RIM充模过程中流动行为研究

本文采用无化学反应的低粘度流体进行ＲＩＭ充模过程的冷态模拟研究。考察了充模过程中的基本流动行为。对稳定铺展流、失稳流、射流和绕流等各种充模现象进行了描述、分析，并提出了各种流动行为的判别准则。     

反应注射充模特性及模具浇口结构设计

对反应注射充模过程中的铺展流、射流、绕流和气泡等特性进行了分析研究，并讨论了模具浇口结构及位置对充模的影响，给出了影响了设计方法。     

超薄注塑中的局部剪切流及混排导光板设计

针对超薄导光板背光模组注塑中出现"暗痕"缺陷,分析了缺陷成因,剖析了局部剪切流流动特性,发现局部剪切流可以提升熔体剪切速率,降低黏度,增强流动性,特别指出了局部剪切流侧向剪切对熔体黏度的影响不容忽略。对于局部剪切流的良好充模能力及其导致成型缺陷的两面性,在超薄导光板设计中,提出了不同微特征混排设计方案;混排设计方案在充模平面内形成规则局部剪切流,不但增强了熔体充模能力,同时保证了充模前沿的平衡性,避免了成型缺陷。在模拟及成型试验中,印证了混排设计方案的可行性与正确性。     

充模过程的Level Set两相流模拟

采用Level Set两相流方法模拟了熔体充模过程,避免了处理复杂的边界以及用Ghost方法将熔体内的速度值外推到熔体外的情况。分别对型腔水平中面与垂直中面的充模过程进行了模拟。讨论了不同注射速度、不同注射口数量以及不同Reynolds数对充模过程的影响,得出了不同时刻各种情况下熔体界面的位置与充模过程刚结束时型腔内的压力分布,分析了熔体在型腔内运动的不同阶段的特点及形成不同阶段的原因。结果表明,在注射口宽度与型腔宽度相差不大的情况下,如果采用中低速充模,则整个充模运动过程以比较平稳的扩展性运动为主,充模较完全,熔体不发生破裂,制件效果较好。充模速度越大,熔体达到平稳流动的时间越短,充模过程越短。数值模拟结果与实验结果一致,同时表明Level Set两相流方法在求解拓扑性质发生较大变化问题时具有很大的优势。     

充模过程熔接缝形成的数值模拟

本文在分析注塑周期熔接缝形成过程的基础上，在充模阶段，利用前沿区喷泉流动的概念，建立“喷泉遭遇流”的物理模型和数学模型，并运用MAC的数值差分方法模拟了“喷泉遭遇流”的流场。为深入了解注塑充模阶段熔接缝的形成机理提供了理论基础。     

反应注射成型充模过程驻留时间分析

在反应注射成型实际生产过程中，如何选择工艺参数是一个一直使操作者为难的问题。本文利用反应注射成型过程中驻留时间的概念，通过对喷泉流模型进行适当的简化分析，得出在ＲＩＭ充模过程中驻留时间与模腔无量纲纵向ｘ坐标和模腔厚度ｚ坐标之间的关系，并得出最大驻留时间线１＝２ｘ３（１－ｚ２），作出充模过程驻留时间分布曲线。忽略ＲＩＭ充模过程的热传导项，无量纲温度Ｔ与反应进度Φ相同，是流体在模腔内驻留时间线的等值线。将数值计算的反应进度值、温度值与模型计算作比较，基本符合，偏差的出现是由于模型中对前流区的简化处理，恒定粘度假设以及忽略热传导作用。为避免在充模过程中出现过早凝胶现象，在反应进度达到凝胶点时驻留时间不应大于１，这一结论有助于ＲＩＭ加工过程工艺参数的选择     

三维非等温非牛顿流体充模过程的建模与模拟

为了避免使用速度延拓法处理自由表面边界条件,更真实地反映非牛顿熔体的充模过程,耦合Navier-Stokes方程组,建立了三维实体气液两相流模型。采用基于SIMPLE算法的同位网格有限体积法求解流场物理量,并结合Level Set界面追踪技术实现了非等温熔体充模阶段的动态模拟。为防止出现三维情形下棋盘型压力场,利用同位网格动量插值技术,解决压力与速度失耦的问题。分析了充模过程中,流场物理量的变化情况,研究了注射速率、入口温度等对充模过程及熔体凝固层厚度的影响,得出了与实验相吻合的模拟结果。数值结果表明,三维实体气液两相流模型能更准确地描述聚合物熔体的充模过程;当注射速率较大、入口温度较高时,充模时间较短,熔体凝固层的厚度较小。     

