• 한국소성가공학회:학술대회논문집
• /
• 한국소성가공학회 2004년도 춘계학술대회 논문집
• /
• pp.198-201
• /
• 2004

Aluminum alloys have high potential for weight reduction in automotive and other applications. But aluminum alloys have relatively low tubular hydroformability which can be enhanced by conducting the hydroforming at elevated temperatures. Hot working processes are commonly used in bulk forming such as forging and rolling, but still is rare in sheet metal forming like hydroforming. In this study hydroforming test at elevated temperatures is performed by special designed induction heating system to investigate the hydroformability of aluminum alloys. The high temperature formability characteristrics are obtained by 1?fitting forming test and circular bulging test and the effects of the process parameters such as feeding amount, internal pressure and temperatures on the tubular forming limits are mainly investigated.

• 한국정밀공학회지
• /
• 제13권2호
• /
• pp.102-109
• /
• 1996

Effects of frictional laws on finite element solutions in metal forming were investigated in this paper. A rigid-viscoplastic finite element formulation was given with emphasis on the frictional laws. The Coulomb friction and the constant shear friction laws were compared through finite element analyses of compression of rings and cylinders with different aspect ratios, ring-gear forging, multi-stage cold extrusion and hot strip rolling under the isothermal condition. It has been shown that two laws may yield quite different results when the aspect ratio of a process and the fractional contact region are large.

• 소성∙가공
• /
• 제17권1호
• /
• pp.5-8
• /
• 2008

As the semi-solid forming technology has a lot of advantages compared to the die casting, squeeze casting and hot/cold forging, it has been studied actively. This paper focuses on the thixoforging of the rheological materials fabricated by the spiral mechanical stirring equipment with A356 casting aluminum alloy and A6061 wrought aluminum alloy. Formability tests of rheological materials fabricated by spiral mechanical stirring were carried out and the microstructures of forged sample were observed. After thixoforging experiment, the heat-treated conditions of forged samples are investigated to improve the mechanical properties. These results are able to suggest the possibility of commercialization for rheological materials fabricated by spiral mechanical stirring.

• 소성∙가공
• /
• 제12권4호
• /
• pp.340-347
• /
• 2003

In the rigid-plastic finite element simulation of hot forging processes using hexahedral mesh, remeshing of a flash is important for design and control of the process to obtain desirable defect-free products. The mesh compression method is a remeshing technique which enables the construction of an effective hexahedral mesh in the flash. However, because the mesh is distorted during the compression procedure of the mesh compression method, when it is used in resuming the analysis, it causes discretization error and decreases the conversance rate. Therefore, mesh smoothing is necessary to improve the mesh quality. In this study, several geometric mesh smoothing techniques and optimization techniques are introduced and modified to improve mesh quality. Then, the most adaptive technique is recommended for the mesh compression method.

• 한국정보처리학회:학술대회논문집
• /
• 한국정보처리학회 2018년도 추계학술발표대회
• /
• pp.641-644
• /
• 2018

열간 자유 단조는 고온으로 가열한 강피에 압력을 가하여 원하는 형상을 빚는 공정이다. 가열로에서 여러 개의 강피를 동시에 가열하며 목표 온도에 도달하면 꺼내어 다음 공정을 진행한다. 이때 가열로에 투입하는 소재의 조합과 후단 공정을 위해 소재를 꺼내는 순서가 가열로의 에너지 효율에 영향을 끼친다. 본 논문에서는 열간 자유 단조의 에너지 효율을 높이기 위한 비용 예측 모형 기반 작업 계획 최적화 방안을 제안한다. 유전 알고리즘을 이용하여 가열로 강피 조합을 최적화하며 각 설비별 작업 할당 규칙에 따라 전체 작업 계획을 수립한다. 시뮬레이션 기반으로 후보 작업 계획을 평가하여 계획을 최적화 하며 이를 위해 각 설비별 공정 소요 시간 및 에너지 사용량 예측 모형을 이용한다. 예측 모형은 공정 데이터를 기반으로 기계 학습 알고리즘을 적용하여 학습한다. 또한 주기적인 재계획을 통해 예측의 불확실성으로 인해 작업의 진행이 계획대로 이루어지지 않는 문제점을 해결하고자 한다.

• 한국산학기술학회논문지
• /
• 제13권1호
• /
• pp.8-13
• /
• 2012

Ti-3Al-2.5V 잉고트를 제작하고 직경 9mm 합금타이타늄 wire로 가공하여 수입소재와 비교하여 그 특성을 조사하였다. 잉고트는 산소함량이 0.11wt%이고 철 함량이 0.085wt%로서 ASTM Gr.9 규격을 만족하였다. 9mm 합금 타이타늄 wire 경도는 225-250Hv로 비슷한 결과를 얻었고, 인장강도는 수입소재가 804MPa이고, 국내 개발품은 734MPa이었다. 연신율은 수입소재가 12%이고 국내 개발품은 22%였다. 직경 400mm 잉고트에서 단조 및 다단 열간 압연공정을 통해 직경 9.0mm 타이타늄합금선재를 제작하는 새로운 제작공정을 개발하였다.

