微注射成型聚丙烯微结构件缺陷分析

通过微注射成型制得了聚丙烯微结构件，微结构部分是直径为130μm、高度为250μm的微型圆柱。分析了模具温度、注射压力、保压时间及模具抽真空对微零件填充性能的影响。研究发现，在不恰当的工艺参数下，微圆柱会出现以下缺陷：填充不足、表面粗糙、烧蚀、中空等。通过实验得到了合理的工艺参数，即在模具温度为90℃、注射压力为100MPa、保压时间为3S、模具抽真空的情况下，微结构部分可以得到完全填充，且没有以上缺陷。     

微注射成型工艺的实验研究

设计了微注射模具的变温系统,加工了通道宽度分别为500μm和100μm的哑铃形微型腔。在此基础上,基于Taguchi实验设计方法进行了成型工艺实验。结合微尺度下熔体充模流动理论及微尺度效应,研究了工艺参数及其交互作用对微结构塑件成型质量的影响规律。实验结果表明,随着微结构塑件特征尺寸的减小,注射压力和模具温度对填充率的影响明显增强;熔体温度对填充率的影响程度有所增加;注射行程对填充率的影响程度有所降低;保压压力和保压时间对填充率的影响相对不明显。     

超声外场对微圆柱阵列结构制件填充质量的影响

针对微小尺寸或局部带有微小结构的制件模塑成型时熔体充模流动困难而影响制件质量的问题,以典型的带有微圆柱阵列结构的薄板型制件为对象,提出将抽真空排气和超声振动技术集成应用到自行设计制造的微注塑模具中,并采用单因素成型实验方法,研究了高密度聚乙烯(HDPE)和聚丙烯(PP)两种聚合物材料在施加与不加超声外场以及不同工艺参数和超声功率变化条件下填充薄板型制件上微圆柱圆角曲率半径的变化规律.结果表明,不加超声外场时提高熔体和模具温度及增大注射速率可使两种材料填充的微圆柱圆角曲率半径逐渐减小,施加超声外场时填充的微圆柱圆角曲率半径可进一步减小,从而有效提高了制件的填充质量;同时发现,无论有无超声作用,HDPE材料填充的微圆柱圆角曲率半径均明显小于PP材料.     

微圆柱阵列注射成型数值模拟及正交优化

针对微圆柱阵列的注射成型过程进行数值模拟研究,比较了不同原料聚丙烯(PP)、聚甲醛(POM)、丙烯腈–丁二烯–苯乙烯塑料(ABS)的成型工艺,并利用正交试验就微注射成型过程中影响熔体填充效果的主要工艺参数如模具温度、熔体温度和注射时间进行了模拟。运用极差分析法和方差分析法对熔体填充率进行分析。结果表明,对于PP而言,填充时间对其填充率的影响占主导地位,而对于POM与ABS,模具温度的影响相对更大。模具温度、熔体温度越高,注射时间越短,塑件填充效果越好。综合考虑,三种聚合物材料对微圆柱阵列填充效果适应性为:PPABSPOM。     

高酸低铜酸性镀铜溶液中添加剂对微盲孔填充效果的影响

在电镀铜填充微盲孔的高酸、低铜酸性镀铜溶液中,以旋转圆盘电极为辅助,通过恒电流计时电位法对不同转速下,不同添加剂浓度的电镀铜溶液阴极电位及电位差的测定,研究了在高酸、低铜酸性镀铜溶液中通过电位差的大小来指导微盲孔填充的方法,发现该方法在对于高深径比的微盲孔填充时存在一定的局限性。通过改善电镀参数实现了对d为100μm,深度为100μm的微盲孔的完全填充。     

