Friction stir welding method and associated welding assembly

Abstract

This method for friction stir welding of a first part (8) onto a second part (9), the first part (8) being arranged on the second part (9), comprises the following steps: - Machining (E1) of a means for positioning and holding the first part on the second part (13, 16, 17) on the first and second parts (8 and 9), the machined positioning and holding means (13, 16, 17) comprising at least one projecting part (13a, 16a, 17a) and at least one groove (13b, 16b, 17b) intended to receive the at least one projecting part (13a, 16a, 17a) for positioning and holding the first part (8) on the second part (9), the at least one projecting part (13a, 16a, 17a) being machined on the first part (8) and the at least one groove (13b, 16b, 17b) being machined in the second part (9), - Activation (E2) of the positioning and holding means (13, 16, 17), - Friction stir welding (E3) of a first welding area (10) of the first part (8) and a second welding area (11) of the second part (9).

Description

[0001] DESCRIPTION

[0002] TITLE: Friction stir welding process and associated welding assembly

[0003] Technical field

[0004] The present invention relates to devices and methods for assembly by friction stir welding, also called "friction stir welding" in English terms.

[0005] In particular, the invention relates to a method of welding two parts by friction stir and an associated welding assembly.

[0006] In general, the invention applies to any type of field requiring assembly by friction kneading of two elements to be assembled.

[0007] Previous techniques

[0008] In industry, and particularly in the aeronautics industry, it is common to have to assemble several elements together. This could be, for example, the assembly of a stiffener on a structural panel of an aircraft in order to stiffen the said structural panel.

[0009] Among the various joining processes, friction stir welding is a joining process which, using welding tools with a rotating tip less than five millimeters in diameter, allows the materials of the elements to be joined to be mixed together and thus create a weld. Friction stir welding is particularly suitable for aluminum alloys.

[0010] To weld two parts together, the parts must be positioned relative to each other and held in position during welding. For this, one of the existing solutions is illustrated in Figure 1, and consists of positioning and holding the parts by a system of pins.

[0011] More particularly, with reference to Figure 1, a welding assembly 1 comprises a first part 2 and a second part 3. Pre-drillings are made in the parts 2 and 3, into which pins 4 are introduced. Thanks to the pins 4, the first part 2 is positioned and held on the second part 3, allowing friction stir welding to be carried out using welding tools 5. In Figure 1, welding is in progress, and a weld bead 6 is produced where the tool 5 has already passed.

[0012] However, this solution has many disadvantages. First of all, the pin and pre-drilling system is bulky and is detrimental to the welding paths and the machine environment. In addition, this solution blocks the passage of the welding tool 5, which cannot be used too close to the pins 4. This results in a limitation of the weld bead 6 to the vicinity of the pins 4. Generally speaking, it is not possible, using the conventional friction stir welding process, to obtain a continuous path of the weld bead 6 between the two parts to be welded. Also, the pins must be removed once the weld has been made, and then leave the pre-drillings free, which must be filled with standard riveting to ensure sealing and aerodynamics.Finally, due to a slight movement of the two parts 2 and 3 relative to each other during welding, the pre-drillings present and aligned on the two parts 2 and 3 may become offset, which causes the pins 4 to tighten and block in the pre-drillings.

[0013] Statement of the invention

[0014] The present invention therefore aims to overcome the aforementioned drawbacks.

[0015] The present invention therefore relates to a method of friction stir welding of a first part onto a second part, the first part being arranged on the second part, comprising the following steps:

[0016] Machining a means for positioning and holding the first part on the second part on the first and second parts, the machined positioning and holding means comprising at least one projecting part and at least one groove intended to receive the at least one projecting part for positioning and holding the first part on the second part, the at least one projecting part being machined on the first part and the at least one groove being machined in the second part,

[0017] Activation of the positioning and holding means, Friction stir welding of a first welding zone of the first part and a second welding zone of the second part.

[0018] Preferably, the step of activating the positioning means comprises the assembly of the at least one projecting part with the at least one groove intended to receive the at least one projecting part.

[0019] Advantageously, the at least one protruding portion is machined on a lower surface of the first part, and the at least one groove is machined in an upper surface of the second part.

[0020] Preferably, the at least one protruding part is machined from an aluminum alloy.

[0021] Advantageously, the at least one protruding portion is machined in the material of the first welding zone.

[0022] Advantageously, the at least one protruding part is machined on the first welding zone of the first part and the at least one groove is machined in a portion of the second welding zone intended to be in contact with the at least one protruding part.

[0023] In one embodiment, the at least one groove is machined in a portion of the second welding zone intended to be in contact with the first welding zone.

