• 한국정밀공학회:학술대회논문집
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• 한국정밀공학회 1996년도 춘계학술대회 논문집
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• pp.206-211
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• 1996

Closed-die forging of external spine is analysed using an upper bound elemental technique. The kinematically admissible velocity field for three-dimensional deformation in forging of the external spine with trapezoidal teeth was obtained. The upper bound to the deforming load necessary and the the deformed configurations are predicted using integration of the formulation of energy expressions which were obtained from B(upset forging method) were considerd in the present analysis and the theoretical results compared with experimental ones Experiments were carried out on plasticine as model material at room temperature where talcum powder was used as a lubricant. The present investigation revealed that the analytical method B predicts a reducet forging load and improved configuration better than method A for the forged products.

• 한국분말재료학회지
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• 제3권2호
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• pp.104-111
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• 1996

In order to obtain homogeneous and high quality products in powder compaction forging process, it is very important to control stress, strain, density and density distributions. Therefore, it is necessary to understand quantitatively the elasto-plastic deformation and densification behaviors of porous metals and metal powders. In this study, elasto-plastic finite element method using Lee-Kim's pressure dependent porous material yield function has been used for the analysis of three dimensional indenting process. The analysis predicts deformed geometry, stress, strain and density distribution and load. The calculated load is in good agreement with experimental one. The calculated results do not show axisymmetric distributions because of the edge effect. The core part which is in contact with the indentor and the outer diagonal edge part are in compressive stress states and the middle part is in tensile stress state. As a results, it can be concluded that three dimensional analysis is more realistic than axisymmetric assumption approach.

• 한국분말야금학회:학술대회논문집
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• 한국분말야금학회 2006년도 Extended Abstracts of 2006 POWDER METALLURGY World Congress Part2
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• pp.710-711
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• 2006

High strength PM aluminium alloys Al-Zn-Mg-Cu (7075 type) were studied by using commercially available powder blends and the sinter-forging technique for component production. Principal areas of focus include the response to PM processing, micro structural assessment and material properties of Aluminium sinter forged products. Green preforms are successfully sintered to near full density by solid-supersolidus liquid phase sintering. Sinter forging method can produce components with net shape and mechanical characteristics of the material have improved greatly. Properties of this new PM Al-alloy were found to be reproducible in an industrial production environment.

• 대한기계학회논문집A
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• 제20권7호
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• pp.2182-2195
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• 1996

Densification characteristics and behavior of tool steel powder compact during high temperature forming processes were investigated under pressure less sintering, sinter forging and hot isostastic pressing. In pressureless sintering, full density was obtained at a closely controlled temperature near the solidus of the material. Finite element calculations from constitutive model for densification by power law creep and diffusional flow were compared with experimental data. Agreements between theoretical calculations and experimental data were good in hot isostatic pressing but not as good in sinter forging.

• 한국정밀공학회:학술대회논문집
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• 한국정밀공학회 2005년도 추계학술대회 논문집
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• pp.158-161
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• 2005

In this paper, the precision electric discharge machining technology, the powder electric discharge machining technology, is applied to making a cold forging die for making the helical type of clutch gear. Various working conditions are investigated with emphasis on reduction of the electrode wear and enhancement of the surface roughness. Through the research work, the key technology of making the helical gear forging dies is achieved.

• 열처리공학회지
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• 제36권5호
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• pp.270-276
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• 2023

In this study, we analyzed two types of cold forging dies commonly used for manufacturing general nuts and screws to investigate the differences in WC powder according to the lifespan. For both Type I and Type II dies, it was observed that as the lifespan of the molds increases, the area fraction of Co becomes larger and the size of the powder becomes smaller. Moreover, there is a trend where the strength also increases as the lifespan gets longer. Actually, the hardness value of the sample with the longest lifespan is ~ 131 HV higher than the specimen of the shortest lifespan, It is noted that the reduction in toughness of the WC-Co mold is caused by insufficient Co and the decrease in contact surface area of WC-Co results in a reduced bonding surface area. The lifespan of cold-working WC molds increases when the W content and the volume fraction of WC are high, and the size of the WC powder is small. The results can significantly enhance producing high-quality molds with an extended lifespan using WC powder for cold forging.

• 소성∙가공
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• 제21권1호
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• pp.13-18
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• 2012

During warm forging, materials are formed in the temperature range of $300^{\circ}C\sim900^{\circ}C$. In this temperature range, the friction between the forging die and the material is very high and has a negative effect on the forming process causing severe die wear and possible defects in the component because of stick-slip. Thus, lubrication characteristics are a very important factor for productivity during warm forging. In this paper, ring compression experiments were conducted to estimate the friction factor between the die and the materials as the main factor in characterizing the lubricant. Also, ring tests using normal graphite power as a lubricant coating system were compared with tests using nano graphite powder. The results confirm that the nano graphite is superior to the normal graphite in view of its lubricating effect. In addition, the friction factor (m) was estimated with respect to the amount of the nano graphite content in the lubricant. With 10 % nano graphite the friction factor had the lowest value as compared to other amounts. It can be concluded that the amount of the nano graphite in the coating system can be optimized to obtain the best lubrication condition between the die and the material using ring test experiments.

• 한국정밀공학회:학술대회논문집
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• 한국정밀공학회 1996년도 추계학술대회 논문집
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• pp.134-138
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• 1996

A simple kinematically admissible velocity field for closed-die forging of clutch teeth is analysed which takes account of the profiled teeth chosen kinematically by approximating these as straight taper teeth. The upper bound load and the deformed configurations are predicted by the velocity field at varying punch movements considering differing frictional factors. Experiments were carried out using a model material of plasticine at room temperature where talcum powder was used as a lubricant. The theoretical predictions of the forging load and the relative pressures are found to be in reasonably good agreement with the experimental results.

• 소성∙가공
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• 제8권2호
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• pp.135-142
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• 1999

Tube Process(TP) is one of the processes to produce permanent magnets. Advantage claimed for this process is that it can accmplish both densification and anisotropication in one step forming. This process is distinguished from other processes since it uses deformable tube for densification of powder magnets. TP has, however, difficulties in manufacturing permanent magnets from Nd-Fe-B green powder due to folding resulted from large height reduction and localized densification. Therefore, an adequate preform is necessary to reduce folding resulted from large height reduction and localized densification. Therefore, an adequate preform is necessary to reduce folding, lead magnets into almost desired final shape and get uniform densification. In this paper, preform design for TP is carried out without a deformable tube to investigate the behaviour of magnet sinter-forging. Preform design is accomplished to increase the effective magnet area with a near net shape and uniform densification.

• 한국분말야금학회:학술대회논문집
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• 한국분말야금학회 2006년도 Extended Abstracts of 2006 POWDER METALLURGY World Congress Part2
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• pp.778-779
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• 2006

Manufacturing technologies of micro parts were studied in nano grained Al-1.5mass%Mg alloy. During compressive test at $300^{\circ}C$, the Al alloy showed stain softening phenomenon by grain boundary sliding regardless of strain rate. Micro spur gear with ten teeth (height of $200{\mu}m$ and pitch of $250{\mu}m$) was fabricated with sound shape by micro forging. During micro forging, increase of applied stress induced by friction between material and die surface was effectively compensated by decrease of stress by strain softening behavior and as a result, flow stress increased only about 50 MPa more than that in compressive test