CRACK STOPPER FOR WELDS

Abstract

A method for joining two structural elements by welding, in particular by butt welding comprises forming a weld line joining the two structural elements; and adding material across the weld line, thereby forming one or more crack stoppers for limiting crack propagation along the weld line. The one or more crack stoppers each have a limited extension along the weld line as seen in relation to a length of the weld line. A structural system comprising two structural elements joined by the method is disclosed. The method may be applied, e.g., to components of aircraft engines.

Claims

1.-45. (canceled)

46. A method for joining or strengthening joinder of two structural elements by welding, comprising: forming a weld line joining the two structural elements; and adding material across the weld line, thereby forming one or more crack stoppers for limiting crack propagation along the weld line; wherein each of the one or more crack stoppers has a limited extension along the weld line as seen in relation to a length of the weld line.

47. The method of claim 46, further comprising forming at least two crack stoppers, each at different positions along the weld line.

48. The method of claim 46, wherein the limited extension of each of the one or more crack stoppers is of a same order of magnitude as one of (i) a width of the weld line and (ii) the width of the weld line plus the heat effected zone.

49. The method of claim 46, wherein the one or more crack stoppers include a plurality of crack stoppers positioned along the weld line, and wherein the sum of the limited extension for all crack stoppers is less than 25% of the length of the weld line.

50. The method of claim 46, wherein each of the one or more crack stoppers spans across one of (i) the weld line and (ii) the weld line and to one or more features located on either or both of the two structural elements; and the face of each of the one or more crack stoppers facing the structural elements and the weld line is substantially completely attached the weld line.

51. The method of claim 46, wherein each of the one or more crack stoppers is formed by metal deposition (MD).

52. The method of claim 46, wherein the one or more crack stoppers include a plurality of crack stoppers formed along the weld line, such that neighbouring crack stoppers are spaced at predetermined distances from each other, wherein the predetermined distances are one of (i) all equal to one another and (ii) not all equal to one another.

53. The method of claim 52, further comprising determining, according to at least one of a strength criterion and a functionality criterion, at least one of (i) a thickness and a size of the crack stopper, and (ii) a maximum allowable crack length along the weld line, wherein the predetermined distances are limited by the maximum allowable crack length along the weld line.

54. The method of claim 53, wherein the at least one of the strength criterion and the functionality criterion is based on expected load cycles of an aircraft engine.

55. The method of claim 46, wherein each of the at least one crack stoppers has an elongated shape extending in a direction of a main axis that is oriented one of perpendicularly to the weld line, at an oblique angle to the weld line, and extending along the weld line.

56. The method of claim 46, wherein each of the at least one crack stoppers has one of a substantially circular shape and a substantially polygonal shape.

57. The method of any claim 46, wherein the crack stopper has a height in a direction normal to the weld line, wherein the height is within a range of 0.5 to 10 times of a thickness of the structural elements.

58. The method of claim 46, further comprising, before adding material across the weld line, forming a weld line joining the two structural elements.

59. The method of claim 46, further comprising allowing the weld line to cool from a temperature obtained during the forming of the weld line before forming the one or more crack stoppers.

60. A system, comprising two structural elements, wherein the two structural elements are combined by : forming a weld line joining the two structural elements; and adding material across the weld line, thereby forming one or more crack stoppers for limiting crack propagation along the weld line; wherein each of the one or more crack stoppers has a limited extension along the weld line as seen in relation to a length of the weld line.

61. The system of claim 60, wherein the structural elements comprise one or more of a jet engine, a fan case, a fan structure, a compressor structure, turbine structure and an engine mount structure.

62. A method of welding two sub-components together, comprising: joining the two sub-components together by a primary weld; and applying at least one secondary weld, said secondary weld extending across the primary weld.

63. The method of claim 62, wherein the at least one secondary weld intersects the primary weld at substantially 90 degrees to the primary weld.

