Forming analysis of a tubular connecting bolt

A visioplastic analysis was conducted on cold-forged samples which were part of the production of connecting bolts. Forming is carried out starting with a cylindrical blank that is pierced in two indirect extrusion passes to produce the tubular part. The strain gradients within each piece were determined using the flow lines of the material, put in evidence by metallographic means, as internal markers. The visioplastic analysis was complemented with microhardness indentation tests made on the pierced specimens and with compression tests made on specimens machined from an undeformed blank. It was found that the strain distribution was heterogeneous; the higher values of the normal components were located at the tubular walls of the pieces, whereas the higher values of the shear and equivalent components were found close to the changes in geometry of the specimens, where the material flow has to change its direction. A good correlation between the values of microhardness and equivalent strain distribution was observed.