Production processes for a stiffened aircraft structural panel by FSW welding

Abstract

A method for producing a stiffened aircraft structural panel, comprising the following steps: – manufacturing a web (2) by forming a metal sheet; – manufacturing a stiffener (3) comprising a fixing edge (7) and a reinforcing edge (5); – positioning the web (2) and the stiffener (3) in a workpiece clamping fixture (13) having a convex molding surface (17) opposite the joining lines; – friction stir welding of the web (2) and the stiffener (3), the rotary welding tool (11) pressing the stirred material against the convex molding surfaces (17) forming two fillets connecting the web (2) and the stiffener (3). Figure for the abstract: Fig. 10

Description

Title of the invention: Methods for producing a stiffened aircraft structural panel by FSW welding Technical field

[0001] The invention relates to the field of aeronautics and more particularly concerns the methods of manufacturing stiffened structural panels used in the construction of an aircraft.

[0002] Stiffened structural panels are generally made of a sheet of material called a sail, which is made rigid by stiffeners. Stiffened structural panels are commonly used in aircraft architecture for elements such as: floors, walls delimiting a landing gear bay, a sealed fuselage bottom, a fuselage skin, a door skin, etc., these elements being able to be pressurized or not. PRIOR ART

[0003] The most frequently used process for the production of stiffened structural panels is assembly by riveting. This assembly is well mastered in the aeronautics field, but it involves numerous operations that are difficult to optimize, such as drilling, application of mastic, installation of fixing rivets, etc. In addition, the creation of shape accidents such as holes penalizes the fatigue resistance of the panel. The mass of the panels obtained by riveting assembly is also not optimal, due to the superposition of material thicknesses and the mass of the fasteners.

[0004] Stiffened structural panels can also be obtained by machining a blank whose thickness corresponds to the total thickness of the panel (wall and stiffeners) that is desired. Machining-based processes make it possible to obtain a finished stiffened structural panel which resolves a certain number of the disadvantages of riveted assembly. However, these machining operations require the removal of a very large quantity of material. The material lost is of the order of 95 to 98% of the mass of the blank. These processes are therefore prohibitively expensive both in terms of raw material and machining costs. They also involve significant machining times and require specific and expensive equipment (large milling machines).

[0005] Furthermore, friction stir welding (FSW) processes offer interesting advantages for the manufacture of stiffened aircraft structural panels, at least from a theoretical point of view. Indeed, many solutions using this welding technology have been explored and patented (see for example patent applications FR3049929 and EP2862795).

[0006] Some of these solutions require the machining of complementary assembly shapes between the stiffeners and the wall. Grooves, for example, may be necessary for assembly. These elements represent a production cost and involve delicate preliminary assembly phases which can lead to defects.

[0007] Other solutions explored for the application of friction stir welding require the positioning of stiffeners on plate junctions forming the web, in order to allow friction stir welding.

[0008] It is also known to use friction stir welding to weld together extruded profiles which each form a stiffener attached to a portion of the web. Although this type of solution is better controlled than the solutions described previously, it is reserved for aluminum grades allowing the extrusion of profiles, for example extrudable aluminum alloys of the 7000 series. These alloys are not the best in terms of corrosion resistance and cannot be used for certain aeronautical applications. These solutions are also very expensive due to the price of the extruded profiles.

[0009] It is also known to use friction stir welding in several parallel passes to weld metal blocks onto a wall. This type of process is firstly expensive due to the various passes required for welding each metal block, and the need for final machining of each metal block to give it the shape of a stiffener. The feasibility range is reduced and the residual deformation is greater. Risks of corrosion also arise with unwelded gaps forming areas of moisture infiltration. These processes also require final machining of the metal block to give it the shape of a stiffener, which further increases the cost.

[0010] None of these solutions for the application of friction stir welding gives complete satisfaction and this welding technique is therefore currently not very widespread for the manufacture of stiffened structural panels, because the control of the final shapes of the weld obtained is not very guaranteed, and not very reproducible, and does not correspond to the safety standards required for aeronautics. Statement of the invention

[0011] The invention aims to improve the methods of producing stiffened aircraft structural panels of the prior art, by allowing the safe use of friction stir welding.

