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。     

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...     

基于Moldflow的手电筒注塑模具流动平衡优化设计

以手电筒的前后盖为实例,在分析了注塑过程中的充填时间、注射压力和压力降等影响熔体不平衡性参数的基础上,对手电筒前后盖的双型腔浇注系统进行优化设计。实验结果表明:优化后的浇注系统能够显著改善注塑模具熔体流动的不平衡性。     

注塑成型组合型腔数值模拟与工艺优化

对某游戏机组合装配件进行了结构工艺分析,结合Moldflow最佳浇口位置分析结果,确定了模具浇口位置,设计了浇注系统与冷却系统。建立了模流分析有限元模型,利用Moldflow进行了塑件组合型腔成型过程数值模拟分析。结果表明,组合型腔采用平衡流道系统结构,存在熔体充填不平衡的问题,对成型参数熔体温度、流动速率、保压压力等进行优化,实现了组合型腔的平衡充填。熔体温度为260℃时可以明显降低塑料熔体在型腔中的流动速度,进而优化型腔的平衡充填。并结合试模,获得了合理的注塑成型工艺参数。     

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.     

鼠标的组合型腔浇注系统优化设计

本文将注塑系统平衡的理论和数值模拟技术紧密结合起采，研究鼠标组合型腔的浇注系统。如果熔体不能同时到达各浇口并充满各个型腔，将导致压力分布不均匀，使制品的质量下降，以至于出现充不满等问题，本研究对浇注系统优化，得出了一组最佳的浇注系统方案，从而保证熔体能够基本上在同一时间充满型腔，实现熔体的平衡流动。从分析结果可知，要平衡熔体在组合型腔内的流动，分流道的截面形状和尺寸起到非常大的作用。     

基于Moldflow的香皂盒套件注塑流动平衡优化

针对香皂盒套件注塑模组合型腔熔体流动不平衡的问题,利用Moldflow软件进行注塑数值模拟。从充填时间,速度/压力（V/P）切换点压力,注射位置处压力三方面对初始方案进行分析,确定浇注系统优化指标,采用流道平衡分析自动优化方案的流道尺寸进行优化设计。结果表明,优化后的浇注系统,型腔间的充填时间的不平衡率低于5 %,压力不平衡值小于5 MPa,注射位置处压力曲线能够平稳上升,有效改善了熔体流动不平衡。     

注塑充模过程中温度场的数值分析

采用有限差分法对注塑过程中充填阶段的温度场的数值分析进行了研究,数学模型是基于非牛顿流体在非等温状态下广义Hele-Shaw流动,可预测非牛顿流体在任意形状薄壁型腔内流动时的温度场,对能量方程进行有限差分近似时,能量方程中的瞬态项和热传导项分别采用向后差分和隐式差分,为保证数值计算过程的稳定性,采用上风法处理对流项,还讨论了模温和流率对温度分布的影响。     

塑料玩具组合型腔流动平衡模拟分析

塑料玩具上下盖组合型腔注塑成型过程中,浇注系统的设计影响熔体流动不平衡,需要优化浇注系统。运用Moldflow软件进行浇口位置、填充及流动平衡分析可以优化浇注系统。通过模拟熔体在型腔的流动情况,比较了三种浇口位置的填充结果,初步优化了浇注系统,得到了初步的流动平衡分析结果。以分析结果为基础,调整了浇注系统的设计,比较了三种浇口尺寸的填充及流动平衡分析。结果表明,优化后的浇注系统,型腔间的填充时间不平衡率低于5%,压力不平衡值小于5 MPa,注射位置压力曲线能够稳定上升,有效改善了熔体流动不平衡。     

组合型腔浇注系统的模拟分析及优化设计

对于组合型腔的浇注系统,如果熔体不能同时到达各浇口并充满各个型腔,将导致压力分布不均匀,使制品的质量下降,浇口可能会出现凝固现象而导致后续过程的不能顺利进料,以至于出现充不满等问题。本文将注塑系统平衡的理论和数值模拟技术紧密结合起来,对浇注系统进行优化,得出了一组最佳的浇注系统方案,从而保证熔体能够基本上在同一时间充满型腔,实现熔体的平衡流动。从分析结果可知,要平衡熔体在组合型腔内的流动,分流道的截面形状和尺寸起到非常大的作用。     

New approach to develop a 3D non-isothermal computational framework for injection molding process based on level set method

