Research On Micro-Bulging By Laser Flexible Shock Metal Foils

With the development of miniaturization and integration,the application of parts with micro features is becoming wider,which promotes the development of micro forming technology.Among them,the micro forming of metal foils is becoming a focus of current research.In this dissertation,the laser flexible shock micro-bulging(LFSB)process of metal foils was established by combining laser shock micro-bulging and flexible die forming.This process used laser shock silicone rubber as the flexible punch to realize the micro bulge forming of metal foils under single pulse laser energy based on the micro-bulging die.Properties of the LFSB of metal foils were studied by experimental research and numerical simulation.Its main research work and conclusions are as following:Firstly,the LFSB experiments of 304 stainless steel foils were conducted to study the effects of different laser energy and workpiece thicknesses on the surface morphology,bulging depth,thickness thinning rate and cross-section hardness of micro-bulging parts.The surface morphology of micro-bulging parts was observed by SEM.It was found that the morphology changed from the approximate spherical surface to the spherical surface with an increase of workpiece thickness and a decrease of laser energy.The bottom defect developed from micro cracks to micro spallation with an increase of workpiece thickness and laser energy.The depth and thickness of micro-bulging parts were measured by KEYENCE VHX-1000 C microscope.The results showed that the depth and thickness thinning rate increased with a decrease of workpiece thickness and an increase of laser energy.The hardness of micro-bulging parts section was tested by nanoindentation instrument.It was found that the hardness of different bulging areas was improved.The microstructure of the bulging region was observed by TEM,and it was found that grain refinement occurred after laser flexible shock.Then,the LFSB experiments of copper foils were conducted to study size effects,including grain size and feature size of micro die,on material deformation behavior.The bulging depth of micro-bulging parts was measured by KEYENCE VHX-1000 C microscope.The results showed that the bulging depth and its deformation non-uniformity increased with the grain size and feature size of micro die.The surface quality of micro-bulging parts was observed by Axio CSM700 confocal microscope.It was found that the surface roughening of micro-bulging parts was increased with an increase of grain size.With the size of die increasing,the degree of surface roughening increased first and then decreased.By measuring the thickness of micro-bulging parts,it was found that the thickness of bottom section was smaller and the sectional plastic deformation unevenness increased with an increase of grain size.With the size of die increasing,the thickness of section changed obviously,especially from the die 1 to the die 2,and the change of thickness was similar from the die 2 to the die 3.Finally,ANSYS/LS-DYNA and LS-PREPOST software were used to simulate the forming process of the LFSB of 304 stainless steel foils with different laser energy and thicknesses and the micro plastic deformation of foils under laser flexible shock loading was investigated.The two stages of the LFSB of metal foils were revealed.The simulation results showed that the bulging depth,thickness thinning rate,elastic-plastic response speed,equivalent stress and equivalent plastic strain distribution of micro-bulging parts.Among them,the variation trend of bulging depth and thickness thinning rate were basically consistent with the experimental results.