Investigation On Pulsed Current Treatment Assisted-laser Shock Microforming

In order to enhance the microplastic deformation ability of alloy materials and further improve the forming quality of micro parts,this dissertation combined the advantages of electroplasticity and laser shock microforming,proposed a new pulsed current assisted laser shock microforming technology.The mechanical properties,microstructure evolution law and laser dynamic shock microforming performance and its improvement mechanism under the assistance of pulsed current were studied in detail.The main research contents and results are as follows:(1)The effects of pulsed current treatment on mechanical properties and microstructure evolution of H62 brass were investigated from the perspectives of elongation,flow stress,fracture section morphology,strain rate sensitivity,dislocation distribution,grain morphology and surface texture.The experimental results show that with the increase of pulse current intensity,the uniform elongation of the material was significantly increased,and the flow stress during the tensile process was significantly decreased,the fracture form of the material was gradually transformed from pure brittle fracture to obvious ductile fracture,and the strain rate sensitivity was also improved correspondingly,which influenced by lower activation volume.Compared with the annealing treatment at the same temperature,influenced by the electronic wind effect and the Joule heat effect,the material treated by pulse current has lower dislocation density,smaller static recrystallized grains and weaker surface texture.The above results indicate that the pulsed current treatment can significantly improve the mechanical properties of materials and affect the evolution of the internal microstructure of materials,which is beneficial to improve the plastic deformation ability of materials.(2)The pulsed current treatment assisted laser shock free micro bulging technology was experimented from the aspects of bulging depth,section reduction ratio and surface quality of the forming parts.The experimental results show that under the same laser energy,the forming depth of the material treated with high intensity pulsed current was significantly increased due to the greatly reduced dislocation density.Due to the numbers fine recrystallized grains improve the fluidity of the material,the necking phenomenon at the transition corners and near the center area of the workpiece after pulsed current treatment was obviously alleviated.Stem from the fine grains weakens the orange peel effect and the low density surface texture reduces the anisotropy of the material,the surface roughness of the materials treated with a certain intensity of pulsed current decreased significantly under the action of laser shock.However,with the further increase of the pulse current intensity,the surface roughness of the formed parts increased slightly.The above research proves the material has a higher microforming performance and quality under this technology.(3)The forming ability of the process on the micro parts with parallel ribs was further studied from the aspects of forming depth and mold bonding rate,microforming uniformity,and the surface roughness of the formed parts.The experimental results show that the lower density of dislocations and the stronger inertial effect further improve the plastic deformation ability of the material,resulting in under the same laser energy,the material treated by the high density pulsed current not only had a higher bounding rate to the mold,but also the corresponding micro rib depth was more consistent.Due to the laser dynamic shock further refined the grain size of the material after pulsed current treatment,the reduction rate of the micro formed parts at the transition fillet decreased to a great extent.Under the combined influence of weak orange peel effect,lower density surface texture and slower evolution rate of surface texture,the inner surface roughness of the material treated by pulsed current decreases significantly after laser shock.The quality of the outer surface was further improved compared with the inner surface due to the flattening effect of the surface of the micro mold.The above research shows that this process can not only guarantee the machining quality of the parts with rib shaped micro parts,but also have the ability to form complex micro characteristics.The pulsed current treatment assisted-laser shock microforming technology studied in this dissertation is beneficial to improve the microforming ability of materials,and can perform high quality forming of complex shapes and micro characteristics parts,which will have a broad development prospect in the field of microparts manufacturing.