气辅注射成型中气体穿透下的聚合物熔体壁厚的形成

针对气辅注射成型模壁表层熔体形成的复杂过程，对薄壁气辅注塑件在气体沿圆形截面气道进行气体穿透推进的充模过程进行了研究分析，通过引入合理的简化和假设，建立了描述气体穿透下模壁表层熔体厚度比β计算的数学模型和近似计算公式。在此基础上，进一步提出了三维薄壁气辅注塑件在气辅注射成型中气体穿透并推动熔体向前充模流动发展变化的熔体／气体前沿处理的程序算法，并用实例进行了数值模拟。研究结果表明，当气体前沿与熔体前沿的压力梯度之比值m在1．0—1．3范围内时，其β的计算结果为0．20—0．43，接近国外学者的实验到定值0．23—0．40，也比较符合实际的气辅注射成型工艺结果。     

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。     

立式离心场下钛合金熔体充填过程数值模拟

本文通过数值模拟方式研究了不同铸造工艺参数对立式离心场下钛合金熔体充填过程的影响,数值模拟结果显示铸型旋转方向直接影响合金熔体的充填顺序,进而影响其凝固顺序及缺陷形成.在给定的转速范围内,钛合金熔体的充填时间随铸型转速的增加而减小,因此,转速的增加有利于加快合金熔体充填速度,使合金熔体在较短的时间内迅速充填型腔.同时熔体的过热度及铸型温度的增加有利于合金熔体的快速充填.     

降低SiCp／Al气孔率的研究EI

分析了ＳｉＣｐ／Ａｌ复合材料中气体的来源。通过理论模型和实验分析，发现颗粒带入熔体中的气体是复合铸造法制备的ＳｉＣｐ／Ａｌ复合材料中气孔的主要来源。颗粒带入的气体可分为ＧⅠ和ＧⅡ两种类型。降低ＳｉＣｐ／Ａｌ的气孔率应从根本上杜绝气体的来源着手，特别应对颗粒带入的气体引起重视。稀释中间复合材料法正是根据这一思路设计的制备ＳｉＣｐ／Ａｌ的新的工艺方法。实验结果表明，利用该工艺制备的ＳｉＣｐ／Ａｌ复合材料的气孔率明显降低。     

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。     

注射模具中的排气结构设计

塑料熔体在充填模具型腔过程中,除了流道、型腔内原有的空气外,还有塑料受热、摩擦及凝固而产生的微量气体,这些气体必须及时排出模具型腔外,否则气体遗留在型腔会导致塑胶制品熔接不良等多种缺陷。本文主要介绍了注射模具中排气槽的设计,以及几种切实可行的排气方法和模具结构。     

纵向超声波辅助微注塑方法

微注塑过程中，聚合物熔体在微小腔体中流动时充模阻力比常规注塑大，这影响了熔体填充效果，同时热量损失的不均衡性和不确定性容易导致注塑精度不高．提出了纵向超声波辅助微注塑方法，并对超声波振动对聚合物熔体的作用机理进行了探讨，分析了超声换能器结构对应力、振幅和响应频率的影响．基于对微注塑过程的模拟结果，开发了纵向超声波辅助微注塑装置．通过在微注塑过程中纵向超声波对熔体的能量作用降低熔体黏度，改善了熔体流动和充填性能．为了验证超声波辅助微注塑的效果，进行了菲涅尔透镜实际注塑实验．实验结果表明，相同的注塑工艺条件下，超声辅助微注塑过程中聚合物熔体的充填性能提高了6．91％．     

共注塑制品芯层熔体的注射温度对制品质量的影响

在共注塑成型中,是否出现前沿突破现象和芯／壳层材料的分布情况是衡量制品质量的主要指标。在成型过程中芯层熔体的注射速度是影响材料充填和最终分布的主要因素。本文采用MPI软件Moidflow进行共注射模拟分析,研究不同的芯层熔体的注射温度对前沿突破现象和芯层材料的分布情况的影响。     

