注射成型多模腔充填不平衡现象的产生机理（Ⅱ）——模具流道系统中熔体温度分布的研究

介绍了注射成型中集成式热电偶在熔体温度测量中的应用，并分别对流道中温度分布以及多型腔“H”型流道系统中靠近上下型腔的熔体温度进行了测量。实验结果表明剪切生热对流道中熔体温度分布影响显著，熔体经过流道分岔口后温度分布形态以及流动方式不再对称于中轴，最终导致型腔的不均衡充填。温度测量结果同可视化实验结果一起全面揭示了充填不平衡现象的产生机理。     

发泡机头流道内PS/CO2均相体系压力场的模拟

利用有限元软件包Polyflow模拟不同条件下发泡机头流道内PS/CO2熔体的流动,获得了压力,计算出压降速率,并分析熔体温度、CO2含量、机头模口流道直径和质量流率对流道内压力和压降速率的影响。结果表明,在加工条件允许的范围内,降低熔体温度,可以显著提高机头流道中的压力和机头模口流道中的压降速率;当熔体温度一定时,机头流道中的压力和机头模口流道中的压降速率随着CO2含量的增加而降低。尤其当熔体温度为150℃,CO2质量含量由1%增加到2%时,机头模口流道中的压降速率急剧降低;减小机头模口流道直径可有效地提高机头流道内的压力和压降速率。熔体温度175℃,CO2质量含量5%、质量流率1kg/h时,模口直径由1mm减小到0.5mm,机头入口段压力由5.9MPa增大到近30MPa。     

温度和速率对磷酸区域熔融过程的影响

区域熔融法是一种有效的制取高纯物质的方法,可被应用于高纯磷酸制备过程中。为了获得最佳的磷酸净化效果,考察了区域熔融过程中冷凝、加热温度和熔区移动速率对于区熔过程的影响。结果表明:在冷凝温度为5℃,加热温度为65℃时,可以得到合适的熔区大小,且此时形成稳定熔区的时间为33 min。冷凝或加热温度过高,熔区明显变大,凝固界面不稳定;冷凝或加热温度过低,熔区变小甚至无法形成熔区,凝固界面晶体生长呈针状。在考察范围内,随着熔区移动速率的增加,Cr,Ca,Mg,Zn,Al和Fe 6种杂质在区域熔融后的脱除效果有不同程度的降低。当移动速率小于25 mm/h时,6种杂质均具有较好的脱除效果,但是实验需要较长的时间,不利于实际应用;当移动速率高于25 mm/h时,Cr,Ca,Zn脱除效果明显下降。移动速率为25 mm/h是最佳移动速率。     

高密度聚乙烯薄壁件注射成型时的结晶特性研究

用Moldflow MPI5.0软件的Flow 3D模块仿真及同步热分析仪分析的方法,研究了熔体温度及注射速率对薄壁件注射成型时结晶特性的影响。结果表明,熔体温度为175、195、215 ℃时,在厚度为0.8 mm的高密度聚乙烯薄壁件的注射成型过程中,在流动方向上,浇口附近的剪切速率和熔融热焓远大于其他各处,且二者均随着与浇口间距离的增加而迅速降低;从距浇口1.5 mm处到制品末端,剪切速率稳定在2000～4000 s-1之间;从距浇口5 mm处至制品末端,熔融热焓的变化不明显;熔体温度为215 ℃时,制品的熔融热焓最高;随着注射速率的增加,浇口处的最大剪切速率亦增加。     

球形转角形状对于改善微结构塑件填充不平衡的实验研究

在流道分级部位设置直角转角、球形转角改善微注塑件充填不平衡.设计带有直径分别为200μm与300μm微圆柱的孔的1模8腔注塑模具,以高密度聚乙烯(PE-HD)材料进行实验.结果表明,随着注射速率和模具温度的逐渐增加,球形转角对改善填充不平衡优于直角转角;随着微圆柱孔特征尺寸的增大,直角转角与球形转角对填充不平衡的改善均...     

如何解决多模穴医疗产品成型流动不平衡的问题

流动平衡是医疗器材在多模穴成型成功与否的关键,好的流动平衡可以协助提升产品质量并降低差异性。高分子熔胶是一种复杂的流体,其黏度会被剪切率和温度影响,尤其是多模穴成型时,流道里的料温不均,造成模穴间很难达到流动平衡。再者,多模穴中有效保压时间和冷却时间都不尽相同,导致产品尺寸、重量甚至功能产生变异。图1就是一个当熔胶进入次流道时填充不平衡的例子。     

超声波对微流道中聚合物流动性能的影响研究

为了研究超声波作用下的聚合物材料流动性能及其影响因素,利用自主开发的聚合物超声波辅助挤出测试系统,进行了超声波作用下聚合物熔体在微流道管壁的剪切力、剪切速率和表观黏度的测试,并在与传统稳态挤出相比较基础上,分析了超声波对微流道中聚合物熔体流动性能的影响。实验结果表明,引入超声振动后,微流道的入口压力降有明显降低,并且随着熔体剪切速率的增加而增大;超声振动作用下聚合物熔体剪切速率存在临界值,当剪切速率小于临界值时,超声下聚合物黏度小于传统稳态挤出聚合物黏度,反之,超声聚合物黏度大于传统挤出聚合物黏度。     

