A study on barrelling in magnesium alloy solid cylinders during cold upset forming

Experiments were carried out to generate data on the upset forming of circular solid cylinders of hot-rolled magnesium alloy ZM-21. During the experimental investigation, the magnesium alloy cylinders were observed to show a change from a circular contact area on the top and bottom surfaces to an elliptical surface area. Calculations were made on the assumptions that the curvature of the barrel surface followed the geometry of both circular and elliptical arcs. It was observed that the measured radius of curvature of the barrel exhibited a straight-line relationship with a new geometrical shape factor, irrespective of the orientations, i.e., irrespective of whether the specimens were machined in the rolling, transverse or thickness direction of the hot-rolled plate. Further, empirical relationships were found to exist between the measured radius of curvature of the barrel and other variables such as the hydrostatic stress and the stress-ratio parameter.