[0012] To this end, the invention relates to a method for producing a stiffened aircraft structural panel, this panel comprising a web on which at least one stiffener is fixed, this method comprising the following steps: - manufacturing a veil by shaping a metal sheet, this veil comprising a first face and a second face; - manufacture of a stiffener extending in a longitudinal direction, this stiffener comprising a fixing edge extending substantially parallel to the longitudinal direction, and a reinforcing edge which is opposite the fixing edge and which extends parallel to the longitudinal direction; - positioning the web and the stiffener in a part-gripping assembly, the fixing edge of the stiffener being arranged against the first face of the web along two junction lines between the web and the stiffener, on either side of the fixing edge, the part-gripping assembly comprising a convex molding surface opposite each of the two junction lines; - friction stir welding of the web and the stiffener, by applying a rotating welding tool to the second face of the web, opposite the fixing edge of the stiffener, and moving the rotating welding tool along the longitudinal direction, the rotating welding tool pressing the mixed material against the convex molding surfaces, forming two fillet joints connecting the web and the stiffener.

[0013] The invention allows the production of stiffened aircraft structural panels using a method that is quick to implement and inexpensive, while avoiding most of the drawbacks of the prior art.

[0014] The invention makes it possible to avoid, compared to certain methods of the prior art, the need to supply profiles. The use of sheets is advantageous from the point of view of raw material cost as well as in the wide choice of metal alloy grades that can be used.

[0015] The invention thus makes it possible to improve the cost, quality, and speed of carrying out the processes.

[0016] The invention also makes it possible to rationalize and make more flexible the production of stiffened structural panels and to obtain productivity gains.

[0017] The method according to the invention may include the following additional characteristics, alone or in combination:

[0018] - in the step of positioning the web and the stiffener, the fixing edge is in plane-to-plane contact with the first face of the veil;

[0019] - the part gripping assembly comprises two anvils clamping the fixing edge of the stiffener, these anvils each comprising a rounding defining the convex molding surface;

[0020] - the convex molding surface is a semi-circular surface;

[0021] - the convex molding surface has a radius greater than or equal to two millimeters;

[0022] - the rotary welding tool comprises a mixing pin, as well as a shoulder of containment, and during the welding step, the kneaded material is pressed against the convex molding surfaces by the containment shoulder;

[0023] - during the welding step, the mixing pin is pushed into the material beyond of the first face of the veil;

[0024] - the mixing pin has a length greater than the thickness of the web;

[0025] - the mixing pin has a diameter substantially equal to the thickness of the edge stiffener attachment;

[0026] - the stiffener and the veil are made of the same aluminum alloy;

[0027] - the stiffener is made from a metal sheet;

[0028] - the stiffener is made from a metal sheet of constant thickness;

[0029] - the stiffener is manufactured by bending said metal sheet to form the edge of reinforcement;

[0030] - the stiffener is manufactured by cutting into said metal sheet;

[0031] - the stiffener is made from a strip of sheet metal;

[0032] - the part gripping assembly comprises an anvil for holding the reinforcing edge of the stiffener;

[0033] - the part gripping assembly comprises a base for holding the web;

[0034] - the fixing edge of the stiffener consists of a foot attached to a web of the stiffener, the foot having a thickness greater than the web;

[0035] - the foot has a connection fillet with the core of the stiffener;

[0036] - the veil is arranged in two portions arranged on either side of the fixing edge of the stiffener;

[0037] - the steps of manufacturing a stiffener, positioning the web and this stiffener, and welding are repeated for a plurality of stiffeners welded to the same web;

[0038] - the method comprises intermediate steps of producing a plurality of elementary structures each comprising a web and at least one stiffener, the stiffened structural panel being obtained by a final step of edge-to-edge welding of the webs of the elementary structures;

[0039] - the edge-to-edge welding of the sails of the elementary structures is carried out in integrating a stiffener at the junction of the sails;

