Research On Laser Shock Liquid Flexible Microforming Of Large Area Array Microfeatures

In view of the shortcomings of laser shock microforming,a novel laser shock liquid flexible microforming process is proposed in this dissertation.This process employs laser energy as energy source,and liquid as pressure transmitting medium to realize the forming of large area array microfeatures on the metal foils.Both experimental and numerical simulation investigations were carried out to study the laser shock liquid flexible microforming.The main research work and results are as follows:Firstly,the experimental system of laser shock liquid flexible microforming was constructed.The effects of polyurethane rubber film thickness,laser energy and foil thickness on the forming of T2 copper foils were studied by experiments with the large area groove array microfeatures die and dome-shaped array microfeatures die.The forming quality of different array microfeatures from the same formed part were compared.Meanwhile,the morphology and surface roughness of the formed parts,and the distribution of thickness thinning and cross-section hardness were analyzed.It was found that this process is feasible for forming large area array microfeatures,and good forming quality can be obtained under reasonable process parameters.As the laser energy increases and the workpiece thickness decreases,the forming quality of workpiece becomes better,and the thinning rate is increased,but it remains unbroken,showing high formability.In addition,by comparing the forming quality of different array microfeatures of the same formed part,it was found that microfeatures have relatively consistent shape contour and dimensional accuracy,which reflects that the shock pressure distribution on the workpiece is relatively uniform because of the liquid as the pressure transmitting medium,which is beneficial for the forming of large area array microfeatures.In addition,using liquid as the pressure transmitting medium can also effectively protect the surface of the workpiece from thermal ablation and damage,obtaining the formed part with relatively high forming quality.Then,the numerical simulation research of laser shock liquid flexible microforming was carried out by HyperMesh/LS-DYNA software.For large areagroove array microfeatures die,the finite element model was established,and the suitable constitutive model was selected for workpiece,polyurethane rubber and fluid materials,and the loading of laser shock wave pressure with spatio-temporal variation was realized through the method of discreting loading area.The numerical simulation and experimental results are in good agreement,and the accuracy of the model is relatively high.(1)The dynamic forming process of the metal foil was investigated,the results showed that the process includes five stages of initial bending stage,deep drawing stage,collision rebound stage and so on.(2)The process of the shock wave propagation in the liquid was studied and the results showed that the water used as the pressure transmitting medium can effectively prolong the duration of the pressure on the workpiece,which suppresses the rebound of the workpiece to a certain extent,improving the forming quality.(3)By comparing the pressure distribution on the upper and lower surface of the liquid,the equalizing pressure effect of the pressure transmitting medium was revealed.Meanwhile,the shape contour of the groove array microfeatures formed by this process and width of the bottom regions are relatively consistent.(4)The simulation revealed the influence of laser energy and foil thickness on the forming quality and the thickness thinning rate,and the overall change trend was basically consistent with the experimental results.(5)The strain distribution of formed microfeatures was studied and it was found that most regions of formed microfeatures show compressive strain and tensile strain distribution in the axial and radial directions respectively.The obvious strain appears at cavity entrance,revealing the law of strain distribution on the microfeatures.The laser shock liquid flexible microforming process is a novel high speed microforming process,which provides an effective method for the forming of large area complex microfeature parts.The experimental and numerical simulation studies carried out in this dissertation lay a foundation for revealing the mechanism and law of laser shock liquid flexible mircoforming,and have a guiding role in the future practical industrial application of laser sock liquid flexible microforming process.