微注射成型超声塑化中黏弹性生热效应

Viscoelastic heating effect in ultrasonic plasticization for micro injection molding

考虑超声衰减,基于广义Maxwell力学模型建立超声塑化聚合物黏弹性生热数学模型,通过数值计算研究聚甲基丙烯酸甲酯（PMMA）黏弹性生热规律和生热过程温度场分布,结合超声塑化PMMA形态演变实验分析黏弹性生热效应在聚合物由玻璃态到黏流态转变中的作用。研究结果表明：聚合物的温度是影响黏弹性生热的重要因素,PMMA的黏弹性生热效应在105~150℃之间作用明显;塑化样品由玻璃态到黏流态的转变过程温度场分布不均,靠近工具头端面和塑化腔壁处先于其他部分达到黏流温度;超声作用初始阶段摩擦生热作用明显,颗粒界面消失后黏弹性生热起主要作用。

A mathematical model of viscoelastic heating in ultrasonic plasticization was built based on generalized Maxwell mechanical model with the consideration of ultrasonic damping. The viscoelastic heating rule of polymethyl methacrylate （PMMA） and temperature field distribution were studied through numerical calculation. The potency of viscoelastic heating was analyzed based on the results of both morphology evolution experiment and numerical calculation when the polymer transforms from glass state to viscous state. The results show that temperature of polymer has a significant effect on viscoelastic heating; the viscoelastic heating is especially noticeable when the temperature is between 105 ℃ and 150 ℃ for PMMA; the temperature field is uneven during the transformation process. Polymer close to the inner wall of plasticizing chamber and sonotrode are the first to reach the viscous flow temperature; friction heating is very noticeable in the initial phase, while the viscoelastic heating plays a major role when the interface of polymer particles disappears.