The increase in using light weight alloys such as aluminum and magnesium sheet materials is accompanied by many challenges in forming these alloys due to their unique mechanical properties and/or low formability. Alternative forming operations, such as warm forming or sheet hydroforming, are potential solutions for the low formability problem of aluminum alloys. Identifying potential difficulties in forming these materials early in the product realization process is important to avoid expensive late changes. Finite Element (FE) simulation is a powerful tool for this purpose provided that the inputs to the FE model, including the flow stress data, are reliable. However, obtaining the flow stress under near production condition (state of stress, strain rate, temperature) may be challenging especially if the flow stress is required at elevated temperature for warm forming applications.
In this study, elevated temperature biaxial Viscous Pressure Bulge (VPB) tests were conducted for Aluminum (AA 5182) and Magnesium (Mg AZ61 L) alloys and the resulting flow stress curves were obtained. Using the Surface Response Method that evaluates the error function gave the prediction of flow stress coefficients K, n and m that fit the Power Law Equation. Results of this work predict the flow stress data under a variable strain rate and thus cannot be directly compared with other results which were conducted under a constant strain rate. The fact that the state of stress in actual stamping processes is almost always biaxial, suggest that the bulge test is a more suitable test for obtaining the flow stress of light weight alloys to be used as an input to FE models.
The sheet hydroforming with punch (SHF-P) process offers great potential for low and medium volume production, especially for forming: (1) lightweight sheet materials such as aluminum and magnesium alloys and (2) thin gage high strength steels (HSS). Aluminum and Magnesium alloys are being increasingly considered for automotive applications, primarily due to their lightweight and high strength-to-weight ratios. However, there is limited experience-based knowledge of process parameter selection and tool design for SHF-P of these materials. Thus, there is a need for a fundamental understanding of the influence of process parameters on part quality.
A Sheet Hydroforming with a Punch (SHF-P) process was successfully simulated using the FE software Pamstamp 2G 2009. The objective was to develop a fundamental understanding of the process to reduce the expensive experimental trial and error. A systematic methodology to design the process was suggested and applied using FE simulation.