Recovery effect in drawing of steel bar for sizing

摘要

Dimensional accuracy characterized by limit deviation in diameter is of great importance for the sized steel used for critical machine parts and tool production. Sized steel is manufactured by cold drawing with small single reductions. One of the ways to improve the dimensional accuracy is to take into account the recovery effect. As a result of the effect above the sized steel diameter after drawing is a bit larger than the die bearing diameter in the non-loaded condition. For some predetermined combinations of the drawing process factors the recovery value is quite comparable with the diameter tolerance limit determined by standards. It is especially characteristic for sized steel more than 10 mm in diameter with yield strength of more than 400 MPa. The study describes the investigation results of the drawing process factors influence the value of sized steel recovery. Using the finite elements method the authors carried out simulation of stress and strain state in the deformation zone during drawing. It was proved that there was a relationship between the radial stresses developed on the sized steel surface on the exit from the die bearing zone and the recovery value. The research group determined the dependence of recovery value on the degree of reduction, the coefficient of contact friction, the die semi-angle and the die bearing length, the bar yield strength and its diameter. The obtained results make it possible to determine the parameters of sized steel drawing with the preset diameter limit deviation taking into account the recovery effect within a wide deviation range of processing factors.