Effect of various stress ratio parameters on cold upset forging of irregular shaped billets using graphite as lubricant under plane and triaxial stress state conditions

This paper examines the effect of various stress ratio parameters on cold upset forging of commercially pure aluminium solid billets of irregular shaped billets, using graphite mixed with oil as lubricant applied on both sides under plane and triaxial stress state conditions. Billets with three different aspect ratios (ratio of height to diameter) namely, 0.5, 0.75 and 1.0, with different ‘b/a’ ratios (ratio of minor to major diameter) namely, 0.6 and 0.7 were prepared and cold forged. Cold deformation on samples were subjected to an incremental deformation steps of 3 metric tones load and at the end of each step, dimensions such as height, contact and bulged diameters being measured. The calculations were made with the assumption that the radius of curvature of the barrel followed the form of a circular arc. Analysis of the experimental data showed that there exist a relationship between the measured barrel radius and various stress ratio parameters namely, (σθ/σz), (σm/σz), (σeff/σz) and (σm/σeff) developed under plane and triaxial stress conditions. An attempt has also been made to relate the percentage height reduction with respect to the stress ratio parameters namely, (σθ/σz), (σm/σz), (σeff/σz) and (σm/σeff) developed under plane and triaxial stress conditions and found to have an increasing trend and a straight line trend with enhanced level of deformation irrespective of aspect ratios and b/a ratios tested or selected.