气体辅助注射成型充填过程的数值模拟

描述了气体辅助注射成型的工艺过程及熔体充填和气体穿入的数学模型,采用有限元/有限差分/控制体积法计算充填阶段的压力场和温度场,确定熔体前沿和熔体/气体界面两类移动边界,并对典型制件充模过程进行了模拟.     

气辅注射成型矩形腔中熔体流动的数值模拟

应用Hele-Shaw物理模型和改进的Ｃross流变模型对辅助射成型过程中充填区域内熔体的流动进行数值模拟,采用控制体积法对充模过程中的熔体前沿、熔体－气体边界进行跟踪,运用有限元／有限差分混合数值方法求解气体注射阶段的速度场、压力场、温度场,以图表的形式列举了不同时刻压力场的分布和充模过程中的流线图。在计算过程中,采用压力场和温度场耦合的方法。     

气体辅助注塑在彩电外壳中的应用

研究彩电外壳注塑和气体辅助注塑充模过程的计算机模拟和实际生产。应用动态应力流变仪测试材料流变性质,得到模拟所需n、B、τ、β、T_b等5个参数。考察熔体注射温度、注射时间、入口位置、材料性质对充模过程的影响,得到优化充模结果;还考察了气体辅助注塑过程熔体预注射量、气体注射压力对充模过程的影响。结果表明,气体辅助注塑成型新工艺采用三浇口,熔体适宜预注入量为95％,注射温度230℃,注射时间5s,用幂律指数n较小的聚合物。     

气体辅助注射在彩电外壳中的应用

研究彩电外壳注塑和气体辅助注塑充模过程的计算机模拟和实际生产。应用动态应力流变仪测试材料流变性质,得到模拟所需ｎ,Ｂ,τ、β,Ｔｂ等５个参数。考虑熔体注射温度,注射时间,入口位置,材料性质对充模过程的影响,得到优化充模结果：结果表明,气体辅助注射成型新工艺采用三浇口,熔体适宜预注入量为９５％,注射温度２３０℃,注射时间５ｓ,用幂律指数ｎ较小的聚合物。     

气体辅助注射成型过程的数值模拟技术

本文描述了气体辅助注射成型过程中熔体充填及气体穿入的数学模型，采用有限元／控制体积法计算充填阶段的压力场，确定两类移动边界，熔体前沿和熔体－气体边界。并对典型制件进行模拟验证了模型的可行性。对不同成型参数如熔体充填百分比及气道直径的影响进行了研究，结果表明熔体充填百分比不够，使气体吹入薄壁，较高的充填比又会阻止气体进入气道；较大直径的气道较小直径的气体不易进入薄壁处。     

气辅成型技术简介

气体辅助注射成型，简称气辅成型，是为克服传统注射成型局限性而发展起来的一种新型注射工艺。即对先注射了一定量或全部注满塑料熔体的模具型腔内再注射经压缩后的惰性气体，利用气体推动熔体完成充模填补因塑料收缩后留下的空隙，而在塑件冷却后再将气体排出的连续过程。     

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.     

气体辅助注射成型充模流动CAE技术

在对气体辅助注射成型充填过程进行流动分析的基础上，开发了气体辅助注射成型充模流动ＣＡＥ软件，并给出了典型算例进行验证。     

注塑制品熔接痕的自动识别

通过对注塑模充模过程中熔接痕形成机理的数学分析，给出了一个结合流动模拟数值实现过程的熔接痕自动识别算法，结合计算机图形学知识，利用计算机自动实现了注塑成型中熔接痕的起始、发展和形成。该算法可预测复杂制件的熔接痕位置，并适用于气体辅助注射成型和反应注射成型。最后通过一个算例验证了该算法的实用性。     

气体辅助共注成型流动分析数学模型

根据气体辅助共注成型流动过程的特点，从流体力学基本理论出发，引入合理的假设和简化，建立了描述气体辅助共注成型熔体充模和气体穿透的数学模型。     

基于数值模拟的气体辅助注射成型工艺控制研究

基于广叉Hele-Shaw流动模型描述了气体辅助注射成型时气体的穿透过程。采用有限元／有限差分／控制体积法计算充填阶段的压力场、温度场,确定熔体前沿和气熔界面,并以实际产品为例分析工艺参数对气体辅助注射成型产品质量的影响。     

