Takeshi Hinata

High Strain Rate Formation of Al Alloy Plate for Car Body

Recently, the automotive performance improvement is requested. The fuel cost of the automotive greatly depends on the weight of the car. We can improve the automotive performance by lightening and car. The body material of the car is being replaced from iron with the aluminum base alloy. The fuel cost of the car made by all aluminum base alloy are said about 35.5 km/litter. However the forming of the aluminum base alloy is very difficult due to the limit of the forced restrictions. In this research, the explosive forming of the aluminum base alloy carried out to improve the deformability of them. A very high performance of the explosive forming of the aluminum base alloy is reported.Copyright

NUMERICAL SIMULATION OF EXPLOSIVE FORMING

Explosive forming is one of the unconventional techniques, in which, most com- monly, the water is used as the pressure transmission medium. The explosive is set at the top of the pressure vessel filled with water, and is detonated by an electric detonator. The underwater shock wave propagates through the water medium and impinges on the metal plate, which in turn, deforms. There is another pressure pulse acting on the metal plate as the secondary by product of the expansion of the gas generated by detonation of explosive. The secondary pressure pulse duration is longer and the peak pressure is lower than the primary shock pressure. However, the intensity of these pressure pulse is based also on the conditions of a pressure vessel. In order to understand the influence of the configuration of the pressure vessel on the deformation of a metal plate, numerical analysis was performed. This paper reports those results.

Deformation Mechanism of Metal Plate on Explosive Forming

The explosive forming is one of the forming methods of a metal plate performed since the 1950s. This method is different from usual static press forming. The metal plate is accelerated by underwater shock wave, which is generated by underwater explosion of an explosive. In order to deform a metal plate in predetermined form with sufficient accuracy using this forming method, it is important to grasp the mechanism. At first, it is necessary to grasp that an underwater shock wave spreads and it collides with the metal plate. And it is also necessary to show clearly what deformation of the metal plate with high-speed. Then, we investigated about the mechanism in the numerical simulation. In this research, LS-DYNA, which is the software for shock analysis was used. Moreover, the experiment was also conducted in order to confirm whether this numerical simulation is exact.Copyright

Numerical Simulation of Free Forming of Aluminum Alloy Using Underwater Shock Wave

The automobile industry has recently been manufacturing cars using aluminum alloys, either #5000 or 6000. However, the forming of these materials as sheet metal by static methods, such as hydro bulge forming or general punching, is very difficult because these materials allow little elongation compared to conventional steel. In order to examine the application of explosive forming, we tried free forming aluminum alloy as the basis of the study. We compared the elongation of the alloy when explosive forming was used to that produced by punching. It was consequently found that the amount of elongation was larger for deformation produced by explosive forming. Recognizing the importance of investigating the deformation process of aluminum plate by explosive forming, we pursued a theoretical framework for elucidating this, completing a numerical simulation by the FDM method. This simulation permits an evaluation of the detonation process of the explosive, the propagation process, and the deformation process of the aluminum alloy. Introduction In recent years, a brisk pace has been set in automobile development with regard to the improvement of fuel efficiency. The number of cars produced using aluminum alloys instead of steel has increased. However aluminum alloys have drawbacks in their forming performance compared to conventional steel. We tried to overcome limits to aluminum alloy’s forming performance by employing the explosive forming method. In order for the potential of this method to be realized, it is necessary to clarify the mechanism of high-speed forming of aluminum plate. Therefore, for this research numerical simulation by the finite difference method (FDM), using the Lagrange coordinate, was performed on the deformation process of explosive forming of aluminum plate [1]. Simulation Method Figure 1 shows the simulation model for explosive forming. Each dimension was determined for the equipment used in the experiment. The analysis area was divided into quadrilateral elements. The aluminum was in the form of a disk with a diameter of 230mm and thickness of 1mm. The aluminum was an annealing material, A5052-O. A water column 130mm in diameter and 50mm in height rested in the center of the aluminum plate. (Although a paper container was used in the experiment, it wasn’t included in the numerical simulation.) Highly explosive SEP was suspended in the water. The distance between the bottom of the explosive and the aluminum plate was 30mm. The curvature Materials Science Forum Online: 2004-09-15 ISSN: 1662-9752, Vols. 465-466, pp 391-396 doi:10.4028/www.scientific.net/MSF.465-466.391

Study on the Effect of Underwater Shock Wave and Gas Expansion in Explosive Forming

Explosive forming is one of the unconventional techniques, in which, most commonly, water is used as the pressure transmission medium. The explosive is set at the top of the pressure vessel filled with water, and is detonated by an electric detonator. The underwater shock wave propagates through the water medium and impinges on the metal plate, which in turn, deforms. There is another pressure pulse acting on the metal plate as the secondary by product of the expansion of the gas generated by detonation of explosive. The secondary pressure pulse duration is longer and the peak pressure is lower than the primary shock pressure. However, the intensity of these pressure pulses is based also on the conditions of a pressure vessel. In order to understand the influence of the configuration of the pressure vessel on the deformation of a metal plate, numerical analysis was performed. This paper reports those results. Introduction When an explosive is detonated underwater, an underwater shock wave is generated which is primarily responsible for the plastic deformation of the metal plate. After the impingement of this primary underwater shock wave on the metal plate, a secondary pressure pulse, generated from the expanding gaseous products of the detonation, impinges on the metal plate. These pressure states of acting on a metal plate change with the type of the container to be used. The shock pressure and gas pressure acting on a metal plate in the case of the sealed pressure vessel can be predicted easily. On the method of explosive forming [1,2] is performed, arbitrary deformation of the metal plate is obtained by changing the position of an explosive. However, in this method, the required forming configuration was obtained with a lidless pressure vessel. Nevertheless, in the case of employing simple water filled container the influence of reflected pressure from sidewall of container is significant. If no container is used then there is almost no influence of gas pressure. Simulation Method Figure 1 shows three simulated models of underwater explosive forming. All models were for axial symmetric free forming operations. Free forming indicates that the metal plate deforms by overhanging. In model 1, the pressure acts on a metal plate without the confinement of pressure vessel. In model 2, there was no lid for the container. The pressure pulse released from the upper part of explosive is unrestricted because of the lidless container. In model 3, an airtight container was used. In all models, the copper plate with 2 mm thick and of diameter 230 mm. The size of an Materials Science Forum Online: 2004-09-15 ISSN: 1662-9752, Vols. 465-466, pp 397-402 doi:10.4028/www.scientific.net/MSF.465-466.397

Numerical Simulation of Sheet Metal Forming Using Underwater Shock Wave

In recent years, aluminum alloy is being used to fabricate car bodies. #5000’s or 6000’s aluminum alloy series is widely employed. However, the sheet metal forming of these materials by the static method, such as the hydro bulge forming and general punching, is very difficult, because the formability characteristics are limited when compared to majority of automobile steels. Hence, the choice of explosive forming is considered for forming these aluminum alloys. Te elongation of aluminum alloy by explosive forming is compared with that obtained by punching. The amount of deformation of aluminum alloy by the explosive forming is found to be larger. In addition, a theoretical elucidation is also done. FDM scheme was employed to solve the numerical simulation. In this simulation the detonation process of the explosive, propagation process and deformation process of aluminum alloy were conducted.Copyright