| As one of the most important earthwork machinery,wheel loader is widely used in national infrastructure construction,water conservancy,mining,real estate and other industries.However,because of the very bad working environment in the working process of the loader,,it is easy to cause the failure of the key structural parts of the loader.In the reliability growth test of A new loader in the trial production stage of a domestic enterprise,it was found that local failures occurred at the hinge point(point A)of the boom and front frame,the beam support plate of the boom,and the outside position of the U-shaped plate of the left/right box of the front frame.After a statistical analysis of the failure cases,it was found that the first failure time of the above positions was about 800～2000h.It’s an early failure problem.Through the failure analysis of the boom and the hinge point(point A)of the front frame,the boom beam support plate and the outside position of the U-shaped plate of the left/right box of the front frame,the failure mode is confirmed,and the failure causes are finally determined as follows: due to unreasonable design,there is stress concentration near the failure position,and the local stress is too high,leading to the premature failure of the structural parts.In order to determine the boundary conditions in the finite element analysis,the working device of the prototype was analyzed for the power trajectory,and the results proved the uniqueness of the movement trajectory of the loader working device.At the same time,the static analysis and calculation of the working device were carried out to obtain the load component of each hinge point position on the working device under various working conditions,which provided the basic theory and data support for the subsequent finite element calculation and analysis.Then,Finite Element Analysis was carried out on the local failure locations in the reliability growth test: the toe of the round lap weld at hinge point A of the boom and front frame,the support plate of the boom beam,and the outside of the U-shaped plate of the left/right box of the front frame.The contents were as follows:(1)According to the structural dimension parameters of the working device of the reliability growth test prototype and the left/right box of the front frame,the three-dimensional model is constructed in the Creo after simplification;(2)The assembled 3D solid model was imported into ANSYS Workbench,and after meshes were divided,the calculation data obtained in the statics analysis process was imported into the software as the boundary conditions of the finite element model,and the finite element calculation results were obtained through calculation by the solver;(3)The finite element calculation results were analyzed,and it was found that high stress areas(close to or greater than the yield strength of the materials used)appeared at the toe of the round lap weld at point A of the boom,the weld toe of the front end of the boom beam support plate,and the outer position of the left/right wing box U-shaped plate of the front frame,which were consistent with the results of failure analysis.The optimization scheme proposed in the failure analysis is used to optimize the structure of the system.The results show that the maximum stress value in the high stress region can be significantly reduced and the stress distribution in the high stress region can be improved after the optimization of the local failure location in the reliability growth test.(4)The safety service life of the above three typical cases is evaluated.Compared with the original scheme,the safety service life of the design reaches 5000h(the current three packages in China).After the installation test tracking,the whole machine has been used for3000 h,and no early toe cracking occurs in the above locations. |
