Method for joining two anodized elements by friction stir welding

Abstract

This method for assembling a first element with a second element comprises a step (18) of anodizing the first element, a step (20) of anodizing the second element, and a step (28) of creating a weld bead by friction stir welding of the first element to the second element. Figure for the abbreviation: Fig 2

Description

Title of the invention: Method for assembling two anodized elements by friction stir welding technical field

[0001] The present invention relates to friction stir welding assembly methods, also called "friction stir welding" in Anglo-Saxon terms.

[0002] In particular, the present invention relates to the protection of surfaces assembled by friction mixing, in particular protection against corrosion.

[0003] In general, the invention applies to any type of field requiring assembly by friction mixing of two elements to be assembled. Previous techniques

[0004] In industry, and particularly in the aeronautical industry, it is common to have to assemble several elements together. This may involve, for example, assembling a stiffener onto a structural panel of an aircraft in order to stiffen said structural panel.

[0005] Among the various assembly methods, manual riveting is the most common and also provides corrosion protection for the assembled components. However, riveting involves lengthy assembly times due to its manual nature.

[0006] Friction stir welding is a faster assembly process that can be automated. Using a rotating pin less than 5 millimeters in diameter, it mixes the materials of the parts to be joined together, thus creating a weld. Stirring is particularly suitable for aluminum alloys.

[0007] Figure 1 schematically illustrates a method of implementing a friction stir welding process. Figure 1 shows a cross-sectional view of the assembly of a structural panel 2 with a stiffener 4, the structural panel 2 and the stiffener 4 each being a few millimeters thick. For the friction stir welding, a pin 6 moves against the stiffener 4 while being held in rotation. The pin 6 stirs and mixes the materials of the stiffener 4 and the structural panel 2 to create a weld bead 8 joining the two elements.

[0008] However, the weld bead 8 does not completely cover the contact surfaces 10 between the structural panel 2 and the stiffener 4. Unwelded areas 12 can become liquid retention areas susceptible to corrosion.

[0009] Solutions to prevent corrosion exist with the addition of an interposition sealant in the non-welded areas 12.

[0010] However, the sealant is damaged and loses its sealing properties at the time of welding and the weld bead 8 loses its mechanical properties due to contamination by incorporation of sealant into the material of the weld bead 8. Description of the invention

[0011] The present invention therefore aims to overcome the aforementioned disadvantages and to provide a friction stir welding assembly method without risk of corrosion of the unwelded areas.

[0012] The present invention relates to a method of assembling a first element with a second element comprising an anodizing step of the first element, an anodizing step of the second element and a step of producing a weld bead by friction stir welding of the first element with the second element.

[0013] Thus, the anodizing of the first and second elements makes it possible to protect the unwelded interface and to prevent corrosion of the first and second elements during friction stir welding at the unwelded areas, welding allowing for rapid and automated assembly.

[0014] In a particular embodiment, the process further includes an oxidation step of the weld bead once the friction stir welding has been carried out.

[0015] Advantageously, the oxidation step of the weld bead is obtained by local anodization or by chemical conversion.

[0016] In one embodiment, the process includes an optional step of reactivating the anodizing of the first element and the second element once the friction stir welding has been carried out.

[0017] Advantageously, the process further includes an optional step of applying a paint system comprising a primer.

[0018] In one embodiment, the method includes a step of applying sealant to a contact area of ​​the first element with the second element so as to seal access to an area not welded by the weld bead.

[0019] Advantageously, at least one of the anodizing steps of the first element or of the anodizing of the second element is a sulfuric or sulfo-tartaric anodizing step.

[0020] Advantageously, the first element and the second element each comprise an aluminum alloy. Brief description of the drawings

[0021] Other objects, features and advantages of the invention will become apparent from the following description, given solely by way of non-limiting example, and made with reference to the accompanying drawings in which:

[0022] [Fig-1] which has already been mentioned is a schematic cross-sectional view of a stiffener and structural panel assembled by a friction stir welding process;

[0023] [Fig.2] is a flowchart schematically illustrating the steps of a process assembly of a first element with a second element according to the invention; and

[0024] [Fig.3] is a schematic cross-sectional view of a first element and a second elements assembled by an assembly process according to the invention; and

[0025] [Fig.4] is a schematic cross-sectional view of a first element and a second elements assembled by an assembly process according to the invention comprising a sealant application step; and

[0026] [Fig.5] is a variant of the schematic cross-sectional view of [Fig.4] illustrating a first element and a second element assembled by an assembly process according to the invention comprising a step of applying sealant. Detailed description of at least one embodiment

[0027] The steps enabling the implementation of a process for assembling a first element with a second element are schematically represented in [Fig.2].

[0028] The first element is, for example, made of aluminum alloy, for example alloy 2219 or any other alloy that can be friction stir welded. Similarly, the second element is made of an aluminum alloy.

[0029] A schematic cross-sectional view of the final assembly of the first element 14 with the second element 16 is visible in [Fig.3]. In this particular embodiment, the first element 14 is a stiffener and the second element 16 is a structural panel of an aircraft.

[0030] To implement this process, a first step 18 of anodizing the first element 14 is carried out.

[0031] In parallel, an anodizing step 20 of the second element 16 is also carried out.

