• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2008.05a
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• pp.39-42
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• 2008

Alloy 718 nozzle component was manufactured by hot working and electron beam welding process. In this process, domestic 718 materials were applied and evaluated. Hot compression tests were carried out at a lot of process conditions and microstructural evaluation was investigated. Using the results, FEM simulations were performed in order to optimize the hot working process. After hot working, forged work-pieces were machined and welded by electron beam. Final nozzle component were heat treated and their microstructure and mechanical properties were investigated.

• Journal of the Korean Society for Precision Engineering
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• v.13 no.3
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• pp.94-101
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• 1996

This paper presents an investigation of the ability of the scheme to simultaneously accomplish both prediction of fracture initiation and analysis of deformation in cold forged products. The Cockcroft-Latham criterion which is successfully applied to a variety of loading situations is used in the present investigation to estimate if and where surface and internal fracture occur during the deformation process. The numerical predictions and experimental results of two types of fundamental cold metal forming process taken into account are compared. Finite element simulation combined with fracture criterion has successfully predicted the site of surface or internal fracture initiation and corresponding to level of deformation observed experimentally.

• Transactions of Materials Processing
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• v.31 no.2
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• pp.51-56
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• 2022

In this study, finite element analyses were performed by applying a stress ring and split die design to relieve the tensile stress acting on the die due to high surface pressure during warm-closed forging. The applied material was a yield-ratio-control-steel (YRCS). It was used without quenching or tempering after forging. In the case of stress rings design, the number of stress rings and the tolerance for shrink fit were different. Vertical and horizontal splits were applied for insert die split design. Case 5 die with three stress rings, 0.2 % shrink fit tolerance, and vertical split was selected as an effective die design for tensile stress reduction. Based on die stress reduction analyses, Case 5 die for warm-closed forging was produced and smooth forgeability was secured, making it possible to manufacture forging product of yoke with the required geometry. In addition, controlled cooling using warm forging heat was applied to secure mechanical properties of yokes. When oil cooling was used for direct controlled cooling after warm-closed forging, a relatively uniform Rockwell hardness distribution and high mechanical properties could be obtained.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 1998.10a
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• pp.17-17
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• 1998

1970년대에 개발된 Ti-15-3 합금은 상온에서 우수한 성형성을 가지고 있어 Ti-6-4 합금보다 성형 공정을 대폭 감소시킬 수 있어 생산비용을 크게 감소시킬 수 있는 장점이 있는 합금이다. 또한, 냉간 성형성이 우수하고 강화 범위가 폭넓기 때문에 항공기의 프레임, 항공기 압력 용기 및 고장력 유압 튜브 등에 많이 사용하고 있으나, 열간 성형성이 Ti-6-4 티타늄 합금보다 좋지 않기 때문에 이제까지의 적용 분야는 판재 성형 등의 한정된 분야에만 적용되어 오고 있는 실정이다.

• Proceedings of the Korean Society of Tribologists and Lubrication Engineers Conference
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• 1995.06a
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• pp.1-10
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• 1995

베어링은 상대운동을 지지하거나 안내하는데 사용되는 부품으로 이의 특성은 원활하게 회전(또는 운동)할 수 있어야 하며 이와 관련된 내구성이 우수해야 하고 또한 신뢰성이 높아야 한다는 것이다. 원활한 회전을 하기위해서는 정밀도 높은 진원가공을 할 수 있어야 하며 이 특성은 베어링이 양산품 이라는 관점에서 경제성있는 생산을 해내야 하는 요구조선이 있다. 양산가공 기술로는 궤도륜에 해당하는 것으로 단조, 전조, 선삭, 연삭 가공기술이 있으며, 부품과 관련해서는 압출, 압조, 사출 가공기술이 있다. 이와 맞물려 양산 조립기술, 공작기계 제작 보수 기술, 정밀 측정기술이 필요하다고 하겠다.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2004.05a
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• pp.264-264
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• 2004

