工艺参数对气辅共注成型过程影响的实验研究

对先进的气辅共注成型工艺进行了系统的实验研究,研究了熔体注射温度、气体压力这两种工艺参数对气辅共注成型气体和芯层熔体穿透形貌的影响规律,并基于聚合物流变学和流体动力学揭示了这些工艺参数对成型过程的影响机理。结果表明,随着芯层熔体温度升高,芯层熔体的黏度会减小,流动阻力减小,使得气腔的穿透深度减小,而穿透宽度和穿透厚度则增大,但芯层熔体的穿透长度变化不明显；随着注气压力增大,气体的穿透深度、穿透宽度和穿透厚度均增大。     

气体辅助共注成型流动分析数学模型

根据气体辅助共注成型流动过程的特点，从流体力学基本理论出发，引入合理的假设和简化，建立了描述气体辅助共注成型熔体充模和气体穿透的数学模型。     

气体注射控制参数对聚合物气辅共注成型过程影响的实验研究

为了建立气辅控制系统的控制模型,系统研究了气辅注射工艺参数对气辅共注成型过程的影响规律。研究表明,保压时间和气体注射延迟时间对气辅共注成型的气体穿透有较大影响,而对芯层熔体的穿透影响不明显。随着保压时间的延长,气体的穿透深度和穿透宽度均增加,而随着气体注射延迟时间的延长,气体穿透深度增大,穿透宽度减小。延长气体注射延迟时间有利于气体的穿透,但易出现指进现象和气体穿透流动的不稳定。     

工艺条件对气体辅助注射成型的影响

基于Hele-Shaw模型,采用CAE技术,利用Moldflow软件对气体辅助注射成型过程中熔体注射温度、熔体预填充量、气体注射压力、延迟时间等重要工艺参数与气体穿透深度、熔体厚度和体积填充时间等重要指标的关系进行了数值模拟.结果表明,熔体注射温度和气体注射压力越高、延迟时间越短,则气体穿透深度越小、熔体厚度越薄、体积填充时间越短;熔体预注射量越大,则气体穿透深度越小、熔体厚度越厚、体积填充时间越短.     

水辅助熔体充模流动的熔体流痕

构建了用于研究水辅助熔体充模的仿真模具,采用红色和绿色着色剂作为示踪剂,通过水辅助着色的聚丙烯(PP)熔体在柱状模腔里充模,获得了能够反映熔体流动痕迹的样品。通过观察流痕,对水作用下熔体的充模流动进行了研究。实验结果表明:在一次穿透中,与注水喷嘴接触的高黏度熔体造成水从喷嘴射入熔体的不稳定,水的穿透导致模壁附近熔体可能产生回流现象,回流沿水的穿透方向呈减弱趋势。在二次穿透中,水前缘熔体黏度和黏度分布对水的穿透影响较大,熔体体积的收缩是近似线性的减小过程,熔体的剪切流动弱于一次穿透。实验中还发现,水前缘的熔体也会产生"喷泉流"。     

夹芯注塑成型过程的计算机可视化模拟分析--材料粘度与工艺参数对芯层熔体穿透深度的影响

采用Moldflow公司MPI软件中的Co-injection分析模块，对夹芯注塑成型过程进行动态模拟分析；以揭示材料粘度以及工艺参数对夹芯注塑成型过程中芯层熔体穿透深度的影响规律。结果发现，芯层熔体穿透深度值随芯／壳层熔体粘度比R值的减小而增大，这主要与芯层和壳层熔体的相对流动能力有关；此外，在工艺参数中，改变熔体注射速度对芯层熔体穿透深度的影响较为突出，而模温和熔体温度对芯层熔体穿透深度的影响相对较弱。     

基于数值模拟的气体辅助注射成型工艺控制研究

基于广叉Hele-Shaw流动模型描述了气体辅助注射成型时气体的穿透过程。采用有限元／有限差分／控制体积法计算充填阶段的压力场、温度场,确定熔体前沿和气熔界面,并以实际产品为例分析工艺参数对气体辅助注射成型产品质量的影响。     

