Optimization of Parts Placement in Autoclave Processing of Composites

The main processing variable in autoclave production, besides pressure and time, is fluid temperature. The different geometry of tools and composite laminates and the fluid dynamic characteristics of each autoclave batch lead to temperature changes in the composites, during heating, soaking and cooling, not easily predicted. The soak time at maximum temperature is considered one of the most critical constraints. This time is computed for the entire autoclave batch when the last composite laminate reaches the specified cure temperature. In this work a completely different approach is presented. Areduction of cure time is achieved identifying a rule for the position of different tools inside the autoclave. An optimization model is derived by defining an objective function in terms of penalty coefficients associated to different tools and different positions into the autoclave. Test cases of the behaviour of autoclave batches have been simulated leading to significant predicted cure time reductions.     

Out-of-autoclave cure cycle study of a resin film infusion process using in situ process monitoring

Liquid resin infusion (LRI) of textile tailored reinforcements (TRs) is increasingly applied in new processing technologies for manufacturing carbon fibre composites. This work presents a cure cycle study of an out-of-autoclave toughened resin film infusion (RFI) process as part of the examination of an alternative manufacturing process for composites. To successfully produce laminates using resin film infusion in combination with a fast-curing process, the flow behaviour of the selected resin material under changed processing conditions was investigated. The effect of processing parameters, specifically heating rates and dwell times, on resin viscosity and laminate infiltration was evaluated through experimental work and supported by in situ process monitoring. A DC-resistance sensor system was applied to track the change in resin viscosity during cure. Results showed that cure cycles with a relatively short dwell time and higher heating rate compared to an autoclave cure led to enhanced flow properties of the toughened resin system. High quality laminates, comparable to autoclave panels, were manufactured with vacuum pressure only by modifying the original vacuum bagging arrangement.     

先进树脂基复合材料制造技术进展

国内先进树脂基复合材料制造技术经过30多年的发展, 已初步形成以热熔预浸料制造、 热压罐和树脂传递模塑(RTM)成型技术为代表的先进树脂基复合材料制造技术体系, 所制备的先进树脂基复合材料已在航空领域得到大量应用。本文中主要介绍国内先进树脂基复合材料热压罐成型技术、 RTM成型技术和自动铺放技术的最新进展以及先进树脂基复合材料制造过程模拟与优化技术, 讨论了国内先进树脂基复合材料制造技术的主要发展方向。     

The hybrid-adjoint method: a semi-analytic gradient evaluation technique applied to composite cure cycle optimization

A method is presented for determining the optimal autoclave temperature history for pre-impregnated thermoset composites based on their failure performance. A coupled finite-element model that incorporates a thermochemical and incremental elastic analysis is used to predict the residual stress distribution at the edge of a thick composite beam. The optimal autoclave temperature is sought using a gradient-based optimization algorithm. The objective is designed to maximize the minimum failure load of the manufactured beam amongst a set of load cases, while the constraints are imposed to ensure that the composite is uniformly cured and does not sustain temperature damage during the manufacturing process. The hybrid-adjoint, a novel semi-analytic gradient evaluation technique is developed, that incorporates elements of both the adjoint and direct sensitivity methods. Results demonstrate that the method is highly accurate and competitive with a full adjoint approach for a moderate number of design variables.     

An approach in modeling the temperature effect in thermo-stamping of woven composites

Made with high-strength continuous fibers, textile composites are of increasing interest in automotive and aerospace industries due to their high-strength/weight performance as compared to sheet metals. Nevertheless, significant reduction in manufacturing cost is required to use textile composites for mass production applications. Highly efficient thermo-stamping operations possess the potential to substantially reduce fabrication time and cost compared to the much slower autoclave forming process. In this paper, thermo-forming of woven fabric-reinforced thermo-plastic composites is simulated using a non-orthogonal material model. The temperature effect is taken into account by modifying the equivalent material properties for the composite sheet based on the contact status between the tooling and the blank. The approach is exemplified on the hemispherical thermo-stamping of a plain weave composite sheet.     

Optimization of the Temperature-Time Curve for the Curing Process of Thermoset Matrix Composites

An intelligent optimization model aiming at off-line or pre-series optimization of the thermal curing cycle of polymer matrix composites is proposed and discussed. The computational procedure is based on the coupling of a finite element thermochemical process model, dynamic artificial neural networks and genetic algorithms. Objective of the optimization routine is the maximization of the composite degree of cure by the definition of the autoclave temperature. Obtained outcomes evidenced the capability of the method as well as its efficiency with respect to hard computing or experimental procedures.     

热压釜成型复合材料波纹梁工艺工时估算

成本估算是目前复合材料领域开发研究的关键问题之一,而工艺工时估算又是制造成本估算的核心。本文中建立复合材料制造工艺工时估算模型,以热压釜成型复合材料波纹梁为研究对象进行理论分析和实验研究,给出此估算模型中估算变量和方程参数的确定方法并应用最小二乘法将所得数据进行拟合,其结果与实验结果基本一致。介绍了估算模型中参数随制件曲度变化的修正方法,为实现不同结构设计的工时估算提供指导。     

Influence of preforming on the quality of curved composite parts manufactured by flexible injection

Flexible Injection is a new processing technique for the manufacture of advanced composites made of continuous reinforcing fibers and thermosetting polymer matrix. The primary objective of this new process is to provide faster and less expensive manufacturing than traditional methods like autoclave processing or Resin Transfer Molding. The present paper investigates the effectiveness of the proposed method to produce composite structures possessing sharp corners. A specially devised setup is used to manufacture out of glass fibers and vinyl ester resin a series of Z-shaped parts with small radii. The quality of the fabricated parts is assessed to detect possible defects induced by the manufacturing process. Each stage of the production cycle is analyzed thoroughly to develop a simplified finite element model reproducing the fiber bed behavior during processing. Parametric studies are conducted to evaluate the impact of processing conditions on the quality of final products. The combination of numerical simulations and experimental observations demonstrates clearly the importance of the preforming stage. At the same time, it provides useful insights on the physical phenomena occurring during Flexible Injection.     

Production planning optimisation for composite aerospace manufacturing

Composite materials proved highly successful for aerospace applications in the last decades, but increased cost pressure forces the composite industry to become more efficient. This requires new manufacturing technologies and optimised processes as raw material costs and labour costs are basically fixed when wanting to keep production on site. Probably the most defining process for aerospace composite production is manual layup of prepreg material with subsequent curing in an autoclave. From production planning view, this combination poses the challenge of transition from discrete layup manufacturing to batch curing processing with the restriction of limited allowed storage time of the prepreg material prior to cure. In this paper, a new approach for production order optimisation at the conjunction of discrete and batch processing is presented. The APOLLO named tool is designed to decrease throughput times, streamline production and increase autoclave utilisation in the composite aerospace industry.     

Residual stresses formation during the manufacturing process of epoxy matrix composites: resin yield stress and anisotropic chemical shrinkage

A study of residual stresses during the curing process of thermosetting resin composites is presented. A methodology is proposed for predicting the formation and the development of the manufacturing residual stresses, this approach is based on the determination of the resin yield stress. A self-consistent model is used to determine the cure-dependent effective mechanical properties, thermal expansion and chemical shrinkage coefficients of the composite material. This model allows considering for the composite material behaviour an anisotropic chemical shrinkage, which is not represented by a classical linear model. Finally, a one dimensional cure simulation and a modelling of residual stresses formation in composite plate are made by using a finite elements code. The effects of the cure-dependent material properties and of the resin yield stress on the residual stress formation are studied.