[0032] Anodizing is also called anodic oxidation and is well known to those skilled in the art. Anodizing can be, for example, sulfuric acid or tartaric acid anodizing. Anodizing can also be sulfoboric acid or chromic acid anodizing. Anodizing creates a first layer 22 around the first element 14 and a second layer 24 around the second element 16, the first and second layers 22 and 24 being electrically insulating and protecting against corrosion. The layers 22 and 24 produced measure, for example, between 2 and 15 micrometers in thickness.

[0033] A step of sealing the anodic layer can be carried out and is known to a person skilled in the art.

[0034] Once the first and second elements 14 and 16 have been anodized, a weld bead 26 is produced during a step 28. The weld bead 26 is produced by friction stir welding.

[0035] For example, friction stir welding is performed with the first element 14 overlapping the second element 16. The flat surfaces of the first and second elements are brought into contact with each other to weld the first element 14 to the second element 16. The material of the second element 16 is stirred by a pin (identical to pin 6 in [Fig. 1]) with the material of the first element 14 through the first element 14. The welding parameters are determined so that the anodizing layers are ground into the weld bead 26 and that the mechanical characteristics of the weld are satisfactory. The key parameters for achieving a well-ground anodizing layer are the choice of tool, the number of passes, the feed and rotation speeds, the tool inclination, and the overlap between passes.Each parameter must be defined according to the material and the thickness of the anodizing layer, the thickness of the anodizing layers depending on the process used, sulfuric anodizing generating thicker layers than chromic anodizing for example.

[0036] Alternatively, the welding can also be carried out by making a butt weld between two already anodized elements, followed by a local touch-up on the weld on the reverse and front sides by chemical conversion or local anodizing.

[0037] Advantageously, anodizing allows the weld bead 26 to meet the necessary mechanical performance requirements even though part of the first and second layers 22 and 24 are mixed and contained within the weld bead 26.

[0038] Optionally, once the weld bead 26 has been made, an oxidation step 30 is carried out on the weld bead 26, in particular on its external face on the side of the first element 14, so as to also protect its surface from corrosion.

[0039] The oxidation step 30 thus makes it possible to create a third layer 32 on the apparent surface of the weld bead 26. The oxidation step 30 is carried out for example by local anodizing or by chemical conversion.

[0040] Optionally, a step 34 for reactivating the anodizing of the first element 14 and the second element 16 can also be performed. This step 34 can be performed directly after the welding step 28, or concurrently with the weld bead oxidation step 30, or even after this step 30. The anodizing reactivation step 34 consists of applying a reactivation product to revive the effects of the anodizing steps 18 and 20 and to to allow better adhesion of a paint system, as layers 22 and 24 may have deteriorated during step 28 of weld bead 26.

[0041] In order to improve corrosion protection of the first and second elements In steps 14 and 16, an optional step 36 is performed, involving the application of a paint system 38. This step can be carried out without having previously performed the preceding steps 30 and 34. However, the paint system application step 36 can be performed after one or both of the oxidation and reactivation steps 30 and 34.

[0042] The paint system 38 includes, for example, a primer, preferably an anti-corrosion primer. Other paint layers can also be applied over the primer.

[0043] In order to ensure the sealing of the assembly, an optional step 40 of applying sealant 42 to a contact area 44 of the first element 14 with the second element 16 is carried out. The sealant 42 is for example applied in the form of a bead along the contact area 44.

[0044] The contact area 44 corresponds to an access area to an unwelded area 46 by the weld bead 26, similar to the unwelded areas 12 shown in [Fig. 1]. This step 40 can be carried out in place of step 36 of applying a paint system 38.

[0045] Two other modes of implementation of the assembly process are also shown in Figures 4 and 5. [Fig.4] illustrates the assembly of the first element 14 with the second element 16 when step 40 of applying sealant 42 is carried out after step 36 of applying a paint system 38.

[0046] Fig. 5 illustrates the assembly of the first element 14 with the second element 16 when step 40 of applying sealant 42 is carried out before step 36 of applying a paint system 38.

Claims

Demands

1. Method of assembling a first element (14) with a second element (16), characterized in that it comprises a step (18) of anodizing the first element (14), a step (20) of anodizing the second element (16) and a step (28) of producing a weld bead (26) by friction stir welding of the first element (14) with the second element (16), the method further comprising a step (30) of oxidizing the weld bead (26) once the friction stir welding has been carried out and a step (34) of reactivating the anodizing of the first element (14) and of the second element (16) once the friction stir welding has been carried out.

2. A method according to claim 1, wherein the step (30) of oxidation of the weld bead (26) is obtained by local anodization or by chemical conversion.

3. A method according to any one of claims 1 and 2, comprising a step (36) of applying a paint system (38) comprising a primer.

4. A method according to any one of claims 1 to 3, further comprising a step (40) of applying sealant (42) to a contact area (44) of the first element (14) with the second element (16) so as to seal access to a non-welded area (46) by the weld bead (26).

5. A method according to any one of claims 1 to 4, wherein at least one of the steps (18; 20) of anodizing the first element (14) or of anodizing the second element (16) is a sulfuric or sulfo-tartaric anodizing step.

6. A method according to any one of claims 1 to 5, wherein the first element (14) and the second element (16) each comprise an aluminum alloy.

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