气辅注射成型运动界面的Level Set方法数值模拟

给出气液两相流数学模型,选取Cross-WLF模型作为熔体的黏度模型,采用Level Set/SIMPLEC方法模拟了气体辅助注射成型中气体穿透过程,追踪到了不同时刻的运动界面(气熔界面和熔体前沿界面),描述了运动过程中不同时刻速度和温度等重要物理量的分布情况,分析了熔体温度、气体延迟时间和注射压力对气体穿透时间和穿透长度的影响。数值结果表明,Level Set/SIMPLEC方法可以准确追踪气体穿透过程中的两个运动界面;熔体温度、延迟时间和气体注射压力对气体穿透长度有显著影响。     

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。     

气辅共注成型工艺中气道截面影响的CAE研究

基于气辅共注成型充填过程控制方程和7参数Cross—WLF黏度模型，采用数值模拟的方法研究了气辅共注成型工艺中气道截面的大小对熔体流动、气体穿透与压力分布的影响。采用改进的控制体积／有限元／有限差分法实现对充填过程中多重运动界面的追踪以及压力、温度等场量分布的预测，编写了相应的模拟程序。对气道等效直径分别为5mm、8mm和12mm的矩形板的气辅共注成型充填过程进行了数值模拟。通过对模拟结果的比较发现：随着气道等效直径的增大，气道中的熔体与薄壁区的熔体流速差越来越大，熔体流动的“跑道”效应越来越突出；“薄壁穿透”缺陷由明显到缓解直至基本消除；压力损失越小，压力分布也变得更为均匀。因而在制件设计时，气道截面尺寸宜稍大而不宜过小。     

Analysis and experimental study of gas penetration in a gas-assisted injection-molded spiral tube

Characteristics of gas penetration and polymer melt flow in gas-assisted injection molded spiral tubes was investigated by simulations and experiments. Distribution of the skin melt thickness along the gas flow direction was measured, and gas penetration in the primary and secondary stages was identified. An algorithm based on the control-volume/tiniteelement method combined with a particle-tracing scheme using a dual-filling-parameter technique is utilized to predict the advancements of both melt front and gas from during the molding process. The simulated distribution of gas penetration shows reasonably good coincidence with experimental observations. © 1995 John Wiley & Sons, Inc.     

Computer simulation of the filling process in gas‐assisted injection molding based on gas‐penetration modeling

Gas‐assisted injection molding can effectively produce parts free of sink marks in thick sections and free of warpage in long plates. This article concerns the numerical simulation of melt flow and gas penetration during the filling stage in gas‐assisted injection molding. By taking the influence of gas penetration on the melt flow as boundary conditions of the melt‐filling region, a hybrid finite‐element/finite‐difference method similar to conventional‐injection molding simulation was used in the gas‐assisted injection molding‐filling simulation. For gas penetration within the gas channel, an analytical formulation of the gas‐penetration thickness ratio was deduced based on the matching asymptotic expansion method. Finally, an experiment was employed to verify this proposed simulation scheme and gas‐penetration model, by comparing the results of the experiment with the simulation. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 90: 2377–2384, 2003     

Simulations of primary and secondary gas penetration for a gas-assisted injection-molded thin part with gas channel

Numerical simulations and experimental studies concerning melt flow and primary as well as secondary gas penetration during the filling and the postfilling stages in gas-assisted injection molding of a thin plate with a semicircular gas channel design were conducted. Distribution of the skin melt thickness along the gas-penetration direction was measured to identify primary and secondary gas penetration. Melt and gas flow within the gas channel of a semicircular cross section is approximated by a model which uses a circular pipe of an equivalent hydraulic diameter superimposed on the thin part. An algorithm based on the control-volume/finite-element method combined with a dual-filling parameter technique suitable for the tracing of two-component flow-front advancements is utilized and numerically implemented to predict both melt- and gas-front advancements during the melt-filling and the gas-assisted filling processes. A flow model of the isotropic melt-shrinkage origin combined with a gapwise layer tracing algorithm was implemented to assist the prediction of secondary gas penetration and melt flow in the post-filling stage. Simulated results on the gas front locations at the end of both primary and secondary penetration phases show reasonably good coincidence with experimental observations. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 67:1553–1564, 1998     

