纤维增强塑料注塑成型集成仿真建模

注射成型过程中的熔体流动分析、纤维断裂和纤维取向预测紧密相关, 并且具有重要的 工程应用价值, 因此对其进行集成仿真是十分有意义的。本文在分析各自特点的基础上, 提出注塑 流动、纤维断裂和纤维取向集成仿真模型, 可对充填和后充填阶段的可压缩流体的非对称流动, 以 及由于熔体流动引起的纤维断裂、三维纤维取向行为进行统一建模, 并且熔体流动和纤维取向相 互耦合。      

基于ANSYS CFX的注塑成型充填过程三维模拟

注塑成型中,熔体在模腔内的流动为非牛顿流体在复杂型腔内的非等温、非稳态流动。充填过程的三维数值模拟能更真实地模拟熔体在型腔内的三维流动状态。本文采用有限元分析软件ANSYS CFX进行二次开发,实现注塑成型充填过程的三维模拟,可求解熔体前沿、压力场、温度场等一系列模拟结果。模拟结果与注塑成型软件MOLDFLOW结果进行对比,验证了该方法的有效性。算例分析结果表明,对于薄壁制品,基于中面模型的注塑成型模拟方法是适用的,但对于非薄壁制品,采用三维模拟方法可以得到更合理更全面的信息。     

注射成型过程中复合材料在型腔内流动行为的可视化实验

利用可视化手段对不同纤维含量热塑性复合材料不同型腔厚度的充填过程进行了动态观察,实验结果表明,尺寸及材料特性对薄壁塑件的熔体流动行为有较大影响,随着壁厚的减薄,复合材料在低速注射条件下熔体充填型腔的速度在后期有突然增大的现象,在高速注射条件下,熔体充填速度会迅速下降,而纤维含量较高的复合材料由于剪切热的作用充填速度下降较小。该研究为薄壁热塑性复合材料注塑成形技术的深入研究提供了参考。     

尺寸效应对多型腔注射成型过程影响的可视化实验

利用可视化注塑模具和高速摄像机对注塑成型过程中熔体在型腔内的充填不平衡现象进行了动态观察,探讨了尺寸效应对熔体充填型腔速率及充填平衡性的影响。实验结果表明,熔体的充填平衡性与型腔的厚度有关,根据实验结果可以较好地描述熔体注射成型过程中充填不平衡现象的产生规律,为薄壁及微细尺寸下的精密注射成型技术的发展提供实验依据。     

玻纤增强聚丙烯多腔微注塑中纤维取向与流动偏移

采用3D模拟技术和各项异性旋转扩散-诱导应变闭合(ARD-RSC)等模型以及集成式热电偶传感器温度测量系统和可视化全息示踪技术,对多型腔微注塑成型过程中玻纤增强聚丙烯(GFRPP)熔体在流道中的纤维取向、温度和流动速度偏移现象进行模拟和分析。结果表明,低速注射时,GFRPP熔体中纤维取向明显,流道表层区域的纤维取向程度大于芯层区域的纤维取向,存在着明显的、不对称的表层-芯层-表层结构,纤维取向加剧了塑料熔体前沿温度与流动速度的向下偏移。高速注射时,纤维取向仍然存在不对称的表层-芯层-表层结构,但比低速注射时不明显得多,纤维取向对熔体前沿高温区和流动速度向下侧偏移幅度的影响也较低速注射时更大。即GFRPP熔体在不同注射速度下熔体的流动速度、流动状态、温度变化相互作用与影响,使得熔体的纤维取向,流动速度、温度分布产生偏移,导致流道系统和型腔充型不均衡。     

聚合物熔体环绕型芯充型流动行为的物理可视化分析

利用自行开发的超声振动辅助注射成型可视化实验装置,对不同注射速度下聚丙烯(PP)在环形型腔内环绕型芯充型流动特性进行可视化试验,观测分析不同注射速度对熔体充型流动行为的影响。分析结果表明,不同注射速度对环形制件注塑成型充型流动行为产生不同程度的影响,在较低注射速度时,型腔内的气体压力变化平稳,熔体流动速度比较平稳无明显变化;在较高注射速度时,在充填过程中型腔内的气体压力急剧变化,熔体速度出现波动且在流动后期熔体的流动速度出现骤降,注射速度对熔体流动前沿的面积变化也有直接影响。在高速注射时,型腔内气体压力的变化是影响熔体充型流动特性的主因;在低速注射时,熔体与型腔表面的热交换是影响熔体充型流动特性的主因。     

不同流道截面型腔的水穿透行为

纤维取向分布直接影响水辅注塑成型制品的使用性能,如冲击强度、屈服强度及拉伸强度等。多样化的流道截面型腔用于满足水辅制品在不同场合中的应用,不同的流道截面型腔势必会影响水辅制品中纤维取向分布。文中旨在研究圆形、上圆下方形及方形的截面流道型腔中短玻纤增强聚丙烯复合材料的水辅助注射成型过程。结果发现,随着熔体温度的升高、注水压力的增大及注水延迟时间的缩短,3种流道截面型腔制品的中间端处残余壁厚减薄及短玻纤沿聚合物熔体流动方向的取向度提高,且在相同加工变量下,圆形截面流道型腔制品的中间端处残余壁厚最薄及短玻纤沿聚合物熔体流动方向的取向度最高,其次是上圆下方形,最后是方形。综合制品的中间端1处及2处残余壁厚可知,聚合物熔体温度在210～230℃、注水压力7～10 MPa及注水延迟时间1～5 s时,上圆下方形截面型腔制品的中间端处残余壁厚及短玻纤沿聚合物熔体流动方向的取向度更趋近于圆形。     

