Stitching Pattern Enabling Fastener-Stitching Composite Joining
Manufacturing
Stitching Pattern Enabling Fastener-Stitching Composite Joining (LAR-TOPS-385)
New Method Enables Small Radii, Fastener-Encapsulating Sinusoidal Stitching
Overview
Several damage modes exist for composite parts made via joining preforms with fasteners, including delamination growing from the edge of the bolt hole, through thickness cracks, etc. Stitching of dry composite preforms has recently emerged as a desirable method of composite aircraft component manufacturing as it allows for the unitization of complex, three-dimensional composite parts. However, despite the possibility of unitization, it may be desirable to incorporate fasteners into the final design of large complex components to ensure fail-safe conditions. Furthermore, certification processes for composite aircraft parts made via stitch joining composite preforms have not yet been developed, meaning a dual joining (fastener-stitching) strategy may be necessary to meet regulatory requirements.
Innovators at NASA’s Langley Research Center have developed a novel, efficient stitching pattern and robotic control schema designed to enable stitch joining of dry composite preforms also simultaneously joined with fasteners, resulting in improved mechanical properties and retardation of common fastener-related failure modes. Originally targeting composite aircraft components, this NASA invention may also prove enabling for manufacturing a variety of structures via composite joining (e.g., cargo containers, marine vessels, railroad cars, and a plethora of additional large structures that could benefit from reduced weight or unitized construction).
The Technology
This NASA invention is a method enabling the use of a robotic arm outfitted with a stitching head to join two or more dry composite preforms previously joined with fasteners. The method accommodates the presence of fasteners via stitching around individual fasteners at a desired radius (termed “encapsulation”). The stitched seam enabled by NASA's invention serves several purposes – it is a means of joining of preforms, providing damage arrestation for cracks that form near fastener holes, and strengthening joints via through-thickness stitching.
NASA’s method entails stitching a partial sinusoid-containing pattern in dry fiber composite preform substrate using a robotic, single-sided or double-sided needle stitching head in the following manner: (1) moving the stitching head to the proper location, (2) inserting the stitching needle and thread and capturing a stitch without moving the needle relative to the substrate, (3) continuing the stitching motion until the needle has returned to its starting position, (4) traversing the next point of entry without rotating the stitching head relative to its forward motion, (5) repeat steps 1-5 along a sinusoidal path.
In addition to the general method, NASA has generated a control schema to develop the G-code that is used to command the stitching head / robotic arm to carry out the required operations. The control schema enables a stitching pattern that turns the stitching path through a 180 degree arc without requiring the stitching head or composite preform to rotate. This reduces the complexity of required stitching tooling and operations (since turning the stitching apparatus through this arc requires sufficient clearance in the “throat” of the apparatus), removes the constraint on preform length in the direction of the stitching path, and enables stitching around fasteners at very small radii.
Benefits
- Enables use of both fasteners and stitching for composite joining: This pattern and associated robotic control scheme stitches around (e.g., “encapsulates”) fasteners at a desired radius in a completed composite part.
- Environmental impact: This NASA invention paves the way for the use of various composite aircraft components that provide reduced aircraft weight and drag (and as a result, reduced fuel burn and emissions).
- Improves composite joint properties: “Encapsulating” fasteners (via stitching) strengthens the composite joint via through-thickness stitching and may provide a means of local damage tolerance (e.g., crack arrestment) near an installed fastener.
- Does not require the stitching head or composite preform to rotate: This reduces the complexity of required stitching tooling and operations, removes the constraint on preform length in the direction of the stitching path, and enables stitching around fasteners at very small radii.
- Hardware agnostic: The control schema can be applied to generate the control G-code for any robotic system and industrial stitching heads.
Applications
- Enables joining of dry composite preforms for use in dual fastener-stitching strategy
- Manufacturing of composite aircraft components
- Manufacturing of other large structures that could benefit from the reduced weight offered by composites (e.g., cargo containers, shipping boats, railroad cars, other transport systems, and more)
Technology Details
Manufacturing
LAR-TOPS-385
LAR-20484-1
Patent Pending
Similar Results
Composite Stitching with Vacuum Consolidation
In a typical resin infused composite manufacturing process, fiber composite preforms are placed into a mold, subjected to vacuum conditions, infused with resin, and then left to cure. Here, prior to the resin infusion, the preform and all other necessary materials are placed within a vacuum bag, sealed, and compressed by attaching a vacuum pump. The compressed (or consolidated) preform is then fixed in place by composite stitching methods while the vacuum pump is running to maintain the consolidation of the preform. Once the stitching is complete, the preform is removed from the stitching head assembly and from the vacuum bag to be prepared as normal for the resin infusion and curing steps.
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LAR-20461-1 may be used in any setting where stitched fiber composites composites (e.g., carbon, fiberglass, etc.) are employed or will be employed in the future, including aerospace, automotive, and architectural applications. The related patent is now available to license. Please note that NASA does not manufacturer products itself for commercial sale.
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The related patent is now available to license. Please note that NASA does not manufacturer products itself for commercial sale.
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