Experimental, analytical, and numerical analysis of the copper wire multi-pass drawing process

In the cold wire drawing process, the stress acting on the wire depends on process parameters, as well as on the material flow stress, including the strain-hardening that occurs step by step. It is essential to ensure that the stress applied to the wire at the exit of the die remains below the material's yield stress, to prevent wire necking and fracture. Industrially, the process is carried out continuously using multi-step-multi-wires machines that deform the material to high strain at elevated strain rate values. The application of analytical models for evaluating the stresses acting on the wire assumes simplified boundary conditions, such as an average distribution of strain and strain rate within the die. Further studies are necessary, considering the entire multi-pass industrial case and involving finite element simulation, which is today the main tool for optimizing industrial processes. In this work, the drawing process applied to ETP Pure Copper (99.9% in weight) is analyzed experimentally, analytically, and numerically. The material was characterized by torsion tests and experimental drawing tests were carried out on four steps of the process. Through the analysis of the different analytical methods, it was shown that a careful evaluation of the friction coefficient values is necessary to reduce errors in estimating the drawing forces. The aim is to provide a reliable numerical model for predicting the stress acting on the wire during the multi-pass drawing process, through an appropriate characterization of the material flow stress and an evaluation of the friction model.