材料流变性能对注塑制品熔接痕的影响

介绍注塑制品熔接痕的分类及其形成,分析材料的流变性能对注塑制品熔接痕外观及性能的影响,着重阐述通过调整注塑工艺参数以改变材料的流变性能,从而改善熔接痕对注塑制品外观及性能的影响,并综合提出减小熔接痕损害的措施与方法。     

热流道顺序浇注成型移除熔接痕研究

为了有效移除注塑制品中的熔接痕,深入分析了熔接痕的形成过程和采用热流道顺序浇注成型移除熔接痕的机理,并使用模流分析软件Moldflow对顺序浇注成型移除熔接痕的过程进行了有限元模拟。模拟分析结果表明,随着阀浇口不同的开闭时机,顺序浇注成型可以有效地控制熔接痕的位置及长度,改善熔接区域的外观和性能,有效避免熔接痕的产生。实验表明,采用顺序浇注成型时制品的熔接痕已基本消除.     

注塑件熔接痕位置预测技术的研究进展

介绍了注塑件充填过程熔接痕形成的数学模型,综述了数值模拟技术、数值模拟技术结合数学规划理论、阀式浇注塑大型注塑成型制品多浇口进料顺序控制技术等3种注塑件熔接痕位置预测、优化和控制方法,介绍了该技术的分析流程、预测方法及国内外的研究进展和应用实例,熔接痕控制技术,尤其是熔接痕消除技术的完善是今后熔接痕研究的一个重要方向。     

快速变模温注塑成型制品的熔接痕显微分析

熔接痕是注塑制品常见缺陷之一,快速变模温技术(RHCM)可改善甚至消除熔接痕。制备不同模具加热温度条件下快速变模温注塑成型制品,采用激光显微镜进行注塑制品熔接痕区域的三维立体观察,并测量熔接痕的宽度和深度尺寸,同时用扫描电子显微镜观察熔接痕所在区域的微观形态,研究模具加热温度对制品熔接痕的影响。结果表明:激光显微镜测量熔接痕尺寸是定量研究熔接痕的有效手段之一,快速变模温技术可显著改善熔接痕质量。     

隔热涂层对注塑制品熔接痕的改善机理研究

将隔热涂层与常规注塑工艺相结合,探究不同厚度涂层对玻纤增强注塑制品熔接痕的影响。研究结果表明:随着涂层厚度的增加,玻纤增强注塑制品熔接痕表面V型槽的深度不断减小,熔接痕处断面纤维取向逐渐趋于一致,界面缠结程度加深,熔接痕的拉伸性能不断增强。当涂层厚度为125μm时,相比于无涂层下成型的玻纤增强注塑制品,熔接痕的深度减少了77.9%,拉伸性能增加了80.9%,有效改善了玻纤增强注塑制品的熔接痕性能。     

依赖EBF神经网络的注塑成型熔接痕长度优化

分析了注塑成型中熔接痕形成原因,分析了浇口位置对形成熔接痕的影响,提出了依赖椭球基函数(EBF)神经网络的注塑成型熔接痕长度优化。通过将EBF神经网络作为注塑成型熔接痕条件,根据注塑成型熔接痕依次构建得到注塑成型熔接痕长度函数与注塑成型熔接痕适应度函数,并以这二个函数作为优化目标。在实现注塑成型熔接痕的基础上,选择李雅普诺夫第二方法来验证EBF神经网络具有稳定解。最后通过仿真结果表明:该算法能够均衡注塑成型熔体长度,提高注塑成型熔接痕长度优化实用性。     

大型注塑制品熔接痕分析及解决对策

在研究大型注塑制品熔接痕形成条件的基础上,从塑料制品材料及其产品结构,模具设计与成型工艺等各环节,分析了影响制品熔接痕的因素,建立熔接痕的数学模型；分析了熔接痕CAE的特点及误差,并针对不同影响因素,给出了相应控制对策。     

轿车保险杠顺序注射成型CAE分析

采用Moldflow软件对轿车后保险杠三点进浇顺序注射成型的过程进行模拟.为了分析阀浇口不同的延迟开启时间对熔接痕形成的影响,进行了两组仿真实验.结果表明,阀浇口不同的延迟开启时间可以对熔接痕的形成施行动态控制,从而影响熔接痕形成的时间、压力及熔体前沿温度的变化,这样有利于降低注塑压力、消除熔接痕或把熔接痕控制在不影响其外观质量的位置,获得最佳制品质量.     