模具中胶料填充厚度对阻燃硅橡胶泡沫制备及性能的影响

采用模压硫化发泡工艺制备了阻燃硅橡胶泡沫材料,研究了模具中胶料填充厚度对材料性能的影响。结果表明,随着模具中胶料填充厚度的增加,阻燃硅橡胶泡沫材料的表观密度呈先降后升趋势,孔隙率呈先升后降趋势,且泡孔逐渐变小,氧指数逐渐提高。当模具中胶料填充厚度小于1.8 mm时,泡孔壁为实体胶。当模具中胶料填充厚度为1.8 mm时,发泡效果较好,表观密度降至0.193 g/cm3,孔隙率高达81.8%。而当模具中胶料填充厚度大于1.8 mm时,泡孔壁内出现大量微孔结构。当模具中胶料填充厚度为3.3 mm时,泡孔直径降至约50μm,氧指数高达25.9%。可通过调节模具中胶料填充厚度,实现对最终泡沫硅橡胶材料在泡孔结构及泡孔直径方面的有效控制,以满足不同的市场需求。     

单分散多孔聚合物微球的制备及其反相色谱应用

用分散聚合的方法制得单分散微米级聚苯乙烯微球(PS),以此聚苯乙烯微球作为种子,以邻苯二甲酸二丁酯为溶胀剂,苯乙烯为单体,二乙烯基苯为交联剂,甲苯为致孔剂,采用种子溶胀聚合的方法制得粒径分布较窄的多孔高交联的聚苯乙烯-二乙烯基苯微球(PS-DVB)。研究了交联剂与致孔剂的加入量对微球形貌、粒径及孔结构参数的影响。结果表明,所得多孔微球球形圆整,库尔特测得平均粒径为5.067~5.520μm,粒径分布窄,D90/D10为1.23~1.56,孔结构可控,并以此多孔微球作为反相色谱填料基质,理论塔板数每米可达6 000~15 000,可以用作高效液相色谱(HPLC)填料。     

羟基磷灰石微球的制备及表征与色谱性能

采用喷雾干燥法制备羟基磷灰石(hydroxyapatite,HA)微球。用扫描电镜、激光粒度分析仪及比表面积分析仪等表征HA的微观结构及性能。结果表明:HA微球具有理想的球形结构、比表面积为44.135m2/g,孔体积为0.2911cm3/g,且其粒度分布较窄。利用高压匀浆法填充HA色谱柱,并用高校液相色谱仪检测性能,结果表明色谱柱柱效较高。     

TiO2微球的水热法制备及其形成机理

本文以硫酸钛为原料,尿素作沉淀剂,采用水热合成法制备了锐钛矿型纳米TiO2微球.用XRD、TEM、SEM等测试手段对所制备粉体的物相组成、形貌等进行了分析.结果表明,所制备的球形粉体为锐钛型纳米TiO2,球形直径分布在1-3μm之间,而且进一步发现这些球形颗粒是由直径为10-20nm的纳米颗粒自组装而成的.最后,对微球...     

陶瓷微球的制备工艺及微球性能研究

以国产铝矾土为原料,采用离心喷雾造粒方法,制备10～100μm的陶瓷微球.探讨微球颗粒尺寸、球形度、与基体材料结合性能的控制技术.对陶瓷微球进行表面改性,喷雾造粒前在泥浆中添加氢氧化钠使钠离子在陶瓷微球表面富集,以增加微球与基体之间的润湿性.研究了陶瓷微球的最佳烧结工艺,采用二次烧成的方法来烧结微球.对陶瓷微球的微观结构和性能进行了表征.该微球可用作复合材料的加强材料.     

Experimental study on filling imbalance of plastic parts with microcylinders

To examine the microscale filling imbalance in the present work, an eight-cavity injecting mold with microcylindrical-hole arrays fabricated by micro-electrical discharge machining milling technology was developed. Polypropylene (PP) was used to carry out single factor filling flow experiments with vacuuming the mold cavities. The filling height difference of micro cylindrical hole at the same position between cavity I and cavity II, which was the index of filling imbalance and the effect of mold temperature and injection rate on the filling imbalance of microholes with diameters of 200 μm and 300 μm was investigated. The results revealed that the maximum height difference reached 101 μm with low process parameters, and the filling imbalance was obvious. With the increase in mold temperature and injection rate, the filling imbalance was weakened. In addition, the impact of the scale effect on filling imbalance was checked. The filling imbalance of micro holes in 200 μm was greater than that in 300 μm using identical process parameters. With the increase in mold temperature and injection rate, the filling height difference of the two kinds of micro holes decreased. POLYM. ENG. SCI., 60:22–31, 2020. © 2019 Society of Plastics Engineers     

微尺度下H形分布流道充模工艺参数对流动不平衡的影响分析

为探究微尺度下的工艺参数对聚合物熔体充填不平衡的影响,考虑模具温度、熔体温度、注射速率以及微流道尺寸,采用聚甲醛(POM),对H形对称分布的半圆形截面微流道系统进行了充模流动数值模拟实验,分析了浇口处对称点间的温差数据.结果表明,微注塑过程中流道系统内存在温度不对称,随着剪切速率的增加,对称点间的温度差也逐渐增加;而熔...     