[0040] - the veil is made from a sheet of an aluminum alloy of the 2000 series, and in that the stiffener is made from a sheet of another 2000 series aluminum alloy. PRESENTATION OF FIGURES

[0041] Other characteristics and advantages of the invention will emerge from the non-limiting description which follows, with reference to the appended drawings in which:

[0042] - [Fig. 1] represents in perspective a stiffened structural panel;

[0043] - [Fig.2] represents a sheet for the manufacture of the panel stiffeners stiffened structural of [Fig.l];

[0044] - [Fig.3] represents the sheet of [Fig.2] after cutting into bars;

[0045] - [Fig.4] represents one of the bars cut out of [Fig.3];

[0046] - [Fig.5] represents a stiffener for the stiffened structural panel;

[0047] - [Fig.6] is a general view of the welding step of the stiffener of [Fig.5] on a veil;

[0048] - [Fig.7] represents in perspective the assembly of the veil and the stiffener;

[0049] - [Fig.8] illustrates the part grip assembly allowing the assembly of [Fig.7]

[0050] - [Fig.9] illustrates the step of welding the stiffener and the web;

[0051] - [Fig. 10] is another illustration of the step of welding the stiffener and the web;

[0052] - [Fig. 11] illustrates the result of the welding step;

[0053] - [Fig. 12] illustrates a stiffened structural panel comprising several stiffeners;

[0054] - [Fig. 13] illustrates a first step in the creation of an elementary structure of stiffened structural panel;

[0055] - [Fig. 14] illustrates a second stage in the production of an elementary structure of stiffened structural panel;

[0056] - [Fig. 15] illustrates a third stage in the production of an elementary structure of stiffened structural panel;

[0057] - [Fig. 16] illustrates an alternative step for the realization of a structure elementary stiffened structural panel;

[0058] - [Fig. 17] illustrates an elementary structure of stiffened structural panels;

[0059] - [Fig. 18] represents a stage in the construction of a stiffened structural panel at start from elementary structures;

[0060] - [Fig. 19] represents another stage in the construction of a structural panel stiffened from elementary structures;

[0061] - [Fig.20] schematically represents an assembly of a stiffener and a veil ;

[0062] - [Fig.21] schematically represents an alternative assembly of a stiffener and a veil;

[0063] - [Fig.22] schematically represents another alternative assembly of a stiffener and a veil;

[0064] - [Fig.23] schematically represents another alternative assembly of a stiffener and a veil.

[0065] Elements similar and common to the various embodiments bear the same reference numbers in the figures. DETAILED DESCRIPTION

[0066] [Fig.l] is a perspective view of a stiffened structural panel 1 of an aircraft.

[0067] Such a panel 1 is for example used as a floor, wall, bottom or covering of a fuselage or door, whether these elements are pressurized or not.

[0068] The panel 1 illustrated in this example has a relatively simple shape falling within two intersecting planes, it being understood that the invention is suitable for stiffened structural panels having shapes ranging from the simplest (a flat plate, for example) to the most complex. The shaping of the sheets used in the method according to the invention is particularly suitable for complex shapes at a controlled cost.

[0069] The panel 1 comprises a web 2, consisting of a sheet of material, and stiffeners 3 which are fixed to different portions of the web 2.

[0070] The panel 1 is thus both light and rigid. In the present example, the panel 1 is made from an aluminum alloy such as those of the 2000 series. The aluminum alloys of this series are particularly advantageous in an implementation according to the invention, for producing an assembly that is not very sensitive to corrosion in its state after friction stir welding.

[0071] Aluminum alloy 2024 is particularly suitable for applications the most demanding aeronautical requirements regarding corrosion resistance, and the invention makes it possible to implement it. Such an aluminum alloy is available in the form of sheets.

[0072] The manufacturing method of this stiffened structural panel 1 will now be described. The web 2 is made from a 2024 aluminum alloy sheet brought to the desired shape by any known means (rolling, stamping, etc.), and the stiffeners 3 are also produced from a 2024 aluminum alloy sheet.