Moldflow在熔接痕分析中的应用

熔接痕是注塑制品中常见的缺陷之一。通过分析熔接痕的形成机理及产生原因,指出MoldFlow中与熔接痕有关的分析结果及相应的评价标准,进行案例分析,为熔接痕问题提供了一套标准化解决方案,具有较强的应用价值。     

CAE技术在数码相机注塑模中的应用

以数码相机的外壳为例,通过比较分析结果来确定制品注塑成型中的浇口位置和数量,并对浇注系统进行了优化,选择出填充均匀、熔接痕不明显和气穴位置集中的成型方案．为探讨注塑成型应用CAE的方法提供借鉴。     

Effect of process conditions on the weld‐line strength and microstructure of microcellular injection molded parts

This study was aimed at understanding how the process conditions affect the weld‐line strength and microstructure of injection molded microcellular parts. A design of experiments (DOE) was performed and polycarbonate tensile test specimens were produced for tensile tests and microscopic analysis. Injection molding trials were performed by systematically adjusting four process parameters (i.e., melt temperature, shot size, supercritical fluid (SCF) level, and injection speed). For comparison, conventional solid specimens were also produced. The tensile strength was measured at the weld line and away from the weld line. The weld‐line strength of injecton molded microcellular parts was lower than that of its solid counterparts. It increased with increasing shot size, melt temperature, and injection speed, and was weakly dependent on the supercritical fluid level. The microstructure of the molded specimens at various cross sections were examined using scanning electron microscope (SEM) and a light microscope to study the variation of cell size and density with different process conditions.     

注塑件成型缺陷分析与解决方案

针对耳罩圈注塑件填充不足和熔接痕的缺陷问题,本文从注塑模具浇注系统分析入手,找出存在的问题,制订出改正措施,并最终解决了这些缺陷问题;在针对使用一模六腔模具成型的护盖注塑件存在缩痕缺陷的问题,通过采用了控制流入模具型腔熔体量平衡的方法,最终达到了消除注塑件缺陷的目的;针对薄壁壳体注塑件变形等缺陷的问题,则采用了脱件板方...     

Untersuchung zur Vorhersage der Bindenahtfestigkeit in spritzgegossenen Formteilen

Weld lines in injection molded parts are often weak spots and should therefore be taken into account as early as possible when developing new parts. The influence of material, nozzle and mold temperature respectively injection speed on weld line strength was investigated. By obtaining the actual temperature in the weld line, the interrelated processing influences can be expressed by a common relation. Physical analysis shows that this is the molecular mobility, which in turn is dependent on temperature. It opens a route backed by experimental results to assess the weld line strength of different materials in dependence of the processing parameters.     

工艺参数对熔接线注塑件应力的影响分析

本文利用有限元方法,将Moldflow软件分析的注射成型结果导入到Ansys软件进行结构力学分析,发现注塑件在外载荷和边界条件等均相同的条件下,随模具温度、保压时间和保压压力的增加最大von Mises应力下降,且幅度各不相同;而随着熔体温度的增加,最大von Mises应力也增加;同时,熔接线使注塑件的von Mises应力明显高于同等条件下没有熔接线的注塑件,而且熔接线还影响工艺参数对注塑件最大von Mises应力的变化规律。     

Evaluation of healing models to predict the weld line strength of the amorphous thermoplastic polystyrene by injection molding simulation

In many injection molded parts weld lines are often unavoidable. These cause optical defects and a reduction of the mechanical properties of the part. Therefore, the predictability of the weld line strength at an early stage of development would provide a significant advantage by avoiding costly iterations of the mold and increases the understanding of the correlation between process history of the melt and weld line strength. For this purpose, a calculation routine has been developed to predict the weld line strength based on injection molding simulation. Different models to calculate the healing of a weld line are compared and analyzed. By adding a factor to consider the shear rate in addition to the temperature and the pressure and after calibration to one design of experiment setting of the experimental data, the prediction of the weld line strength shows good agreement for all examined process setpoints of the experimental data for polystyrene.     

