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.