• Transactions of Materials Processing
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• v.19 no.1
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• pp.17-24
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• 2010

A stretch forming method has been widely used in sheet metal forming process. Especially, this process has been adopted in aircraft and high-speed train industries for skin structure forming having a variety of curvature. Until now, solid dies, which are designed with respect to the specific shapes and manufactured as a single piece, have been usually applied to stretch forming process. Therefore, a great number of solid dies has to be developed according to the shapes of the curved skin structure. Accordingly, a flexible die is proposed in this study. It replaces the conventional solid dies with a set of height adjustable punch array. A usefulness of the flexible die is verified through a formability comparison with the solid die using finite element method considering an elastic recovery and the stretch forming apparatus with the flexible die is developed.

• Design & Manufacturing
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• v.7 no.1
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• pp.28-33
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• 2013

During the cold forming, due to high working pressure acting on the die surface, failure mechanics must be considered before die design. One of the main reasons of die failure in industrial application of metal forming technologies is wear. The mechanisms of wear are consisted of adhesion, abrasion, erosion and so on. Die wear affects the tolerances of formed parts, metal flow, and costs of process. The only way to control these failures is to develop a prediction method on die wear suitable in the design state in order to optimize the process. The wear system is used to analyse 'operating variables' and 'system structure'. In this study, with AISI D2, AISI 1020, AISI 304SS materials, a series of the wear experiments of pin-on-disk type to obtain the wear coefficients from Archard's wear model and the upsetting processes are carried out to observe the wear phenomenon during the cold forming process. The analysis of upsetting processes are performed by the rigid-plastic finite element method. The result of the analysis is used to investigate the die wear the processes, and the analysis simulated die wear profiles are compared with the experimental measured die wear profiles.

• Transactions of the Korean Society of Mechanical Engineers
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• v.19 no.3
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• pp.877-885
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• 1995

Cold forging die for metal scissor is made by electric discharge machine. The impression of female die is made by electric discharge machine, the heat treatment is applied, and the impression is polished. When we forge goods by using this kind of die, the abrasion is severe and the crack occurs after forging about 240 strokes. Because the die should be frequently produced in the case, the cost rises, the work is delayed, and the precesion of goods is not good. Therefore, the electric discharge machine was not used in this study. Main die was produced by making hob, installing the hob to cold hobbing press, indenting the die material, and cold hobbing the impression. The die life was increased to 5,000-6,000 strokes in this case. In the future study, the die life will be increased to 10,000 strokes by changing the following : (1) the pre-treatment of slug, (2) the structure of die block, (3) the heat treatment of die material

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2000.11a
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• pp.846-849
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• 2000

In this paper backward extrusion process with lower die rotation was studied to improve the conventional backward extrusion problems ; requirement of large forming machine, the difficulty to selecting of die material caused by high surface pressure, high cost of forming machine caused by improvement of noise and vibration, and etc. In this experiment, model material, plasticine, was used of specimen. The result values of torsional and conventional backward extrusions were analyzed and compared. FE-simulation is used for analysis with DEFPRM-3D. These results show that the torsional backward extrusion is very useful process because this process can obtain the homogeneous deformation, low forming load. Decreasing forming load improves die life and makes it possible to use press of relatively low capacity. Also this process can reduce corner cavity, improve the initial cast-structure, owing to the high deformation and uniform starin distribution.

• Journal of the Korean Society of Manufacturing Process Engineers
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• v.1 no.1
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• pp.63-70
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• 2002

In the field of design and making tool for press working, the progressive die for very thick sheet metal(SS41, 4mm) is a specific division. In order to prevent the defects, the optimum design of the production part, Strip layout, die design, die making and tryout etc. are necessary. They require analysis of many kinds of important factors, i.e. theory and practice of metal working process and its phenomena, die structure, machining condition for die making, die materials, heat treatment of die component, know-how and so on. In this study, we designed and constructed a progressive die of multi stage and tried out through the I-DEAS, DEFORM, and CAD/CAM application. Out of these processes, the die development could be taken advanced technology. Especially the result of try out and its analysis become to the characteristic of this study.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2004.04b
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• pp.129-132
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• 2004

