• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 1995.10a
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• pp.143-149
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• 1995

A simple kinematically admissible velocity field is proposed to drtermine the final-stage extrusion load and the average extruded length in the square-die forward extrusion of non-axisymmetric bars from circular billets. The proposed velocity field is applied to the square-die extrusion of trochoidal gear-shaped bars and rectangular-shaped bars, the profile function of a rectangular being approximated by using a Fourier series. Experiments have been carried out with hard solder billets at room temperature. The theoretical predictions of the extrusion load are in good agreements with the experimental results and there is generally reasonable agreements in average extruded length between theory and experiment.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2004.10a
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• pp.99-102
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• 2004

In rheo forming process, slurry making is very important factor because the microstructure of slurry affects the quality of final products. To control the microstructure of slurry, slurry making by new rheo die casting was studied. In new rheocasting method, processes parameters are degree of overheat in molten metal, cooling condition, high frequency induction heating condition and cup temperature. Microstructures according to these parameters were observed. By image analysis, equivalent diameter and roundness of grain were investigated and discussed. To find out mechanical properties of grain controlled aluminum part by rheo die casting, tensile tests were carried out to the T6 heat treatment.

• Transactions of Materials Processing
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• v.4 no.4
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• pp.390-397
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• 1995

A simple kinematically admissible velocity field is proposed to determine the final-stage extrusion load and the average extruded length in the square-die forward extrusion of non-axisymmetric bars from circular billets. The proposed velocity field is applied to the square-die extrusion of trochoidal gear-shaped bars and rectangular-shaped bars. The profile function of a rectangle is approximated by using a Fourier series. Experiments have been carried out with hard solder billets at room temperature. The theoretical predictions of the extrusion load are in good agreements with the experimental results and there is generally reasonable agreements in average extruded length between theory and experiment.

• Journal of the Korean Society for Precision Engineering
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• v.20 no.2
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• pp.66-75
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• 2003

This paper describes about the estimation method of die lift by wear and plastic deformation in hot forging process. The thermal load and the thermal softening are happened by the high temperature in hot forging process. Tool lift decreases considerably due to the softening of the surface layer of a tool caused by high thermal load and long contact time between tool and billet. Also, tool life is to a large extent limited by wear, heat crack and plastic deformation in hot forging process. Above all, the main factors which affects die accuracy and tool lift are wear and the plastic deformation of a die. The new developed technique for predicting tool life applied to estimate the production quantity for a spindle component and these techniques assist to improve the tool life in hot forging process.

• Transactions of Materials Processing
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• v.8 no.6
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• pp.569-575
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• 1999

Computer programs have been developed to design the forging dies of turbine and compressor blades. The design of forging dies is based the side force and the filling of die cavity. In this study, slab method has been applied to simulate forging processes numerically. the program composed of Visual Basic also provides the informations of mean stress, total forging load, distribution of temperature, position of neutral line, total volume and volume of flash in the final stage to users. The preform position is predicted by the reverse slab method. The program has been successfully applied to various types of turbine blades.

• Transactions of Materials Processing
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• v.8 no.2
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• pp.188-199
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• 1999

Semi-Solid Forming Process(Thixoforming, Rheocasting) is a novel forming process which has some advantages compared with conventional die casting, squeeze casting and hot/cold forging. In this study. Thixoforming process was selected as analysis processing in terms of billet handling and easiness of automation process. The Thixoforming process consists of reheating process of billet, billet handling, filling inot the die cavity and solidification of SSM part. In filling process, two rheology models which were Newtonian and Non-Nettonian model (Ostwald-deWaele)were verified with experimental results. The Ostwald-deWaele model shows the good agreement to the real flow and filling phenomena in die cavity. To give a boost the economical efficiency of Thixoforming process and to ensure the good forming result, reheating device coupled die set was proposed and the initial billet temperature for system that was found from experimental resluts. This study presents an overview of application of numerical analysis for simulation of semi-solid metal forming process to reduce the lead time for development of manufacturing part in industrial field.

