Experimental investigation on electromagnetic punching process of hybrid CFRP/Al stacks under different discharge energies

Abstract

Abstract Machining holes on composites/metal stacks usually accompanied by burrs, chips and delamination damage. To solve those problems, this paper proposed a high speed punching technology for CFRP/Al stacks: electromagnetic punching (EMP). The machined hole qualities of CFRP/Al stacks (e.g. microscopic morphology, delamination damage and dimensional accuracy) for EMP process with various discharge energies were investigated. Besides, conventional quasi-static punching was performed as a comparing process. Note that the CFRP/Al stacks were fabricated with eight unidirectional CFRP plies and an aluminum alloy sheet, cured in an autoclave. The results showed that burrs of EMP were less than quasi-static punching, the heights of burnish zone under the discharge energies of 5 kJ, 6 kJ and 7 kJ (the corresponding maximum punching speed are 5.46 m/s, 7.63 m/s and 9.50 m/s) were respectively 32.5%, 40.0% and 55% higher than that of quasi-static punching process. Based on the results, the shear mechanism for the punching process was analyzed. The punching process could be divided into four stages, CFRP layers and Al sheet were sheared off sequentially. The dimension measurement results showed that diameter deviation between the hole entrance and exit became smaller under higher discharge energy. While the delamination was aggravated as the discharge energy exceeded 7 kJ, the discharge energy of 6 kJ was the most appropriate to machine holes on the CFRP/Al stacks.