Manufacturing of a hemispherical component combining incremental forming and superplastic forming

The interest towards magnesium (Mg) alloys for the fabrication of light weight components has been continuously increasing, especially for transportation, since the payload is strictly related to the energy (fuel or electricity) consumption. Super plastic forming (SPF) and single point incremental forming (SPIF) are viable processes for manufacturing light weight parts since they allow to produce components with superior characteristics and quite complex geometries, even in the case of the poorly formable Mg alloys. But, since both the processes are characterized by stretching, thinning is a key issue to be addressed. On the other side, in order to fulfil the structural and corrosion resistance characteristics required by aerospace and automotive applications, components with a uniform thickness distribution have to be produced. Such an aspect is even more important when the shape complexity of the component increases. SPF and SPIF have never been combined or hybridized so far but, in order to produce parts with a uniform thickness distribution, a possible strategy based on the blank pre-forming by SPIF prior to the SPF has been proposed in the present paper. In particular, the initial blank shape to be obtained by SPIF was designed using a numerical optimization approach and effectively created using the sine law to predict the wall angle and design the tool path. A hemispherical component in AZ31B-H24 was used as case study. The thickness profile of the component obtained by SPF revealed to be highly uniform in a large area (the portion from the centre of the sample to its periphery corresponding to about 70%) being characterized by a thickness equal to about 0.5 mm. The quality in terms of finishing of the component produced by SPF resulted to be good, irrespective of the roughness increase exhibited by the blank after the pre-forming by SPIF.