Investigation on the inner hole spiral-groove of cross wedge rolling of hollow shafts with mandrel

The cross wedge rolling (CWR) is an efficient and green process for manufacturing hollow shafts. The mandrel plays an important role in controlling hole shape during the process of hollow shafts CWR with mandrel. To obtain high-precision rolled parts, it is necessary to control dimensional fluctuations. Finite element (FE) simulation and CWR experiments were presented, and the results showed that the inner hole spiral-groove causes periodic fluctuations of inner diameter along axial direction and an uneven microstructure. The spiral-groove on the outer surface causes metal overlaps and cracks. The formation mechanism of the inner hole spiral-groove was studied. The inner hole spiral-groove is caused by the joint effect of CWR dies and mandrel. The formation reason of inner hole spiral-groove is that the metal in inner hole flows toward reverse-stretching direction under the effect of CWR dies and mandrel. The inner hole spiral-groove intensifies with the non-uniformity of instantaneous radial deformation. The effect of process parameters on the inner hole spiral-groove was investigated. The inner hole spiral-groove intensifies with the increasing forming angle, stretching angle, compress ratio, and initial pipe thickness. The inner hole spiral-groove decreases with the increasing relative mandrel diameter. The results reveal the reason of the inner hole spiral-groove of hollow shafts CWR with mandrel and provide theoretical guidance for the selecting of process parameters in production application.