• 소성∙가공
• /
• 제22권6호
• /
• pp.323-327
• /
• 2013

In this paper, the flow lines as a function of product design as well as the forging process design are explored using typical application examples. The prediction of flow lines using metal forming simulation technology is introduced along with their characterization. Experimental studies have shown that the metal flow lines have a strong influence on the structural rigidity of the final product. In this study we present several typical applications. One example is the case of severely cut metal flow lines during machining, especially in the region where periodic contacting forces are applied. Another example is the case of abnormal distortion of flow lines which can cause too much elongation or hot shortness due to viscous heating in the region of distortion. A third example is the case of a macrosegregation region which needs to be controlled so it is not adjacent to the region where the force is applied in the use of the final component. An example of weight reduction for an automobile component with improved flow lines is also introduced. These typical applications can provide process engineers with the insight in designing automobile or mechanical components as well as in designing the manufacturing methods to produce various parts.

• 한국추진공학회지
• /
• 제4권1호
• /
• pp.1-12
• /
• 2000

유도탄의 성능 향상을 위해 추진기관의 경량화가 요구되고 있으며 연소관 모타 마개의 경우, Ti 합금 (Ti-6Al-4V)이 사용되고 있다. 제작 과정 중에 열간 형단조 공정이 이용되나 이 과정에서 Ti alloy의 좁은 성형 온도 구간 관계로 단조시 국부적 소성 변형 집중에 의한 결함이 단조품의 다수 생성되며, 심한 경우 전단 파단까지 이르고 있다. 성형 과정에서 금형과의 접촉에 의한 Ti 합금 온도 하강이 전단 파단 발생과 밀접한 관계를 갖고 있으며 따라서 각 단조 조건에 따른 Ti 합금의 내부 및 표면에 대한 변형 및 온도의 분포가 관찰되었다. 아울러 전단 밴드 형성에 대한 별도의 분석도 포함되었다.

• 한국분말야금학회:학술대회논문집
• /
• 한국분말야금학회 1997년도 추계학술강연 및 발표대회 강연 및 발표논문 초록집
• /
• pp.7-7
• /
• 1997

During sintering of very porous green bodies, as obtained by compaction of hard powders - such as tungsten carbide or ceramics - or by injection moulding, important shrinkage occurs. Due to heterogeneous green density field, gravity effects, friction on the support, thermal gradients, etc., this shrinkage is often non-uniform, which' may induce significant shape changes. As the ratio of compact dimension to powder size is very high, the mechanics of continuum is relevant to model such phenomena. Thus numerical techniques, such as the finite element method can be used to simulate the sintering process and predict the final shape of the sintered part. Such type of simulation has much been developed in the last decade firstly for hot isostatic pressing and next for die compaction. Finite element modelling has been recently applied to free sintering. The simulation of sintering should be based on constitutive equations describing the thermo-mechanical behaviour of the material under any state of stress and any temperature which may arise within the sintering body. These equations can be drawn either from experimental data or from micromechanical models. The experiments usually consist in free sintering and sinter-forging tests. Indeed applying more complex loading conditions at high temperature under controlled atmosphere is delicate. Micromechanical models describe the constitutive behaviour of aggregates of spheres from the deformation of two-sphere contact either by viscous flow or grain boundary diffusion. Such models are not able to describe complex microstructure and mechanisms as observed in real materials but they can give some basic information on the formulation of constitutive equations. Practically both experimental and theoretical approaches can be coupled to identify the constitutive equations. Such procedure has been performed for modelling the sintering of compacts obtained by die pressing of a mixture of tungsten carbide and cobalt powders. The constitutive behaviour of this material during sintering has been described by a linear viscous constitutive model, whose functions have been fitted from results of free sintering and sinter-forging experiments. This model has next been introduced in ABAQUS finite element code to simulate the sintering of heterogeneous green compacts of various geometries at constant temperature. Examples of simulations are shown and compared with experiments.

• 한국분말재료학회지
• /
• 제31권1호
• /
• pp.50-56
• /
• 2024

We report the effect of plastic deformation on the thermoelectric properties of n-type Bi₂Te_2.5Se_0.5 compounds. N-type Bi₂Te_2.5Se_0.5 powders are synthesized by an oxide-reduction process and consolidated via spark-plasma sintering. To explore the effect of plastic deformation on the thermoelectric properties, the sintered bodies are subjected to uniaxial pressure to induce a controlled amount of compressive strains (-0.2, -0.3, and -0.4). The shaping temperature is set using a thermochemical analyzer, and the plastic deformation effect is assessed without altering the material composition through differential scanning calorimetry. This strategy is crucial because the conventional hot-forging process can often lead to alterations in material composition due to the high volatility of chalcogen elements. With increasing compressive strain, the (00l) planes become aligned in the direction perpendicular to the pressure axis. Furthermore, an increase in the carrier concentration is observed upon compressive plastic deformation, i.e., the donor-like effect of the plastic deformation in n-type Bi₂Te_2.5Se_0.5 compounds. Owing to the increased electrical conductivity through the preferred orientation and the donor-like effect, an improved ZT is achieved in n-type Bi₂Te_2.5Se_0.5 through the compressive-forming process.