• Design & Manufacturing
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• 제17권1호
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• pp.56-63
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• 2023

In this study, the vibration signal of the mold was measured and analyzed to monitor the process information and characteristics during the press molding process. A necklace-type picture frame mold was used for press molding, and the vibration signal was measured by GY-61 acceleration sensor module attached to the surface of the upper (movable) mold base. The change of the vibration signal of the mold according to press speed was analyzed. As a result, the vibration signal had a large change at five sections: "Holder contact", "Punch contact and start of pressing", "End of pressing", "Mold open", and "Demolding". The time difference between "Punch contact and start of pressing" and "End of pressing" means the pressing time which is the actual time the material is molded under pressing pressure. The time intervals for each section, represented by the time interval between "Holder contact" and "Punch contact and start of pressing", can be used to compare and evaluate the press speed applied to the process. By comparing the vibration signals at 60 rpm and 90 rpm, the amplitude at the section of "Punch contact and start of pressing" increased as the press speed increased. This result means that as the press speed increases, more force and pressure is applied to the material. Also, the peak values of the other sections were found to increase as the press speed increased. It was found that the pressing time, the time interval between "Punch contact and start of pressing" and "End of pressing", decreases as the pressing speed increases. Similarly, press speed factor, the time interval between "Holder contact", and "Punch contact and start of pressing", is found to be shorter. Therefore, based on the result of this study, the pressing time, press speed, pressing(punching) pressure of each cycle can be monitored by measuring the vibration signal of the mold. Also, it was confirmed that the level and trend of process information and characterization can be evaluated as the change of the mold vibration during press molding.

• 한국정밀공학회:학술대회논문집
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• 한국정밀공학회 2005년도 춘계학술대회 논문집
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• pp.1294-1298
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• 2005

In this study, combined micro press and surface finishing process are proposed to fabricate the micro nozzle array on a stainless steel sheet metal. In micro hole punching process the burr occurs inevitably, but the burr must be minimized in order to improve the quality and accuracy of the product. For this reason, subsequent magnetic field-assisted finishing technique is applied to remove the burr which exists around the nozzles for ink-jet printer head and proved to be a feasible for deburring by experiment. The deburring characteristics of sheet metals were investigated changing with polishing time and magnetic abrasive size. After the deburring, the burr size has remarkably reduced and roundness of the hole also has improved.

• 한국정밀공학회:학술대회논문집
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• 한국정밀공학회 2003년도 춘계학술대회 논문집
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• pp.1824-1827
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• 2003

The sheet metal shearing process is normally used in the precision elements such as semi-conductor components. In precision elements, burrs usually reduce the quality of machined parts and cause interference, jamming and misalignment during assembly procedures and because of their sharpness, they can be safety hazard to personnel. Furthermore, not only burrs are hard to predict and avoid, but also deburring, the process of removing burrs, is time-consuming and costly. In order to get the burr-free parts, therefore, we developed the precise burr measuring system using the laser. The laser burr measuring system consists of the laser probe, the photo detector, the achromatic doublet lens, and the rotary ＆ the X-Y table. In previous reports, we used simple vertical measuring method. But, as we used relatively bigger laser spot diameter and had the limited reflection angle, it was difficult to obtain the precise measuring results. So called, the spot size effect makes the profile of burr measured distorted and the burr height measured smaller. By introducing the novel laser measuring method which employing the achromatic lens system and the tilting mechanism, we could make the spot size smaller and get the appropriate beam direction angle. Through the experiments, the accuracy of the developed system is proved. The burr height measured during the punching process can be used for automatic deburring and in-situ aligning.

