Research On Superplastic Forming And Diffusion Bonding Technology With Laser Pre-welding

The multi-sheet structure with integration,high precision and complex shape,manufactured by Superplastic forming and Diffusion bonding,has found widely used in aerospace industry.However,the conventional SPF/DB process for forming four-sheet structure has a series of disadvantages,such as the difficulty of coating stop-off and long time thermal exposure.When SPF/DB is combined with LBW,diffusion bonding of truss is replaced by welding,the above problems will be solved.And Laser welding with the advantages of high energy density,good penetrability,small heat affected zone and deformation zone,can cut down the thermal cycle time and eliminate core sheets creep deformation at high temperature,improve the mechanical properties.In this thesis,research on Superplastic forming and Diffusion bonding technology with Laser pre-welding was carried out,the main researches are as follows:1.This paper expounds the superplastic of material and the basic principle of diffusion bonding,as well as the basic theory of Laser beam welding.According to relevant theories,the fine grain superplastic properties of TC4 titanium alloy was detailed analysed through the constant strain rate tensile method and velocity mutation method.The result shows,when strain rate is 1.04x10-3,strain rate sensitivity index m=0.535,in the condition of temperature 920?.2.The laser beam welding experiment for TC4 titanium alloy was detailed analysed.the five groups of different joint weld of the welding pool width can be used to research the relationship between the welding pool width and internal stiffeners in four-sheet structure.And analysis of the mechanical properties of welded joint are discussed,the relationship between weld size and welding parameters,and the weld microstructure,hardness and fracture morphology are analyzed.3.Based on laser welding in advance of four-sheet structure molding process has carried on the finite element numerical simulation,considering the interaction in sheet metal,and the optimized pressure of time control curve was obtained.the simulation results show that the improved process methods in the center of thickness is greater than the traditional process method,can enhance the core board in the weak area.4.Research on Superplastic forming and Diffusion bonding technology with Laser pre-welding was carried out,the quality of structure was discussed and the thickness between the experimental results and simulation results were analysised.The results show that the grain size grows up evidently,increased about 35% ~ 35%,lower than the traditional process method.Finally,the relationship between the welding pool width and internal stiffeners in four-sheet structure were analysised.