注塑制品微结构的三维数值模拟分析

构建带有圆柱阵列微结构的微注射制品3D模型,采用聚丙烯为原料,应用针对不可压缩性流体的三维有限元方法,根据优化的有限元网格实现体积控制来预测熔体的前沿流动。结果发现基于3D数值模拟方法很好的模拟出微注射制品不同填充阶段的流动状态、温度场和速度分布。厚度方向微结构的充填过程滞后于流动前沿径向的推进,因此不利于微结构区域气体的排出;微圆柱结构充填时具有喷泉状流动前沿。     

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。     

注塑成型充填过程的可压缩流动分析

注塑成型过程中,熔体在型腔中的流动和传热对制品质量性能有重要的影响.为了预测注塑制品的收缩、翘曲和力学性能,精确预测充填过程的流动及传热历史是十分必要的.本文考虑熔体的可压缩性及相变的影响,将充填过程中熔体的流动视为非牛顿可压流体在非等温状态下的广义Hele-Shaw流动.采用有限元/有限差分混合方法求解压力场和温度场,采用控制体积法跟踪熔体流动前沿,并应用Visual C++实现了注塑充填过程的可压缩流动分析.为了保证能量方程各项在单元内边界的连续性,结点能量方程各项由单元形心处的离散值加权平均获得,因而,能量方程在计算区域内整体求解.对两个算例进行了分析,模拟结果与实验结果的对比,验证了本文数值算法及程序.     

基于二次三角形单元的注塑充填数值模拟

采用有限单元方法,用二次三角形单元对注塑成型制品典型截面的充填过程进行数值模拟.其中速度场采用6结点三角形插值,压力场采用3结点三角形插值.并通过算例给出熔体充填过程中典型截面的速度场、压力场分布,模拟出熔体前沿在截面方向上的喷泉流动效应.     

基于Moldex3D的嵌件注射成型浇注系统优化分析

利用Moldex3D软件中嵌件成型模块对热敏性嵌件成型薄壁制品进行分析,针对不同浇注系统得到充模流动模拟和保压过程模拟结果。通过对成型过程熔体压力场和温度场分布结果、熔体流动前沿温度分布结果的对比分析,结合熔接痕等品质缺陷预测结果,最终得出成型稳定性较优的浇注系统设计方案。     

淋浴器花洒夹座注塑件浇注系统的CAE分析

浇口的位置、浇口与流道的尺寸和几何形状对塑料熔体在型腔中的流动、塑件的成型质量以及模具的结构密切相关.采用Moldflow模拟分析软件,对淋浴器花洒夹座的最佳浇口位置进行了分析,并且,结合产品结构,设计了 2种不同的浇注系统,并对注塑成型过程进行了模流分析.对比分析了 2种浇注系统方案中熔体的充填时间、流动前沿温度、体...     

黏弹特性对模内微装配成型热流固耦合变形的影响

建立了综合考虑二次成型黏弹性熔体充填流动约束环境影响的模内微装配成型过程黏弹性热流固耦合变形机理的理论模型,并通过有限元数值模拟,研究了二次成型熔体黏度对模内微装配成型过程黏弹性热流固耦合变形的影响规律。结果表明,黏弹性热流固耦合作用诱导的预成型微型轴变形的驱动力来源于微装配界面形成的热流固耦合压力和黏性拖曳剪应力,而二次成型熔体流动的弹性正应力对耦合变形具有抑制作用,微装配界面的热流固耦合载荷和微型轴的变形均随着二次充填熔体的黏度增大而增大,减小二次成型熔体黏度有利于提高其微装配加工精度。     

熔体剪切变稀特性对聚合物水辅共注射成型过程的影响

通过建立的全三维非稳态非等温水辅共注射成型过程有限元数值模拟算法与技术,系统研究了芯层熔体剪切变稀特性对水辅共注射成型中水与芯层熔体的穿透过程和前沿界面运动稳定性的影响规律,并揭示了其机理。结果表明,随着芯层熔体剪切变稀特性增加,水辅共注射成型水和芯层穿的透深度增大,这有利于细长制品的水辅共注射成型。然而芯层熔体剪切变稀特性的增加会使水与芯层熔体前沿移动界面流动趋于不稳定,严重影响制品内表面成型品质。     

