Numerical evaluation of the die geometry influence on the residual stresses produced during the wire drawing process of steel bars

ABSTRACT

Wire drawing is a metalworking process used to reduce the cross-section of a wire by pulling the wire through drawing dies. The generated strains are non-homogeneous through the cross section of the material, leading to residual stresses that can contribute to the appearance of shape distortions, crack propagation and shortening of the product life time. In this work, the influence of the die geometry in the generated residual stresses on a typical case of wire rod drawing operation (production of straight AISI 1045 steel bars with 11% reduction from an initial diameter of 21,46 mm) was investigated. The objective was to obtain a new tool design able to reduce the residual stresses in relation to a typical design of the tools which includes the use of a drawing angle of 15º in one single pass. Compression and ring compression tests were performed in order to obtain the material stress-strain curve and the friction coefficient of the process, respectively. The developed numerical models were initially validated by analyzing simulated residual stress profiles regarding the equilibrium conditions for the problem, as well as by comparison with literature data. Furthermore, the principal strains and the contact pressure (between the bar and the die) values obtained from the simulation were compared with calculated ones. Initially, simulations were carried out for different bearing lengths and it was found that for relations of bearing length to diameter of the drawn bar between 0.4 and 0.6, a reduction in the axial residual stresses can be achieved. A large reduction in the axial residual stresses at the surface of 65% in relation to the typical industrial design was found in the case of the design with a double conical region, showing to be a promising solution for die design improvement.

Keywords:
wire drawing; residual stresses; numerical simulation