A method of manufacturing wing structures.

The present invention relates to a method of manufacturing wing structures.

For a better understanding of the state of the art and the problems associated therewith, firstly a method of the known type will be described with reference to Figures 5 to 9. As is known, the wings of modern aircraft have an inner structure 20 composed of spars and ribs and covered externally by a bottom panel 10 and a top panel 12. According to the current technology, a wing is initially constructed by fixing the bottom panel to a static support structure (so-called construction base, not shown) which is substantially vertical and keeps the panel in the correct form according to the predetermined wing profile. The spars and the ribs forming the inner structure of the wing are then arranged and subsequently riveted onto the top surface of the bottom panel.

In order for the wing to have the wing profile specified at the design stage it is essential that the top panel is fixed to the remainder of the wing over an area which matches or corresponds precisely to the predetermined wing profile. Those skilled in the art know that if the top panel were to be riveted directly on top of the spars and ribs already assembled, it would form an irregular undulating surface, with tensions induced by deformations imparted locally in order to adapt the top panel to the upper surface of the structure consisting of spars and ribs. It is therefore necessary to arrange between the upper surface of the inner structure and the bottom surface of the top covering panel a spacer which is varyingly shaped and has a variable height so that the top panel may rest continuously on a precise contact surface so as to assume the predetermined wing profile.

At present, as shown in Figure 5, a subassembly 30 of the wing being constructed, comprising the bottom panel 10 and the inner structure 20 fixed onto it, is transferred by means of a transportation apparatus T from the construction base to a compaction plant station. Here (Figure 6) the wing subassembly is arranged horizontally and, by means of a robot, an adhesive shim S consisting of a hardening resin (usually a dual-component resin reinforced with glass fibres, aluminium or the like) is applied along the top 21 of the inner

structure 20, said resin being intended to fill the gap between the top of the inner structure and the bottom surface of the top panel 12. Then (Figure 7), by means of the apparatus T, the top panel 12 is placed on the top 21 of the inner structure where the shim S was applied. The compaction plant is then closed (Figure 8): the top panel 12 is then pressed downwards (Figure 8) by means of a bar structure U which is suitably shaped so as to force the top panel to assume the wing profile specified during design. It is then necessary to wait about 24 hours in order for the shim to harden at least partly. Closing of the compaction plant causes the top panel to rest at certain points on the inner structure, while in the remaining zones it compresses the shim which has been applied in an excess amount. Then the compaction plant is opened, the top panel 12 is removed (Figure 9) and, using a milling cutter C, the excess shim which emerges laterally from the spars and the ribs of the inner structure is trimmed, with removal of the shavings by means of suction. It is then possible to re-transfer the wing from the shim application station back to the construction base and assembly of the wing may be continued. It is known that, during this stage, it is necessary to access the inner space in order to arrange the various devices and systems there, before, mounting the top panel.

The method discussed above has various disadvantages: the wing under construction must in fact be transferred twice from the base to the shim application station; there exists downtime due to the need to allow polymerisation of the shim: a compaction plant must be prepared and used; finally, the excess shim must be trimmed and the resultant shavings removed by means of suction. Moreover, shims of varying consistency must be used when the thickness to be filled or compensated for exceeds a certain height, usually when it exceeds 1.5 mm. The operator must have a considerable amount of experience in order to establish or predict, before the shim is applied, at which points the thickness will be greater than the predetermined height and the need, therefore, to apply locally a mixture with a different consistency and/or provide a spacing strip.

A general object of the present invention is to propose a manufacturing method which is able to overcome the abovementioned drawbacks, solving principally the problem of optimising the production stages and reducing the associated times and costs. Another

specific object of the invention is to produce wing structures which have a precise profile. A further object of the invention is to reduce to a minimum the transfer and movement stages, both in order to reduce the apparatus required for this purpose and in order to increase the level of safety for the operating personnel.

These objects and advantages, which will be understood more clearly below, are achieved according to the invention by a method as defined in the accompanying claims.

A preferred but non-limiting embodiment of the invention will now be described. Reference is made to the accompanying drawings in which:

Figure 1 is a perspective view which shows a stage involving scanning of two parts of a wing under construction;

Figure 2 shows a computer for processing the digital images generated by the scanning operations according to Figure 1 ; Figure 3 shows schematically a certain number of compensation inserts;

Figure 4 shows application of the inserts according to Figure 3 onto one of the wing parts shown in Figure 1 ;

Figures 5 to 9 show the operating stages of a conventional method of manufacturing an aircraft wing.

