Method and equipment for forming and assembling uncured spars for the horizontal stabilizers of aircraft

The present invention relates to a method and equipment for forming and assembling uncured spars shaped as "H-beams" made from carbon-resin, particularly for horizontal stabilizers of aircraft.

As shown schematically in Figure 1, a spar of the type to which the invention relates is formed by the assembly of two coupled C-sections made from carbon-resin, to which triangular-section fillers are applied. The C-shape is imparted to each initially flat section by thermo forming. A layer of adhesive is then applied along the joining area of each of the two sections, which are then assembled by superimposing the two webs on each other. The fillers are applied along the two longitudinal recesses located in the joining areas between the webs and the flanges of the sections.

Up to the present time, most of the operations for handling the components of spars of the aforesaid type, and for assembling these components, have been carried out manually or in a non-automated way.

The object of the present invention is to assemble spars of the aforesaid type with the maximum amount of automation, in order to provide all the benefits of high productivity and precision which automated processes offer for mass production. In this way, initial materials such as preimpregnated and adhesive tapes, or intermediate products such as flat laminates, are processed with a high degree of repeatability into highly complex intermediate products such as H-beam spars with profiles which may be curved.

In particular, it is desirable to establish an optimal spar formation cycle which is repetitive and controlled, takes place in conditions of uniform temperature, does not cause the initiation of the laminate curing process, ensures a gradual and uniform cooling of the laminate after forming, and minimizes the presence of wrinkles on the laminate.

These and other objects and advantages, which will be made clearer below, are achieved

according to the invention by a method as defined in Claim 1. According to another aspect of the invention, a forming device as defined in Claim 7 is proposed. Preferred embodiments of the invention are specified in the dependent claims.

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

Figure 1 is an exploded view which shows the components of a spar;

Figure 2 is a schematic perspective view of a cell for the production of spars;

Figure 3 is a plan view of the cell of Figure 3;

Figure 4 is a perspective view of a device for forming C-sections;

Figure 5 is a perspective view of an overhead travelling crane for manipulating the cell of Figure 2;

Figure 6 is an enlarged view of part of the overhead travelling crane of Figure 5;

Figure 7 is a perspective view of a platform for manipulating the cell of Figure 2;

Figure 8 is a perspective view of part of a thermo forming apparatus of the cell of Figure 2;

Figure 9 is a schematic lateral view of two forming devices with corresponding C- sections superimposed;

Figure 10 is a perspective view of an apparatus for forming fillers in the cell of Figure 2;

Figure 11 is an enlarged schematic lateral view of part of the apparatus of Figure 10; and

Figure 12 is a schematic elevation of a vacuum compaction apparatus of the cell of Figure 2.

With initial reference to Figures 2 and 3, these show a manufacturing cell or unit for forming spars of the horizontal stabilizers of an aircraft. The cell comprises a group of work stations, mechanisms for transferring the materials between these, and storage areas. In the preferred embodiment which is shown, the cell comprises two overhead travelling cranes 10 and 11 which can run on common rails 12 in a direction which in this case is specified as longitudinal, two apparatuses 20 and 21 for hot forming carbon-resin sections 13 and 14 with a C- or U-shaped cross section, an apparatus 30 for forming fillers 15, a

store 40 for forming devices, a store 41 for flat carbon-resin blanks (also to be hot formed), and a plurality of parallel platforms 50-57, elongated in transverse directions, for the assembly and manipulation of the spars and their components.

A forming device indicated as a whole by 60 (Figure 4) comprises an elongate core 61 having a substantially rectangular cross section, fixed securely to a rigid flat plate 62 having an insulating surface 63 which extends around the whole of the core 61. Centring holes or recesses 64, whose function is explained below, are formed in the plate 62.

Various forming devices and initially flat blanks of different formats, for the manufacture of spars of different sizes, are kept in the stores 40 and 41. One of the overhead travelling cranes initially picks up one of the forming devices 60 from the store 40 and transfers it to the first preparation platform 50 (Figure 3). All the movements of the overhead travelling crane are automated and produced by commands issued by a programmed processing unit which supervises the operation of the cell as a whole, and therefore also supervises the operation of all the other motor and actuator members described here, according to specified operating sequences. The overhead travelling crane is provided with proximity sensors which, when activated in various combinations, enable the supervision system to recognize the forming device which is moved.

