• 기계와재료
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• v.23 no.3
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• pp.96-113
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• 2011

녹색기술 및 친환경 공정의 필요성이 급증함에 따라 재료이용률 향상을 지향하는 차세대 압출공정의 대두가 필요하게 됨에 따라 유압 CNC(Servo) 제어를 이용한 가변단면 압출기술을 개발하게 되었다. 이러한 가변단면 압출(Varied section extrusion, VSE)기술은 공정 중에 압출구를 빠져 나가는 소재의 단면 형상을 변화시켜 재료이용률을 향상을 도모하였으며, 후가공 공정의 생략도 가능하여 국내 압출업체의 생산원가 절감 및 글로벌 기술경쟁력 확보에 큰 도움을 줄 수 있을 것이다. 아직은 소수의 선진국에서 시도한바 있으나 양산품 적용에는 생산원가 및 생산속도, 상품성 등에 문제가 있어 자동차 부품 적용에 한계를 보이고 있는 기술이다. 따라서 본 연구팀이 가변단면 압출용 금형을 포함한 최적의 압출공정 및 양산성 문제의 해결점을 거의 확보하고 있는 단계로 세계를 선도하는 리딩기술(Leading technology)을 보유하게 됨으로써 국가의 기술경쟁력 향상에 중요한 역할을 수행할 수 있을 것이다. 본 연구의 내용을 요약하여 정리해 보면 첫째로는 CNC 제어 가변단면 압출공정에 대하여 자세하게 소개하고 특징 및 장 단점을 설명하였으며, 자동차 부품군에로의 적용에 많은 이점들을 갖고 있음을 설명하였다. 두 번째로는 가변단면 압출을 위한 이동 금형(Moving die)부품을 갖는 구조의 압출금형에 관하여 기존의 압출금형과 비교하여 설명하였으며, 가변단면 압출용 금형의 구조 및 메커니즘의 최적화를 이루고자 하였다. 세 번째로는 가변단면 압출공정을 실현하기 위한 CNC 제어 압출시스템에 대하여 간략히 설명하였다. 네 번째로는 자동차 부품 적용을 위한 정밀 압출공정으로서 가변단면 압출공정에 대하여 유한요소해석을 통하여 가변단면 압출공정 변수 및 금형 변수 등에 대한 엄격한 검토를 선행적으로 수행하여 양산성 확보를 위한 정보들을 분석 정리하였다. 끝으로는 세 가지 단면형태를 갖는 가변단면 압출제 시제품에 대하여 CNC 제어 가변 단면 압출공정의 상용화 가능성을 확인 적용성 검토를 완료하였다. CNC 제어 가변단면 압출기술은 압출공정에 있어서 많은 경험과 기술적 검토가 선행되어져야 하는 고부가가치 성형공정으로써 재료 이용률을 획기적으로 향상시킬 수 있는 압출공법으로 향후 자동차 부품 뿐만아니라 다양한 알루미늄 제품군에 적용이 가능하다고 판단된다.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.34 no.3
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• pp.299-305
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• 2010

In general, the flexible forming die that has been used in the flexible forming process has the identical punch size; hence, its flexibility is relatively low because the range of allowable curvature radii is limited due to the uniform punch tip radius. Hence, a conceptual design of a sectional flexible die is presented for enhancing the flexibility of the forming process. Two punches of different sizes are used to configure the arbitrary forming surface. For a forming region with a relatively large curvature radius, a large punch array block is used; on the other hand, for the forming regions with small curvature radii, a small punch block is used. The cross-sectional profiles are compared with the target shape for evaluating the effectiveness of the process. Consequently, it is confirmed that the sectional flexible die can be used along with a combination of punch blocks of different sizes for manufacturing objective surfaces of complex shapes.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.37 no.1
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• pp.35-41
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• 2013

In injection molding, the mold temperature is one of most important process parameters that affect the flow characteristics and part deformation. The mold temperature usually varies periodically owing to the effects of the hot polymer melt and the cold coolant as the molding cycle repeats. In this study, a pulsed mold temperature control was proposed to improve the part quality as well as the productivity by alternatively circulating hot water and cold water before and after the molding stage, respectively. Transient thermal-fluid coupled analyses were performed to investigate the heat transfer characteristics of the proposed pulsed mold heating and cooling system. The simulation results were then compared with those of the conventional mold cooling system in terms of the heating and cooling efficiencies of the proposed pulsed mold temperature control system.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.34 no.5
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• pp.549-556
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• 2010

In general, materials that can be used to form elastic pads, such as urethane and rubber, are often used in flexible forming processes by inserting the pads between a blank and flexible die for smoothing the forming surface that is formed by a reconfigurable die. In this study, the effects of the elastic pad on formability in the flexible forming process for sheet metals are investigated by performing numerical simulations. In the simulation, the hyperelastic material model is used, where the urethane elastic pads serve as elastic cushions. Case studies are carried out for elastic materials with different hardness values and thicknesses. The results are used to evaluate formability by comparing the configuration of the deformed blank and its major cross-sectional profiles. It is verified that the elastic pad used in the flexible forming process for sheet materials should be hard and that its thickness should be chosen appropriately.

