Study On Mechanism Of Two-Dimensional Ultrasonic Vibration Assisted Micro-Injection Molding

Ultrasonic vibration assisted micro-injection molding technology plays an important role in the improvement of polymer melt filling capacity,the reduction of polymer materials deformations,and the enhancement of polymer materials properties.However,the longitudinal ultrasonic vibration has a limited effect on the improvement of melt flow performance in the complex shape cavity,and it promotes the polymer molecular orientation and increases the anisotropy of molding parts performance,which affects the material properties of molding parts.In order to improve the filling capacity of polymer melt in the complex shape cavity,the mechanisms of the flow evolution,rheological properties,wall slip,and molecular chain disorientation of polymer melt under two-dimensional ultrasonic vibration are investigated.By analyzing the formation mechanism of polymer melt unstable flow under two-dimensional ultrasonic vibration,the rheological model,wall slip model,and crystallization kinetics model of polymer melt under two-dimensional ultrasonic vibration are established.The distribution of melt flow field and the disorientation behavior of molecular chain under two-dimensional ultrasonic vibration are analyzed.The influence mechanisms of two-dimensional ultrasonic vibration on the rheological behavior and aggregation behavior of polymer melt in the complex shape cavity are clarified.Detailed contents of this work are summarized as follows:(1)Based on the flow stability theory,the evolution mechanism of polymer melt velocity perturbation in the cavity under two-dimensional ultrasonic vibration is analyzed from two aspects of absolute instability and convective instability.The formulas of melt velocity perturbation under two-dimensional ultrasonic vibration are established,and the velocity field of polymer melt in the cavity under two-dimensional ultrasonic vibration is numerically analyzed.The evolution mechanism of polymer melt unstable flow and its influence on the filling ability of polymer melt under twodimensional ultrasonic vibration are clarified.(2)The rheological model of polymer melt in the unstable flow field under twodimensional ultrasonic vibration is established.The melt flow fields in the cavity under the three conditions which are no ultrasonic vibration,one-dimensional ultrasonic vibration,and two-dimensional ultrasonic vibration,are compared and analyzed.The influences of unstable flow state on the distributions of melt velocity,shear rate,and viscosity are clarified.The influence mechanism of two-dimensional ultrasonic vibration on the melt flow field in the cavity and the improvement mechanism of the melt filling uniformity are clarified.(3)Based on the formation mechanisms of the adhesion-detachment wall slip and entanglement-disentanglement wall slip of polymer melt,a wall slip model of polymer melt in the unstable flow under two-dimensional ultrasonic vibration is established.The melt flow field in the micro cavity under two-dimensional ultrasonic vibration is analyzed,and the change of melt shear stress in the unstable flow state under twodimensional ultrasonic vibration is clarified.The influence law of two-dimensional ultrasonic vibration on the flow performance of polymer melt is obtained.(4)The influence mechanism of two-dimensional ultrasonic vibration on the dynamic coupling of polymer shear force is analyzed,and the crystallization kinetics model of polymer melt under two-dimensional ultrasonic vibration is established.The distribution of polymer shear stress field and the change of polymer crystallinity under two-dimensional ultrasonic vibration are analyzed by numerical simulation.The mechanism of polymer disorientation behavior induced by two-dimensional ultrasonic vibration and the improvement mechanism of polymer material properties are revealed.