Each overhead travelling crane has a pick-up and movement unit 16 which is transversely elongated and vertically movable, and which can be turned over about its transverse axis. The pick-up unit 16 comprises a set of suction pads 17 (Figure 6) connected to a suction system, and a set of pins 18 which are extendable and retractable. These pins are extended to engage in the centring holes 64 of the plate 62, and, in order to keep the plate sealed, the holes are covered by circular cover elements or "caps". To ensure that both the position and the orientation of the plate are correct, each plate has at least two of these centring holes. Extendable centring pins 18 are also advantageously provided on the various assembly and manipulation platforms 50-57.

When the device 60 has been placed on the platform 50, one of the two overhead travelling cranes activates its suction cups 17 to pick up from the store 41 a flat carbon-resin blank

corresponding to the core which has been picked up, and places it on the core which is located on the preparation platform 50. This platform is preferably provided with a bed of free-running balls 56 on its upper surface to form supporting elements for the plate 62 and to enable the position and orientation of the forming device 60 to be adjusted and corrected.

The device with the blank to be formed is transferred to the adjacent manipulation platform 51 by actuating groups of powered rollers 19 (Figures 5 and 6) of the overhead travelling crane. The platform 51 and its neighbouring platform 52 are each divided into a sequence of alternating sections 51a, 51b (Figure 7), provided respectively with free-running rollers 151a with transverse axes and with powered rollers 151b with longitudinal axes. The sections 51b with powered longitudinal rollers can be raised so as to engage with the base of the plate 62 and enable the device 60 to be transferred, by the actuation of the powered rollers 151b, into the adjacent thermoforming apparatus 20 (or 21).

Figure 8 shows a portion of the two thermoforming apparatuses 20 and 21. Each of these is provided with infrared lamps 22 which heat the blank to a temperature of not more than about 70°-90°C in order to soften the blank. When the desired temperature has been reached, a vacuum is created in the lower part of the apparatus. A silicone membrane 23 is drawn downwards by the action of the vacuum, thus forcing the "flanges" of the blank to bend downwards and reproduce the shape of the core. In this way, the C shape of the section 13 or 14 is produced (Figure 1). In order to make the thermoforming process adiabatic, each of the apparatuses 20 and 21 is provided with a vertically movable hood 25 with a polyurethane perimetric bottom gasket 26 which engages to form a hermetic seal with a fixed frame (not shown) of the hot forming apparatus.

When the hot forming has been completed, the C-sections are conveyed, together with their cores and the corresponding plates, to the platforms 53 and 54, where a line of adhesive is applied manually to the joining area of the section. The section, with its core, which is located on the platform 53 is picked up by the overhead travelling crane, turned over, held by the pick-up unit 16 of the overhead travelling crane, and superimposed on and joined to the section located on the platform 54 (Figure 9).

The two sections which have been joined, together with their forming devices, are then transferred to the platform 55, where two fillers are applied manually to the longitudinal cavities on the two opposite sides of the C-sections which have been joined together. The fillers, which have an essentially triangular cross section, are formed by an apparatus 30 (Figures 10 and 11) from a set of reels of adhesive film 15a and of unidirectional carbon fibre strip 15b, which are initially laminated, then heated in a chamber 31 with resistance lamps 32, corrugated in their longitudinal direction by means of counter-rotating rollers 33 with corrugated profiles, bent and compacted laterally, and drawn through extruder rollers 34 which impart the desired triangular cross section to the fillers. The fillers are finally cut into portions whose length matches that of the spar which is to be formed.

The uncured spar produced in this way is transferred to the compaction platform 56, where a compaction apparatus 70 applies a vacuum which forces a membrane 71 to compact the sections and fillers together. In this stage also, the flat edge surface of the plate 62 surrounding the core interacts in a sealed way with a gasket of the compaction apparatus during the application of the vacuum.

As will be understood, the plate 62 helps to prevent the deflection of the core, provides hermetic sealing surfaces both in the C-section thermoforming apparatus and in the filler compaction apparatus 70, and has centring recesses for the precise positioning and orientation of the core in all the work stations.