1990년에 일본 혼다 기연공업의 고성능 스포츠카(NSX)는, 올 알루미늄합금보디등에 알루미늄을 이용, 대폭 경량화시켜 화제를 모았으며 90년 전후부터는 스포츠카나 스페셜리티카로 불리우는 고성능 승용차의 보디외판과 발주위부품에 알루미늄부품이 잇달아 채용되기 시작하였다. 알루미늄부품의 채용이 정착한 최근에 와서, 승용차의 알루미늄화 움직임에 변화가 생겼다. 90년 이전에는 승용차의 발주위부품은 알루미늄단조품으로 경량화하는 것이 보통이었는데, 91년 가을경부터, 이것을 알루미늄 주조품으로 대체하는 방향으로 흐름이 바뀌었다.(중략)

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2008.10a
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• pp.431-434
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• 2008

In the present study, direct quenching of alloyed steel after hot forging was simulated using commercial finite element program, $FORGE^{TM}$. A typical heat treatment of alloyed steels consists of quenching for hard martensite and subsequent tempering for toughness. In the practice, forgings which cool down to room temperature are heated to temperature of austenite regime. As investigated in the present study, direct quenching of hot forged stock would be beneficial in terms of energy saving. This process has already been propose and termed as ausforging or forged hardening. However, it is well known that quenching temperature would be the most critical factor to control heat treated forging properties. And it is very difficult to control quenching temperature when forged stock gets directly quenched after forging. In this study, we have calculated final forging temperature of stock. Also, quenching simulation was conducted using a series of material parameter which were also calculated using JMATpro, a commercial program for physical properties of materials.

• Transactions of Materials Processing
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• v.17 no.7
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• pp.523-527
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• 2008

In this study, mechanical properties of Alloy 718 welded after forgings for jet propulsion component was investigated. Hot-forged and machined work-pieces($230mm\times70mm\times15mm$) which have different grain sizes are welded by electron beam welding technique. After welding, the components were solution heat-treated and aged. Samples were sectioned to analyze the microstructural evolution and formation of micro-crack. It was found that HAZ grain boundary liquation crack generally initiates in the coarse grains rather than the fine grains. Needle-like phases with high Nb contents were found at the outer part near the base metal. Vickers hardness and tensile tests were carried out at room temperature and at $649^{\circ}C$. The tensile properties of electron beam welding specimens exhibited around 100MPa and 10% decrease in strength and elongation, respectively.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 1997.04a
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• pp.584-588
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• 1997

Lots of forginfs used in automobile and aerospce industries are made in hot or cold working conditions, depending on the size and shape of a product. Usually the die design for new items has been first made on the basis of experiences and many know-hows accumulated in the company and then slightly modified through trial and error method to get the desired forgings without defects. Most of drawings at the die design stage have been manually drawn, butrecently some of forging companies have begun to apply a computer-aided drafting technique to the die design for reducing drafting time as well as repeatedly utilizing standardized parts form registerd data base. In this paper the automated die design technique for forward extrusion of axisymmetric forgings is developed by using AutoLISP language. For this study the representative die system is determined form the investigation of several types of forging dies being currently employed in the metal forming field and the design rules for cold extrusion die are summarized and programmed on a personal computer. A few design examples of forward extrusion die are given and discusses.

• Journal of the Korean Society for Heat Treatment
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• v.13 no.5
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• pp.303-308
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• 2000

The ring gears of automobile parts are manufactured generally process chart of which is as follows : forging ${\rightarrow}$ annealing or normalizing ${\rightarrow}$ rough machining ${\rightarrow}$ hardening(Quenching-Tempering or carburizing process) ${\rightarrow}$ finish machining. Isothermal annealing process after forging is most effective in the side of improvment of machinability. On this study we selected two kinds of steel;SCM415, SCM435 of most universal and investigated microstructures to find out most suitable condition of heat treatment in proportion continuous cooling and isothermal annealing. As the cooling rate is $5^{\circ}C$ per minute in continuous cooling process, martensite and bainite are coexisted with ferrite and pearlite in SCM435 steel. If the cooling rate is slower than $5^{\circ}C$ per minute, microstructure were only ferrite and pearlite but formation of band structure can't be avoid. On the other hand, microstructure is only ferrite and pearlite regardless of cooling rate because carbon content of SCM415 steel is low. Moreover formation of band structure isn't exposed by faster cooling rate. Most optimal temperature of the isothermal annealing is from $650^{\circ}C$ to $680^{\circ}C$ in SCM435 steel. When holding time is 60 minute with $650^{\circ}C$, the identical ferrite and pearlite microstructures can be obtained.