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     

Variations in surface gloss on parts made by gas assisted injection moulding

Abstract

Gas assisted injection moulding has proved to be a breakthrough in moulding technology for thermoplastic materials. However, there are still unsolved problems that limit the overall success of this technique. The aim of this work was to study the phenomenon of gloss variations occurring across the surfaces of gas assisted injection moulded parts. Experiments were carried out on an 80 t injection moulding machine equipped with a high pressure, nitrogen gas injection unit. The materials used were pigmented acrylonitrile/butadiene/ styrene and polypropylene. A plate cavity with a gas channel across its centre was used to mould the parts. Various processing parameters were varied: melt temperature; mould temperature; melt filling speed; short shot size; gas pressure; and gas injection delay time. After moulding, a glossmeter was used to determine the effects of these processing parameters on the surface gloss profiles of the parts. A roughness meter and scanning electronic microscope were also employed to characterise the surface quality of moulded parts. In addition, a numerical analysis of the filling process was carried out to help better understand the mechanisms responsible for the phenomenon of surface gloss variations. It was found that the surface gloss difference occurs mainly in the transition area between channel and plate in the moulded parts, which might be the result of the shear stress gradient in the polymer melt during the filling process. Surface roughness of moulded parts might also be another factor resulting in the gloss difference problem. PRC/1720     

聚合物气辅共注成型工艺的实验研究

针对气辅共注成型中多相分层流动存在着各分层界面应力间的相互耦合,使得其成型过程具有特殊的流动输运规律和动力学特征,对气辅共注成型工艺进行了系统的实验研究。通过实验研究了熔体注射温度、气体填充量和气体延迟时间3种工艺参数对气辅共注成型的影响规律,并在此基础上通过理论分析揭示了工艺参数对气辅共注成型的影响机理。     

Injection Moulding: Evaluation of Appropriate Melt Injection Points for the Gas Injection Technique

In gas assisted injection moulding the melt front advancement has a considerable effect on the gas penetration. The evaluation of an appropriate melt filling is an important step to avoid instabilities in the process sequence. Taking a sample moulded part a procedure is presented that enables the part designer to evaluate required melt and gas injection points according to the gas injection technique. Using finite element simulations, different calculations for the melt front advancement lead to the correct gate location.

Presentation of different degrees of filling for the optimised article geometry.     

Primary and secondary gas penetration during gas‐assisted injection molding. Part I: Formulation and modeling

A theoretical study has been carried out on the transient gas‐liquid interface development and gas penetration behavior during the cavity filling and gas packing stage in the gas‐assisted injection molding (GAIM) of a tube cavity. A mathematical formulation describing the evolution of the gas/melt interface and the distribution of the residual wall thickness of skin melt along with the advancement of gas/melt front is presented. The physical model is put forward on the basis of Hele‐Shaw approximation and interface kinematics and dynamics. Numerical simulation is implemented on a fixed mesh covering the entire cavity. The model and simulation can deal with both primary and secondary gas penetrations. The predicted and measuredresults are compared in Part II of this study to validate the theoretical model. Polym. Eng. Sci. 44:983–991, 2004. © 2004 Society of Plastics Engineers.     

The influence of processing parameters on fingering formation in fluid‐assisted injection‐molded disks

One of the problems encountered in fluid‐assisted injection‐molded parts is the gas or water “fingering” phenomenon, in which gas (water) bubbles penetrate nonuniformly into the core of the parts and form finger‐shape branches. Severe fingerings can lead to significant reductions in part stiffness. This study investigated the fingering phenomenon in fluid‐assisted injection‐molded disk parts. Experiments were carried out on a reciprocating injection‐molding machine equipped with gas‐ and water‐injection units. The material used was virgin polypropylene. A disk cavity with two different thicknesses was used for all experiments. The effects of various processing parameters on the fingering were examined. It was found that the melt short shot size and mold temperature were the principal parameters affecting the formation of part fingerings. In addition, the formation mechanism of part fingerings has also been proposed to better understand the formation of part fingerings. It has been shown that the fluid‐assisted filling process is an unstable system by nature. Any small perturbation by material viscosity or by temperature gradient can trigger the unbalance of gas (water) penetrations in the parts and result in fingerings. POLYM. ENG. SCI., 2009. © 2009 Society of Plastics Engineers     

工艺参数与气肋设计对气辅注塑成型的影响

主要介绍了欠料注射量、延迟时间、气体注射压力和熔体温度等气辅注塑工艺参数及气肋截面设计对成型的影响,包括对气泡长度、抗弯曲强度、翘曲度和手指效应的影响。截面设计成矩形的制件能获得较好的气辅性能[1]。     

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。