• 한국분말야금학회:학술대회논문집
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• 한국분말야금학회 2006년도 Extended Abstracts of 2006 POWDER METALLURGY World Congress Part2
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• pp.742-743
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• 2006

Filling of the tool die directly influences dimensional tolerances and density variation. To minimize the variations in filling, both within different sections of the cavity and from part to part, are of great importance for produce high quality P/M parts. Filling of the tool die is also one of the limiting factors in the productivity in powder pressing. By using aeration filling in combination with bonded powder mixes, both weight scatter and productivity can be improved. In this presentation results are presented showing the benefit of using aeration filling for different types of powders

• 한국세라믹학회지
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• 제32권4호
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• pp.462-470
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• 1995

The characteristics of spray-dried granules are important for dry pressing operation since they have great influences on die-filling, compaction ratio, and resulting green microstructure. An attempt was made to control granule morphology and the packing structure of fine Si3N4 particles in granules by adjusting suspension property. Mercury porosimetry was used to characterize the pore structures of both granules and green compacts. Finally, the effects of particle packing structure in granules and green microstructure on sintering behavior were investigated.

• 소성∙가공
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• 제12권3호
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• pp.228-235
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• 2003

In this paper, the workability of flange in the radial extrusion is analyzed in terms of the deformation pattern, the punch load and the forming limit by using simulation and experiment. A single action pressing is applied to both simulation and experiment. The analysis in this study is focused on the transient extrusion into the gap in radial direction with various gap heights and die corner radius. Based on the surface strains where surface cracking occurs, the forming patterns and strain-fracture relationships in producing radially extruded flange are obtained.

• 한국정밀공학회지
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• 제13권8호
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• pp.13-27
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• 1996

소성가공이란 원재료를 소성변형(Plastic deformation)을 통해서 고체의 제품을 만드는 가공법이다. 가공중에 물체의 질량과 체적에는 크게 변화가 없다. 소성 가공중 주응력이 어떻게 작용하느냐에 따라서 소성가공을 여러가지로 분류하고 있다. 즉, Metal Forming은 다음과 같이 분류할 수 있다. 1) Compound Forming에는, Rolling, Free forming, Die forming, Stamping, Pressing 2) Tension compression forming에는, Drawing, Deep-drawing, Rimming, Spinning, Bulge forming 3) Tension forming에는 Lengthening, Widning, Deepening 4) Bending에는 Bending with linear tool motion, Bending with rotary tool motion 5) Thrust forming에는 Swaging, Twisting이 있다.

• 한국분말야금학회:학술대회논문집
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• 한국분말야금학회 2006년도 Extended Abstracts of 2006 POWDER METALLURGY World Congress Part 1
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• pp.260-261
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• 2006

The behaviour of steel powder compacts during sintering has been investigated by dilatometry and X-ray computed microtomography. Dilatometry measurements showed that the anisotropic deformation results from various phenomena arising at different moments of the cycle including the delubrication stage. Microtomography provided 3D images of the microstructure induced by prior die pressing and its changes throughout sintering. Finally a schematic description of the main phenomena responsible for the deformation of metal powder compacts during sintering is proposed.

• 한국자기학회:학술대회 개요집
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• 한국자기학회 2002년도 동계연구발표회 논문개요집
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• pp.232-233
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• 2002

Nanostructed high energy Nd-Fe-B based bulk magnet can be prepared by hot-working process (hot press and die-upset) from melt-spun amorphous or nanocrystalline powder.[1] Recently, we have investigated a modified method, current-applied pressure-assisted (CAPA) process, to produce nanocrystalline isotropic and anisotropic NdFeB magnets. The process consists of current-applied pressing the melt-spun powders to obtain isotropic precursor subsequent current-applied deforming the precursor to obtain textured magnet.[2-3] (omitted)

• 한국기계가공학회지
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• 제11권1호
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• pp.101-106
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• 2012

The press bulging process is very useful and productive method to produce round-type mechanical components which have not been able to be manufactured because of limitation of the conventional press technology. The application of the press bulging process has expanded very quickly in the hydraulic and electronic industry and more recently it has been used to produce other mechanical parts such as the automobile and shipping parts. This expanding application also has brought some unsolved problems and leads many researchers to put their effort into the die design of the press bulging process. In this study, to obtain the optimum die shape for the press bulging process, various process parameters have been considered such as corner radius, bulging height, pressing length, and forming load, etc. The main interest of this paper is to verify the press bulging process which has more than 4.0 in height-length ratio. From this aspect, Finite Element analysis shows great ability to simulate the precise deformation process and gives us manufacturing database. Consideration of strain, stress, and strain-rate for the various cases has been also taken to keep the forming load within a particular range.

• 한국군사과학기술학회지
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• 제11권4호
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• pp.83-91
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• 2008

The development of the equal channel angular pressing(ECAP) process in metals has recently provided a feasible solution to produce ultra-fine or nano-grained bulk materials with tailored material properties. However, ECAP process is difficult to scale up commercially due to requirements of an excessive load. In this paper, a new Hybrid-ECAP process with torsional die is considered to obtain materials of ultra-fine grain structure under low forming load. An upper bound analysis and numerical simulation (DEFORM 3D, a commercial FEM code) are carried out on the torsional die. By the upper bound analysis, analytical expression for the compression force and rotation speed are obtained. By the FEM analysis, the distribution of strain, stress and deformation are obtained. These results show that the Hybrid-ECAP is a useful process because this process can obtain the homogeneous deformations with relatively low forming load. Additionally, due to decreased forming load, die life can be improve.

• 한국정밀공학회지
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• 제18권1호
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• pp.44-55
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• 2001

The flow behavior of semi-solid materials (SSM) is required to assist the industrial application of thixoforming technology. Particularly, to reduce many lead times, many numerical analysis packages have been developed to simulate required metal forming processes. The objectives of the development of SEMI-FORM for thixoforming process design are to predict the effect of various process variables such as pressing force, die temperature, and die velocity. However, there have not been any reports which adapt these packages to the specific characteristics of SSM. SO, this paper presents an overview of the development of thixoforming simulator of SEMI-FORM. The solver and post-processor of SEMI-FORM S/W for an automated thixoforming process design with arbitrarily shaped die are composed of FORTRAN Power Station 4.0 and Visual Basic 5.0, respectively. This developing SEMI-FORM S/W would be very useful for thixoforming practitioners and engineers to select the optimal process conditions to produce automotive parts with high quality.

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