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。     

聚合物熔体在不同挤出口模内流动的数值模拟研究

构建了3种构型的圆棒挤出口模，采用有限元分析软件POLYFLOW对聚合物熔体在挤出口模中的二维等温流动进行了数值模拟，分析了熔体在不同口模内的速度和压力分布。结果表明，直线形口模在入口处易产生局部环流，而喇叭形和流线形口模可有效消除局部二次流动。在相同条件下，喇叭形口模在出口处存在较大的挤出负压，为-172．9MPa，而流线形口模为-43．72MPa，两者相比，后者压力降低了75％。因此流线形口模在3种几何构型中结构最为合理。     

气辅注射充模流动压力及速度场数值模拟

本文以矩形平板为例,在等温条件下对气辅注塑成型过程中充填区域内熔体流动的速度场和压力场进行了数值模拟,给出了不同时刻熔体内的等压力线和流线图。本文的目的是为了揭示气辅注塑成型过程中熔体的流动过程,以便指导生产     

注塑充模过程平均模腔压力的研究

本文采用有限元法，根据连续性、动量和能量守恒方程，建立数学模型，模拟ＬＤＰＥ在注塑过程中的流动，获得了平均模腔压力和充模时间．模拟结果已由实验值得到证实．从而为研究不同工艺参数条件下模具型腔内的压力变化规律提供了理论依据     

聚合物熔体在异型材三维动态挤出口模内的停留时间分布

利用ANSYS软件对受口模入口处周期性振动的压力驱动的聚合物熔体在“Y”形和“L”形异型材挤出口模内的停留时间分布进行了数值模拟。设熔体流动为三维等温广义牛顿幂律流动，在求得速度场后，应用路线示踪法跟踪流场中任一粒子的流动轨迹，进而求得熔体在口模中的停留时间分布。通过改变振动参数再重复计算，总结出振动参数对停留时间分布的影响规律。结果表明：压力的振动能有效地缩短熔体在口模内的停留时间，振幅和频率越高则停留时间越短，而且在靠近口模流道壁面处停留时间的缩短最明显，表明振动的引入可以降低壁面附近的流动阻力，使截面上的流速更平稳，从而改善挤出制品的表观质量。     

聚氨酯反应注射成型充模流动研究

聚氨酯原料体系反应注射成型（ＲＩＭ）制品在汽车构件、商用机器外壳等制造方面得到越业越广泛的应用，同时ＲＩＭ制品也朝着体积大、注射速度快的方向发展。但目前在模具设计及工艺参数选择中仍采用经验或尝试的方法，耗费大量人力物力。为此，本文对长扁平板模聚氨酯反应注射成型（ＲＩＭ）充模流动过程进行了实验研究并建立了计算模型。得出的压力计算公式与实验结果进行了对比。结果表明在弃模时间ｔｆ远小于凝胶时间ｔｑｍ时充     

注塑充模流动过程灵敏度数值分析

从注塑模充模过程控制方程出发,建立了注塑成型充模过程物理场对设计参数瞬态连续灵敏度分析理论,得到了充模过程压力场、温度场、速度场等物理场对设计参数的灵敏度控制方程.数值分析沿用了注塑模流动分析的基本思想,压力灵敏度采用有限元法、通过对时间和厚度方向的差分求解温度灵敏度,借助于控制体积的概念得到运动边界灵敏度分析.数值算例分析了注射压力对注射流率、熔体温度的设计灵敏度,与数值实验吻合良好.     

塑料注射模微机辅助流动分析系统

在塑料注射模计算机辅助工程(CAE)中,对塑料注射成型充模过程进行计算机辅助流动分析是极其重要的一环。通过分析,可以预测熔体在模腔里的流动情形及压力、温度等的分布情况,优化模具设计方案及工艺参数,从而避免了盲目性。     

中心浇口圆盘模腔正弦脉动充模分析

聚合物动态注射成型通过螺杆的轴向振动实现熔体脉动充模。利用Tanner本构模型建立了中心浇口圆盘模腔正弦脉动充模过程的数学模型,分析了振动参数对注射压力及熔体输送功率的影响。当充模过程的平均注射速率不变时,在一定频率与振幅范围内,模腔入口处的压力随振动源振幅(频率)的增大而增大,但其平均值降低;充模过程中输送熔体所需要的功率降低。     

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。     

A basic experimental study of sandwich injection molding with sequential injection

An experimental study of sandwich injection molding is reported which involves sequential injection of polymer melts with differing melt viscosity into a mold. In isothermal injection molding the relative viscosity of the two melts is the primary variable determining the phase distribution in the mold. Generally the most uniform skin-core structure occurs when the second melt entering the mold has a slightly higher viscosity than the first melt injected. Large viscosity inequalities lead to nonuniform skin thicknesses. The influence of blowing agents and non-uniform temperature fields on the extent of encapsulation is described. Temperature fields are very important especially if the first polymer melt injected has a greater activation energy of viscous flow (or a greater temperature dependence of the viscosity function).     

Throughput calculation with considerations of leakage flow on injection molding plasticizing units

The metering time or melt throughput frequently dictates the cost efficiency of the injection molding process, which means that as accurate as possible an advance calculation must be guaranteed. In the past, leakage flow via the screw flights was neglected in pressure/throughput calculations for plasticizing units on injection molding machines. This paper presents equations for the melt throughput calculation of isothermal/non-isothermal Power Law fluid in multi-zone screws when considering the leakage flow over the screw flights. The concluding comparison of experimental and calculated throughputs shows a good level of agreement.     