[0024] In this embodiment, during the welding step, at least a portion of the positioning and holding means is friction stir welded to the first and second welding zones.

[0025] In one embodiment, the method comprises a step of applying an insulating element in the at least one groove, prior to the step of activating the positioning and holding means.

[0026] Preferably, the insulating element is putty.

[0027] The invention also relates to a weld obtained from the implementation of a friction stir welding method as defined previously on a welding assembly comprising a first part arranged on a second part.

[0028] Brief description of the drawings

[0029] Other aims, characteristics and advantages will appear on reading the following description, given solely by way of non-limiting example, and made with reference to the appended drawings in which:

[0030] [Fig l] illustrates an example of implementation of a friction stir welding process known from the state of the art on a welding assembly.;

[0031] [Fig2] illustrates an initial welding assembly in cross-section before implementing the method according to the invention;

[0032] [Fig3] illustrates an example of a friction stir welding process in accordance with the present disclosure;

[0033] [Fig4] illustrates a first example of implementation of the method of figure 3 in accordance with the present disclosure on the welding assembly of figure 2, illustrated in longitudinal section;

[0034] [Fig5] illustrates the example of Figure 4 in cross-section;

[0035] [Fig6] illustrates the example of figure 4 in top view;

[0036] [Fig7] illustrates a second example of implementation of the method of Figure 3 in accordance with the present disclosure on the welding assembly of Figure 2, illustrated in cross-section;

[0037] [Fig8] illustrates the example of figure 7 in top view;

[0038] [Fig9] illustrates a third example of implementation of the method of Figure 3 in accordance with the present disclosure on the welding assembly of Figure 2, illustrated in cross-section.

[0039] Detailed description

[0040] Figure 2 schematically shows an initial welding assembly 7 before the application of a friction stir welding method according to the invention shown in Figure 3. The welding assembly 7 comprises a first part 8 and a second part 9, illustrated schematically in cross section.

[0041] For the purposes of the description, reference is made to a direct orthonormal reference frame, in which the X axis designates the longitudinal direction of the welding assembly 7, the Y axis designates the direction along the width of the welding assembly 7, and the Z axis designates the vertical direction, oriented upwards.

[0042] Figure 2 therefore illustrates a cross-section along a plane parallel to the Y axis of the welding assembly 7.

[0043] For example, the first part 8 is a stiffener and the second part 9 is an aircraft structural panel.

[0044] The first part 8 and the second part 9 are intended to be welded together by friction stir in transparency, that is to say one on the other. Thus, the first part 8 comprises a lower surface 8a preferably resting entirely on an upper surface 9a of the second part 9.

[0045] More specifically, the first part 8 comprises a first welding zone 10 and the second part 9 comprises a second welding zone 11, which define respective portions of the parts 8 and 9 intended to be mixed together during friction stir welding.

[0046] The first welding zone 10 thus comprises at least a portion of the lower surface 8a and the second welding zone 11 comprises at least a portion of the upper surface 9a which is intended to be in contact with the first welding zone 10. Thus, the first welding zone 10 and the second welding zone 11 are in fact positioned in contact with each other.

[0047] As a non-limiting example within the framework of the present disclosure, the first part 8 illustrated in FIG. 2 is an L-shaped stiffener, comprising a base 12a and a shoulder 12b.

[0048] The first part 8 and the second part 9 are made of materials suitable for friction stir welding. In particular, the first part 8 and the second part 9 are made from aluminum alloys, possibly different from each other.

[0049] Figure 3 illustrates a friction stir welding method of the first part 8 on the second part 9 capable of being implemented on the welding assembly 7. The steps of the method are described below. In a first step E1, a positioning and holding means is machined on the first and second parts 8 and 9, the positioning and holding means comprising at least one projecting part and at least one groove intended to receive the projecting part, the at least one projecting part being machined on the lower surface 8a of the first part 8 and the at least one groove being machined in the upper surface 9a of the second part 9.

[0050] Once the holding and positioning means has been machined, a step E2 comprises the installation of the first part 8 on the second part 9, and the activation of the positioning and holding means to ensure the correct positioning and holding of the first part 8 on the second part 9. The activation of the positioning and holding means consists of the insertion of the at least one projecting part into the at least one corresponding groove. In this way, the first part 8 is correctly positioned and held on the second part 9, allowing in a third step E3 to carry out the friction stir welding of the first welding zone 10 and the second welding zone 11.

[0051] Optionally, the method comprises a step E4 between the first and second steps E1 and E2, in which an insulating element is applied in the at least one groove.

