• Composites Research
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• 제26권1호
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• pp.42-47
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• 2013

In this study, an economical and effective processing technique to form multiple dimples on the surface of a composite part, which are known to be useful to improve aerodynamic performance and heat dissipation. Forming dimples on the surface using molds is an expensive processing because forming multiple tiny positive spheres on the surface of the mold requires much time and effort. In this study, plates with multiple round holes are utilized as a core to form dimples on the carbon/epoxy composite skin covering the core. A vacuum bagging process is used to apply pressure on the surface while curing. Composite parts which have multiple dimples on the surface can be utilized in the field which needs high aerodynamic performance and heat dissipation ability such as high speed sports car bodies.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• 제18권12호
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• pp.1359-1369
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• 2007

This paper describes the technique of satellite direction finding and main beam steering of the adaptive array antenna system which is used for mobile TT&C(Tracking Telemetry&Command) system. To be able to control the satellite on mobile vehicle while moving, the relative directional information of the satellite to the mobile vehicle is necessary to make main beam to the direction of satellite. To do this MUSIC, which is one of the super-resolution algorithm of wave direction finding, is used and then the performance analysis and quantization problem of phase shifter are addressed. This paper is valuable in the respect of showing feasibility of designing the moble TT&C using adative array antenna system.

• Korean Journal of Computational Design and Engineering
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• 제12권4호
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• pp.255-262
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• 2007

In the finite element analysis of forming process, objects are described with a finite number of elements and nodes and the approximated solutions can be obtained by the variational principle. One of the shortcomings of a finite element analysis is that the structure of mesh has become inefficient and unusable because discretization error increases as deformation proceeds due to severe distortion of elements. If the state of current mesh satisfies a certain remeshing criterion, analysis is stopped instantly and resumed with a reconstructed mesh. In the study, a new remeshing algorithm using tetrahedral elements has been developed, which is adapted to the desired mesh density. In order to reduce the discretization error, desired mesh sizes in each lesion of the workpiece are calculated using the Zinkiewicz and Zhu's a-posteriori error estimation scheme. The pre-constructed mesh is constructed based on the modified point insertion technique which is adapted to the density function. The object domain is divided into uniformly-sized sub-domains and the numbers of nodes in each sub-domain are redistributed, respectively. After finishing the redistribution process of nodes, a tetrahedral mesh is reconstructed with the redistributed nodes, which is adapted to the density map and resulting in good mesh quality. A goodness and adaptability of the constructed mesh is verified with a testing measure. The proposed remeshing technique is applied to the finite element analyses of forging processes.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• 제17권6호
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• pp.580-585
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• 2004

Silicon dioxide (SiO$_2$) is widely used as a gate dielectric material for thin film transistors (TFT) and semiconductor devices. In this paper, SiO$_2$ films were grown by APCVD(Atmospheric Pressure chemical vapor deposition) at the high temperature. Experimental investigations were carried out as a function of $O_2$ gas flow ratios from 0 to 200 1pm. This article presents the SiO$_2$ gate dielectric studies in terms of deposition rate, refrative index, FT-IR, C-V for the gate dielectric layer of thin film transistor applications. We also study defect passivation technique for improvement interface or surface properties in thin films. Our passivation technique is Forming Gas Annealing treatment. FGA acts passivation of interface and surface impurity or defects in SiO$_2$ film. We used RTP system for FGA and gained results that reduced surface fixed charge and trap density of midgap value.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 한국소성가공학회 2009년도 추계학술대회 논문집
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• pp.267-270
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• 2009

In the present investigation, we are newly developing a new forming process which can fabricate micro patterns on large-area polymeric substrates for high speed mass production. The key idea of the new process is to pressurize multiple vacuum-packed substrate-mold stacks above the glass transition temperature ($T_g$) of the polymeric substrates. The new process is thought to be promising micro-pattern fabrication technique in three aspects; firstly, isostatic pressing ensures the uniform micro-pattern replicating condition regardless of the substrate area. Secondly, the control of forming condition such as temperature and pressure can realize well-defined process condition exploited in the conventional hot embossing research field. Thirdly, multiple substrates can be patterned at the same time. A prototype forming machine for the new process was developed with the design consideration realizing the present idea. With a developed machine, micro prismatic array patterns with 50 um in size were successfully made on the $380{\times}300{\times}6\;mm$ PMMA plate.

