Optimal distribution of drawing strains in the two-pass tube drawing process

Abstract

A multiple-pass tube-drawing process is often used to obtain large cross-sectional reductions in tubular components. For a multi-pass drawing process, it is important to distribute the strains among the individual passes. With even distribution of the strains, there is less chance to exceed the formability limit of the material in any one pass, thus preventing defects such as drawing cracks from occurring. In the present study, an analytical model is developed, which determines the appropriate intermediate tube geometry to ensure uniform strain distributions for a two-pass drawing process. The model is based on the evaluation of the cross-sectional changes of the tube after each pass. For a desired product geometry, the model provides the intermediate diameter and intermediate thickness that should be used to distribute evenly the drawing strains between the two passes. Finite element modelling of the two-pass tube-drawing process confirms the viability and validity of the analytical model. The model has also been used to develop criteria curves for various limit strains. These criteria curves can be used to determine whether the tube will fail or will be successfully drawn in a two-pass process.