Theoretical Study On Ultrasonic Plasticizing Viscoelastic Heat Generation Of Micro Devices

In the field of micro-device manufacturing,the introduction of ultrasonic vibration into the process of polymer melt plasticization can effectively improve the problems of uneven plasticization and poor molding quality of micro-devices.Domestic and international scholars use simulation methods to study the effect of ultrasonic vibration on the heat generation of amorphous polymers.Generally,the natural frequency and amplitude of the ultrasonic transducer are assumed to be fixed.Periodicity of amplitude changes with time and the effect of the structural parameters of the transducer on the natural frequency and amplitude are ignored.Based on the problems in the process of ultrasonic plasticization,this article focuses on the analysis of the viscoelastic heat generation mechanism of amorphous polymers and the effects of transducer structural parameters and vibration modes on the viscoelastic heat generation process of polymers.The specific research contents are as follows:Firstly,an amorphous polymer mechanical model is created,and the mechanical properties and properties of the polymer are analyzed.Based on the principle of time-temperature equivalence,the temperature-dependent relaxation time formula of the polymer is derived.Based on the law of conservation of energy,the viscoelastic heat generation rate equation of the polymer is derived.Secondly,based on the equivalent circuit method,the natural frequency and amplitude equations of the longitudinal vibration ultrasonic transducer are derived.Mathematica software is used to calculate the natural frequency and output amplitude of the longitudinal vibration transducer under different structural parameters.The natural frequency and amplitude are brought into the heat generation rate equation,and the MATLAB software is used to numerically analyze the effect of different structural parameters of the longitudinal vibration transducer on the viscoelastic heat generation rate of the polymer.From the analysis results,it can be seen that the amplification ratio has the greatest influence on the frequency of the longitudinal vibration transducer,followed by the thickness of the rear cover plate,the thicknessof the front cover plate and the length of the tool head.The minimum impact on the frequency of the longitudinal vibration transducer are the thickness of the ceramic sheet and the length of the horn.When the temperature of the polymer is lower than the glass transition temperature(105?),the viscoelastic heat generation rate of the polymer is relatively low.When the temperature exceeds 105?,the heat generation rate of the polymer rises rapidly,and there is a maximum value.After reaching a certain temperature,the heat generation rate gradually decreases.Thirdly,the ANSYS software is used to establish the finite element model of ultrasonic longitudinal vibration transducer and polymer viscoelastic heat generation.The output frequency and maximum amplitude variations under different structural parameters is simulated and analyzed.The effect of different structural parameters on the viscoelastic heat generation process of polymer was studied.The results show that the viscoelastic heat generation temperature of the polymer increases nonlinearly with the increase of the longitudinal vibration excitation time,and the temperature change law is basically the same.At the beginning,the temperature rises slowly.Within a period of time after reaching the PMMA glass transition temperature(105°C),the temperature rises rapidly.After rising to a certain temperature,the temperature rise becomes slow.With the increase of the length of the back cover,ceramic plate,front cover and horn,the longitudinal vibration excitation time required for the aggregate to reach 105 ? decreases first and then increases.As the amplification ratio increases,the required longitudinal vibration excitation time gradually decreases.The magnification ratio has the greatest effect on the viscoelastic heat generation process of the polymer,followed by the thickness of the back cover,the thickness of the front cover and the length of the tool head.The smallest effect is the thickness of the ceramic sheet and the length of the horn.The analytical value and the simulated value of the output frequency and heat generation rate of the ultrasonic transducer are compared,and the error is within the allowable range.Finally,the longitudinal-torsional transducer was designed,and the structural model of the longitudinal-torsional transducer was established using ANSYS APDL language.The natural frequency of the transducer and the maximum displacement ofthe tool head particle under different structural parameters are analyzed through modal and transient analysis.It was found that the rear cover,front cover and amplification ratio have a greater impact on the transducer output excitation.Through simulation analysis,the heat generation law of viscoelastic polymer under the effects of longitudinal vibration excitation,torsional vibration excitation and longitudinal torsional excitation under different thicknesses of rear cover plate,front cover plate thickness and magnification ratio are analyzed.The results show that the heat generation rate of the polymer under the longitudinal-torsional hybrid excitation mode is greater than the heat generation rate under the single longitudinal vibration or torsional vibration excitation;the viscoelastic heat generation rate of the polymer gradually decreases with the increase of the thickness of the cover plate and the front cover plate,and gradually increases with the increase of the magnification ratio.