Multimodal ultrasonic vibration assisted multi-stage forming of 6061 aluminum alloy: mechanisms, modeling, and optimization

The forming performance and quality of aluminum alloy micro-parts in multi-stage forming are limited by size dependent deformation, severe interfacial friction, and residual stress accumulation. To address these problems, multimodal ultrasonic vibration (UV), including tool vibration (TV), mold vibration (MV), and compound vibration (CV), was applied to a multi-stage forming process for 6061 aluminum alloy. The stage-dependent effects of UV modes and amplitudes on forming load, filling behavior, microstructure evolution, and mechanical properties were systematically investigated. The results showed that CV achieved a maximum forming load reduction of 35.85% compared with TV, and improved the material flow stability in the initial stage. Applying MV effectively reduces interfacial friction and improves strain uniformity in the intermediate stage. In the final stage, applying CV promotes residual stress relaxation and grain refinement, leading to an improvement in dimensional accuracy of about 12.4% and a reduction in surface roughness by about 25%. A coupled analytical model considering ultrasonic softening and friction reduction was established, and the prediction accuracy reached R 2 values above 0.96. These results indicate that stage-matched UV mode sequencing is effective for improving load reduction, formability, and surface integrity in multi-stage forming processes.