Research On Thickness Measurement Of Large Propeller Blade Based On Ultrasonic Measurement Technology

Large-sized screw propeller is mainly used to provide power for ships. The blade thickness is one of the important parameters to control blade shape, the measurements of the blade thickness have great significance to the manufacturing process and the reasonable distribution of the machining allowance. At present, most domestic manufacturers use artificial calipers to get blade thickness, this method not only shows low repetition accuracy, high labor intensity and strong dependence on human, but also restricts the development of propeller processing and detection integrated. Based on the current situation, this paper is funded by Natural Science Foundation of Innovation Groups Project: basic research of high-performance digital manufacturing preparation. The research focuses on ultrasound technology to carry out applied research for large propeller blade thickness measurements. According to the principle of ultrasonic thickness measurement and blade structure, an effective method for measuring blade thickness is determined.Firstly, it analyzes the characteristics of propeller structure and caliper measuring thickness process; Based on the principle of ultrasonic thickness measurement, it analyzes and determines the reasonable method of ultrasonic thickness; The blade of ultrasonic thickness influence factors are also analyzed. And according to the research content, an ultrasonic thickness and signal acquisition experiment platform is designed and built.Secondly, this paper analyzes the source and characteristics of echo signal of mixed noise in process of measuring the blade thickness. And based on wavelet multi-resolution analysis theory, a complete, effective implementation of noise reduction is determined so that noise reduction of the echo signal and bottom echo feature extraction is effectively realized. Mainly, the selection of wavelet base, the determination of optimal decomposition layers and threshold processing method are studied.Then, based on the time domain of the echo processing of bottom surface, the calculation method of blade thickness is studied. And through the simulation experiment of the specimens, the impact of the blade surface roughness of the particles and the surface angle of the measurement results is analyzed and validated. And according to the experience of the project, proper compensation and correction scheme is presented.Finally, the high repetitive nature of ultrasonic measurement results is verified by ultrasonic thickness experiment on blank propeller blade. Further, capturing and through the wire-cutting the local surface on the propeller blade which is captured before, the measured values of each point thickness of section line ultrasonic measurement result are obtained. Then comparing them with the result of ultrasonic measurement and referring to the values of blade thickness tolerance grade of blade thickness, the ultrasonic method of blade thickness is verified the validated.