基于SPH方法的微注射成型数值模拟

基于无网格方法和黏性本构方程,开展微注射成型数值模拟的研究。采用光滑粒子流体动力学的粒子近似法离散N-S 控制方程组,求解速度场、压力场、温度场等物理场的变化规律。以应用于生物医学领域带有细微针头的聚合物微针为例,进行充型过程的数值模拟,模拟结果与实验结果基本一致。     

自然平衡流道结构对多型腔模具非平衡充填的影响

在验证国内外已有的关于几何对称型腔非平衡充填研究结论的基础上,设计了可更换流道的实验模具,研究了流道尺寸及浇口形式的变化对非平衡充填的影响,并考察了整个充模过程中塑料熔体在型腔中的流动情况.结果表明,改变流道尺寸及浇口形式有利于改善非平衡充填程度,并指出整个充模过程的非平衡充填是一个动态演化过程.     

聚丙烯/超临界氮气微孔注塑充模过程工艺参数研究

以聚丙烯(PP)为原料,超临界氮气(N2)为发泡剂,通过自行设计的一种扁平螺旋线形流道模具探究了注塑制品充模长度与减重比、泡孔结构之间的关系,并设计正交试验研究了注气压差、注气时间、注射压力和注射速率对制品充模长度的影响.结果表明,在一定范围内,熔体背压越高,制品充模长度越长,且随着充模长度增加,制品的减重比呈先缓慢增...     

Experimental and theoretical study on filling imbalance in geometrically balanced injection molds

Experimental and theoretical studies were performed on filling imbalance in geometrically balanced injection molds. Balancing the melt flow between cavities was investigated using several different runner systems at various operating conditions. Experiments indicate that injection rate, mold, and melt temperatures substantially affect the filling imbalance. It is strongly dependent on runners layouts geometry, and it has never been eliminated completely. It is most difficult to remove for high injection rates and low melt temperatures. Standard element geometry and circled element geometry cause positive imbalance which means that inner cavities fills faster, and it is opposite for one/two overturn element geometries which induce negative imbalance. A special modeling procedure is required to simulate properly the imbalance. This includes inertia effects, geometrical modeling of the nozzle where the imbalance starts, 3D tetrahedron meshing with minimum 12 layers. Simulations were consistent with experiment, however, when the imbalance increased, the discrepancies between simulation and experiment also increased. It can be stated that filling imbalance problem is still unsolved. There are serious thermo‐rheological aspects to explain for better understanding this phenomenon. Trends in modeling of injection molding are presented and new concepts solving the problem are discussed including simulation/optimization approach and a novel concept of global modeling of injection molding process. POLYM. ENG. SCI., 59:233–245, 2019. © 2018 Society of Plastics Engineers     

Studies on structural foam processing II. Bubble dynamics in foam injection molding