铜锍转炉中气液两相流动的数值模拟

采用流体体积方法对铜锍转炉熔池内造铜期吹炼过程中气液两相流动进行单喷嘴数值模拟,研究了气体喷入熔体时的喷流运动现象和性质、气流穿透距离、风口压力变化、风口侧壁面剪切应力分布和气含率分布规律. 结果表明,气泡连续产生和分离是风口处气体的运动形式,气流穿透距离约为风口内径的3.6倍,风口处脉冲压力的形成周期为0.2 s,持续时间约为0.04 s;风口侧壁面剪切应力较大的区域集中在风口附近及其上方壁面;风口以上气含率随熔体高度增加而增加,在靠近自由液面处约为21%,部分模拟结果与文献报道和实际生产情况吻合.     

Three‐dimensional simulation of primary and secondary penetration in a clip‐shaped square tube during a gas‐assisted injection molding process

This article proposes a generalized Newtonian model to predict the three‐dimensional gas penetration phenomenon in the GAIM process, where the gas and melt compressibility are both taken into account and hence the primary and secondary penetrations in GAIM processes are able to be quantitatively predicted. Additionally, an incompressible model requiring no outflow boundary is also presented to emphasis the influence of gas compressibility on the primary penetration. Based on a finite volume discretization, the proposed numerical model solves the complete momentum equation with two front transport equations, which are employed to track the gas/melt and air/melt interfaces. The modified Cross‐WLF model is adopted to describe the melt rheological behavior. The two‐domain modified Tait equation is exploited to represent the melt compressibility, while a polytropic model is employed to express the gas compressibility. The proposed schemes are quantitatively validated by the gas penetration characteristics in a clip‐shaped square tube, where good prediction accuracy is obtained. The influences of five major molding parameters, such as the injection pressure, mold temperature, melt temperature, delay time, and melt material on the gas penetration characteristics in the same clip‐shaped square tube via the proposed numerical approach are extensively presented and discussed. POLYM. ENG. SCI., 2008. © 2008 Society of Plastics Engineers     

Flow direction when fan shaped geometry is applied in gas-assisted injection molding: 2. Development of flow model and its predictions

In part 2 of the paper simplified unsteady-mass (and momentum-) balance equations of melt polymer resin in the cavities of GAIM were proposed, as a time-dependent rule of thumb, to constitute a novel flow model in GAIM under the configuration of two fan-shaped geometries connected with a gas nozzle. Upon performing a simulation on them with commercial software (MOLDFLOW), we compared the time evolution of simulated gas penetration lengths with the those of unsteady trajectory on the gas flow in GAIM by the suggested novel flow model in the fan-shaped cavities in order to check the precision of model-predicted gas penetration lengths as well as the consistency of its predicted direction. The results by the suggested novel flow model were satisfactory to fit the trajectory simulated with commercial software (MOLDFLOW).     

基于气体穿透效果数值模拟的气体辅助注射成型工艺优化

对气体辅助注射成型工艺进行分析，阐述了气体辅助注射成型的关键技术要求在分析熔料流动、气体穿透物理模型的基础上，探讨了气体辅助注射成型数值分析的实现原理运用MPI／Gas模块对一T型支架进行了气体辅助注射成型CAE分析，模拟不同工艺条件下的气体穿透效果，确定了合理的工艺参数。     

Description of second flow field via the deformation of polystyrene phase in high‐density polyethylene matrix

Real flow field has been critical in all kinds of injection molding, not only for understanding morphological evolution, but also for tailoring polymer physical property. Since the relaxation of PS phase in the HDPE matrix is successfully retarded by introduction of additional gas cooling, here, the second flow field in gas‐assisted injection molding is first calculated with the classical models for predicting the shapes of dispersed droplets in immiscible blend. The results indicate high gas penetration pressure facilitates strong second flow field. Gas penetration time is inversely proportional to the triggered flow intensity, which can be used for the qualitative comparison of the flow fields under various conditions. Importantly, the flow field can be designed by tailoring melt advancing rate, such as the penetration power and/or the penetration resistance of second fluid, which contributes to realizing the optimum coupling between external fields and chain architectures. Besides, this work opens a window for the understanding of real flow field under various processing conditions. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 43374.