• Journal of Ocean Engineering and Technology
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• v.16 no.6
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• pp.49-54
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• 2002

The Finite Element Method is applied to the determination of the deformed bulge profile and strain distribution during upset forming of cylindrical billets. From the results of simulation, the bulging along the z-axis becomes more severe with increasing eight reduction, and with increasing friction at the die-material interface. The present method can be used for the simple prediction of the deformed shape and strain distribution in upset forging of cylindrical billets with dissimilar fictional conditions at the die-material interfaces.

• Journal of the Korean Society for Precision Engineering
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• v.12 no.11
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• pp.91-97
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• 1995

In this study, a deformation model for the regular polygonal-shaped tubes from hollow-cylindrical billets is proposed and a kinematically admissible velocity field is obtained from this deformation model. The final stage upper-bound extrusion load and the average extruded length are determined by minimizing the total power consumption with respect to chosen parameters. 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 agreement in average extruded height between theory and experiment.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 1995.03a
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• pp.41-53
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• 1995

Forging of spur gears has been investigated by means of upper-bound method. The term forging means forging of spur gears with solid cylindrical billets, hollow billets with flat punch. Kinematically admissbile velocity field for forging of spur gears has been proposed in this study. The 1/2 pitch of spur gear has been divided into seven dieformation regions, wherein, an involute curve has been introduced to represent the shape of die profile. Especially neutral surface has been introduced intor forging of hollow gears from hollow billets. By using the kinematically admissible velocity field, the powder requirements and suitable conditions for forging fo spur gears were successfully calculated with numerical method. According to the analysis , the acceptable number of teeth for forging of spur gears is from 15 to 20.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2003.04a
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• pp.23-26
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• 2003

Solid-state extrusion technique was employed for the improvement of mechanical properties of polylactic acid (PLLA) widely used as biodegradable internal fixation devices currently. Cylindrical billets were machined out from the vacuum compression-molded PLLA to have various diameters, and solid-state extrusion of the billets was performed at various drawing rates and at the extrusion temperature of $130^{\circ}C$. Throughout the whole processes the decrease in molecular weight was significantly suppressed to be about $10\%$. Flexural modulus and strength of PLLA increased up to 8.3 GPa and 221 MPa, respectively. Studies on the orientation and crystallinity of extruded PLLA could reveal the effects of billet morphology, draw ratio, and drawing rate on the flexural strengths of PLLA.

• Journal of the Korean Society for Precision Engineering
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• v.13 no.1
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• pp.108-115
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• 1996

Forging of trapezoidal spline, serration and square spline with solid cylindrical billets and hollow one has been investigated by means of upper bound method. Kinematically admissible velocity fields for forging of splines have been proposed in this study. The half pitch of spline has been divided into several deformation regions. The neutral surface is introduced into forging of splines with flat punch and, for each step, it is assumed as a circle with its radius $r_n$. Upper bound solutions obtained by proposed kinematically admissible velocity fields are useful to predict the loads for forging of splines.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 1997.10a
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• pp.220-223
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• 1997

This paper presents the prediction of microstructure of Inconel 718 disk forgings. The experiments are carried out to examine the recrystallization ratio and grain growth in the forgings. In the experiments, cylindrical billets are forged by two operations with variations of forging temperature and reduction ratio of deformation. Also the finite element program, developed here for the prediction, is used for the analysis, and the results are compared with the experimental ones. It is noted that the comparison appears in sound agreement.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.25 no.9
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• pp.1438-1443
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• 2001

The significance of the casting/forging process for reducing the production cost of large components is being noted in these days. This casting/forging process is a method of forging a workpiece preformed by casting into the final shape. In this study, the casting/forging process has been applied in manufacturing a large aluminum flange in order to reduce press capacity and material cost. Firstly, a hot compression test was performed with cast cylindrical billets in order to determine the optimum forging condition of the aluminum flange. The optimum range of forging temperature of Al 5083 was from 420$\^{C}$ to 450$\^{C}$. The suitable strain rate was 1.5 sec(sup)-1. The deformation amount of a preform of a preform in a forging process is a key role in the mechanical properties of casting/forging products. In order to find the change of mechanical properties according to effective stain of cast aluminum billets, a hot upsetting test were performed with rectangular blocks and then a uniaxial tensile test was performed with specimens cut from the upsetted billets. The tensile strength and the elongation of cast/upsetted aluminum billets were increased largely until the effective strain was 0.7. FE analysis was performed to determine the configurations of case preform and die for an aluminum flange. In the FE analysis, the forging load-limit was fixed 1500ton for low equipment cost. The cast preform was designed so that the effective stain around the neck of a flange exceeded 0.7. From the result of FE analysis, optimal configurations of the cast preform and the die were designed for a large flange. The filling and solidification analysis for a sound cast-preform was carried out with MAGMA soft. In the forging experiment for an aluminum flange, it was confirmed that the optimal configuration of the cast preform predicted by FE analysis was very useful. The cast/forged products using designed preform were made perfectly without any defects.

• Journal of the Korean Society for Precision Engineering
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• v.12 no.8
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• pp.63-72
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• 1995

Closed-die forging of spur gears with hollow cylindrical billet has been analysed by using the upper-bound method. A kinematically admissible velocity field has been developed, wherein, an involute curve has been introduced to represent the forging die profile. In the analysis, the deformation region has been divided into nine zones. A constant frictional stress has been assumed on the contacting surfaces. Utilizing the formulated velocity field, numerical calculations have been carried out to investigate the effects of various parameters, such as module, number of teeth and friction factor, on the forging of spur gears. Hardness and accuracy of forged gears are measured. The following results have been obtained: (1) It is verified that an axisymmetric deformation zone exists between root circle and center of gear through forged gears. (2) The average relative forging pressure is predominantly dependent on the number of teeth and increases near the final filling stage as the addendum modification coefficient increases. (3) Close agreement was found between the predicted values of forging load and those obtained from experimental results.

• Transactions of Materials Processing
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• v.7 no.3
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• pp.197-206
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• 1998

This paper presents the prediction of dynamic recrystallization behavior during hot forging of Inconel 718. Another experiment of pancake forging was also carried out to examine the recrystallization ration dynamically recrystallizaed grain size, and grain growth in the forging. In experiments cylindrical billets were forged by two operations with variations of forging temperature, reduction ration of deformation. and preheating process at each forging step. Also the finite element program, developed here for the prediction using the metallurgical models was used for the analysis of to Inconel 718 upsetting and the results were compared with experimental ones.

• Journal of the Korean Society for Precision Engineering
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• v.12 no.9
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• pp.126-136
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• 1995

Copper magnetron anode of a microsave-over consists of an cylindrical outer-tube and various inner-vanes. The magnetron anode is produced by the complex processes; vane blanking, pipe cutting and silver-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 roral power consumption with repect 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.