This paper describes the design, fabrication and characteristics of a piezoelectric valve using MCA(Multilayer ceramic actuator). The MCA valve, which has the buckling effect, consists of three separate structures; MCA, a valve actuator die and an a seat die. The design of the actuator die was done by FEM modeling and displacement measurement, respectively. The valve seat die with 6 trenches was made, and the actuator die, which is driven to MCA under optimized conditions, was also fabricated. After Si-wafer direct bonding between the seat die and the actuator die, MCA was also anodic bonded to the seat/actuator die structure. PDMS sealing pad was fabricated to minimize a leak-rate. It was also bonded to seat die and SUS package. The MCA valve shows a flow rate of 9.13 sccm at a supplied voltage of 100 V with a 50 % duty cycle, maximum non-linearity was 2.24 % FS and leak rate was $3.03{\times}10^{-8}\;pa{\cdot}m^3/cm^2$. Therefore, the fabricated MCA valve is suitable for a variety of flow control equipment, a medical bio-system, automobile and air transportation industry.

• Journal of Sensor Science and Technology
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• v.13 no.3
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• pp.230-235
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• 2004

This paper describes the design, fabrication and characteristics of a piezoelectric valve using MCA(Multilayer ceramic actuator). The MCA valve, which has the buckling effect, consists of three separate structures; MCA, a valve actuator die and an a seat die. The design of the actuator die was done by FEM modeling and displacement measurement, respectively. The valve seat die with 6 trenches was made, and the actuator die, which is driven to MCA under optimized conditions, was also fabricated. After Si-wafer direct bonding between the seat die and the actuator die, MCA was also anodic bonded to the seat/actuator die structure. PDMS sealing pad was fabricated to minimize a leak-rate. It was also bonded to seat die and SUS package. The MCA valve shows a flow rate of 9.13 seem at a supplied voltage of 100 V with a 50% duty cycle, maximum non-linearity was 2.24% FS and leak rate was $3.03{\times}10^{-8}pa{\codt}m^{3}/cm^{2}$. Therefore, the fabricated MCA valve is suitable for a variety of flow control equipment, a medical bio-system, automobile and air transportation industry.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2008.10a
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• pp.118-121
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• 2008

Flexible die is more efficacious than fixed die which is generally used in stretch forming process in view of production cost. Accordingly, in order to verily the validity of the flexible forming process, curved thin skin structure forming analyses using the fixed and flexible die were performed. As results, merit and demerit with regard to the fixed and flexible die were confirmed. The result of the stretch forming process analysis using the flexible die was better than that using the fixed die in view of the elastic recovery. However wrinkles were occurred on the sheet material due to die cavities between the punches in the flexible forming process, thus the solutions against these problems were presented.

• Proceedings of the Korea Committee for Ocean Resources and Engineering Conference
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• 2001.10a
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• pp.253-257
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• 2001

This study reveals the sheet metal working with multi-forming type ultra precision process. They require analysis of many kinds of important factors, i.e. theory and practice of metal press working and its phenomena, die structure, machining condition for die making, die material, heat treatment of die components, know-how and so on. In this study, we designed and constructed a multi-forming ultra precision progressive die as a bending and drawing working of multi-stage and performed through the try out for thin sheet metal. This part I of papers related to the analysis of production part and strip process layout design through the metal forming simulation by DEFORM and IDEAS.

• Journal of the Korean Society for Precision Engineering
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• v.16 no.6
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• pp.114-122
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• 1999

By using the FEM, a method for the stress analysis of the presented dies has been proposed. In this method, FEM and Lame equation are used for the analysis of the die insert and the stress ring, respectively. The proposed method includes the calculation of the contact pressure between the die insert and the stress ring. To show the validity, the proposed method has been applied to the simple test problem. The results of the stress analysis have been compared with the results of ANSYS, a commercial FE-code. Cold extrusion has been simulated by using the rigid-plastic FEM and the results of the deformation analysis have been used as the input of the die structure analysis. The stress states of the prestressed extrusion die have been obtained. The stress analysis of the die insert with stress rings has also been performed during extrusion.