Increase of wire stress stability depending on anti-tension action when friction coefficient is inconstant

The strain parameters instability causes variable axial stress during the drawing process. Contact friction specification varies in the shortest time and depends on many factors: homogeneity physico-mechanical properties of the processed material along the length of the pulled billet, quality of technological lubrication, stability of tension force of the billet at the entrance of deformation center and cooling intensity of the fiber, suction drums, washers, rollers, etc. To estimate the effect of friction coefficient on stability of drawing force (stress), first derivative with respect to friction coefficient in drawing equation is used. The first derivative dependence on drawing coefficient is constructed for different hardening models and deformation parameters. Action of anti-tension was investigated when drawing on stressed state of a circular continuous profile. Studies have been carried out for simulation models of hardening. In the course of study, it was proved that it is possible to estimate instability of stressed state by the first derivative with respect to magnitude, depending on friction coefficient of the equation that determines drawing stress. For different deformation parameters, the first derivative with respect to friction coefficient is calculated for the equation determining axial drawing stress. A decrease in magnitude of the derivative is shown with an increase in anti-tension, which indicates expediency of drawing with antitension to stabilize drawing force and to reduce fatigue wear of dies working surface. Calculations were performed for different values of friction coefficient for drawing under the conditions of presence and absence of drawing cylinder and slope angle of drawing cone to drawing axis, mechanical properties of the billet for drawing, and for various coefficients of its hardening. The stabilizing effect of drawing cylinder of dies on drawing stresses with an increased friction coefficient is shown. Instability of drawing stress from deviation of nominal value of friction coefficient depends on values of other strain parameters. In conditions of drawing cylinder presence and small amount of deformation in drawing path and smaller initial friction coefficient, change in its magnitude has a greater effect on stability of the stressed state. Increase in drawing stress stability positively affects quality of wire, operational stability of units and drawing-line elements, for example, due to decrease in fatigue wear of die working surfaces, drawing drums, bypass and straightening rollers. Drawing with anti-tension and the use of special drawing tools stabilize stress state in deformation zone.