Investigations into surface visual quality of gas-assisted injection moulded polypropylene parts

Abstract

Although gas-assisted injection moulding (GAIM) provides many advantages compared with conventional injection moulding (CIM), its applications are limited to surface visual quality studies. In the present study, polypropylene plate parts designed with gas channels having five different types of cross-section but with same cross-sectional area were gas-assisted injection moulded. In addition, various plate thickness parts designed with semicircular gas channels of different radius were also moulded. The surface visual quality of GAIM parts was investigated via gloss and chromatics measurements. The effects of processing parameters and geometrical factors, introduced by part thickness, shape and associated dimensions of gas channels on glossy difference and chromatic aberration of GAIM parts were investigated. The effect on the surface visual quality of gas channel with fillet design and cavity surface with texturing treatment was also examined. It was found that glossy difference is very sensitive to the degree of crystallinity whereas gas channel residual skin melt thickness plays a dominant factor for chromatic aberration. The processing conditions significantly affect surface visual quality. Gas channel design of semicircular cross-section (shape A) provides a better surface visual quality than the other designs. In addition, in order to obtain best surface visual quality, the ratio of equivalent radius to plate thickness should be approximately equal to 2.3. Alternatively, surface visual quality can be improved by texturing treatment on the cavity surface of the core-side. The present study provided part design guidelines for choosing the most effective gas channel design to achieve the best surface visual quality.     

基于正交试验的气体辅助注射成型工艺参数优化

以21英寸彩电前壳为例,将Moldflow 2010作为CAE模拟试验平台,以熔体温度、模具温度、熔体注射时间、气体延迟时间、气体压力为关键工艺因素,考察了气体辅助注射成型时制品的翘曲变形量和气体穿透情况.采用正交试验法及极差分析法对Moldflow模拟试验结果进行分析,确定并验证了较优工艺参数组合的正确性.     

复杂壳体类塑料件气体辅助注射成型工艺参数优化研究

以21英寸彩电前壳作为研究对象,将Moldflow 2010作为CAE模拟试验平台,以熔体温度、模具温度、熔体注射时间、气体延迟时间、气体压力为关键工艺因素,考察了复杂壳体类塑料件气体辅助注射成型(GAIM)时制件的翘曲变形量和气体穿透情况。以正交试验设计方法为基础,利用遗传算法并结合径向基神经网络建立GAIM工艺参数优化系统,可用于工艺参数组合的快速确定,为GAIM过程中工艺参数优化提供了一种新的求解思路。     

气辅注塑CAE技术在彩电前壳模具设计中的应用

利用注塑模CAE技术可在模具制造之前对模具设计方案进行模拟分析,预测潜在的缺陷并及时修改。在彩电前壳气体辅助注射成型(GAIM)注塑模设计中,应用注塑CAE技术对模具浇口设置、气道布置及熔体充填形态进行模拟分析,并对注塑件壁厚进行优化。结果表明,运用CAE技术能够显著提高模具首试和GAIM技术应用的成功率,缩短模具开发周期,节省模具设计和制造成本。     

基于气体穿透效果数值模拟的气体辅助注射成型工艺优化

对气体辅助注射成型工艺进行分析，阐述了气体辅助注射成型的关键技术要求在分析熔料流动、气体穿透物理模型的基础上，探讨了气体辅助注射成型数值分析的实现原理运用MPI／Gas模块对一T型支架进行了气体辅助注射成型CAE分析，模拟不同工艺条件下的气体穿透效果，确定了合理的工艺参数。     

气体辅助注射成型工艺参数优化研究

为了解决气体辅助注射成型(GAIM)中制品所出现的缺陷,采用数值模拟方法对影响制品质量的工艺参数进行了优化研究.首先,建立GAIM过程的数学模型,得出影响GAIM制品质量的主要工艺因素;随后,利用数值模拟法分析熔体预注射量、熔体/气体延迟时间、充气压力与熔体注射温度等关键工艺因素与GAIM制品缺陷的关系;最后,基于数值模拟分析结果,对GAIM制品的工艺参数进行了优化选择与设定.     

