注射成型过程中非牛顿塑料熔体的粘度模型

本文在探讨塑料熔体粘度模型基础上,重点讨论了一种适用范围更广的Cross粘度模型,并根据塑料熔体在注射成型过程的流动特点,采用Arrhenius方程建立了适用于注射充填过程的五参数Cross粘度模型和利用WLF方程建立起适用于注射保压过程的七参数Cross粘度模型。具体讨论模型的特征和适用范围,为注射模设计和成型模拟提供了理论依据。     

塑料注射成型熔体前沿的流动模拟

讨论了塑料注射成型流动过程分析中熔体前沿喷泉效应的近似处理方法和数值分析方法。     

气辅成型技术简介

气体辅助注射成型，简称气辅成型，是为克服传统注射成型局限性而发展起来的一种新型注射工艺。即对先注射了一定量或全部注满塑料熔体的模具型腔内再注射经压缩后的惰性气体，利用气体推动熔体完成充模填补因塑料收缩后留下的空隙，而在塑件冷却后再将气体排出的连续过程。     

粉末注射成型技术及其发展

从塑料加工成型的角度详细讨论了粉末注射成型的工艺过程和技术特点，该技术的关键是配制分散良好的喂料、在尽可能少用黏结剂和获得良好的熔体流动性之间达成平衡，并精确控制注射过程的温度、压力和速度。通过2个粉末注射成型实例进一步说明了粉末注射工艺控制的高要求。对粉末注射成型工艺的最新发展进行的总结表明，粉末注射成型与其他新工艺技术的结合是这一技术进一步发展的趋势。最后分析了我国粉末注射成型的现状，建议我国粉末注射成型的未来发展应该注重加强粉末冶金、高分子材料、塑料加工等多个学科研究人员的密切合作。     

多级注射成型工艺的设计

通过对多级注射成型工艺的研究发现,多级注射成型工艺的核心是如何进行多级分段和如何选择工艺参数。在介绍塑料熔体充模流动特征的基础上,通过系统分析理想充模模型,并联系多级注射原理,提出了分段设计原则及参数选择方案。     

气辅注塑成型工艺过程及其关键技术

气体辅助注塑成型工艺包含塑料熔体注射和气体注射两部分,由气体推动塑料熔体充满模具型腔,因此具有普通注塑成型工艺所没有的优点,但在应用上也带来了特殊的技术要求。本文介绍了几种常用的气体辅助注塑成型工艺过程,并从制品设计、模具技术和工艺控制三方面分析了应用气体辅助注塑成型工艺的关键技术。     

高速微注射成型中熔体充填模式及裹气机理研究

塑料为了准确模拟聚合物熔体在型腔中的流动及前沿位置和形态,建立了熔体、气体两相流流动模型,构造了熔体流动的黏弹性本构关系,用无量纲方法建立了熔体流动前沿的气体、熔体流动的统一控制方程和本构方程,并采用水平集方法预测和跟踪熔体流动前沿,模拟了熔体在低速、中速、高速条件下的流动状态和充填模式,分析了高速微注射成型中气孔产生的原因和可能出现的位置,开展了实际产品的高速微注射成型实验,比较了模拟结果和实验结果。研究表明,熔体充填模式与注射速度、材料特性、型腔尺寸密切相关,在喷射充填模式下可能产生裹气。     

PP注射成型中的压力及熔体流动过程

讨论了聚丙烯在注射成型中充模、增密、保压、冷却各个阶段的压力变化情况和熔体流动过程，以及二者对制品成功质量的影响。认为在聚丙烯注射成型过程中，要保证制品成型质量，不应以升温的办法来降低熔体的粘度，而应以提高注塑压力和剪切速率为主。     

有机硅脱模剂及其应用

1 塑料加工脱模剂的基本工作原理 热塑性塑料在注射或挤出的过程中,塑料熔体与模具表面接触,在熔体和模具之间往往会形成负压,或二者之间因物理吸附或化学键合而致黏结;热固性塑料的成型过程同时采用加压和加热工艺,这将更加剧成型树脂与模具间的吸附或粘接.     

振动气体辅助注射成型新技术

介绍了一项关于塑料制品的气体辅助注射成型新技术———振动气体辅助注射成型(VGAIM)。结合目前的塑料气体辅助注射成型及动态注射成型研究成果,详细叙述了振动气体辅助注射成型技术产生的背景及其基本原理,且具体介绍了振动气体辅助注射成型的工艺实现装置,并就其在改善制品结构性能和改进聚合物熔体填充机理中的应用进行了探讨。最后对其应用前景提出了展望。     

热流道注射模中充模力的计算

就热流道注射模具，根据塑件形状不同，分析了熔体在等温流动和非等温流动时，流经不同位置时的压力损失。推导出了计算充模压力的数学模型。     

脉动注射对螺线槽模腔熔体流动性能的影响

采用阿基米德螺线槽模具对脉动注射充模过程中聚合物熔体的流变行为进行了实验研究,分析了振动力场对聚合物熔体充模流动性及模腔不同位置聚合物熔体充模压力的影响。结果表明,振动力场的引入有利于降低聚合物熔体的表观粘度,改善熔体的流动性,减小熔体在充模过程的压力损失。这种效果尤其对表观粘度高的聚合物熔体更为明显。     

气辅共注射成型工艺的实验研究

通过对现有注塑、气辅设备的改造,时气辅共注射成型工艺进行了实验研究。考察了材料流变性能、注射量和气体注射延迟时间对材料层厚分布及气体在熔体中穿透的影响规律。实验表明,芯皮层材料层厚分布主要受芯皮层熔体粘度比和芯皮层注射量的影响;气体在熔体中的穿透主要受熔体的总注射量和注气延迟时间的影响。     

