Study On The Optimization And Design Of Ultrasonic Plasticizing-molding System For Micro-nano Devices

Micro injection molding is one of the major technologies for the manufacture of micro-nano devices,however,there are many problems in injection molding,such as micro channel effect,inhomogeneous plasticization,poor molding quality of micronano devices and the mismatch between the molding equipment and the sizes of the micro-nano devices,therefore,which has emerged the new technology of ultrasonic micro injection molding.At present,the research of ultrasonic micro injection mainly focused on experiments and simulations,the simulation research is mostly based on the two-dimensional ultrasonic plasticizing model,the ultrasonic transducer with fixed amplitude and frequency is used to replace the actual output of the transducer,but the effect of the structural parameters on the output amplitude and the frequency is not considered,the periodic change of the output amplitude of the transducer is not also considered.In view of the above problems,based on the design of the prototype of the ultrasonic plasticizing-molding system for micro devices,this paper focused on the influence mechanism of the structural parameters of the transducer on the ultrasonic plasticizing process,and proposed a new method and theory for designing ultrasonic plasticizing-molding system for micro-nano devices.The specific research contents are as follows:First,the mechanism of melting and plasticizing heat generation of polymer particles under the longitudinal vibration excitation is studied,and the mechanism of the interfacial friction plasticizing heat generation of polymer particles is analyzed.The resonant frequency and the output amplitude equation of the ultrasonic transducer are derived,the mathematical model of the relationship between the structural parameters of the ultrasonic transducer and the interfacial friction plasticizing heating rate of polymer particles is established,which used Mathematica software to numerically analyze the influence of the structural parameters of the ultrasonic transducer on the interfacial friction plasticizing heating rate of polymer particles under the longitudinal vibration excitation.The research results demonstrate that the amplification ratio has the greatest effect on the interfacial frication plasticizing heating rate of polymer particles,followed by the length of the front cover and the ultrasonic tool head,the influence of the horn length,the rear cover length and the piezoelectric ceramic pieces thickness are smallest.Second,to verify the correctness of the analytical method to analyze the interfacial friction plasticizing heating rate of polymer particles under the longitudinal vibration excitation,a three-dimensional heating model of the interfacial friction plasticizing polymer particles is established using LS-DYNA,the actual output longitudinal vibration excitation of the ultrasonic transducer under different structural parameters is obtained using ANSYS simulation analysis,then directly loaded into the heating model,and the influence of the structural parameters of the ultrasonic transducer on the interfacial friction plasticizing heat generation of polymer particles under the longitudinal vibration excitation is fully studied using simulation analysis.The research results show that the temperature of the interfacial friction plasticizing heat generation of polymer particles increases nonlinearly with the increase of the longitudinal vibration excitation time,and the interfacial friction plasticizing heat generation of polymer particles is a transient process.The temperature change with time of the interfacial friction plasticizing heat generation of polymer particles under different structural parameters of the ultrasonic transducer vary greatly,which has a great influence on the required longitudinal vibration excitation time to reach the viscous flow temperature of polymer particles.The amplification ratio has the greatest effect on the interfacial friction plasticizing heating rate of polymer particles under the longitudinal vibration excitation,followed by the length of the front cover and the ultrasonic tool head,the influence of the horn length,the rear cover length and the piezoelectric ceramic pieces thickness are smallest.The results of the interfacial friction plasticizing heating rate of polymer particles under the longitudinal vibration excitation are compared with the analytical method and simulation method,the two methods have good consistency.Third,considering the influence of the annular clearance between the ultrasonic tool head and the plasticizing cavity on the injection process,the annular clearance model is established,the ANSYS CFX is used to analyze the influence of both the annular clearance and the inlet total pressure on the leakage and the friction of the ultrasonic tool head.The research results show that the annular clearance is between 0.1 and 0.15 mm,the inlet total pressure is between 10 and 20 MPa,the leakage and friction are both smaller,and the better annular clearance and the inlet total pressure are obtained.Fourth,the ultrasonic plasticizing and molding system matching with the structural sizes of the micro-nano devices is designed,the structural parameters of the ultrasonic transducer are optimized by using the theoretical and simulation results of the influence of the structural parameters of the ultrasonic transducer on the heating rate.The research results demonstrate that the maximum output amplitude after optimization increased by 12.9%,the time of the longitudinal vibration excitation reduced by 24%,and the heating rate increased by 33.3%.The plasticization cavity is optimized by using the better annular clearance value obtained by the simulation analysis.The mold system matching with the molding micro gear devices is designed in detail by adopting the mosaic and side pumping module.