• 소성∙가공
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• 제4권1호
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• pp.69-78
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• 1995

The arbitrary Lagrangian-Eulerian(ALE) finite element analysis is applied to the axisymmetric hot extrusion through continuous dies. In order to simulate hot forming problems, an ALE scheme for temperature analysis is proposed. The computed results are compared with experimental results as with those by pure Lagrangian method. In the present study mesh control is accomplished by the use of isoparametric mapping of quadrilaterals.

• 소성∙가공
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• 제8권2호
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• pp.178-187
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• 1999

The Cross rolling between flat jaws, as a kind of hot forging, is the forming method to make the axisymmetric multi-step shaft by its rotation and pressure between flat jaws which move in opposite direction. The purpose of this study is to propose the optimal geometric data for shape development of the forward forming region. All data described on this paper are quantified by experiment from initial shape design to final shape development. As the result, proper geometric data are proved that lenth of the first forming area in the forward forming region is 1.5 times larger than circumference of work-piece and the progress angle changes 3 times smoothly.

• 한국기계가공학회지
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• 제17권4호
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• pp.83-90
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• 2018

In this research, we developed a process design hot-forging technology that precisely forms an inner race. The inner race transmits power to a one-way clutch of an automatic transmission and minimizes the CNC machining allowance. For a multi-stage hollow shape (inner race), we proposed several shapes of blocker and finisher for the precision hot-forging process and analyzed the forging process using DEFORM. The hot-forging process was optimized for several parameters, such as metal flow pattern, forging defect, and forming load. Blockers and finisher dies in the hot-forging process were designed to select optimal shapes from finite element analysis, and experiments were conducted to optimize the hot-forging process.

• 대한기계학회논문집A
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• 제37권7호
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• pp.913-919
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• 2013

본 연구에서는 마그네슘 합금 AZ31을 적용한 배터리 팩 케이스를 개발하여 자체 진동 및 외부 충격으로부터 배터리를 보호하도록 하며, 기존 스틸 소재 대비 50% 이상 경량화하여 친환경 기술개발을 목적으로 한다. 또한, 제품의 복잡한 형상 및 마그네슘 소재의 특성으로 제품을 성형하기에는 힘든 측면이 많으므로 이를 해결하기 위해 마그네슘 합금소재의 온도별 최적성형조건을 제시하고자 한다. 즉 AZ31의 성형방법에 따라 상온, $230^{\circ}C$, $250^{\circ}C$ 및 $270^{\circ}C$의 4가지 조건하의 시험편으로 인장시험, 경도시험, 부식시험 및 피로시험 등을 실시하여 기계적 특성을 정량적으로 분석하였고, 또 FEM해석을 통하여 자동차 부품 배터리 팩 케이스 개발에 적용토록 하였다.

• Composites Research
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• 제35권2호
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• pp.93-97
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• 2022

열가소성 복합재의 핫프레스 성형공정에서 근적외선 가열의 적용은 소재를 성형온도까지 고속가열함으로써 공정 전체의 생산성을 확보할 수 있으나, 고에너지, 높은 성형온도, 고속가열에 의해 소재의 열화가 발생하여 재용융 성능 등의 소재 특성이 저하될 수 있다. 이에 본 연구는 고성능 항공소재로 활발히 연구개발되고 있는 Carbon fiber reinforced Polyetherketoneketone(CF/PEKK) 복합재에 적합한 핫프레스 성형공정의 최적화된 공정조건을 확립하기 위하여 근적외선 고속가열을 적용하였을 때, CF/PEKK 복합재에서 발생할 수 있는 열화 메커니즘과 그 특성을 형태학적, 열적 특성 및 기계적 성능 시험을 통해 평가하였다. 열화 반응에 따른 메커니즘 규명은 광학현미경을 활용하여 PEKK의 결정구조의 형태학적 조사를 기반으로 분석하였다. 그 결과, 열화가 진행됨에 따라 구결정의 크기가 감소하며 최종적으로 완전 열화 시 구결정이 소멸되는 것을 확인하였다. 열적 특성은 용융온도, 결정화온도, 발열량이 열화가 진행됨에 따라 감소하는 경향이 관찰되며, 460℃ 장시간 노출에서 결정구조가 소멸된 것을 확인하였다. 랩전단강도(Lap shear strength)시험 결과, 열화된 표면에서는 낮은 접합강도가 관찰되며, 접합면 분석에서 특정 면에서는 열에 의한 용융 특성이 나타나지 않았다. 결론적으로 CF/PEKK 복합재의 근적외선 고속가열 적용에 있어 특정 온도에서 열화 진행되며, 이에 구결정의 형태학적 변화와 열가소성 소재의 재용융 특성의 저하를 확인하였다.

