Investigation of Thermal-Related Effects in Hot SPIF of Ti–6Al–4V Alloy

The present work focuses on a new approach to hot form hard-to-work materials by Single Point Incremental Forming (SPIF) technology using a global heating of the sheet. A set of trials was carried out in order to identify the optimum temperature cycles to minimize geometric distortions associated to each process stage on the fabrication of parts made of Ti–6Al–4V. On the one hand, heating trials allowed defining the optimal procedure to improve the temperature distribution homogeneity along the sheet and consequently to minimize its thermal distortion previous to the forming stage. On the other hand, the influence of both working temperature and the applied cooling on the geometric accuracy was evaluated by means of SPIF trials. For this purpose, a generic asymmetric design with typical aeronautical features was used. These trials pointed out that high forming temperatures allow reducing significantly the material springback whereas a controlled cooling (with an intermediate stress relief treatment) minimizes both the distortion of the part during the cooling and the mechanical stresses accumulated on the clamping system. Furthermore, the work includes a post-forming material evaluation to determinate the influence of the employed processing conditions on microcracks, alpha-case layer, microstructure and hardness.