基于CAE技术的塑料光学元件双折射行为研究

以光学镜片为分析实例,采用CAE数值仿真技术对其熔体充填过程、保压过程、冷却过程进行了模拟,直观预测了制品的翘曲变形量、残余应力及光的相位移等结果,并分析了成型制品的双折射行为。结果表明:在整个注塑过程中,塑料熔体的充填情况较好、流动前沿温度比较均匀,透镜的整体收缩趋于一致,翘曲变形量仅为0.008 9 mm。通过改进模具设计、调整工艺参数,透镜的光相位移和迟滞量均较小,除了浇口附近外,其他处没有发生明显的双折射现象,产品符合光学元件的质量要求。     

聚合物流变性能对共注射成型的影响

在共注射成型多相分层流动充模成型机理的基础上，揭示了芯壳层熔体对共注射成型的分层界面形貌和芯层熔体前沿突破的影响，并模拟了芯壳层熔体粘度比对共注射成型的影响，建立了芯壳层熔体粘度与分层界面和前沿移动界面菜貌的关系。本文的模拟研究结果与一些文献的实验结果相吻合。     

A method for determining the flow front velocity of a plastic melt in an injection molding process

During the filling phase of an injection molding process, the flow front velocity of the plastics melt has a decisive influence on the form part quality. It has been believed that a constant flow front velocity of the melt leads to distortion‐free and residual stress‐free form parts. A process control strategy based on a constant flow front velocity of the melt, however, requires the full understanding of the flow front position as a function of the screw position of the injection molding machine. With current methods, this can only be achieved by direct measurements using a number of sensors inside the mold, which leads to complicated structure, great efforts, and high cost for the tooling equipment. This article proposes, designs, and develops an innovative method for determining the flow front velocity of a plastic melt in an injection molding using only one pressure sensor at the front of the screw and based on the idea of mapping a simulated filling process to a real injection molding process. The mapping ensues that the characteristic event points are identified and matched for both the simulated and real filling process. The results of the simulation analysis and experimental evaluation show that the proposed method can be used to determine the flow front position and the resulting flow front velocity of the melt within the cavity of the mold and provide evidence that the new method offers great potential to process control strategies based on machine independent parameters. POLYM. ENG. SCI., 59:1132–1145 2019. © 2019 Society of Plastics Engineers     

Modeling fountain flow and filling front shape in reaction injection molding

A numerical model of the reaction injection molding process was developed to test front shape and flow approximations employed in previous models. The model was two-dimensional and simulated the flow, reaction, and heat transfer in the typically long axial dimension and the typically small thickness dimension of a mold. The filling front shape and the velocity profiles in the filling fluid were determined by numerical solution of the momentum equation with the appropriate stress boundary conditions using the method of Patankar (1980). The predicted temperature and conversion results agreed with calculations assuming that the front was flat perpendicular to the flow and that a parabolic velocity profile existed behind the fountain flow region at the front. Thus, simple assumptions about front shape and velocity in the thin dimension of a reaction injection mold can be employed without significant loss of accuracy in modeling reaction injection molding.     

