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

Abstract

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 microbending, 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.

Influence of size effects on material properties and springback behavior of metal foils in micro bending: A review

“…2(a). This "thinner is weaker" effect has been verified via different metal sheets, such as aluminum [14] and brass [17]. It is caused by the increasing share of surface grains in the overall volume when the sheet thickness decreases.…”

“…Wang et al [17] investigated three different thicknesses of copper alloy C2680 with different annealing conditions. The flow stress is found to decrease with the increase of grain size when the foil thickness 09010-p. 3 keeps constant.…”

“…The investigations of how foil thickness affects springback angle are usually conducted by three-point bending [16,28,29], V-bending [30], U-bending [17] and free-bending experiments [10,20,31].…”

“…Wang et al [17] conducted micro U-bending experiments of C2680 brass with thicknesses ranging from 100-400 m and found the springback angle increases with the decrease of foil thickness no matter how large the grain size is.…”

Effect of Grain Size on Springback and System Energy in Micro V-Bending with Phosphor Bronze Foil

“…Similarly, Wang et al [17] investigated the grain size effect on springback in micro U-bending. They also proposed a constitutive model based on the surface layer model to study the materials' mechanical response, and linked it with springback behaviour.…”