Theoretical And Experimentical Study Of Advanced Technology Of Deformation Control In Polymer In-mold Assembly Of Micro Machinery

With developments of the application of micro-electromechanical systems in miniature optical,mechanical manufacturing and other areas,the need of micro-mechanical is becoming ever more intense,polymer have major advantages such as light weight?corrosion resistance and good insulation,etc.,which is one of the main materials of micro mechanical systems,nowadays the processing of micro mechanical system using polymer materials has become a hot research area.Common technical problem confronting the molding of micro mechanical system is the manufacturing and processing of micro parts as well as the micro-assembly technology.In-mold assembly of polymer micro mechanical parts is a new technology featuring the integration of molding process and assembling process,which can deal with the technical bottlenecks in the micro-assembly of micro-mechanical parts,however,deformation can be caused by thermal-fluid-solid coupling effect as high temperature viscoelastic polymer melts flow past the preformed micro part in in-mold assembly molding process,which make it difficult to maintain the target size and shape of the molding parts,thus precise control and prediction of thermal-fluid-solid coupling deformation are needed to solve these key issues before massive industry application is possible.Based on viscoelastic fluid CFD theory and ANSYS workbench,the virtual simulation platform was established in which the thermal-fluid-solid coupling deformation process of preformed micro part under thermal-fluid-solid coupling environment was modeled,the influencing rule and influencing mechanism of die wall slipping condition on preformed micro shaft thermal-fluid-solid coupling effect and deformation under the high temperature viscoelastic melt flow environment was studied by the virtual simulation platform,key regulatory parameters of thermal-fluid-solid coupling deformation in die wall slipping in-mold micro assembly molding process was clarified;Die wall slipping in-mold micro assembly precision processing technology of superhydrophobic self-lubricating function graphite film was developed,which provides technical support for massive micro-mechanical precision molding technology.The main innovations and achievements as follows:(1)Based on viscoelastic fluid CFD theory and ANSYS workbench,the virtual simulation platform was established in which the thermal-fluid-solid coupling deformation process of preformed micro part under thermal-fluid-solid coupling environment was modeled,(2)The influencing rule and influencing mechanism of variable combination mould wall slipping condition on preformed micro shaft thermal-fluid-solid coupling effect and deformation under the high temperature viscoelastic melt flow environment was studied by the virtual simulation platform,the research result show that preformed micro shaft thermal-fluid-solid coupling deformation induced by the secondary filling melt flow will decrease with decreasing of die wall slipping coefficient(scilicet increasing with die wall slipping degree).When the wall transforms from the adhesive no slipping state into full slipping state,the maximum preformed micro shaft thermal-fluid-solid coupling deformation induced by the secondary filling melt flow can be reduced 61%,which shows viscoelastic melt slipping in die wall can effectively control the thermal-fluid-solid coupling deformation.(3)The rheology Mechanism in which preformed micro shaft thermal-fluid-solid coupling deformation induced by the secondary filling melt flow will decrease with decreasing of die wall slipping coefficient is that simulation results show that the thermal-fluid-solid coupling pressure,viscoelastic supporting normal stress and viscous friction drag shear stress induced by the thermal-fluid-solid coupling effect of secondary viscoelastic melt filling flow and perform micro shaft assembly interface shall reduce with decreasing of die wall slipping coefficient.Meanwhile,the thermal-fluid-solid coupling deformation of the preformed micro shaft is positively proportional to the thermal-fluid-solid coupling pressure and viscous friction drag shear stress,and negatively proportional to the thermal-fluid-solid coupling viscoelastic supporting normal stress and preformed micro shaft stiffness,eventually,decreasing of wall slip coefficient will result in decreasing of in mold micro-assembly molding thermal-fluid-solid coupling interface pressure,viscoelastic supporting normal stress,viscous friction drag shear stress and preformed micro shaft temperature,which make shaft elastic modulus and stiffness increase,This will inevitably lead to thermal-fluid-solid coupling deformation decreases with mold wall slip coefficient decreases.(4)The rheology Mechanism in which the thermal-fluid-solid coupling pressure,viscoelastic supporting normal stress and viscous friction drag shear stress induced by the thermal-fluid-solid coupling effect between secondary viscoelastic melt filling flow and performed micro shaft assembly interface shall reduce with decreasing of die wall slipping coefficient is that when the wall transforms from the adhesive no slipping state into full slipping state,viscoelastic melt flow will transform from shear flow with Inhomogeneous velocity distribution to plug flow with homogeneous velocity distribution,die wall full sliding make plug flow tends to homogeneous velocity distribution,which causes shear deformation rate tends to decrease,due to shear deformation rate is the velocity gradient.The rheological theory shows viscoelastic supporting normal stress and viscous friction drag shear stress is positively proportional to shear deformation rate,which make viscoelastic supporting normal stress and viscous friction drag shear stress reduce with decreasing of die wall slipping coefficient,at the same time,make flow resistance bypassing micro shaft reduce with decreasing of die wall slipping coefficient,Resulting in thermal fluid-structure coupling effect between melt flow and micro assembly interface is weakened,therefore the thermal-fluid-solid coupling pressure must reduce.(5)Based on above numerical simulation research findings,variable combination mould wall slipping in-mold micro assembly precision processing innovation technology was firstly proposed,which the superhydrophobic self-lubricating function graphite film was formed by special technology on variable combination mould wall,experimental research results have shown that the superhydrophobic self-lubricating function graphite film make viscoelastic melt form full slipping condition on variable combination mould wall.comparative experimental research on the thermal-fluid-solid coupling deformation between die wall full slipping in-mold micro assembly molding and no slipping in-mold micro assembly molding show die wall slipping in-mold micro assembly precision processing technology of superhydrophobic self-lubricating function graphite film can effectively control the thermal-fluid-solid coupling deformation of preformed micro shaft in the secondary molding process,which can implement polymer micro parts precision molding and micromachines precision assembly,die wall slipping in-mold micro assembly precision processing innovative technology of superhydrophobic self-lubricating function graphite film can make the thermal-fluid-solid coupling deformation reduced 40-60%...