A novel micro-rolling & incremental sheet forming hybrid process: Deformation behavior and microstructure evolution

Thin-walled metal parts with functional micro-featured surface have broad application prospects in the fields of resistance reduction, noise reduction, etc. In this study, a novel micro-rolling & incremental sheet forming hybrid process (μR-ISF) is proposed to fabricate thin-walled metal parts with microgroove arrays. An analytical model which relates the rolling force and microgroove depth in the micro-rolling stage was first established. Then, the formation mechanism of microgroove morphology during both micro-rolling stage and macro-shape forming stage are investigated. After the micro-grooved sheet being incrementally formed, a significant reduction (between 21% to nearly 60%) is occurred in the depth of both transverse and longitudinal grooves compared to the flat sheet. Meanwhile, the width of transverse grooves decreases slightly by about 10% on average, while the width of longitudinal microgrooves increases significantly by more than 30% on average. After micro-rolling, 85°{1012} tensile twins appear on the micro-grooved sheet and the percentage of 65°{1122} compressive twins increases. After incremental forming, the percentage of low-angle grain boundaries and the density of geometrically necessary dislocations in the formed part increase significantly, and the grain size distribution becomes more uniform. The present work provides a new strategy for the fabrication of 3D metal thin-walled components with surface micro-features.