[0073] With reference to Figures 2 to 5, the stiffeners 3 are produced from a sheet metal 31 shown schematically in [Fig.2]. The sheet 31 is cut by any known means suitable for obtaining bars of material with the dimensions, tolerances, and geometric quality required for the application (cutting, machining, laser cutting, water jet, etc.).

[0074] From the sheet 31, bars 4 are thus obtained by cutting.

[0075] [Fig.4] illustrates one of these bars 4 which here has the shape of a parallelepiped whose thickness corresponds to the thickness of the sheet metal in [Fig.2] and whose width and the length results from the cutting operations with a view to its positioning on a predetermined zone of the veil 2. The bar 4 extends along a longitudinal axis 8.

[0076] This bar of [Fig.4] is then plastically deformed to bend one of its longitudinal edges. The bar 4 is for example placed in a rolling machine, or in a folding machine, which bends a portion of it to form a reinforcing edge providing a longitudinally rigid character to the bar 4.

[0077] [Fig.5] illustrates the profile of the bar 4 after this bending operation, which leads to the production of a stiffener 3.

[0078] Alternatively to the examples of Figures 2 to 4, the stiffeners 3 can be produced from a very long strip of sheet metal, having the appropriate width and wound in the form of a coil. This coil of sheet metal is then unwound and continuous rolling is carried out to obtain the desired profile, and the stiffeners are finally cut to the desired length.

[0079] This stiffener 3 thus comprises a reinforcing edge 5 obtained by the rolling or folding operation and an unfolded portion of the stiffener 3 forms a core 6. The core 6 is extended, opposite the reinforcing edge 5, by a fixing edge 7.

[0080] The reinforcing edge 5 and the fixing edge 7 extend parallel to the longitudinal direction 8.

[0081] The manufacture of the stiffeners 3 is thus carried out quickly and inexpensively, from a sheet metal according to a wide choice of alloys.

[0082] In the present example, the stiffeners 3 are made from a sheet whose thickness is equal to half the thickness of the sheet constituting the web 2. For example, 6 mm thick for the web 2 and 3 mm thick for the stiffeners 3.

[0083] [Fig.6] is a schematic profile view illustrating a portion of the web 2 which here is simply made up of a flat sheet, and which comprises a first face 9 and a second face 10. [Fig.6] is a general view illustrating a step of assembling a stiffener 3 and the web 2 by friction stir welding, to produce a stiffened structural panel.

[0084] The fixing edge 7 of the stiffener 3 is placed in position against the first face 9 of the web 2.

[0085] A rotary friction stir welding tool 11 is applied to the second face 10 of the web 2. The tool 11 is thus applied to the face of the web 2 which is opposite the face against which the stiffener 3 is positioned.

[0086] [Fig.7] is a detailed perspective view of the positioning of the stiffener 3 against the web 2. The fixing edge 7 of the stiffener 3 comes into plane-on-plane contact with the web 2, thus defining two junction lines 12 on either side of the fixing edge 7.

[0087] The junction lines 12 are the lines along which each of the faces of the stiffener 3 meets the plane of the first face 9 of the web 2. These junction lines 12 are sensitive areas that the invention allows to be welded in a secure and repeatable manner. The invention guarantees that the weld produced will encompass these junction lines 12, thus guaranteeing the absence of an interface likely to cause cracks or contain moisture.

[0088] [Fig.8] illustrates in detail the part gripping assembly 13 allowing this positioning of the stiffener 3 relative to the web 2 (this assembly 13 was not shown in figures 6 and 7).

[0089] In this example, the assembly 13 comprises a pair of anvils 14 acting as clamping jaws for holding the stiffener 3 between them. The part-gripping assembly 13 also comprises an element for positioning the web 2, shown diagrammatically in [Fig.8] by a double base 15.

[0090] The assembly 13 further comprises a third anvil 16 comprising a V-shaped section portion intended to hold the reinforcing edge 5 of the stiffener 3.

