On the control of thickness in gas blow metal sheet forming processes: A review

Although the advantages of formability are notable, blow-forming processes, which are classified as sheet metal stretching processes, present limits in terms of uniformity of the thicknesses of the produced product. This is a review paper that collects the numerical and experimental studies of the literature on the new metal sheet forming techniques to improve formability and production efficiency. In particular, the focus is on (a) the multi-phase forming technique and (b) the techniques involving a blank with a profile of variable initial thickness. These techniques promote a strategic decrease of the thickness in some areas of the part to be formed to improve the final distribution of thicknesses in those most critical areas of the component to be made. The paper presents the finite element modelling works of the literature to predict the accuracy of a formed part in terms of the uniformity of its thickness that avoids breakups; thus, allowing to design and establish the feasibility of new forming techniques. The parameters influencing the forming processes were analysed by comparing the results of the finite element simulations in terms of the thickness distribution of the finished product and forming times. This paper presents also the experimental forming tests that verified these forming techniques and provided a thickness profile that reduces maximum thinning and forming times in comparison with the traditional processes. The conclusion of the paper demonstrates that these forming techniques allow to obtain a more uniform thickness of the formed part in a shorter processing time.