Abstract: A new technology of solid granule medium forming (SGMF) is proposed to overcome the disadvantages of the traditional flexible die forming which has advanced the development of tube forming technology. The new technology not only can resolve the sealing problems in fluid medium forming and viscous medium forming, but also has advantages of nonuniform distribution of inter-pressure, easy control of workpiece forming, and improvement in material forming limit, thereby providing a new means for material preparation and manufacturing. In view of the pressure-transmitting characteristic of solid granule medium, the linear loading model and the cosinoidal loading model are presented. Plasticity theory is adopted to research the plastic deformation in free deformation area in the process of pipe forming under the action of nonuniform inter-pressure, and the theory of which is established. The formulas for calculating the stress, strain and wall thickness of the free forming area are derived and verified practically through experiments.

Key words: Forming process, Solid granule medium, Tube