聚苯乙烯制品熔接线区域的双折射行为分析

基于双折射实验原理,利用偏光显微镜,运用"楔形法",测定了聚苯乙烯注塑制品熔接线区域厚度面上双折射行为分布。结果表明:距离嵌件的不同位置处,由于流动行为的差异导致了完全不同的双折射行为,根据应力-光学定律,这种行为也体现了塑料制品的分子取向、残余应力的分布情形。     

注塑成型熔接线截面熔接过程数值模拟

在多浇口和带嵌件注塑制品的成型过程中必然存在熔体的熔接过程,从而形成熔接线。熔接线沿厚度方向的熔接过程是影响该区域的力学强度以及纤维取向等制品性能的重要因素。本文采用有限元法针对注塑制品的典型截面建立数学模型,采用T6P3单元(速度二次插值,压力线性插值),数值模拟了注塑制品熔接线的截面熔接过程。通过等厚度截面和非等厚度截面两个算例,给出了两股熔体熔接过程中的截面速度场和压力场分布。讨论了熔接线区域的壁厚均匀程度对熔接过程的影响。该计算结果可以为制品力学性能以及纤维取向等数值模拟提供数据支持。     

注射成型聚苯乙烯制品双折射的光弹测试与分析

分析了无定形聚合物注射成型双折射行为及其产生机理,利用光弹法测试了不同工艺条件下聚苯乙烯(PS)平面内双折射分布,考察了熔体温度和保压压力变化对制品双折射和流动残余应力的影响。结果表明,PS制品残余双折射值在流动方向上从浇口附近至流动末端逐渐降低,并且最大双折射值随保压压力增加和熔体温度降低而升高;保压压力对浇口附近双折射分布影响明显。根据双折射的光弹测试结果分析了P制品分子取向和流动残余应力的分布趋势。     

注射成型参数对透明制品双折射影响仿真研究

以透明塑料制品的平均双折射为质量目标,利用Moldflow分析计算了不同工艺条件下的制品平均双折射。采用正交实验分析法找出了最佳的成型工艺条件,然后采用单因素分析法仿真研究了显著因素对制品平均双折射的影响规律。实验结果表明,保压时间和熔体温度对制品平均双折射影响最为显著,但二者对平均双折射的影响机理却不一样, 保压时间仅对近浇口区域的双折射值影响显著,熔体温度则对制品整个区域的双折射值有较大影响。     

基于Moldex3D的嵌件注射成型浇注系统优化分析

利用Moldex3D软件中嵌件成型模块对热敏性嵌件成型薄壁制品进行分析,针对不同浇注系统得到充模流动模拟和保压过程模拟结果。通过对成型过程熔体压力场和温度场分布结果、熔体流动前沿温度分布结果的对比分析,结合熔接痕等品质缺陷预测结果,最终得出成型稳定性较优的浇注系统设计方案。     

纤维增强注塑熔接线强度预测模型与实验研究

熔接线是影响注塑制品强度的关键因素之一,而目前以汇合角预测熔接线强度的力学模型并没有体现注塑工艺的影响。为了科学定量地认识熔接线区域强度的变化规律,准确预测熔接线力学性能,首先对带扇形孔的制品进行注塑模拟分析,研究了注塑温度、注射速率以及保压压力对熔接线汇合角的影响,结果显示注塑温度、保压压力不是通过改变熔体前沿汇合角来影响熔接线强度。基于此,为全面体现注塑工艺、汇合角对熔接线强度的影响,在现有模型基础上通过引入注塑工艺影响因子重新构造了体现注塑工艺、汇合角对熔接线区域强度影响的预测模型。设计并制造了用于成型扇形孔制品的注射模具,开展了不同工艺条件下30%长玻纤增强聚丙烯扇形孔制品注塑实验,根据实验结果推导出了体现注塑温度和保压压力影响的注塑工艺影响因子数学表达式,利用实验数据拟合确定了模型中的相关参数,并对模型进行了回归分析。结果表明,新构建的强度预测模型可以准确计算不同注塑温度、保压压力下熔接线不同位置的强度。     

