Application of numerical simulation in the bending of aluminium-alloy profiles

Abstract

This paper deals with 3D elasto-plastic finite-element analyses of the production bending of aluminium extrusions. The overall objective of the study is to determine the applicability of using the general purpose software MARC K5.2 in analysing industrial rotary draw bending and stretch bending. The main focus is placed on the effects of material behaviour, slenderness of cross-sectional members, and die geometry on geometrical tolerances. The influence of applying external pre-stretching and internal support for obtaining better tolerances is demonstrated also. The results have been validated by a number of tests carried out in the laboratory and using industrial bending machines. The results show that wrinkles and sagging, or ‘suck-in’ of the flanges, can be eliminated by applying a stationary internal mandrel in combination with an internal web, even with tight radii. Furthermore, external pre-stretching is shown to be advantageous in order to reduce local buckling and spring-back. It has been found that the thickness variation expected after extrusion is of the same importance as anisotropy with respect to sagging in stretch bending. Elastic spring-back is influenced by the strain-hardening characteristic and the amount of axial loading applied, both decreased strain hardening and increased tension ensuring reduced spring-back. The experimental and numerical results appear to be in excellent agreement, indicating that extrapolation of the results to cases, other than those tested, may be possible. It is concluded that finite-element analysis has proven to be a well-suited numerical tool for design and product optimisation in industrial bending.