• Transactions of the Korean Society of Mechanical Engineers A
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• 제24권1호
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• pp.87-93
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• 2000

Warm, forming technique which is one of the new forming technologies to improve formability of sheet metal is applied to the cylindrical cup drawing of stainless-aluminum. clad sheets. In experiments the temperature of die and blank holder is varied from room temperature to 18$0^{\circ}C$, while the punch is cooled by circulation of coolant to increase the fracture strength of workpiece on the punch corner area. Test materials chosen for experiments are STS304-A1050-STS304, STS304-A1050-STS430 clad sheets and A1050-0 aluminum sheet. Teflon film as a lubricant is used on both sides of a workpiece. The limit drawing ratio as well as quality of drawn cups(distribution of thickness and hardness)are investigated and validity of warm drawing process is also discussed.

• Journal of the Society of Naval Architects of Korea
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• 제35권2호
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• pp.104-113
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• 1998

The line heating method is a popular technique used to form ship hull in shipyards. In order to promote shipbuilding productivity, some researchers have made progress in their studies on automatic fabrication system for plate forming. These researches have, however, focused on heat-induced plate deformation with particular mechanical modelings, and do not yet propose the heating paths applicable to actual plate forming process. In this paper, a new algorithm to determine heating lines is developed to simulate the line heating process. The important feature of this algorithm is that it calculates principal curvatures of deflection difference surface which represents difference between target surface and surface in fabrication. Several trials to typical surface types show its usefulness and good applicability to tactical use.

• Transactions of the Korean Society of Mechanical Engineers A
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• 제24권2호
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• pp.526-534
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• 2000

Near-net-shape forming of zirconia powder was investigated under the combination of cold die and isostatic pressing and pressureless sintering. A novel combination pressing technique, i.e., die com paction under cold isostatic pressing, allowed to produce a complex shaped ceramic powder compact with the controlled dimensions and relatively uniform density distributions. The constitutive models proposed by Kim and co-workers for densification of ceramic powder under cold compaction and high temperature were implemented into a finite element program (ABAQUS). Experimental data for relative density distributions and deformations of zirconia powder compacts produced by cold combination pressing and pressureless sintering were compared with finite element results. Finite element results agreed well with experimental data.

• Journal of the Korean Society of Manufacturing Technology Engineers
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• 제26권1호
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• pp.59-65
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• 2017

A seat track product is a car seat part that provides a base for vehicle seats. An ultra-high strength steel sheet is used to reduce the weight of vehicle body parts. However, the formability of an ultra-high strength steel sheet is poor because of its very low elongation and very high elastic deformation. For this reason, a new forming technology of an ultra-high strength steel sheet is required. The influence of spring-back of seat track parts on the shape freeze in forming processes was investigated to be solved by adjusting the appropriate tool design such as minus clearance between punch and die, and punch angle. This paper describes how to apply the spring-back prevention technique for improving shape freeze by using the ultra-high strength steel sheet with 980MPa to develop lightweight seat tract parts.

• Transactions of the Korean Society of Automotive Engineers
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• 제4권5호
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• pp.16-25
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• 1996

In the present work a rigid-plastic finite element formulation using dynamic explicit time integration scheme is proposed for numerical analysis of auto-body panel stamping processes. The rigid-plastic finite element method based on membrane elements has long been employed as a useful numerical technique for the analysis of sheet metal forming because of its time effectiveness. A damping scheme is proposed in order to achieve a stable solution procedure in dynamic sheet forming problems. In order to improve the drawbacks of the conventional membrane elements, BEAM(abbreviated from Bending Energy Augmented Membrane) elements are employed. Rotational damping and spring about the drilling direction are introduced to prevent a zero energy mode. The lumping scheme is employed for the diagonal mass matrix and linearizing dynamic formulation. A contact scheme is developed by combining the skew boundary condition and the direct trial-and-error method. Computations are carried out for analysis of complicated auto-body panel stamping processes such as forming of an oilpan, a fuel tank and a front fender. The numerical results of explicit analysis are compared with the implicit results with good agreements and it is shown that the explicit scheme requires much shorter computational time, especially when the problem becomes more complicated. It is thus shown that the proposed dynamic explicit rigid-plastic finite element method enables an effective computation for complicated autobody panel stamping processes.