非均匀壁厚塑件的充填不平衡现象

壁厚不均是引起注塑制品缺陷的重要原因之一。为研究壁厚对注塑模内熔体充填平衡性的影响,文章应用可视化实验和数值模拟的方法,以壁厚串联式和壁厚并联式2种结构作为模型,分别对其充填规律进行分析。研究发现:塑件壁厚的不均匀性对注塑流动过程影响很大,不同壁厚区域的熔体会有明显速度差,成型制品易产生熔接线、收缩、应力集中等缺陷。     

聚碳酸酯注射成型分子取向分布的双折射实验研究

运用楔块法研究了聚碳酸酯(PC)注塑平板不同位置处厚度方向上的双折射和分子取向分布,同时考察了注射成型工艺和退火处理对制品双折射分布的影响。结果表明,在制品侧壁处出现沿厚度方向上双折射非对称分布的现象;在靠近冷模壁侧,次表层出现双折射峰值或不连续分布;熔体温度和保压压力对厚度方向双折射影响较大;退火处理几乎不影响双折射和分子取向分布。     

吹塑薄膜用螺旋芯棒机头的设计要点

本文阐述了吹塑薄膜用螺旋芯棒机头设计的主要结构参数:螺旋槽数、芯棒和机头体之间的初始间隙、螺旋槽的螺旋升角等对熔体流动分布均匀性和薄膜厚度均匀性的影响。作者认为螺旋芯棒机头是解决熔接线提高制品质量的较好办法,应推广到管材挤出生产中去。     

注塑零件熔接线缺陷浅析

以塑胶材料熔体的流动理论为基础，结合前辈学者对熔接线的相关研究，运用模流分析工具，对熔接线的形成过程和微观特性进行了阐述，探索了模流分析联合结构分析预测纤维增强塑胶材料的熔接线强度的方法。总结了熔接线缺陷的影响因子和改善措施。     

Effect of process conditions on birefringence development in injection-molded parts. I. Numerical analysis

Analysis of the injection-molding process based on Leonov viscoelastic fluid model has been employed to study the effects of process conditions on the residual stress and birefringence development in injection-molded parts during the entire molding process. An integrated formulation was derived and numerically implemented to solve the nonisothermal, compressible, and viscoelastic nature of polymer melt flow. Simulations under process conditions of different melt temperatures, mold temperatures, filling speeds, and packing pressures are performed to predict the birefringence variation in both gapwise and planar direction. It has been found that melt temperature and the associated frozen layer thickness are the dominant factors that determine the birefringence development within the molded part. For a higher mold temperature, melt temperature, and injection speed, the averaged birefringence along gapwise direction is lower. The birefringence also increases significantly with the increased packing pressure especially along gate area. The simulated results show good consistency with those measured experimentally. © 1995 John Wiley & Sons, Inc.     

工艺参数对注塑件熔接痕性能的影响

概述了注塑件熔接痕的分类及特点；分析了工艺参数主要包括熔体温度、模具温度、充模速度、注射时间、注射压力、保压压力、后处理等对熔接痕的外观及性能的影响。着重阐述了各工艺参数对熔接痕性能影响的研究进展；综述了优化工艺参数和研究工艺参数对熔接痕影响程度的研究以及数值模拟技术，并从工艺方面提出了减小熔接痕损害的方法。     

The unique flow of polypropylene at the weld line behind an obstacle in injection molding

In this article, a weld line placed behind an obstacle in an injection‐molded plaque made of metallic mold‐in‐color polypropylene (PP) was investigated. A broad uneven glossy section was visually observed along the weld line after the v‐notch weld disappeared. Although disk‐shaped metallic pigments were oriented parallel to the wall according to laminar flow, the pigment particles at the weld behind the obstacle were ordered vertically at the center of the depth direction. In PP molded without pigment, a black line was observed at the same position in the metallic weld. Based on a measurement of the crystal structure, the black line was caused by the rapid cooling of molten PP. Elongational flow occurred along the weld line after the diminishing v‐notch weld. The unique flow ordered the pigments obliquely at the advancing flow front and disturbed the subsequent flow of hot PP which transferred heat to the crystallizing mass. POLYM. ENG. SCI., 2011. © 2010 Society of Plastics Engineers     

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。     

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.     

