• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2008.10a
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• pp.122-125
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• 2008

Generally, in shipbuilding, large curved block components which have large curvature radius along various directions are used for huge ships such as LPG-vessel and oil tanker ships. Lots of the blocks are manufactured by line heating method which uses a heat source to bend the thick plate materials. The conventional forming process is entirely dependent on the experience of experts because it is done by manual method thus the curvatures and qualities are not uniform even for same part. However, it is hard to adopt the press forming process using die tool sets fur the manufacturing because of the characteristics of the industry that based on the small quantity and variety in the products. In this study, flexible forming technology using numbers of punches is investigated based on the simulation to substitute for the conventional forming method. Thick plate material model was applied to the proposed process to verify the feasibility for hull structure block forming process. The press forming processes were simulated by adopting the explicit-to-implicit sequential solution. Moreover, experiment of the flexible forming process was also conducted and its results were compared with that of simulation.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2012.05a
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• pp.941-942
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• 2012

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2008.05a
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• pp.220-223
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• 2008

Large curved plate blocks are widely used to construct hull structure in shipbuilding industry. Most curved plates are manufactured by using manual method called as line heating that use deformation caused by residual stress after local heating along a line which is perpendicular to the curvature direction. However, its working environment is poor and its formability is totally dependent on an experienced technician. In view of that, multi-point dieless forming (MDF) technology that use reconfigurable punch arrays instead of one piece die is proposed in this study. The MDF process is based on a concept of equivalent die surface made by numbers of punches which has round tip at the end of it. In this study, numerical simulation for common curvature type such as saddle shape was carried out. In addition, experiments in the plate forming process were also conducted to compare with the numerical results in view of final configuration. Consequently, it was noted that the proposed dieless forming method has considerable feasibility to substitute the new process for conventional manual method.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2013.05a
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• pp.1519-1520
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• 2013

• Journal of the Korean Society for Precision Engineering
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• v.30 no.8
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• pp.815-823
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• 2013

The hot curvature forming of large aluminum plates is a process used to produce spherical liquefied natural gas (LNG) tanks. In this study, we describe a method to determine the optimum shape of blanks to minimize the root gap in the forming process. The method proposed in this study was applied to a small-scale model for thick plates with a curvature of 1500 mm and thickness of 6 mm. First, the shape of the curved shells was determined as the target shape, and then a coordinate transform was used to determine the optimum blank shape, which was then iteratively modified using the results of finite element method (FEM) simulations, including heat transfer, until the shape error was minimized. Experiments in forming using Al5083 thick plate were carried out, showing that the method can determine the optimum blank shape within an allowable root gap of 0.1 mm.

• Transactions of Materials Processing
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• v.21 no.7
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• pp.453-458
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• 2012

The flange hub is a main component of an automotive steering system. Dimensional precision of the flange hub is very important for precise control of the steering force. Consequently, the process design for precision forming of a flange hub is required. The teeth of the flange hub are generally formed by bending. In this study, the formability of flange bending was investigated using FE simulations. For the optimum process conditions, the flange is bent by movement of an insert die, and the die angle and bending length are selected as $90^{\circ}$ and 4mm respectively.

• Transactions of Materials Processing
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• v.25 no.4
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• pp.227-234
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• 2016

In the transportation between countries using container, too many empty containers must be transported due to the transportation unbalance. For transportation efficiency, therefore, foldable containers are being developed. Hinge brackets are important parts of foldable containers because great force is applied on the hinges during loading onto and unloading from ships. In this study, the hinge bracket for a foldable container is designed to be made using thick plate or bulk materials to endure the heavy loads. The forming process for the hinge bracket using a thick plate is designed via numerical analysis. First of all, the shape of bracket is designed for the better formability. Bending and successive side wall thickening processes are employed for the forming of the hinge bracket. Maximum thickening that can be achieved in a single stage of forming without a folding defect is determined and three stage of thickening processes are designed.

