• 대한기계학회논문집
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• 제19권6호
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• pp.1411-1421
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• 1995

A rigid visco-plastic finite element method has been developed for modeling superplastic forming processes. The optimum pressure-time relationship for a target strain rate and thickness distributions was predicted using two-node line element based on membrane approximation for plane strain and axisymmetric condition. Analysis of superplastic forming was carried out using the developed program and the numerical results were compared to the values available in the literature for plane strain problems. For description of the contact between the dies and sheet, the direct projection method was applied to the complicated problem and the validity of the scheme was tested. Experiments for the various geometries such as hemisphere and cone were performed with the developed forming machine using the calculated optimum pressure-time curves. Comparison between analysis and experiments showed good agreement.

• 한국정밀공학회:학술대회논문집
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• 한국정밀공학회 2004년도 추계학술대회 논문집
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• pp.796-799
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• 2004

The effects of forming presure, organic binder content and moisture on flexural strength were investigated. As moisture content increased in the granules during compaction, the density and strength of the green body were increased. Green strengths were found to improve more strongly with increasing forming pressure in the case of using the granules of higher organic content. The sintered strength was the highest with the organic content of 0.2wt％ under all forming pressures.

• 소성∙가공
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• 제24권1호
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• pp.20-27
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• 2015

Hot tensile tests were conducted at different temperatures ranging from $20^{\circ}C$ to $550^{\circ}C$ to evaluate the mechanical properties of Al5052 seamless tubes. Such tubes can provide the technological foundation for complex forming using hot air bulging. Hot air bulging is one of the recently developed hydroforming techniques and it has some limitations in terms of cycle times. The benefits of hot air bulging are weight and cost savings through part consolidation and reduced post-forming processes such as welding and piercing. In order to extend the forming limits of Al lightweight material hot air bulging was investigated. A heated tube was placed in a heated die and sealed at the ends by sealing cylinders. The heated tube was subsequently expanded against the die cavity wall by internal pressure using air medium. The results of the current study show that axial feeding speed and air pressure have an effect on the formability of Al tubes during air bulging at elevated temperatures.

• 한국정밀공학회지
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• 제16권11호
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• pp.122-132
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• 1999

This study describes a dynamic model of the hydroforming process which is used for precision forming of sheet metals. To help the controller design for the control of the forming pressure needed for this process as well as to investigate the effect of system parameters on the dynamic behavior, dynamic modeling is performed with emphasis on hydraulic servo system which actuates the forming machine. Since the model contains several unknown parameters, these were estimated via a least square parameter identification method. Based upon the identified model, a series of simulations were performed for various operating conditions. The results were compared with those of the experiments to verify the validity of the proposed model. The comparison study shows that the proposed dynamic model can describe dynamic behavior of the forming pressure of the hydroforming process to desirable accuracy.

• 연구논문집
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• 통권29호
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• pp.185-194
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• 1999

The shape and thickness distribution according to the pressure-time curve were carried out using the FEM and experiment. Also, mechanical properties were investigated. The square cup parts have been formed with pressure-time curve generated by result of analysis. The tensile strength and elongation have been investigated according to applied pressure conditions using the tensile test specimen obtained from the superplastic formed cup. We can use to predict the shape of formed part under the applied pressure using the FEM analysis. In the case of optimum pressure condition, the thickness distribution and mechanical properties were improved. From this study, we can find the important of optimum pressure-time condition. We have investigated about the forming of airplane part and fuel tank for motorcycle. If the applied load used in boundary conditions was appropriate, the simulation result coincides with the formed part. However, it is very difficult to define the pressure condition in complicated shape. Thus, it is need to develop the optimum pressure condition for superplastic forming.

• 한국산학기술학회논문지
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• 제19권9호
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• pp.1-6
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• 2018

