EFFECT OF DOUBLE MONOLITHIC DIES ON RESIDUAL STRESSES AFTER WIRE DRAWING

Abstract

Residual stresses that form in wire during drawing in a monolithic die have a significant impact on the performance properties of metal products. Managing the level and distribution of residual stresses in the metal improves the corrosion and relaxation resistance, durability, fatigue strength, and ductility of finished products. A study of the effect of twin dies on residual stresses was conducted using computer simulation of drawing 3.00 mm diameter wire from a 3.50 mm blank made of grade 10 steel. The study found that twin dies have a positive effect on residual stress formation. Twin dies reduce radial compressive stress by 100 MPa compared to drawing in a single die, provided the total reductions are the same. Splitting the reduction into two dies reduces the compressive stress in the center of the wire by 60 MPa compared to a twin die.  The use of a twin die has an ambiguous effect on the distribution of tangential residual stresses across the wire cross-section. Compressive stresses in the central layers of the wire decrease by 70–100 MPa compared to a single die. However, tensile stresses on the surface increase by 50–60 MPa. The increase in residual axial stresses– compressive in the center and tensile on the surface – observed during twin die drawing is due to the fragmentation of the reductions and increased deformation non-uniformity across the wire cross-section. Therefore, when selecting the geometric parameters of twin die dies, deformation non-uniformity should be reduced by matching the unit strain rate to the working angle of the die.