气辅注射成型圆管制品中空率

气体辅助注射成型的工艺参数与最后制件的中空程度有直接的关系。采用计算机模拟技术;分析了熔体温度、模具温度、气体延迟时间、预注射量和进气压力对中空率的影响。得到预注射量和进气压力对中空率的变化最为敏感;熔体温度升到一定范围后对中空率没有影响;对于圆管制件;气体延迟时间对中空率影响不明显的结论。     

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.     

Real time diagnostics of gas/water assisted injection moulding using integrated ultrasonic sensors

Abstract

An ultrasound sensor system has been applied to the mould of both the water and gas assisted injection moulding processes. The mould has a cavity wall mounted pressure sensor and instrumentation to monitor the injection moulding machine. Two ultrasound sensors are used to monitor the arrival of the fluid (gas or water) bubble tip through the detection of reflected ultrasound energy from the fluid polymer boundary and the fluid bubble tip velocity through the polymer melt is estimated. The polymer contact with the cavity wall is observed through the reflected ultrasound energy from that boundary. A theoretically based estimation of the residual wall thickness is made using the ultrasound reflection from the fluid (gas or water) polymer boundary while the samples are still inside the mould and a good correlation with a physical measurement is observed.     

气辅成型模具与工艺的优化

运用MoldFlow软件对把手零件的气辅注塑成型过程进行CAE分析,结合气辅成型原理优化了浇口、进气口的位置,总结了气辅CAE的工作流程,分析了各工艺参数对产品壁厚、气道长度的影响,并调整参数,得到了满足设计要求的制品。     

Integrated compounding and injection moulding of short fibre reinforced composites

Abstract

Composites of high density polyethylene (HDPE) and carbon fibre (C fibre) were compounded and moulded into tensile test bars in compounding injection moulding (CIM) equipment that combines a twin-screw extruder and an injection moulding unit. Two HDPE grades exhibiting different rheological behaviours were used as matrices. The mechanical properties of the moulded parts were assessed by both tensile and impact tests. The respective morphologies were characterised by scanning electron microscopy (SEM) and the semicrystalline structures of the matrices investigated by X-ray diffraction. The final fibre length distribution and fibre orientation profiles along the part thickness were also quantified. The composites with lower viscosity exhibit higher stiffness, higher strength and superior impact performance. Both composites exhibit a three layer laminated morphology, featuring two shell zones and a core region. Interfacial interaction is favoured by a lower melt viscosity that enhances the wetting of the fibre surfaces and promotes mechanical interlocking. The composites display a bimodal fibre length distribution that accounts for significant fibre length degradation upon processing. The dimensions of the transversely orientated core differ for the two composites, which is attributed to the dissimilar pseudoplastic behaviour of the two HDPE grades and the different thermal levels of the compounds during injection moulding. Further improvements in mechanical performance are expected through the optimisation of the processing conditions, tailoring of the rheological behaviour of the compound and the use of more adequate mould designs.     

气体辅助注射成型过程中工艺参数对产品质量的影响

以一个管状与平板相结合的气体辅助注射成型制品作为研究对象,引入了正交实验法和CAE技术,首先筛选出了影响制品质量的关键因素,再通过实际的气体辅助注塑成型实验,着重讨论了气体注射延迟时间和气体注射压力两个工艺参数对制品质量的影响,通过调节气体注射延迟时间和气体注射压力两个工艺参数的设置,参考气体穿透的变化情况,均能获得较好气体穿透效果的工艺参数组合.     

