Research On Synergistic Damage Mechanism Of Thermal Fluid Structure Coupling For Micro-in Mold Assembly Molding

Polymer in-mold micro-assembly molding technology is an innovative processing technology for manufacturing micro-polymer machinery.In the process of secondary molding filling,The main technical challenge of the two step forming filling flow is the thermal elastoplastic necking fusing of the preformed micro axis.How to accurately predict and accurately control the prevention of pre-molded micro-shaft hot-vibration elasto-plastic necking fuse is a common key scientific and technical problem of in-mold micro-assembly molding.This subject takes the micro-machine motion sub-mode micro-assembly molding as the research object,and develops a simulation platform for accurately predicting the thermal viscoelastic plastic necking fusion process of preformed micro shafts,and simulates and studies the molding process parameters,structure morphology and material properties.The influence laws of the thermal viscoelastic and plastic necking fusion of pre-molded microshafts are revealed,and the mechanism is revealed.It provides technical and theoretical support for preventing and controlling the thermal viscoelastic and plastic necking fracture of pre-molded micro shafts.The main innovations and conclusions of the study are as follows:Based on the thermo-elastic elasto-plastic constitutive relation and the thermo-fluid-solid coupling theory of polymer,the process of describing the influence of the near-surface phase change evolution of the preform is described.The theoretical model based on the secondary development builds a simulation platform based on ANSYS WORKBENCH for in-mold micro-assembly molding induced preformed micro shaft thermal viscoelastic plastic necking fusion process.The key control parameters of the thermal-viscoelastic elastoplastic necking fuse are the thermal fluid-structure coupling temperature of the preformed microshaft,the hot-viscoelastic-plastic properties and the structural dimensions of the material.When the preform thermofluid coupling temperature exceeds the glass transition temperature of the PMMA material by +20K,the PMMA material’s thermo-elastic elasto-plastic true stress-strain curve has the characteristic of strain softening after transient initial stress drop.Under the effects of heat-fluid coupling temperature and axial tensile coupling,if the average cross-sectional Von Mises equivalent stress reaches the initial yield stress of the preformed microelement,the strain softening phenomenon will be induced,and once the induced strain softening,the thermoviscous elastic plasticity will be generated.Collapsing fuse damage.Studies have shown that the initial yield stress of the preformed microelements is the key parameter for controlling the thermoviscoelastic plastic neck fracture at the glass transition temperature +20K of the PMMA material,which is controlled by the secondary molding injection speed and the injection temperature.It has a positive correlation with the injection rate of the overmolding and a negative correlation with the injection molding temperature.The pre-molded miniature round shafts have a thermo-mechanical-coupled average temperature that spans the glass transition temperature of the material by +20 K.The material is in a highly elastic state without strain-softening characteristics,and the stress and strain are positively related,resulting in the preformed miniature round shaft The axial tensile force increases with the increase of displacement loading time.After reaching the maximum value,the phenomenon of necking fracture occurs instantaneously,and the strain softening phase is not experienced.The study shows that the maximum critical axial tensile force of the hot-vibratory elastoplastic necking fracture is the key parameter to control the thermoviscoelastic plastic neck fracture at the glass transition temperature +20K above the material,and it is controlled by the secondary molding injection speed.And the injection temperature was positively correlated with the overmolding injection speed,but negatively correlated with the injection molding temperature.Increasing the secondary melt injection speed or lowering the secondary molding melt injection temperature is beneficial to suppress the thermal viscoelastic and plastic necking fusion failure.