• 한국소성가공학회:학술대회논문집
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• 한국소성가공학회 2003년도 춘계학술대회논문집
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• pp.23-26
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• 2003

This paper explains the die cooling method for improving tool life in the hot forging process. In continuous forming operation such as hot forging process, performed at high speeds, temperature increases of several hundred degrees may be involved. Die hardness was reduced due to thermal softening. Factor of die fracture are wear and plastic deformation of die due to hardness reduction by high temperature. Because die service life was reduced due to this phenomenon during hot forging, quantified data for optimal die cooling method is required. The new developed techniques for predicting tool life applied to estimate the production quantity for a spindle component and these techniques can be applied to improve the tool life in hot forging process

• 한국소성가공학회:학술대회논문집
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• 한국소성가공학회 2000년도 추계학술대회 논문집
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• pp.25-28
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• 2000

The flow stress of 304 stainless steel during high during hot forming process were determined by conducting hot compression tests at the range of 1273 K-1423 K and 0.05 /s-2.0 /s as these are typical temperature and strain rate in hot forging operation. Based on the observed phenomena, a constitutive model of flow stress was assumed as a function of strain, strain rate, temperature. Dynamic recrystallization was found to be the major softening mechanism with this conditions as previous studies. A finite element analysis was performed to predict the recrystallized volume fraction and the mean grain size in hot compression of 304 stainless steel.

• 소성∙가공
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• 제10권7호
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• pp.573-578
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• 2001

The flow stress of 304 stainless steel during hot forming process were determined by conducting hot compression tests at the range of 1273 K∼1423 K and 0.05 /s∼2.0 /s as these are typical temperature and strain rate in hot forging operation. In this material, Dynamic recrystallization was found to be the major softening mechanism with this conditions as Previous studies. Based on the observed phenomena, a constitutive model of flow stress was assumed as a function of strain, strain rate, temperature. In the constitutive model, the effects of strain hardening and dynamic recrystallization were taken into consideration. A finite element method connected to constitutive model was performed to predict the dynamic recrystallization behaviors and also stress-strain curves in hot compression of 304 stainless steel.

• 소성∙가공
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• 제24권1호
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• pp.13-19
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• 2015

For an accurate analysis of hot stamping, a coupled simulation with different aspects of the process(i.e. mechanical, thermal, and phase transformation) is needed. However, coupled simulations are time consuming and costly. Therefore, the current study proposes a simplified method focused on the forming for the hot stamping simulation of a coupled torsion beam axle (CTBA) tubular beam. In this simplified method, non-isothermal conditions were assumed and only conduction was considered, since it represents the majority of the heat transfer during hot stamping. In addition, temperature and strain rate effects were also included. Moreover, an isothermal simulation was conducted and compared with a non-isothermal simulation. Finally, the simulations were verified by experiments. In conclusion, the proposed method is shown to be effective for the development of tube-type parts, and it effectively predicts the deformation of the tubular beam during hot stamping.

• 한국소성가공학회:학술대회논문집
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• 한국소성가공학회 2007년도 춘계학술대회 논문집
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• pp.131-134
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• 2007

A semi-solid forming technology has a lot of advantages compared to the die casting, squeeze casting and hot/cold forging, so semi-solid forming has been studied actively. Semi-solid forming has two methods. One is thixoforming with reheating of prepared billet, the other is rheoforming with cooled melt until semi-solid state. Thixoforging technology can produce non-dendritic alloys for semi-solid forming complex shaped parts in metal alloys. In this study, the thixoforging was experimented with made rheology materials by the spiral stirrer equipment. Rheology materials for forging were made by A356 casting aluminum alloy and A6061 wrought aluminum alloy. After experiment, forged samples were measured microstructure and were heat treated for high mechanical properties.