Effect of supercritical nitrogen content on the weld lines and mechanical properties of microcellular injection molded double gate PP/Al parts

Injection molding products made of aluminum flakes and polymer blends exhibit a distinctive esthetic effect. However, during the filling process, the melt flows in different directions converge and collide, resulting in the flop effect of the aluminum flake and consequent weld line formation. Herein, microcellular injection molding (MIM) was employed to fabricate polypropylene/aluminum flakes (PP/Al) composite foamed parts with distinct weld lines using supercritical nitrogen (scN₂) as the physical blowing agent. The scN₂ content has a significant effect on cell diameter and cell density. When the scN₂ content was 0.6%, the weld line width of the foamed part was 13.03 μm, while it was 30.41 μm for the solid counterpart due to the expansion and rupture of cells in the flow front during filling. Moreover, the orientation of Al flakes was mostly along the flow direction for the foamed parts, while it was generally aligned perpendicular to the flow direction for solid parts in the weld line region. In addition, the flexural modulus of foamed parts was increased by 29% compared with the solid parts, although the tensile strength was reduced by 18% due to the alignment of Al flakes and the stress concentration on the cell walls. Therefore, this work provides insight into the improvement of flexural property and the mitigation of weld lines for injection molded composite parts using MIM.     

Enhancement of weld line mechanical strength using a novel ejector‐pins compression system

This study proposes a novel ejector‐pins compression system (EPCS) to improve the mechanical strength of weld lines that are formed in the injection molding process. Weld lines are significant defects that affect injection molding quality, causing the poor appearance and low mechanical strength of injection‐molded parts. In this experiment, several ejector pins are placed intentionally near the weld lines appearing, and are initially sunken beneath the cavity surface to form a reflow trap such that some of the molten plastics are allowed to flow into it during the filling process. These molten plastics are then compressed by the arisen ejector pins. Accordingly, the compressed molten plastics reflow through the weld lines, disordering the molecular orientation. Experimental verification revealed that the use of an EPCS can efficiently eliminate the orientation of the molecules parallel to the weld line. The specimens' impact strength of using EPCS can increase to between one and two times than that of conventionally injection‐molded. Therefore, this simple and novel method is feasible for greatly improving the mechanical strength of weld lines. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2013     

Weld line morphology of injection molded polypropylene

The weakness of plastics at weld lines provides serious difficulties for the design and long term durability of injection molded parts. The goal of this work was to identify the cause of weld line weakness in polypropylene (PP) systems. The morphology of weld lines in a high molecular weight PP has been studied. It was found that the PP contains a hindered phenolic antioxidant additive that is not soluble in the polymer at the standard processing conditions. Transmission electron microscopy (TEM) pictures reveal the additive existing as a dispersed phase in the bulk polymer. Even though very small concentrations of this additive are normally used, (0.1–0.5%) large quantities were found at weld lines in a band approximately 100 nm wide and penetrating about 10 μm into the surface of the part, hindering strength development at the weld line. X-ray photoelectron spectroscopy (XPS) results confirm enhanced concentrations of antioxidant on the flow front and mold wall surface of short shot samples. The mechanical properties (Izod impact, tensile strength) are measured for samples molded at various processing conditions, varying amounts of antioxidant additive and with and without weld lines. The results are consistent with the presence of the additive playing a key role in strength development at PP weld lines.     

注射成型熔接线区域流动诱导双折射行为

带有熔接线的透明聚苯乙烯平板制品通过带嵌件的模具注射成型,利用光弹测试考察了不同工艺条件下的制品双折射行为,探讨了嵌件造成的相邻熔接线区域熔体流动行为及对制品双折射分布的影响。结果表明,保压压力和熔体温度对制品双折射整体分布影响明显;嵌件后熔接缝区域与制品其他区域的双折射行为有较大差异,其变化与熔体相遇后流动行为和熔接部位分子取向分布有关;制品最大双折射值出现在嵌件后一定距离处。热收缩实验进一步验证了上述结果。