[0091] Thus, the anvils 14, 16 hold the stiffener 3 in position and the web 2 is held in position by the base 15. The mutual positioning of the elements of the part gripping assembly 13 is arranged so that the fixing edge 7 of the stiffener 3 comes against the web 2 as explained previously.

[0092] The two anvils 14 each further comprise a convex molding surface 17 located opposite one of the junction lines 12.

[0093] Each of the anvils 14 thus comprises a first contact surface 18 with the web 2, and a second contact surface 19 with the stiffener 3. The convex molding surface 17 is located at the junction between this first contact surface 18 and this second contact surface 19. In the present example, the convex molding surfaces 17 are produced by rounded parts connecting these surfaces 18, 19, of semi-circular shape and whose radius is greater than two millimeters.

[0094] With the assembly illustrated in [Fig.8], the friction stir welding operation is then carried out to secure the stiffener 3 and the web 2.

[0095] [Fig.9] is a detailed view of the junction of the web 2 and the stiffener 3 showing the rotary welding tool 11 during welding.

[0096] The rotary welding tool 11 was first set in rotation, then was applied to the second face 10 of the web 2, opposite the fixing edge 7 of the stiffener 3. In the present example, the axis of rotation of the tool 11 is contained in the median plane 20 which extends between the two faces of the stiffener 3, at the level of the fixing edge 7.

[0097] The rotary welding tool 11 is actuated and moved by any known means such as a milling machine or a polyarticulated robot. The tool 11 comprises a mixing pin 21 intended for softening and mixing the material and further comprises a containment shoulder 22 applying pressure to the second face 10 of the web 2.

[0098] The tool 11 is first rotated, then is driven into the material of the web 2, as this material softens. The tool 11 passes through the entire thickness of the web 2 and also drives into the material of the stiffener 3, up to the position illustrated in [Fig.9], in which the shoulder 22 comes into contact with the second face 10 of the web 2.

[0099] The tool 11 is then moved along the longitudinal direction 8 with a feed rate allowing friction stir welding.

[0100] The anvils 14, 16 and the base 15 also take up the forces produced by the rotary welding tool 11.

[0101] In the present example, the pin 21 has a diameter substantially equal to the thickness 23 of the fixing edge 7 of the stiffener 3, that is to say to the spacing between the two faces of the sheet metal forming the stiffener 3 at the level of the fixing edge 7, so as to push the material beyond the contours of the fixing edge 7.

[0102] Furthermore, the pin 21 has a length 24 (the distance between the shoulder 22 and the end of the pin 21, along its axis of rotation) which is greater than the thickness of the web 2. Thus, the pin 21 passes through the entire thickness of the web 2 and partially penetrates into the material of the stiffener 3.

[0103] Thanks to the geometry of the pin 21, and the containment of the shoulder 22, the material of the stiffener 3 and of the web 2 is thus, in addition to being welded by friction stir, pushed against the convex molding surfaces 17 and thus takes on the shape of these surfaces 17 by a phenomenon comparable to a molding shape.

[0104] [Fig. 10] is a schematic sectional view showing the working of the material during the welding step. The material softened by the tool 11 is located in a zone 32 shown diagrammatically in wavy lines. In this zone, the material is mixed in a conventional manner in friction stir welding, and is further pushed towards the convex molding surfaces 17 (see arrows).

[0105] The result of this welding operation is illustrated in [Fig.11]. [Fig.11] is a sectional view of the stiffened structural panel 1 thus obtained, showing the junction between the stiffener 3 and the web 2, with its weld 26.

[0106] Friction stir welding ensures a junction of the stiffener 3 directly onto the web 2, without requiring any groove or junctions of different parts of the web 2.

[0107] At the junction between the stiffener 3 and the first face 9 of the web 2, the panel 1 comprises fillet joints 25 whose profile is controlled and has been obtained by molding on the convex molding surfaces 17.

