Numerical and experimental study of the size effect on deformation behavior and quality of microembossed multi-channel structures

With an uptrend of product miniaturization and precision manufacturing, the microembossing process of sheet metal has been widely used, and the corresponding researches have been conducted from the aspects of both experimental and theoretical explorations. Many unknowns, however, remain, such as size effect and it-induced scatters of deformation behaviors and product qualities. In this research, the multi-channel structures with various thicknesses made by a microembossing system using pure copper sheets were employed as case studies. The crystal plasticity finite element method simulations and experiments were conducted to study the effects of grain size and sheet thickness on the process and product of microembossing in terms of load-stroke relation, dimensional accuracy, and surface quality. From both the experimental and numerical results, it is revealed that the grain size effect causes deviated load and non-uniformity in deformation. The dimensional accuracy designated by the variations in thickness and height is affected by both grain size and sheet thickness. As grain size increases, the thickness reduction becomes more dramatic, and the thinnest location is at the corner zone. The height of the channel bottom increases with grain size, while the peak height fluctuation due to grain size is relatively minor. In addition, various surface defects on the surface of the embossed multi-channel structure were observed, including microvoids and micro scratches on the sidewalls, and wrinkles and grooves on the peak and bottom surfaces. From the inner to outer of the structures, microvoids gradually change to micro scratches, which become denser and longer as grain size increases in 100 μm thick copper sheets and also more severe with the increasing sheet thickness. All of these enrich the understanding of sheet metal microembossing and facilitate design solution generation in the optimization of the microembossing process and the quality of the embossed structures.