Formability Study for Stamping Aluminum Alloy Sheets
Date Issued
2011
Date
2011
Author(s)
Lin, Chien-Wei
Abstract
In recent year, customers had raising demands for the coziness of spaces and multi-functions, which makes the sizes and weights of vehicles increased. However, when facing the energy crisis and the deteriorating living environment, it is essential to decrease the emission of greenhouse gases. To produce light-weighted parts then becomes the goal of most sheet metal factories. In European and American countries, some factories have even launched aluminum alloy automotives and aluminum alloy yachts one after another.
The weight of aluminum alloy is approximately one-third of steel; as a result, aluminum alloy has gradually substituted for steel. Aluminum alloy bears its own advantages of light-weight and better corrosion resistance, but its formability is inferior to that of steel. In the stamping process, except that aluminum alloy would crack easily, the low elastic modulus makes the aluminum alloy easier to produce a significant springback defect, which would lead to variation of accuracy hard to grapple with. As a result, the design concept of stamping conventional steel sheets cannot be completely applied to the die design of aluminum alloy, which causes the tooling maker to spend more time and money to develop a set of stamping dies. And thus, the computer-aided engineering (CAE)technology becomes even more necessary in helping the die design.
It is well known that the material model including the yield criterion and the hardening rule plays an important role in the CAE analysis for predicting the springback. In the present study, the tension-compression reversal tests were conducted to obtain the stress-strain relations and the Bauschinger effect exhibited in the A5083-O and A6181-T4 sheets. The test results were fitted into different yield criteria and work hardening rules used in different finite element software. The finite element simulations were then preformed for V-bending and U-hat drawing of A5083-O and A6181-T4 sheets, and the results of springback and side-wall curl were compared with those obtained from experiments. It can be concluded from the comparison that the material model which includes the Bauschinger effect renders a more consistent results with the experimental data.
The formability of stamping an engine hood with A6181-T4 was also examined in the present study. The aging phenomenon of A6181-T4 was first observed from aging tests and the test results were included in the subsequent finite element simulations. In order to investigate the difference of forming characteristics between conventional steel and A6181-T4 in the stamping process of an engine hood, the effects of material properties, such as n-value, r-value and yield stress, on the different forming modes were systematically analyzed by the finite element simulations.
In addition, the stamping process of the outer panels of a yacht with A5083-O sheets was developed in the present study to replace the current welding process. Due to the V-shaped deep drawing, the defects of wrinkling and fracture are apt to occurring in the stamping process. In order to avoid the presence of these defects, the deformation mechanism in the stamping process of the yacht outer panels were characterized by the finite element simulations. An optimum die face shape with a proper addendum design was then developed according to the finite element analysis, and an actual stamping die set is scheduled to be manufactured following the suggested die design.
Subjects
aluminum alloy
stamping
springback
aging
yield criteria
Bauschinger effect
engine hood
yacht outer panels
addendums
die design
Type
thesis
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