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微流控芯片注射成型脱模系统研究
【作者】 翟瞻宇；
【导师】 蒋炳炎；
【作者基本信息】 中南大学 ， 机械制造及其自动化， 2010， 硕士
【摘要】 注射成型是生产聚合物微流控芯片的主要技术之一。脱模作为注射成型的一个重要阶段,在很大程度上决定着微流控芯片的最终成型质量。脱模系统设计不合理、工艺参数选择不当都有可能使芯片出现拉断、变形甚至毁坏等缺陷。本文以翘曲量和脱模应力作为衡量微流控芯片脱模质量的指标,对其脱模过程进行系统深入分析,设计合理的微流控芯片脱模系统以提高脱模质量,主要研究工作如下：首先为提高微流控芯片脱模质量,对其脱模过程进行深入的分析,仿真研究了微流控芯片的热收缩应力及脱模应力的分布规律,并针对微流控芯片脱模过程出现的受力不均的现象设计了三种顶杆脱模方案,仿真研究了三种脱模方案下微流控芯片脱模应力的变化规律。研究表明随着顶杆数目的增多,微流控芯片的脱模应力逐渐降低,但过多的使用顶杆可能会与模具的冷却系统发生干涉,根据以上研究成果,将透气钢作为脱模介质,研制微流控芯片的自动无损脱模系统,为验证透气钢作为气动脱模介质的可行性提供一个实验平台。其次,在仿真研究的基础上实验研究脱模温度对微流控芯片翘曲量的影响规律,随着模具温度的增加,微流控芯片的脱模应力逐渐降低,但翘曲量逐渐增加,在模具温度为90℃时会出现芯片拉断现象。研究结果建议选取微流控芯片的最佳的脱模温度范围为70-80℃。最后实验评价分析了微流控芯片在顶杆脱模系统和基于透气钢的气动脱模系统下的脱模质量优劣性。采用相同的工艺条件,对比两种脱模方式下成型盖片的翘曲量,实验表明基于透气钢的气动脱模系统可以有效的降低盖片的翘曲量,和顶杆脱模系统下的盖片比较,其降幅可最大达到38%。
【Abstract】 Injection molding is one of the most important methods to produce microfluidic chip. As an important stage in injection molding, demolding determines the final quality of formed components to a great extent. Microfluidic chip may be fractured, deformed and even destroyed in the demolding process, if demolding system is designed improperly or unsuitable process parameters are chosen. The main work carried out in this paper, as listed below, aims to devise a better micro-fluidic chip demolding system after an in-depth and systematic analysis of the demolding process by taking the chip warpage and demolding stress as the measuring indexes of demolding quality.Firstly, in order to improve the demolding quality of injection molded parts, an in-depth analysis of micro-fluidic chip demolding process was done and thermal shrinkage and demolding stress distributions were obtained through numerical simulation. Three different demolding setups using ejector pins were designed to improve the uniformity of demolding force distribution. Variation patten of demolding stress in the three setups was studied. Results revealed that an increase in the number of ejector pins leads to a decrease of demolding stress but also causes worse surface quality and even an interference between ejector pins and cooling channels. Based on the above results, an automatic non-destructive demolding system integrating porous steel as media was developed, which served as a platform to verify the feasibility of porous steel as a pneumatic demolding media.Secondly, based on numerical simulation results, injection molding experiments were performed to study the influence of demolding temperature on the chip warpage. It was observed that the increase of demolding temperature leads to a gradual decrease of demolding stress and a gradual increase of warpage, and that fracture occurred at a mold temperature of 90℃.According to the results, the optimum temperature is suggested to be within 70-80℃.Finally, ejector pin demolding and pneumatic demolding were compared in terms of chip demolding quality through experiments under the same processing conditions, in which the warpage of molded covers ejected by those two demolding mechanisms was compared. Results indicated that porous steel based pneumatic demolding is effective in reducing warpage of the cover by as much as 38% compared to ejector pin demolding.