Study On The Deformation Law Of Polymer In External Gas Assisted Injection Molding

External gas assisted injection molding(EGAIM)is a kind of process with great potential for production,which compensates the shrinkage of polymer through the deformation process under the action of gas,so as to improve the sink marks of polymer.However,the EGAIM is not widely used in practical production at present,because the deformation laws of different kinds of polymers under the action of gas are not complete and clear,so it is urgent to carry out further in-depth systematic research.Aiming at the problem that the deformation laws of different kinds of polymers are not complete and clear,this paper systematically studies the mechanical properties under the deformation laws of polymer,and the deformation mechanism of polymers,which provides theoretical basis for guiding industrial application.The main research of this paper are shown as following:(1)The mechanical properties of polymer under the deformation law were studied,which laid the theoretical foundation for the study of the deformation law of polymer.The mechanical model of amorphous polymer and crystalline polymer were modified,which described quantitatively the mechanical properties of amorphous polymer and crystalline polymer with different crystallinity under different temperatures.Based on the mechanical property of amorphous polymer at different temperatures,the mechanical models above and below the glass transition temperature were established,which also verified by tensile experiments at the corresponding temperature.According to the mechanical property of crystalline polymer at the same temperature,the mechanical models of elastic stage,yield point and strain softening stage were established and verified respectively(2)The influence of gas on the temperature of polymer in the deformation law of polymer was analyzed,which determined the temperature environment of polymer deformation.Based on the modified one-dimensional heat conduction model,the influence of gas on the temperature of amorphous polymer was studied theoretically,simulatedly and experimentally in EGAIM.The enthalpy of crystalline polymer was introduced into the modified one-dimensional heat conduction model,which made the latent heat of crystallization considered in the study of deformation temperature environment of crystalline polymer,and the numerical calculation method was used for determining the effect of gas on the temperature of crystalline polymer.The aforementioned study provides a theoretical basis for investigating whether the effect of gas on polymer temperature is considered in the study of deformation law.(3)The deformation mechanism of amorphous polymer was clarified,the deformation conditions of amorphous polymer were determined and the reason for improving the sink marks of amorphous polymer was also explored.Based on the study of deformation temperature environment and mechanical model of amorphous polymer,the stress field and sink marks histories of amorphous polymer in EGAIM were simulated,and then the deformation mechanism of amorphous polymer was explored based on the simulation results.A model for determining the deformation condition of amorphous polymer was established based on the Mises yield criterion.The deformation condition of amorphous polymer was determined by the comparison between the yield stress and simulated stress of amorphous polymer,which also verified by the measuring the sink marks of amorphous polymer with different gas action time.Based on the analysis of the results of stress and sink marks histories of amorphous polymer under different gas parameters,the reasons for improving the sink marks of amorphous polymer were determined,and the effects of gas pressure and gas delay time on the sink marks of polymer were also studied.(4)The deformation mechanism of crystalline polymer was clarified,the deformation conditions of crystalline polymer were determined and the reason for improving the sink marks of crystalline polymer was also explored.The crystallinity of crystalline polymer was introduced into the judgment model of deformation condition of amorphous polymer and the simulation method in the forming process of amorphous polymer for studing the deformation mechanism of crystalline polymer,which also were verified,the effects of gas pressure and gas delay time on the sink marks of polymer were also studied.