• The Korean Journal of Physiology and Pharmacology
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• v.22 no.6
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• pp.705-712
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• 2018

The tube formation assay is a widely used in vitro experiment model to evaluate angiogenic properties by measuring the formation of tubular structures from vascular endothelial cells (ECs). In vitro experimental results are crucial when considered the advisability of moving forward to in vivo studies. Thus, the additional attentions to the in vitro assay is necessary to improve the quality of the pre-clinical data, leading to better decision-making for successful drug discovery. In this study, we improved the tube formation assay system in three aspects. First, we used human endothelial colony forming cells (ECFCs), which are endothelial precursors that have a robust proliferative capacity and more defined angiogenic characteristics compared to mature ECs. Second, we utilized a real-time cell recorder to track the progression of tube formation for 48 hours. Third, to minimize analysis error due to the limited observation area, we used image-stitching software to increase the microscope field of view to a $2{\times}2$ stitched area from the $4{\times}$ object lens. Our advanced tube formation assay system successfully demonstrated the time-dependent dynamic progression of tube formation in the presence and absence of VEGF and FGF-2. Vatalanib, VEGF inhibitor, was tested by our assay system. Of note, $IC_{50}$ values of vatalanib was different at each observation time point. Collectively, these results indicate that our advanced tube formation assay system replicates the dynamic progression of tube formation in response to angiogenic modulators. Therefore, this new system provides a sensitive and versatile assay model for evaluating pro- or anti-angiogenic drugs.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2001.10a
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• pp.50-53
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• 2001

Hydroforming process has become an effective manufacturing process because it can be adaptable to forming of complex structural components. Tube hydroforming has been successfully developed in the real industrial field by many researchers. However, there still remains the constraint about shape which can be manufactured by tube hydroforming. In order to improve this constraint of shape and formability of conventional sheet metal forming, hydroforming process of sheet metal pairs becomes an important technology. In the present work, the finite element analysis of hydroforming process of sheet metal pairs is presented. After basic study about experimental parameters based on numerical analysis, hydroforming process of sheet metal pairs is developed which uses hydraulic pressure as a main forming source.

• Transactions of Materials Processing
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• v.17 no.4
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• pp.263-271
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• 2008

Process design is carried out for a press forming of a CTBA in the rear suspension assembly based on the result of the finite element analysis. The analysis simulates the two-stage stamping process with the initial design and it fully reveals the unfavorable mechanism which develops inferiorities during forming. In this paper, a new design guideline is proposed to modify the process and tool shapes for a single-stage forming process. With the improved tool design, prototypes are fabricated after several try-out processes. Results of the durability tests show that the design requirement of the part is satisfied and the effective weight reduction is achieved.

• Transactions of Materials Processing
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• v.12 no.6
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• pp.558-565
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• 2003

Rotary swaging is one of the incremental forming process which is a chipless metal forming process for the reduction of cross-sections of bars, tubes and wires. In the present work, the rotary swaging machine and dies were designed to investigate the formability of TDS(Tube Drive Shaft) used in automotive industry. The process variables such as the speed of forming, the shape of the formed materials and the reduction of area were also estimated to study experimental analyses of rotary swaging process using the materials of 34Mn5 and S45C. From experimental results, it was found that the process variables affected the quality of TDS in terms of hardness, the precision of products and the surface roughness. The hardness after swaging approved to be Increased with the increase in the reduction of diameter. And it was found that the grain size became smaller and the elongated grains were formed in the axis direction.

• Transactions of the Korean Society of Automotive Engineers
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• v.23 no.1
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• pp.41-48
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• 2015

In the automotive industry, it is required to reduce weight of the car and improve fuel efficiency. Competitive pricing is also a very important issue. That's why application of welded steel tube is increasing in order to produce a vehicle with a competitive price. Also, hydroforming technology is asking more and more for thinner tubing to realize to a lighter vehicle design. Steel tube is produced through a multi-stage process called roll forming. In that case, bucking and work hardening should be considered key forming technology is to prevent buckling and minimize work hardening during steel tubing for hydroforming To prevent buckling, it is required to optimize forming process in order to minimize stretching in edge sections and hold tightly cross-section during welding. And to minimize work hardening, it is needed to know the proper process to avoid reforming.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2008.05a
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• pp.353-356
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• 2008

