METHOD AND APPARATUS FOR FABRICATION OF LATTICE COMPOSITE FUSELAGE FOR COMMERCIAL AIRCRAFT EMPLOYING STEERED FIBER LAY UP
A system for fabrication of an aerospace structure incorporates a mold having a surface and at least one unidirectional SFL head adapted to lay down a plurality of collimated tows in a predetermined laminated pattern on the mold surface to produce a fuselage skin. At least one cross plied laminate SFL head is adapted to lay down a cross plied laminate base interface on the fuselage skin to establish a lattice rib shape for each of a plurality of lattice ribs. The cross plied laminate SFL head has a band placement head steerable to avoid structural design features and to maintain spacing from adjacent steered lattice ribs. The unidirectional SFL head is further adapted to lay down a plurality of collimated tows on the base interface of each of the plurality of lattice ribs for a first plurality of unidirectional tow plies in each lattice rib. The unidirectional SFL head has a fiber placement head steerable to match the lattice rib shape to avoid structural design features and to maintain spacing from adjacent steered lattice ribs.
Embodiments of the disclosure relate generally to fabrication of composite structures for aircraft and more particularly to fabrication of aircraft fuselages having a modified lattice structure for carrying structural loads created with steered fiber layup using two or more heads for fiber placement with unidirectional tows and cross plied laminates providing high damage tolerance.
BackgroundComposite fuselages employed in existing commercial aircraft use composite skin supported by separately fabricated stiffening elements. Frames and stringers carry the substantial operational loads and are added to the composite skin after fabrication similar to metallic structural assembly approaches (a.k.a. “Black Aluminum” design). Skin, Frames and Stringers are typically fabricated based on different manufacturing technologies which require different manufacturing equipment, transportation of fuselage components from different production sites to the final assembly facility and final assembly of components (co-bonding, co-curing, fastening) to produce a section of fuselage. Furthermore, existing designs are based on the concept of orthotropic material which does not take full advantage of the available anisotropic properties of modern composite unidirectional materials. This results in excessive weight and cost, in growth of both Non-Recurring and Recurring Expenses (NRE, RE) in the course of manufacturing of composite fuselages. An alternative design concept has been used in space applications which is based on a uniform lattice structure (geodesic design) stiffening the skin. However, a uniform Lattice is less efficient in aircraft structures like fuselage sections which incorporate doors, windows, other openings and design features which disrupt the geometric lattice pattern.
Wet Filament Winding (WFW), which typically is used with a mandrel for fabrication, has been combined with lattice design to fabricate lattice-based cylindrical-shaped structures which are used in a number of space applications. Lattice design eliminates the need for stringers and frames to support structural requirements which make such structures more weight and cost efficient. WFW processes do not allow variation of the lattice geometry and rib shape in the course of the winding of the structure to incorporate doors, windows and other design-driven features. To address this problem design and fabrication of a uniform but non-optimal lattice structure is accomplished and then, after such uniform lattice is produced, required openings (cut outs) in the lattice are manually introduced and reinforced areas around openings are separately fabricated with additional plies of composite materials. Such an approach results in non-optimal structural efficiency, loss of potential weight savings and in increase of manufacturing cost. Further, WFW cannot be employed for a concave manufactured surface.
Traditional Automated Tape Lay-up (TATL) of slit tape with ATL machines is used to produce skin for sections of fuselage in current commercial aircraft production. TATL allows lay up in an automatic mode of fuselage skin incorporating required openings and reinforcements. However, frames and stringers must be fabricated based on different technologies which require different manufacturing equipment. As previously noted, transportation of the fuselage components from different locations to the final assembly facility and final assembly of components (co-bonding, co-curing, fastening) are then required.
It is therefore desirable to provide an apparatus and method for commercial aircraft fuselage construction which overcomes the disadvantages of the prior art.