气体辅助CAE技术在彩电前壳模具设计中的应用

应用流动模拟软件C-MOLD，对彩电前壳模具结构设计进行了气体辅助CAE模拟分析。通过几种方案的分析比较，解决了彩电前壳模具气辅成型中遇到的气体手指效应，获得了比较满意的成型效果。结果表明，在模具结构设计阶段，应用CAE软件对气辅成型技术中塑料充填形态，气道设计以及气辅成型工艺三个重要条件进行模拟分析优化。可以大大提高模具首试成功率，降低模具制造成本。     

Analysis of resin injection molding in molds with preplaced fiber mats. II: Numerical simulation and experiments of mold filling

This work presents the results of numerical simulation and experimental visualization of the mold filling process in resin injection molding with preplaced fiber mats. The mold filling experiments were conducted with various mat stacks consisting of continuous random glass fiber mats and bidirectional stitched glass fiber mats. The use of two different mat types in the mat stack created porosity and permeability variations. The effect of these permeability variations was studied by taking flow pressure measurements and observing the progress of the flow front of a non-reactive fluid filling a clear acrylic mold that contained the reinforcement mat stack. Numerical simulation corresponding to each experiment was also carried out. The numerical results were compared to the experimental measurements.     

Numerical Simulation for Injection Molding with a Rapidly Heated Mold,Part I: Flow Simulation for Thin Wall Parts

The rapid thermal response (RTR) injection molding is a novel process developed to raise the mold surface temperature rapidly to the polymer melt temperature prior to the injection stage and then cool rapidly. The resulting filling process is achieved inside a hot mold cavity by prohibiting formation of frozen layer so as to enable thin wall injection molding without filling difficulty. The present work covers flow simulation of thin wall injection molding using the RTR molding process. Both 2.5-D shell analysis and 3-D solid analysis were performed, and the simulation results were compared with the prior experimental results. Coupled analysis with transient heat transfer simulation was also studied to realize more reliable thin-wall-flow estimation for the RTR molding process. The proposed coupled simulation approach based on solid elements provides reliable flow estimation by accounting for the effects of the unique thermal boundary conditions of the RTR mold.     

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.     

轿车后视镜外罩成型模拟研究

基于流体运动的基本理论，建立了塑料熔体填充流动的数学模型，利用Moldflow软件对轿车后视镜外罩进行了模拟仿真，分析了壁厚、浇口位置、流动平衡、流动前沿温度、熔接痕以及气穴位置等对成型结果的影响，为模具设计、注射工艺的确定提供了量化指导。     

Molecular orientation distributions during injection molding of liquid crystalline polymers: Ex situ investigation of partially filled moldings

The development of molecular orientation in thermotropic liquid crystalline polymers (TLCPs) during injection molding has been investigated using two‐dimensional wide‐angle X‐ray scattering coordinated with numerical computations employing the Larson–Doi polydomain model. Orientation distributions were measured in “short shot” moldings to characterize structural evolution prior to completion of mold filling, in both thin and thick rectangular plaques. Distinct orientation patterns are observed near the filling front. In particular, strong extension at the melt front results in nearly transverse molecular alignment. Far away from the flow front shear competes with extension to produce complex spatial distributions of orientation. The relative influence of shear is stronger in the thin plaque, producing orientation along the filling direction. Exploiting an analogy between the Larson–Doi model and a fiber orientation model, we test the ability of process simulation tools to predict TLCP orientation distributions during molding. Substantial discrepancies between model predictions and experimental measurements are found near the flow front in partially filled short shots, attributed to the limits of the Hele–Shaw approximation used in the computations. Much of the flow front effect is however “washed out” by subsequent shear flow as mold filling progresses, leading to improved agreement between experiment and corresponding numerical predictions. POLYM. ENG. SCI.,, 2011. © 2011 Society of Plastics Engineers     

Prediction of flow–induced process variables based on similarity analysis in the liquid molding process

In general, a numerical scheme is a widely accepted technique for estimating resin flow in the liquid molding process. A numerical mold filling analysis is essential to optimize the manufacturing process of a composite. However, finding an optimal condition from the numerical analysis requires many numerical calculations. The efforts can be greatly reduced if a similarity solution replaces the repeated numerical calculations. In this study, similarity relations are proposed to predict the flow‐induced process variables. such as resin pressure, resin velocity, and flow front evolution time, during mold filling. Numerical simulations are performed for two cases where a material property, an injection condition or a part shape is different. The model is verified by applying the similarity relation for two numerical results obtained from the thin shell structure.