Research On Process And Mechanism Of Electromagnetic Punching On CFRP/Al Stacks

Electromagnetic punching is a new punching technology based on electromagnetic force loading.The main features are high punching speed,suitable for thin plate processing and no pollution,which makes it a green manufacturing process.The CFRP/Al stack has both the advantages of composite material(high strength,low density)and metal alloys(high bearing strength,high impact strength).It is a lightweight material with excellent performance and has broad application prospects in the automotive and aerospace fields.This paper investigated the electromagnetic punching on CFRP/Al stacks in the aspect of punching clearance,process parameter,and punching mechanism.Firstly,the influence of punching clearance on electromagnetic punching qualities was investigated.The results showed that the punching force decreased with the increase of punching clearance.Under smaller punching clearance,the CFRP burrs were fewer,burnish zone height of Al layer increased,the hole surface was more smooth and the surface roughness decreased.What’s more,the dimensional accuracy of holes increased.But when the punching clearance was too small,delamination occurred between the CFRP plies.It was concluded that under the punching clearance of 4%t,the punched holes possessed better qualities.Secondly,the experiment investigation of discharge energy was carried out under the punching clearance of 4%t,and conventional quasi-static punching was performed as a comparing process.The results showed that the punching efficiency of electromagnetic punching is much higher than that of quasi-static punching,but the punching force was higher,increasing of discharge energy could decrease the punching force.Under the higher discharge energy,the quality of punched holes improved.But when it increased to 7 k J,the broken fibers were extruded into the CFRP plies to form delamination damage due to the high punching speed.The results of ultrasonic C-scan showed that the delamination damage of electromagnetic punching was smaller than that of quasi-static punching,and it reached the smallest when the discharge energy was 6 k J.Finally,the finite element model of electromagnetic punching on CFRP/Al stack was established in ABAQUS/Explicit,and it was used to analyze the fracture process,stress,strain and delamination of the stack.The results showed that the fracture order of the plate was that the upper CFRP plies broke first,followed by the lower CFRP plies,finally the aluminum layer broke.The results of delaminati on damage analysis showed that the delamination between plies increased first and then decreased along the thickness direction.The main factor affecting the delamination was the degree of bending deformation of the fibers during the fracture process.Based on the simulation results,in the analysis of the punching mechanism,the punching process was divided into four stages,respectively corresponding to the four peaks of the punching force-displacement curve.