Investigation of the combined effect of friction and interstand tension on the work conditions of a two-stands reversing cold mill

Cold-rolled strips are largely used in various fields of applications, such as electric works, automobiles, home appliances, and light industry. In addition to the growing demand for cold-rolled strips, customers are increasingly concerned about the final quality of the products. The factors that affect the performance of steel strips can be divided into two categories: material parameters and rolling conditions. The latter are generally unknown and, therefore, a systematic methodology to inversely determine the coefficients of friction is of utmost importance. Moreover, when dealing with more complex systems, as in the case of a two-stands rolling mill, the friction conditions are strictly connected to the interstand state of tension, and their calibration becomes even more difficult. This paper investigates the combined effect of the friction and the interstand tension during the cold rolling of the SAE1006 steel grade. Experimental data were taken directly on-site from the two-stands reversing cold mill (RCM). The rolling process was modelled using the commercial finite element (FE) code Abaqus/CAE: rolls were modelled as elastic bodies (to account for their flattening during the rolling operations) and the process parameters from RCM were simulated. A full factorial plan of simulations was arranged by varying the coefficient of friction in the first stand (indicated as CoF1) and the one in the second stand (indicated as CoF2): numerical results were collected in terms of rolling force and interstand stress and compared with the data obtained by on-site measurements. It was demonstrated that the proper values of CoF1 and CoF2 could be successfully determined (by minimizing the error function between numerical and experimental data) only when considering also their effect on the interstand state of stress.