Research On Inhomogeneous Deformation Behavior Of Metal Bipolar Plates In Laser Shock Incremental Forming

Hydrogen fuel cell as a new type of green energy has a broad prospect in the future.The metal bipolar plate is an important component of hydrogen fuel cell.However,due to the limitation of characteristic size,the traditional forming method is easy to produce forming defects such as springback and fracture,and it is difficult to ensure machining accuracy.Therefore,it is urgent to develop new forming methods of high precision,high performance,and high reliability for metal bipolar plate parts.The laser shock incremental forming process combines the advantages of laser shock forming and incremental forming and has the advantages of high forming precision,high forming limit,flexibility,and easy control,which can meet the requirements of metal bipolar plate forming.However,the material is prone to inhomogeneous deformation in the laser shock incremental forming process.The influence law of this inhomogeneous deformation on the forming accuracy,microstructure,and mechanical properties of parts is still unclear,and there is a lack of quantitative evaluation methods for inhomogeneous deformation,so it is urgent to carry out relevant research.In this paper,TA1 pure titanium was taken as the research object to carry out the experimental and numerical simulation study on the inhomogeneous deformation process of laser shock incremental forming for metal bipolar plates.The inhomogeneous deformation behavior of metal bipolar plates under different forming conditions was analyzed and the evaluation criteria of inhomogeneous deformation was proposed.The differences between different forming methods in deformation behavior,microstructure,and mechanical properties were compared.The main research contents and results are as follows:(1)By changing the rubber thickness,overlapping rate,laser energy,and loading pass,the influences of process parameters on the three-dimensional morphology for metal bipolar plate,the morphology of the bottom surface for the channel,forming angle,section profile,and section thickness were discussed,and an evaluation method for inhomogeneous deformation was established.The experimental results show that the degree of inhomogeneous deformation for the metal bipolar plate decreases first and then increases with the increase of rubber thickness and overlapping rate.The increase of laser energy can improve the forming accuracy for the metal bipolar plate but has little effect on the inhomogeneous deformation.The lowenergy multi-pass loading strategy is beneficial to improve the accuracy of laser shock incremental forming and restrain inhomogeneous deformation.Under the conditions studied in this paper,the optimal process parameters are 0.2 mm rubber thickness,60%overlapping rate,1.5 J laser energy,and multi-pass loading strategy.(2)The quasi-static tensile mechanical properties and dynamic Hopkinson tensile bar test were completed,the Johnson-Cook constitutive of TA1 pure titanium was established,and the numerical simulation of the laser shock incremental forming process for the metal bipolar plate was carried out.The material flow behavior of the metal bipolar at different deformation stages,as well as the distribution characteristics of strain and stress and springback behavior were discussed.The attenuation law of stress wave in titanium foil was calculated,and the temperature variation during the laser shock incremental forming process was estimated.It was proved that the thermal effect had no obvious influence on the plastic forming of the material.(3)The effect of forming method on the inhomogeneous deformation,microstructure,and properties of the metal bipolar plate was studied.The experimental results show that the laser shock forming method can improve the forming accuracy of the channel,and the inhomogeneous deformation can be effectively suppressed under reasonable laser.parameters.The homogeneity of the channel section thickness is close to the conventional stamping forming.The finite element simulation results show that there are significant differences in the deformation process,material flow,strain distribution,stress distribution,and springback behavior of the metal bipolar plate under different forming methods.The test results show that the laser shock forming method can promote the proliferation of dislocation and the formation of deformation twins,change the configuration of dislocation,and enhance the mechanical properties of the channel.