SUMMARYExemplary embodiments provide a method for fabrication of an aerospace structure. At least one unidirectional Steered Fiber Lay-up (SFL) head is employed to lay down a plurality of collimated tows in a predetermined laminated pattern on a mold surface to produce a fuselage skin. At least one cross plied laminate SFL head is then employed to lay down a cross plied laminate base interface on the fuselage skin to establish a lattice rib shape for each of a plurality of lattice ribs. A band placement head in the cross plied laminate SFL head is steered to avoid structural design features and to maintain spacing from adjacent steered lattice ribs. The unidirectional SFL head is then employed to lay down a plurality of collimated tows on the base interface of each of the plurality of lattice ribs for a first plurality of unidirectional tow plies in each lattice rib. A fiber placement head in the unidirectional SFL head is steered to match the lattice rib shape to avoid structural design features and to maintain spacing from adjacent steered lattice ribs. The cross plied laminate SFL head is then employed to lay a cap over the plurality of unidirectional tow plies in each of the plurality of lattice ribs and a band placement head in the cross plied laminate SFL head is steered to track the lattice rib shape and position the cap over the plurality of unidirectional tow plies.
A system for fabrication of an aerospace structure usable in the described method incorporates a mold having a surface and at least one unidirectional SFL head adapted to lay down a plurality of collimated tows in a predetermined laminated pattern on the mold surface to produce a fuselage skin. At least one cross plied laminate SFL head is adapted to lay down a cross plied laminate base interface on the fuselage skin to establish a lattice rib shape for each of a plurality of lattice ribs. The cross plied laminate SFL head has a band placement head steerable to avoid structural design features and to maintain spacing from adjacent steered lattice ribs. The unidirectional SFL head is further adapted to lay down a plurality of collimated tows on the base interface of each of the plurality of lattice ribs for a first plurality of unidirectional tow plies in each lattice rib. The unidirectional SFL head has a fiber placement head steerable to match the lattice rib shape to avoid structural design features and to maintain spacing from adjacent steered lattice ribs.
The method and system for fabrication provide a damage tolerant lattice rib structure having a skin formed from a plurality of collimated tows in a predetermined laminated pattern. A cross plied laminate base interface is laid on the fuselage skin to establish a lattice rib shape for each of a plurality of lattice ribs with the lattice ribs steered for lateral displacement from features in the skin. A first plurality of collimated tows is laid on the base interface of each of the plurality of lattice ribs for a first plurality of unidirectional tow plies in each lattice rib. A first cap is laid over the plurality of unidirectional tow plies in each of the plurality of lattice ribs. A second plurality of collimated tows is laid on the first cap of each of the plurality of lattice ribs for a second plurality of unidirectional tow plies in each lattice rib. A second cap is then laid over the second plurality of unidirectional tow plies in each of the plurality of lattice ribs.
The features, functions, and advantages that have been discussed can be achieved independently in various embodiments of the present disclosure or may be combined in yet other embodiments, further details of which can be seen with reference to the following description and drawings.
The embodiments and methods described herein provide combined use of automated Steered Fiber Lay-up (SFL) and lattice design to fabricate integrally stiffened, stringerless sections of composite fuselage which incorporate windows, doors and other design features. The fuselage skin and stiffening lattice are fabricated as integral structure on the surface of a mold employing an automatic layup machine. This approach eliminates the need to separately produce skin, stringers and frames by different manufacturing equipment and a final assembly using co-curing, co-bonding, fastening. Use of automated SFL allows variation in lattice geometry and rib shape to accommodate local design features or disruptions. Unlike WFW no manual layup is required to support local reinforcement in areas of features or disruptions such as fuselage openings.
Referring to the drawings,
As seen in
Upon completion of the SFL skin layup, a lattice rib structure 28, as previously described with respect to
The unidirectional tow plies 56, 60 in each lattice rib 54 are laid down employing a unidirectional SFL head 30 as described with respect to
Cross plied fiber laminate bands are created with warp and weft laydown as is known in the art. The cross plied laminate may be created in sheets and cut or slit into the desired band widths. The laminate bands are then prewound onto cassettes 72.
For the lattice rib structure, both the unidirectional SFL heads 30 and cross plied laminate SFL heads 70 are steerable for lateral divergence from a baseline geodesic lattice layout. As seen in
Similarly, a second example lattice rib 94 is laid down in a second geodesic direction (complimentary to the first geodesic direction). Without steering, the lattice rib 94 would also intersect the window 16 as represented by geodesic line 96. SFL heads 30 and 70 are steered during placement of unidirectional collimated tows and cross plied laminate band to laterally displace the lattice rib 94, as represented by arrows 98, in a smooth contour around the window 16 and then rejoin the geodesic line 96. This allows the lattice rib 94 to be continuous with resulting continuity of stress reaction along the length of the rib and around the disrupting feature such as window 16.
