During eccentric rotary swaging, the material is severely strained with a high amount of shear stress leading to ultra-fine grained microstructures. The workpiece is fed axially into the swaging head and is formed radially with consecutive forming steps. Due to the volume constancy, the reduction of the diameter leads to an elongation of the workpiece. Hence, the incremental forming causes a local material flow both in radial as well as in axial directions. Axially, the material flows not only in feed direction but also backwards. However, this effect cannot be measured in the final product. Therefore, a new method is proposed for the visualization of the axial material flow along the formed part. Special dies with flat surfaces and a small cam at one of the three dies were designed and tested in this study. By one stroke, the diameter of the part is reduced and additionally, the cam element forms a notch. In combination with a defined stroke following angle ∆ϕ (the difference between the rotation angle of the workpiece and the rotation angle of the die between consecutive strokes) and axial feed per stroke shapes a helical channel during the process. The pitch of the resulting thread is correlated to the axial flow in feed direction. The results show, that the pitch is not constant over the whole length of the swaged part. Additionally, micrographs show fluctuations of the internal material flow. The locally resolved pitch of the helical channel as a method enables new insights into the material flow during rotary swaging.
