Regional control of sheet metal formability via establishing differentiated pressure field using heterogeneous elastomers in flexible die forming process

Isostatic pressure-carrying properties of conventional flexible dies commonly fail to adapt to the forming of shell with sharp geometry change since pressure required by local region of sheet metal is unequal. In order to deal with this problem, a forming method based on differentiated pressure field was proposed in this work. Heterogeneous elastomers fabricated from partitioned elastomers with different mechanical properties were employed to create a differentiated and adjustable pressure field. Analytical modeling, finite element analysis, and bulge tests of the proposed forming process were carried out. Concretely, when heterogeneous elastomers’ ratio of shore hardness of two partitions (ζ) decreased from 34 to 1, filling ratio (ω) of sheet metal corresponding to the “softer” side of the flexible die reduced from 48.76% to 40.71%, and deviation of the filling ratio (λ) decreased from 12.09% to 0, showing the descending filling capacity and deformation nonuniformity. In addition, position of bulged dome shifted from center to one side where sheet metal was in contact with the “stiffer” partition of heterogeneous elastomers along the radial direction. The controllable nonuniform deformation and strain in different regions could be induced. Numerical results showed that through adjusting ζ of heterogeneous elastomers to enhance or weaken the pressure on one side of the sheet metal, stress path deviated or approached the equal biaxial tension stress state, which explained the mechanics of the proposed forming method. Further applications of the proposed method in the forming of nonsymmetric shell components will be expectable. Graphical Abstract: [Figure not available: see fulltext.]