하이드로포밍 기술은 지난 20년간 자동차부품의 적용을 중심으로 비약적인 발전을 해 왔다. 이 기술은 자동차 산업응용분야에 많은 장점을 가지고 있는데 이는 더 나은 구조적 강건성, 부품수 감소에 기인한 비용절감, 재료절약, 무게감소, 낮은 스프링백현상, 개선된 강도, 내구성 향상, 설계 유연성 등이다. 하이드로포밍 부품의 성형성 검토를 위하여 다양한 컴퓨터 시뮬레이션 기술 등이 발달해 왔으며 이를 통해 성형 가능성을 검토하는 것과 동시에 성형을 위하여 벤딩 공정, 프리포밍공정, 다이클로징 공정 등의 효율적인 공정을 수립하여 하이드로포밍 부품들을 설계하고 있다. 이에 본 연구에서는 하이드로포밍 부품 설계 시 고려사항 중 성형량, 부품의 단면길이(하이드로포밍 프레스 용량에 맞는), 최소 곡률(하이드로포밍 압력에 따른 곡률 영향 평가) 등을 제시하고 실제 자동차용 리어 서브-프레임 부품의 단면분석을 실시함으로써 하이드로포밍 성형을 위한 설계 방안을 제시하고자 한다. 아울러 하이드로포밍 공정인자 중 프리벤딩, 축피딩, 유압 압력, 프레스 하중, 마찰 등의 효과를 분석하여 이들 공정이 직접적인 하이드로포밍 성형에 필요인자 인지 등을 고찰하였다.

• 한국산학기술학회논문지
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• 제17권7호
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• pp.256-262
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• 2016

본 연구에서는 자동차 자동변속기의 핵심 부품인 아웃풋 허브 및 리액션 허브의 치형 미성형 구간의 최소화를 위한 배압 냉간 단조 성형 공법에 대한 유한요소해석을 수행하였다. 변위제어해석으로 펀치 하중 및 슬리브 배압력을 도출하였고, 도출된 하중 및 배압력을 이용한 하중제어해석을 수행하여 상호 검증을 하였다. 변위제어해석과 하중제어해석이 유사한 경향을 보였으며, 아웃풋 허브와 리액션 허브의 미성형 구간을 기준 이하로 만족시키기 위한 펀치 하중과 슬리브 배압력을 구하였다. 리액션 허브의 펀치 하중이 아웃풋 허브 보다 큰 이유는 상부 치형 가공 시 리액션 허브의 단면감소율이 아웃풋 허브 보다 크기 때문인 것으로 판단되며, 슬리브 배압력이 아웃풋허브와 리액션 허브에서 차이가 나는 것 또한 슬리브 단면적의 차이에 기인한 것으로 판단된다. 본 연구에서 제시한 배압 냉간 단조 성형 해석 과정과 결과를 적용한 실제 치형 가공의 미성형 구간 결과와 비교하여 검증 평가하였으며, 치형 제품의 품질 개선 및 생산성 향상을 위해 요구되는 성형가공 조건을 도출하는데 유용하게 활용될 수 있을 것이다.

• 한국소성가공학회:학술대회논문집
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• 한국소성가공학회 2003년도 추계학술대회논문집
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• pp.225-228
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• 2003

This paper is concerned with pressure welding, which has been known as a main bonding mechanism for the cold and warm clad forming. Bonding characteristics of pressure welding between the copper and aluminum plates are experimentally investigated. Experiments are performed at the cold and warm temperature range with the variation of important factors such as magnitude of pressure, surface roughness of Cu and Al plates, and pressure holding time. It could be concluded that the bonding criterion might be given as a function of bonding pressure and surface roughness for the cold and warm temperature ranges.

• 한국소성가공학회:학술대회논문집
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• 한국소성가공학회 2007년도 춘계학술대회 논문집
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• pp.314-317
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• 2007

Automotive rear subframe of aluminum tube was developed by using hydroforming process, based on the numerical analysis and physical tryouts. In the previous study, the effect of prebending was evaluated on the basis of forming limit diagram which had been obtained from free bulging, T-shape forming and cross-shape forming, using the developed tube hydroformability testing system. In order to get the sound products, appropriate internal pressure is to be imposed corresponding to the axial feeding. In this study, the loading path, the combination of internal pressure and axial feeding during the process, was optimized to ensure minimum thickness variation and dimensional accuracy, by using response surface method.

• 한국세라믹학회지
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• 제16권3호
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• pp.178-183
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• 1979

The carborundum abrasive specimens bonded with a soda-borosilicate glass were prepared. Samples fired at specified temperatures with various mixing ratio and forming pressure were examined in terms of the structure, bonding strength, and microscopic observations. Increasing the forming pressure up to 400kg/$\cm^2$, the structure became denser in proportion to the forming pressure. The bonding strength was generally increased with increasing the mixing ratio (Vb/Vg), but the bloating phenomena were observed when samples were fired above 95$0^{\circ}C$ with mixing ratio above 20%, consequently, the bonding strength was decreased. Samples fired at the temperature range 900~95$0^{\circ}C$ with mixing ratio 15~30% had the dense structure with various grades.