Numerical Simulation And Experimental Study Of Laser Shock Liquid Microforming

In recent years,laser shock microforming technology has become a research hotspot in the field of microforming.In this dissertation,a new laser shock liquid microforming process,with laser as shock source and liquid as the force transmitting medium is studied,which is suitable for the formation of large-area array micro-features.This dissertation first explores the feasibility and forming process by numerical simulation,and optimizes the process parameters on the basis of numerical simulation,which provides guidance for the experimental research.The main research work and achievements are as follows:Firstly,the basic theory of laser shock liquid microforming process was studied.The interaction mechanism between laser and materials,and the dynamic response of the materials at high strain rate were described.The expression of laser power density and the laser induced shock wave pressure model considering the spatiotemporal distribution characteristics were derived.The motion equation of fluid and structure in fluid-structure interaction was discussed.The arbitrary Lagrangian-Eulerian(ALE)method in fluid-structure interaction analysis and the ALE method in nonlinear analysis were studied.Next,the numerical simulation of laser shock liquid microforming process was carried out by HyperMesh/LS-DYNA.For large-area pit array micro-feature mould,the finite element model was established considering fluid-solid coupling,the laser source model with spatiotemporal variation was loaded and the ALE algorithm was used to realize the fluid-structure coupling calculation.The numerical simulation results showed that this process was feasible and effective in forming large area array micro-features.Meanwhile,the numerical simulation results were basically consistent with the experimental results.The results showed that the whole forming process can be divided into four main stages and the continuous action of liquid effectively suppressed the rebound of the workpiece.In addition,the liquid as a force transmitting medium can significantly prolong the impact time and equalize the impact pressure which was beneficial for the forming of large-area array micro-features.According to the analysis of the plastic strain distribution of workpiece,it was found that the most obvious strain gradient occurred at the entrance of the micro cavity,andthe strain in the bottom region of the pit feature was also relatively large before the end of the forming.The width of the flat area on the pit feature increased with the increase of laser energy,and decreased with the increase of the workpiece thickness and the height of the liquid chamber.The change of the spot diameter mainly affected the forming consistency of the array features.Then,based on the numerical simulation results,Central Composite Design method(CCD)was uesd to plan the experiments for the laser shock liquid microforming process.A mathematical model between laser spot diameter,laser energy,liquid chamber height,rubber layer thickness and forming quality response was established using the Response Surface Method(RSM).The model was tested for suitability by analysis of variance.The interactive influence trend of different process parameters on forming quality was discussed.The multi-objective optimization of process parameters was carried out under two optimization criteria using RSM.The results of optimal process parameters were verified and the results showed that the optimization had a high consistency with the numerical simulation results.Finally,the feasibility of laser shock liquid microforming process was studied by using large-area pit array micro-feature mould.The influence of different parameters on forming quality was discussed.The two-dimensional and three-dimensional morphology of the formed parts were carried out by VHX-1000 C microscope.The experimental results showed that the flat area width of the pit features on the formed workpiece increased with the increase of the laser energy,and decreased with the increase of the workpiece thickness and the rubber layer thickness.The differences of the forming depth and the flat area width between the outer pit feature and the inner pit feature were within 5%,which proved the superiority of this process in forming large-area array micro-features.In this dissertation,the new laser shock liquid microforming process was firstly studied by numerical simulation.Then based on the numerical results,the process parameters were optimized to provide guidance for experimental research.This method of using numerical simulation to lay the foundation for experimental research is of certain value.