Theoretical analysis and numerical modeling of the evolution mechanism of polymer melt unstable flow in two‐dimensional ultrasonic‐assisted micro‐injection molding

Abstract

Micro polymer parts are usually fabricated by ultrasonic-assisted micro-injection molding which is an effective and low-cost method. This method solves some injection molding defects such as short shot by reducing the melt viscosity, and the clarification of its mechanism is a challenge. This article is aimed at studying the evolution mechanism of two-dimensional ultrasonic vibration on the polymer melt unstable flow. A two-dimensional ultrasonic vibration, whose displacements components in the x-and y-directions are large, is applied to the polymer melt. The unstable flow is a flow field with perturbations. The formulas of perturbation stream function and velocity perturbations are established based on the theories of absolute instability and convective instability. The established formulas are verified by numerical analysis. The results show that the flow of