Design of Caliber Rolls Incorporating Load Path Dependent Damage Evolution

Abstract

Caliber rolling is an important forming process to produce semi-finished parts. In caliber rolling, the process route can be varied with respect to the caliber geometry at intermediate passes without changing the initial and end geometry. Usually these intermediate passes are optimized with regard to the filling degree, which depends on the axis ratio of the oval caliber and on the area reduction in each pass. In order to improve the service life of products, this paper considers the damage evolution additionally. For a roll-sequence round-oval-round two rolling routes are found with adequate filling degree in each roll pass. The variation of the process route leads to a significantly different loading path, which is defined as the strain-dependent development of stress triaxiality and Lode parameter. In this study, the influence of the loading path variation on the damage evolution is investigated. Meanwhile, damage criteria, e.g. Oyane criterion, are applied to predict the progressive damage level. The results indicate a remarkable difference in damage at the end of the process due to the loading path variation and higher damage always occurs near the symmetric axis of the workpiece according to FE simulations.