Study On Wear And Life Assessment Of MoS₂ Lubricated Spherical Hinges Under Reciprocating Oscillating Conditions

Spherical hinges are widely used in parallel mechanisms,industrial robots,automobiles and other equipment.Their friction and wear performance and wear life affect the service time and reliability of the equipment.For precision spherical hinges lubricated with molybdenum disulfide（MoS₂）,the wear of the solid lubricant layer is the main failure form of spherical hinges.Since the spherical hinges reciprocating oscillate under external loads,the friction and wear process is complex,so it is very difficult to establish a wear model of spherical hinges considering the coupling effects of multiple factors.In addition,there is currently a lack of wear failure evaluation methods of the spherical hinges based on mechanism accuracy,which makes it impossible to accurately predict the wear life of spherical hinges in precision mechanisms.In this paper,through theoretical analysis,numerical simulation and experimental research methods,the wear model of MoS₂ lubricated spherical hinges was established,and the wear life evaluation of the spherical hinges was carried out,and the wear mechanism of the MoS₂ lubricated spherical hinges under the reciprocating oscillating condition was clarified.Based on the Hertz contact theory,the friction factor model of the MoS₂ film was established.On this basis,according to the frictional dissipation energy method,the wear model of the MoS₂ film was established.The model can simply and effectively predict the wear of solid lubricating film under the coupled action of normal load and sliding velocity.The effects of substrate surface roughness on the friction and wear properties of MoS₂-based lubricating films were further studied under dry friction,solid-oil composite lubrication and solid-grease composite lubrication.When the surface roughness of the substrate was between 0.01 and 0.26μm,the MoS₂-based film under the solid-oil composite lubrication has better wear resistance,and the MoS₂-based film under the solid-grease composite lubrication has the worst friction and wear performance.According to the coordinated contact theory,a complete spherical contact mechanical model of the MoS₂ film/substrate system was established,verified and corrected by finite element simulation technology,and the film/substrate system contact mechanical model was applied to the structural optimization of the solid lubricated spherical hinge.Combined with the wear model of MoS₂ films,the wear model of MoS₂ lubricated spherical hinge was established,and the wear rate of solid lubricated spherical hinges under single rotation,single tilt and compound reciprocating oscillation was calculated respectively,and the prediction of the wear rate of solid lubricated spherical hinge under complex working conditions was realized.The effect of oscillating angle and oscillating frequency on the wear rate of solid lubricated spherical hinges was further studied.The friction and wear test machine of the spherical hinge under the reciprocating oscillating condition was developed.The influence of oscillating modes,external loads and oscillating frequencies on the friction and wear properties of MoS₂lubricated spherical hinges was studied,and the wear mechanism was analyzed.In the reciprocating oscillating mode of the spherical hinge,the abrasive particles of MoS₂films participated in the lubrication process,which could effectively reduce the wear rate of the spherical hinge.Through the friction and wear experiment of the spherical hinge under the reciprocating oscillating condition,the wear model of MoS₂lubricated spherical hinges was further verified,and the correction method of the dynamic load coefficient was proposed.Based on the mechanism accuracy,the wear life evaluation system of the spherical hinge was constructed.The system adopted the absolute value accuracy index and dimensionless accuracy index,which could quantitatively analyze the accuracy characteristics of the mechanism.A method to establish the mapping relationship between the wear clearance of spherical hinges and the mechanism accuracy index was proposed,and the maximum allowable wear clearance and the maximum allowable wear depth were obtained through the mechanism accuracy threshold.According to the randomness of wear rate and maximum allowable wear depth,a probabilistic reliability model of MoS₂ lubricated spherical hinge was established,and further,a fuzzy reliability model of spherical hinges was established according to the ambiguity of maximum allowable wear depth.Taking the classic 3-RPS parallel mechanism as an example,it was clarified that there was a significant linear relationship between the wear clearance of the MoS₂lubricated spherical hinge and the mechanism accuracy index,and the wear life of the MoS₂ lubricated spherical hinge was calculated by using the probabilistic reliability model and fuzzy reliability model respectively.The comparative analysis showed that the fuzzy reliability model of MoS₂ lubricated spherical hinge could more realistically reflect the safety degree of wear and could be used to predict the wear life of solid lubricated spherical hinges.In addition,the fuzzy reliability wear life of MoS₂lubricated spherical hinges was studied in the mechanical system with multiple spherical hinges and vacuum environment,which could approach the engineering practice objectively.