Experimental Research And Numerical Simulation Of Laser Shock Mask Micro-forming

Nowadays,with the rapid development of miniaturization and precision,more and more micro devices attract people's attention and appear in people's daily life,work and other fields.As a result,many new micro-forming processes have emerged,such as laser shock forming.In this dissertation,a new technology of laser shock mask micro-forming is put forward.In the process,the mask is used to change the shape of the pulse spot instead of the traditional convex model,and the soft mold replaces the traditional concave model.The experimental platform of laser shock mask micro-forming is built,and the new mask micro-forming technology is systematically studied,the main contents of this dissertation are as follows:Firstly,the formation mechanism of laser induced shock wave and the mechanical model are described,and the calculation method of laser power density and induced shock wave peak pressure are deduced;the yield conditions of strain rate and plastic deformation of materials under high speed laser loading are studied;the micro plastic flow stress model of Hall-Petch is analyzed,which provides a theoretical basis for the subsequent experiments and simulation studies.Then,the four types of masks are fabricated by using the EDM technology,such as a rectangle mask,a complex mask(U and cross shape)and a rectangular array mask.KEYENCE VHX-1000 C,Axio CSM 700 and other testing equipment are used to test the shape of the 3D morphology.The influence of different process parameters(pulse energy,impact times)on the forming effect was studied.The surface roughening behavior and the thinning rate were analyzed.The experimental results show that the use of PMMA as a constraint layer has not only better transmittance,but also has strong impact resistance.By using the forming process,the specimen with clear outline,complete surface and rectangular shape can be obtained,which is composed of a direct forming region and an indirect forming region.At the single pulse,the displacement of the sample increases with the increase of laser energy;under the condition of multiple pulse and high energy,the forming depth remained unchanged.In addition,the effect of grain size on forming result is different.Under the same energy,the depth of formation and the surface roughness of coarse grain are higher than that of fine grain,and the forming depth and surface roughness of coarse and fine crystal are increased with the increase of laser energy.In addition,different grain sizes have different forming effects.By using the new micro-forming process,the parts with uniform thickness can be obtained without any local compression fracture.The result of experiments on complex mask and array mask shows that the shape of the mask can be well formed on the surface of the work piece: U shape is clearly visible;only part of the cross shape is display because the light spot is not right and the rectangular array is formed on the surface of the copper foil,and there is no influence on the mutual characteristics.The hardness of the samples is tested and analyzed.It is found that the hardness and elastic modulus of the samples were improved to some extent compared with the area where there is no impact.Finally,based on the finite element software,the numerical simulation of laser shock mask micro-forming is carried out which shows that the forming process under high strain rate can be divided into three stages: the joint forming stage;the work piece and the soft mold separation stage;the work piece and the soft mold coincidence stage.The influence of different energy on the displacement is simulated,and the simulation results are consistent with the experimental results.The displacement distribution and pressure distribution of the work piece under two kinds of hardness are analyzed.The simulation results show that the distribution of displacement field corresponds well with the velocity of the pressure.Laser shock mask micro-forming is a new technology and provides a new way to manufacture the complex parts under the condition of mold-free and provide some theoretical and experiment value.