• Transactions of Materials Processing
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• v.14 no.7 s.79
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• pp.607-612
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• 2005

In this paper, warm deep drawing process with local heating and cooling technique was attempted to improve the formability of AZ31 magnesium alloy which is impossibly to form by conventional methods at room temperature by finite element method and experiment. For FE analysis, in first model with considering heat transfer, both die and blankholder were heated to 573K while the punch was kept at room temperature by cooling water. Also distribution of thickness and von Mises stress at room temperature and 498k for warm deep drawing were compared by FEM. Uniaxial tension tests at elevated temperature were done in order to obtain the temperature dependence of material constant under temperature of $293K\~573K$ and cross head velocity of $5\~500mm/min$. The phenomenological model for warm deep drawing process in this work was based on the hardening law and power law strain rate dependency. Deep drawing experiment were conducted at temperatures of room temperature, 373K, 423K, 473K, 498K, 523K, and 573K for the blank and deep drawing tools(holder and die) and at a punch speed of 10mm/min.

• Journal of the Korean Society for Heat Treatment
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• v.7 no.1
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• pp.61-71
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• 1994

This study is to investigate the stress distributions, crystal orientations and magnetic properties during die-upsetting according to working temperature of Nd-Fe-B-Cu alloys. The stress distributions in the specimens during compressing process were calculated by a finite element method program(SPID). The calculated stresses were effective stress (${\sigma}_{eff}$), compression stress(${\sigma}_z$), radial direction stress(${\sigma}_r$) rotational direction stress(${\sigma}_e$) and shear stress(${\tau}_{rz}$). The stress distributions of ${\sigma}_z$, obtained by a computer simulation showed that the stress components causing the magnetic alignment during die-upsetting of the cast magnets were very high at the center-part of a specimen, and decreased toward the periphery-part of a specimen. In view of the above results the magnetic properties should be better at the center-part of a specimen than any other parts. But the measured magnetic properties were better at the mid-part. These results should be due to the fact that the specimens were casted. Normally the magnetic properties are affected by the casting process as well as by the stress levels. ${\sigma}_r$, ${\sigma}_e$ are thought to affect the liquid phase flowing and domain patterns, respectively. The influence of ${\tau}_{rz}$ was trivial, ${\sigma}_{eff}$ distributed similar throughout the specimen. The Nd-rich phase appeared at the peripheral of the specimen where the stress level of ${\sigma}_r$, ${\sigma}_z$, was low or the stress level of ${\sigma}_e$ was high. The Nd-rich phase was squeezed out during die-upsetting. This phase had an effect on the crystal orientation and grain growth. The stress distributions of alloy were irregular at the parts of the specimen where the die contacted with specimen.

• Journal of the Korean Society for Precision Engineering
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• v.27 no.1
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• pp.119-124
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• 2010

This paper addresses the design and fabrication of desktop die-sinking dry electrical discharge machining (EDM) system and its experimental performance analysis. The developed desktop dry EDM machine has the horizontal configuration with the size of $300{\times}200{\times}260mm$. The experimental performance analysis is conducted to investigate the effects of EDM conditions and dielectric gas temperature on the surface roughness of EDMed slots and number of EDM sparks. The experimental results demonstrate that low feed rate and large electrode displacement are good for better surface roughness and more number of EDM sparks. In addition, low temperature of dielectric gas results in better surface roughness.

• Design & Manufacturing
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• v.6 no.1
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• pp.52-57
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• 2012

Aspect of filling imbalance that is originated from imbalanced share rate in runner is changed by material property, runner layout that are factors of changing viscosity and by injection pressure, injection speed, melt temperature and mold temperature that are injection conditions. In this paper, we made a study of runner system that is one of factor of filling imbalance and Sharp Conner Effect and Groove Corner Effect that are recently released. The study are showed that filling rate of between inside and outside cavity was influenced on shape of runner. Also, we suggested runner system for filling imbalance by adapting the two effects at multi cavity of unary branch type and theoretical investigated flow in the Shrap Conner runner type.