Deformation characteristic and geometrical size effect in continuous manufacturing of cylindrical and variable-thickness flanged microparts

The most critical issues in microforming technologies are tailoring the desirable product quality and ensuring the high productivity from application perspective. This is also the case for fabrication of cylindrical micro-pin and flanged micropart with nonuniform thickness. To realize continuous micromanufacturing of the hollow flanged micropart with variable thickness, an efficient progressive microforming method is proposed by using an integrated hole flanging-ironing process. In this process, size effect and its affected deformation behavior and forming quality of the micropart are still not well known and knowing of them well is crucial in forming of the accurate shape and geometry of the microparts, tailoring the needed product properties and assuring the required qualities. This study thus aims at addressing these issues in terms of deformation load, forming kinematics, dimensional accuracy, defect formation and microstructural evolution based on an unequal-thickness flanged micropart produced by the developed progressive microforming system in which shearing, hole flanging-ironing and blanking operations are realized progressively. The experimental results reveal that the length of the flanged micropart is reduced with the increasing grain size, while both the tapering angle and its scatter present an opposite tendency, which could be explained by the coupled model of free surface roughening and open-closed lubricant pockets. Furthermore, the dimensional accuracy, surface appearance and the defects including curved profile, singularity, wrinkling and irregularity are closely related to the initial material microstructure. Through realization and examination of the developed progressive microforming system and the finished microparts, the progressive hole flanging-ironing process is proven to be promising and efficient for continuous micromanufacturing of micro-scaled hollow geometries with higher flange and variable thickness.