短玻璃纤维增强聚合物注塑充填过程及纤维取向数值模拟

基于Hele-Shaw理论及广义非牛顿流体本构方程,建立了纤维增强聚合物三维薄壁注塑成型充填阶段数学模型,根据Folgar-Tucker取向模型,建立了纤维取向张量模型。采用Moldflow对拉伸试样的注塑流动过程进行模拟,研究纤维含量f和纤维间相互作用系数Ci对纤维取向的影响。结果表明,随着Ci增大,平均纤维的取向性呈减小的趋势;试样不同部位的纤维取向不同;f对纤维取向性影响较小,且存在一个最佳含量百分比数值。     

微注塑薄壁制品可成型性及充填过程中的流动现象分析

基于一组薄壁微制品的微注塑成型实验,研究不同尺度(100μm、200μm、500μm、1mm)制品的可成型性及充填过程中的流动现象,获得注塑速度、模具温度和熔体温度对不同厚度制品充填性能的影响,并对成型过程中出现的流动不平衡现象及前沿面形状变化的机理进行了分析。结果表明,型腔充填率随着注塑速度、模具温度、熔体温度的升高而增大,且随着型腔厚度减小,制品实现完整充填越来越困难,工艺操作窗口变窄且注塑速度和模具温度都维持在高水平状态。     

基于超声的注塑成形在线监测技术

目的 在传感器与熔体不接触的条件下获取注射成形过程中熔体流动固化收缩等准确信息。方法 基于超声传感技术,建立适用于塑料注塑成形过程的超声监测系统,通过超声探头采集型腔中某点的超声反射信号强度,结合压力传感器数据与有限元仿真结果对超声信号特征峰值进行分析,并在不同注塑压力、速度、冷却时间等工艺条件下进行多组实验。结果 超声信号特征峰值能够精确感知注射成形过程中熔体流动前沿到达、型腔充填完成、V/P转换、冷却收缩等型腔内实时信息。结论 与压力传感器等技术手段相比,通过超声技术可在与熔体不接触的条件下获取型腔内熔体演变的更多信息。     

A study of fiber orientation in short fiber-reinforced composites with simultaneous mold filling and phase change effects

Most of the properties of injection molded short fiber-reinforced composites are highly dependent on the patterns of their fiber orientation, which are induced by the flow. On the other hand, in most practical injection molding processes, both filling and solidification of the molten suspension takes place simultaneously. This behavior indicates that both filling and phase change for solidification can occur at the same time and therefore affect the flow behavior of the suspension, hence the fiber orientation. The aim of the current work is to present a numerical analysis of fiber orientation prediction in a three-dimensional rectangular cavity considering simultaneous mold filling and phase change of the suspending polymer. To trace the flow front during the filling process, the volume of fluid method (VOF) has been used, while an enthalpy-based approach was used to model the solidification. The standard Hybrid closure model of Advani and Tucker was applied to approximate the evolved fourth order orientation tensor during the fiber orientation calculation. To validate the developed numerical model, the results of the simulation model were compared with available experimental data for the rectangular cavity. The simulation results showed that they are in good agreement with the experimental data. Hence, the numerical model could assist in decisions regarding the design of polymer composite products.     

超声振动对玻纤增强聚丙烯复合材料注射成型特性的影响

为了研究超声振动对纤维增强复合材料注射成型特性的影响,利用自行开发的超声辅助可视化注射成型实验装置对不同玻纤(GF)含量的GF增强聚丙烯(PP)复合材料进行了超声外场作用下的可视化实验,观测分析了超声功率对复合熔体充填流动行为的影响。此外,通过对试样不同部位的金相观察,分析了超声功率对复合材料纤维取向的影响。结果表明:超声功率会对复合材料注射成型的充填流动行为及制品的纤维取向产生影响,而复合材料纤维含量对超声振动的效果也有直接影响。在纤维含量较低时,超声振动对基体材料微观形态的作用为影响复合材料充填流动性及纤维取向的主因;在纤维含量较高时,超声振动对纤维的作用为影响复合材料充填流动性及纤维取向的主因。研究结果为复合材料超声辅助成型技术的发展提供了依据。     

A numerical study of filling process through multilayer preforms in resin injection/compression molding

In resin injection/compression molding (RI/CM), a preform often comprises layers of different fiber reinforcements. Each fiber reinforcement has unique through thickness and in-plane permeabilities as well as compressibility, creating a heterogeneous porous medium in the mold cavity. In the present article, numerical simulation is utilized to investigate the filling process of RI/CM in such a heterogeneous porous medium. The filling stage is simulated in a full three-dimensional space by using control volume/finite element method and based upon an appropriate filling algorithm. The flow in the open gap which may be present in the mold cavity is modeled by Darcy’s law using an equivalent permeability. Numerical simulations of filling process for preforms containing two and three layers of different reinforcements in various stacking sequences are conducted with the aid of computer code developed in this study. Results show that the injection time as well as flow front progression depends on fiber types in the whole preform, fiber stacking sequence and open gap provided in the mold cavity. Simulated results also suggest that the presence of open gap at top of reinforcement can lead to both low injection time and uniform flow pattern.     