ABS熔体在微尺度通道中粘性耗散效应的研究

针对微尺度通道中粘性耗散效应对非牛顿聚合物熔体流动特性的影响,采用毛细管流变仪、高精度温度传感器和微尺度口模等组成的粘性耗散测量装置,对非结晶型ABS(Acrylonitrile Butadiene Styrene,ABS)聚合物材料,在不同入口温度和剪切速率下,流经直径分别为350μm和500μm,长径比不同的微通道时的粘性耗散效应,进行了实验测量和数值模拟。结果表明,微通道入口熔体温度一定时,粘性耗散效应引起的出口熔体温升,均随剪切速率的增大而近似线性增加;而剪切速率一定时,微通道的出口熔体温升则随其长径比的增大和入口熔体温度的降低而明显升高。     

对顶式内衬层生产线挤出机机头流道优化分析

采用Ansys-polyflow软件对对顶式内衬层生产线挤出机机头流道流场进行优化分析。机头流道结构直接影响挤出出口断面宽度方向胶料流速、温度、压力和剪切速率分布的均匀性。减小机头流道中部区域的阻尼,可有效解决半成品中间壁厚偏小和两边壁厚偏大的问题;增大机头流道分散角有助于优化胶料流动,有效减小出口断面宽度方向不同部位胶料流速、压力、温度和剪切速率差值。优化设计挤出机机头流道呈鱼尾状,流经流道的胶料呈压缩式层流流动,基本实现了出口断面宽度方向胶料流速、压力、温度和剪切速率分布均匀。     

注射成型充填不平衡分析及流道设计改进

针对注射成型一模多腔充填不平衡问题, 通过简化模型及数值模拟分析,得出由于流道中熔体剪切摩擦产生的黏性耗散热不同,会导致流道中流场分布不同,引起对称型腔不能同时充满。在此基础上,在流道分级部位增加不同几何形状凹槽,改变分流道入口部位熔体温度场。数值模拟结果表明,熔体能够几乎同时充满两个模具型腔,较大程度上改善了一模多腔不平衡现象,提高塑件质量一致性。     

Experimental study on filling imbalance of plastic parts with microcylinders

To examine the microscale filling imbalance in the present work, an eight-cavity injecting mold with microcylindrical-hole arrays fabricated by micro-electrical discharge machining milling technology was developed. Polypropylene (PP) was used to carry out single factor filling flow experiments with vacuuming the mold cavities. The filling height difference of micro cylindrical hole at the same position between cavity I and cavity II, which was the index of filling imbalance and the effect of mold temperature and injection rate on the filling imbalance of microholes with diameters of 200 μm and 300 μm was investigated. The results revealed that the maximum height difference reached 101 μm with low process parameters, and the filling imbalance was obvious. With the increase in mold temperature and injection rate, the filling imbalance was weakened. In addition, the impact of the scale effect on filling imbalance was checked. The filling imbalance of micro holes in 200 μm was greater than that in 300 μm using identical process parameters. With the increase in mold temperature and injection rate, the filling height difference of the two kinds of micro holes decreased. POLYM. ENG. SCI., 60:22–31, 2020. © 2019 Society of Plastics Engineers     

熔体温度对水穿透行为影响的可视化研究

利用水辅助注塑可视化模具和自主研发的注水系统,以聚苯乙烯(PS)为原料,对不同熔体温度下的水辅助熔体流动充模的过程进行了观察,并研究了水的穿透行为。结果表明：熔体温度低,水前缘熔体的惯性力增大,产生"折线"水道,水在后半模腔熔体的穿透中,水前缘速度与水前缘熔体速度相近;熔体黏度高,水前缘速度大于水前缘熔体速度;熔体温度越高,射流穿透的时间越长,水在前半模腔穿透用时越少。     

Experimental and numerical studies of injection molding with microfeatures

Injection molding with microstructures was investigated both experimentally and theoretically. A series of injection molding experiments with PP and PMMA was carried out in a long and a short rectangular mold containing microchannels with the thickness of either 50 or 100 μm and an aspect ratio of 5. The filling lengths in the microchannels were affected by injection speed, mold temperature, and channel location. A high injection speed or high mold temperature resulted in a longer filling length. The filling length in the microchannels decreased as the filling time in the main flow region increased. All filling lengths can be merged into a single curve vs. Fourier number based on the microchannel thickness. Comparison was also made between the experimental measurements and numerical simulation. The mold/melt heat transfer coefficient was found to be a critical factor in determining the filling lengths. The local heat transfer coefficient provided a much better agreement than a constant heat transfer coefficient. POLYM. ENG. SCI., 45:866–875, 2005. © 2005 Society of Plastics Engineers     

