Fatigue Strength Research On The Connecting Bolt Of Walking Frame Of A Hydraulic Excavator

Hydraulic excavator is one of the main equipments of engineering and construction machinery,and it has been widely used in many aspects of national economic construction.As the working environment of the hydraulic excavator is very poor,the reliability of the key connection points becomes the key part of the design,especially for the large hydraulic excavator,the working environment is even worse and the parts of the important connection position are bearing considerable loads,so it is very important to study the load condition and fatigue strength of the important connection of hydraulic excavator.In this paper,the parts of the connecting bolts for chassis and caterpillar track beam of two of the four test prototypes are fractured in fatigue during the test phase.After a preliminary study,the main reasons for the failure of the bolts include the design and selection of the bolt cannot meet the demand of working under the limit conditions,manufacturing process or assemble process cannot meet the requirements,the mechanical structure of chassis and caterpillar track beam is unreasonable or not operating according to the specifications.In this paper,the research is mainly focuses on the aspect of the design and selection of the bolts which causes the fatigue fracture.Firstly,According to the modeling method of building virtual prototype and the corresponding model simplification principle to build the 3D model of the hydraulic excavator based on Pro/E software.It provides accurate 3D model for the follow-up kinematics and dynamics simulation analysis.Secondly,establish the dynamics simulation model of hydraulic excavator in ADAMS software,and then do the kinematic simulation of the working device of the virtual prototype under the condition of sequential action of the hydraulic cylinder of working device to obtain the basic work performance parameters of working device,such as the bucket tip trajectory,the maximum digging radius,the maximum digging height,and the maximum digging depth etc.Thirdly,according to the maximum working size parameters obtained from the kinematics simulation and hydraulic excavator test specification requirements,six kinds of limit conditions are selected.Use the step function provided by the ADAMS software to write the driving function of three hydraulic cylinders of working device,and add the material gravity and cutting force on the corresponding position on bucket of the virtual prototype,so as to carry out the dynamic simulation analysis of the connecting bolt groups under the six conditions,and then the loading curve of the connecting bolts under the six conditions,the maximum load condition and the maximum load value under this condition are obtained;Finally,according to the bolt load maximum load value obtained from dynamic simulation,and based on the VDI2230 bolt fatigue strength criterion to analysis the fatigue strength of the walking frame bolt groups under the condition of maximum load.The results show that the design and selection of the bolt meet the requirements,therefore,the main reason for fatigue fracture of bolts is not caused by unreasonable design and selection of the bolts.And the failure reason analysis is required to study on the other three directions.The research provides the theory basis to improve the quality of the products and provides the directions to study the failure of the walk frame connecting bolts.