• Proceedings of the Korean Society of Precision Engineering Conference
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• 2005.10a
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• pp.993-996
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• 2005

This paper is concerned with transfer process on hot forging of bearing hub. Workers on hot forging have difficulty in working by high temperature and weight workpiece. And In conventional got forging of bearing hub, the material wasted to the flash accounts approximately 10% of the original workpiece. It is need manufacture automation and reduce the cost of forged products. Surface treatment of die and lubricant are investigated from experiment and FE-simulation for analysis of forming simulation. In order to hot forging process design considered flash thickness and blocker geometry and initial temperature of die and billet. This transfer process gave comparatively good results compared with actual products.

• Journal of the Korean Society for Precision Engineering
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• v.15 no.9
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• pp.75-81
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• 1998

Simulations of warm and hot forming processes need reliable expressions of flow stress at high temperatures. To get flow stress of the materials usually tension, compression and torsion tests are conducted. In this study, hot compression tests were adopted to get flow stress of medium carbon steel. Experiments have been conducted under both isothermal, near constant strain rate in the temperature ranges 650～100$0^{\circ}C$. Phase transformation takes place by temperature changes for steels in hot and warm forging stage. So Constitutive equation are formulated as the function of strain, strain rate and temperature for isothermal conditions and phase transformation.

• Journal of Korea Foundry Society
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• v.17 no.5
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• pp.494-501
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• 1997

In order to manufacture large rod preforms of 2014 Al alloy with a good mechanical property by spray forming method, it was spray-formed at a droplet temperature of $715^{\circ}C$, a droplet flight distance of 400mm, and a spraying angle of $35^{\circ}$. The rod preforms were extruded at $397^{\circ}C$ with the die temperature of $420^{\circ}C$ under the hot extrusion ratio 21:1 and T6 heat treatment was performed. The 2014 Al alloys cast by hot top process were also extruded and heat-treated at the same condition as a reference material. Microstructural observation and tensile test were carried out to investigate the effects of extrusion on microstructure and mechanical property of spray-formed Al alloy. Spray-formed Al alloys had many porosities due to inappropriate process conditions such as long droplet flight distance and low droplet temperature but have fine equiaxed grain. These porosities were reduced with decreasing in grain size by hot extrusion. Ultimate tensile strength and yield strength of spray formed-extruded 2014 Al alloy were inferior to those of the normal cast-extruded 2014 Al alloy, but elongations were superior. The control of porosity was important to get spray formed preform with a good mechanical property.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2012.05a
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• pp.941-942
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• 2012

• Journal of the Korean Society of Industry Convergence
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• v.21 no.6
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• pp.419-427
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• 2018

In case high strength steels are applied for press-formed automotive parts, it is very difficult to secure forming accuracy due to large springback compared to moderate strength steels. In this study, a repetitive step-wise forming analyses based on secant method was proposed as the die design method for mandrel(bending tool) for the 2-axis bending equipments. A bending die with circular mandrel was designed for the DP780 blow motor case of which diameter and thickness are 70.8mm and 2.0mm respectively. Forming tests were performed to verify the validity of established die design and the results were compared with that of conventional HGI(Hot galvanized iron steel) blow motor case. For additional improvement in forming accuracy, an elliptical mandrel was proposed and its validity was verified using forming analyses based on secant method.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.36 no.3
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• pp.319-324
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• 2012

The hot-stamping technique is a forming method for manufacturing high-strength parts, in which the part is cooled rapidly after press forming above the austenite transformation temperature. Boron steel, which contains a very small amount of boron, is one of the materials used for hot stamping. The purpose of this study is to investigate the microstructure and mechanical properties according to the heat-treatment conditions. Die-quenching from various temperatures was conducted for different elapsed heat-treatment times. Laser-welded boron steel after quenching has a tensile strength of 1454 MPa and an elongation of 6 %. It has 94 % of the tensile strength of the base metal (1522 MPa). These properties can provide practical information for the use of boron steels for hot stamping.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.37 no.4
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• pp.547-554
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• 2013

The fuel storage vessel installed in CNG vehicles can be largely divided into 3 parts: head, cylinder, and dome. Studies of the cylinder and dome parts have already been performed, but sufficient design data is not available about the head part. Therefore, expert field engineers heavily depend upon trial-and-error methods. Therefore, FE analysis is performed to review the hot spinning process for forming the head part of the CNG vessel using the Arbitrary Lagrangian-Eulerian (ALE) method. The effects of forming factors on the load were analyzed. The values of the factors were chosen to avoid defects in the head part and buckling, and the forming feasibility of the head part was investigated. Furthermore, a bursting test was performed to evaluate the safety of the storage vessel.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2004.05a
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• pp.198-201
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• 2004

Aluminum alloys have high potential for weight reduction in automotive and other applications. But aluminum alloys have relatively low tubular hydroformability which can be enhanced by conducting the hydroforming at elevated temperatures. Hot working processes are commonly used in bulk forming such as forging and rolling, but still is rare in sheet metal forming like hydroforming. In this study hydroforming test at elevated temperatures is performed by special designed induction heating system to investigate the hydroformability of aluminum alloys. The high temperature formability characteristrics are obtained by 1?fitting forming test and circular bulging test and the effects of the process parameters such as feeding amount, internal pressure and temperatures on the tubular forming limits are mainly investigated.

• 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.19 no.2
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• pp.127-131
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• 2010

Carbon-epoxy prepreg has been introduced in the forming of the upper and lower swash plates that control the pitch of rotor blade of unmanned helicopter because of its lightweight. Taguchi experimental method has been used by introducing the variables such as arrangement angle, laminated number and forming temperature, in order to obtain the proper forming method by using prepreg satisfying the required strength of the swash plate. In the evaluation of structural safety for the swash plates, three kinds of models are considered by using FE-analysis. In comparison of the hot forged products with Al6061-T6 and the formed products with prepreg, it was found that ultimate tensile strength of the products with prepreg is three times higher than that of the Al6061-T6, and the weight reduction of 68.5g can be achieved by using prepreg swash plates.