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Analysis of the Size Effect on Springback Behavior in Micro-Scaled U-Bending Process of Sheet Metals


  • The authors would like to thank the funding support to this research from the General Research Fund of Hong Kong Government under the project of B-Q33F and the projects of G-YK10, G-YM93 and G-U923 from The Hong Kong Polytechnic University.


In the micro-bending process of sheet metals, springback caused by the considerable elastic recovery during unloading has a significant effect on the dimension precision of micro-bent sheet metal parts. In design of micro-bent parts and bending process, this phenomenon needs to be considered. However, the traditional well-established knowledge for analysis of macro-scaled sheet metal bending processes may not be very suitable and efficient in analysis of micro-scaled sheet metal bending due to the geometry and microstructure size effects in the process. To explore the unloading springback of sheet metals after micro-bending, the experimental studies on the interactive influence of a few significant parameters including sheet thickness, grain size, and punch radius on the springback in micro U-bending process of copper alloy sheets were conducted. An appropriate constitutive model based on the surface layer model, which is widely used in micro-scaled forming processes, is proposed to predict the amount of springback and the relationship among these parameters is further established. The research shows that the springback angle generally increases with the decreasing sheet thickness, and for different punch radii, the springback angle has different variation trends for the sheet metals with different grain sizes. The developed analysis method is verified via the comparison of the calculated stress–strain curves with the tensile test results of three kinds of copper alloy sheets. The findings on how the size effects affect the springback behaviors of in micro-bending process are validated by the experimental results, finite element simulation, and the comparison in-between.

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