Research On Plastic Welding System Based On Power Ultrasonic Technology

Ultrasonic plastic welding is a fast,efficient and environmentally friendly assembly process,which is widely used in medical testing,industrial production,military aviation and other fields.It is a widely used advanced assembly technology.However,in the field of ultrasonic plastic welding,welding strength is insufficient and over-welding occurs from time to time,which is mainly caused by domestic manufacturers’ lack of basic knowledge of ultrasonic transducer and understanding of the working mechanism of ultrasonic welding.In order to achieve better welding effect,this thesis developed an ultrasonic welding power supply integrated with automatic frequency tracking module,and built a welding experiment platform based on it.Combining theory and experiment,the following aspects were studied with Polyvinyl chloride(PVC)plastic as the research object:1.Combined with the equivalent circuit model of the ultrasonic transducer,the impedance characteristics of the piezoelectric ceramic transducer are analyzed in this thesis.The inductance capacitance matching model which is most suitable for ultrasonic welding is selected and applied in the experiment.The results show that the matching model is relatively stable.2.The influence degree of temperature on ultrasonic transducer was explored,and the influence degree of temperature on dynamic inductance,dynamic capacitance,resonant frequency and other parameters of ultrasonic transducer was verified by designing thermostat experiments.The experimental results show that when the initial temperature of the ultrasonic transducer rises from 25℃ to 65℃,the resonant frequency of the ultrasonic transducer changes by about 73-103 Hz,which verifies the necessity of frequency chasing strategy for the stable operation of the ultrasonic transducer.3.Based on the high requirements of ultrasonic welding on frequency chasing speed and precision,this thesis developed a kind of ultrasonic welding power supply which integrated automatic frequency chasing module and had two Microcontroller units(MCU).A single MCU was used to control the dedicated frequency chasing chip HZ6686.It can control the frequency chasing speed of welding system within 80 ms,and achieve the frequency chasing precision of 0.1Hz,and has high stability.4.In the actual welding scene,the stability of the output amplitude of the transducer determines the welding quality of the welding parts.This thesis makes a theoretical derivation of the amplitude factors affecting the ultrasonic transducer,and establishes the corresponding relationship between the driving current and the amplitude.When the transducer drive current fluctuates about 0.2A,the transducer amplitude will fluctuate 3～4μm.5.Aiming at the problem that the quality of plastic welding is difficult to be guaranteed,this thesis puts forward the amplitude separation welding method.Through the COMSOL simulation software,the welding part modeling and welding temperature field simulation are carried out,and the simulation curve of welding temperature field temperature change over time and the simulation curve of the influence degree of different welding parameters on the temperature change are obtained.The simulation results are further verified by temperature measurement experiment based on thermocouple.Finally,the comparison experiment is designed to prove that the welding strength of each welding part is obviously improved in different degrees after using the amplitude grading technology.