Flow-induced folding in multi-scaled bulk forming of axisymmetric flanged parts and its prediction and avoidance

The quality of manufactured parts and the efficiency of forming processes are crucial in deformation-based manufacturing. In product miniaturization and micro-manufacturing, size effect induces many unknowns. Flow-induced folding related to size effect is one of them and has not yet been fully studied. In this research, the formation mechanism of folding defects in axisymmetric bulk forming was investigated, and a design-based method was employed to evaluate different tooling and process route designs for making a case-study multi-flanged part with three features and to explore the design-based avoidance of folding defects. In addition, a design evaluating framework of folding-free bulk forming was proposed, implemented, and validated. Via analysis of the material flow, energy consumption, folding formation, and product precision of the four proposed forming processes for the case-study part, an upsetting-extrusion forming method via using a nested punch was found to be the most desirable. It was then implemented in the physical forming with three size scales. The results revealed that the flow-induced folding in the macropart was severe and regularly circuitous, but it is slight and irregular in meso- and micro-scale. These findings are useful in the defect-free forming of multi-flanged structures and multi-scaled axisymmetric parts.