Analysis of pressure profile and flow progression in the vacuum infusion process

New experimental set-ups are presented for measuring the pressure profile and fill-times in the Vacuum Infusion (VI) process. In these set-ups, the injection can either be from one of the mould faces (resulting in a rectilinear flow) or from a central port (resulting in a radial flow). From these measurements, the validity of previously reported analytical formulations is investigated. At the start of injection, the experimental results show a marked difference from analytical predictions. However, with flow progression, they change to match with analytical predictions. This phenomenon has not been observed previously and its analysis enhances the current understanding of the process physics, mainly the impact of compliance on the reinforcement thickness and flow progression.     

真空辅助成型工艺中预成型体的厚度变化与过流控制

采用无接触式电涡流位移传感系统, 对真空辅助成型工艺中预成型体的厚度变化进行了实时监测。揭示了该成型工艺过程中预成型体的厚度变化规律, 并考察了树脂过流控制时间对制件厚度与纤维体积含量的影响。结果表明, 在整个工艺过程中预成型体的厚度变化可分为三个阶段: 在树脂浸入后, 预成型体厚度迅速增加; 在树脂过流控制阶段, 预成型体厚度变化较小且保持在较高水平; 在树脂管关闭后, 预成型体厚度迅速下降并逐渐趋于稳定。制件厚度与树脂过流控制时间的变化关系类似于正弦曲线, 在树脂过流控制时间约为10 min时, 纤维体积分数最低, 较无过流控制降低1.7%; 在树脂过流控制时间约为40 min时, 纤维体积分数最高, 较无过流控制提高1.6%。     

Active control of the vacuum infusion process

Through infusion experiments, fibrous preforms are shown to have an inherent heterogeneity in the permeability. This heterogeneity can lead to unforeseen, unpredictable and potentially, problematic flow patterns. A new active control system is proposed to address this issue, capable of monitoring the resin flow, identifying flow disturbances and taking an appropriate corrective action in real-time, through computer-controlled injection ports. A simple technique is also proposed for monitoring the resin flow in closed moulding processes such as Vacuum Infusion (VI), where at least one side of the mould is visible. This uses a low cost web-camera to capture images at fixed time intervals during the infusion phase and analyses them to identify flow disturbances. The control system then uses this information to take corrective action in real-time. To demonstrate the potential of the system, it has been implemented and validated through numerical simulations and infusion experiments.     

真空渗透成型工艺制件厚度变化规律

为了解决真空渗透成型(VIP) 工艺中凝胶时间与充摸时间难以匹配的问题, 通过对不同层数的VIP 制件厚度变化规律的研究, 得到了厚度与树脂流动距离和增强纤维层数之间的经验公式, 并验证了公式的可行性。分析了试验过程中存在的问题和样品出现的缺陷, 探讨了改进试验的方法, 以提高工程实际应用中成型工艺效率及最终产品质量。      

真空导入模塑工艺中织物预成型体的可压缩性

采用真空加载方法研究了循环加载、织物形态、纤维种类、织物层数、铺层方式和混杂方式等参数对真空导入模塑工艺(VIMP)中纤维织物预成型体压缩行为的影响。结果表明: 预成型体纤维体积分数随着压缩循环加载次数的增加而逐渐增大, 但增幅呈现逐渐减小的趋势; 在相同的压缩载荷下, 预成型体的纤维体积分数随着织物层数的增加而增大, 但增幅很小, 对于VIMP制备复合材料构件基本可以忽略; 纤维预成型体在压缩载荷下的响应方式与织物形态、纤维种类、铺层方式和混杂方式等因素密切相关, 单向铺层比正交铺层更容易压缩而获得较高的纤维体积分数, 夹芯混杂比层间混杂方式更容易压缩。      

真空导入模塑工艺树脂体系化学流变特性及流变模型

采用DSC热分析技术和黏度实验方法,研究了真空导入模塑工艺专用不饱和聚酯树脂体系(Palatal1777-G-4)的固化特性和化学流变特性,建立和对比了树脂体系的修正双阿累尼乌斯流变模型和工程黏度模型,并依据所建立的流变模型预报 Palatal1777-G-4树脂体系的真空导入模塑工艺操作窗口。对比结果表明：修正双阿累尼乌斯流变模型和工程黏度模型分别能较好地反映树脂体系凝胶点前的低黏度平台特性和凝胶点后的黏度变化规律,结合两模型可有效模拟树脂体系在不同工艺条件下的黏度行为,准确预报树脂体系的低黏度平台工艺窗口,为优化真空导入模塑工艺参数和保证制品质量提供科学依据。模型预测结果表明,Palatal1777-G-4 树脂体系在20～38℃温度范围内满足真空导入模塑工艺操作的基本要求,黏度低于300 mPa·s的工艺操作时间长于30 min。     

Simulation of the reinforcement compaction and resin flow during the complete resin infusion process

