| Aerospace manufacturing is a typical representative of the equipment manufacturing industry,the product quality represents the highest level of advanced manufacturing in China.Most of the aerospace components are large-scale thin-walled parts with complex structures,they are generally processed by five-axis CNC machine tools.As an important performance index of thin-walled parts,thickness results the performance of subsequent products.Five-axis CNC machine tools are used to process thin-walled parts,which may lead to plastic deformation of thin-walled parts and damage the final machining accuracy.Therefore,it is necessary to measure the thickness of the parts many times during the machining process,so as to compensate the machining error and ensure the final machining accuracy.At present,the unmanned production mode is developing rapidly,so it is urgent to carry out unmanned field application extension research on the previously developed tool holder on-machine ultrasonic thickness measuring device.Based on many factors in the field,such as the surface roughness of the workpiece during measurement and the angle between the probe and the surface of the workpiece,the field uncertainty of the thickness measuring device is explored.Lastly,aiming at the shortcomings of the thickness measuring device in measurement accuracy and field measurement adaptability,the performance of the thickness measuring device is improved through the analysis of relevant theory.The main research of this thesis is as follows:(1)Based on the basic theory of ultrasonic thickness measurement,the performance enhancement of the thickness measuring device is studied.According to the theory of ultrasonic pulse reflection method,the acoustic wave propagation of the thickness measuring device is analyzed,and the conclusion that the angle of ultrasonic echo will introduce nonlinear error is gained.Especially in the process of small thickness(< 4mm)measurement,the nonlinear measurement error of the thickness measuring device is investigated based on this conclusion.When the peak-to-peak method is used to measure the small thickness(< 4mm),the waveform folding phenomenon will lead to the inability to accurately extract the thickness feature.Therefore,the peak-to-peak feature extraction algorithm is optimized for this phenomenon and combined with the actual echo waveform.The ultimate goal is to achieve an improvement in the performance and accuracy of the thickness measurement device.(2)The uncertainty evaluation and analysis of ultrasonic thickness measurement device were carried out on the thickness measurement field.Aiming at the complex measurement environment,the main sources of uncertainty are analyzed,and the mathematical model of uncertainty propagation is established.Then,based on the uncertainty propagation model of the ’ start-up echo method ’ and the ’ negative peak-topeak method ’,the evaluation of the A-type and B-type uncertainty components is completed respectively,and the combined standard uncertainty is finally gained,so as to ensure the field measurement confidence of the entire thickness measuring device.(3)The unmanned thickness measurement system is studied and implemented on the thickness measurement field.For the unmanned field measurement environment,the overall scheme of unmanned application of thickness measuring device is designed,and the charging endurance and communication control of thickness measuring device are studied and realized according to the scheme.And then by planning the related functions of the upper computer software part,the application of the thickness measuring device in the unmanned field is realized.Lastly,the performance improvement effect of the thickness measuring device is verified by designing corresponding experiments,and the measurement accuracy achieves ± 0.02 mm.The functions of the unmanned thickness measuring system and the field measurement accuracy are verified on the thickness measuring field,and the field accuracy is also better than ± 0.02 mm. |
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