Lattice ribs of the geodesic pattern proximate lattice rib 88 and lattice rib 94 are steered during placement to maintain spacing from adjacent ribs. Spacing of lattice ribs is compressed in the proximity of the design features such as window 16 which are steered around resulting in a modified geodesic pattern for the ribs as seen in
To accommodate steering for placement of the unidirectional collimated fiber bands and cross plied laminate bands in the lattice ribs, the fiber placement heads 34 and band placement heads 76 of SFL heads 30 and 70 are laterally translatable relative to the direction of head travel (48 and 86) as represented by arrows 100 in
While described herein for a concave mold, the processes and apparatus disclosed may be employed for molds having a convex surface or mixed concave/convex surface.
Establishing the requirements for layout and machine programming to accommodate the desired combination of laminated skin and modified geodesic lattice ribs is accomplished as shown in
Operation of the programmed SFL heads employed in the disclosed embodiments is described in
Having now described various embodiments of the disclosure in detail as required by the patent statutes, those skilled in the art will recognize modifications and substitutions to the specific embodiments disclosed herein. Such modifications are within the scope and intent of the present disclosure as defined in the following claims.
Claims
1. A method for fabrication of an aerospace structure comprising:
- employing at least one unidirectional steered fiber layup head to lay down a plurality of collimated tows in a predetermined laminated pattern on a mold surface to produce a fuselage skin;
- employing at least one cross plied laminate steered fiber layup head to lay down a cross plied laminate base interface on the fuselage skin to establish a lattice rib shape for each of a plurality of lattice ribs;
- steering a band placement head in the at least one cross plied laminate steered fiber layup head laterally diverging from a baseline geodesie lattice to avoid structural design features and to maintain spacing from adjacent steered lattice ribs;
- employing the at least one unidirectional steered fiber layup head to lay down a plurality of collimated tows on the base interface of each of the plurality of lattice ribs for a plurality of unidirectional tow plies in each lattice rib;
- steering a fiber placement head in the at least one unidirectional steered fiber layup head to match the lattice rib shape laterally diverging from the baseline geodesie lattice to avoid structural design features and to maintain spacing from adjacent steered lattice ribs;
- employing the at least one cross plied laminate steered fiber layup head to lay a cap over the plurality of unidirectional tow plies in each of the plurality of lattice ribs; and
- steering a band placement head in the at least one cross plied laminate steered fiber layup head to track the lattice rib shape and position the cap over the plurality of unidirectional tow plies.
2. canceled
3. canceled
4. The method as defined in claim 2 wherein steering of the fiber placement head additionally includes rotating the fiber placement head about a nominal axis perpendicular to a mold surface to maintain fiber alignment with a direction of travel.
5. The method as defined in claim 3 wherein steering of the band placement head additionally includes rotating the band placement head about a nominal axis perpendicular to a mold surface to maintain band alignment with the direction of travel.
6. The method as defined in claim 1 wherein the step of employing at least one unidirectional steered fiber layup head to lay down a plurality of collimated tows in a predetermined laminated pattern on a mold surface to produce a fuselage skin further includes employing a tow cutter and clamp mechanism in a fiber placement head to terminate and restart the collimated tows at the design features.
7. The method as defined in claim 1 wherein the step of employing the at least one cross plied laminate steered fiber layup head to lay a cap over the plurality of unidirectional tow plies further comprises draping of the cap over the plurality of tow plies.
8. The method as defined in claim 7 further comprising extending the draped cap over a surface of the skin adjacent the lattice rib.
9. A system for fabrication of an aerospace structure comprising:
- a mold having a surface;
- at least one unidirectional steered fiber layup head adapted to lay down a plurality of first collimated tows in a predetermined laminated pattern on the mold surface to produce a fuselage skin;
- at least one cross plied laminate steered fiber layup head adapted to lay down a cross plied laminate base interface on the fuselage skin to establish a lattice rib shape for each of a plurality of lattice ribs in a lattice layup, said at least one cross plied laminate steered fiber layup head having a band placement head steerable to diverage from a baseline geodesie lattice pattern to avoid structural design features and to maintain spacing from adjacent steered lattice ribs; and,
- said at least one unidirectional steered fiber layup head further adapted to lay down a plurality of second collimated tows on the base interface of each of the plurality of lattice ribs for a first plurality of unidirectional tow plies in each lattice rib, said at least one unidirectional steered fiber layup head having a fiber placement head steerable to match the lattice rib shape to avoid the structural design features and to maintain spacing from the adjacent steered lattice ribs.