• 한국운동역학회지
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• 제13권3호
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• pp.151-162
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• 2003

The purpose of this study was to investigate the frequency of sports injury among Korean junior elite golf players. The survey was made through the questionnaire which consist of eight categories and 280 valid answers were used to perform frequency analysis. The results indicated that 197 out of 280 participants experienced golf injuries (30%: during a game, 70%: during a practice) and 70% of them also experienced injuries within a year. The frequency analysis for the site of injury has shown that back was the most vulnerable area for all players(33%), followed by the right wrist, left shoulder and elbow for male players. Among female players, left wrist was the second weak site of injury, followed by the right wrist, right thoracic spine, and left shoulder. A few of them also have shown abnormal symptoms of ruptured lumbar disk, scoliosis, and lordosis and these injuries might be caused by the lack of flexibility and the fatigue due to over-practice. High frequency of wrist injury also demonstrated that excessive chopping or punching shot and poor environmental course conditions may cause this injury to be common. Overall, lack of warm up time, lack of strength and flexibility, and excessive amount of practice were the major reasons of injury for the junior elite golfers in Korea. The study also proved that these young Korean golfers actually had more chances to be faced with the injury than average. Thus, it is necessary to develop systematic and scientific methods of training, and prevention, treatment of these injuries with medical professionals.

• Steel and Composite Structures
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• 제17권3호
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• pp.339-358
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• 2014

Exodermic deck systems are new composite steel grid deck systems which have been used in various projects during the past decade. One of the eminent features of this system is considerable reduction in the structure weight compared to the ordinary reinforced concrete decks and also reduction in construction time by using precast Exodermic decks. In this study, dynamic properties of the Exodermic deck bridges with alternative perfobond shear connectors are investigated experimentally. In order to evaluate the dynamic properties of the decks, peak picking and Nyquist circle fit methods are employed. Frequencies obtained experimentally are in good agreement with the results of the finite-element solution, and the experimental results show that the first mode is the most effective mode among the obtained modes. The first four modes are the rigid translational motion modes, and the next two modes seem to be rigid rotational motion modes around a horizontal axis. From the 7th mode onwards, modes are flexible. The range of damping ratios is about 0.5%. Furthermore, the static behavior of the Exodermic decks under a static load applied at the center of the decks was investigated. Failure of the decks under positive bending was punching-shear. The bending strength of the decks under negative bending was about 50 percent of their strength under positive bending. In addition, the weight of an Exodermic deck is about 40% of that of an equivalent reinforced concrete slab.

• 전산구조공학
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• 제4권4호
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• pp.79-89
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• 1991

유한요소법을 이용하여 적용범위가 제한되고 부정확한 기존의 설계방법을 대치할 수 있는 새로운 철근 콘크리트 슬래브 설계법을 제시하였다. 제시된 방법을 이용하면 어떠한 기하형태의 슬래브 시스템에 대해서도 정확하고 효율적인 설계결과를 얻게된다. 슬래브 설계에 사용되는 등매개 판요소는 적분에 소요되는 계산기간을 절감할 수 있도록 매우 효율적으로 유도되었다. 슬래브 철근의 설계는 강도설계법을 이용하였고, 시방서 최소 철근량과도 비교하였다. 해석결과 모멘트와 설계철근량은 컴퓨터 그래픽을 이용하여 일목요연한 등고선으로 도시하여 설계편의를 제고시켰다. 등매개 판요소의 정확한 전단력을 이용하여 전단에 대한 적절한 검토도 할 수 있게 하였다. 철근과 콘크리트의 균열을 고려한 비탄성 처짐계수법을 개발하여 사용하중하의 처짐을 적합하게 계산할 수 있도록 하므로써 슬래브의 사용성도 검토할 수 있도록 하였다. 개구부가 있는 원형 슬래브 예를 들어 비정형 슬래브 설계에도 제시하는 방법이 손쉽게 적용될 수 있음을 보여주었다.

• 콘크리트학회논문집
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• 제22권1호
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• pp.3-10
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• 2010

이 연구에서는 중력 전단비에 따른 철근콘크리트 플랫 플레이트 골조의 내진성능을 평가하였다. 이를 위하여, 이 연구에서는 3층, 7층 골조를 중력하중만 고려하여 설계하고, 대상 건물에 대한 비선형 정적 푸쉬 오버 해석과 비선형 동적 해석을 수행하였다. 그리고 이 연구는 그 비선형 해석에서 중력 전단비의 차이에 따른 뚫림 전단과 파괴 메커니즘을 예측할 수 있도록 제안한 슬래브-기둥 접합부 모델을 사용하였다. 이 연구 결과에 따르면 중력 전단비가 골조의 내진성능에 큰 영향을 미치는 것으로 나타났다. 특히 중력 전단비가 커짐에 따라 골조 접합부의 파괴가 취성적인 파괴를 나타내어 내진 성능이 떨어지는 것으로 나타났다.

