Surface Crack in Hydrostatic Extrusion of Brittle Metal

抄録

Surface crack produced during hydrostatic extrusion of brittle metal was investigated. The effect of die angle, length of die bearing and frictional force on the critical back pressure which prevents cracking was studied. It was found that the surface crack is initially produced in the perpendicular direction to the axis near the exit of deformation zone. Then, under some conditions, the crack propagates in the inclined direction to the axis, which is usually called the "fir-tree crack". It was suggested that the surface crack is produced by the axial tensile stress acting on the surface at the exit, which results from non-uniform deformation of the billet at the exit, elastic repulsive force of the die and frictional force between the die bearing and the billet.