With reference now to Figure 1, initially a subassembly 30 consisting of the bottom panel 10 of the wing with the inner structure 20 of the wing fixed onto the top or inner surface 11 of the panel by means of processes known per se is preassembled. The top panel 12 of the wing is also preassembled. Throughout the present description and the claims the terms and expressions indicating positions and directions such as "top" and "bottom" are understood as referring to the condition when mounted on an aircraft. Expressions such as "inner" and "outer" instead refer to positions inside and outside the body of the wing.

The subassembly 30 and the top panel 12 are retained by respective templates or racks 40 so that they adopt the respective shape conditions specified during design in keeping with the desired wing profile. One or more optical reading means, such as scanners 50, are used

to perform respective scanning of the top surface 21 of the inner structure 20 of the wing and the bottom surface 13 of the top panel, or at least the zones (indicated by broken lines 14 in Figure 1) of this surface which it is envisaged must be positioned, once the top panel has been mounted, so as to be aligned with or situated opposite the top surface 21 of the inner structure.

The scanners 50 generate a three-dimensional digital model or image of each surface and transmit these to a processing and control unit 60 - typically a PLC (Programmable Logic Controller) or a PC (Personal Computer) - provided with application software for acquiring digital images, processing them and for generating a single three-dimensional mathematical model representing the compensation thickness which must be provided between the top surface 21 of the inner structure 20 and the parts 14 of the bottom surface 13 of the top panel 12, so that the latter assumes the form specified during design. The three-dimensional model of the compensation thickness is then transferred to rapid manufacturing machines which produce one or more spacers or inserts 70 (Figure 3). These are members which, in plan view, have forms corresponding to the top surface 21 of the inner structure or to portions thereof and a variable thickness so that, by arranging them between the two surfaces 14 and 21, they suitably space the structure 20 from the top panel so that the latter assumes a profile coinciding exactly with the predetermined wing profile. In other words, the inserts 70 together provide an upper support surface which is as extensive and continuous as possible, corresponding to that of the desired wing profile.

The techniques and the means necessary both for scanning the surfaces 14, 21 between which the compensation insert (or inserts) must be placed and the choice of the particular technology for production of the inserts, are not per se relevant for the purposes of understanding the invention and will therefore not be described here in detail. As regards the technology to be used for manufacture of the compensation insert, it may be chosen from among the modern rapid prototyping and manufacturing techniques. These techniques allow the reproduction of very intricate structures and of finer details, also of the subassemblies. By way of example it is possible to use growth techniques where the object is constructed by means of growth with successive addition and aggregation of particles,

strands or layers of material. These techniques include, for example, stereolithography (based on photopolymerization), selective laser sintering based on the direct sintering of powders using laser, laminated object manufacturing based on the superimposition of layers of thermoadhesive paper, fused deposition modelling based on the heating and extrusion of filaments of thermoplastic material, solid ground curing based on the solidification of photopolymer liquid or 3-D Printing based on the sintering of powders using laser, or multi-jet modelling based on an ink jet of thermoplastic material.

It is important to mention that, while the operations of scanning, creation of the various three-dimensional mathematical models and practical production of the spacer are being performed, it is possible to continue working on the open wing, arranging inside it the various devices and systems required.

The one or more compensation inserts 70 are then applied onto the top surface 21 of the inner structure, preferably using a structural adhesive. Finally the top panel 12 is placed on the compensation insert and riveted definitively in accordance with its correct aerodynamic profile.

As may be appreciated, as a result of the present invention, it is possible to avoid various conventional operations as discussed in the introductory part of the description, hi particular, it is not required to remove the wing under construction from the base nor perform other transfer movements. Scanning of the bottom or inner surface of the top panel and the upper surface of the inner structure of the wing is performed with the latter retained on the base, without the need for removal thereof. Since it is not required to apply any adhesive shim, it is also not required to provide apparatus for pressing the top apparatus onto the shim applied. The conventional downtime for allowing hardening of the shim is eliminated. It is not necessary to open the wing again and remove the top panel, it is not required to perform milling in order to trim the excess shim from the edges of the structure, nor do the shavings have to be removed by means of suction. There is no longer any need to prepare various operating structures for application of the shim and for movement and transfer of the wing parts under construction.

Finally, it will be appreciated that the joining spacer may be created in a very small amount of time, that the method is extremely flexible, and that the final quality of the wing produced improves.

It is understood that the invention is not limited to the embodiment described and illustrated here which is to be regarded as an example of the method; the invention may instead be subject to modifications relating to the form and arrangement of parts, choice of technology to be used for manufacture of the spacer and the constructional details of the latter. For example, the software which manages the production of the spacer may establish that for the zones where the two facing surfaces 14 and 21 are situated at less than a predetermined minimum distance from each other, no spacer must be produced. Consequently, the number of inserts used to cover the top surface 21 of the inner structure may vary depending both on the dimensions of the area which each insert must cover and on constraints determined by zones of minimum thickness.