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The Rheological Mechanism And Experimental Study Of High-aspect-ratio Parts Based On Ultrasonic-assisted Vibration Micro-injection

Posted on:2021-03-31Degree:MasterType:Thesis
Country:ChinaCandidate:J J XiongFull Text:PDF
GTID:2481306545959429Subject:Mechanical engineering
Abstract/Summary:PDF Full Text Request
Polymer is widely used in micro electro mechanical system because of its unique physical and chemical properties as microelectronic components and optical components.However,in the process of injection molding of high aspect ratio microstructure,because of its small structure,large aspect ratio and high precision requirements,there are various molding defects under the micro scale,so improving the molding performance of microstructure has become a key problem in the field of microstructure molding.Ultrasonic assisted micro injection molding is a kind of molding technology which can add ultrasonic to the mold or experimental materials of injection equipment.The addition of ultrasonic can improve the rheological properties of polymer melt and reduce the molding defects of microstructure.Based on the rheological mechanism of polymer melt and the design principle of injection mold,an experimental platform of ultrasonic micro injection molding is designed and manufactured in this paper.The high aspect ratio(3:1,5:1,10:1)micro structure inserts are designed and manufactured,and placed in the fixed mold core.At the same time,the ultrasonic wave acts on the fixed mold core through the horn,so as to realize the auxiliary molding of the polymer by the ultrasonic wave.The rheological mechanism of polymer was analyzed and the micro viscosity model(MU)was established.Based on the traditional power-law model of polymer melt flow,the influence of ultrasonic energy on non-Newtonian index n and consistency coefficient K is analyzed,and the viscosity model of polymer melt flow state under the action of ultrasonic is established.At the same time,the ultrasonic viscosity model is modified according to the influence of micro scale factors(molecular chain segment and characteristic size)on the rheological properties of polymer melt.The applicability and accuracy of the established ultrasonic micro viscosity model(MU)were verified.The ultrasonic micro viscosity model of polypropylene(PP)material was established,which was substituted into the simulation of micro injection molding.The simulation results were compared with the experimental results of ultrasonic micro injection molding.Then,the ultrasonic micro viscosity model of PS material is established,which is substituted into the rheological simulation,and the pressure difference results of simulation and rheological test are compared.The results show that the ultrasonic micro viscosity model has good accuracy.Finally,the ultrasonic micro injection experiment of PP material was carried out to test the filling performance of the high aspect ratio plastic parts,and to explore the influence of ultrasonic on the crystallization performance of the material.Different injection pressure,injection speed and ultrasonic amplitude were set to carry out the micro injection filling experiment of single factor high aspect ratio micro groove.The results show that with the increase of the ratio of depth to width of microstructure,the effect of ultrasonic assisted vibration is more obvious.In the scope of this study,the filling rate of micro injection molding can be increased by 13.4%;with the increase of ultrasonic energy,the polymer melt flow performance and the filling rate of micro structure increase.The differential scanning calorimetry(DSC)and X-ray diffraction(XRD)experiments were carried out on the ultrasonic micro injection molded parts and the micro injection molded parts.The results show that the crystallinity of the polymer decreases and the crystalline grains are refined after the ultrasonic treatment,which indicates that the ultrasonic treatment can activate the movement of the molecular segments of the polymer and increase the flow ability of the polymer melt.
Keywords/Search Tags:Ultrasonic, Micro Injection, High Aspect Ratio, Viscosity Model, Filling rate
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