Analysis of the influence of back-pull during drawing of aluminium wires

A laboratory wire-drawing process was investigated with respect to friction conditions in the die-wire interface by a combined experimental and numerical analysis using the finite element method. Back-pull on the wire was provided during the experiments by placing two dies in sequence. The drawing force of the first die then provided back-pull into the second die. Experiments without back-pull were also performed as reference by pulling the wire through a single die. Dies of different geometry and different reductions were used in the investigation. A fluid lubricant was used, and the wire material consisted of an AA 6082 aluminium alloy heat-treated to a hard and a soft condition, respectively. The Bridgman-corrected flow curve for different wire material variants was determined by tensile testing. A power-law stress-strain relationship was then obtained by curve-fitting. In the experiments, the drawing conditions, and thus also the contact conditions in the die-wire interface, were varied within broad limits. Moreover, the drawing forces were measured in each experiment. All experiments were reproduced by FE-simulation in order to determine the friction conditions in this indirect way. The investigation showed that there was good correspondence with respect to drawing forces between experiments and simulations, when friction was modelled as Coulomb friction with an approximately constant coefficient of friction. The influence of back-pull on the drawing process was studied by performing simulations of two corresponding drawing operations, one with, and the other without back-pull. The simulations showed that the main effect of back-pull was to alter the stress conditions inside the plastic zone in such a manner that the contact pressure between die and wire was reduced.