Browse Topic: Drying
The Autoclave processing is commonly used in manufacturing high-performance fibre-reinforced thermoset composite components in the aerospace industry. Variations in the cure cycle, sometimes even apparently minor deviations from the prescribed cure cycle, can harm the laminate properties. Given the costly and time-consuming autoclave manufacturing process, there is a strong need to cure the maximum number of parts in the shortest possible time without compromising quality. In order to achieve high-rate automated manufacturing with the optimized autoclave process, it is important to construct a digital twin modelling approach to mirror the physical composite curing process in the virtual domain based on the integration of high-fidelity multi-physics models. The resulting digital twin includes a thermal CFD model, a thermo-chemo-mechanical module, and an efficient and accurate block coupling between these two modules. The customized Abaqus driven by local and spatial variation of the turbulence-induced heat transfer coefficient (HTC) imposed through one-way coupling determines the thermo-mechanical response in composite parts. Using the developed digital twin tool (SMARTCLAVE), HTC's spatial and temporal variation can be generated digitally without invoking an expensive and time-consuming experimental approach. The predicted local boundary conditions are used in SMARTCLAVE to determine the cure kinetics, temperature distribution, and thermal-mechanical response that drives the residual stress and distortion of composite parts after curing. The accuracy of the digital twin for autoclaving is demonstrated first using a benchmark problem followed by the capability demonstration with a single-part L-beam assembly. The benefits of using the digital twin tool are illustrated via the optimal placement of multiple parts in an autoclave to balance the throughput and quality.
ABSTRACT The current method used for bonding liners onto dynamic components requires the use of spring-loaded clamps, vacuum bags, and ovens. This process works well for our smaller articles although has posed problems for our larger bonding requirements. The primary problem for our large bonded components is our ovens would take up to 3.5 hrs. to heat the thickest areas up to bonding temperature. For the adhesives that we use the recommended temperature ramp-up time is 20-60 minutes. In addition, the thinner areas reach temperature sooner and would exceed the recommended maximum curing time of 60 min. A minimum of 25 pounds per square inch (PSI) is required to achieve a sound bondline. The clamps used during cure cycles rely on springs to apply pressure to the liner being bonded. The pressure they exert is not exact, and tends to vary. A vacuum bag can only apply the pressure that is supplied by shop air, 14.7 psi. The solution to achieving uniform and accurate pressure during bonding operations is to have a flexible zoned system that can bring all the areas, thick and thin, to temperature simultaneously, apply even amounts of pressure to the liners, and record all zones of temperature and pressure during the bonding process. Through the entire process, the zones are monitored, recorded, and graphed. This system can be moved anywhere within the factory because the heating elements and the air bladders are incorporated into the fixture.
ABSTRACT When designing tooling for autoclave curing of close tolerance composite components there is always the tradeoff between the cost and durability of the tooling. Composite tooling can be easily constructed but is not very durable, whereas metal tooling made from low expansion alloy - Invar - is extremely durable but more costly to fabricate. The expense of Invar tooling is greatly affected by the complexity of the part, particularly for large components, which may have to be fabricated from welded and machined assemblies. Recent developments in the casting industry have lead to significant improvements in the design and fabrication of Invar tooling. Simulation systems for mold design and pattern-less mold preparation technologies have greatly reduced the mold design time, enhanced first-time yield and design change flexibility. It is now possible to incorporate last minute design changes shortly before the casting is poured. Thus it is possible to produce a complex near net-shape thin walled casting with all of the stiffening features that would otherwise be welded, machined and heat treated fabricated assembly. The presentation will give examples of the size and complexity of aerospace grade Invar tooling that is being used for the production of composite helicopter and aircraft components.
Methods were developed for forming an insulating material that combines a polysilazane, a cross-linking compound, and a gas-generating compound to form a reaction mixture, and curing the reaction mixture to form a modified polysilazane. The gas-generating compound may be water, an alcohol, an amine, or a matrix comprising one of a reaction product of a polysilazane and an isocyanate, and a reaction product of a polysilazane and an epoxy resin. The matrix also comprises a plurality of interconnected pores produced from a reaction of the polysilazane and the epoxy resin.
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