【作者】 杨灿；

【导师】 黄汉雄； Jose Castro； Allen Yi；

【作者基本信息】 华南理工大学 ， 机械设计及理论， 2011， 博士

【摘要】 微注塑技术可用于生产微小或含微细结构的塑料制品,具有制造成本低、生产周期短和易实现批量化生产等优点。目前,微注塑制品已被广泛用于微流控装置、生物医疗、光电通讯和微机电系统等领域,具有非常广阔的应用前景。然而,当前关于微注塑的研究主要集中于工艺参数和几何参数对制品复制性能的影响。鉴于此,本文循序渐进地从聚合物材料的流变特性、不同纵横比微结构的复制性能、微结构的表面形态以及微注塑制品的结晶形态等方面,对微注塑过程的若干问题进行研究。本文首先设计了小纵横比微结构,通过改变成型材料、工艺参数以及几何参数,研究了微结构的复制性能。研究表明:不同材料微结构的高度复制率有明显的差别,PMMA成型微结构的高度复制率在4.4~99.5%范围内,而PP成型微结构的高度复制率均大于92.3%;对于PMMA,熔体温度、模具温度和注射速度对微结构高度复制率有较大的影响,而保压压力和保压时间的影响很小;对于PP,熔体温度和注射速度对微结构宽度复制率的影响最为明显,而模具温度、保压压力和保压时间的影响较小;几何参数中,微结构的纵横比和位置对复制性能均有不同程度的影响。在上述基础上,通过改变微结构的布置形式、截面形状、表面粗糙度以及工艺参数,进一步研究了大纵横比微结构的复制性能。研究发现:在相同的工艺参数下,垂直布置微结构的填充长度要大于平行布置微结构的填充长度;按照三角形、矩形和半圆形截面的顺序,微结构的填充长度逐渐增大,并且这种现象在平行布置形式中更为明显;当微型腔表面粗糙度增大时,微结构的填充长度相应减小;此外,由于熔体填充阶段残余气体的阻力不同,两种布置形式中工艺参数对微结构填充长度的影响有所不同。为了研究微结构的表面形态,对各种条件下成型的微结构表面进行了扫描电子显微镜(SEM)观察,发现如下现象:平行布置微结构的表面非常清晰与光滑,没有出现任何明显的表面缺陷;垂直布置微结构的表面出现了不同程度的表面缺陷,并且表面缺陷程度与工艺参数、熔体在主型腔内的流动方向等因素有关,提高熔体温度与(或)注射速度能改善甚至完全消除此类表面缺陷;短射实验表明:成型微结构表面缺陷的产生主要与微流道入口位置的熔体温度和熔体压力以及微流道内熔体的冷却速率有关,而与微结构本身的截面形状关系不大。借助SEM和差示扫描量热仪,研究了不同尺寸注塑制品内部的结晶形态。对于普通注塑制品,整个厚度上晶片都呈无规则排列;当制品厚度逐渐减小时,从制品的表层开始逐渐出现取向晶片结构,并且取向晶片的密度随制品厚度的减小而增大;对于厚度仅为175μm的微注塑制品,在整个厚度上均出现了“类串晶”微晶结构。最后,本文结合实际研究了微流体混合器和精密光学透镜的成型过程。研究表明,掌握微结构的复制性能及形态的影响因素和影响规律对微注塑实际生产具有很大的指导意义。更多还原

【Abstract】 The micro-injection molding technology is capable of producing plastic micro-parts or parts with micro-features. The advantages of this technology include low cost, short cycle time and easiness for volume production and so forth. Nowadays, the micro-injection molded parts have been widely used in many applications such as the micro-fluidic devices, biomedicine, photoelectric communication, and micro-mechanical-electronic-systems and so on, with a huge application potential in the future. However, the current study on the micro-injection molding is mainly focused on the effects of the processing condition and geometric factors on the replication capability of the molded parts. In this regard, in order to resolve certain issues encountered in micro-injection molding process, the present work aims to gradually investigate the rheological properties of the polymer, replication capability of the micro-features with various aspect ratios, surface morphology of the molded micro-features, and the crystal morphology of the micro-injection molded parts.First of all, the micro-features with small aspect ratio were designed in order to investigate the replication capability with different molding materials, processing conditions, and geometric factors. The results showed that various materials had different effects on the replicated height of the micro-features. The replicated height of the molded PMMA micro-features fell into a large range of 4.4~99.5%, while that for molded PP micro-features was higher than 92.3%. Moreover, for PMMA micro-features, the melt temperature, mold temperature and injection velocity were found to be important factors influencing the replication height, while the packing pressure and packing time had no obvious effect; for PP micro-features, the melt temperature and injection veloctiy were the most important factors, followed by the mold temperature, packing pressure and packing time. As for the geometric factors, the aspect ratio and the distance from the micro-feature to the injection gate had different effect on the replication capability of the molded micro-features.Based on the aforementioned study, effects of the layout, cross sectional shape, surface roughness, and the processing condition on replication capability of the micro-features with large aspect ratio were futher investigated. It was found that with the same processing conditon, the micro-feature molded with transverse layout had larger filled length than that with parallel layout. The filled length of the micro-features increased with the cross section in the order of triangle, rectangle, and semicircle, and this is especially the case in the parallel layout. In addition, the filled length decreased with increasing surface roughness of the micro-channels. Furthermore, the effect of the processing condition on the filled length of the micro-features in parallel and transverse layouts was different due to the various resistance of the trapped air inside micro-channels during the injection process.In additon, the surface morphology of the micro-features molded under different conditions was investigated using scanning electron microscope (SEM). It was found that the surfaces of micro-features molded in parallel layout were very smooth and clear. As comparison, there were defects on the surface of the micro-features molded in transverse layout, and the appearance of defects strongly depended on the processing condition and flow direction in the main cavity. Increase in melt temperature and/or injection velocity could improve or even eliminate the surface defects. The short shot experiment indicated that the formation of the surface defect was mainly influenced by the melt temperature and melt pressure at the entrance, and the cooling rate of the melt inside the micro-channel, however, independent of the cross sectional shape of the micro-features.Using the SEM and differential scanning calorimetry, the crystal morphology of the injection molded parts with different dimensions was investigated. For conventional injection molded parts, there were only lamellae disorderly arranged throughout the entire thickness. With the dimension decreasing, the oriented lamellae started to appear from the skin layer of the parts, and the density of the lamellae increased. For the micro-injection molded part with a thickness of only 175μm, there were many shish-kebab-like structures in the tickness direction.At last, from a practical viewpoint, the micro-injection molding of the micro-mixer and precision optical lens was investigated. It was found that it is fairly important to master the influencing factors and the corresponding rule of the replication capability and morphology of the micro-features for practical production.更多还原