Investigation On Laser Shock Hydraulic Micro Forming Of Metal Foil

With the development of miniaturization and light weight of products,the application of micro-devices has become extensive,which has promoted the development of micro-forming.Due to the shortage of laser shock micro forming,a novel micro forming process called laser shock hydraulic micro forming(LSHMF)was proposed.The metal foil was deformed through impact liquid pressure which generated by laser shock rubber layer.In this paper,the LSHMF technology is systematically studied through experimental investigation and numerical simulation.The main research work and results are as follows:Firstly,a LSHMF experiment was performed on 55 ?m thick copper.The experiment used the KEYENCE VHX-1000 C microscope to measure the forming depth and thickness thinning rate so as to preliminarily reveal the formability and deformation law of the LSHMF process.It was found that the process is feasible for the micro bulging and shows great forming results under reasonable laser energy;The surface morphology and roughness values of the workpiece were observed and measured by the Zeiss Axio CSM700 confocal microscope.It was found that the roughening of the workpiece surface is not obvious,also,there is no heat affected zone on the surface of the workpiece,which indicates that the LSHMF technology can produce high surface quality parts;The section hardness of different positions was measured by HXD-1000TMC/LCD micro hardness tester to reveal the change of material mechanical properties after hydraulic impact.It was found that the workpiece is impact-strengthened and obviously reflected in the annealed material.Secondly,the micro-bowl features with micro-concave on the bottom were fabricated on 30?m thick copper by LSHMF process.It was verified that the process has the feasibility of forming local micro features.The overall morphology and fittability under different laser energies were measured.It was found that due to the great fluidity of the liquid medium,the workpiece can accurately replicate the mold shape at 1550 mJ energy;Through the investigation of the thickness distribution,it was found that as the laser energy increased,the thickness thinning rate increased,but the pit with the largest thinning was not cracked,which shows the great formability of the process;From the investigation of surface quality,it was found that mold with great surface quality has a flattening effect on the bottom surface of the formed part,which can reduce the surface roughening caused by the deformation.LSHMF process can ensure the forming quality of micro forming which can also provide an effective process for complex characteristic microforming.Finally,Hypermesh/LS-DYNA was used for the numerical simulation of LSHMF which can fill the blank of experimental investigation.The deformation process,strain distribution and the velocity of the typical node at the bottom of the workpiece with time when the laser energy is 1550 mJ were explored.It was found that the deformation process can be divided into five stages: stress accumulation phase,free bulging stage,metal sheet collision with the die bottom stage,die filling stage and spring back stage;In the free bulging stage,the workpiece was mainly subjected to axial tensile strain and radial compression strain.After colliding with the bottom of the mold,the workpiece was mainly subjected to axial compressive strain and radial tensile strain;The bottom node displacement time and velocity time curves showed that the bottom node velocity and displacement fluctuations are not obvious,indicating that the process has the effect of suppressing rebound.Numerical simulation results can be used as a reference for experiments,further guiding and perfecting experimental parameters,and also provide a method for predicting the shape of the partsThe LSHMF process proposed in this paper provides an effective process for complex feature micro forming.The research reveals the forming mechanism and deformation law of LSHMF,providing theoretical and experimental guidance for the future industrial application of the process.