基于数值模拟的注塑模熔体前沿速度优化

在注塑成型的过程中,非均匀的熔体前沿充填速度将导致非一致的取向,以及非均匀收缩和翘曲变形,理想的充填模式应尽可能使熔体在充填过程中保持熔体前沿速度为常数.文中将数值模拟技术与遗传算法相结合用于注塑成型熔体前沿速度的优化,确定螺杆行程中的最佳分段控制点,以及控制点处的注射体积流率或螺杆速度的最优值以获得均匀一致的熔体前沿速度.数值分析采用广义的Hele-Shaw流动模型,耦合利用有限元/有限差分来求解控制方程,并利用控制体积概念实现熔体前沿的自动更替和推进.算例表明,优化的工艺条件设置可以使熔体前沿速度的均匀性提高50%左右.     

短纤维增强塑料注射成型中三维纤维取向的数值预测

在建立聚合物熔体在型腔中充填流动以及短纤维取向的数学模型的基础上，对平面薄壁型腔内纤维取向的预测算法加以推广，提出适合于具有任意几何形状的三维薄壁型腔内纤维取向的数值预测技术，并且给出一个熔体充填三维薄壁壳体状型腔的算例，预测的结果与由流动引起的纤维取向定性规律相符合。     

玻纤增强HDPE气体辅助注射成型制品的形态

采用气体辅助注射成型(GAIM)和普通注射成型(CIM)制备了玻纤(GF)增强高密度聚乙烯(HDPE)复合材料。通过扫描电镜对复合材料中的玻纤取向进行了研究,发现CIM试样的玻纤仅在表层有轻微取向,而GAIM试样在整个横截面上玻纤均发生了明显的取向,且在次表层处取向强烈,排列十分规整。在此前研究工作的基础上,进一步探讨了玻纤取向结构的形成机理。     

Flow-induced fiber orientation in gas-assisted injection molded part

Polyamide 66 with 33 wt.% glass fiber (DuPont, Zytel 70G33) was molded by gas-assisted injection molding (GAIM). Scanning electron microscope (SEM) micrographs indicated that fibers orientated notably in the core layer and slightly in the region near the mold wall, but aligned disorderly in the region near the gas channel. However, fibers orientated remarkably in the center of the thickness of the GAIM part, which was greatly different from the fiber orientation behavior in the samples molded by the conventional injection molding (CIM) and the water-assisted injection molding (WAIM) as reported in the literatures. Combining with a previous simulation dealing with gas penetration, the mechanisms for fiber orientation in the GAIM part are also discussed.     

气体辅助注塑成型制件开发工艺研究

对塑料家俱制件进行了气辅注塑工艺开发与研究,考察了塑料转奇扶手的气辅加工中气嘴位置,熔体注入量,熔体注射温度,延迟时间、气休注射压力等对充模过程的影响,应用气辅注射模拟软件Ｃ－Ｍｏｌｄ对该制件的气辅助才不同工艺条件对气辅制件的影响做了模拟,并和生产实际进行了比较。     

气体辅助注射成型PC/PE共混物的形态

通过扫描电镜(SEM)对气体辅助注射成型(GA IM)PC/PE共混物制品相形态的观察,发现作为分散相PC的形变规律与在常规注射成型(C IM)制品中的情况有很大差异。在形态分析的基础上,探讨了气体穿透对气体辅助注射成型制品形态的形成和形态分布影响的机理。     

Heating/cooling channels design for an automotive interior part and its evaluation in rapid heat cycle molding

Rapid heat cycle molding (RHCM) is a recently developed innovative injection molding technology. Rapid heating and cooling of the injection mold is the most crucial technique in RHCM because it not only has a significant effect on part quality but also has direct influence on productivity and cost-efficiency. Accordingly, Heating and cooling system design plays a very important role in RHCM mold design. This study focuses on the heating/cooling system design for a three-dimensional complex-shaped automotive interior part. Heat transfer simulation based on finite element analysis (FEA) was conducted to evaluate the thermal response of the injection mold and thereby improve heating/cooling channels design. Baffles were introduced for heating/cooling channels to improve heating/cooling efficiency and uniformity of the mold. A series of thermal response experiments based on full factorial experimental design were conducted to verify the effectiveness of the improved heating/cooling channels design with baffles. A mathematical model was developed by regression analysis to predict the thermal response of the injection mold. The effects of the cavity surface temperature on weld mark and surface gloss of the part were investigated by experiments. The results show that the developed baffle-based heating/cooling channels can greatly improve thermal response efficiency and uniformity of the mold. The developed mathematical model supplies an efficient approach for precise predication of mold thermal response. As the cavity surface temperature raises to a high enough level, automotive interior parts with high gloss and non-weld mark surface can be obtained.     