[0052] Different examples of implementation of this method of Figure 3 on the initial welding assembly 7 of Figure 2 will be described in the following. In particular, Figures 4, 5 and 6 illustrate a first example of implementation of the method of Figure 3, Figures 7 and 8 illustrate a second example and Figure 9 illustrates a third example.

[0053] Only the third example includes the optional step E4.

[0054] The first example of implementation of the method of Figure 3 on the welding assembly 7 of Figure 2 is illustrated in Figures 4, 5 and 6.

[0055] In particular, Figure 4 illustrates a longitudinal section along a plane parallel to the X axis of the welding assembly 7 during step E3 of the first example of implementation of the welding method of Figure 3, Figure 5 illustrates a section along a plane parallel to the Y axis of the welding assembly 7 of Figure 4, and Figure 6 illustrates a top view along a plane perpendicular to the Z axis of the welding assembly 7 at the end of step E2 of the first example of implementation of the welding method of Figure 3.

[0056] During the first step E1 of this first example of implementation of the method of FIG. 3, a positioning and holding means 13 is machined on the first and second parts 8 and 9. More precisely, the positioning and holding means 13 comprises at least one projecting part 13a machined on the first part 8 and at least one corresponding groove 13b made on the second part 9 and intended to receive and cooperate with the projecting part 13a. The projecting part 13a can thus be described as a male portion of the first part 8 cooperating with the groove 13b of the second part 9 which can be described as a female portion.

[0057] The projecting portion 13a is machined on the lower surface 8a of the first part 8, and more particularly on the portion of the lower surface 8a included in the first welding zone 10 of the first part 8. The projecting portion therefore extends downwards when the lower surface 8a is arranged on the upper surface 9a.

[0058] Correspondingly, the groove 13b corresponding to said projecting part 13a is machined in the upper surface 9a of the second part 9, and more particularly in the portion of the upper surface 9a included in the second welding zone 11 and which is intended to be in contact with the first welding zone 10. This portion of the upper surface 9a on which the groove 13b is machined is also intended to be in contact with the projecting part 13a.

[0059] In Figure 6 illustrating a top view of the welding assembly 7, the base 12a is shown in transparency so as to reveal the projecting part 13a and the groove 13b.

[0060] In this first example shown in figures 4, 5 and 6, the projecting part 13a extends over the entire length along the X axis of the lower surface 8a of the first part 8. Similarly, the groove 13b is machined in a corresponding manner over the entire length along the X axis of the upper surface 9a of the second part 9 in contact with the lower surface 8a. The dimension of the projecting part 13a along the Y axis is less than 30% of the dimension along the Y axis of the first part 8. The groove 13b likewise extends along the Y axis over a distance less than 30% of the dimension along the Y axis of the first part 8, this distance nevertheless being greater by a few millimeters than the dimension along the Y axis of the projecting part 13a, so that the groove 13b is configured to receive and grip the projecting part 13a.

[0061] Thus, the projecting portion 13a and the groove 13b are well configured to cooperate so that the groove is able to receive the projecting portion 13a when the lower surface 8a of the first part 8 is correctly arranged on the upper surface 9a of the second part 9.

[0062] The holding and positioning means 13 is machined from an aluminum alloy, possibly identical to the alloy used to manufacture one of the welding zones 10 and 11. For example, the projecting part 13a is machined from the same material as the first welding zone 10.

[0063] The holding and positioning means 13 is sized to be included in the first and second welding zones 10 and 11. Thus, the holding and positioning means 13 is configured to be friction stir welded at least partially to the first and second parts 9 and 10, and therefore to the first and second welding zones 10 and 11.

[0064] In step E2, the first part 8 is positioned on the part 9 and the positioning and holding means 13 is activated. More precisely, the activation of the positioning and holding means 13 comprises a phase of assembling the projecting part 13a with the corresponding groove 13b. The projecting part 13a is thus inserted into the corresponding groove 13b. In this way, the first part 8 is correctly positioned and held on the second part 9.

[0065] In the third step E3, friction stir welding of the first welding zone 10 and the second welding zone 11 is carried out.

[0066] In particular, the welding step E3 is carried out using friction stir welding equipment 14, and consists of a first phase of setting up the friction stir welding equipment for welding the first part 8 to the second part 9. The setting up consists of positioning the assembly 7 of the two parts 8 and 9 assembled and secured by the positioning and holding means 13 on a welding frame of the welding equipment intended to support the lower surface 9b of the second part 9.

[0067] The friction stir welding tool 14 comprises a rotating tip 14a for friction stir welding and a shoulder 14b carrying the tip 14a at one of its ends. The thickness of the tip 14a determines the size of the welding zones 10 and 11, and therefore the dimensions of the projecting part 13a perpendicular to the surface 8a.

