• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2003.10a
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• pp.241-244
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• 2003

The productivity of hydroforming process can be increased by combining pre-forming process and post-forming process such as the bending, piercing and the embedding process. Therefore in this study, integrated studies on the hydro-embedding technology have been performed by analyzing the deformed mode of the tubes and the optimal process parameters. In the case of the embedding test the characteristics of the embedded parts, such as the shape of the screw tip, screw thread and shape of thread were investigated at various process conditions. To measure the clamping force between the embedded part and the tube, special measuring device was used.

• Transactions of Materials Processing
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• v.15 no.5 s.86
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• pp.373-381
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• 2006

The key technologies necessary to develop and utilize a double-action link-type hydraulic die set for the enclosed die forging are presented in this paper. Various die sets for the enclosed die forging are investigated and the technologies necessary to develop and to utilize a double-action link-type hydraulic die set are introduced in detail with emphasis on the mechanism of the die set and its kinematical behaviors, the force transmission mechanism, the criterion on the enclosed die forging and its application, the forming load prediction and the stress distribution of the link. A double-action link-type hydraulic die set is developed and it is applied to the enclosed die forging of a bevel gear.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2003.05a
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• pp.283-287
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• 2003

In recent years, design of an optimal blank shape is very important for sheet metal forming process in the automobile industry because the raw material cost rate is significant part in the automobile industry. With the design of an optimal blank shape, the engineer can protect a blank from an excessive holding force to improve the quality and reduce the ratio of material scrap. Therefore design of an optimal blank shape is inevitable in sheet metal forming process. However, if it causes a complicated shape of blank, it may be difficult to do the blank layout optimally. In this study, we developed software of optimal blank layout connected with the software of optimal blank shape design which was created in the past by the present authors. And by using these softwares, we would like to present the method in order to get optimal utilization ratio easily and precisely within short time for the sequence of works from design to blank layout.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 1999.03a
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• pp.18-21
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• 1999

The wrinkling of thin sheet metal induced by compressive instability is one of major defects in sheet metal forming processes. compressive instability is influence by many factors such as mechanical properties of the sheet material geometry of the sheet contact conditions and plastic anisotropy. The analysis of compressive instability in a plastically deforming body is rather difficult because the effects of the above-mentioned factors are rather complex and the instability behavior may show swide variations even for small deviations of the factors. in this work the bifurcation theory is introduced for the finite elemental analysis of the instability behavior of a thin sheet with initially sound geometry and property. All the above-mentioned factors are conveniently considered by the finite element method. The instability limit is found by introducing a criterion scheme into the incremental analysis and the post-bifurcation behavior is analyzed by introducing the branching scheme. Wrinkling initiation and growth in the deep drawing process are analyzed.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2000.10a
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• pp.70-73
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• 2000

A finite element analysis model is suggested for analysis of forming process of milli structure whose size is from a few hundreds ${\mu}m$ to a few mm. In this paper, finite element formulation which assemble crystal plasticity theory considering texture development with damage mechanics is developed, since orientation development and growth of micro voids became the primary factors for deformation aspects in large deformation of milli structure. Applying to, extremely, extrusion process of single crystal and extrusion/drawing process of polycrystal milli-size bar, extrusion force, preferred orientation, and damage evolution are examined to understand the characteristics of deformation of milii-size bar.

• Transactions of Materials Processing
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• v.6 no.5
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• pp.425-434
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• 1997

A superplastic material, aluminum-lithium alloy 8090, was examined with uniaxial tensile tests to investigate its thermomechanical behavior. The tests were carried out at the strain rate ranging from $2X10^4 to 1X10^2$ and at the temperature from 48$0^{\circ}C$ to 54$0^{\circ}C$. The experiments produced force-dis-placement curves which were converted to stress-strain curves. From the curves, the optimum conditions of superplastic forming were obtained by deteriming the strain rate sensitivety, the optimum strain rate, and the strength coefficient for various forming temperatures.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2004.05a
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• pp.206-209
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• 2004

In the hydroforming process the number of process can be reduced by combining pre-forming process and post-forming process such as the bending, piercing and the embedding process. Integrated studies on the embedding manufacturing technology have been performed by analyzing the deformed mode of the tubes and the optimal process parameters. In this study, a simulation model that can prove clamping force between the clamping element and tube has been investigated by FEM. The characteristics of the embedded parts, such as the shape of the screw tip, screw thread and shape of thread were investigated at various clamping element conditions.

• Transactions of Materials Processing
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• v.16 no.6
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• pp.447-451
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• 2007

The springback characteristics of AZ31B magnesium alloy sheet was investigated in OSU draw/bend test Springback is the elastically-driven change of shape of a part after forming and it should be estimated and controlled to manufacture more precise products in sheet forming. Magnesium alloy sheets have unique mechanical properties such as high in-plane anisotropy/asymmetry of yield stress and hardening response. So, there will be a difference in the prediction of springback with symmetric mechanical properties for magnesium alloy sheets. In this work, the Strip draw/bend tests were conducted with various conditions - die radius, sheet thickness and controlled tensile force and the tendency of springback angle was observed from the tests.

• Proceedings of the Korean Society of Machine Tool Engineers Conference
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• 2003.10a
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• pp.406-411
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• 2003

It is clearly demonstrated that deeper cups could be formed by single and double stretch-drawings from smaller circular blanks due to such wall-thinning action than in the usual deep-drawing of larger blanks. From this fact, it is emphasized that the deep-drawability of a sheet metal Is not evaluated simply by the conventional L.D.R (limiting drawing ratio), but the depth of the drawn cup should also be taken into account. Many experimental data about various metals and thicknesses given in this paper offer a valuable information in this process for more general use which recommends to replace the conventional deep-drawing process by the stretch-drawing process both for single and double operations. In the single stretch-drawing, it is also confirmed that a deeper cup can be produced by raising the blank-holding force at later stage of operation.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 1995.03a
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• pp.31-40
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• 1995

Powder metallurgy process has many advantages such as hight efficientyof material, mass productivity and complex shape production with good mechanical properties. Among the powder forming processes, incremental forging allows the consolidation to be achieved with amaller force then those required by conventional forging. In particular the proces known as rotary forging is an unique and prodominant process known as rotary forging is an unique and prodominant process in which the working constraints approximate to those in normal closed die forging. This study is concerned with the powder compaction by rotary forging process. An experimental rotary forging press with 500kN load capacity has been developed, which is equippe dwith the rotational conicla die inclined to the central axis of the press at arbitrary angle. It is found that the highly densified P/M parts can be obtained by rotary forging process and the material properties are superior to those of the conventrional sintered parts. The detailedcomparision of the mechanical properties by rotary forging process with those by conventional process are given.