Visualization of counter pressure mechanism in gas-assisted injection molding process

Abstract

Gas-assisted injection molding (GAIM) refers to injecting gas into the short shot melt during the filling stage. Compressed gas is used as the medium to push the melt and to provide the packing pressure. In GAIM, the hollow area and penetration length are the main factors that will affect the quality of molded parts. This study has applied a Gas Counter Pressure (GCP) mechanism and has discussed the effect of GCP in the GAIM process with in-mold visualization of this complex molding flow. This study introduces a counter pressure mechanism in a thick paper-clip-shaped cavity design. The flow field under different counter pressure conditions is observed by high-speed photography, the fiber orientations are analyzed with SEM, and the affected penetration length and hollow area are measured relatively. The experimental results show that when the GCP is applied to GAIM, although the hollow area is reduced, the penetration length will be increased, so as to make the quality of molded part more uniform and reduce the shrinkage. And a quantitative measuring method of two-stage penetration time span is proposed to get more in-depth discussion about the interactions between GCP and GAIM.     

The role of gas penetration on morphological formation of polycarbonate/polyethylene blend molded by gas-assisted injection molding

Polycarbonate (PC)/polyethylene (PE) blend was molded respectively by short shot (SS) and gas-assisted injection molding (GAIM). In order to investigate the origin of the “skin-core” structure during GAIM process, the morphology of the two parts molded by SS and GAIM, far from skin, was studied. The results indicate that the structure of the SS part (SSP) is similar to that molded by conventional injection molding (CIM), while the structure of the GAIM part (GAIMP) shows an unusual gradient structure. Many coarse, short PC fibrils arise in sub skin, while such fibrils become more well-defined and reduce in number towards core layer. And the PC phase at the non-gate end, experiences more severe deformation than that at the gate end, which is also different from that in CIM parts. In addition, Moldflow 5.1, a commercial simulation package, was employed to determine the flow behaviors during SS and gas penetration processes. The experimental and simulated results indicate that shear rate and cooling rate are significant for the gradient structure formation during GAIM.     

气体辅助注射成型聚丙烯的多层次结构

用扫描电镜(SEM)观察了气体辅助注射成型(GAIM)和常规注射成型(CIM)等规聚丙烯(iPP)在不同部位的结晶形态。发现CIM试样的"皮-芯"结构不明显,而GAIM试样在不同部位则形成了包括球晶、串晶和取向片晶,进而表现出明显的多层次结构。在结晶形态分析的基础上,初步探讨了GAIM制品多层次结构的形成机理。     

Parameter identification and computational simulation of polyurethane foaming process by finite pointset method

Numerical simulation of the polyurethane foaming process is a valuable method to analyze the molding process at an early stage of product development to shorten time-to-market cycles and cut costs by using fewer prototypes. However, this process involves highly coupled thermo-chemo-rheological modeling and needs adequate model parameters’ identification. A theoretical model including chemical reactions and thermo-rheological coupling of conservation equations was developed. Based on the theoretical model, three-dimensional numerical simulation for mold filling of the polyurethane foam was carried out by using Finite Pointset Method (FPM) to predict flow field, flow front advancement, temperature and density distributions during mold filling. A FOAMAT system was used to monitor foam height rise and reaction temperature on a cylindrical test tube and foam viscosity was measured by using a dynamic rotational rheometer with parallel-plate system. The parameters of the model were identified by an inverse analysis method which consists in determining the parameters by comparing the computed quantities to those measured experimentally. The overall modeling was validated by using short shot foams obtained with a panel mold cavity. Mold filling of an automotive underlay carpet cavity was investigated numerically. Flow front results were successfully compared to short shot foams obtained with the industrial mold cavity.