A new method of determining forming limit diagram for sheet materials by gas blow forming

A new methodology is proposed to obtain forming limit diagrams (FLDs) of sheet materials using gas blow forming process at elevated temperatures. Tension–tension side of the forming FLD is achieved by using circular as well as elliptical dies of different aspect ratios. To achieve tension–compression side of FLD un-bonded bi-layer specimen with slots are utilized. The widths between the slots are varied to achieve different strain paths. A correlation is established between the hemispherical punch-based tests and GBF tests of samples with slots to achieve different strain paths. FLDs for automotive AZ31 magnesium sheet at 300°C and 400°C in two different orientations are determined. Increase in forming limits of AZ31 with increase in temperature is observed.