共查询到19条相似文献,搜索用时 187 毫秒
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根据吹制成型玻璃产品的特点,建立了成型过程熔体流动和模具传热的数学模型,开发出了成型模拟仿真软件GlassMolding.基于该软件,开展了初模和成模中熔体流动形态和温度分布模拟研究,揭示了扑气环缺陷产生的机理,即两段料温度差异导致不一致的膨胀所造成,料温差异则由扑气等环节引起.而在吹制成型中扑气压实环节是必不可少的,该缺陷是吹制工艺固有属性决定的,那么开展基于模拟仿真的初模设计和工艺优化来改善该缺陷,对实际生产具有重要指导意义. 相似文献
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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。 相似文献
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由于聚合物模内组装成型的微型机械制造精度和组装配合精度主要受控于二次成型熔体充填流动与一次成型固体微型零件之间的流固耦合作用,因此通过有限元数值模拟,系统研究了二次成型熔体注射温度对流固耦合变形的影响,并揭示了其影响机理。研究结果表明,增加二次成型熔体的注射温度,可使二次成型熔体的充填流动与一次成型固体微型轴表面间的流固耦合作用效应减弱,并使一次成型固体微型轴整体温度场趋于不均匀,从而导致一次成型固体微型轴流固耦合弯曲应力和弯曲变形减小,而热应力和热变形增加。增加二次成型熔体的注射温度可减小流固耦合变形,但二次成型熔体的注射温度过大,又会导致一次成型固体微型轴表面融化,影响装配配合界面的成型质量。 相似文献
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建立水辅助注射成型二维、瞬态、非定常流动模型,采用黏度幂律模型,在k ω湍流模型下,充分考虑注射水的湍流特性以及熔体前沿的喷注效应,采用有限体积法(VOF)对充填过程中的注水速度、注水温度和注水延迟时间等注水控制参数的影响进行数值模拟。结果表明,注水速度的增加会增加水在熔体中的穿透长度,并且会减小残余壁厚;注水温度对水的穿透长度和残余壁厚的影响均不显著;随着注水延迟时间的增长,水的穿透长度和残余壁厚均有增加的趋势。 相似文献
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The thickness of the melt film and the temperature profiles within the melt film in the weld zone are key process variables governing the development of weld‐zone microstructures and the resulting development of weld strengths, during vibration welding of thermoplastics. The mathematical model described in this report is aimed at investigating the role of the rheology of the melt—specifically the magnitude and shear‐rate as well as temperature dependence of the melt viscosity—in governing the process variables such as the molten film thickness and the viscosities, stresses, and the temperatures within the melt film during vibration welding. The analysis is focused on the steady‐state penetration phase (phase III) of vibration welding. The coupled steady‐state momentum balance and heat transfer within the melt film, formulated using the Cross‐WLF (Williams‐Landel‐Ferry) relationship for viscosity, are solved in an iterative finite element framework. The model has been implemented for two different polymers displaying significant differences in viscosities and shear thinning behaviors. An attempt has been made to correlate the trends in the estimated melt film variables with the experimentally measured weld quality. POLYM. ENG. SCI., 2012. © 2011 Society of Plastics Engineers 相似文献
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针对浮法玻璃成形过程,提出了锡槽入口段简化稳态多相模型,并采用Ansys Fluent 2019 R3软件,模拟研究了500 t/d锡槽入口段玻璃液的流动与成形过程,分析了拉引量、玻璃液黏度对唇砖与八字砖区玻璃液流动与液层厚度分布的影响。结果表明,拉引量过小或黏度过低时液层出现不连续,拉引量过大或黏度过高时液层横向厚度均匀性变差,案例锡槽实现浮法玻璃均匀稳定成形的工艺操作范围是拉引量400~550 t/d,黏度400~600 Pa·s。 相似文献
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建立了综合考虑二次成型黏弹性熔体充填流动约束环境影响的模内微装配成型过程黏弹性热流固耦合变形机理的理论模型,并通过有限元数值模拟,研究了二次成型熔体黏度对模内微装配成型过程黏弹性热流固耦合变形的影响规律。结果表明,黏弹性热流固耦合作用诱导的预成型微型轴变形的驱动力来源于微装配界面形成的热流固耦合压力和黏性拖曳剪应力,而二次成型熔体流动的弹性正应力对耦合变形具有抑制作用,微装配界面的热流固耦合载荷和微型轴的变形均随着二次充填熔体的黏度增大而增大,减小二次成型熔体黏度有利于提高其微装配加工精度。 相似文献
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Anh Tuan Vu Anh Ngoc Vu Gang Liu Tim Grunwald Olaf Dambon Fritz Klocke Thomas Bergs 《Journal of the American Ceramic Society》2019,102(4):2116-2134
Nonisothermal glass molding has recently become a promising technology solution for the cost-efficient production of complex precision glass optical components. During the molding process, the glass temperature and its temperature distribution have crucial effects on the accuracy of molded optics. In nonisothermal molding, the glass temperature is greatly influenced by thermal contact conductance because there is a large temperature difference between the glass and mold parts. Though widely agreed to be varied during the molding process, the contact conductance was usually assumed as constant coefficients in most early works without sufficient experimental justifications. This paper presents an experiment approach to determine the thermal contact coefficient derived from transient temperature measurements by using infrared thermographic camera. The transient method demonstrates a beneficially short processing time and the adequate measurement at desirable molding temperature without glass sticking. Particularly, this method promises the avoidance of the overestimated contact coefficients derived from steady-state approach due to the viscoelastic deformation of glass during the inevitably long period of holding force. Based on this method, the dependency of thermal contact conductance on mold surface roughness, contact pressure, and interfacial temperature ranging from slightly below-to-above glass transition temperature was investigated. The results reveal the dominance of interfacial temperature on the contact conductance while the linear pressure-dependent conductance with an identical slope observed for all roughness and mold temperatures. The accurate determination of the contact heat transfer coefficients will eventually improve the predictions of the form accuracy, the optical properties, and possible defects such as chill ripples or glass breakage of molded lenses by the nonisothermal glass molding process. 相似文献
