| Metal bipolar plates are widely used in PEMFC due to their advantages such as higher conductivity,simple processing technology and lower production cost.As an important part of the manufacturing process,the connection technology of metal bipolar plate has been the focus of research.Among them,laser welding has become the first choice for metal bipolar plate connection because of its advantages such as fast speed,good tightness,small heat affected zone and fine weld grain,but this welding process still has welding defects such as burn through,virtual welding,large deformation after welding,surface sag and splash.Therefore,this paper will make an in-depth study on the laser welding process of metal bipolar plate,to explore the best un-melted welding process of metal bipolar plate,so as to provide experimental basis and theoretical guidance for the laser welding of metal bipolar plate in the industrial fuel cell.The main research work and conclusions of this paper are as follows:(1)The laser non-penetration welding process of metal bipolar plate is a kind of lap welding process,and the upper and lower plates must always keep close contact to ensure the effective implementation of welding.Therefore,this paper designs a welding fixture according to the welding requirements.The welding fixture is applied to the laser welding test of metal bipolar plate,and a better welding effect is obtained.(2)The laser welding process of PEMFC metal bipolar plate was simulated by using finite element analysis software.The simulation results show that the temperature field distribution of the stainless steel bipolar plate is basically the distribution of Gaussian heat source when any laser pulse is loaded on the plate.It is found that the main form of welding deformation is Angle deformation.The overall deformation trend is that the material inside the weld bulges upward,and the deformation displacement is roughly between 0.36 mm and 0.54 mm.The material outside the welding seam deforms greatly,and the maximum deformation displacement is about 1.65 mm.According to the simulation results,the welding fixture designed in this paper can improve its deformation to a large extent,and the maximum deformation displacement can be achieved less than 0.2mm.(3)The laser laminated welding of 0.15 mm stainless steel bipolar plate was studied by using pulsed fiber laser.The influence of welding parameters on the weld was studied by single factor test.The results show that all the welding parameters have influence on the formation of the defects such as the depth of the weld section,the surface sag,the spatter and the dummy welding.The influence of laser power on these defects is the greatest.The welding speed mainly affects the formation of surface spatter and periodic soldering,while the pulse width mainly affects the formation of periodic soldering.The defocus has a great effect on the surface melting width and cross section melting depth.In addition,the welding parameters can affect the shear strength of the bipolar welded joint by affecting the weld penetration.(4)On the basis of single factor test and simulation analysis,orthogonal test was carried out.Through the intuitive analysis method,it was obtained that the primary and secondary order of the influence of each welding parameter on the shear strength of the welded joint was laser power,welding speed,defocus and pulse width.Finally,considering the surface defects of the weld and the requirements of the non-penetration welding of the bipolar plate comprehensively,and combining the results of the single factor test and simulation analysis,it is obtained that in the laser welding process of the bipolar plate,when the laser power is set at80 W,the welding speed is 40 mm/s,the defocus is 0 mm and the pulse width is 50 ns,Stainless steel bipolar plate welding effect is the best. |
PDF Full Text Request