LASER WELDING PROCESS

Abstract

This process includes: - positioning first and second pieces (206n, 206n+1) on a first face (302) of a third piece (208), at a distance from each other; - two welding operations during each of which a laser beam (310) is moved on a second face (304) of the third piece (208), opposite the first piece (206n), respectively second piece (206n+1), to respectively create two fused zones (Zn; Zn+1) through the third piece (208) and at least a part of the first piece (206n), respectively second piece (206n+1). Between these two welding operations, the laser beam (310) is maintained and moved onto the second face (304), specifically opposite the exposed portion (306n) of the first face (302), to create, in the third part (208), an intermediate weld zone (Z1n, Z2n, Z3n) that does not reach the exposed portion (306n) of the first face (302). Figure for the abbreviation: Fig. 2

Description

Title of the invention: LASER WELDING METHOD Technical field of the invention

[0001] The present invention relates to a laser welding process, an assembly obtained with such a process and an aircraft comprising such an assembly. Technological background

[0002] It is known to reinforce a shell, for example an exhaust casing of an aircraft turbine, by means of a stiffener surrounding that shell. The stiffener is fixed by a circumferential laser weld bead passing through the stiffener to reach the shell.

[0003] However, the cladding may include openings which are covered by the stiffener.

[0004] Thus, due to the presence of these openings, it is not possible to weld around the entire circumference, to prevent the weld from penetrating the stiffener at the openings. Indeed, there would then be a risk of piercing the stiffener at the openings, because the energy of the laser beam is designed for the thickness of the stiffener and the shell, and not for the stiffener alone.

[0005] These problems generally arise whenever first and second parts must be laser-welded to a third part, these two parts being located at a distance from each other. In the specific case of the ferrule and the stiffener, the stiffener forms the third part, and the portions of the ferrule on either side of the opening form the first and second parts, respectively.

[0006] Thus, it is known to use a transparent laser welding process of first and second parts to a third part, the process comprising: - a positioning of the first and second pieces on one face of the third piece, at a distance from each other so that part of this first face remains uncovered; - a first welding operation during which a laser beam is moved onto a second face of the third piece, opposite the first piece, to perform a partial or full penetration transparent weld by creating a first fused zone through the third piece and at least part of the first piece; and - a second welding operation during which the laser beam is moved to the second face of the third piece, opposite the second piece, to perform a transparent weld with partial or complete penetration by creating a second fused zone through the third piece and at least part of the second piece.

[0007]

[0008]

[0009]

[0010]

[0011] In this known process, the laser is interrupted between the two welding operations. Therefore, assembling the exhaust housing requires numerous weld beads. However, each laser interruption wastes time and increases the risk of weld defects, particularly in areas where the laser beam fades, where crater-like cracks can form. To mitigate this, power reduction ramps are generally used to limit pronounced crater formation and the potential for cracking. It may therefore be desirable to provide a laser welding process that makes it possible to overcome at least some of the aforementioned problems and constraints. Summary of the invention A transparent laser welding process is therefore proposed for first and second parts with a third part, the process comprising: - positioning the first and second parts on a first face of the third part, at a distance from each other so that part of this first face remains uncovered; - a first welding operation during which a laser beam is moved onto a second face of the third piece, opposite the first piece, to perform a partial or full penetration transparent weld by creating a first fused zone through the third piece and at least part of the first piece; and - a second welding operation during which the laser beam is moved to the second face of the third piece, opposite the second piece, to perform a transparent partial or full penetration weld by creating a second fused zone through the third piece and at least part of the second piece; characterized in that the laser beam is held between the first and second welding operations and moved to the second face of the third piece, in particular opposite the exposed part of the first face of the third piece, to create, in the third piece, an intermediate fused zone not reaching the exposed part of the first face of the third piece. Indeed, a laser typically has a minimum power level below which the laser beam regulation deteriorates, potentially causing the laser beam to become discontinuous. This can lead to uncontrolled shutdowns, resulting in weld defects such as crater-like cracks. Thanks to this invention, the laser beam can be maintained above this minimum power level in continuous operation, thus preventing uncontrolled shutdowns and the resulting downtime. This allows for maximizing the effective beam length. of the cord and to minimize the number of welds, and therefore the complete fading of the beam.

