Research On Laser Shock Forming And Mechanism Of Metal Micro Mold

Laser shock molding is a technology that utilizes the high pressure plasma shock wave generated by pulsed laser irradiation on the surface of absorption layer to realize material forming and strengthening.It has the advantages of high precision of target material forming and small processing scale,which is suitable for the fabrication of metal molds by micro-scale molding process.Polymer has unique characteristics such as high light transmittance and biocompatibility,and can process functional surfaces and optical devices for a variety of purposes by transferring the microstructure of mold surface to polymer through micro-nano replication technology.Therefore,high strength mold is one of the focuses of polymer molding research.In this paper,the experimental and numerical simulation methods were used to systematically study the forming process and forming rules of laser shock molding for making high-precision polymer hot embossing molds,and the changes in properties such as the strength of the formed microstructure were explored.Combined with experimental accumulation and theoretical analysis,the production of micro-scale molds was gradually in-depth from micron to Nano-scale molds.First of all,the theory of laser shock molding technology was systematically discussed,including the interaction between laser pulse and material,processing principle,shock wave propagation,high strain rate deformation characteristics caused by laser shock and polymer hot embossing mechanism,which provided a theoretical basis for subsequent experiments and numerical simulation.Then the experimental platform of laser shock molding for micron and nanometer scale was built.According to the characteristics of laser machining and the theoretical model of high strain rate plastic deformation,a numerical simulation model was established for the laser shock forming experiments under different conditions in this paper.Secondly,the method of making micrometer metal mold by laser shock molding is proposed.It is found that the yield strength of the target material and the size of the microstructural cavity have significant influence on the forming effect in the micro and nano scale,and the influence of the friction force on the forming interface is analyzed.In order to obtain a higher strength mold,the theory of the influence of the ratio of the forming depth to the thickness of the target material on the forming effect is proposed.By controlling the ratio,the microstructure could be fully formed and the back of the target material could not be depressed.Combined with the numerical simulation results,the residual stress analysis of the forming microstructure under different thickness of the target material was carried out.TEM and EBSD were used to observe the internal texture and microdefects of the material before and after laser shock,and the forming and strengthening mechanism of the material were revealed.Then,combining with the characteristics and theoretical research of microstructure forming at micron scale,the fabrication of microstructure mold at nanometer scale was successfully carried out.Nano-scale microstructure forming process is very strict to the target material,so the preparation of flattened target material is carried out first.By analyzing the parameters of aluminum foil flattening experiment and the characteristics of target material,it is finally concluded that 0.25 J energy and 75% spot lap rate are the optimal parameters for experimental effect and experimental efficiency,and the roughness of aluminum foil obtained under these parameters can reach 5.71 nm.Then,in order to reduce the yield strength of the target material,the flattened aluminum foil was annealed and the Nano-imprint test was carried out.In order to protect the target material and silicon master plate,through the analysis of the experimental results,the nano-microstructure forming experiment was carried out at 0.1J energy finally,and the high-precision nano-metal mold was obtained.Finally,the influence of pulse energy in the process of flattening on the springback of ultra-thin target material is analyzed by numerical simulation.Finally,the use of micron and nanometer scale mold for hot embossing experiment,tested the mold application performance and stability in the process of polymer molding effect,the effects of temperature and pressure and demoulding resistance on the strength of the mold were studied,and analyzes the high elastic state flow filling cavity of polymer molding process.Finally,it is concluded that the hardness,elastic modulus and morphology of the micron scale mold are consistent before and after hot embossing experiment,and the morphology,height distribution and surface tribological properties of the nanometer scale mold are also stable before and after hot embossing experiment.There are 61 figures,2 tables and 95 references in this paper.