Size Effects on Formability of Copper Foil in Flexible Micro-Bending Process

Abstract:

The occurrence of size effects in the microforming leads to the uncertainties in process determination and quality control. In this research, a series of experiments were conducted in UTM4104 testing machine to investigate the grain size effect and feature size effect in micro-bending. Different grain size (d), thickness to grain size ratio () and micro-mold feature size (W) were prepared to explore size effects on formability of copper foil. The formability characterized by forming depth, deformation uniformity and surface integrity was discussed. It was found that the normalized forming depth presented a gradually rise and then declined markedly when N value further decreased to 0.79. The ductile fracture mode was observed for all grain-sized workpiece and the corresponding limit forming depth decreased with increasing grain size. Besides, the thickness thinning distribution and microhardness distribution showed the similar variation tendency like M. Both the standard deviation of thickness reduction and the roughed degree of surface topography indicated the worsening deformation uniformity of the foils with a larger grain size. The inhomogeneous plastic flow of material may be the reason to explain the depression near fracture location which is only observed in coarse-grained workpiece. Overall, it is concluded that the fine-grained copper exhibited better formability as the coarse-grained workpiece experienced severe strain incompatibility.

• Periodical: Key Engineering Materials (Volume 723)
• Pages: 207-213
• DOI: https://doi.org/10.4028/www.scientific.net/KEM.723.207
• Online since: December 2016
• Authors: You Juan Ma*, Xiao Wang, Qing Qian, Zong Bao Shen
• Keywords: Copper Foil, Flexible Rubber, Micro-Forming, Size Effects

References

[1] F. Vollertsen, Z. Hu, H. S. Niehoff, C. Theiler, State of the art in microforming and investigations into micro deep drawing, J. Mater. Process. Technol. 151(1-3) (2002) 70-79.

DOI: 10.1016/j.jmatprotec.2004.04.266

[2] M. Ramezani, Z. M. Ripin, R. Ahmad, Sheet metal forming with the aid of flexible punch, numerical approach and experimental validation, CIRP J. Manuf. Sci. Technol. 3(3) (2010) 196-203.

DOI: 10.1016/j.cirpj.2010.11.002

[3] F. Vollertsen, D. Biermann, H. N. Hansen, I. S. Jawahir, K. Kuzman, Size effects in manufacturing of metallic components, CIRP Annals-Manuf. Technol. 58(2) (2009) 566-587.

DOI: 10.1016/j.cirp.2009.09.002

[4] D. B. Shan, C. J. Wang, B. Guo, X. W. Wang, Effect of thickness and grain size on material behavior in micro-bending, T. Nonferrous Metals Soc. China. 19(S2) (2009) s507-s510.

DOI: 10.1016/s1003-6326(10)60098-2

[5] L. V. Raulea, A. M. Goijaerts, L. E. Govaert, F. P. T. Baaijens, Size effects in the processing of thin metal sheets, J. Mater. Process. Technol. 115(1) (2001) 44-48.

DOI: 10.1016/s0924-0136(01)00770-1

[6] C. Keller, E. Hug, X. Feaugas, Microstructural size effects on mechanical properties of high purity nickel, Int. J. Plast. 27(4) (2011) 635-654.

DOI: 10.1016/j.ijplas.2010.08.002

[7] X. Wang, D. Z. Du, H. Zhang, Z. B. Shen, H. X. Liu, J. Z. Zhou, H. Liu, Y. Hu, C. X. Gu, Investigation of microscale laser dynamic flexible forming process—Simulation and experiments, Int. J. Mach. Tools Manuf. 67 (2013) 8-17.

DOI: 10.1016/j.ijmachtools.2012.12.003

[8] S. Miyazaki, K. Shibata, H. Fujita, Effect of specimen thickness on mechanical properties of polycrystalline aggregates with various grain sizes, Acta Metallurgica. 27(5) (1979) 855-862.

DOI: 10.1016/0001-6160(79)90120-2

[9] Z. T. Xu, L. F. Peng, X. M. Lai, M. W. Fu, Geometry and grain size effects on the forming limit of sheet metals in micro-scaled plastic deformation, Mater. Sci. Eng. A. 611(2014) 345-353.

DOI: 10.1016/j.msea.2014.05.060

[10] V. E. Panin, Methodology of physical mesomechanics as a basis for model construction in computer-aided design of materials, Russ. Phys. J. 38(11) (1995) 1117-1131.

DOI: 10.1007/bf00559394

[11] M. W. Fu, W. L. Chan, Geometry and grain size effects on the fracture behavior of sheet metal in micro-scale plastic deformation, Mater. Des. 32(10) (2011) 4738-4746.

DOI: 10.1016/j.matdes.2011.06.039

[12] B. Meng, M. W. Fu, Size effect on deformation behavior and ductile fracture in microforming of pure copper sheets considering free surface roughening, Mater. Des. 83 (2015) 400-412.

DOI: 10.1016/j.matdes.2015.06.067