[0012] The invention may further include one or more of the following optional features, according to any technically possible combination.

[0013] Preferably, the intermediate weld zone has, from the first weld zone, a depth decreasing by at most 1 mm for every millimeter of laser beam advance, and / or the intermediate weld zone has, to reach the second weld zone, a depth increasing by at most 1 mm for every millimeter of laser beam advance. Thus, it is possible to achieve a partial gradual fading and / or gradual emergence, further reducing the risk of defects appearing in the weld.

[0014] Preferably also, the depth of the intermediate melted zone is modified by playing on a power of the laser beam and / or on a speed of movement of the laser beam.

[0015] Preferably, the speed of movement is also kept constant and the power of the laser beam is varied. Indeed, it is easier to control the power of the laser beam than its speed of movement.

[0016] Preferably, the laser beam power is also changed in steps. Indeed, some lasers are not designed to gradually change their power.

[0017] Preferably also, on at least part of the intermediate fused zone, the power of the laser beam is less than half that of the first and second welding operations.

[0018] Preferably also, the first and second parts are respectively two panels of a ferrule-shaped casing of an exhaust casing of an aircraft turbomachine, the two panels being separated from each other by an opening made in the casing, and the third part is a ferrule-shaped stiffener, surrounding the casing and at least partially covering the opening.

[0019] A transparent welding method for the first and second ferrules, one enveloping the other, is also proposed. The first ferrule has at least one opening covered by the second ferrule. The welding is carried out according to a method of the invention, wherein the first and second parts are respectively two panels of the first ferrule separated by the opening, and the third part is the second ferrule. The ferrules are parts of revolution.

[0020] An assembly obtained by a process according to the invention is also proposed.

[0021] An aircraft comprising an assembly according to the invention is also proposed. Brief description of the figures

[0022] The invention will be better understood with the aid of the following description, given solely as an example and made with reference to the attached drawings in which: - [Fig. 1] is a cross-sectional view of a casing and stiffener of an exhaust housing, with an illustrated welding laser, - [Fig.2] is an enlargement of the casing and stiffener of [Fig.1], illustrating areas melted by the laser, and - [Fig.3] is a block diagram illustrating the steps of a laser welding process from stiffener to cladding. Detailed description of the invention

[0023] With reference to [Fig. 1], an exhaust casing 102 of an aircraft turbomachine first comprises a ferrule-shaped housing 202. Circumferentially distributed openings 204i ... 204n are provided in the housing 202. These openings 204i ... 204n delimit circumferentially successive lateral panels 206i ... 206N of the housing 202. Thus, each pair of consecutive panels 206i ... 206n are spaced apart by one of the respective openings 204i ... 204n.

[0024] The openings 204i.. .204N can remain empty or receive other elements of the turbomachine, for example elements that must not be damaged in particular by a welding operation.

[0025] The exhaust housing 102 further includes a stiffener 208 in the form of a ferrule surrounding the cover 202. The stiffener 208 is thus superimposed on the cover 202 and at least partially covers the openings 204i.. .204N.

[0026] At least one circumferential weld bead is made to fix the stiffener 208 to the casing 202.

[0027] The stiffener 208 has an inner face 302 pressed against the casing 202, and in particular against its panels 206i.. .206N, and an outer face 304 opposite the casing 202, and in particular its panels 206i.. .206N. Thus, each opening 204i.. .204n leaves a portion 306i.. .306N of the inner face 302 of the stiffener 208 exposed.

[0028] The weld beads are produced by laser welding using a laser 308 designed to provide a laser beam 310 directed along a pointing axis 312. The laser 308 is located outside the stiffener 208 and oriented so that the laser beam 310 reaches the outer face 304 of the stiffener 208. Each weld bead is then obtained by rotating the laser 308 circumferentially around the stiffener 208 while keeping the laser beam 310 pointed at the outer face 304 of the stiffener 208.

[0029] As can be seen in [Fig. 1], for at least one of the weld beads, during the circumvolution of the laser 308 around the stiffener 208, the pointing axis 312 passes, after passing through the stiffener 208, alternately through one of the panels 206i .. .206n and one of the openings 204i.. .204N of the cladding 202.

