Initial stress in the hot forging of a cylindrical blank

Abstract

A model is proposed for the hot extension of small-diameter cylindrical steel blanks in complex faces to obtain round forgings. Plane deformation is considered. The stress state is calculated on the basis of the Michell problem for an elastic wedge, the Flamant problem for a semiinfinite plate, and a method proposed earlier for assessing the transition of a blank to the plastic state on extension in plane faces. The thermal stress is disregarded; the elastic modulus of the blank depends on the temperature. The distribution of elastic stress tensors in the blank due to the action of three point forces is determined. The total stress field is established; it depends on the vertex angle in the V-shaped lower face. The stress in the plastic-flow zone within the blank’s cross section is estimated, on the basis of the limiting effective elastic stress tensor due to the action of three point forces. As an example, the extension of a steel 45 blank is considered. The limiting effective elastic strain ɛel is assumed to be the elastic limit ɛ0.2 = 0.002. On the assumption that the elastic modulus of steel 45 is 100 GPa at 950°C, the load coefficient when part of the blank passes to the plastic state is determined. The distribution of the components of the total stress tensor is also established. The effective stress corresponding to transition to the plastic state determines the boundary of the plastic zone. The corresponding graphs are plotted. The influence of the vertex angle in the V-shaped lower face on the distribution of the stress-tensor components is established. The optimal value is 120°.