The simulation of three-dimensional (3D) non-isothermal, non-Newtonian fluid filling process is an extremely difficult task and remains a challenging problem, which includes polymer melt flow with free surface coupled with transient heat transfer. This paper presents a full 3D non-isothermal two-phase flow model to predict the complex flowinmelt filling process,where the Cross-WLFmodel is applied to characterize the rheological behavior of polymer melt. The governing equations are solved using finite volume method with SIMPLEC algorithm on collocated grids and the melt front is accurately captured by a high resolution level set method. A domain extension technique is adopted to dealwith the complex cavities, which greatly reduces the computational burden. To verify the validity of the developed 3D approach, the melts filling processes in two thin rectangular cavities (one of them with a cylindrical insert) are simulated. The predicted melt front interfaces are in good agreement with the experiment and commercial software prediction. For a case with a rather complex cavity, the dynamic filling process in a hemispherical shell is successfully simulated. All of the numerical results show that the developed numerical procedure can provide a reasonable prediction for injection molding process.     

Boundary conditions in the modeling of injection mold-filling of thin cavities

A governing equation for injection mold-filling of thin cavities with a power-law fluid is derived. The interaction between upstream delivery channel flow and cavity flow results in a continuously changing gate condition as the total viscous dissipation of the delivery channel-cavity assembly is minimized. Depending upon the relative magnitude of pressure drops or viscous dissipation across the channel and the cavity, the boundary conditions which determine the cavity filling process will lie between the following two limiting cases: a Cauchy type gate condition such that the location of the melt front is completely determined by the upstream flow; a Cauchy type melt front condition in which the gate condition is controlled by the downstream flow. For most injection molding cases this may be manifested as equilibration of dissipation density on the melt front. Experimentally observed melt front locations from isothermal, Newtonian filling of a constant gap rectangular cavity and of a bi-gap rectangular cavity are reported and the validity of the limiting cases are tested.     

纤维增强塑料的充模流动和纤维取向的耦合仿真模型

分析充模流动、纤维取向耦合仿真的特点,在此基础上提出充模流动、纤维取向耦合仿真模型,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三维纤维取向行为进行统一建模,并且两者相互耦合,在耦合程度上考虑了由于增强纤维存在并且取向引起的熔体流动类型、流变学性质和本构方程的变化.     

Analysis of filling,packing, and cooling stages in injection molding of disk cavities

This research tried to simulate three stages of injection molding cycles (filling, packing, and cooling) for polypropylene. The cavity used was a center-grated disk-shaped mold. During the filling stage, we assumed the polymer fluid obeyed the CEF equation and flowed nonisothermally. The packing stage was represented by isothermal flow of Newtonian fluid, and, during cooling stage, we took into account the effect of pressure drop on the energy balance. By finite difference method, we could solve the partial differential equations numerically. The results showed. (1) Elastic effect was not significant at the filling stage. (2) Pressure buildup in the cavity was very quick at the packing stage. (3) At the cooling stage, temperatures predicted by taking into account pressure drop were lower than those without considering pressure drop. In addition, the influences of mold temperature, flow rate, and inlet melt temperature on the three stages of injection molding process were discussed.     

Three‐dimensional simulation of microchip encapsulation process

A finite element simulation of moving boundaries in a three‐dimensional inertiafree, incompressible flow is presented. A control volume scheme with a fixed finite element mesh is employed to predict fluid front advancement. Fluid front advancement and pressure variation in a flow domain similar to the mold cavity used for microchip encapsulation are predicted. The predicted fluid front advancement and pressure variation are in good agreement with the corresponding experimental results. As the difference in the thicknesses of mold cavities above and below the microchip is changed, the weld line location and pressure variation during mold filling are found to change significantly.     

面向家族制模具多异型腔不平衡充填的快速优化设计

由于家族制模具多异型腔结构的不平衡性,极易在注射成型过程中产生局部充填不满、迟滞效应等缺陷,很大程度上制约着制品的品质。在对塑料熔体流动分析的基础上,发现流道截面半径和长度是影响熔体体积流量和压力分布的重要因素。针对指示灯柱产品多异型腔组合结构的注射成型特征,提出将不同型腔间充填末端的最大平均压力差作为不平衡因子,集成一种基于均匀设计多维结构变量的快速优化机制,结合遗传算法全局优化获得指标最优的流道方案。模拟验证结果表明,结构参数改进后的流道系统充填平衡效果明显优于初始结果。     

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