Uni‐ and biaxial impact behavior of double‐gated nanoclay‐reinforced polypropylene injection moldings

Polypopylene/nanoclay three‐dimensional parts were produced without intermediate steps by direct injection molding to explore the influence of flow features and nanoclay incorporation in their impact performance. The nanocomposite was obtained by direct compounding of commercial PP with nanoclay masterbatch. The as‐molded morphology was analyzed by X‐ray and TEM analyses in terms of skin‐core structure and nanoclay particle dispersion. The nanoclay particles induced the reduction of β‐form spherulites, a known toughener. The impact behavior was assessed in tensile and biaxial modes. The PP nanocomposite molding toughness was practically unaffected by the processing melt temperature and flow rate. Conversely the nanoclay presence is influent in the impact performance. Under biaxial stress impact, the regions close to weld lines are tougher than the bulk and the fracture develops with main crack paths along the flow direction and the weld line. Cracking along the weld line results from less macromolecular interpenetration and chain entanglement, and unfavorable nanoparticle orientation. It seems that a failure mechanism which involves nanoclay delamination and multiple matrix crazing explains the toughening of PP in the directions where the nanoparticle orientation with respect to loading is adequate. POLYM. ENG. SCI. 2013. © 2012 Society of Plastics Engineers     

Visualization of the flow history contours at the cross-section of a weld-line in an injected molded part

This article presents visualization of flow history contours at the cross-section of an injection molded part along the weld-line originated by an obstacle pin in a plate-shaped cavity. The visualized flow history contours unveiled the interface of the two adjacent flows through which the penetration of one flow front to the other at the interface was observed. The penetration which was the most at the core of the part behind the obstacle pin was inferred to be originated from an eccentricity in the position of the obstacle pin. Applying image processing techniques, a sequence of the variation in the shape of the interface along the weld-line was extracted from which the amount of penetration at different distances behind the obstacle was measured. Experimental results revealed an oscillation in the direction of the penetration along the weld-line at the core of the part. A scanning electron microscope micrography was also applied to characterize the V-notch along the weld-line at the surface of the molded part. V-notch characterization was used to investigate the possible correlation between the internal and external behaviors of the molten plastic during weld-line formation by which an obstruction affected zone at the weld-line area behind the obstacle pin was distinguished. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

纤维增强PA66注塑熔接线拉伸性能的研究

通过对相同工艺条件下PA66(Zytel 70G33L)熔体绕过不同障碍物数值和实验研究，发现决定熔接线强度的主要因素是两股熔体相遇时的熔接角，熔接线强度会随着熔接角的增大而加强。而通过对不同成型温度条件下熔接线试样的拉伸实验研究，发现随着熔体温度的升高，有或无熔接线的试样拉伸强度都会随着温度的升高而升高，但变化的程度不同。     

Joining laser-sintered with injection-molded parts made of PA12 using infrared welding

Laser-sintering offers the possibility to produce complex and individualized components cost-effectively. To fully exploit the advantages of laser-sintering in assemblies with mass-produced components, high-performance joining processes like welding are necessary. Thus, a cost-effective customization of products can be enabled, which allows to follow the increasing trend of individualization. Infrared welding, in particular, can also be suitable for complex laser-sintered parts due to the reduced transverse forces during joining, compared to other welding processes. The investigations show that high strength between PA12 laser-sintered and injection-molded components can be achieved by infrared welding. The bond strength is mainly influenced by the welding parameters. Especially a low weld pressure leads to high achievable strengths and failure outside the weld seam. Joints between laser-sintered parts and glass fiber reinforced injection-molded components demonstrate the transferability of the obtained knowledge. The residual melt layer thickness of the joint decreases with increasing weld pressure, as the morphological characterization shows. Besides, the typical morphological seam structure can be seen on the side of the injection-molded component. In the area of the laser-sintered components, a deviating morphological structure can be observed. Distinctive flow lines can be observed, spherulitic structures can only partially be seen as well as deformed spherulites.