| With the development of the machinery industry,miniaturized products have been widely used in many fields such as microelectronic components,aerospace equipment,and new energy equipment due to their small size,light weight,low energy consumption,and high sensitivity.Metal microplastic forming technology has outstanding advantages such as high precision,high efficiency and low cost,and has gradually become an important manufacturing method for miniaturized products.However,the mechanism of the effect of the scale effect on the forming law in the process of microplastic forming is still lack of systematic research.Therefore,this thesis is supported by National Natural Science Foundation of China " Fundamental Research on Design and Manufacturing of Microreactor for Hydrogen Production from Porous Metal-Corrugated Substrates Stacked Autothermal Reforming”(No.U180920041)and the Zhejiang Provincial Science and Technology Plan Project "Key Technologies for Proton Exchange Membrane Hydrogen Fuel Cell Stacks for High-Performance Vehicles"(No.2018C01053),the microbending forming of SUS304 stainless steel sheet was carried out.This model and simulation modeling considering the microstructure of grain boundaries were developed and analyzed.The influence mechanism of material microstructure on sheet metal forming performance was studied.The influence of mold parameters on the bending performance of fuel cell side-by-side flow path was experimentally studied.The main research work completed in this paper is as follows:In Chapter 1,the research background and significance of this thesis is described,the research status of metal microplastic forming technology,metal microplastic forming scale effect and sheet metal microbending forming at home and abroad and the existing problems are summarized,and then proposes the research content and framework of this thesis are presented.In Chapter 2,the effects of specimen thickness,grain size,and the ratio of the two on the flow stress of the material are investigated through unidirectional tensile experiments of SUS304 stainless steel sheet.The micro-bending forming die for thin plate was designed and the corresponding micro-bending experimental platform was set up.The micro-bending experiment was used to study the influence of specimen thickness,grain size,and the ratio of the two on the material flow stress and the bending rebound angle.In Chapter 3,based on the surface layer model,the constitutive equation of the SUS304 stainless steel material considering the grain boundary microstructure of the grain is established,and the construction of the material grain boundary simulation geometric model is completed by the Vironoi method,using Abaqus limited The secondary development function of the metasoftware establishes a finite element model of the microbending forming process of stainless steel sheet based on the polycrystalline plasticity theory.In Chapter 4,based on the experimental parameters,a simulation model considering the grain boundary structure is established,and a microbend simulation model without the grain boundary structure is also established as a control.The simulation results of the two are compared with the experimental data to verify the consideration of the crystal.The correctness of the constitutive model of the grain boundary structure and the material model based on the improved Vironoi method are analyzed.The simulation results are analyzed,and a micro-explanation of the bending angle change rule is proposed.In Chapter 5: forming dies with different parameters and setting up corresponding experimental platforms were designed,conducting side-by-side multi-bend micro-bending forming experiments on characteristic regions of fuel cell bipolar plates,and studying mold fillets,convex and concave die clearances,and convex dies The influence of the width and the number of runners on the forming performance of runners.In Chapter 6,the main research work of the paper was summarized,and the further research subjects were proposed. |
PDF Full Text Request