Active material flow control and deformation mechanism in sheet metal deep drawing with a partitioned magnetorheological flexible-die

In aviation, aerospace, and industrial manufacturing, lightweight integrated thin-walled sheet components with local high curvature gradients and complex geometric features are increasingly applied. However, a generic challenge in forming asymmetric components using conventional flexible-die forming is that isostatic pressure often causes insufficient material inflow in deep regions, local excessive thinning, and low dimensional accuracy, which requires effective material flow control methods to improve forming quality. To address this, the study proposed a partitioned magnetorheological flexible-die forming method for asymmetric parts, aiming to provide a scalable approach for active material flow control in sheet deep drawing. By constructing a gradient magnetic field in the working area, differentiated flexible-die properties are imparted to forming regions to promote material flow and coordinated deformation. The research shows that the gradient magnetic field can be constructed by combining iron cores and a coil. When using a 40 mm high iron core group, the maximum magnetic flux density gradient reached 401 mT. Using 5A06-O aluminum alloy hemispherical parts as a validation case, the influence of partitioned flexible-die control on material inflow, loading curves, configuration, strain, and wall thickness distribution was systematically analyzed. Results showed that partitioned control could significantly influence the material inflow rate and deformation behavior. When no input current was applied, the material inflow ratio between the iron core side and the non-iron core side of the specimen was approximately 1, the maximum forming height was located at the center, and the maximum thinning rate was 25.2%. When the input current increased to 10 A, the material inflow ratio reached 2.2, the strain distribution became asymmetric, the position of maximum height shifted towards the iron core side, the thinning rate dropped to 13.6%, and the wall thickness became more uniform. Furthermore, a universal design approach for gradient magnetic fields is established to guide the process optimization of magnetorheological flexible forming. Partitioned magnetorheological flexible-die control strategy achieves active, adjustable material flow under constant blank holder force, providing a universal solution to material flow inhomogeneity for asymmetric parts forming.