IMPACT OF DRAWING PROCESS PARAMETERS ON UNIFORMITY OF STRAIN IN SPRING WIRE

Shear deformation of subsurface layers in wire drawing leads to marked non-uniformity of strain across the wire cross section. In wires intended for products operating under dynamic loads, such as ropes and springs, the variance in work hardening level across the cross section may cause fatigue fractures. <In this paper we used mathematical modelling in an attempt to show how the non-uniformity of strain in drawing can be reduced by changing key process parameters. For this purpose, a full factorial experiment involving three factors was undertaken. (The factors included the approach angle 2 alpha, friction coefficient mu and single pass strain Q(d) or the number of passes n.) The simulation involved drawing of 2.5 mm C75 steel spring wire from 5.5 mm thick rolled rod. FormFEM 1.6 simulation software was used for the modelling. For the purpose of this experiment, the strain non-uniformity is defined as the difference between the maximum (normally on or just below the surface) and minimum (in the centre of the wire) levels of strain intensity. In addition to this key parameter, the impact of other factors (and their combinations) on the total drawing power will be evaluated as well. Mathematical analysis revealed that the strain distribution across the wire cross section strongly depends on the single-pass strain (the lower this reduction, the greater the difference between the maximum and minimum levels) and on the reduction zone angle (the greater the angle the less uniform the strain intensity). Then, the impact of friction is only significant in regard to the overall drawing power.