Prediction of fiber orientation structure for injection molded short fiber composites

Structure of fiber orientation in injection molded short fiber composites is predicted by the numerical analysis. To analyze the packing stage as well as the filling stage, a compressible generalized Hele-Shaw model is adopted. A numerical scheme free from coordinate transformation is developed for three-dimensional shell-like geometry. Flow-induced fiber orientation can be predicted by solving evolution equations for the orientation tensor with a suitable closure approximation. Fibers are mainly oriented toward the flow direction near the top cavity wall due to high shear rates, while they are randomly oriented near the centerline of cavity where low shear rates prevail. Thus, the molded parts show the skin-core structure of orientation. Structure of fiber orientation continues to change during the packing stage due to additional velocity gradients – which are likely to align fibers more towards the flow direction. Electronic Publication     

剪切场作用下短纤维复合材料纤维取向的耗散粒子动力学研究

为了描述短纤维复合材料注射充模过程的介观结构生成、演化规律,借鉴硬棒模型和粒子模型,建立了一种修正的耗散粒子动力学模型,采用修正的Verlet算法对剪切场作用下短纤维复合材料熔体纤维取向进行研究,模拟结果与实际基本符合.     

注射条件对LCM工艺非饱和流动特性影响

双尺度多孔纤维预制体填充过程中延迟浸润的非饱和流动现象,对基于树脂流过区域为完全饱和区域的充模理论及模拟方法提出了挑战。通过控制体/有限单元（CV/FE）法结合沉浸函数实现了液体模塑成型工艺（LCM）中非饱和填充浸润的数值模拟,并对比了恒压下的实验结果,验证了其可靠性。分析讨论了注射口压力、流量和液体黏度对双尺度多孔纤维织物非饱和填充浸润特性的影响。结果表明:在允许误差内,该数值模拟结果可靠,可用于分析讨论各因素对双尺度多孔织物非饱和流动特性的影响;填充浸润过程中,纤维织物内部非饱和区域长度并非保持不变,而是随着填充浸润的进行经历了4个变化过程;不同注射条件下,压力、流量及黏度对非饱和流动特性影响不同。研究结果对合理控制注射条件及流体特性实现双尺度多孔纤维预制件的完全浸润具有指导意义。      

Analysis of non-isothermal mold filling process in resin transfer molding (RTM) and structural reaction injection molding (SRIM)

In this paper, we present a modeling and numerical simulation of a mold filling process in resin transfer molding/structural reaction injection molding utilizing the homogenization method. Conventionally, most of the mold filling analyses have been based on a macroscopic flow model utilizing Darcy's law. While Darcy's law is successful in describing the averaged flow field within the mold cavity packed with a porous fiber preform, it requires experiments to obtain the permeability tensor and is limited to the case of porous fiber preform-it can not be used to model the resin flow through a double porous fiber preform. In the current approach, the actual flow field is considered, to which the homogenization method is applied to obtain the averaged flow model. The advantages of the current approach are: parameters such as the permeability and effective heat conductivity of the impregnanted fiber preform can be calculated; the actual flow field as well as averaged flow field can be obtained; and the resin flow through a double porous fiber preform can be modelled. In the presentation, we first derive the averaged flow model for the resin flow through a porous fiber preform and compare it with that of other methods. Next, we extend the result to the case of double porous fiber preform. An averaged flow model for the resin flow through a double porous fiber preform is derived, and a simulation program is developed which is capable of predicting the flow pattern and temperature distribution in the mold filling process. Finally, an example of a three dimensional part is provided.     

双尺度纤维织物二维非饱和流动的数值模拟与实验

液体模塑成型工艺(LCM)中非饱和流动的填充模拟对于在虚拟空间中快速、高效地优化工艺参数具有重要意义。采用了一种模拟双尺度纤维织物在等温条件下非饱和流动的双尺度计算模型,通过引入沉浸函数求解宏观-微观流动控制方程组,同时考虑了在微观浸渍中毛细压力的影响,在有限元/控制体积算法中实现了对非饱和流动的数值模拟。随后对三向缝合纤维织物进行了二维径向填充实验,将实验结果与数值模拟的预测值对比。结果表明,该计算模型可以较精确地模拟双尺度纤维织物中的非饱和流动。在此计算模型的基础上,讨论了流体黏度、注射流量及纤维束孔隙率对非饱和填充浸润的影响。结果表明,不同流体黏度、注射流量及纤维束孔隙率对纤维织物填充过程中非饱和区域长度、入口压力曲线及填充时间影响不同。研究结果可以对合理预测纤维织物的浸润及树脂填充过程中入口压力提供指导。