Research On Theory And Application Of Ultrasonic Welding At Megasonic Level

As an important joining process,ultrasonic welding has been successfully applied in many fields.The current ultrasonic welding technology mainly focuses on the traditional low-frequency ultrasonic region,but the research on theory and application of high-frequency ultrasonic welding at megahertz(MHz)level is rarely reported.A method of high frequency ultrasonic welding at megaonic level was proposed,and an ultrasonic welding vibrator with working frequency of 1.7MHz was designed and manufactured based on the theory of sound wave transmission and finite element analysis in this dissertation.The research on the theory and application of megahertz frequency ultrasonic welding was carried out with the polyvinyl chloride(PVC),a common medical packaging material,as the welding object.Firstly,the working principle of piezoelectric vibrators and the causes of coupling vibration of thin circular piezoelectric ceramic components were analyzed in detail,and vibration mode of high frequency piezoelectric ceramic wafer as sound source component was simulated by finite element method.Acoustic matching layer was provided according to the theoretical calculation result of sound transmission coefficient,and its thickness was selected,which provides a theoretical basis for improving the electric-acoustic conversion efficiency.Secondly,two heat generation mechanisms of ultrasonic welding were analyzed in detail,which provides a theoretical reference for the design and optimization of welding vibrator.Megahertz ultrasonic welding vibrator with matching layer structure was optimized based on the results of finite element modal analysis and harmonic response analysis,and its manufacturing process was completed.The vibration characteristics and loading stability were tested experimentally and its results are in good agreement with the simulation analysis.In addition,for the purpose of realizing the megahertz frequency ultrasonic welding experiment,a megahertz frequency ultrasonic welding system was established,and factors affecting welding quality were analyzed in detail.Welding experiment was conducted and the strength of welding specimens was tested under different ultrasonic welding process parameters.The ideal combination of adjustable process parameters was found by orthogonal experiment,and the tensile strength was compared with the adhesive method of PVC in practical production,proving the feasibility of the application of megahertz ultrasonic welding.Based on the results of the orthogonal experiment,the influence intensity of ultrasonic welding process parameters on welding quality was investigated by using the range analysis,which provides useful guideline for the adjustment of ultrasonic welding parameters in practical production and application.Finally,the scheme that the vibration of welding vibrator with MHz frequency is not affected during assembly was given,which provides guidance for practical application.