塑料注射成型保压过程数学描述

在对塑料注射成型中保压过程进行深入分析的基础上,提出了合理的假设并进行了必要的简化,利用连续介质力学的基本方程导出了可压缩、非牛顿粘性流体在模具型腔中非等温流动的控制方程,选用了恰当的材料性质模型,建立了可对保压过程进行数值模拟的数学模型。     

Effects of oxidative functionalized and aminosilanized carbon nanotubes on the crystallization behaviour of polyamide-6 nanocomposites

The purpose of this study is to investigate effects of oxidative functionalized and aminosilanized carbon nanotubes on the (1) isothermal and (2) non-isothermal crystallization kinetics of polyamide-6 by DSC analyses, and (3) crystal structure of injection molded specimens by XRD analyses. Nanocomposites were compounded by using melt mixing technique via twin screw extrusion. Due to basically very effective heterogeneous nucleation effect, both increasing amount and surface functionalization of carbon nanotubes by oxidation and aminosilanization resulted in higher relative crystallinity for all three cases. The increases were as much as 40 % for the isothermal and non-isothermal crystallization, and it was up to more than two times in the injection molding. Crystallization parameters and Avrami constants indicated that crystallization rate increases in isothermal crystallization while it decreases in non-isothermal crystallization due to the delayed conformational mobility of polymer chains via physical hindrance of carbon nanotubes. Parameters also revealed that growth mechanism of crystallites might change during isothermal crystallization while there was no significant change during non-isothermal crystallization. XRD deconvolution analyses indicated that during injection molding, due to the constraints of carbon nanotubes only α-crystal structure was formed.     

注塑成型保压阶段的分析

本文主要研究二维矩形模腔的非等温、可压缩无定形聚合物的保压阶段。流体是广义牛顿型的，可压缩行为服从Ｔａｉｔ的ｐ—ｖ—Ｔ状态方程。本文在展示保压阶段速度、压力的分布，密度沿着厚度方向的变化的基础上，讨论了保压阶段压力和密度的分布对最终产品的内应力、收缩和翘曲的影响。研究结果表明，保压阶段是注塑成型过程中一个非常复杂的阶段，其压力、温度、速度、密度的变化强烈地依赖于熔体的粘度和模腔的边界条件     

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.     

Primary and secondary crystallization kinetic analysis of nylon 1212

The isothermal and non‐isothermal melt‐crystallization kinetics of nylon 1212 were investigated by differential scanning calorimetry. Primary and secondary crystallization behaviors were analysed based on different approaches. The results obtained suggested that primary crystallization under isothermal conditions involves three‐dimensional spherulite growth initiated by athermal nucleation, while under non‐isothermal conditions, the mechanism of primary crystallization is more complex. Secondary crystallization displays a lower‐dimensional crystal growth, both in the isothermal and non‐isothermal processes. The crystallite morphology of nylon 1212, isothermally crystallized at various temperatures, was observed by polarized optical microscopy. The activation energies of crystallization under isothermal and non‐isothermal conditions were also calculated based on different approaches. Copyright © 2004 Society of Chemical Industry     

Preparation and characterization of biodegradable poly(ϵ‐caprolactone) self‐reinforced composites and their crystallization behavior

Self‐reinforced poly(?‐caprolactone) (PCL) composites were prepared by dispersing a homologous nucleating agent within the PCL matrix through melt mixing. Coalesced PCL, featuring more orderly chain arrangements, acted as the nucleating agent leading to improvement of crystallization for the melt PCL matrix. Non‐isothermal melt crystallization behavior, isothermal melt crystallization kinetics, spherulitic morphology and the crystal structure of neat PCL and the PCL self‐reinforced composites were studied in detail. The results indicated that both non‐isothermal and isothermal melt crystallization of PCL composites were enhanced significantly by the homologous nucleating agent, while the crystallization mechanism and crystal structures remained unchanged. The results of tensile mechanical tests showed that the Young's modulus of the composites was improved by up to 77% with the incorporation of 20 wt% nucleating agent. Biocompatibility tests demonstrated that the cells could adhere to and proliferate well on the surface of the self‐reinforced PCL composites. © 2017 Society of Chemical Industry     

Birefringence prediction of optical media

The flow and thermally induced birefringence of injection‐compression molded optical media such as compact discs and digital video discs is predicted by applying a stress‐optical rule to the flow and thermally induced stresses, which are estimated with a viscoelastic material model integrated into a non‐isothermal compressible flow simulation. The resulting model considers flow and cooling induced molecular orientation, and the transient effect of thermal stress and pressure. Contrary to previous research for polystyrene, the validated results indicate that, for polycarbonate, the magnitude of the thermally induced birefringence is comparable to the flow induced birefringence. Simulation results of the flow and thermally induced in‐plane birefringence for compact‐disc‐recordable moldings with an optical grade of polycarbonate compared well with experimental observations at different mold and melt temperatures. Both simulation and experiments indicate that mold and melt temperatures have a significant effect on the level of birefringence; increasing mold or melt temperature significantly reduces the birefringence. Polym. Eng. Sci. 44:814–824, 2004. © 2004 Society of Plastics Engineers.     

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.