64. The method of claim 62, wherein the at least one secondary weld is a plurality of secondary welds applied at intervals along the primary weld.

65. The method of claim 64, wherein the secondary welds are uniformly spaced along the length of the primary weld.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0059] The present disclosure will hereinafter be further explained by means of non-limiting examples with reference to the appended figures where:

[0060] FIG. 1 schematically shows an aircraft engine in cross section,

[0061] FIG. 2 schematically shows the formation of a crack stopper,

[0062] FIG. 3A schematically shows a weld line comprising a crack stopper,

[0063] FIG. 3B shows a weld line comprising a plurality of irregularly spaced crack stoppers,

[0064] FIG. 3C shows a weld line comprising a plurality of regularly spaced crack stoppers,

[0065] FIG. 4 schematically illustrates a compressor structure provided with crack stoppers,

[0066] FIG. 5 schematically illustrates a detail of a compressor structure provided with crack stoppers, and

[0067] FIG. 6 schematically illustrates two alternative crack-preventing weld patterns.

DETAILED DESCRIPTION

[0068] An aircraft engine 1 is shown schematically in FIG. 1. The aircraft engine extends around a central axis 2.

[0069] The main parts of the aircraft engine 1 are a fan case 4 surrounding a fan 6, a low pressure compressor 8, a compressor structure 10, a high pressure compressor 12, a combustor 14, a high pressure turbine 16, a low pressure turbine 18 and a turbine structure 20, arranged in this order along the axis 2.

[0070] The compression section, comprising the low pressure compressor 8 followed by the high pressure compressor 12, compresses at least a part of the air entering the engine through the inlet 3 before it is made to enter the combustor 14. A part of the air entering via the inlet may be led through a by-pass flow path (not shown) such as to generate forward thrust. In the combustion section the combustion takes place, by ignition and burning of a mixture of air and fuel. The combustion products are made to expand through the turbine section comprising the high pressure turbine 16 and the low pressure turbine 18, thereby making the turbines rotate around the axis 2. The high pressure turbine 16 and the high pressure compressor 12 are mounted on a common shaft (not shown), such that the high pressure turbine drives the rotation of the high pressure compressor. The high pressure turbine 16 is followed by the low pressure turbine 18, which is mounted on a shaft common with the low pressure compressor 8 and the fan 6, such that the low pressure turbine 18 makes the fan 6 and the low pressure compressor 8 rotate. Both shafts are concentric and rotate around the engine central axis 2.

[0071] The compressor structure 10 is a structure located between the low pressure compressor 8 and the high pressure compressor 12. It is a static component within the load path transmitting thrust from the engine to the aircraft body, thereby driving the aircraft forward. The specific construction and design of the compressor structure depends, as mentioned above, on the specific engine construction, and are known under various terminology. Different manufacturers use different terminology and have different architectural constructions. The terms intermediate compressor case (ICC), intermediate case (IMC), and fan hub frame (FHF) all refer to constructions located between the low pressure compression section and the high pressure compression section. The crack stopper technique described herein may be applied to weld lines comprised in any of the above listed engine structures.

[0072] As indicated in FIG. 1, the compressor structure 10 comprises thrust lugs 22 or similar elements, allowing mounting the engine to a pylon via thrust links 24. The pylon is, in turn, connected to the wing of the aircraft. The thrust driving the air craft forward is transmitted from the engine to the air craft body via this structure. Part of an engine structure, in the vicinity of an engine mount or thrust lug, may be considered as a primary structure element (PSE), hence thereby dimensioned by crack propagation also in regions without any welds. The crack stopper technique described herein may be applied to any structural element considered as primary structure element (PSE) comprised in any of the above listed engine structures. Especially, the crack stopper technique may be applied to weld lines comprised in the PSE. It may also be applied at other locations of the air frame structures, such as the nacelle and pylons.