[0108] As many stiffeners 3 as necessary can thus be fixed to the web 2 by the method described previously. [Fig. 12] illustrates a panel 1 comprising multiple stiffeners, which are each welded by the method described above, with a single tool 11 (and a single assembly 13, not shown) moving over each stiffener 3. Alternatively (see dotted lines) all the stiffeners 3 can be welded simultaneously with a tool 11, and the corresponding assembly 13, dedicated to each stiffener.

[0109] An application of the method described above in the context of a rationalization of the production of stiffened structural panels 1 will now be described with reference to figures 13 to 19.

[0110] According to this method, portions similar to extruded profiles are first produced and then assembled as required.

[0111] With reference to [Fig. 13], a first stiffener 3A is produced and welded to a web 2 according to the method described previously.

[0112] With reference to [Fig. 14], a second stiffener 3B is also produced and welded parallel to the first stiffener 3A, at a predetermined distance from the latter, also by the method described above.

[0113] With reference to [Fig. 15], a third stiffener 3C is also produced and welded parallel to the second stiffener 3B, at a predetermined distance from the latter, also by the method described above.

[0114] The stiffeners 3A, 3B, 3C are all obtained from a sheet (and possibly from the same sheet) as described with reference to FIGS. 2 to 5.

[0115] Alternatively, with reference to [Fig. 16], the welding of the three stiffeners 3A, 3B, 3C on the web 2 can be carried out simultaneously using three part gripping assemblies (not shown) and three tools 11 working simultaneously.

[0116] The elementary panel structure 27 thus produced is illustrated in [Fig. 17]. This elementary structure 27 is comparable to a standardized profile which is produced in series, small or large, depending on the application. This elementary structure 27 can be produced as a construction element of a stiffened structural panel, independently of the latter. This mass production takes place on a dedicated line at a predetermined rate and the elementary structures 27 can be stored. Production gains, and rationalization of production and supplies are thus achieved.

[0117] The elementary structures 27 have industrialization advantages close to those of extruded profiles, while being much more economically advantageous (rolled sheet metal is less expensive by a factor of 10 than an extruded profile), and without limitation from the point of view of the alloy used.

[0118] According to the method, a stiffened structural panel 1 can then be produced from an assembly of these elementary structures 27 previously produced and stored.

[0119] The elementary structures 27 can for example themselves be assembled by friction stir welding, in a conventional manner. [Fig. 18] illustrates such an operation of welding two elementary structures 27 produced by a conventional tool 28. The webs 2 of two elementary structures 27 are here welded edge to edge.

[0120] [Fig. 19] illustrates a subsequent step in which a third elementary structure 27 is welded edge to edge at one end of the assembly, on the same machine, by the tool 28.

[0121] As many elementary structures 27 as necessary are thus added edge to edge to form the final stiffened structural panel 1.

[0122] In the illustrative examples of Figures 18 and 19, the panels are assembled in the same plane, with the understanding that they may be welded at an angle to each other to form more complex stiffened structural panels.

[0123] Figures 20 to 23 relate to variants of the joining process between a stiffener 3 and the web 2. These figures relate to the positioning of the parts before the friction stir welding operation.

[0124] Each of these variants concerns the positioning of the stiffener 3 relative to the web 2. [Fig.20] schematically illustrates the positioning which served as an example for the description of the method relating to figures 6 to 9: the fixing edge 7 of the stiffener 3 is arranged with a plane-on-plane contact against the first face 9 of the web 2. In this schematic view, the part gripping assembly has not been shown, it is in accordance with the assembly described previously.

[0125] In the same way as the schematic view of [Fig.20], [Fig.21] presents a positioning alternative in which the fixing edge 7 of the stiffener 3 is taken between two portions 2A, 2B of the web 2.

[0126] The two portions 2A, 2B are therefore each in contact plane on plane with one of the walls of the stiffener 3. Although this variant requires a web made in several parts 2A, 2B and thus has fewer advantages than the embodiment described previously, it can however be implemented with the same part gripping assembly and the same rotary welding tool as previously to advantageously obtain the same fillet joints 25.