• Journal of Chest Surgery
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• v.41 no.5
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• pp.580-585
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• 2008

Background: Many types of tricuspid annuloplasty are used in surgical correction of functional tricuspid regurgitation (FTR). We evaluated the mid-term and long-term outcomes in patients treated with a posterior annular plication technique (a modified Davila technique) for FTR. Material and Method: Between January 1991 and August 2006, 58 adult patients (male, 22; female, 36) with FTR of grade 2/4 or more or with tricuspid annular dilatation of more than 5.0cm in diameter, even with an FTR of less than grade 2, had received a posterior annular placation. Preoperatively, 26 patients (44.8%) had a grade 3 or more FTR. All patients had received a mitral valve replacement, and 20 (34.5%) had concomitant aortic valve replacement. Result: During the mean follow-up period of $101.4{\pm}51.6$ months, FTR disappeared or remained trivial in 28 patients (49.1%), was grade $2{\sim}3$ (${\geq}$grade 2 and $2.66{\pm}0.73\;vs.\;0.82{\pm}0.89$; p<0.0001). Patients did not require a second surgery for FTR and did not show further FTR aggravation. Conclusion: The modified Davila posterior annular plication technique for FTR has reasonable mid-term and long-term results and is a useful surgical procedure.

• Journal of Chest Surgery
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• v.36 no.9
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• pp.646-650
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• 2003

Many surgical techniques for ischemic mitral regurgitation (IMR) have been used with their excellent results and advantages. Here, we report our simple posterior annuloplasty techniques using vascular graft strip with their early results. Material and Method: Twenty two patients (13 male) underwent the operations for IMR (excluding the papillary muscle rupture) from December 2001 to January 2003. Preoperative risk factors were low ejection fraction (<35％, n=9), hypertension (n=13), diabetes (n=9), and renal failure (Cr>2.5, n=4). The wide dissection beneath the both vena cavae and interatrial groove after bicaval cannulation enabled the easy exposure of mitral valve even in the small left atrium. After eight or nine interrupted sutures in posterior annulus for anchoring the 6 mm width vascular graft strip, symmetric (n=8) or asymmetric (n=14) annuloplasty were done. Combined surgeries were CABG (n=21), Dor procedures (n=3), tricuspid valve annuloplasty (n=1), Maze operation (n=1), and aorto-right subclavian artery bypass (n=1). Result: Except for one surgical mortality, all the patients were doing well and the mean grade of regurgitation was decreased from 2.95 to 0.88, however the ejection fraction had not changed significantly just before discharge. Post-operative valve function evaluated before discharge revealed no residual regurgitation in 8 (including 1 patient with mild stenosis due to over reduction), minimal in 11, mild in 2, and mild to moderate regurgitation in 1. One patient who had ischemic cardiomyopathy and renal failure died of the arrhythmia during the hemodialysis. Conclusion: These observations suggest that the annuloplasty with vascular graft strip could be a safe and cost effective techniques for ischemic mitral regurgitation. However, the long term evaluation for the mitral valve function should be defined for the final conclusion.

• Journal of Korean Society of Steel Construction
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• v.16 no.1 s.68
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• pp.33-42
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• 2004

Making use of SN steel in the building structure should be a prerequisite to adopt the design strength of said steel. As a preceding study, the material properties of STKN400B/490B tubes and SPAP235/325 and SPAR295 square pipes manufactured using SN400B/490B plates were evaluated. Compared with the yield and ultimate strengths of SN400B/490B plates, those of STKN400B/490B tubes increase. Nonetheless, the yield and ultimate strengths of STKN400B/490B tubes satisfied the design codes of STKN400B/490B tubes even though the tubes were fabricated via roll bending or press forming. On the other hand, the yield and ultimate strengths at the edges of SPAP235/325 square pipes did not satisfy the design codes based on the values at the sides. The maximum tensile and compressive residual stresses at the SN490B tube were equal to and 40% of the yield strength of the SN490B plate, respectively, In the case of the SPAP325 square pipe, both the maximum tensile and compressive residual stresses were 80% of the yield strength of the SN490B plate. The axial compressive loaded column test results snowed that the buckling strengths were not very different regardless of the mode of fabrication of STKN490B tunes. i.e., through roll bending or press forming. On the other hand, the buckling strength of the SPAP325 square pipe was higher than that of the built-up square pipe.