Surface contours in the axi-symmetric upsetting of solid cylinders

Abstract

Surface flow contours during the axi-symmetric upsetting of aluminium, Sn-Pb eutectic alloy and Plasticine have been studied as a function of the extent of deformation, frictional condition and height-to-diameter ratio. The roughness of the end faces after upsetting has also been measured. The results have been explained in terms of the changes in the frictional condition, the strain-rate sensitivity and the local strain rate and it is concluded (a) that cold upsetting of a material of negligible strain-rate sensitivity gives rise to a parabolically-shaped barrel, (b) that hot upsetting the Sn-Pb alloy specimens of height-to-diameter ratio 1.5 results in a linear increase in diameter from the top to the bottom of specimens, due to a linear decrease in strain rate in the same direction, (c) that hot compression of Plasticine specimens and Sn-Pb alloy specimens of height-to-diameter ratio 2.0 leads to complex shape changes which cannot be predicted using the present knowledge concerning the upsetting of strain-rate sensitive materials and (d) that the greater increase in roughness following significant compression of the end faces of lubricated specimens, compared with that observed for unlubricated specimens, is due to enhanced surface metal flow with a decrease in frictional constraints.