工艺参数对水辅注塑弯管壁厚的影响

利用华南理工大学自主研发的注水系统和水辅注塑弯管模具,研究了熔体温度、模具温度、注水延迟时间、熔体注射量、注水压力、注水温度、熔体注射速率和熔体注射压力等8个水辅成型主要工艺参数对聚丙烯制品壁厚偏差率的影响,并分析了影响机理。结果表明,部分工艺参数对于制品弯曲段的壁厚偏差率有影响;增加注水延迟时间,降低注水压力和模具温度,短射填充区的制品壁厚的偏差率有所减小;提高熔体温度,壁厚偏差率的波动幅度增大。     

Numerical and experimental investigations on polymer melt flow phenomenon in a vario‐thermal mold cavity

Mold temperature is one of the key factors affecting the morphology and quality of plastic parts. This article explores the melt flow phenomena in a vario‐thermal mold cavity. A coupled numerical method, considering the conjugate heat transfer between the mold and melt, is developed for the melt flow simulation. Mold temperature variations and melt flow phenomena for short shot injection in an electrical heated mold cavity are numerically studied and verified by experiments. The results indicate that the melt flow length and cavity filling ratio increase significantly with the elongation of the preheating time before injection. Melt filling ratio increased nearly linearly with the increasing of electric heating time. The smaller the injection pressure is, the bigger the relative filling ratio increment is. Therefore, polymer melt can flow much longer or the mold cavity can be filled up with a smaller injection pressure when the cavity is preheated. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 45193.     

Experimental investigation of key parameters on the effects of cavity surface roughness in microinjection molding

For microinjection molding, it is envisaged that cavity surface roughness plays an important role in the cavity filling of polymer melt. This article presents an experimental investigation into the surface roughness effects on the flow area of a microthickness disk through injection molding. Three core inserts, each of which has different surface roughness on its two semicircular halves but with the same roughness mean lines, were machined and formed the mold cavity. The difference in flow area (or volume) between these two semicircular halves of the molded part was investigated by varying the mold and melt temperatures. Regressive analysis of the significance of mold and melt temperatures and cavity thickness on the surface roughness effects was carried out. Experimental results obtained indicated that the flow area on the smoother half is larger than that on the rougher half during cavity filling. For the same surface roughness, its effect on cavity filling is a function of mold temperature, melt temperature, and cavity thickness. An increase in mold temperature or melt temperature will result in smaller surface roughness effect on the flow area. When cavity thickness is reduced, the surface roughness effect will become more significant. Moreover, a larger difference in the surface roughness between the two semicircular halves of the insert will result in a larger difference in the flow area between the two halves of the molded part. POLYM. ENG. SCI., 2008. © 2008 Society of Plastics Engineers.     

Experimental investigation and molecular dynamics simulations of the effect of processing parameters on the filling quality of injection-molded micropillars

Microinjection molding has been attracting increasing attention and application in fabricating products with functional surface microstructures. The processing parameters, packing pressure, and melt temperature have important effects on the filling quality. In order to study the mechanisms of the packing pressure and melt temperature on the filling quality of micropillars, a simulation model of injection molding of nanopillars was constructed by molecular dynamics software and a series of injection molding experiments of micropillars were carried out in this paper. Subsequently, the mechanisms were analyzed qualitatively. The results showed that the frozen layers were formed at the interface between the polymer melt and mold under the action of heat transfer, which prevented effective filling of the polymer melt. The filling quality of the micropillars could be improved significantly via increasing the melt temperature and the packing pressure, but the mechanisms were different. To be specific, the increase of the packing pressure could make more polymer melts fill into the cavity fully. Thus, the density of the micropillars was increased and the filling quality could be improved. The forming rate of frozen layers could be slowed down by increasing the melt temperature. As a result, the purpose of improving the filling quality was achieved.     

自然平衡流道结构对多型腔模具非平衡充填的影响

在验证国内外已有的关于几何对称型腔非平衡充填研究结论的基础上,设计了可更换流道的实验模具,研究了流道尺寸及浇口形式的变化对非平衡充填的影响,并考察了整个充模过程中塑料熔体在型腔中的流动情况.结果表明,改变流道尺寸及浇口形式有利于改善非平衡充填程度,并指出整个充模过程的非平衡充填是一个动态演化过程.     

Coupled Part and Mold Temperature Simulation for Injection Molding Based on Solid Geometry

This paper presents a coupled method that determines the interface temperatures by filling and cooling analyses simultaneously to simulate the mold and part temperature distributions for injection molding. The mold temperature is assumed to be changing and is calculated with melt together at the filling stage instead of keeping constants as is usually done in conventional methods. The mold temperature is first determined with a 3-D finite element method by specifying the heat-flow rate at the interface between mold and part. Then the finite difference approach is employed to solve the melt thermal problem to get melt temperature distributions inside the cavity and the heat-flow rate at the interface. The under-relax scheme is used to correct the boundary condition and to resolve both mold and melt thermal problems until the solutions are convergent. This method can simulate transient and multicycle problems with more complex process conditions. The simulated results agree with experimental data.