Research On Micro-bending Process Of SUS304 Stainless Steel Foils

With the progress in science and the living quality, all kinds of industrial products and electronic products are developing towards precision intelligence and minimization. Correspondingly, the demand for the micro parts is increasing dramatically. Compared with other processing technology, micro forming, one of the most promising manufacturing approaches, presents attractive advantages of fabricating metallic micro parts efficiently with high productivity, low production cost and good forming quality.In recent years, with the booming development of micro forming, the demand on the accuracy of the metallic micro parts is elevating and has stimulated the research on the precision evaluation of micro-formed parts. In terms of micro bending process, the springback, caused by elastic recovery during unloading, is an important factor significantly affects the dimensional accuracy of micro-bent parts. Over the past decades, macro-scale bending of metal sheets was widely investigated experimentally, numerically and analytically. Some factors affecting springback such as material properties, tooling geometry and process parameters, have been extensively studied and reviewed. For micro bending parts, when the geometry dimension of micro-bent parts is downscaled to micro-scale, the conventional knowledge of macro-scaled bending process could not be directly applied in micro bending die and process, due to the socalled size effect showed obvious size effect.Therefore, this thesis intends to study investigate the size effect on the springback of the micro-bending forming processes.and on this basis, design the bending die of an unsymmetrical bending part with no gap and produce the micro-bending parts with the shape size meets the requirements.In this paper, the micro u-shaped bending die with different punch radius of 0.1, 0.2 and 0.4mm, were designed and processed, and the experimental studies were conducted to explore the interactive influence of a few significant parameters including punch radius sheet thickness,and the average grain size on the springback of SUS304 stainless steel foils after micro-bending. The metallographic microscope, Olympus GX71, was used to measure bending springback AngleThe U-shaped free-bending experiments results showed that, the velocity of the punch had no effect on the springback. With the same thickness,the springback angle generally increases with the decrease of grain size. At the same condition, the springback angle increases with the average grain size. The bending springback angle of the 80μm-thickness foils increases along with the t/d significantly greater than foils with thickness of 150μm and 180μm. For the cases with different punch radiio, foils with thickness of 150μm and 180μm,the springback angle increases with the relative bending radius(r/t) in the same trend. While the sheet with 80μm has no significant change along with r/t.Based on the studies of U-shaped free micro-bending forming,design the bending molding for an unsymmetrical bending part with no gap. The impact of punch stroke to thinning of the bottom edge and springback angle was tested. At the same time, analyze the influences of the average grain size to the springback angle. At last, we can decide the suitable technology parameter and the suitable thermal treatment to produce the micro-bending parts with the shape size meets the requirements.