Investigation Of Pulsed Laser Shock Hydroforming Method On Micro Tubes And Foils

In recent years,as the trend of miniaturization and integration in manufacturing has become prominent,the application of micro parts has become widely,thus promoting the development of micro-forming technology.Given the shortcomings of the traditional microforming process and the quasi-static poor microscale material formability,combining the advantages of the micro-hydroforming and the laser impact microforming,the laser shock micro-hydroforming is proposed.This study combines the experimental and numerical methods to research the laser impact microhydroforming process on micro tubes and foils,in which the numerical simulation considers fluid-solid interaction.The main research and the work are as follows:(1)This dissertation first discusses concerned theories.They explain the generation mechanism of laser-induced shock waves,the coupling mechanism of fluid and solid,and the change of pressure when propagating between materials with different acoustic impedance.These theories provide fundamentals for experiments and numerical simulation.(2)Laser shock hydroforming on micro tubes: 1)Analysis of its dynamic forming process reveals the mechanism of laser shock hydroforming,that is,the pressure in the middle of the bulging region is the lowest due to the propagation characteristics of pressure waves in the liquid,causing the middle region has less deformation;2)Using the Keyence VHX-1000 C ultra-depth 3D microscope to measure the thickness of the intermediate region of formed micro tubes,the results show that,compared with the quasi-static forming method,the uniformity of the thickness distribution has been improved.Numerical simulation has been used to analyze the reasons for its improvement.The results show that,due to the characteristics of dynamic loading,there is a periodic gap between the tube wall and the die,which reduces the friction force,thereby promoting the material flow and inhibiting local excessive thinning;3)The reason for the increase in formability is analyzed from the perspective of contact stress.The results of numerical simulation confirm that the impact of the microtube on the mold is the reason for the increase of the compressive stress in thickness direction.The increase of the compressive stress is beneficial to the improvement of the formability;4)Comparing the speed and strain rates of die-bulging and free-bulging,it is found that the speed and strain rates of diebulging are higher than free-bulging under the same laser energy,proving that the die is a factor to improve the formability.(3)Laser shock hydroforming on foils: 1)The laser shock hydroforming freebulging and die-bulging were carried out.It is found that the formability of foils in free-bulging becomes worse as the laser energy increases,while,in die-bulging,the formability only improves when the laser energy exceeds the threshold;2)The crosssectional thickness of the workpiece is measured.The results show that the thinning ratio of the workpiece is higher in die-bulging,but no failure occurrs,indicating that the workpiece in die-bulging has a higher forming limit;3)To disclose the forming process of foils and study the factors that improve the formability,a FEM of laser shock hydroforming is established.The forming process,forming speed,contact stress and strain rate.They explain the mechanism of formability enhancement;4)It is found that the pressure becomes uniform when propagates in the liquid,beneficial to continuity of workpieces.Analysis shows that the pressure equalization is most likely due to pressure waves being reflected by the rigid sidewall of the liquid chamber.With theory,experiment and numerical simulation,this dissertation analyzes the laser shock hydroforming on micro tubes and foils,proving the effectiveness and advantages of this novel microforming process.