气辅注射成型对HDPE结晶形态的影响及其数值模拟

通过扫描电子显微镜(SEM)研究了气辅注射成型(GAIM)对高密度聚乙烯(HDPE)结晶形态的影响,发现制品中存在显著的多层次结构;采用CAE模拟分析软件Moldflow对HDPE在GAIM过程的剪切场、温度场分布及其变化进行了分析,探讨了GAIM过程的剪切场、温度场对制品结晶形态的影响;基于上述分析,讨论了剪切场和温度场对制品结晶形态以及制品性能的影响.     

气体辅助注射成型聚乙烯制品的结晶形态及性能

介绍了气体辅助注射成型(GAIM)过程中聚乙烯分子参数和成型条件对制品结晶形态的影响以及结晶形态与力学性能之间的关系。GAIM成型过程中熔体短射和气体多次穿透引起的强剪切场使聚乙烯分子链沿流动方向取向,经独特的冷却过程后制品内形成了多层次形态结构。最后结合聚乙烯分子参数和GAIM成型过程探讨了多层次形态结构的形成机理。     

气体辅助注射成型工艺参数优化研究

为了解决气体辅助注射成型(GAIM)中制品所出现的缺陷,采用数值模拟方法对影响制品质量的工艺参数进行了优化研究.首先,建立GAIM过程的数学模型,得出影响GAIM制品质量的主要工艺因素;随后,利用数值模拟法分析熔体预注射量、熔体/气体延迟时间、充气压力与熔体注射温度等关键工艺因素与GAIM制品缺陷的关系;最后,基于数值模拟分析结果,对GAIM制品的工艺参数进行了优化选择与设定.     

聚丙烯气体辅助注射成型冷却过程中温度分布的研究

通过对聚合物气体辅助注射成型冷却过程进行合理的假设与简化,对聚丙烯（PP）气体辅助注射成型冷却过程进行了实验与数值模拟研究。结果表明,注射氮气后,PP的冷却速度显著加快,并在气-熔界面处出现小范围的结晶平台。采用MATLAB软件对氮气辅助注射成型PP冷却过程中的温度分布进行了数值模拟,将计算所得模拟值与温度采集的实验值进行比较,发现在熔体降温阶段温度分布的模拟值与实验值吻合程度很高;在固相冷却阶段由于聚合物本身复杂特性以及气体的渗透效应,PP的模拟值略高于实验值,而氮气的模拟值低于实验值。     

复杂壳体类塑料件气体辅助注射成型工艺参数优化研究

以21英寸彩电前壳作为研究对象,将Moldflow 2010作为CAE模拟试验平台,以熔体温度、模具温度、熔体注射时间、气体延迟时间、气体压力为关键工艺因素,考察了复杂壳体类塑料件气体辅助注射成型(GAIM)时制件的翘曲变形量和气体穿透情况。以正交试验设计方法为基础,利用遗传算法并结合径向基神经网络建立GAIM工艺参数优化系统,可用于工艺参数组合的快速确定,为GAIM过程中工艺参数优化提供了一种新的求解思路。     

基于Moldflow的竖梁基座气体辅助注射成型工艺优化

通过Moldflow软件对家电产品零件竖梁基座进行了气体辅助注射成型(GAIM)过程模拟仿真,并对比了不同工艺参数方案,优化得出了较好的气道布局和气体穿透效果,能够有效避免表面缩痕等产品缺陷,可以为模具设计及GAIM提供指导。     

气体辅助注射成型充填过程的数值模拟

描述了气体辅助注射成型的工艺过程及熔体充填和气体穿入的数学模型,采用有限元/有限差分/控制体积法计算充填阶段的压力场和温度场,确定熔体前沿和熔体/气体界面两类移动边界,并对典型制件充模过程进行了模拟.     

管状模腔的气辅注射成型气体穿透机理的数值模拟分析

介绍了圆管内气辅注射成型充填/后充填模拟的数学模型及其数值实现,通过算例验证,对圆管内的气辅注射成型气体穿透过程及其基本规律和影响因素进行了讨论和分析。     

聚碳酸酯气体辅助注射成型制品内应力分布及改善工艺

聚碳酸酯(PC)注塑制品出模后在无外加约束条件下内部应力得不到松弛释放,易导致制品产生开裂,严重影响制品的服役性能。为探究PC制品内应力分布规律,找到有效降低内应力的工艺措施,基于气体辅助注射成型(GAIM)工艺和自行设计制造的带有半圆形加强筋的平板试验模具,结合光弹法和溶剂检测法,研究GAIM制品内应力的分布特点,讨论注气压力和气体保压压力两种工艺参数对GAIM制品内应力的影响规律,提出两种改善制品内应力的工艺方法。研究发现：通过光弹法观测到的应力条纹分布与溶剂浸泡后的裂纹开裂区域一致,即GAIM制品末端及边缘处内应力较大,沿气道两侧应力分布较均匀;较高的注气压力和较低的气体保压压力可以更加有效减小GAIM制品的内应力;通过对GAIM制品24 h即时退火和延长二次注气的卸压时间可以有效降低制品内应力。     

