• Transactions of Materials Processing
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• v.10 no.3
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• pp.214-222
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• 2001

The homogeneous distribution of solid region without liquid segregation is important in terms of high quality component during thixoforming process. In closed die semi-solid forging process, liquid segregation is strongly affected by injection velocity than solid fraction because the material has to travel relatively long distance to fill the cavity through a narrow gate. The designed die by computer simulation data was used to thixoforging process. The thixoforming velocity to prediction the liquid segregation had been determined with strain rate associated with multistage velocity control during compression test of semi-solid material. The optimal forging velocity and die temperature were investigated to produce the near-net-shape compressor component. The mechanical properties of thixoformed component were tested with various die and material temperatures before and after heat treatment.

• Proceedings of the Korean Powder Metallurgy Institute Conference
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• 2006.09a
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• pp.97-98
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• 2006

Gas-permeable metal die materials are developed using tool steel powder, packed in a mold having the insertion of orthogonally arrayed polymer wires. Linear gas-permeable channels in orthogonal array are thus developed by the burning out of the polymer wires, which yield a microstructure with wear resistance value and air permeability much larger than those of the conventional gas-permeable die material.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2007.11a
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• pp.390-391
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• 2007

LED Packaging 과정 중 Die bond 재료로 Silver epoxy를 사용하여 Packaging 한 후 T3Ster 장비로 열 저항 값(Rth)을 측정하였다. Silver epoxy 의 접착 두께를 조절하여 열 저항 값을 측정하였고, 열전도도 값이 다른 Silver epoxy를 사용하여 열 저항 값을 측정하였다. Silver epoxy 접착 두께가 충분하여 Chip 전면에 고루 분포되었을 경우 그렇지 않은 경우보다 평균 4.8K/W 낮은 13.23K/W의 열 저항 값을 나타내었고, 열전도도가 높은 Silver epoxy 일수록 열전도도가 낮은 재료보다 평균 4.1K/W 낮은 12K/W의 열 저항 값을 나타내었다.

• Design & Manufacturing
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• v.12 no.2
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• pp.34-39
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• 2018

The biggest topics in the automobile industry are light weightening and fuel efficiency improvement. There's a lot of research going on. It is focused on light weight materials. Light weight material is seen as the best way to reduce fuel consumption and to solve the problem of environmental pollution and resource depletion. For the light weight materials, new materials such as aluminum, magnesium, and carbon-hardening materials can be found. Research on the joining techniques of dual materials, improvement of material properties by improving the method of manufacture of existing materials, and studies on ultra-high strength steel sheets are expected to take up the most weight in lightweight materials. As the strength of the ultra-high strength steel sheets increases during forming, it is difficult to obtain dimensional precision due to the increase in elastic restoring force compared to mild or high strength steel sheets. Spring back is known to be affected by a number of factors due to poor plastic molding, and can be divided into the effects of the material spraying and the process. The study on the plasticitic variables were studied as plasticitic factors that can be controlled by a part company. Tensile testing of ultra-high strength materials was conducted to derive properties for plasticitic analysis and to analyze spring back with two factors controlling the height of the bead and blank holding force by adding tensile force and controlling the flow rate.

• Transactions of Materials Processing
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• v.10 no.4
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• pp.311-318
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• 2001

Porthole die extrusion has a great advantage in the forming of long hollow section tubes. It is difficult to produce long hollow section tubes with complicated section by the conventional extrusion process with a mandrel on the stem Because of the limit of the length of mandrel and the complexity of cross section. Porthole die extrusion is affected by many parameters, such as extrusion ratio, extrusion speed, die geometry, porthole number, bearing length etc. Up to now, most of studies about porthole die extrusion have been investigated by experiments or steady state FE-analysis. However, in this paper, porthole die extrusion is analysed by the unsteady state 3D FE-simulation. And the result of unsteady state analysis is compared with the experimental result. Also, the surface state of extruded tubes are examined for the various process conditions.

• Journal of Korea Foundry Society
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• v.22 no.4
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• pp.155-159
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• 2002

Magnesium alloys have high strength to weight ratio and are extremely attractive for applications in transport industry. Most of structural magnesium alloys are manufactured by die casting process. The tensile properties of AZ91HP magnesium alloy were investigated after die casting under various die casting conditions. After die casting by using cold chamber machine, the volume porosity of specimens was examined with density method. With the increase of the volume porosity of specimens, both the tensile strength and elongation were significantly decreased, however the 0.2% offset strength was almost independent of the amount of porosity. With the increase of crystal pressure from 500 to 900 bar during die casting, the volume porosity was decreased, which resulted in the increase of the tensile strength. The mould temperature within the range of $150{\sim}250^{\circ}C$ has not influenced the microstructure with the eutectic phase and tensile properties of specimens. The tensile strength was the highest at 90m/sec of gate speed.

• Transactions of Materials Processing
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• v.10 no.5
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• pp.373-382
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• 2001

Die design by computer simulation has some advantages compared with the conventional method which has performed by designer's experiences and trials and errors. The die filling and solidification process of thixoforming process were simulated by MAGMAsoft/thixo module. Furthermore, the die design for thixoforming was performed with the various geometry shape. The effect of designed gate dimension on filling phenomenon was estimated by filling simulation. The calculated results was compared with experimental data. The free surface phenomenon obtained by experiment have good agreement with computer simulation results. The solidification effect much as prosity and shrinkage for designed semi-solid forging die had been predicted by computer simulation. The designed die for semi-solid forging had been applied to produce of the frame part which is used to airconditious system.

• Transactions of Materials Processing
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• v.8 no.3
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• pp.262-268
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• 1999

This paper reviews the rules for optimizing die design and the process variables such as die shoulder radius and punch to die clearance, which are important factors in drawing the sheet metal without failures during deep drawing. To find the optimum conditions for improving deep drawability, a series of the experiments are performed, and the wall thinning and thickening variations are investigated in each process of deep drawing for a complex cylindrical shell. From the results of this proposed experiment, the optimum values of process variables are examined and discussed, and the usefulness of the present suggestion is shown.

• Transactions of Materials Processing
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• v.16 no.4 s.94
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• pp.260-265
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• 2007

Rubber compounds have high viscoelastic property. One of the viscoelastic behaviors during profile extrusion is the swelling of extrudate. In this study, die swells of rubber compounds at the capillary die have been investigated through experiment and computer simulation. Experiments and simulations have been performed using fluidity tester and commercial CFD code, Polyflow respectively. Die swells of rubber compounds in a capillary die were predicted using non-linear differential viscoelastic model, Phan-Thien-Tanner(PTT) model for various relaxation times and relaxation modes. The results of simulation were compared with the experiments. Pressure and velocity distribution, and circulation flows at the comer of capillary die have been investigated through computer simulation. It is concluded that the PTT model successfully represented the amount of the die swell of rubber compounds for various relaxation times at different modes.

• Journal of the Korean Society for Precision Engineering
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• v.18 no.12
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• pp.145-151
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• 2001

The dimensional accuracy of the cold forged part is depended on the elastic characteristics of the die. To increase the stiffness of the prestressed die, the first stress ring of the tungsten carbide alloy (WC) is considered. For the design, Lame's equation is used. Diameter ratios and interferences have been determinated by maximum inner pressure without yielding of materials. The design of the prestressed die has been compared with the conventional one. For the comparison, the FE-analysis using ANSYS has been performed. The results indicate that the prestressed die with the high stiffness can be obtained by the using the high stiffness material as the first stress ring.