The manufacturing of metal bellows consists of four main forming processes; deep drawing, ironing, tube bulging and folding. Among these, tube bulging and folding are critically important processes. Tube bulging and folding are usually done in successive operations for a single cycle of the bellows forming machine. The quality of metal bellows is greatly influenced by the forming conditions of these processes. Especially the effect of hydraulic pressure on bellows forming should be investigated for the proper design of the process.
The present study is concerned with the analysis of tube bulging and folding in the bellows forming process by the upper-bound method. The validity of the proposed analysis is checked by the finite element method for the tube bulging process. Experiments are carried out for phosphor-bronze bellows in a bellows forming machine. For the tube bulging process, the upper-bound solution is in excellent agreement with the finite element analysis as well as with the experimental observation. In the folding process, the theoretical analysis is in good agreement with the experimental results in the recommended forming range of hydraulic pressure. It is thus shown that the present method is applicable to the effective design of the bellows forming process.
