Determination of limiting and legitimate values of drawing coeffi cient and delta-criterion for deformation zone shape during wire drawing

Abstract

The limiting and legitimate values of the drawing coefficient and delta-criterion Δ for the deformation zone shape depending on the friction coefficient for different models of hardening and the values of the drawing angle and the back-pull stress are determined by numerically solving the corresponding equations. The limiting and legitimate values of the drawing coefficient decrease with increase in the friction coefficient, while the analogous values of the criterion increase. Increase in the safety factor causes decrease in the allowable drawing and increase in the delta-criterion. The limiting and legitimate values of the drawing coefficient decrease from the application of back tension in the absence of strain hardening. The nature of the effect of back tension on the limiting and legitimate values of the drawing coefficient and the delta-criterion depends on the deformation parameters with intensive hardening and significant value of the friction coefficient. The possibility of the absence of limiting values of the drawing coefficient and criterion Δ under hypothetical drawing conditions is shown: intensive hardening of the wire material at low friction coefficient and the calculation of the limiting values of these indicators based on the value of the I.L. Perlin safety factor, equal to 1. The estimation of the reliability of the approximate equality is carried out to determine the nature of the relationship between the criterion Δ and the index of the deformed state. It is shown that with small value of the delta-criterion (Δ < 2) wire breakage at the die exit is not guaranteed, since the limiting value of the drawing coefficient is slightly greater than 1. The drawing production technologist needs assessment of the limiting and legitimate values of the drawing coefficient and delta-criterion for predicting of wire (rod) breakage at given deformation parameters.