[0030] With reference to [Fig.2] and [Fig.3], an example of a laser welding process 500 according to the invention will now be described.

[0031] During a step 502, the stiffener 208 is placed around the cladding 202. Thus, the panels 206i.. .206N of the cladding 202 are positioned on the inner face 302 of the stiffener 208.

[0032] During a step 504, a welding operation is performed to weld together the stiffener 208 and one 206n of the panels 206i.. .206N. For this, the laser beam 310 is moved along a welding path Cn on the external face 304 of the stiffener 208, opposite the panel 206n of the cladding 202, so that the pointing axis 312 passes successively through the stiffener 208 and the panel 206n of the cladding 202. The laser beam 310 is driven to provide, along the entire length of the welding path Cn, sufficient energy to create a weld zone Zn with a depth passing through the stiffener 208 and at least part of the panel 206n of the cladding. In the illustrated example, the Zn fused area also passes through the entire 206n panel. For example, the 310 laser beam is advanced at a constant speed V and constant power P along the Cn welding path, for example 2 kW.

[0033] During a step 506, the laser beam 310 is maintained and moved along an intermediate path C'n on the outer face 304 of the stiffener 208, to reach the next panel 206n+i. Step 506 includes, for example, the following steps.

[0034] During a step 506-2, the laser beam 310 is first directed to provide decreasing energy along a first portion Pln of the intermediate path C'n, to create a fused zone Zln with a decreasing depth until it extends only into the stiffener 208, i.e., to stop before its inner face 302. For example, the depth decreases by at most 1 mm for every millimeter the laser beam 310 advances along the first portion Pln of the intermediate path C'n. For example, the fused zone Zln stops between 0.6 and 0.7 millimeters before the inner face 302.

[0035] For example, the laser beam 310 is always advanced at the same constant speed V, but with a decreasing power P along the first portion Pln of the intermediate path C'n. For example, the power P is decreased in steps.

[0036] Along this first portion Pln of the intermediate path C'n, the pointing axis 312 passes successively through the stiffener 208 and the panel 206n of the cladding 202, then (optionally, not illustrated in figure 4) through the stiffener 208 and the opening 204n.

[0037] During a step 506-4, the laser beam 310 is then driven to provide sufficiently low energy along a second portion P2n of the intermediate path C'n, to create a fused zone Z2n with a depth traversing by 302. For example, the welded zone Z2n has a penetration thickness of between 6 and 7 tenths of a millimeter from the inner face 302. For example, the laser beam 310 is always advanced at the same constant speed V, with a constant power P, but lower than that used during the welding operation of step 504. For example, the power is at least half as much, for example 800 W instead of 2 kW during step 504.

[0038] Along this second portion P2n of the intermediate path C'n, the pointing axis 312 passes (optionally, as illustrated in Figure 4) through the stiffener 208 and the panel 206n of the cladding 202, then through the stiffener 208 and the opening 204n, then (optionally, not illustrated in Figure 4) through the stiffener 208 and the next panel 206n+i of the cladding 202.

[0039] In a step 506-6, the laser beam 310 is then driven to provide increasing energy along a third portion P3n of the intermediate path C'n, to create a fused zone Z3n with increasing depth until it passes through the stiffener 208 and at least part of the following panel 206n+i. For example, the depth decreases by at most 1 mm for every millimeter the laser beam 310 advances along the third portion P3n of the intermediate path C'n.

[0040] Along this third portion P3n of the intermediate path C'n, the pointing axis 312 passes (optionally, not shown in Figure 4) through the stiffener 208 and the opening 204n, then through the stiffener 208 and the next panel 206n of the cladding 202. For example, the laser beam 310 is always advanced at the same constant speed V, but with increasing power P along the third portion P3n of the welding path Cn. For example, the power P is increased in steps.

[0041] The process 500 then returns to step 504 to weld together the stiffener 208 and the next panel 206n+i.

[0042] The Zln, Z2n, Z3n molten zones thus form an intermediate molten zone connecting the Zn molten zone and the Zn+i molten zone.

