Engineers are forced to come up with better prognoses for forming processes. Therefore, it is important to provide a practical and efficient method to predict deformation behaviours. Sivanandini et al. (2012) describe flow forming generally as an incremental forming process for tubes. One process modification, postulated by Birk (1985), is ball spinning. Similar to a ball bearing, the balls are controlled by a cage (Fig. 1). The diameter of the tube or rod is reduced by the rotating balls and is adjusted by the diameter of the leading ring. This process is applied in the production of cookware, automobile parts and military applications
The ball spinning process is characterized by a complex stress
state (Kuss and Buchmayr, 2015). Since this stress state is overlaid
with the local stress state of the ballplane contact to a significant damage at the workpiece. This ballplane contact was firstly
described by Heinrich Rudolf Hertz (1857–1894). The particular
feature of the ballplane contact is, that the highest surface pressure
occurring at the top of the plane, injects shear stresses underneath
the surface.