基于神经网络和遗传算法的薄壳件注塑成型工艺参数优化

建立了基于神经网络和遗传算法并结合正交试验的薄壳件注塑成型工艺参数优化系统。正交试验法用来设计神经网络的训练样本，人工神经网络有效的创建了翘曲预测模型；遗传算法完成了对影响薄壳塑件翘曲变形的工艺参数（模具温度、注射温度、注射压力、保压时间、保压压力和冷却时间等）的优化，并计算出了它们的优化值。按该参数进行试验，效果良好，可以有效地减小薄壳塑件翘曲变形，其试验数值与计算数值基本相符，说明所提出的方法是可行的。     

Dependence of bulk viscosity of polypropylene on strain,strain rate,and melt temperature

The relations between bulk viscosity, strain, strain rate, and melt temperature of polypropylene are investigated in uniaxial compression similar to the measurement of PVT diagram of a polymer. A new and more practical bulk viscosity model for the simulation of injection molding is proposed. The bulk viscosity increased with the increase of compression deformation and decreased when the compression speed and the melt temperature are higher. This dependency is attributed to the orientation and occupancy of the molecule within the free interstitial space. In addition, the magnitude of the bulk viscosity was found to be significantly greater than the shear viscosity at high compression deformation and low strain rate. Thus, not only shear viscosity but also the bulk viscosity should be considered in the simulation of the packing‐holding stage of the plastic injection molding process. POLYM. ENG. SCI., 57:830–837, 2017. © 2016 Society of Plastics Engineers     

模内热切注塑模设计与挤切因素工程分析

现有的部分企业在模内热切注塑技术规范中,规定了与切刀运动方向垂直的切刀横截面面积须小于注塑机喷嘴截面积,但在多切刀模内热切注塑模中,这一规定并不适用。针对此问题,首先介绍了典型模内热切注塑模的主要结构,以这种结构为案例,结合熔融塑料的体积弹性模量估算,通过熔融塑料在受切刀挤压时熔融塑料体积变化与压力增量的关系分析,得出若在注塑结束、塑料熔体尚未凝固时启动切刀,则压力变化很小,因此切刀的截面积小于注塑机喷嘴截面积不是必要条件;若切刀启动时间较迟,则流道和浇口处的塑料熔体已经凝固,被挤出的半熔融塑料并不是被挤回到注塑机中,而是被容纳于切刀附近的溢料槽。由此明确了切刀动作在注塑行程过程中时机优化的指导思想,以及溢料槽设计的补充思想。     

Study of mouldability in gas-assisted injection moulded fibre-reinforced Nylon parts

Abstract

Investigation of the characteristics of gas penetration in gas-assisted injection moulding (GAIM) of parts plays an important role in the successful application of gas-assisted injection moulding. Although these have been proposed by various investigators, quantitative rules based on well designed experiments on fibre-reinforced plastic materials have not been reported previously. Additions of glass-fibre bring about rather dramatic changes in material viscosity and heat conductivity, etc. In the present paper, spiral tube moulds with uniform diameters of 8 and 10 mm, respectively, and a plate mould of 3 mm thickness with gas channel design of semicircular crosssection were moulded using glass-fibre reinforced Nylon resin. The effects of fibre content, tube diameter, and processing parameters, including gas pressure, delay time, and injection stroke on gas penetration characteristics and mouldability for fibre-reinforced Nylon parts were investigated experimentally. It was found that the coating melt thickness decreases with increasing gas pressure, until the gas pressure reaches a critical value, when the coating melt thickness becomes relatively constant for the spiral tube. Meanwhile, using a longer delay time for gas injection will increase the skin melt thickness. The hollowed core ratio increases with increasing diameter of spiral tube. Alternatively, the hollowed core ratio of GAIM plate and spiral tube parts increases when the content of glass-fibre is increased. However, when the fibre content is over 10 wt-%, it shows less influence on the hollowed core ratio for plate parts. Furthermore, although the area of the moulding window decreases with increasing content of fibre, they all show good mouldability. From these results, one can provide an empirical formula to CAE simulation designers and part/mould designers for GAIM fibre-reinforced Nylon parts to achieve suitable mouldability and accurate CAE simulation.     

壳体制品注塑工艺参数CAE优化分析

应用Moldflow软件对壳体制品注射成型工艺参数进行了优化分析,模拟出制品成型过程中的最佳注塑压力、锁模力、模具温度、熔体温度、注射时间、保压压力和保压时间、冷却时间。采用该成型工艺参数结合合理的注塑模具能注塑出最佳的塑料制品,为成型过程的顺利进行提供指导依据,模拟结果具有一定的理论意义及实际指导价值。     

Effect of molecular weight and molding conditions on the replication of injection moldings with micro‐scale v‐groove features

Injection molded optical plastic parts require accurate replication of micro‐scale features. The effects of melt viscosity and molding conditions on replication of microscopic v‐groove features in injection molded parts were examined for PC with different molecular weight. The micro‐scale feature size was a continuous v‐groove with 20 μm in depth and 50 μm in width. For injection molding conditions, melt temperature, mold temperature, injection velocity and holding pressure were varied in three levels. As the result, the mold temperature had significantly affected replication for all polymers with different molecular weight. Additionally, the molding conditions that lower melt viscosity led to improved replication. In the case of polymer with high molecular weight, the viscosity decreased with increasing melt temperature. It has been found that high replication of micro‐scale features could be achieved by higher mold temperature and higher melt temperature even with high viscosity PC. POLYM. ENG. SCI., 2008. © 2008 Society of Plastics Engineers