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W. TRIER 《Journal of the American Ceramic Society》1961,44(7):339-345
A new method is described that helps to determine the temperature distribution of glass in blank molds. The effective coefficient of thermal conductivity, the heat flow within the glass, and the proportions of radiation and conduction may all be deduced from temperature profiles depending on the duration of contact between the glass and the mold. The results obtained lead to deductions as to the mechanism of heat transfer between glass and mold surfaces. 相似文献
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A simple analytical model for estimation of melt film variables in thermoplastic vibration welding 下载免费PDF全文
The strength of vibration welds of thermoplastics is governed by the weld zone microstructure, which in turn, is closely tied to the welding process variables, such as the thickness of the weld melt film and the temperature profiles therein. The mathematical model described in this report is aimed at describing the role of the rheology of the melt—specifically the magnitude and shear rate dependence of the melt viscosity—in governing the melt film variables during the steady state penetration phase (Phase III) of vibration welding. The steady state momentum balance and heat transfer within the melt film are solved by using the power law model for viscosity. Closed‐form analytical expressions are obtained for estimating the melt film thickness, the shear rates, and the temperature field within the film. This model has been used to estimate weld zone variables for four different polymers displaying a wide range of viscosities and shear thinning behaviors. POLYM. ENG. SCI., 54:499–511, 2014. © 2013 Society of Plastics Engineers 相似文献
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Z. J. Yang E. Harkin‐Jones G. H. Menary C. G. Armstrong 《Polymer Engineering and Science》2004,44(7):1379-1390
A non‐isothermal finite element (FE) model for the injection stretch‐blow molding (ISBM) process of polyethylene terephthalate (PET) bottles is presented in this paper. The constitutive behavior of PET is modeled by the physically based Buckley glass‐rubber model in form of UMAT in ABAQUS. The heat transfer between the stretch rod, the preform, and the mold is modeled. Particular attention is paid to thermal and contact modeling, material model, and selection of proper element types. Extensive FE simulations are carried out to model ISBM of a 20 g‐330 ml bottle made in plant tests. Comparisons of numerical results with the measurements demonstrate that the model can satisfactorily predict the bottle thickness and material distributions. Significant nonlinear differentials are found in strain, temperature, and temperature reduction rate in both bottle thickness and length direction during the process. A volume approach is therefore necessary for accurate predictions of final bottle properties because they are governed by orientation and crystallinity, which are highly temperature and strain dependent. Parametric studies on contact modeling and heat transfer coefficient are also conducted and the results are discussed. Polym. Eng. Sci. 44:1379–1390, 2004. © 2004 Society of Plastics Engineers. 相似文献
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Tham Nguyen‐Chung Gábor Jüttner Cindy Löser Tung Pham Michael Gehde 《Polymer Engineering and Science》2010,50(1):165-173
The filling process of a micro‐cavity was analyzed by modeling the compressible filling stage by using pressure‐dependent viscosity and adjusted heat transfer coefficients. Experimental filling studies were carried out at the same time on an accurately controlled microinjection molding machine. On the basis of the relationship between the injection pressure and the filling degree, essential factors for the quality of the simulation can be identified. It can be shown that the flow behavior of the melt in a micro‐cavity with a high aspect ratio is extremely dependent on the melt compressibility in the injection cylinder. This phenomenon needs to be considered in the simulation to predict an accurate flow rate. The heat transfer coefficient between the melt and the mold wall that was determined by the reverse engineering varies significantly even during the filling stage. With increasing injection speed and increasing cavity thickness, the heat transfer coefficient decreases. It is believed that the level of the cavity pressure is responsible for the resulting heat transfer between the polymer and the mold. A pressure‐dependent model for the heat transfer coefficient would be able to significantly improve the quality of the process simulation. POLYM. ENG. SCI., 2010. © 2009 Society of Plastics Engineers 相似文献
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熔窑内玻璃液流动与传热的模型实验 总被引:3,自引:0,他引:3
熔窑内玻璃液流动与传热的模型实验赵国昌,胡桅林,陈泽敬,过增元(清华大学工程力学系100084)ModelExperimentforGlassMeltFlowandHeatTransferinTankFurnace¥ZhaoGuochang;HuWe... 相似文献