Optimization Of The Cold Expansion Process For Titanium Holes

International audience; Cold expansion of metallic holes is widely used in the aerospace industry as an efficient industrial process for improving fatigue performance of mechanical assemblies. To increase the efficiency of the process, it is worth considering the possibility of carrying out the expansion twice in succession in the same hole. This paper discusses the consequences of such an operation on a single titanium hole through a numerical and experimental study. More precisely, dedicated finite element modelling of the cold expansion process has been developed in order to simulate cases where the expansion is carried out twice: in the same direction and in opposite directions. The residual fields generated are analyzed and the results compared with experimental results. Furthermore, we propose in this study to assess a new methodology for measurement of the intensity of the compressive residual stresses generated at the hole edge. Specifically, we will use the incremental hole drilling technique to characterize the expanded holes, including or not a reaming operation of the cold worked hole. Results show that double expansion has a very positive impact on the homogeneity of the compressive fields generated as long as the direction of expansion is properly selected to guarantee the efficiency of the process.