Tool design is carried out for a press forming of a cross member in the rear suspension assembly based on the result of the finite element analysis. The analysis simulates the two-stage stamping process with the initial design and it fully reveals the unfavorable mechanism which develops inferiorities during forming. In this paper, a new design guideline is proposed to modify the process and tool shapes for a single-stage forming process. With the improved tool design, this study fabricates prototypes that satisfy the durability requirement.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2007.05a
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• pp.310-313
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• 2007

This paper covers finite element simulations to evaluate the bending limit of double pipe for tube-hydroforming. The tube-hydroforming process starts with a straight precut tube. The tube is often prebent in a rotary draw bending machine to fit the hydroforming tool. During the bending the tube undergoes significant deformation. So forming defects such as wrinkling, thinning and flattening are generated in the tube. Consequently we analyzed the effect of process parameters in rotary draw bending process and searched the optimized combination of process parameters to minimize the forming defects using orthogonal arrays. The characteristic to evaluate the effects of the process parameters is the bending angle which wrinkling is generated, we define the bending angle at that time as bending limit. Of many process parameters, the process parameters of the bending process such as gab between inner and outer tube, boosting force, dimensions of mandrel were analyzed. And we observed the deformation modes of bent double pipe at specific bending angle in each parameter combination.

• International Journal of Automotive Technology
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• v.7 no.2
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• pp.209-216
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• 2006

A study has been conducted for an optimal processing and an apparatus for manufacturing a laser welded tube for one-body formed bumper beam. The tube dimensions used in calculation were the thickness of 1.4 mm, the diameter of 105.4 mm and the length of 2000 mm. The tube was formed of a cold rolled high strength steel plate(tensile strength of 600 MPa). The two-roll bending method was the optimal tube forming process in comparison with the UO-bending method, the bending method on the press brake, the multi-step continuous roll-forming method and the 3-roll bending method. Monitoring of the welding quality was conducted and the seam tracking along the butt-joint lengthwise to the tube axis was also examined. The longitudinal butt-joint was welded by using a $CO_2$ laser welding machine equipped with a seam tracker and a plasma sensor. The $CO_2$ laser tube welding machine could be used for precise seam tracking and real-time monitoring of the welding quality. As a result, the developed laser welded tube could be used for a one-body formed automobile bumper beam.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2009.10a
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• pp.177-180
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• 2009

Tube hydroforming provides a number of advantages over the conventional stamping process, including fewer secondary operations, weight reduction, assembly simplification, adaptability to forming of complex structural components and improved structural strength and stiffness. A hydroformed vehicle body component has an attachment flange or the like-formed as an integral part of the hydroforming process. For a given flange shape, a parting plane for the dies is established relative to which the various surfaces of the flange shape, in cross section, have no significant reverse curvature. This study shows analysis results that form the flanged tubular parts in the hydroforming. The thickness variations and defects during the hydroforming for flange forming could be analyzed by FE analysis. FE analysis was performed by LS-DYNA/Dynaform 5.5.

• Proceedings of the Korea Institute of Applied Superconductivity and Cryogenics Conference
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• 2001.02a
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• pp.25-28
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• 2001

Bi-2212 HTS tube was fabricated by centrifugal forming process(CFP). As a variation of melt casting process(MCP) or centrifugal casting technique, the centrifugal forming process is a flexible method for manufacturing Bi-2212 bulk tubes and has been optimized to achieve smooth surface and uniform thickness. At this process, the slurry was prepared in the mixing ratio of 10:1 between Bi-2212 powder and binder and initially charged into the rotating mold under the speed of 300~450 rpm Heat-treatment was performed at the temperature ranges of 860 ~ $890^{\circ}C$ in air for partial melting. The HTS tube fabricated by centrifugal forming process at $890^{\circ}C$ under the rotating speed of 450 rpm was highly densified and the plate-like grains with more than 20$\mu$m were well oriented along the rotating axis. The measured Tc and Jc at 10K were around 85K and 3,000A/cm2 respectively.