• Transactions of Materials Processing
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• v.8 no.5
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• pp.437-448
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• 1999

The reheating of the billet in the semi-solid state as quickly and homogeneously as possible is one of the most imposrtant parts. To obtain a fine globular microstructure in cross section of billet, the optimal design of the induction coil for variation of alloys and specimen sizes is necessary. For the thixo-forging process the construction of the reheating data base is very important, because the reheating conditions are different for variation of SSM and billet sizes. So in this study, the optimal coil design of A356 (ALTHIX) and Aι2024 with d×ι=60×90 (mm) to obtain the globular microstructure is theoretically proposed. The suitability of an optimal coil design will be demonstrated by reheating experiments. Finally, the thixoformability of an arbitrarily shaped product is evaluated by its forming variables. The defects and mechanical properties are also investigated.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2003.05a
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• pp.343-346
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• 2003

In order to construct the extrusion die surface of arbitrarily shaped sections, an automatic surface construction method based on NURBS surface and area mapping method is proposed in the present work. In the present study, a center point for area mapping is determined by introducing the marring concept based on constant area proportionality between original billet and final product. The characteristic points of inlet profile is determined using the traditional area mapping method and the root finding numerical method. The inlet and outlet profiles are precisely described with NURBS curves using the characteristic points of entry and exit sections. For the construction of NURBS surface, an interpolation method for the pre-determined two section curves has been developed to be used in the generation of interior control points and weights. To show the validity of the proposed method, automatic die surface generation is carried out for the several kinds of shaped sections.

• Transactions of Materials Processing
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• v.12 no.4
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• pp.348-357
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• 2003

In order to construct the extrusion die surface of arbitrarily shaped sections, an automatic surface construction method based on NURBS surface and area mapping method is proposed in the present work. A center point fur area mapping is determined by introducing the mapping concept based on constant area proportionality between original billet and final product. The characteristic points of inlet profile are determined using the traditional area mapping method and the root finding numerical method. The inlet and outlet profiles are precisely described with NURBS curves using the characteristic points of entry and exit sections. For the construction of NURBS surface, an interpolation method for the pre-determined two section curves has been developed to be used in the generation of interior control points and weights. To show the validity of the proposed method, automatic die surface generation is carried out for the several kinds of shaped sections.

• Journal of the Korean Society for Precision Engineering
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• v.29 no.1
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• pp.114-120
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• 2012

We present a simple and low-cost method to fabricate poly(methyl-methacrylate) (PMMA) nanochannels with various shapes by combining the standard optical lithography with a PMMA layer transfer and collapse technique. We utilized PMMA membrane reflowing/collapsing phenomena into microchannels to fabricate nanochannels at both corners of arbitrarily-shaped microchannels. This allows nanochannels with various shapes such as curved nanochannels as well as straight nanochannels to be easily fabricated since the shape of the microchannel determines the shape of the nanochannels. This nanochannel fabrication method is simple, flexible, and low-cost since the standard optical lithography with low-resolution optical masks can be used to fabricate nanoscale channels as small as 100 nm wide with various shapes. Also, the sealing of nanochannels can be naturally achieved while the nanochannels are formed through the polymer layer transfer and collapse.

• Transactions of the Korean Society of Mechanical Engineers
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• v.9 no.4
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• pp.452-462
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• 1985

The axisymmetric forward extrusion is analyzed by using the rigid-plastic finite element formulation. The distribution of stresses and strains as well as the deformation pattern in solid extrusion is very important for the improvement of product quality. The initial velocity field is determined by assuming the material as a Newtonian fluid through an arbitrarily shaped axisymmetric die. The workhardening effect and the friction of the die-material interface are considered in the formulation. Some reduction of area and die shapes(conical and biquadratic-curved) are chosen for computation. Experiments are carried out for steel alloy(SCM4) specimens using conical and curved dies. It is found that experimental observation is in good agreement with FEM results. The strain distribution is curved(biquadratic) dies is shown to be more uniform than in conical dies at the same reduction of area.