Research On The Friction Characteristics Of Interference Connection Assembly During Ultrasonic Press-fitting

Interference connection assembly is widely used in various fields of mechanical industry.The connection quality directly determines the quality and service life of the whole device.At present,the press-fit method is a common approach to assembling interference joints.However,the press-in method is susceptible to excessive interfacial friction force,which may cause serious frictional wear and impair bonding strength and assembly qualification rate.Therefore,traditional press-fit method of the interference connection assembly badly needs to be improved.In this paper,the ultrasonic vibration technology is applied in the assembly of interference joints,in order to reduce the interface friction force of the interference joints during the assembly process,reduce the wear of the interface material,and improve the connection performance.Combined with the theory of thick wall cylinder,the main influence mechanism of ultrasonic vibration on the interface friction force of interference connection assembly in the process of assembling was determined,according to the influence of relative moving speed of the component interface contact points on macro friction force,the main factors that affect interface friction during ultrasonic press-fitting process were analyzed.Based on the ABAQUS simulation platform,the whole finite element model of the interference components with ultrasonic indenter was established.The influence of the interference of the components and the vibration amplitude on the interface friction force of interference components was analyzed.Under the condition of ordinary pressing fit and ultrasonic assisted pressing fit,the interface friction force of the components was obtained and compared.The simulation results show that the ratio of the latter to the former,that is the friction reduction rate,is positively correlated with the interference amount and downward loading velocity of indenter,and is negatively correlated with the amplitude of indenter.The relative motion velocity of a pair of contact points was extracted from the simulation results,the time domain and frequency domain responses were obtained.The relative motion between the shaft and the sleeve was represented by the harmonic oscillation,and the ratio of the steady state component to the harmonic component was calculated.The results show that the friction reduction rate increases with the increase of the ratio,which further verifies the mechanism of friction reduction.According to the design theory of ultrasonic vibration system,the finite element modal analysis method can verify the ladder horn and the indenter producing longitudinal vibration near the ultrasonic excitation frequency.A set of ultrasonic assisted press-fit testing platform was designed,which can realize the process of ultrasonic assembling.The test platform is composed of ultrasonic generator,ultrasonic transducer,pressure feed mechanism and measurement system.The experimental measurement show that the less the interference amount is,the more effective the friction-reducing is.When the interference amount is 7?m,the macroscopic friction force under ultrasonic assisted press-fit reduces to 65.57% of that under normal press-fit.The friction force calculated by simulation is basically consistent with the experimental data.The connection force of the components was measured by extrusion experiment.And scanning electron microscope and surface roughness meter were used to observe the surface condition of interference connection assembly.The extrusion force and the surface condition obtained from these above experiments show that the ultrasonic vibration assisted pressing process can improve the connection performance and assembly quality.