Research On The Technology And Mechanism Of Graphite Coating Assisted Microinjection Molding

Graphite coating assisted polymer micro-injection molding technology is an innovative micro-injection molding process that effectively solves the bottleneck of injection molding of micro-structure characteristic products(short shot and high injection pressure).Recently,it has attracted many scholars' attention,and the relevant mechanism research is seriously lacking,which seriously restricts the industrialization promotion of graphite coating assisted micro-injection molding innovation process.In this paper,the mechanism theoretical model and the virtual simulation platform of the graphite coating assisted micro-injection molding process were established based on the characteristics of the graphite coating assisted micro-injection molding process,and the influence rules and mechanism of the parameters of the boundary conditions and process parameters and polymer melt flow parameters on the micro-injection molding process of the viscoelastic melt were studied in this paper.The key influencing parameters of graphite coating assisted polymer microinjection molding process were clarified,and the scientific theoretical foundation was established for the industrialization application of the graphite coating assisted polymer micro-injection molding innovation technology.The main innovation and research conclusions are as follows:(1)The theoretical model of the sliding flow boundary between the filling melt and die wall is the key scientific problem of the mechanism theory and the research on the molding mechanism of graphite coating assisted micro-injection molding process.Based on the characteristics of the graphite coating assisted micro-injection molding process and the Asymptotic law sliding model,the theoretical model of the pure viscosity and viscoelastic mechanism of the graphite coating assisted micro-injection molding process is established in this paper,and the virtual simulation platform of the molding process that is suitable for the theoretical model of pure viscosity and viscoelastic mechanism is established.(2)Graphite coating assisted micro injection molding can greatly reduce the micro injection molding pressure,its rheological mechanism is graphite coating which has self-lubricating function can make effective slip formed between filling flow melt and mold wall,which make the shear filling flow with the non-slip uneven parabola distribution velocity of injection molding is transformed the plunger flow with the full slip uniformly distributed velocity evenly.and the piston filling flow of graphite coating assisted polymer micro-injection molding will make shear deformation rate decreases,and the mold wall viscous friction shear stress and shear deformation rate was positively correlation,which results in viscous friction shear stress(flow resistance)decreases,so as to make the graphite coating assisted micro injection molding can sharply reduce the micro injection molding pressure,and the injection molding pressure and the sliding coefficient of graphite self-lubricating function coating was a positive correlation;(3)A new study finds that the rheological mechanism for influence of viscoelastic melt relaxation time on molding injection pressure is that when the melt filling flow observation time is less than the relaxation time of the melt,in other words,response time is less than the relaxation time,t? ?,viscoelastic melt tend to elastic characteristic,and the injection molding pressure was positively correlated with the viscous flow resistance,thus relaxation time influences injection molding pressure weakly.And when the melt filling flow observation time is greater than the relaxation time,that is to say response time is greater than the relaxation time,t ? ?,viscoelastic melt tend to be viscous characteristic,and the injection molding pressure was positively correlated with the viscous flow resistance,thus influence of relaxation time on the injection molding pressure is obvious.Moreover,the larger the difference of the filling flow time over the relaxation time,the more the viscoelastic melt tends to show the tendency of viscous characteristic,the greater the influence degree.Means when the melt filling flow observation time t is given,The smaller the relaxation time of the viscoelastic melt,the stronger viscoelastic melt tend to be viscous characteristics,and the higher injection molding pressure.The influence of the viscoelastic melt relaxation time on the injection pressure is controlled by the relative magnitude of the filling flow observation time and the relaxation time of the melt.