10. The system as defined in claim 9 wherein said at least one cross plied laminate steered fiber layup head is further adapted to lay a cap over the plurality of unidirectional tow plies in each of the plurality of lattice ribs, said band placement head further steerable to track the lattice rib shape and position the cap over the plurality of unidirectional tow plies.
11. The system as defined in claim 9 wherein the band placement head is laterally translatable relative to a baseline geodesic lattice.
12. The system as defined in claim 11 wherein the band placement head is rotatable about a nominal axis matinained perpendicular to the surface of the mold to maintain band alignment with a direction of travel.
13. The system as defined in claim 9 wherein the fiber placement head is laterally translatable relative to a baseline geodesic lattice.
14. The system as defined in claim 13 wherein the fiber placement head is rotatable about a nominal axis maintained perpendicular to the surface of the mold to maintain fiber alignment with a direction of travel.
15. The system as defined in claim 9 wherein the at least one unidirectional steered fiber layup head further comprises a plurality of spindles each carrying tows of structural fiber, said tows of structural fiber dispensed from the spindles with controlled tension to the fiber placement head as individual tows.
16. The system as defined in claim 15 further comprising:
- a band collimator in the fiber placement head adapted to combine the individual tows into the first or second collimated tows;
- tow restart rollers receiving the first or second collimated tows from the band collimator,
- a compaction roller adapted to press the first or second collimated tows from the tow restart rollers initially onto the surface of the mold and subsequently on prior laid first collimated tows, laminate interface or second collimated tows to produce multiple layer structures; and
- a controlled heat source proximate the compaction roller for adhering the first or seocnd collimated tows; and, a band cutter and clamp mechanism adapted to terminate each fiber band along a direction of head travel.
17. The system as defined in claim 9 wherein the at least one cross plied laminate SFL head further comprises a plurality of cassettes each cassette having rolled cross plied fiber laminate bands of determined widths for the caps and base layer, each cross plied laminate band fed under controlled tension to the band placement head.
18. The system as defined in claim 17 further comprising:
- band restart rollers receiving cross plied laminate band;
- a compaction roller adapted to press initially each cross plied laminate band onto the skin as the laminate base interface or prior laid unidirectional tow plies; and,
- a controlled heat source proximate the compaction roller for adhering each cross plied laminate band;
- a band cutter and clamp mechanism adapted to terminate a run of each cross plied laminate band along a direction of head travel.
19. A damage tolerant lattice rib structure comprising:
- a skin having a plurality of collimated tows in a predetermined laminated pattern;
- a cross plied laminate base interface laid on the skin to establish a lattice rib shape for each of a plurality of lattice ribs, said lattice ribs steered for lateral displacement from features in the skin;
- a first plurality of collimated tows laid on the base interface of each of the plurality of lattice ribs for a first plurality of unidirectional tow plies in each lattice rib;
- a first cap laid over the plurality of unidirectional tow plies in each of the plurality of lattice ribs;
- a second plurality of collimated tows laid on the first cap of each of the plurality of lattice ribs for a second plurality of unidirectional tow plies in each lattice rib; and,
- a second cap laid over the second plurality of unidirectional tow plies in each of the plurality of lattice ribs.
20. The damage tolerant lattice rib structure as defined in claim 19 wherein the first cap has a width relative to a width of the first plurality of unidirectional tow plies sufficient to drape over the first plurality of unidirectional tow plies to a surface of the skin.
21. The damage tolerant lattice rib structure as defined in claim 19 wherein the second cap has a width relative to a width of the first plurality of unidirectional tow plies sufficient to drape over the first plurality of unidirectional tow plies and second plurality of unidirectional tow plies to a surface of the skin.
Type: Application
Filed: Mar 23, 2017
Publication Date: Sep 27, 2018
Inventors: Boris B. Sokolov (Renton, WA), Mostafa Rassaian (Bellevue, WA), Marc J. Piehl (Renton, WA)
Application Number: 15/467,980