Experimental Study On Laser-induced Cavitation Micro Forming

Microscale foil plate under micro forming technology mainly through precision mold and laser processing.The micro-precision mold forming process has problems such as drive equipment complex,rigid punch losses in intensive.Laser processing technology has disadvantages such as thermal ablation,absorption layer cannot be compensated due to multiple processing issues,to solve the problems existing in the micro forming process,this paper proposed to use the plasma shock wave and collapse shock wave generated by laserinduced cavitation and the cavitation load formed by high-speed jet to carry out the nonmechanical contact machining of the workpiece.The laser-induced cavitation micro-forming technology can realize precise positioning and loading,and the liquid absorption layer can be automatically compensated.It has the advantages of controllable cavitation load and continuous processing so that the same workpiece can be formed in incremental form.In this paper,a range of basic research has been implemented on the characteristics of laser-induced cavitation and the forming law of workpiece under cavitation load.The main work includes the following aspects:The mechanism of the influence of process parameters on the laser-induced cavitation characteristics is explored.Firstly,the refractive distance generated when the laser is focused on the water is calculated,and the laser focus value is corrected.Design of the liquid viscosity,the laser focus position,guided hole,and the contrast experiment of laser parameters such as energy,using high-speed camera records of the laser-induced cavitation bubble pulsation characteristics,combined with pin-type hydrophone of guided hole shock wave pressure waveform record results are analyzed,and the results show as follow: The pulsation characteristics of cavitation and the intensity of plasma shock wave formed by cavitation are different under different process parameters.The effects of 1060 pure aluminum foil thickness and strain rate on the flow stress,yield strength,and elongation of aluminum foil are studied by tensile test.It is found that the flow stress,elongation,and yield strength of the material decrease with the decrease of the thickness of the sample.With the increase of strain rate,the yield strength of the sample increases to a certain extent.When the strain rate increases to 100?500 mm/min,the specimen is not sensitive to the change of strain rate.Design laser-induced cavitation micro forming device,the laser energy,laser focus position,and thickness of aluminum foil in a single copy of degree and the forming of cylindrical concave die forming regional quality assessment,find forming under the single micro forming a morphology for the "bowl",change the laser energy and focus position will affect plasma shock wave intensity and the propagation distance,when the laser energy increases from 5.7 m J to 34.7 m J,the shock wave strength also increases,which makes the forming depth increase from 39.25 ?m to 152.91 ?m.Orthogonal experiments are designed to obtain the significant order of influence of process parameters on forming depth.When the laser energy is too large or the laser focus is relatively close to the workpiece,it will produce an ablation effect on the workpiece,thus affecting the forming quality.The experimental results show that when the laser energy E=10 m J and the laser focus position H=2 mm,the single forming quality is better.Given the single processing appear unable to complete the replication of cylindrical concave die,multiple load incremental forming technology is adopted,the experimental results show that the cylinder dies under the condition of depth to diameter ratio is 1/3,aluminum foil shape of morphology for the "bowl" shape,the forming depth under multiple loads increasing until the rupture failure,but never touch the bottom of the concave die,the thinning rate at the center of the workpiece reaches the maximum of 25.32% under 4 pulses.The ratio of depth to diameter of the die is designed as 1/6,and the incremental forming experiment is carried out again.The obtained results show that the aluminum foil forming morphology completes the transformation from a "bowl" shape to a cylindrical shape.By reducing the depth of die,aluminum foil forming morphology completes the "bowl" shape to the cylindrical shape.With the decrease of the thickness of the cylinder forming part,the Angle between the sidewall of the forming part and the inner wall of the die decreases from 43.7° to17.1°,and the fitting degree becomes better.Through finite element analysis software for the mechanism of the two aspects of research: analysis of the laser-induced cavitation pulse shape change,in the process of cavitation area change and the guided hole flow field of shock wave pressure convergence ability,combined with the experimental results,the characteristics of laser-induced cavitation are further discussed.Then,contrast two kinds of results and analysis of the difference,the simulation model of laser-induced cavitation micro forming is established,and the changes of forming morphology and thickness of aluminum foil under cavitation load are explored.