[0068] In a second phase of step E3, the welding tool 14 is inserted into the first part 8 up to the welding zones 10 and 11, as illustrated in FIG. 4. The welding tool 14 is inserted so as to be in contact with the positioning means 13 and the welding zones 10 and 11. The third phase of step E3, which is welding, then begins, and a weld bead 15 is formed in the welding zones 10 and 11 as the tool 14 advances and the welding zones 10 and 11 are locally heated due to the action of the rotating tip 14a. The direction of advancement of the welding tool 14 in FIG. 4 is from right to left. In the first example of implementation, the positioning and holding means 13 is thus welded at least partially to the first and second parts 8 and 9.

[0069] The welding path followed by the welding tool 14 then follows the positioning means 13, as illustrated in FIG. 2, and is not limited by a pin. The positioning and welding means 13 is completely welded to the first and second welding zones 10 and 11 of the parts 8 and 9 at the end of step E3.

[0070] It is therefore understood that the holding and positioning means 13 has the function of holding the first and second parts 8 and 9 together, which makes it possible to dispense with the use of pins, and consequently, to limit pre-drilling and the subsequent use of rivets or other solutions for plugging these holes. The holding and positioning means 13 thus eliminates the obstacles to obtaining a continuous weld bead 15. More generally, it is thus possible to use the welding tool 14 in all the required areas between the two parts without problems of accessibility and space requirements. It is thus not necessary to adapt the trajectory of the weld beads or to have to stop the bead before the pin areas. In addition, no element needs to be removed at the end of welding, and no element such as riveting needs to be added.

[0071] The second example of implementation of the method of Figure 3 on the welding assembly 7 of Figure 2 is illustrated in the figures

[0072] 7 and 8. More specifically, like figure 4, figure 7 illustrates a longitudinal section along a plane parallel to the X axis of the welding assembly 7 during step E3 of the second example of implementation of the welding method of figure 3. Similarly, like figure 6, figure 8 illustrates a top view along a plane perpendicular to the Z axis of the welding assembly 7 at the end of step E2 of the second example of implementation of the welding method of figure 3.

[0073] As for the first example, a positioning and holding means 16 is machined during step E1 on the first and second parts 8 and 9.

[0074] The positioning means 16 differs from the first example in that it comprises several projecting parts 16a and several corresponding grooves 16b intended to each receive one of the projecting parts 16a for positioning and holding the first part.

[0075] 8 on the second part 9. In the example illustrated in figures 7 and 8, two projecting parts 16a are machined on the portion of the lower surface 8a included in the first welding zone 10, and two grooves 16b are made in the portion of the upper surface 9a included in the second welding zone 11 intended to be in contact with the projecting parts 16a.

[0076] The positioning means 16 also differs from the first example in that the corresponding projecting parts 16a and grooves 16b do not have the same dimension along the X axis. Indeed, the two projecting parts 16a, as well as the two grooves 16b, have a dimension along the X axis of between 5% and 15% of the dimension along the X axis of the first part 9. The dimensions along the Y axis of the projecting parts 16a of the grooves 16b are the same as in the first example.

[0077] In addition, one of the two grooved parts 16b has a dimension along the X axis greater by at least 50% than the dimension along the X axis of the other groove, so that the longest groove along the X axis is configured to allow an additional degree of freedom of movement of the projecting part 16a that it receives during step E2, in order to prevent the two parts 8 and 9 from being hyperstatic. In the example illustrated in Figures 7 and 8, the groove 16b allowing an additional degree of freedom is the right-hand groove.

[0078] Steps E2 and E3 are performed in the same way as for the first implementation example.

[0079] The third example of implementation of the method of figure 3 on the welding assembly 7 of figure 2 is illustrated in figure 9. More precisely, like figure 5, figure 9 illustrates a section along a plane parallel to the Y axis of the welding assembly 7 at the end of step E3 of the third example of implementation of the welding method of figure 3.

[0080] As for the first two examples, a positioning and holding means 17 is machined during step E1 on the first and second parts 8 and 9. The positioning means 17 comprises two projecting parts 17a and two grooves 17b configured to receive and grip the projecting parts 17a.

[0081] The dimensions along the X axis and along the Y axis of the projecting parts 17a and the grooves 17b are identical to the dimensions along these same axes of the projecting part 13a and the groove 13b of the first example of implementation.

[0082] The two projecting parts 17a are machined parallel on the lower surface 8a of the first part 8, outside and on either side of the first welding zone 10. Similarly, the two grooves 17b are machined parallel on the upper surface 9a of the second part 9, outside and on either side of the second welding zone 11. The positioning and holding means 17 is thus not intended to be welded during step E3, unlike the first two examples.