气辅注塑CAE技术在彩电前壳模具设计中的应用

利用注塑模CAE技术可在模具制造之前对模具设计方案进行模拟分析,预测潜在的缺陷并及时修改。在彩电前壳气体辅助注射成型(GAIM)注塑模设计中,应用注塑CAE技术对模具浇口设置、气道布置及熔体充填形态进行模拟分析,并对注塑件壁厚进行优化。结果表明,运用CAE技术能够显著提高模具首试和GAIM技术应用的成功率,缩短模具开发周期,节省模具设计和制造成本。     

Integrated simulations of structural performance,molding process,and warpage for gas‐assisted injection‐molded parts. III. Simulation of cyclic,transient variations in mold wall temperatures

Whether it is feasible to perform an integrated simulation for structural analysis, process simulation, as well as warpage calculation based on a unified CAE model for gas‐assisted injection molding (GAIM) is a great concern. In the present study, numerical algorithms based on the same CAE model used for process simulation regarding filling and packing stages were developed to simulate the cooling phase of GAIM considering the influence of the cooling system. The cycle‐averaged mold cavity surface temperature distribution within a steady cycle is first calculated based on a steady‐state approach to count for overall heat balance using three‐dimensional modified boundary element technique. The part temperature distribution and profiles, as well as the associated transient heat flux on plastic–mold interface, are then computed by a finite difference method in a decoupled manner. Finally, the difference between cycle‐averaged heat flux and transient heat flux is analyzed to obtain the cyclic, transient mold cavity surface temperatures. The analysis results for GAIM plates with semicircular gas channel design are illustrated and discussed. It was found that the difference in cycle‐averaged mold wall temperatures may be as high as 10°C and within a steady cycle, part temperatures may also vary ∼ 15°C. The conversion of gas channel into equivalent circular pipe and further simplified to two‐node elements using a line source approach not only affects the mold wall temperature calculation very slightly, but also reduces the computer time by 95%. This investigation indicates that it is feasible to achieve an integrated process simulation for GAIM under one CAE model, resulting in great computational efficiency for industrial application. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 71: 339–351, 1999     

Temperature and shear rate distributions of gas-assisted injection molded (GAIM) polypropylene and the application in forecast of cooling time

An umbrella handle product of polypropylene molded by gas-assisted injection molding (GAIM) was studied from both aspects: theoretical modeling and simulation as well as in situ temperature measurement. The simulation was primarily through the use of the commercial software Moldflow (version 6.1) coupled with enthalpy transformation method (ETM) in an attempt to investigate the shear rate and temperature fields during GAIM process. A four-parameter model (FPM) was used to nonlinearly fit the temperature decays during the GAIM cooling stage on the basis of a three-parameter model (TPM) raised previously in our group. The FPM showed perfect fitting effect as well as presented fairly acceptable cooling time (t_c) prediction in comparison to experimental data, which could better reflect the nature of crystalline polymers during melt crystallization process. The understanding of the shear rate and temperature fields would be of practical importance to the further research on relationship of “processing–structure–property” as well as the optimization of cooling parameters for industrial GAIM operations of crystalline polymers. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 47390.     

Banded spherulites of HDPE molded by gas-assisted and conventional injection molding

Crystal morphologies of high density polyethylene (HDPE) with low molecular weight obtained by gas-assisted injection molding (GAIM), conventional injection molding (CIM), and spontaneous cooling, respectively, were studied by scanning electronic microscopy (SEM). It is found that banded spherulites are generated in the inner zone of GAIM parts and the outer zone of CIM parts but are absent in quiescent parts. According to the results, the representative morphologies of crystal change with gradual increment of instantaneous flow field in crystallization from non-banded spherulite to banded spherulite and then to oriented lamellae. This morphological evolution indicates that banded spherulites could be induced by flow field with certain intensity, which is confined by both an upper critical value and a lower one.     

