The deformation behavior and temperature change in the cylindrical deep drawing of an AZ31 magnesium alloy sheet at elevated temperatures are simulated by the combination of the rigid-plastic and heat conduction finite element methods. The flow stresses of the sheet at elevated temperatures are measured, and given in the simulation with a simple formula composed of the functions of strain, strain rate and temperature. A comparison with the experimental results shows that the forming limit is successfully predicted by the simulation. It is clarified that an appropriate distribution of flow stress depending on temperature must exist in the sheet for realizing a high limiting drawing ratio.
The effect of peripheral softening on stretch formability was investigated for high-strength aluminum alloy sheets. The peripheral of 6061-T6 circular blanks were locally heated to soften the blanks using ring-shaped pre-heating plates. Graded blanks of various strength were prepared using various heating conditions. The stretch height of the peripherally softened blank was larger than that of a uniform T6 blank. The maximum stretch height was obtained under the heating condition of 400°C for about 2 s. Three types of failure occurred depending on the heating conditions used. These were failures at the punch head, die corner and free stretching region. The thickness reduction of the punch head of the peripherally softened blank was more uniform than that of the solution-treated blank. The effects of peripheral softening on stretch formability and optimal strength gradient for obtaining the maximum stretch height were predicted by finite element method analysis.
Healthy hair catches a lot of people's attention. Because of this, the effects of some properties of scissors on hair are determined. First, hair sections cut by different methods are compared. The hair sections cut by hair-cutting and stationary scissors are prepared. These hair sections are heated by a hair drier in a manner similar to daily hair care. The hair section cut by stationary scissors is dried for a longer time than that cut by hair-cutting scissors, because of its rougher surface. This indicates that a hair section with a rough surface can not maintain moisture. From this result, it is possible to evaluate the cut hair section in terms of the rough surface area ratio. Several scissors with different properties are used for such an evaluation. The rough surface area ratios of the hair sections cut by these scissors are measured. The results indicate that the most important property of scissors is the edge radius. To examine the effect of this property on live hair, hair sections are obtained from four persons using the scissors with a large edge radius. Two months later, 40% of one hair section was damaged.
When a bent part is unloaded at a certain stage in a V-bending process, a springback phenomenon does not occur. The purpose of this study was to develop a practical V-bending process to exploit a springback-less phenomenon. The mechanism of this springback-less phenomenon is as follows. Under a certain punch stroke in the V-bending process, the “springback” factor due to tensile stress on the outer side of the bend is precisely balanced by the “spring-go” factor due to tensile stress on the inner side of the bend, which occurs by the unbending of the flange portion of the bent part at the punch shoulder. To realize this bending method, it was shown that it is possible to predict where in the punch stroke the springback-less state will occur, regardless of the thickness and property changes of the sheet metal, and dimensional changes of the bending die. It was also shown that the bending die specifications for a right-angle bending can be predicted on the basis of the thickness and property of the sheet metal. Examination was performed with press brakes attached to a device for measuring the bending load, bending angle and punch stroke. In addition, the FEM simulation of the bending process was carried out.
The joinability of aluminum alloy and steel sheets using a self-piercing rivet was evaluated using a finite element simulation and experiment. Self-piercing riveting is a potential replacement of spot resistance welding generally used for steel sheets, because it is not easy to apply resistance welding to the joining of aluminum and steel sheets of vastly different melting points. To obtain optimum joining conditions, joining defects are categorized into (1) penetration through the lower sheet, (2) necking of the lower sheet and (3) separation of the sheets. The penetration, the necking and separation defects are caused by a small total thickness, a small thickness of the lower sheet and a large total thickness, respectively. The joining range for the combination of an upper sheet of steel and a lower sheet of aluminum is wider than that of the reverse combination. The joint strength is influenced by not only the deformation of the sheets and rivets but also the thickness and strength of the sheets.
In recent years, thin aluminum alloy extruded tubes have been applied to structural parts such as automobile space frames to save energy. If the aluminum tubes could be processed in a greater variety of ways, such as bending, the range of applications would expand. In our previous study, we evaluated the bending of thin extruded square tubes. In the current study, we examined the bending formability of aluminum alloy pipes with reinforcing ribs using the finite element method (FEM). The influence of the reinforcing ribs on the form accuracy of the aluminum pipes in draw bending was investigated. The effective arrangement and thickness of a reinforcing rib was also investigated. As a result, it was clarified that two types of buckling arise for the reinforcing rib. Furthermore, a critical ratio T=t2/t1 (t1: a periphery part thickness of pipe, t2: a thickness of rib) for controlling the buckling and the flattening distortion were proposed.