Abstract
A cylindrical deep drawing test was conducted for the purpose of improving the drawability, product accuracy, and quality in warm deep drawing using a superplastic material with large strain rate dependence. Then, the effects of blank holding force (BHF) and punch speed (SPD) on the flange wrinkle behavior and wall thickness distribution were investigated by experiments and theoretical analysis. A Zn-22Al-0.5Cu-0.01Mg alloy superplastic material SPZ2 with a sheet thickness of 1 mm was employed as the experimental material, and a cylindrical deep drawing experiment with the drawing ratio (DR) of 3.1 and 5 was performed at 250 °C. A good agreement was qualitatively obtained between the elementary theory on the flange wrinkle limit, the fracture limit, and the experimental results. In addition, the authors examined each variable BHF and SPD method obtained from the theory and experimentally demonstrated that the variable BHF method has a great effect on uniform wall thickness distribution and that variable SPD has a great effect on shortening the processing time for superplastic materials. Furthermore, the authors demonstrated the effectiveness of the variable BHF/SPD deep drawing method that varies both BHF and SPD simultaneously.
Highlights
Superplastic materials have a high strain rate sensitivity index, m, and the property of exhibiting a huge elongation with a breaking elongation of several hundred percent or more under the conditions in which the superplastic phenomenon appears [1]
For the magnesium alloy AZ31 in a warm deep drawing process with a flange temperature of 400 ◦ C which is thought to exhibit superplasticity, an limit drawing ratio (LDR) of 5 or more has been successful under the variable blank holder force (BHF) [3]
The authors examined the effects of the mechanical properties and dimensions of the blank, the friction coefficient and punch speed of the forming conditions on the flange wrinkle limit, and fracture limit BHFs in the cylindrical deep drawing are studied by a simplified theory based on the constitutive equation, taking into account both strain hardening and strain rate dependence
Summary
Superplastic materials have a high strain rate sensitivity index, m, and the property of exhibiting a huge elongation with a breaking elongation of several hundred percent or more under the conditions in which the superplastic phenomenon appears [1]. The authors examined the effects of the mechanical properties and dimensions of the blank, the friction coefficient and punch speed of the forming conditions on the flange wrinkle limit, and fracture limit BHFs in the cylindrical deep drawing are studied by a simplified theory based on the constitutive equation, taking into account both strain hardening and strain rate dependence. To study the effect of the m value and strain rate on the wrinkling behavior, experimental research on deep drawing using a superplastic material with a high strain rate dependence and a large blank with a wide flange surface is required. To clarify the detail wrinkling phenomenon of SPZ2 superplastic material in warm deep drawing process, the occurrence and behavior of flange wrinkles are focused on, and the effects of BHF and SPD on the wrinkle limit for a blank of larger DR are investigated. The effectiveness of each VBHF and VSPD method and the combined VBHF/VSPD method in the warm superplastic deep drawing is validated
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