One prior art method for producing workpieces is known from DE 10 2005 057 945 A1. In such methods, rotationally symmetrical preforms are processed by pressure rollers to produce various products, such as, for example, support rolls, automotive parts and gas bottles. In view of the stress such products are exposed to, it is desirable to stiffen certain areas as early as possible when being formed. In utilization such products, in particular central sections thereof, are subjected to a stronger stress, so material reinforcement is preferable in this area. Designs with concave or conical inner surfaces are particularly preferred, however, they cannot be produced by known flow-forming methods.
Accordingly, one object of the invention therefore is to provide a method of the above-mentioned character which enables the production of workpieces, from a perform, having a concave or conical inner surfaces.