Interference Fit Assembly Of Precision Miniature Components And Connection Force Ultrasonic Measurement

Precision interference fits of miniature components are widely used in aerospace,instrumentation and precision machinery due to their high load carrying capacity,good alternating and impact load performance,such as armature and jet disc,which have a mating size of several millimeters and assembly accuracy of the order of microns.At present,there are still some problems in the design,assembly and quality evaluation of precision interference fits of miniature components,which limits the further improvement of the performance of the components.The design method of the component mainly adopts the Thick-walled Cylinder Theory(TCT),but the analysis results of stress distribution and press-mounting force have significant errors for ignoring the influence of the noncontact region.For the assembly of precision interference fits of miniature components in aerospace field,the manual press-fitting method is mainly used,which has low assembly accuracy,poor consistency,and it is difficult to meet the needs of industrial modernization.For the connection quality evaluation,force-displacement curve is ususly used for preliminary evaluation.Since the force-displacement curve cannot accurately reflect the contact status between the mating surfaces,this method is difficult to obtain accurate evaluation results.In response to the above problems,the following research was carried out:Through the optimization of theoretical model,the prediction accuracy of press-mounting force and stress distribution is improved,which provides theoretical support for the design and quality evaluation of interference components.For the assembly of armature and spring tube,an automatic precision press-fitting equipment was developed to improve the assembly accuracy,qualification rate and consistency.The ultrasonic stress measurement method was studied,and accurate measurement of the stress distribution and connection force of interference components was achieved based on this method.In the study of theoretical methods of interference fits,the Finite Element Method(FEM)and TCT were used to analyze the stress distribution and deformation during the press-fit process of the armature component.The results show that the prediction error of the TCT is caused by the deformation resistance generated by noncontact regions.Through the reasonable simplification of the noncontact region,the theoretical formula of deformation resistance was built,and then the theoretical model of the press-mounting force was established by combining the TCT.The theoretical model of the stress distribution was obtained by simplifying the interference component to the problem that non-uniform load acting on a portion of the straight boundary of a semi-infinitely plate.The accuracy of the theoretical model was verified by FEM and press-fit experiments.The prediction errors of press-mounting force and maximum contact stress are 15%and 20%,respectively.In terms of precision assembly of interference components,the posture deviation of the armature component is difficult to adjust,which lead to low assembly accuracy.Therefore,an automatic precision press-fitting equipment was developed,and calibration and automatic assembly methods were proposed.The equipment is mainly composed of clamping module(upper and lower),binocular vision module,precision automatic adjustment module and force-displacement measurement module,and its function is to ensure reliable clamping and positioning of parts,automatic measurement and adjustment of posture deviation,as well as real-time measurement and control of press-mounting force and displacement.Automatic precision assembly of armature component is realized based on calibration and automatic assembly methods.The reasonable range of the force-displacement curve was obtained based on the theoretical analysis model obtained in Chapter 2,and finally the preliminary evaluation of the connection quality was achieved.The results of the assembly experiments show that the device has high assembly accuracy and good consistency,and can achieve precision assembly of armature and spring tube.In the aspect of connection quality evaluation of interference components,the ultrasonic stress measurement method and the ultrasonic measurement of the stress distribution and connection force of interference components were studied.Firstly,through the experimental study on the influence of roughness,frequency,couplant,oil lubrication,contact boundary and material hardness on the measurement results,the influence law of each factor was determined,and established a measurement error compensation model for covered boundary and stiffness analysis model of oil film lubricated interface.Then,a stress distribution ultrasonic measuring device was designed and built according to the principle of ultrasonic stress measurement.The stress distribution of the interference components with different interference,hardness,lubrication conditions and geometry was measured,and the connection force was calculated.Finally,the calculation results are compared with the experimental results.The results show that the method can achieve accurate measurement of the connection force,and the relative error is less than 20%.In summary,this paper improves the accuracy of theoretical model,guarantees the assembly quality of armature components,and realizes accurate measurement of connection force by optimizing the theoretical model of press-mounting force and stress distribution,and proposing automatic precision assembly methods and connection quality evaluation methods based on ultrasonic stress measurement.This paper has completed the application of the proposed theory and technology in precision miniature interference components,and achieved theoretical and technical innovation and practical application results.It not only solves some problems in the assembly process of precision miniature components in the aerospace field,but also enriches,improves and develops the theoretical method of interference fit,which provides a powerful theory and technical support for the design,automatic assembly and quality assessment of interference components.