| Automotive drive shaft assembly is one of the key parts of automobile.And the automobile transmission shafts are made of 45 steel hollow tube and 40 Cr solid shaft by welding,which can effectively reduce the cost and the overall weight.It has great significance for improving the quality of automobile transmission shaft welding to research laser welding technology.There are two main problems to adopt Laser welding technology to weld the transmission shaft: in the process of laser welding joint performance is not the same because of the different material and shaft girth welding is prone to defects.Therefore,in order to solve the problem,the main contents of the study are as follows,Firstly,the method of offset the laser spot is proposed to solve the problem that dissimilar steel welding joint performance is not consistent.First,the optimization experiment is done for laser power and welding speed.Then Based on the mechanism of laser welding and the optimizedparameters above,the method of leaser beam offset is proposed to solve the problem that the penetration of heterogeneous steel is not synchronized.And the experiment on the effects of leaser beam offset on the properties of welded joint is studied.In addition,the welding micro-structure and mechanical property were compared under different process parameters.The results show that a favorable quality of weld surface is obtained under the optimal combination of process parameters of laser power 4.2 k W,welding speed 1.2 m · min-1 and defocusing amount-2mm.Laser offset 0.1 mm.When laser bias of 40 Cr steel side 0.1mm,a good weld forming with symmetrical about cable distribution is obtained.The micro-structure of the weld zone is more uniform.It is mainly marten-site.The micro hardness of cross section is at least 3 times higher than the base metal.The tensile strength of the welded joint is over45 steel.Secondly,the 45 steel Shaft tube is used for improving the laser welding defects in shaft pipe girth by experiment.Real-time variable parameter method was proposed to solve the problem of shaft parts caused by welding defects.Choosing laser power as a variable,the advantages and disadvantages of the welded joint have been studied under different laser power trend.And combining with theoretical analysis and experimental results,high-quality welding joint was obtained at the optimization of laser power transformation trend.Theresults show that there are two main welding defect of shaft tube.The one is aft defect caused by the heat input at the ending.The other one is uneven welding defect caused by different temperatures at the different periods of welding foundation.It can effectively solve the problems by adjusting the laser power in different parts of the weld.Finally,the torsion test research of transmission shaft welded sample was conducted.It was welded under the optimal combination of process parameters obtained before.The maximum torque of the welded joints after laser welding was compared with the friction welding.In addition,a special fixture is designed for the shaft tube welding.The results show that favorable forming qualities and less machining process are obtained with laser welding.The maximum torque of the welded joints are 4572.5N·m which is higher than 4200 N·m of the transmission shaft standard sample,and the crack angles are small.The results show that the method of this paper can effectively improve the dissimilar steel shaft tube laser welded joint performance and it is feasible for the shaft to weld by laser. |
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