Resin infusion (a.k.a. VARTM) is one of the LCM processes, for which liquid resin is drawn into dry reinforcements. Significant cavity thickness changes occur during processing, due to the flexibility of the vacuum bag used as one side of the tool, and the complex stress balance within the laminate. While the magnitude of thickness change is often small, the influence is significant on reinforcement properties. Changes in permeability during filling and post-filling have the potential to significantly affect the process. To simulate this behaviour, it is important to accurately model compaction and unloading of reinforcement in dry and wet states. A series of tests were completed to determine compaction behaviour of an isotropic glass fibre mat. From these tests several non-linear elastic compaction models have been determined, and applied within a resin infusion simulation which addresses pre-filling, filling and post-filling. This simulation was then used to assess different post-filling strategies.     

导流介质对真空导入模塑工艺树脂流动行为的影响

采用可视化流动实验方法研究了高渗透率导流介质对真空导入模塑工艺中树脂流动行为的影响。结果表明: 导流介质能较大幅度地减少树脂的充模流动时间, 且充模时间随着导流介质使用比例的增加而呈线性减少的关系; 导流介质的提速作用随着预成型体厚度的增加而逐渐减弱; 预成型体上下表面树脂流动前沿位置差距与预成型体厚度呈良好的线性增加关系, 说明导流介质的影响作用具有明显的厚度效应。厚度效应原理为真空导入模塑工艺过程的参数优化和保证制品质量提供了理论依据。      

Uncertainty analysis of the high vacuum part of the orifice-flow-type pressure standard

The orifice-flow-type pressure standard is commonly accepted as primary standard for vacuum gauge calibration in the high vacuum gas pressure range. It consists of two parts—a high vacuum part and a flowmeter. Practical questions arising at design of the standard have to be answered based on the standard uncertainty analysis.The analysis of the uncertainty sources in the high vacuum part except deviations from the Maxwellian distribution is given in the paper. Uncertainty of a precise flowmeter is taken from references for comparison. It follows from the analysis that uncertainties caused by some sources at routinely achievable parameters are negligibly small and further improvement brings no benefit. The crucial quantities influencing the total uncertainty are the temperature of the chamber and the flowmeter, the outgassing rate from the inner surfaces, the ultimate pressure of the pump and the additional (detrimental) pumping speed. The pumping speed of the main pump has to be “sufficiently higher” than the orifice conductance.     

Analysis of the vacuum infusion moulding process: I. Analytical formulation

The present work is primarily concerned with the analytical formulation of governing equations for flow of incompressible fluids through compacting porous media and their application to vacuum infusion (VI) of composite materials. The literature on VI and the effects of compacting media on permeability and flow is reviewed. A complete development of the proposed governing equation is shown along with a suggested numerical solution. The proposed model is subsequently used to quantify the effect of process parameters such as inlet and outlet pressures, fibre architecture and lay-up. Implications for industrial production are discussed.     

Modelling vacuum cooling process of cooked meat—part 1: analysis of vacuum cooling system

A mathematical model is developed to analyse the performance of a vacuum cooler. The model is based on the mass conservation of air and vapour in the vacuum chamber. In the chamber, the vapour evaporated from foods under the vacuum and the vapour removed by the vapour-condenser and vacuum pump contribute to the variation in the vapour partial pressure, and the ingress air and the air released by the pump cause the change of air partial pressure. Experiments were carried out on vacuum cooling of water to validate the model. The predicted vacuum pressure and temperature histories are compared with the measured values. The maximum deviation between the predicted and measured vacuum pressure is within 110 Pa (for the chamber pressure between 12,000 and 2200 Pa), while the maximum deviation between the predicted and measured temperature of water is less than 2 °C. The model can, therefore, be used to predict the transient vacuum pressure profiles for analysing the vacuum cooling process of foods such as cooked meat.     

真空压力下树脂沿织物铺层厚度渗透速率

为了考察树脂膜熔渗(RFI)工艺过程中树脂在高温条件下沿织物铺层厚度方向的不饱和渗透特性, 应用自行设计的测试系统, 考察了液体沿织物铺层厚度方向流动前锋的影响因素, 测试并分析了液体沿玻璃纤维铺层厚度方向渗透速率的主要影响因素及其变化规律。结果表明, 液体沿纤维织物厚度方向流动为宏观上的一维流动。 真空压力增大、 树脂温度升高、 纤维体积分数减小, 均可使液体的渗透速率加快。另外, 对比发现, 70℃ E-51 环氧树脂沿玻璃纤维铺层厚度方向的渗透特性与室温下硅油的渗透特性基本相当。      

Resin infusion under flexible tooling process and structural design optimization of the complex composite part

Employing optimum structural design strategies and accompanying optimal production processing while employing efficient and cost effective methods is a key for the expansion of composite structures in various industrial applications. Within this context, Resin Infusion under Flexible Tooling (RIFT) process has become a rapidly growing manufacturing approach for large scale and complex parts. In this study, replacement of automotive body parts with glass woven fabric/epoxy composite manufactured by RIFT Type I (RIFT I) process is investigated both experimentally and numerically to improve the mechanical characteristics with weight saving. The optimization of the laminate stacking sequence is the first step taken. Then the simulation of resin infusion for the optimum location of gates and vents in order to shorten the filling time, decrease dry spots and voids, and avoid costly and time consuming trial-and-error procedures. Numerical results of the filling time and fluid front position over time are assessed by comparison with the experimental data and good accuracy was obtained. Based on the results of the optimization, an automotive part with a complex geometry is fabricated with 50% weight saving relative to steel.     

