Mechanical Analysis And Precision Manufacturing Technology Research Of Ellipsoidal Plain Bearings

As a new type of spherical sliding bearing with special structures,self-lubricating spherical plain bearing possesses advantages of compact structure,small friction coefficient,impact resistance,corrosion resistance and maintenance-free,so it is widely used in important parts of aeronautics and astronautics devices.The wear failure of the self-lubricating layer is the main failure form of self-lubricating spherical plain bearings.Due to the spherical contact characteristics of the traditional self-lubricating spherical plain bearings,the contact pressure in the middle contact region of the bearing is far greater than that in the edge contact area when subjected to radial load conditions,so it will enter the wear failure state earlier and seriously affect the service life of the bearing.In addition,self-lubricating spherical plain bearings are made up of three parts,inner ring,outer ring and self-lubricating layer,and they are manufactured separately.Therefore,it is difficult to realize the precise control of the bearing clearance during assembly process,and it will inevitably cause the damage of self-lubricating layer,which is difficult to meet the requirements of manufacturing accuracy.Therefore,a novel self-lubricating ellipsoidal plain bearing was proposed in this paper.Based on the theoretical analysis of its contact performance and wear characteristics,the integer assembly manufacturing technology of outer ring radial contraction extrusion of self-lubricating ellipsoidal plain bearings was put forward.In addition,the radial basis function(RBF)neural network and Particle swarm optimization(PSO)algorithm were used to control the manufacturing process of the self-lubricating ellipsoidal plain bearings.At last,the tribological properties of self-lubricating ellipsoidal plain bearings were evaluated by the reciprocating friction and wear tests.The mechanism of the contact form of the friction pair on the tribological properties of self-lubricating spherical plain bearings was revealed,and the anti-friction and anti-wear resistance mechanism of the self-lubricating ellipsoidal plain bearing was clarified.Based on the universal Hertz non-conformal contact theory,a frictionless conformal contact model of complete spherical surfaces was established.In addition,an analytical model for calculating the contact pressure of self-lubricating spherical plain bearings with incomplete spherical surface was proposed by using the equivalent force principle.The contact mechanics analysis showed that the contact stress of the self-lubricating spherical plain bearing was large in center contact region when subjected to the radial force,and the contact stress at the two ends was small.In order to solve the problem of the uneven distribution of contact stress for self-lubricating spherical plain bearings,the self-lubricating ellipsoidal plain bearing was put forward,and its geometric model and contact mechanics theoretical analytical model were established.The elastic properties and Archard wear model of the fabric liner were obtained by the finite element simulation and linear reciprocating wear tests,respectively.Based on the material parameters,the contact performances as well as the wear characteristics of self-lubricating spherical/ellipsoidal plain bearings were simulated numerically.The influences of geometrical structure,radial load and initial clearance on the contact stress and wear morphology of self-lubricating spherical/ellipsoidal plain bearings were analyzed,which provided the theoretical support for the analysis of wear failure and optimization design of self-lubricating spherical plain bearings.The integer assembly manufacturing technology of outer ring radial contraction extrusion was proposed to fabricate self-lubricating spherical/ellipsoidal plain bearings.The outer ring of the bearing was extruded by a conical hole die to make it plastic deformation,then assembled with the inner ring,and finally the integer assembly of the bearing was achieved.Based on the analysis of the principle of forming process,the forming process of self-lubricating ellipsoidal plain bearings with typical size was investigated by numerical simulation.On the basis of the process principle analysis,a self-lubricating ellipsoidal plain bearing with typical size was taken as an example,the key technological parameters were optimized combined with the numerical simulation and the RBF-PSO optimization algorithm.The precision forming and assembly tests of self-lubricating spherical/ellipsoidal plain bearings were carried out.The test results showed that the deviation between measurement radius and design radius of the inner surface of the outer ring can be controlled within 0.01 mm,and thus the precise control of the manufacturing process of self-lubricating spherical/ellipsoidal plain bearings was realized.The tribological performance evaluation tests of self-lubricating spherical/ellipsoidal plain bearings were carried out on the service property evaluation tester for aviation self-lubricating spherical plain bearings at low velocity and heavy load condition.Combined with the wear morphology,wear depth,friction torque and friction temperature of the fabric liner,the service performances of self-lubricating spherical plain bearings with different structures were analyzed.Thus,the mechanism of anti-friction and anti-wear of self-lubricating ellipsoidal plain bearings fabricated by outer ring radial contraction extrusion process was revealed from the aspect of contact mechanics.The design rules of self-lubricating ellipsoidal plain bearings were obtained.Taking a certain type of spherical plain bearing as an example,the design parameters and precision manufacturing parameters of the bearing subjected to radial light load 5kN and heavy load 25 kN were obtained,respectively.Under radial light load 5kN condition,the flattening of the bearing should be 0.005.While under the radial heavy load 25 kN condition,the flattening of the bearing should be 0.009.The greater the flattening of the self-lubricating ellipsoidal plain bearing,the greater the renla value of the outer ring blank should be.