Combined sealing and mandrel

The invention relates to a combined sealing and mandrel (1) for sealing a in a plastic injection molding tool (5) inserted hollow structure (6) during injection molding and for subsequent mechanical expansion of the hollow structure (6) by insertion of the sealing and expansion mandrel (1) in same. This makes it possible to establish quickly and easily a plastic injection-molded component (7) with integrated hollow structure (6).