Research On Reliability Of Loader Boom Cylinder

Based on analyzing the current situation of the domestic industry on engineering machinery hydraulic cylinder and the internal and external research on reliability, in connection with the fact that the cylinders made in China are far less reliable than the ones of international advanced level, in order to improve the reliability of the hydraulic cylinder the analysis and practice on reliability are conducted by taking the methods such as analysis, prediction and design on reliability.By collecting field data and taking the method of failure mode effects and criticality analysis, the reliability analysis of hydraulic cylinders is conducted and 15 kinds of failure modes are conducted. And the causes, effects on the system, the detection methods and improvements of each failure mode are initially analyzed. Then 7 kinds of failure modes with higher criticality are obtained by conducting criticality analysis of each failure mode.Through classifying the 7 kinds of key failure modes, a conclusion is reached that in order to improve the reliability of hydraulic cylinders more quicklily, the problems of cylinder leakage and strength damage on piston rod should be deeply studied first and corresponding precautions, improvements and controlling measures should be taken.Considering that the failure mode of the piston rod fracture seriously thereatens personal safety, when the piston rod is in full stroke position the static stress analysis is conducted by using ANSYS software and the stress-strength interference model method is taken to seperatelly predict the reliability of piston rod in the normal force and in the lateral force. Through analysis and comparison, it is concluded that the root cause of the piston rod breakage is that the parallelism of the 2 pin holes at both ends of the hydraulic cylinder is beyond the limit. And by analyzing the contradiction between cost of production and reliability of products, the best parallelism is determined.For the problem of the hydraulic cylinder leakage, by using the method of fault tree analysis the fault tree with the cylinder leakage as top event is established and the minimal cut sets is obtained. According to the fault tree, in order to reduce the leakage rate and improve the reliability of cylinder, the cylinder structure, seal assembly and parts store is improved from the prospective of reliability design. From the perspective of improving the process capability, by doing process capability analysis and carrying out 2 experiments ultimately the optimum process parameters are determined and corresponding measures for improvement are proposed.