Study For The Effect Of Ultrasonic On Viscous Dissipation And Convective Heat Transfer Of Micro Melt

The rapid development of Micro-electroechanical Systems technology and its products need the higher quality of micro injection molding parts. However, for its total or partial structure size is tiny when the polymer micro part is forming, resulting in the micro scale effects such as the viscous dissipation, wall slippage, convective heat transfer and surface tension become enhanced, especially the effect of viscous dissipation and convective heat transfer on melt flow properties, making the changes in viscosity and flow field velocity of flow when melt filling, thus influence the filling quality of micro-mold cavity.Based on the melt flow properties of micro-injection molding process and deep analysis of the effect of melt flowing micro scale factors. Theoretical analysis, numerical simulation and forming test of combining methods are proposed to study viscous dissipation and convective heat transfer behaviors of flowing melts and the effect of theirs coupling on melts flow. Firstly, based on the theory of polymer rheology and features of melt flow through micro scale channels, viscous dissipation and convective heat transfer behavior of melt flow in micro channels and its impact on the melt flow properties are deeply analyzed with and without applying ultrasound field. Considering the ultrasound field effect, mathematical model of viscous dissipation is established. Meanwhile, different polymer melts flow through cross-sectional dimensions of 300×300μm、length 12mm of micro channel is simulated by POLYFLOW software under different process parameters. The results show that viscous dissipation is stronger than convective heat transfer.Ultrasonic vibration-assisted micro injection mold is applied. with PP、HDPE、POM and ABS as its targets, micro channel temperature difference caused by viscous dissipation and convective heat transfer is test measured by different melt temperatures、mold temperatures、 injection pressures and injection speeds whether applying ultrasonic field or not. The results show that temperature difference of four materials increases with the increasing of injection pressure and injection speed, while decreases with the increasing of melt temperature and mold temperature no matter whether applying ultrasonic field or not. Meanwhile, their values with ultrasonic is higher than that of without applying ultrasonic field. At a certain micro-channel cross-sectional dimension and process parameter and ultrasonic power, the micro channel out and inlet temperature difference of polymer materials having different molecular structures and physical properties is significantly different. But out and inlet temperature difference of the micro channel can be further increased by increasing ultrasonic power. This indicates that the viscous dissipation effect of melt flow through micro channel can be significantly increased with ultrasound field, but the change is not significant for convective heat transfer. the variation of out and inlet melt temperature difference obtained by experimental results、theoretical models and numerical simulation results are exactly the same, but test values are less than the values of theoretical calculations and numerical simulation, which is due to the impact of microscopic channel wall slip and surface tension factors has not be considered in theoretical calculations and numerical simulation, while these factors are exist in test measurements.