Investigation of 2D ultrasonic-assisted micro-injection molding

Abstract

A two-dimensional ultrasonic-assisted micro-injection molding (2DUμIM) method is proposed, and the feasibility and superiority of 2D ultrasonic vibration in improving the molding quality of the micro polymer part with complex structure are validated. The experiment results show that the increases in the filling areas along the z- and y-directions of the parts molded by the 2DUμIM method are more than double and triple those by the one-dimensional ultrasonic-assisted micro-injection molding (1DUμIM) method, respectively. Simultaneously, the surface roughness of the parts molded by the 2DUμIM method is reduced by 25.2% compared with that by the 1DUμIM method. Moreover, compared with the 1DUμIM results, the cavity temperature increases, the pressure loss decreases, and the pressure difference of the flow field is reduced by 62.2% in the 2DUμIM, showing that the 2D ultrasonic vibration notably weakens the flow resistance and enhances the melt fluidity and flow uniformity, which improves the qualities of mold-filling and surface replication. Furthermore, to clarify the action mechanism of 2D ultrasonic vibration on the flow behavior of the polymer melt, a rheological model of the melt in an unstable flow field caused by 2D ultrasonic vibration is established. The model indicates that the rheological properties of the melt are radically improved by the 2D ultrasonic vibration promoting the mechanical energy, degradation, and viscoelastic heating of the melt. The simulation results of the unstable flow field indicate that, benefiting from the energy transportation, dissipation, and diffusion effects of the unstable flow, the 2D ultrasonic vibration is more significant in increasing the melt shear rate, reducing the melt viscosity, and promoting the melt fluidity and flow uniformities than the 1D ultrasonic vibration, which enhances the filling performance of the melts in multiple dimensions and in corner regions of the micro cavity, and facilitates the melt flow over a longer distance.