Cobonded structures are an assembly of two or more subcomponents made from melt-miscible materials that are bonded together during an automated fiber placement process. These assemblies, which can contain a wide variety of frames, stiffeners, and longerons, require no adhesives or fasteners. For 25 years, Automated Dynamics (now part of Trelleborg Group) has been demonstrating what is possible with this process. We have made a variety of structures of assorted sizes and complexity which have demonstrated the viability and benefits of cobonding.
Thermoplastic materials such as PEEK or PEKK are ideal since their semi-crystalline structure provides superior chemical and wear resistance along with the strength and damage tolerance that normally comes with thermoplastics. These materials come with the added benefit of not needing an autoclave to consolidate.
First steps involve creating frames or stiffeners with a material that is melt-miscible with a thermoplastic skin. These can be made using Automated Fiber Placement (AFP), Continuous Compression Molding (CCM), or any other method that can process thermoplastic materials into the required cross-section. Next, a tool is created to fiber place the “skin” that will house the stiffeners. Since there is no need to submit this tool to an autoclave, it can be made from relatively inexpensive material such as aluminum or steel. The fiber placement process does not transfer enough heat to cause any expansion problems as the initial plies work to insulate the tool.
When the tool is assembled with all stiffeners in place, the fiber placement process can begin. Automated Dynamics processes thermoplastic materials in-situ. This means that we apply enough heat and pressure to consolidate the material in process. Once the skin is fiber placed on top of a frame or stiffener, the separate components bond with the same strength of interlaminar plies. The in-situ process allows manufactures to avoid the costs and challenges associated with bagging and autoclaving a complex part.
Cobonded thermoplastic structures offer benefits that are not normally seen in the modern-day composites industry. These structures utilize the strength, damage tolerance, and environmental resistances associated with thermoplastics while not requiring any adhesives, fasteners, bagging, or autoclave cycles. Automated Dynamics is continuing development efforts on several fronts to bring cobonded thermoplastic structures to the mainstream.
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