薄壁塑件注射成型可控制造的研究

【作者】 尹湘林；

【导师】 蒋炳炎；

【作者基本信息】 中南大学 ， 机械制造及其自动化， 2008， 硕士

【摘要】 随着笔记本电脑和手提电话等3C产品逐渐朝着“轻、薄、短、小”方向发展,薄壁注射成型因具有减轻产品重量及减小产品外观尺寸、节约材料和降低成本等优点成为了研究的热点。由于对该技术的研究才刚刚开始,还没有形成基本的理论体系,而且国内对这方面的研究非常少,所以本研究的开展将为研究薄壁注射成型特性积累经验,并为深入开展薄壁零件注射成型的可控制造的研究打下良好的基础。本课题设计了一套一模四腔模具,可以同时成型4种不同壁厚（0.3mm、0.5mm、0.8mm、1.0mm）零件。采用Moldflow MPI5.0软件Flow/3D仿真分析和实验研究了不同参数（熔体温度、注射速度、零件壁厚）对薄壁件注射成型特性的影响。采用Moldflow MPI/Flow 3D仿真研究了熔体温度、注射速度、制品厚度等参数对薄壁成型时其剪切速率分布的影响,结果表明:在制品流动方向上,浇口附近的剪切速率远大于其它各处的剪切速率,并随着距离的增加而迅速降低。距浇口1.5mm附近处到制品的末端,剪切速率的变化并不明显,稳定在2000～4000S^-1之间。在厚度方向上,芯层的剪切速率最低,向次表层方向逐渐增大,并在距表面0.1mm处达到最大值,然后再往表层逐渐降低,直至表层,但表层的剪切速率仍然大于芯部。薄壁越薄,浇口处的剪切速率越大,但在末端则相差无几。采用同步热分析仪,实验研究了薄壁制品在流动方向和厚度方向上其结晶度的分布规律,结果表明:从制品流动方向上来看,浇口处的熔融热焓明显要高于其他位置上的;沿着熔体流动方向,熔融热焓随着与浇口距离的增大而减小,在5mm处至制品末端,其变化不明显;从制品厚度方向上来看,从中心到表面,结晶热焓随着距离的增加而增大,直到表面附近0.08mm达到最大,随后表面的结晶热焓又降低,但是仍然比中心部位的大很多。根据薄壁塑件使用性能对结晶度高低的不同要求,可以通过调整薄壁塑件注射成型时的熔体温度和注射速率参数,以控制成型后薄壁塑件的结晶度,从而实现薄壁塑件的可控制造。更多还原

【Abstract】 With the 3C（computer, communication and consumer electronics） products such as notebook computer and mobile telephone etc. becoming lighter, thinner, shorter and smaller, Thin wall injection molding（TWIM） becomes one hotspot of research because of reducing products weights, minifying size, economizing materials and lowing costs etc. Because the research on TWIM is still at the primary stage, and the theory system has not formed completely, moreover, it is few in domestic, this paper can reinforce domestic research in this domain, and will built the good foundation for the future research.A mould was designed in this paper, which can simultaneously mold four parts of different thickness （0.3, 0.5, 0.8, 1.0 mm）. By utilizing the Moldflow MPI5.0 software Flow/3D module simulation analysis and injection molding experiment, we studied the effect of different process parameters （melt temperature, injection rate and the thickness of parts） to thin-wall injection molding characteristics.The effects of the different parameters （melt temperature, injection rate and the thickness of parts） to the distribution of shear rate in thin-wall injection molding were researched by MPI/Flow 3D software. The results show the shear rate close to the gate is much higher than at other positions, and decreases with the distance to the gate; The change of the shear rate is not evidence from 1.5 mm to the end of part at flow direction, and the shear rate is 2000～4000s^-1; the shear rate at the core layer is lowest, increases from the core layer to the sub-skin layer, and come to a maximum, and then decreases to the skin layer. However the shear rate at skin layer is higher than at core layer. The thinner the thickness of the parts, the greater the shear rate close to the gate, but the difference is not in evidence at the end.By utilizing simultane thermoanalyse （STA）, the distribution rule of crystallinity along the flow direction and the thickness direction of thin-wall parts were researched. The results show the crystallinity close to the gate is higher than at other positions; the crystallinity decreases rapidly near the gate, and then gets to a nearly unconverted condition farther than 5 mm or so from the gate; The crystallinity close to the skin layer is higher than that at the core layer. The crystallinity increases from the skin to sub-skin layer and then decreases gradually to its minimum at the core layer; The melt temperature influences the crystallinity in thin-wall injection molding, which have little effect on the crystallinity at lower value, while higher melt temperature have more effect.According to the different crystallinity requirement of the performance, thin wall part’s controllable fabrication can be realized by adjusting the melt temperature and injection velocity parameters so as to control the crystallinity of the forming part.更多还原