[0127] In the same way as the schematic view of [Fig.20], [Fig.22] illustrates another variant in which the fixing edge 7 of the stiffener 3 consists of an enlarged foot 29. The foot 29 is for example produced by plastic deformation or machining.

[0128] The foot 29 is itself connected by a connecting fillet 30 with the core 6 of the stiffener 3.

[0129] The junction is then made by a part gripping assembly 13 which comprises two anvils 14 identical to those described previously, except that these anvils 14 only grip the foot 29 when holding the stiffener 3.

[0130] Following the welding step, the panel thus obtained will therefore include fillet joints 25 connecting the first face 9 of the web 2 to the foot 29, as well as the connecting fillets between the foot 29 and the rest of the stiffener 3.

[0131] In the same schematic representation mode as [Fig.20], [Fig.23] illustrates another variant combining the variants of [Fig.21] and [Fig.22].

[0132] The stiffener 3 then comprises a foot 29 which is sandwiched between two portions 2A, 2B of the web 2.

[0133] As previously, the final assembly will thus include a connection fillet 30 between the core 6 of the stiffener 3 and will also include the fillet joints 25 at the junction between the foot 29 and the wall 2.

[0134] The variants of figures 21 and 23 can also be used to assemble two elementary structures 27 by then placing a stiffener 3 at each junction between two elementary structures 27.

[0135] Furthermore, the invention aims at a combination of the described method with the heterogeneous assembly of alloy grades. The research carried out has led to the application of the method for the production of assemblies which cannot be produced by known welding methods.

[0136] In a particularly advantageous application example, the method is used for the production of a stiffened aircraft structural panel, the web of which, on the one hand, and the stiffeners on the other hand, are made of two different aluminum alloys of the 2000 series. For example, two aluminum alloys from among the alloys 2024, 2524, and 2198 can be thus assembled. These alloys are all available in large-scale thin sheet metal, at costs much lower than those of extruded profiles, and are therefore compatible with the principles of the method.

[0137] The stiffeners can thus be produced from sheets of a first aluminum alloy of the 2000 series, having characteristics desired for the stiffeners (rigidity, etc.) and the web is produced from sheets of another aluminum alloy of the 2000 series having other characteristics desired for the web (protection of the space enclosed by the panel, etc.).

[0138] One of these particularly advantageous application examples is the production of stiffeners in 2024 aluminum alloy (whose mechanical characteristics are conducive to stiffening) and the production of the veil in 2524 aluminum alloy in order to benefit from the greater damage tolerance capacity of 2524 alloys.

[0139] The method according to the invention thus makes it possible to obtain stiffened aircraft structural panels by an optimized method with a significant reduction in costs, while obtaining a more efficient final structure, with a combination of alloys each adapted to its function within the panel.

[0140] Alternative embodiments of the method described may be envisaged. In particular, the examples described refer to stiffeners 3 which are fixed perpendicularly to a web 2, it being understood that the invention applies to a web 2 which may have a curved shape and to stiffeners 3 which may be fixed according to other angular configurations, for example obliquely relative to the plane tangent to the web.

[0141] The embodiments described may also be combined.

Claims

Claims

1. A method of producing a stiffened aircraft structural panel, this panel comprising a web (2) on which at least one stiffener (3) is fixed, this method being characterized in that it comprises the following steps: - manufacturing a web (2) by shaping a metal sheet, this web (2) comprising a first face (9) and a second face (10); - manufacturing a stiffener (3) extending in a longitudinal direction (8), this stiffener (3) comprising a fixing edge (7) extending substantially parallel to the longitudinal direction (8), and a reinforcing edge (5) which is opposite the fixing edge (7) and which extends parallel to the longitudinal direction (8);- positioning the web (2) and the stiffener (3) in a part-gripping assembly (13), the fixing edge (7) of the stiffener (3) being arranged against the first face (9) of the web (2) along two junction lines (12) between the web (2) and the stiffener (3), on either side of the fixing edge (7), the part-gripping assembly (13) comprising two anvils (14) clamping the fixing edge (7) of the stiffener (3), these anvils (14) each comprising a rounding defining a convex molding surface (17) opposite each of the two junction lines (12);- friction stir welding of the web (2) and the stiffener (3), by applying a rotary welding tool (11) to the second face (10) of the web (2), opposite the fixing edge (7) of the stiffener (3), and moving the rotary welding tool (11) along the longitudinal direction (8), the rotary welding tool (11) pressing the kneaded material against the convex molding surfaces (17) forming two fillet joints (25) connecting the web (2) and the stiffener (3).;