皇冠轿车前保险杠注塑模设计和熔体动态充模研究

就日本丰田皇冠轿车前保险杠注塑模的总设计方案及所用原料进行了分析和确定；对型腔压力、熔体温度及动模垫板的形变选用了微机监控；对模具结构，包括浇注系统、成型零件和导向装置、侧向分型抽芯机构、模温控制装置等的设计进行了介绍；对浇注系统的冷热流道及浇口的开设采用Ｃ－ｍｏｌｄ软件进行了熔体充模流动的动态模拟分析。由模拟分析的结果表明，采用计算机Ｃ－ｍｏｌｄ软件对浇口充模进行动态模拟，可直观地了解皇冠前保险杠制品所需充模的最大压力和锁模力的真实情况，并能确知熔融前锋料流速度和熔接痕的牢度，它为指导大型注塑模具浇口的开设和最终尺寸的确定提供了科学依据，有极高的应用和研究价值。     

CAE在彩电后壳浇注系统中的应用

应用美国AC－TECH公司的C－MOLD软件对29寸（74cm)彩电后壳的模具浇注系统进行了计算机辅助工程（CAE）分析。结果表明，采用计算机C－MOLD软件对充模进行动态模拟，可直观地了解彩电后制品所需充模的最大压力和锁模力，并能确定熔融前锋料流速度的分布和熔接痕的位置分布，它为指导大型注塑模具的设计提供了科学依据，有较高的应用和研究价值。     

螺杆轴向振动对圆盘模腔充模功率的影响

探讨注射成型过程中振动力场对圆盘模腔充模过程的影响，建立起数学模型，推导出相应的功率表达式，分析了振动频率和振幅对圆盘模腔充模功率的影响，而且通过实验验证了振动力场的引入使得圆盘模腔充模功率降低。     

A semi-empirical algorithm for flow balancing in multi-cavity transfer molding

Multi-cavity transfer molding is an important process step in several electronic and photonic technologies. In some applications, uniform filling of the cavities of the mold, or mold balancing, is required. A semi-empirical flow model to predict mold filling patterns was developed. The algorithm is a one-dimensional network flow simulation that uses experimental pressure drop data to determine the volumetric flow rate through the gates and runners. A comprehensive experimental program was undertaken to determine these hydraulic resistances for different flow rates and mold geometries. A theoretical treatment is also described to compute hydraulic resistance from gate geometry. Uniform gate resistances provide unbalanced filling and higher velocities in the cavities. Balanced filling can significantly reduce the molding compound velocity and the flow induced stresses, but imperfect balancing compromises the benefits. Experimental filling patterns were obtained for two sets of gates. The agreement between the model and the experiments was satisfactory, and the discrepancies were attributed to correctable phenomena.     

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。     

基于压力梯度的注塑模浇口位置优化算法

给出了判断熔体充模流动是否平衡的判据,并根据熔体充模流动的物理本质,构造了基于压力梯度的搜索方法来优化浇口位置,以实现熔体平衡充填模具型腔的目的。算例表明基于压力梯度的搜索方案简单有效。     

Numerical analysis on reaction injection molding of polyurethane foam by using a finite volume method

Foam reaction injection molding (FRIM) is one of the most popular and useful processes for producing polyurethane foam with a complex geometry. A theoretical model which includes chemical reactions, foaming, and mold filling was developed to analyze FRIM. Energy balance equation was derived by considering polyurethane reaction, water-isocyanate reaction, and evaporation of physical blowing agents. Density and viscosity model was proposed for the bubble suspension, which was assumed to be a homogeneous phase. Based on the theoretical model, three-dimensional numerical simulation for mold filling of the polyurethane foam was carried out to predict flow field, flow front advancement, and density distribution during mold filling. Mold filling of a refrigerator cavity was investigated numerically. The density and thermal conductivity of the foam in the flow front was higher than those in the initially filled region.     