• Maxillofacial Plastic and Reconstructive Surgery
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• 제34권2호
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• pp.91-99
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• 2012

Purpose: The purpose of this study was to evaluate the expression of osteogenic genes associated with bone regeneration on anodizing titanium surface. Methods: $20{\times}20{\times}1$ (mm) commercially pure titanium plate was made, one group was pure titanium, second group was punched, and last group was punched and anodized by electrochemical method. Through the osteogenic cell culture model, the expression of extracellular matrix proteins, such as bone morphogenetic protein-2, bone sialoprotein, aggrecan, osteocalcin, Alkaline phosphatase, collagen I had been evaluated by Real-time polymerase chain reaction, and the morphology of growing cells was evaluated by scanning electron microscopy. Results: The attachment of mesenchymal stem cell was even and well-oriented on all Ti surfaces. The osteogene expression was increased on punching groups but, decreased on anodizing surfaces in 3 week samples. Conclusion: Punched anodizing Ti has possibility be using as a dental implant material, but further in vivo study would be needed.

• 소성∙가공
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• 제30권6호
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• pp.291-300
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• 2021

Currently, starting with electric vehicles, the application of ultra-high-strength steel sheets and light metals has expanded to improve mileage by reducing vehicle weight. At a time when internal combustion engine vehicles are rapidly changing to electric vehicles, the application of ultra-high-strength steel is expanding to satisfy both weight reductions and the performance safety of the chassis parts. There is an urgent need to improve the quality of parts without defects. It is particularly difficult to estimate the part formability through the finite element method (FEM) in the burring operation, so product design has been based on the hole expansion ratio (HER) and experience. In this study, design of experiment (DOE), analysis of variance (ANOVA), and regression analysis were combined to optimize the formability by adjusting the process variables affecting the burring formability of ultra-high-strength steel parts. The optimal variables were derived by analyzing the influence of variables and the correlation between the variables through FE analysis. Finally, the optimized process parameters were verified by comparing experiment with simulation. As for the main influence of each process variable, the initial hole diameter of the piercing process and the shape height of the preforming process had the greatest effects on burring formability, while the effect of a lower round of punching in the burring process was the least. Moreover, as the diameter of the initial hole increased, the thickness reduction rate in the burring part decreased, and the final burring height increased as the shape height during preforming increased.

• Nuclear Engineering and Technology
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• 제54권10호
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• pp.3745-3765
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• 2022

The concrete structures related to nuclear safety are threatened by accidental impact loadings, mainly including the low-velocity drop-weight impact (e.g., spent fuel cask and assembly, etc. with the velocity less than 20 m/s) and high-speed projectile impact (e.g., steel pipe, valve, turbine bucket, etc. with the velocity higher than 20 m/s), while the existing studies are still limited in the impact resistant design of nuclear power plant (NPP), especially the primary RC slab. This paper aims to propose the numerical simulation and theoretical approaches to assist the impact-resistant design of RC slab in NPP. Firstly, the continuous surface cap (CSC) model parameters for concrete with the compressive strength of 20-70 MPa are fully calibrated and verified, and the refined numerical simulation approach is proposed. Secondly, the two-degree freedom (TDOF) model with considering the mutual effect of flexural and shear resistance of RC slab are developed. Furthermore, based on the low-velocity drop hammer tests and high-speed soft/hard projectile impact tests on RC slabs, the adopted numerical simulation and TDOF model approaches are fully validated by the flexural and punching shear damage, deflection, and impact force time-histories of RC slabs. Finally, as for the two low-velocity impact scenarios, the design procedure of RC slab based on TDOF model is validated and recommended. Meanwhile, as for the four actual high-speed impact scenarios, the impact-resistant design specification in Chinese code NB/T 20012-2019 is evaluated, the over conservation of which is found, and the proposed numerical approach is recommended. The present work could beneficially guide the impact-resistant design and safety assessment of NPPs against the accidental impact loadings.