Metal working – Method of mechanical manufacture – Structural member making
Reexamination Certificate
2002-02-12
2004-05-18
Jordan, Charles T. (Department: 3644)
Metal working
Method of mechanical manufacture
Structural member making
C029S897320, C029S419100, C029S448000, C029S458000, C029S462000, C029S527200, C244S126000
Reexamination Certificate
active
06735866
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates in general to methods for manufacturing a composite material structure, in which on a precured element (skin) are glued other uncured elements (beams) by placing an adhesive layer between them (between the precured element and each uncured element), thereby obtaining a structural union. The adhesive is cured at the same time as the latter elements.
More specifically, the object of the invention is to develop the required theoretical concepts and the corresponding manufacturing methods for providing a union system by co-bonding of one or several elements (beams) made from composite materials and uncured, and a base (skin) also made of composite material but which is precured, with multiple changes in thickness. A precise adjustment must be obtained of the uncured elements, both with the adhesive surface (skin) and with the other, upper surface.
For this purpose, the tooling used is the most relevant factor, which is in this case a rigid invar rod (described in detail below) with a direct bag that allows to obtain a high dimensional precision at the same time as a tight positioning tolerance. To clarify the term “direct bag”, it should be pointed out that the direct vacuum bag concept relates to the fact that the elements comprising the vacuum bag (FEP or fluoro-ethylene-propylene, AIRWEAVE type aerator and bag plastic) are directly on the part to be cured without any interposed tooling. This ensures a uniform consolidating pressure.
The union is achieved by curing the adhesive layer under strict pressure conditions and at its polymerization temperature, which must match that of the resin of the uncured elements as both chemical processes take place simultaneously in the same autoclave cycle.
Likewise, the union effected is designed to withstand shear loads applied to the skin by the beams, due to deflections of the structure, and detachment forces applied on the beams by the skins, as well as various types of internal pressures such as those of a fluid when the torsion box is the fuel tank.
BACKGROUND OF THE INVENTION
The most remarkable characteristic of the present invention is the use of a rigid tooling (a system of rigid tools and rakes) for the bonded union, combined with applying autoclave pressure using a scheme with a vacuum bag in direct contact with the elements to be bonded and cured.
In order to bond the uncured elements to a precured skin which must match another complex surface at the unbonded end, a manufacturing system was initially developed with a flexible tooling using the “inflatable tool” technique. These tools were made from an elastomer material stiffened as required with carbon fiber.
The high cost and low reliability of this tooling spurred the development of a rigid tooling system to solve these problems; this is the co-bonding system with rigid tools.
During the development stage of the rigid tooling trials were performed with tools of various configurations:
Several configurations were tested with steel material, which were discarded because of the thermal gradients generated which resulted in deformations of the part to the point of not obtaining the required quality.
Two constructive solutions have been tested using invar:
Rigid tools made from welded sheets which are later machined. This solution is the lightest but its construction is extremely complex and involves several deformation and straightening operations during fabrication.
It is also possible to leave a small wall thickness after machining, with the resulting risk of collapse of the tool in the autoclave. The resulting weight does not allow manual handling.
Rigid tools made from a sheet with a sufficient thickness and enlightened by machining, and later covered by a welded plate.
The enlightened material weighs ≈25 kg as compared to a weight of the solid tool of around 150 kg. This enlightening is not justified due to handling issues as it greatly increases the tool fabrication cycle and its handling still requires additional means.
As well as the use of different materials and configurations of the rigid tools, another basic aspect in the use of this type of blade-shaped rigid tooling is the distance between the edge of the rigid tool and the radius of the beam foot. The following configurations were tested:
The rigid tool extending 2 mm into the radius.
The rigid tool remaining 2 mm above the radius.
The rigid tool extending as far as the middle of the radius.
It was concluded that the rigid tool should end above the radius of the foot, as this configuration provides the best dimensional and quality results, as well as facilitates demolding.
Later studies led to an optimization of the distance between the rigid tool and the beam foot radius, arriving at the conclusion that the ideal distance was 3 mm from the edge of the rigid tool to the start of the beam foot radius.
The results obtained indicate that rigid tools should be made of solid invar, as this simplifies their construction and improves dimensional tolerance. Additionally, they are handled in all cases with auxiliary means and not manually, regardless of their configuration.
As regards the bonded unions, using a different type of tooling, the prior art closest to the application are those relating to:
1. Joining beam stiffeners of the torsion box for the A330-340 airplane horizontal stabilizer (currently in the production stage).
2. Joining the longitudinal stiffeners for the skin of the torsion box of the CASA 3000 airplane wing (in prototype stage).
3. Joining auxiliary longitudinal beams to the skin of the torsion box of test FB.5-1 of the technological development program for large airfoils (GSS) to be applied to the horizontal stabilizer of the A3XX.
From the results of the above experiences and from other relevant manufacturing studies and tests it was concluded that the application of the method of the present invention is feasible and reliable for its use in parts of highly demanded withstanding structures and with high quality requirements, with complex shapes and strict dimensional tolerances.
FIELD OF APPLICATION OF THE INVENTION
This invention is applicable to the manufacture of structures made of composite materials in which participate a precured element (skin) and other uncured elements (beams) that are cured simultaneously to their union to the precured element.
The structures for which this technique would be applicable are such as:
Airplane structures and controls, such as airfoils, moving airfoil surfaces, fuselages.
Space ships
Marine and land vehicles
Industrial machinery and equipment.
The various manufacturing stages which comprise the full process are:
Fabrication of the Skin
Tape laying on a curved tool.
Placing the vacuum bag on a laminate.
Curing in an autoclave.
There is no demolding operation nor a non-destruction inspection.
Fabrication of the J-beams
Flat tape laying.
2D cutting in fresh state on patterns.
Mounting patterns until final configuration of the beam cloths.
A first hot forming cycle to obtain two L-shaped beam halves.
Placing one half on the other.
A second hot-forming cycle, to provide the final J-shaped beam.
3D cutting of the uncured beam rises as well as other cutting to obtain the final size of the beam after the curing cycle.
Fabrication of the Vacuum Bag
Approximate flat layout of the final bag configuration.
Tracing the bag in a flat machine with numerical control or manually with jigs or Mylar. The position of the beams and fasteners on the radii is traced.
Formation and manual attachment of the fasteners.
Fabrication of the Final Structure: Co-bonding
Assembling the beams on rigid invar tools on auxiliary preassembly benches. Each bench has two rigid tools to allow ergonomic working conditions.
Placing all possible elements of the final vacuum bag on the beams in the preassembly benches. Additionally, a consolidation is carried out to ensure adjustment on the skin. For this, the preassembly benches are provided with a surface which perfectly resembles the surface of the skin.
Transfer of rigid tools+rakes+be
Cerezo Pancorbo Carlos
Garcia Garcia Aquilino
Nogueroles Vi{overscore (n)}es Pedro
Airbus Espana S.L.
Jordan Charles T.
Ladas & Parry
Nguyen Trinh
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