Barrelling of aluminium solid cylinders during cold upset forging with constraint at both ends

Experiments were carried out to generate data on the cold upset forging of solid cylinders of annealed aluminium using different lubricants with dies at both ends. The friction factor ‘m’ for the different lubricants used were determined by conducting ring compression tests. The dies created back extrusion of metal through a die hole at both ends and developed two barrels in the unrestrained portion of the cylindrical specimens. The curvatures of the barrels, namely, top and bottom, developed in the unrestrained portion were found conform one to one to the calculated values using the experimental data. The calculations were made on the assumption that the curvatures of the barrels followed the geometry of a circular arc. It was further found that the measured radius of curvature of both barrels exhibited a straight-line relationship against the new geometrical shape factor irrespective of the aspect ratios of the cylinders. Further empirical relations were found to exist between the measured radius of curvature of both barrels and other variables such as the hydrostatic stress and stress ratio parameter.