注塑模温度场的计算机模拟

本文运用有限元法，采用二次等参单元，对注塑模二维非稳态温度场进行了数值分析，推导了有限元数值求解方程并研制了有限元求解程序软件。实例所得温度场等温线与实验所得结果基本相符，验证了计算机求解的可靠性。通过计算机模拟分析，可了解各瞬时模具温度场的分布状态，观察模具体能否使塑件均匀冷却，如不合理，可通过改变冷却管道参数，达到温度场均匀一致，从而提高塑件质量。通过程序运转，根据塑件的热定型温度，可以预知最短冷却时间，从而缩短冷却周期，提高塑件生产率     

A simple method for forecast of cooling time of high‐density polyethylene during gas‐assisted injection molding

Gas‐assisted injection molding (GAIM) is an innovative plastic processing technology, which was developed from the conventional injection molding, and has currently found wide industrial applications. About 70% of the whole gas‐assisted injection molding cycle is actually occupied by the cooling stage. The quality and production efficiency of molded parts are considerably affected by the cooling stage. Hence, it is necessary to study the solidification behaviors during the cooling stage. In this work, a simple experimental method was designed to simulate the solidification behaviors of high‐density polyethylene during cooling stage of GAIM. The enthalpy transformation approach, coupled with the control‐volume/finite difference techniques, was adopted to deal with the transient heat transfer problems with phase change effects. In situ measurements of the temperature decreases in the cavity were also carried out. Reasonable agreements between the experimental values and the simulated results such as cooling time, cooling rates, and temperature curves were obtained, which proved that this simple experimental method was effective. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

PMMA/PC复合平板叠层注射压缩成型翘曲变形计算模拟

建立了一种基于注射成型模拟软件Moldflow和有限元软件ABAQUS联合计算模拟的方法,以用于分析聚甲基丙烯酸甲酯/聚碳酸酯（PMMA/PC）复合平板叠层注射压缩成型的翘曲变形。通过两步法完成翘曲变形的数值模拟：首先采用Moldflow软件对叠层注射压缩成型进行充填、保压和模具内冷却分析;然后将Moldflow获得的制件脱模时温度场和网格文件导入ABAQUS进行分析,计算脱模后制件完全冷却至室温的翘曲量,将应力释放的翘曲值与完全冷却的翘曲值线性相加得到平板的最终翘曲。同时通过注射成型实验实测PMMA/PC复合平板的翘曲变形。结果表明,联合计算模拟结果与实验结果的匹配性较好。     

注塑模具随形冷却结构对制品成型的热响应分析

研究了模具随形冷却结构对制品成型的热响应变化,利用有限元软件Ansys对线性与随形2种冷却结构进行瞬态热响应分析与对比,得到了2种结构模式的冷却效率和型腔温度场分布规律,并借助Moldflow和计算流体动力学（CFD）软件对注塑制品在随形冷却结构模式下成型所得到的温度场分布及其可能产生的缺陷进行了分析研究。结果表明,随形冷却结构较传统水道具有更均匀的冷却效果,冷却时间缩短了50 %,体积收缩率降低了15 %,且能更迅速地调控模具温度,更快地进入稳定的工作状态。     

Simulation of a mold‐cooling process for gas‐assisted injection molded parts designed with a top rib on the gas channel

The same CAE model used for the filling and packing stage in the gas‐assisted injection molding (GAIM) process simulation was also applied to simulate the cooling phase. This was made possible by using the line source method for modeling cooling channels. The cycle‐averaged and cyclic transient mold cavity surface temperature distribution within a steady cycle was calculated using the three‐dimensional modified boundary element technique similar to that used in conventional injection molding. The analysis results for GAIM plates of a semicircular gas channel design attached with a top rib are illustrated and discussed. It was found that the difference in cycle‐averaged mold wall temperatures may be as high as 10°C, and within a steady cycle, part temperatures may also vary by about 15°C. The conversion of the gas channel into equivalent circular pipe and further simplification into two‐node elements using the line source method not only affects the mold wall temperature calculation very slightly but also reduces the computer time by 93%. This indicates that it is feasible to achieve an integrated process simulation for GAIM under one CAE model, resulting in great computational efficiency for industrial application.     

Predictive Modeling of Non-Isothermal Crystallization in the Solidification of Polyoxymethylene Melt

The predictive modeling of non-isothermal crystallization of polyoxymethylene (POM) melt was proposed based on an isothermal crystallization experiment. The development of crystallinity and crystallization morphological evolution was simulated by considering the process of crystallization includes the three steps: nucleus, growth and ripening and the pre-ripened degree was considered explicit simultaneously. Double-scale computational modeling of the solidification phase transition of the semi-crystalline polymer POM melt was then numerical implemented. The heat flow equation coupling the evolution of crystallinity was computed by the finite different numerical method. The result of the cooling stage of POM melt shows the method can produce more visual information about the processing of crystallize and a relative reasonable detail about the temperature field.