一种真空室箱体门的压紧机构设计

借用气缸的推拉力,设计了一种新型门压紧机构,代替原来靠人工转动的纯机械式门压紧机构.该机构结构简单,操作方便,省事省力,且制造成本低,使用寿命长.在实际的应用过程中,生产效率提升明显.     

Textile fiber-reinforced anionic polyamide-6 composites. Part I: The vacuum infusion process

In order to manufacture thicker, larger and more integrated thermoplastic composite parts than currently can be achieved by melt processing, a vacuum infusion process is currently being developed at the Delft University of Technology using a reactive thermoplastic polymer called anionic polyamide-6 (APA-6). In previous studies it was demonstrated that the anionic polyamide-6 (APA-6) resin that is used has excellent mechanical properties. The present study assesses infused thermoplastic composites and focuses on fiber-matrix interactions. Part I of this study focuses on the thermal effects, causes for deactivation of the initiator and the restriction caused by the low in-plane permeability of the fiber textiles on various transport phenomena. It will be shown that addition of pre-heated fibers not only shortens the infusion window, but also influences the matrix properties by reducing the exothermic heat production. In addition, the low in-plane permeability of the fiber textiles influences the infusion time and causes the entrapment of voids. Finally, reactions between the matrix and the fiber surface can lead to deactivation of the initiator and bond formation with the activator. Interfacial bonding, however, is discussed in more detail in Part II of this study, whereas the effect of adding a nucleating agent is discussed in Part III.     

Fiber optic sensors for monitoring flow in vacuum enhanced resin infusion technology (VERITy) process

Today, with cost becoming a very important factor, alternate processes for manufacturing composite structures, wherein the cost can be reduced but having similar properties to prepreg systems are being explored. National Aerospace Laboratories, India is developing the VERITy process, which is essentially a hybridization of the VARTM and the autoclave moulding process. One of the concerns in this process, especially when making large integrated co-cured structures with varying thickness, is the knowledge of the resin flow front location at all times. A network of flow-sensors, which could provide information on the flow front location, would be very useful. This paper discusses the experimental studies carried out towards the development of a flow-sensor in the optical domain to determine the presence of resin qualitatively. Three different approaches have been attempted to detect the arrival of the resin flow front and these results are presented.     

Gas pressure effects on thickness uniformity and circumvented deposition during sputter deposition process

In sputter deposition processes, the thickness distribution of the film is affected by experimental conditions such as gas pressure, target-substrate (T-S) distance and target elements. To study these effects, we have designed a sample holder with three quartz crystal microbalance (QCM) thickness monitors on its surface and measured the distribution of the depositing flux around the sample holder, including the circumvented deposition onto the back face. As for the gas pressure dependence for a T-S distance of about 50 mm, the relative deposition flux on the back face was found to be at its maximum at pressures of 1-2 Pa. Above this pressure, the uniformity of the flux on the front face became gradually worse. The observed characteristics could be reproduced by a Monte-Carlo simulation of the particle transport process. The reduction of the circumvented deposition and the uniformity degradation at high gas pressures were ascribed to the start of thermalization of sputtered particles and the shrinkage of its spatial profile toward the target.     

真空浸渍工艺的研究与应用

在低压和常压状态下进行了浸渍工艺的对比性试验研究。由于真空机制对浸渍介质中浸渍物质渗透性和化学反应活性的改善作用，真空浸渍的过程大幅度加快，浸渍物质用量明显减少。本文还介绍了真空浸渍技术的某些生产应用及其显著成效。     

Macrokinetics of the process of SHS compaction

Dependences are considered for the characteristic times of the main stages of the SHS compaction process—synthesis, compaction, and cooling — on the geometric size of a charge billet and the composition of a synthesized hard alloy. The existence is shown of two critical sizes for a starting billet which limit the region of producing a nonporous material. The presence of the critical conditions depending on the liquid phase fraction formed in the synthesis of a hard alloy is established. A satisfactory qualitative and quantitative agreement of calculated and experimental results is obtained.Institute of Structural Macrokinetics, Russian Academy of Sciences, Chernogolovka. Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 63, No. 5, pp. 583–592, November, 1992.