Investigations into moulding window of gas assisted injection moulded polystyrene plates with various gas channel designs

Abstract

The design of the gas channel plays an important role in the successful application of gas assisted injection moulding. Although empirical guidelines for gas channel design have been proposed by the various equipment suppliers, quantitative rules based on well designed experiments have not been reported previously. To investigate the effects of geometry on gas penetration for two plate thicknesses, transparent polystyrene (PS) plates designed with semicircular gas channels of differing radii and with rectangular gas channels of differing width to height ratios have been produced using gas assisted injection moulding. Moulding windows and criteria for gas penetration were also chosen so that design rules could be defined quantitatively. The mouldability index was also classified into five levels (excellent, good, fair, poor, and bad) based on the relative areas of the moulding windows. From a plot of mouldability index against R eq , the ratio of equivalent gas channel radius to plate thickness, it was found that to obtain an appropriate moulding window (i.e at least a fair mouldability index) R _eq should be greater than 2. Gas channels with a semicircular cross-section provide better mouldability than those with rectangular cross-sections of the same cross-sectional area. For the same equivalent radius, the ratio of width to height in rectangular gas channels also affects the mouldability index. The present investigation provides part designers with preliminary quantitative design/moulding guidelines for choosing the effective gas channel design that allows the parts to be moulded within an appropriate moulding window, so that the uncertainty in both simulation and process control can be overcome. A methodology for the establishment of guidelines for quantitative design of gas channels is also proposed.     

基于气辅注射成型工艺CAE优化的汽车手柄模具设计

针对塑件壁厚大收缩变形大的成型问题,首先借助计算机辅助工程（CAE）分析确定了塑件的成型方式采用气辅注射成型（GAIM）工艺,经优化后,采用单点侧浇口进行浇注,两点注气口进行注气辅助成型。经注塑参数优化、注气参数优化后,能将塑件的收缩变形能控制在0.3 %~0.42 %之间。基于CAE分析,设计了塑件的一模两腔两次打开气辅成型两板模具,模具中,设置了一种复合式两次抽芯哈弗滑块机构、一种通用型斜导柱哈弗滑块机构来进行侧抽芯脱模。复合式机构中,先通过动模垫板与动模板之间的第一次打开,先实现斜型芯的抽芯,而后再通过定模板与动模板之间的第二次打开,来驱动哈弗滑块体进行侧抽芯。CAE优化分析对气辅注射成型模具结构的设计具有非常重要的指导作用,有利于整体设计效率的提升。     

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     

Investigation of gas-assisted injection molding. Part III: Effect of gas channel design on part bending strength

Numerical simulation and experimental measurements were carried out to investigate the effect of gas channel design on the bending performance of gas-assisted injection molded parts. Plate parts designed with various channel geometries were gas-assisted injection molded. Part flexible strength were measured via bending tests. It was found that part stiffness basically increases linearly with the inertia moment of the plate. The gas channel introduces an additional moment of inertia, the amount of which is determined by the shape and the dimension of the channel section as well as the hollowed core geometry. An analysis algorithm based on DKT/VRT elements superimposed with beam elements representing gas channels of various section geometries was developed to evaluate part bending behavior. An equivalent diameter was assigned to the beam element so that both the original gas channel and the circular beam have the same moment of inertia. The analyzed results from this model of 2 1/2-D characteristics were also verified with both 3-D and 2 1/2-D analyses using ANSYS. The present simulations show reasonable accuracy as compared with experimental measurements and predictions from ANSYS. This investigation also indicates that it may be feasible to use the same CAE finite element model implemented for process simulation of gas-assisted injection when performing part structural analysis as well as warpage calculation, resulting in great computational efficiency for industrial application.     

Hierarchical crystalline structure of HDPE molded by gas-assisted injection molding

To understand the crystalline morphology of the parts molded by gas-assisted injection molding (GAIM), in this work, the hierarchical structures and the crystalline morphology of gas-assisted injection molded high-density polyethylene (HDPE) were investigated. According to the comparison between the results of the GAIM part and those of the conventional injection molded counterpart, it is found that gas penetration can remarkably enhance the shear rate during GAIM process and oriented lamellar structure, shish-kebab structure and common spherulites arise in the skin, subskin and gas channel region, respectively, owing to the different shear rate in these regions. Meanwhile, cooling rate also plays an important role in the formation of the oriented crystalline structure.     