[0083] The third example is the only example described in which the optional step E4 is carried out. Thus, at the end of step E1, an insulating element 18 is applied in the grooves 17b. The insulating element is, for example, mastic.

[0084] During step E2 of activating the positioning and holding means 17, the insertion of the projecting parts 17a into the grooves 17b causes the insulating element 18 to flow back into a free space 19 between the walls of the grooves 17b and the walls of the projecting parts 17a, this free space resulting from the difference in dimension of a few millimeters between the grooves 17b and the projecting parts 17a. In this way, the insulating element 18 makes it possible to seal the positioning and holding means 17 by filling the free space.

[0085] In the last step E3, the first welding zone 10 is welded to the second welding zone 11 by friction stir, so that the welding path is traced between the two projecting parts 17a inserted in the grooves 17b. In this way, the positioning and holding means 17 is not welded to the first and second part, unlike the first two examples described. A welding bead 20 is therefore formed between the two projecting parts 17a inserted in the grooves 17b during step E3.

[0086] Step E4 is optional and makes it possible to overcome cases, as illustrated in the first two examples described, where the welding path does not allow the entire positioning and holding means machined in step E1 to be welded to the welding zones.

[0087] 10 and 11. Indeed, when the positioning and holding means is not completely welded to the welding zones 10 and 11, the difference between the dimensions of the projecting parts and the grooves causes the presence of free spaces between the walls of the projecting parts and the grooves, resulting in a lack of sealing of the welded assembly.

[0088] Conversely, when the positioning and holding means machined in step E1 is completely welded with the welding zones 10 and

[0089] 11 during step E3, the mixing of the materials welded by friction stir makes it possible to fill the initial free space and to seal the welded assembly.

[0090] 5

Claims

CLAIMS 1. Method of friction stir welding a first part (8) onto a second part (9), the first part (8) being arranged on the second part (9), comprising the following steps: Machining (El) of a means for positioning and holding the first part on the second part (13, 16, 17) on the first and second parts (8 and 9), the machined positioning and holding means (13, 16, 17) comprising at least one projecting part (13a, 16a, 17a) and at least one groove (13b, 16b, 17b) intended to receive the at least one projecting part (13a, 16a, 17a) for positioning and holding the first part (8) on the second part (9), the at least one projecting part (13a, 16a, 17a) being machined on the first part (8) and the at least one groove (13b, 16b, 17b) being machined in the second part (9), Activation (E2) of the positioning and holding means (13, 16, 17), Friction stir welding (E3) of a first welding zone (10) of the first part (8) and a second welding zone (11) of the second part (9).

2. Welding method according to claim 1, in which the step of activating (E2) the positioning and holding means (13, 16, 17) comprises assembling the at least one projecting part (13a, 16a, 17a) with the at least one groove (13b, 16b, 17b) intended to receive the at least one projecting part (13a, 16b, 17b).

3. Welding method according to one of claims 1 or 2, wherein the at least one protruding portion (13a, 16a, 17a) is machined on a lower surface (8a) of the first part (8), and the at least one groove (13b, 16b, 17b) is machined in an upper surface (9a) of the second part (9).

4. Welding method according to any one of claims 1 to 3, in which the at least one protruding part (13a, 16a, 17a) is machined from an aluminum alloy.

5. Welding method according to any one of claims 1 to 4, wherein the at least one protruding portion (13a, 16a, 17a) is machined in the material of the first welding zone (10).

6. Welding method according to any one of claims 1 to 5, wherein the at least one projecting part (13a, 16a, 17a) is machined on the first welding zone (10) of the first part (8) and the at least one groove (13b, 16b, 17b) is machined in a portion of the second welding zone (11) intended to be in contact with the at least one projecting part (13a, 16a, 17a).

7. Welding method according to any one of claims 1 to 6, in which the at least one groove (13b, 16b) is machined in a portion of the second welding zone (11) intended to be in contact with the first welding zone (10).

8. Welding method according to any one of claims 1 to 7, wherein during the welding step (E3), at least a portion of the positioning and holding means (13, 16) is welded by friction stir to the first and second welding zones (10 and 11).

9. Welding method according to any one of claims 1 to 7, comprising a step (E4) of applying an insulating element (18) in the at least one groove (17b), prior to the step (E2) of activating the positioning and holding means (17).

10. The method of claim 8, wherein the insulating element (18) is putty.

11. Weld obtained from the implementation of a friction stir welding method according to any one of claims 1 to 10 on a welding assembly (7) comprising a first part (8) arranged on a second part (9).

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