[0043] Thus, thanks to the process 500, all the panels 206i.. .206N are successively welded to the stiffener 208, with the laser 308 always kept on, but without the intermediate fused zones Zln, Z2n, Z3n reaching the exposed parts 306i .. .306n of the inner face 302 of the stiffener 208.

[0044] It should also be noted that the invention is not limited to the embodiments described above. It will indeed be apparent to those skilled in the art that various modifications can be made to the embodiments described above, in light of the information just disclosed to them.

[0045] For example, in the described example, only one part (the casing 202) is welded to the stiffener. However, several stacked parts could be welded to the stiffener at each welding operation.

[0046] In the detailed presentation of the invention given above, the terms used shall not be interpreted as limiting the invention to the embodiments set forth in this description, but shall be interpreted as including all equivalents which can be foreseen by a person skilled in the art by applying their general knowledge to the implementation of the teaching which has just been disclosed to them.

Claims

Demands

1. A method (500) for laser welding in transparency of first and second parts (206n, 206n+i) with a third part (208), the method (500) comprising: - a positioning of the first and second pieces (206n, 206n+i) on a first face (302) of the third piece (208), the first and second pieces being at a distance from each other so that a part (306n) of this first face (302) remains uncovered; - a first welding operation (504) during which a laser beam (310) is moved onto a second face (304) of the third part (208), opposite the first part (206n), to perform a partial or full penetration transparent weld by creating a first molten zone (Zn) through the third part (208) and at least part of the first part (206n); and - a second welding operation (504) during which the laser beam (310) is moved to the second face (304) of the third part (208), opposite the second part (206n+i), to perform a partial or full penetration transparent weld by creating a second fused zone (Zn+i) through the third part (208) and at least part of the second part (206n+i); characterized in that the laser beam (310) is maintained between the first and second welding operations and moved onto the second face (304) of the third piece (208), in particular opposite the exposed part (306n) of the first face (302) of the third piece (208), to create, in the third piece (208), an intermediate fused zone (Zln, Z2n, Z3n) not reaching the exposed part (306n) of the first face (302) of the third piece (208).

2. A method (500) according to claim 1, wherein the intermediate fused zone (Zln, Z2n, Z3n) has, from the first fused zone (Zn), a depth decreasing by at most 1 mm for every millimeter of advance of the laser beam (310) and / or wherein the intermediate fused zone (Zln, Z2n, Z3n) has, to reach the second molten zone (Zn+i), a depth increasing by at most 1 mm every millimeter of advance of the laser beam (310).

3. Method (500) according to claim 2, wherein the depth of the intermediate melt zone (Zln, Z2n, Z3n) is modified by playing on a power (P) of the laser beam (310) and / or a speed of movement (V) of the laser beam (310).

4. Method (500) according to claim 3, wherein the travel speed (V) is kept constant and wherein the power (P) of the laser beam (310) is modified.

5. Method (500) according to claim 4, wherein the power (P) of the laser beam (310) is modified in steps.

6. A method according to claim 4 or 5, wherein, on at least a part (Z2n) of the intermediate fused zone (Zln, Z2n, Z3n), the power (P) of the laser beam (310) is less than half that of the first and second welding operations (504).

7. A method (500) according to any one of claims 1 to 6, wherein the first and second parts (206n, 206n+i) are respectively two panels of a first ferrule (202), the two panels (206n, 206n+i) being separated from each other by an opening (204n) formed in the ferrule (202), and wherein the third part (208) is a second ferrule, one of the ferrules enveloping the other so that the second ferrule at least partially covers the opening (204n).

8. A method for transparent welding of first and second ferrules (202, 208), one enveloping the other, the first ferrule (202) having at least one opening (204n) covered by the second ferrule (208), the welding being carried out in accordance with a method according to any one of claims 1 to 7, wherein the first and second pieces are respectively two panels (206n, 206n+i) of the first ferrule (202) separated by the opening (204n) and wherein the third piece is the second ferrule (208).

9. Assembly obtained by a process (500) according to any one of claims 1 to 8.

10. Aircraft comprising an assembly according to claim 9.

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