• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2006.05a
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• pp.277-280
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• 2006

The hydroformability of aluminum alloy sheets at elevated temperatures have been investigated in this study. It is necessary to analyze the variations of the mechanical properties that depend on the forming temperature and the heat conduction during warm hydroforming. Therefore, in this study a coupled simulation of plastic deformation and temperature distribution in the warm hydroforming process is performed and compared with experimental data. The multi-purpose code DEFORM-2D can handle this type of calculations but it takes high computation time if contact heat transfer between die, tube and pressure medium occurs. Experiments were conducted by high temperature tribometer(pin-on-disk) allowing measuring the friction coefficients of the aluminum alloys at several temperatures and these results are applied to the coupled simulation by which the optimal process parameters such as internal pressure and preset temperature on hydroformability can be determined. The comparison of the FE analysis with the experimental results has shown that hydroformability given by bulge height, and temperature distribution of the tube specimen make a little difference with the FE results but the trend predicted by simulation agrees well with experiments.

• Journal of the Korean Society for Precision Engineering
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• v.34 no.2
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• pp.83-87
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• 2017

A multi-step warm forging process for subminiature screws is investigated. Due to the low formability of Titanium alloys, bit forming of Titanium screws is difficult by cold forging. In order to overcome this low formability of Titanium alloys, two candidate processes, i.e., multi-step forging and warm forging are introduced. First, a multi-step (two-step) forging process is investigated. The punch shape and stroke of forging during the first step is designed via various analyses. Finally, the bit formability is investigated at different forging temperatures. Analyses are carried out for two-step forging at various temperatures and the formability under these thermal conditions is compared.

• Design & Manufacturing
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• v.12 no.3
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• pp.42-47
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• 2018

Recently, in the surge of global environmental issues, there has been a great attention to lightweight materials in purpose of saving energy. Magnesium alloys not only have low specific gravity, and superb specific stiffness, but are also excellent in blocking vibrations and electromagnetic waves. So demand for this material is getting bigger rapidly throughout the industry. In this study, we examined the improvement of formability of magnesium alloy AZ31 material in warm working. Drawing, bending and shearing process were carried out by varying the forming temperature and the forming speed, and the influence of the variables on each process was studied. In the experiments, the high forming temperature and low forming speed results in high formability in the drawing process and the bending process. In the shearing process, as the forming temperature increases, the length of the fracture decreases.

• Transactions of Materials Processing
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• v.19 no.8
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• pp.447-451
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• 2010

In this paper, a useful die system for warm plate forging of a large axle housing of heavy-duty trucks is presented. A die system composed of material flow guide pin as well as upper die and lower die is proposed to reduce the inherent thickness reduction along the bent corner of the product which deteriorates structural strength and fatigue life in its service. The role of the pin assembled in the upper die is to prevent formation of sharp corner in early forming stage and to supply material in the lower die cavity sufficient enough to thicken the bent corner at the final stroke. The mechanism of the die system is given and its effect on corner thickness of the product is revealed by two-dimensional finite element analysis under plain strain assumption. Three-dimensional finite element solutions are also given to verify validity of the two dimensional approach and to show the mechanics of the die system in detail. The die system has been successfully applied to manufacturing the axle housing of heavy-duty trucks.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 1995.04b
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• pp.204-208
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• 1995

Copper magnetron anode of a microwave-oven consists of an cylindrical outer-tube and various inner-vanes. The magnetron anode is produced by the complex process ; vane blanking, pipe cutting and sliver-alloy brazing of vanes. Recently, the backward extrusion process for forming vanes has been developed to avoid the complex procedures. The developed process is analyzed by using upper-bound elemental technique(UBET). In the UBET analysis, the upper-bound load, the configuration and the vane-height of final extruded product are determined by minimizing the total power consumption with respect to chosen parameters. To verify theoretical analysis, experiments have been carried out with pure plasticine billets at room temperature, using different web-thickness and number of vanes. The theoretical predictions both for forming load and vane-height are in reasonable agreement with the experimental results.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 1996.05a
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• pp.197-205
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• 1996