• Journal of the Korean Society of Manufacturing Process Engineers
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• v.19 no.6
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• pp.29-35
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• 2020

Transition Nozzles are used in industrial air-cooled heat exchangers and widely used in industrial sites as an important component in the heat energy transfer between a heat source and an actuating fluid. There is a worldwide demand for transition nozzles with various materials and shapes, depending on the use environment. This paper aims to improve the transition nozzle forging process suitable for the production of many varieties using Steps 1 to 6 of the TRIZ Methodology for Problem Solving. By utilizing the TRIZ Methodology, this study derives a method to design a variable mold, which is more efficient and can reduce costs compared with having to use several molds. To verify the suitability of the methods derived using the TRIZ technique, a forging analysis is performed on a transition nozzle using DEFORMⓇ, a commercial program for plasticity analysis, and the nozzle material is evaluated for damage as a result of deformation of the transition nozzle thickness. The derived methods can be applied to transition nozzle formation equipment to improve the efficiency of the formation process.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2007.10a
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• pp.275-278
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• 2007

In family mold, defects are frequently occurred by an excessive packing the smaller volume cavity during molding. Although runner size could be optimized by CAE analysis or experimental data, the filling imbalance is hardly avoided in the actual injection molding process by various means. Before this study, we developed a variable-runner system for balancing the cavity-filling for three resins (ABS, LDPE, and PA66) in the family-mold, and examined the effect of cross-sectional area reduction of a runner in the system. In this study, we examined the conditions of the pressure and temperature in the system with a CAE analysis. We also analyzed the influence of the rheological characteristic of resins to the balancing-capability of the system in order to help mold designers easily adopt the variable-runner system to their design.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2009.10a
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• pp.281-284
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• 2009

Flexible forming process for sheet metal using reconfigurable die is introduced based on numerical simulation. Numerical simulation of sheet metal forming process is carried out by using flexible dies model instead of conventional matched die set. Elastic cushion which has high resilience behavior from excessive deformation are inserted between forming punches and blank material for smoothing the forming surface which has discrete due to characteristics of the flexile die. As an elastic cushion, urethane pads are utilized using hyperelastic material model in the simulation. Formability in view of surface defect such as onset of dimple is compared with regard to various punch sizes. Consequently, it is confirmed that the flexible forming process for sheet material has appropriate capability and feasibility for manufacturing of smoothly curved surface instead of conventional die forming process.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.34 no.11
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• pp.1623-1630
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• 2010

In this study, effective forming methods for reducing the roll-over of a sector tooth, which is a main component of an automotive seat recliner, are proposed. Due to the large amount of roll-over, accurate contact between the inner gear of a sector tooth and the outer gear of a pawl tooth cannot be normally achieved; thus sensitivity and safety for the passengers decrease. To overcome the aforementioned drawback, we investigated the effect of flowcontrol forming methods involving local embossing die, coining punch, and VIC (Variable Inverse Clearance) on the roll-over depth by FE-analysis and an experiment. The results of a fine-blanking experiment for verifying the proposed methods showed that VIC type is decidedly superior from the aspects of reduction of roll-over and tool strength of the sector tooth.

• Design & Manufacturing
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• v.2 no.6
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• pp.23-27
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• 2008

It is well known that the family-mold has an advantage to reduce the cost for production and mold. However, defects are frequently occurred by over packing the smaller volume cavity during molding, especially when the family-mold has a volumetric difference between two cavities. In this study, the cavity-filling imbalance was confirmed by the temperature and the pressure sensors, and a variable-runner system was developed for balancing the cavity-filling. Experiments of balancing the cavity filling was carried out in the family-mold with the variable-runner system, and balancing the cavity-filling was confirmed by changing the cross-sectional area of a runner in the variable-runner system with the temperature and pressure sensors. The influence of the injection speed to the balancing-capability of the variable-runner system was also examined in the experiment.

• Transactions of the Korean Society of Mechanical Engineers
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• v.19 no.4
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• pp.896-907
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• 1995

Titanium 6242(.alpha. + .betha.) alloy has a good strength/weight ratio and is used for aircraft components such as engine disks and compressor blades. When this material is forged at an elevated temperature, the process parameters should be carefully controlled because the process window of this material is quite narrow. In the present investigation, a rigid-thermoviscoplastic finite element method is used to predict the deformation behavior and temperature/strain distributions in an engine disk during near-net shape hot forging. The purpose of the investigation is to obtain a proper ram speed profile, assuming the hydraulic press used in the forging is capable of varying ram speed during loading. In result, it was found that the ram speed at constant strain-rate of 0.5/sec shows a sound deformation behavior, a relatively uniform deformation and a good temperature distribution. This information is also valuable in predicting resulting microstructures in the disk.