2. Method according to claim 1, characterized in that, in the step of positioning the web (2) and the stiffener (3), the fixing edge (7) is in plane-to-plane contact with the first face (9) of the web (2).

3. Method according to one of claims 1 or 2, characterized in that the convex molding surface (17) is a semi-circular surface.

4. Method according to claim 4, characterized in that the convex molding surface (17) has a radius greater than or equal to two millimeters.

5. Method according to one of the preceding claims, characterized in that the rotary welding tool (11) comprises a kneading pin (21), as well as a retaining shoulder (22), and during the welding step, the kneaded material is pressed against the convex molding surfaces (17) by the retaining shoulder (22).

6. Method according to claim 6, characterized in that, during the welding step, the mixing pin (21) is pushed into the material beyond the first face (9) of the web (2).

7. Method according to claim 7, characterized in that the kneading pin (21) has a length (24) greater than the thickness of the web (2).

8. Method according to one of claims 6 to 8, characterized in that the mixing pin (21) has a diameter substantially equal to the thickness (23) of the fixing edge (7) of the stiffener (3).

9. Method according to one of the preceding claims, characterized in that the stiffener (3) and the web (2) are manufactured from the same aluminum alloy.

10. Method according to one of the preceding claims, characterized in that the stiffener (3) is manufactured from a metal sheet.

11. Method according to claim 11, characterized in that the stiffener (3) is manufactured from a metal sheet of constant thickness.

12. Method according to one of claims 11 or 12, characterized in that the stiffener (3) is manufactured by bending said metal sheet to form the reinforcing edge (5).

13. Method according to one of claims 10 to 13, characterized in that the stiffener (3) is manufactured by cutting from said metal sheet.

14. Method according to one of claims 10 to 13, characterized in that the stiffener (3) is manufactured from a sheet metal strip.

15. Method according to one of the preceding claims, characterized in that the part gripping assembly (13) comprises an anvil (16) for holding the reinforcing edge (5) of the stiffener (3).

16. Method according to one of the preceding claims, characterized in that the part gripping assembly (13) comprises a base (15) for holding the web (2).

17. Method according to one of the preceding claims, characterized in that the fixing edge (7) of the stiffener (3) consists of a foot (29) attached to a web (6) of the stiffener (3), the foot (29) having a thickness greater than the web (6).

18. Method according to claim 18, characterized in that the foot (29) comprises a fillet (30) for connection with the core (6) of the stiffener (3).

19. Method according to one of claims 3 to 19, characterized in that the web (2) is arranged in two portions (2A, 2B) arranged on either side of the fixing edge (7) of the stiffener (3).

20. Method according to one of the preceding claims, characterized in that the steps of manufacturing a stiffener (3), positioning the web (2) and this stiffener (3), and welding are repeated for a plurality of stiffeners (3) welded to the same web (2).

21. Method according to one of the preceding claims, characterized in that it comprises intermediate steps of producing a plurality of elementary structures (27) each comprising a web (2) and at least one stiffener (3A, 3B, 3C), the stiffened structural panel being obtained by a final step of edge-to-edge welding of the webs (2) of the elementary structures (27).

22. Method according to claim 22, characterized in that the edge-to-edge welding of the sails (2) of the elementary structures (27) is carried out by integrating a stiffener at the junction of the sails (2).

23. Method according to one of the preceding claims, characterized in that the web (2) is made from a sheet of an aluminum alloy of the 2000 series, and in that the stiffener (3) is made from a sheet of another aluminum alloy of the 2000 series.

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