Modeling and simulation of fiber‐reinforced polymer mold‐filling with phase change

A gas‐solid‐liquid three‐phase model for the simulation of fiber‐reinforced composites mold‐filling with phase change is established. The influence of fluid flow on the fibers is described by Newton's law of motion, and the influence of fibers on fluid flow is described by the momentum exchange source term in the model. A revised enthalpy method that can be used for both the melt and air in the mold cavity is proposed to describe the phase change during the mold‐filling. The finite‐volume method on a non‐staggered grid coupled with a level set method for viscoelastic‐Newtonian fluid flow is used to solve the model. The “frozen skin” layers are simulated successfully. Information regarding the fiber transformation and orientation is obtained in the mold‐filling process. The results show that fibers in the cavity are divided into five layers during the mold‐filling process, which is in accordance with experimental studies. Fibers have disturbance on these physical quantities, and the disturbance increases as the slenderness ratio increases. During mold‐filling process with two injection inlets, fiber orientation around the weld line area is in accordance with the experimental results. At the same time, single fiber's trajectory in the cavity, and physical quantities such as velocity, pressure, temperature, and stresses distributions in the cavity at end of mold‐filling process are also obtained. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 42881.     

Some relationships between injection molding conditions and the characteristics of vitrified molded parts

The various mold filling phenomena influencing the characteristics of fabricated parts are surveyed. The phenomena leading to jetting in injection mold filling are considered. These are associated with the magnitude of swell by the melt as it exits the gate into the mold. Special attention is given to the influence of non-isothermal runner flow. A theory of extrudate swell of polymer melts with temperature profiles is developed using Tanner's unconstrained recovery theory. In the. absence of jetting, mold filling by a simple advancing front takes place. The hydrodynamics of the advancing front and the stress fields in the flowing melt are determined. Analysis and modeling are presented based on the use of hydrodynamic lubrication theory involving a solid layer along the mold wall and a hot isothermal melt core. This theory is compared with experimental measurements of pressure losses in mold filling. The development of birefringence in injection molding processes is analyzed. Birefringence distributions are due to frozen-in flow birefringence. A new experimental study is presented and its results compared with theoretical predictions. The problem of thermal stresses in injection molded parts is considered.     

Cavity Pressure Response and Melt Flow Length During Dynamic Injection Molding

Employing a spiral channel mold and a set of cavity pressure measurement equipments from Kistler, the cavity pressure response and the maximum flow length during dynamic injection molding were studied. The processing conditions include injection velocity, injection pressure, mold temperature, vibration frequency, and vibration amplitude. The result shows that the maximum flow length can be improved by the dynamic injection molding. Especially at the lower injection pressure, the maximum flow length can be improved about 15%. From the curves of cavity pressure, we found that the cavity pressure undulated regularly in the dynamic filling phase, which is conduced by the screw vibration. During dynamic injection molding, the viscosity of the polymer flow reduces, and the capability of mold filling improves.     

RTM一维单向流动模型的理论概况及研究

本文研究了牛顿流体在铺置纤维预制件的RTM平板模具中,一维单向恒流和恒压流动的渗流模型.通过求解析解,求出模型的各个可测量物理量之间的关系,对传统的解析方程进行了拓展和改进,提供了在不透明模具中测定渗透率的方法.即在恒流条件下,只需利用压力传感器和恒流泵的读数即可测定预制件的一维渗透率;或者在恒压条件下,利用数字流量计和压力表的读数测得一维渗透率.而这些解析解的关系式也可用于实验预估模具中的压力分布、充模时间等.     

RTM二维径向流动模型的理论概况及研究

综述了牛顿流体在放置了各向同性和各向异性预制件的RTM平板模具中二维径向恒流和恒压渗流的流动模型.对各个模型的可测量物理量之间的关系通过求解其解析解进行了必要的拓展补充推导和研究分析,对传统的二维解析方程进行了拓展和改进,提供了在不透明模具中测定渗透率的方法.即在恒流条件下利用压力传感器和恒流泵测定预制件的二维渗透率;或者在恒压条件下利用数字流量计和压力表测得二维渗透率.这些解析解的关系式也可用于实验预估模具中的压力分布及充模时间等.