An experimental study was carried out to gain a better understanding of the dynamic behavior of gas bubbles during the structural foam injection molding operation. For the study, a rectangular mold cavity with glass windows on both sides was constructed, which permitted us to record on a movie film the dynamic behavior of gas bubbles in the mold cavity as a molten polymer containing inert gas was injected into it. The mold was designed so that either isothermal or nonisothermal injection molding could be carried out. Materials used were polystyrene, high-density polyethylene, and polycarbonate. As chemical blowing agents, sodium bicarbonate (which generates carbon dioxide), a proprietary hydrazide and 5-phenyl tetrazole, both generating nitrogen, were used. Injection pressure, injection melt temperature, and mold temperature were varied to investigate the kinetics of bubble growth (and collapse) during the foam injection molding operation. It was found that the processing variables (e.g., the mold temperature, the injection pressure, the concentration of blowing agent) have a profound influence on the nucleation and growth rates of gas bubbles during mold filling. Some specific observations made from the present study are as follows: an increase in melt temperature, blowing agent concentration, and mold temperature brings about an increase in bubble growth but more non-uniform cell size and its distribution, whereas an increase in injection pressure (and hence injection speed) brings about a decrease in bubble growth but more uniform cell size and its distribution. Whereas almost all the theoretical studies published in the literature deal with the growth (or collapse) of a stationary single spherical gas bubble under isothermal conditions, in structural foam injection molding the shape of the bubble is not spherical because the fluid is in motion during mold filling. Moreover, a temperature gradient exists in the mold cavity and the cooling subsequent to mold filling influences bubble growth significantly. It is suggested that theoretical study be carried out on bubble growth in an imposed shear field under nonisothermal conditions.     

Experimental analysis and numerical modeling of flow channel effects in resin transfer molding

Composite manufacturing by Liquid Composite Molding (LCM) processes such as Resin Transfer Molding involve the impregnation of a net‐shape fiber reinforcing perform a mold cavity by a polymeric resin. The success of the process and part manufacture depends on the complete impregnation of the dry fiber preform. Race tracking refers to the common phenomenon occurring near corners, bends, airgaps and other geometrical complexities involving sharp curvatures within a mold cavity creating fiber free and highly porous regions. These regions provide paths of low flow resistance to the resin filling the mold, and may drastically affect flow front advancement, injection and mold pressures. While racetracking has traditionally been viewed as an unwanted effect, pre‐determined racetracking due to flow channels can be used to enhance the mold filling process. Advantages obtained through controlled use of racetracking include, reduction of injection and mold pressures required to fill a mold, for constant flow rate injection, or shorter mold filling times for constant pressure injection. Flow channels may also allow for the resin to be channeled to areas of the mold that need to be filled early in the process. Modeling and integration of the flow channel effects in the available LCM flow simulations based on Darcian flow equations require the determination of equivalent permeabilities to define the resistance to flow through well‐defined flow channels. These permeabilities can then be applied directly within existing LCM flow simulations. The present work experimentally investigates mold filling during resin transfer molding in the presence of flow channels within a simple mold configuration. Experimental flow frot and pressure data measurements are employed to experimentally validate and demonstrate the positive effect of flow channels. Transient flow progression and pressure data obtained during the experiments are employed to investigate and validate the analytical predictions of equivalent permeability for a rectangular flow channel. Both experimental data and numerical simulations are presented to validate and characterize the equivalent permeability model and approach, while demonstrating the role of flow channels in reducing the injection and mold pressures and redistributing the flow.     

聚丙烯微阵列结构制品熔体充填行为

根据微阵列结构制品熔体的充填特性,设计直径为500 μm的微圆柱阵列结构制品模型,并加工注射成型模具,对微圆柱结构制品熔体的充填规律进行实验和模拟研究。结果表明:微结构制品熔体的充填过程和流动前沿形态的实验结果与模拟分析虽然在趋势上比较一致,但在微圆柱成型过程中,流动前沿的形成过程和充填高度的模拟变化规律与实验结果有一定偏差;实验还发现,前期充填阶段对微圆柱成型的贡献较小,微圆柱内流动前沿的形成受到熔体流动速度、微圆柱模壁、熔体流动惯性影响较大,熔体流经微圆柱结构时产生向上的流动涡流,流动前沿形状呈偏心椭球冠状并逐渐发展成球冠状。     

Effects of mold dimensions on rheological of feedstock in micro powder injection molding

Micro powder injection molding (µPIM) differs from conventional powder injection molding (PIM) with respect to the effects of the mold dimensions. In this study, the rheological properties of the feedstock (mixture of carbonyl iron powders and binder) in molds with different diameters were analyzed by numerical simulation based on the powder-binder two fluid model. Viscosity, temperature, shear strain rate, velocity and the flow distance of the feedstock varied for different molds, but did not just reduce by proportion when the mold was smaller which would lead to many defects in green parts. The inner wall of the mold that was the key factor influencing the filling step in µPIM needed more studies.