• Transactions of Materials Processing
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• v.7 no.6
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• pp.610-619
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• 1998

The superplastic blow forming technology has advantages of cost reduction and low material consumption. compared to the conventional sheet metal forming technology due to the capability of precisely forming with high elongation and low flow stress. however it has a disadvantage that its partial thickness distribution is non-uniform. A processing technology like diaphragm forming has been developed even though it is difficult to prepare materials for superplastic blow forming. in this study a hemisphere forming of sheet before superplastic forming. It was found that the rotary forming material was less in quantity of cavitation at pole than that of hemisphere part that was superplastic formed without rotary forming treatment. Also discussed are the critical strain which is closely related to cavity shape and size.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2006.05a
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• pp.67-69
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• 2006

Since magnesium alloy has a limited formability at room temperature, forming should be carried out at the elevated temperature. If the initial grain size is small, superplasticity could be expected over $400^{\circ}C$. Using superplastic behavior, blow forming can be used to overcome the low formability of Mg alloys. In the present study, the optimization of blow forming of AZ31 alloy at the elevated temperature was investigated. Finite element simulation was carried out and verified with the blow forming experiments.

• Transactions of Materials Processing
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• v.7 no.3
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• pp.207-214
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• 1998

Influence of final thickness distribution in superplastic forming processes on mechanical properties of the product becomes very crucial. We should improve the thickness distribution of products by combining process parameters adequately In this paper we adopt a non-linear optimization technique for optimal process design of superplastic forming. And optimum design variable which makes the most adequate thickness distribution in combined stretc/blow forming and blow forming is predicted by this optimization scheme and rigid-viscoplastic finite element method.

• Journal of the Korean Society for Precision Engineering
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• v.11 no.1
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• pp.129-137
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• 1994

A rigid-viscoplastic finite element method has been used for modeling superplastic stretch/blow process design to improve thickness distribution. Punch velocity-time relationship of the stretch forming and pressure-time cycle of the blow forming for a given strain rate are calculated. A superplastic material is assumed to be isotropic and a plane-strain line element based on membrane approximation is employed for the formulation. The effects of the width, corner radius and height of the punch during stretch forming are examined for the final thickness distribution, and the process design to improve thickness distribution can be established.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2006.06a
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• pp.99-102
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• 2006

In the present study, the blow forming characteristics of AZ31 sheet was investigated to test the feasibility of the practical application of wrought Mg alloys. Mg alloys have drawn a huge attention in the field of transportation and consumer electronics industries since it is the lightest alloy which could be industrially applicable. Most Mg alloy components have been fabricated by casting method. However, there have been a lot of research activities on the wrought alloys and their plastic forming process recently. Shallow cups for the small electronics cases have been stamped with warm die system. However, some technical issues will challenge Mg forming when large parts are considered with warm die system over $200^{\circ}C$. Most of all, thermal expansion of die system will deteriorate a die accuracy. On the other hand, blow forming does not have a problem with inaccuracy with die system. In this study, tensile tests were followed by blow forming at various temperature and pressure. AZ31 sheet showed a superplastic deformation behavior with extensive grain boundary sliding at the temperature above $300^{\circ}C$. However, the deformation behavior was likely to differ depending on stress condition.

• Transactions of Materials Processing
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• v.8 no.1
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• pp.92-100
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• 1999

A procedure is proposed for determining the initial thickness distribution in oder to produce a specified final thickness distribution for the axisymmetrical superplastic blow forming processes. Weighted parameter is introduced to improve the simple ad $d_traction method and the initial blank thickness distribution is obtained by optimizing the weighted parameter. This method is applied to superplastic free bulging process with the uniform thickness distribution of final shape to confirm its validity. The optimum initial blank thickness distributions is obtained from arbitrary axisymmetrical superplastic blow forming processes such as dome, cone and cylindrical cup forming with die contact. It is concluded that the ad $d_traction method with weighted parameter is an effective method for an optimum blank thickness distribution design.esign.

• Transactions of Materials Processing
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• v.20 no.8
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• pp.601-610
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• 2011

Based on the facts that AZ31 magnesium alloy can be blow formed just like superplastic aluminum alloys and that most superplastic alloys fail by cavitation, the present study was undertaken to investigate the cavitation behavior of a fine-grained AZ31 sheet during blow forming at the elevated temperature. Other points of interest included the much lower strain rate and temperature dependencies of the magnesium alloy compared with conventional superplastic alloys. It was also aimed to find if cavitation in the AZ31 alloy can be suppressed by hydrostatic pressure, as is the case in most superplastic alloys. Interestingly, the application of hydrostatic pressure did not increase the blow formability of AZ31 sheet, even though it reduced the degree of cavitation. A possible reason for this behavior is discussed.

• 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 Materials Processing
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• v.21 no.3
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• pp.151-159
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• 2012

Finite element simulations were conducted to investigate the influence of grain growth in the superplastic blow forming process. A microstructure-based constitutive model considering grain growth effects is proposed and used in the simulations. Also, a grain growth rate equation accounting for both static and dynamic grain growth is implemented. The simulations were made using a 2D plane-strain model for constrained blow forming and an axisymmetric model for free bulging. These two models showed different features during the forming stages. However, the forming pressure-time curve and the thickness distribution obtained by both simulations explained well the deformation hardening induced by the grain growth during superplastic forming. This study shows that grain growth is an important factor in determining the material behavior during superplastic deformation.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2008.11a
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• pp.559-560
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• 2008