Experimental study of weldline caused by flow lead effect in gas assisted injection moulded parts

Abstract

Gas assisted injection moulding has become one of the most important methods for the manufacture of plastic products. However, there are several unsolved problems that confound the overall success of this technique. The weldline caused by the flow lead effect in the polymer melt is one of them. In this report, an L′18 orthogonal array design based on the Taguchi method has been conducted to investigate the flow lead induced weldlines in gas assisted injection moulded parts. A plate cavity with a gas channel on the side was used for moulding. Experiments were carried out on an 80 t reciprocating screw injection moulding machine equipped with a high pressure gas injection unit. After moulding, the depth of the weldline was measured. For the factors selected in the main experiments, melt injection temperature and mould temperature were found to be the principal factors affecting the weldline depth of gas assisted injection moulded parts. Experimental investigation of a gas assisted injection moulding problem can help in better understanding the weldlines caused by flow lead effects, so that steps can be taken to optimise the surface quality of moulded parts. PRC/1755     

Integrated simulations of structural performance,molding process,and warpage for gas-assisted injection-molded parts. I. Analysis of part structural performance

Whether it is feasible to perform an integrated simulation for structural analysis, process simulation, as well as warpage calculation based on a unified CAE model for gas-assisted injection molding (GAIM) is a great concern. In the present study, numerical algorithms based on the same finite element mesh used for process simulation were developed to simulate the bending performance of gas-assisted injection-molded parts. Polystyrene and nylon plates designed with five different channel geometries were gas-assisted injection-molded. Part flexible strength was measured via bending tests. It was found that part stiffness basically increases linearly with the inertia moment of the plate. Gas channel design results in part structural reinforcement by introducing an additional moment of inertia determined by the shape and the dimension of the channel section as well as the hollowed-core geometry. An analysis algorithm based on VRT/DKT elements superimposed over beam elements representing gas channels of various section geometries was developed to evaluate part bending behavior. An equivalent diameter was assigned to the beam element so that both the original gas channel and the circular beam have the same moment of inertia. The simulated results were also verified with ANSYS 3-D and 2 ½-D analysis. The simulations show reasonable accuracy as compared with measured results and predictions from ANSYS. This investigation indicates that it may be feasible to achieve an integrated simulation for GAIM under one CAE model, resulting in great computational efficiency for industrial application. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 68: 417–428, 1998     

Characteristics of mould separation and its effects on qualities of thin wall injection moulded parts

Abstract

Precision injection moulding of thin walled parts has become an important concern in the computer, communication, and consumer electronics plastics industry. Previous studies in precision injection moulding control focus on the injection screw and the associated operations. In the present study, the influence of relevant parameters including injection speed, melt temperature, mould temperature, filling-packing switchover, and packing pressure on the mould plate separation under different clamping pressure were investigated as part of precision moulding control. A two cavity tensile test specimen mould equipped with four linear variable displacement transducers across the parting surfaces of the mould was used. A computer based monitoring system was built to detect the mould separation signals. Mould separation can also be identified from part weight and thickness variation and exhibits relevant correspondence with them. It was found that owing to the high injection speed required for thin wall moulding, mould separation is not negligible. In all situations, mould separation decreases with increasing clamping pressure. As melttemperature andmouldtemperatureincrease,mouldseparationincreases, resulting in an increase in part weight and thickness. Similarly, when packing pressure and injection speed increase, mould separation also increases. Earlier switchover from filling to packing can decrease mould separation as well as part weight and thickness. Among all the parameters studied, packing pressure exhibits the greatest influence on mould separation and on the associated weight and thickness change. This influence also becomes larger when the moulded part becomes thinner, owing to the larger injection moulding pressure. PRC/1746