The Effects Of Cavitation Water Jet Shock Microforming Of Metallic Foils

Product miniaturization is a major developmental trend for many industries.This development of micro-products requires effective micro-machining technology.In this research study,a new microforming process of metal foil shocked by cavitation water jet is proposed,which uses the high-pressure shock generated by cavitation collapse bubbles in cavitation jet as the driving force to achieve the microforming of a metallic foil.Based on the cavitation water jet technology,through theoretical analysis,the forming mechanism of cavitation jet and generation,the growth,development,and collapse process of cavitation,as well as the generation and propagation of shock wave pressure are studied in this work,which lays a theoretical foundation for the use of cavitation water jet technology to achieve metallic foil microforming.The experimental study was carried out on the cavitation water jet device built by the research team.The cavitation shotless peening experiment was carried out by using 4 mm thick8090Al-Li alloy as the experimental material,and the cavitation shock field range of cavitation water jet on the surface of the 8090Al-Li alloy was initially studied.The experimental results showed that when the incident pressure was 20 MPa,and the target distance was 120 mm,the cavitation shock region showed a maximum ring with a radius 3.5 mm ～ 21.4 mm.In addition,the feasibility of cavitation water jet shock on metallic foil was verified by large area array characteristics and single feature microforming experiments.Based on this,the forming properties and mechanism of 304 stainless steel foil with 100 μm thickness by cavitating water jet shock were studied in the microforming process.In this study,Keyence VHX 1000 C digital microscope,shape measurement laser microscopy system(VK-X250K),S-3400 N scanning electron microscope,a confocal laser scanning microscope(Axio CSM 700),and micro Vickers hardness tester were utilized to observe the surface morphology,forming depth,surface roughness,blanking analysis,thickness distribution rate and mechanical properties(nano hardness and elastic modulus)of the formed workpiece surface under different process parameters such as incident pressures,impact time and target distances.In addition,a finite element model was developed using ANSYS/LS-DYNA to simulate the microforming of the metallic foil.The experimental results indicated that the surface morphology of the metal foils attained good geometrical features under this dynamic microforming method,and there were no cracks or fractures.The forming depth increases gradually with the increase of incident pressure and impact time,and the forming depth increases first and then decreases with the increase of target distance.In addition,the analysis of blanking phenomenon results shows that when the incident pressure continues to increase,there is a risk of cracking at the rounded corners of the microformed parts.When the pressure increased to30 MPa,the micro blanking sample of 100 μm thickness steel foil could be obtained.The surface roughness of the microformed parts increased with the incident pressure and the impact time.In addition,the forming depth of the target distance first increased and then decreased.The thickness thinning ratio of microformed parts was generally between 2.31% and 15.76%,and the thickness was relatively uniform.The nano-hardness and elastic modulus also increased significantly with the incident pressure,that is the hardness increased more than 122%,and the elastic modulus increased more than 76% with the incident pressure of 20 MPa and impact time of 2 min.In addition,the SEM analysis indicated that,as the incident pressure increased,the surface morphology of the formed part changes from approximately spherical to spherical,and the spherical roundness increased.The comparison analysis between the simulation results of ANSYS/LS-DYNA and the test results show that when the peak value of impact pressure Pmax= 2.2 GPa and the duration of impact pressure T = 40 ns.The forming curve and thinning result of the simulated sample was closest to the experimental results at a pressure of 20 MPa,at a target distance of 120 mm,and impact time of 2 min.The final study was conducted on the forming depth,surface quality,thickness distribution,and section hardness distributions under different incident pressures(8 MPa – 20 MPa),a time of 5 min,and a target distance of 120 mm.The results indicated that the forming depth increased from 124.7 μm to 327.8 μm as the incident pressure increased from 8 MPa to 20 MPa.The surface roughness increased from0.685 to 1.159 as the incident pressure increased from 8 MPa to 20 MPa.Hence,the surface roughness of the center region of the forming components gradually improved.The maximum thickness thinning ratio of the formed foils was 21.27% with the incident pressure of 20 MPa and 14.13% with the incident pressure of 8 MPa.Therefore,this indicated that the thickness thinning ratio increased with the increase of the incident pressure.The tested hardness indicated that during the cold-rolled state of the sample,the hardness of the sample increased slightly along the cross-section of the formed region and the hardness of the annealed 304 stainless steel foils increased significantly along the cross-sectional region.In general,the above results indicate that cavitation water jet shock microforming holds the advantage to produce micro parts of thin metallic foils using different processing parameters and a micro-die as a forming source.