Experimental And Numerical Simulation Of Laser Shock Micro-bulk Forming

In this dissertation,combining the advantages of traditional micro-plastic bulk forming and laser shock micro-forming,a new type of laser shock micro-bulk forming method is proposed.The laser shock micro-bulk forming of metal bars is studied by a combination of theory,experiment and numerical simulation.The main research contents and results are as follows:Firstly,the mechanism and mechanical model of laser-induced shock wave generation,the strain rate effect in the high-speed forming process,the metal plastic deformation theory,the Hall-Petch model,the surface layer theory,and the coupled Euler-Lagrangian method(CEL)and coupled smooth particle-finite element(SPH-FE)methods and other theories related to laser shock micro-volume forming have laid the foundation for subsequent experimental research and numerical simulation research.Secondly,according to the experimental principle,the laser shock micro-bulk forming experiment platform was built,and the laser shock micro-bulk forming experiment was carried out on the T2 copper rod,which verified the feasibility of the process.The influence law of laser energy,thickness of confinement layer and grain size on forming depth is studied,and the influence law and mechanism of grain size on the roughness of different regions of the formed part are revealed.(1)The analysis results of the forming depth show that the increase of laser energy significantly increases the peak pressure of the shock wave,and the forming depth of the formed part increases accordingly,and the high laser energy and the restraint of the mold are also beneficial to enhance the forming uniformity.(2)The thicker K9 glass is not easy to break in the experiment,which is beneficial to increase the peak pressure of the shock wave,prolong the pressure action time,and increase the forming depth.(3)By comparing the forming depth of the cold drawn sample and the annealed sample,it is found that the cold drawn sample has poor plasticity and small forming depth.Compared with the samples with small grain size,the samples with large grain size have higher forming depth,which can be explained by the Hall-Petch model and the surface layer grain model: the samples with large grain size have smaller overall flow stress and are more prone to plastic deformation.(4)By studying the changes in the roughness of different areas of the formed part,it is found that the roughness of the area with obvious plastic deformation is affected by the grain size Larger,and the roughness of the directly pressed area is closer to the roughness of the micro-mold.Finally,numerical simulation models of CEL method and SPH-FE coupling method were established by ABAQUS software respectively to simulate the laser shock micro-bulk forming process of T2 copper rods.(1)After comprehensively comparing the advantages and disadvantages of the two simulation methods in terms of forming depth,stress distribution and calculation efficiency,it is found that the SPH-FE method is more accurate and effective in simulating the forming effect,and is suitable for assisting in the study of the laser shock micro-bulk forming process,the simulation results are consistent with the experimental results.(2)By comparing the distribution of stress and strain at different times,it is found that there is a stress wave propagation phenomenon in the laser shock micro-bulk forming process,the stress wave includes a slow-velocity plastic wave and a fast-velocity elastic wave.(3)Through the change of cross-sectional stress at different moments,it can be seen that the laser shock microbulk forming process is as follows.Mushroom upsetting occurs first at the impacted part of the rod top.With the action of inertial force and the propagation of stress wave,the metal at the bottom of the bar has radial flow,which also leads to upsetting.Finally,under the action of inertia,the metal gradually fills the micro mold completely and forms the micro characteristics.(4)The analysis results of velocity cloud map show that the flow velocity of metal is basically consistent with the impact velocity under the action of inertia effect.(5)By analyzing the changes of the displacement cloud and strain cloud,it is found that the main flow direction in the process of metal filling trapezoidal grooves is axial flow,and the strain distribution of trapezoidal teeth is relatively uniform,which reflects good forming uniformity,and provides an important basis for guiding mold design.In this dissertation,the experimental and numerical simulation research on laser shock micro-bulk forming process lays a foundation for revealing the mechanism of laser shock micro-bulk forming process,which not only enriches the research of microplastic bulk forming,but also broadens the application of laser shock micro-forming range.