A combined extrusion process studied here consists of forward and backward extrusion, and it is formed in single operation. The metal flow involved in the operation has appeared to be difficult to analyze accurately because of mixed directions of the flow. In this study, conventional two operations of a forward and a backward extrusions is transformed into one operation of mixed extrusion. A process designed by an industry expert is simulated by the rigid-plastic finite element method to investigate the metal flow and defects. In addition to the FEM simulation, experimental analysis has been carried out to confirm the design in industry, which includes material characterization, preliminary expriment, and whole experimental forming operation. The experimental results show that warm forming of extrusion is more desirable than cold working and hot forming in view of grain growth. Also two conditions of lubrication between workpiece and die has been investigated.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2009.05a
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• pp.139-142
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• 2009

As important mechanical elements, gears have been used widely in power transferring systems such as automobile transmission and there have been several researches trying to make gear parts with cold or warm forging in order to reduce cost and time required to gear manufacturing process. Although forging processes of spur and bevel gears have been developed as practical level owing to active previous researches in Korea, the manufacturing of helical gear has been still depended on traditional gear cutting processes such as hobbing, deburring and shaving. In order to manufacture helical gears with cold forging process, a research project supported by government has been conducted by Daegu university, KIMS and TAK and this paper deals with effects of back pressure forming technique to cold forging of helical gear as a fundamental research.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2008.10a
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• pp.66-70
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• 2008

In this study, the formability of AZ31B magnesium alloy sheets was investigated by the analytical and experimental approaches. Tensile tests and limit dome height tests were rallied out at several temperatures between $25^{\circ}C$ and $300^{\circ}C$ to obtain the mechanical properties and forming limit diagram (FLD). The FLD-based criterion considering the strain-path and the blank temperature was used to predict the forming limit in a deep-drawing process of cross-shaped cup by finite element analysis. This criterion proved to be very useful in determining the optimal process conditions such as blank shape, punch velocity, minimum comer radius, fillet size, and so on, through the comparison between FEA and experimental data. In particular, the temperature of each tool that provided the best formability of the blank was determined by coupled temperature-deformation analyses. A practical method that can greatly reduce the forming time by increasing the punch speed during the forming process was suggested.

• Transactions of Materials Processing
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• v.17 no.6
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• pp.412-419
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• 2008

Using lightweight materials in vehicle manufacturing in order to reduce energy consumption is one of the most effective approach to decrease pollutant emissions. As a lightweight material, magnesium is increasingly employed in automotive parts. However, because of its hexagonal closed-packed(HCP) crystal structure, in which only the basal plane can move, the magnesium alloy sheets show low ductility and formability at room temperature. Thus the press forming of magnesium alloy sheets has been performed at elevated temperature within range of $200^{\circ}C{\sim}250^{\circ}C$. Here we try the possibility of sheet metal forming at room temperature by adopting incremental forming technique with rotating tool, which is so called as rotational-incremental sheet forming(RISF). In this rotational-incremental sheet forming the spindle tool rotates on the surface of the sheet metal and moves incrementally with small pitch to fit the sheet metal on the desired shape. There are various variables defining the formability of sheet metals in the incremental forming such as speed of spindle, pitch size, lubricants, etc. In this study, we clarified the effects of spindle speed and pitch size upon formability of magnesium alloy sheets at room temperature. In case of 0.2, 0.3 and 0.4mm of pitch size with hemispherical rotating tool of 6.0mm radius, the maximum temperature at contact area between rotating tool and sheet metal were $119.2^{\circ}C,\;130.8^{\circ}C,\;and\;177.3^{\circ}C$. Also in case of 300, 500, and 700rpm of spindle speed, the maximum temperature at the contact area were $109.7^{\circ}C,\;130.8^{\circ}C\;and\;189.8^{\circ}C$.

• Transactions of Materials Processing
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• v.21 no.1
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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.