forward direction to that in backward direction, decreases. The various punch angles have slight influence on the forming load. length ratio and volume ratio. However friction factor have little effect on the forming characteristics such as the forming load, volume ratio and so on. In addition the forming load increases as diameter ratio (DR), the outer diameter of a can in forward direction to that in backward direction, increases. Furthermore the extruded length ratio is lowest with a certain value of DR=0.85 among diameter ratios. Pressure distribution exerted on the die-material interface is illustrated schematically.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2004.05a
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• pp.91-94
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• 2004

Preform design techniques have been investigated in efforts to reduce die wear and forming load and to improve material flow, filing ratio, etc. In hot forging processes, a thin deformed part of a workpiece, known as a flash, is formed in the narrow gap between the upper and lower tools. Although designers make tools that generate a flash intentionally in order to improve flow properties, excessive flash increases die wear and forming load. Therefore, it is necessary to make a preform shape that can reduce the excessive flash without changing flow properties. In this paper, a new preform design technique is proposed to reduce the excessive flash in a metal forging process. After a finite element simulation of the process is carried out with an initial billet, the flow of material in the flash region is traced from the final shape to the initial billet. The region belonging to the flash is then easily found in the initial billet. The finite element simulation is then carried out again with the modified billet from which the selected region has been removed. In several iterations of this technique, the optimal preform shape that minimizes the amount of flash without changing the forgeability can be obtained.

• Transactions of Materials Processing
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• v.1 no.1
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• pp.66-74
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• 1992

According to the variation of hydrostatic pressure on the central axis of deformable material, the V-shaped central bursting defect may be created in extrusion or drawing processes. The process factors which affect the generation of defects are semi-angle of die, reduction ratio of cross-sectional area, friction factor, material properties and so on. The combination of these factors can determine the possibility of defect creation and the shape of various round holes which have been created inside already. By the rigid plastic finite element method, this paper describes the observations of change in shape of round holes with process conditions such as semi-angle of die, reduction ratio of cross-sectional area and friction factor at the non-steady state of axisymmetrical extrusion process when the round hole is already existed inside the original billet. Also, the effects of process factors are investigated to prevent the possible defects.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2007.10a
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• pp.173-176
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• 2007

The characteristics of the tool system give many effects into the costs and qualities for the finished components. This study proposes a new method for manufacturing of high manufacturing productivity, production process reduction and low cost through back pressure forming. The Lock-up hub is manufactured through many processes, such as upsetting($1^{st}$ Forming), piercing, direct extrusion($2^{nd}$ Forming), final sizing process($3^{rd}$ Forming). In this study, process design for closed-die forging of a Lock-up hub used for a component of automobile transmission was made using three-dimensional finite element simulations, and the strain distributions and velocity distributions are investigated through the post processor. The rigid-plastic finite-element method for back pressure forging has been used in order to reduce development time and die cost. Using the FEM simulation, we found the optimum value of back pressure. The prototypes of Lock-up hub parts were forged into the net-shape. In the experiment, lead precision of tooth are measured by the CCMM(Contact Coordinate Measuring Machine). The dimensional accuracy of forged part was improved up to the 40% when back press was applied.

• Design & Manufacturing
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• v.11 no.2
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• pp.15-19
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• 2017

Carbon fiber reinforced plastic (CFRP) is applied as structural material. CFRP is excellent in plane strength / stiffness and don't haves rust. Lightweight, rigid and robust at the same time as transportation material. Aluminum alloy and reinforcement material The application is increasing rapidly. In this study, the prototype of a semi - Monocoque structure frame, Longeron, Stringer, Skin of the aircraft, restraining the rigidity Clips of the aircraft was designated as the target product and the experiment was conducted. ln the experiment, (1) For CFRTP 3 points, data on heating, transfer, and cooling were measured using Thermo Couple, and optimum temperature required for flexible state was obtained. Heating was performed at a temperature 15% higher than the provided temperature. (2) By using a pneumatic press during molding, by dividing LH, center and RH according to the cooling time, thickness parameter of the target product due to the load is measured, and thickness control and time-deviations were analyzed and cross sections were observed with a low magnification microscope.