[0073] A method of joining two structural elements, here illustrated by a first component 26 and a second component 28, by welding according to some embodiments of the present disclosure is illustrated schematically in FIG. 2. The method comprises two main steps. In the first main step a weld line 30 is formed joining the first component 26 and the second component 28. This weld line 30 can be formed by various, known methods of welding. In the second step, which is illustrated in FIG. 2, material 32 is added across the weld line 30, thereby forming a crack stopper 34 for limiting crack propagation along the weld line 30. The crack stopper 34 spans from the first component 26, over the weld line 30, to the second component 28. The crack stopper 34 has a limited extension along the weld line 30 as seen in relation to a length of the weld line. It is thereby not the purpose to cover the length of the weld line 30 with additional material 32, but to form discrete features in the form of one or more crack stoppers 34 along the weld line 30. The extension of the crack stopper may be of the same order of magnitude as the width of the weld line or the heat effected zone, as described above.

[0074] In the embodiment of the method illustrated in FIG. 2, the crack stopper 34 is formed by a method known as metal deposition (MD). In this method, weld material 32 may be in the form of a wire, which is fed by a wire feeder 36, and is melted by an energy source, here in the form of laser light 38, on top of the existing weld line 30. Thereby, a crack stopper 34 extending from the first component 26, across the weld line 30, to the second component 28 is formed. Alternatively, the material 32 may be provided in the form of powder distributed by a powder source. The powder may be circulated in the air above the weld line using a blower, and melted onto the underlying surface using e.g. laser light 38.

[0075] During the MD process, the surface, on top of which the crack stopper 34 is to be formed, may be heated in order to achieve a good homogenisation between the deposited metal and the surfaces of the first and second component 26, 28 and the weld line 30. Thereby, the crack stopper may be substantially completely attached to the underlying surface. The process of melting additional material 32 is continued until a crack stopper 34 having a certain size is obtained.

[0076] The wire feeder 36 and the laser light source 38 may be moved relative to the weld line 30, such as to form a plurality of crack stoppers 34 along the weld line.

[0077] The steps of forming a weld line and forming a crack stopper may be performed using the same method. For example, both steps may be performed using the metal deposition method described with reference to FIG. 2. Thereby, two different welding apparatuses may be used, or both steps may be performed using the same apparatus. The weld line 30 and the crack stopper 34 may be formed of the same material. Even more, it may be possible to form the weld line 30 and the crack stoppers 34 from the same material as the two structural elements. Within the type of applications described herein, common materials are titanium (Ti) alloy, nickel (Ni) superalloys, and aluminium (Al).

[0078] The weld line may be allowed to cool in relation to a temperature obtained during the forming of the weld line before forming the crack stoppers. The first and the second steps may thereby be performed substantially subsequent to each other. However, it is also possible to add crack stoppers 34 by the method illustrated in FIG. 2 on already existing weld lines.

[0079] FIG. 3A to 3C schematically illustrate structural systems 40 comprising two structural elements which have been joined by a method as described with reference to FIG. 2. Each system 40 comprises a first component 26 and a second component 28, which are joined by a weld line 30, and one or more crack stoppers 34 arranged across the weld line 30. The purpose of the crack stopper 34 is to limit the growth of a crack 42 propagating along the weld line 30.

[0080] FIG. 3A illustrates a system 40 comprising one crack stopper 34, limiting propagation of the crack 42 along the weld line 30. The crack 42 indicated in FIG. 3A may be limited in the other direction by a further geometrical feature (not shown) present in a component comprising the structural system 40.

[0081] FIG. 3B and 3C illustrate systems 40 where a plurality of crack stoppers 34 has been formed at different positions along the weld line 30. Thereby, a plurality of crack stoppers 34 may be arranged along the weld line 30, such that neighbouring crack stoppers (c1, c2, . . . cn) are spaced at predetermined distances (d1,2, d2,3, . . . , dn-1,n) from each other. The crack stoppers 34 may thereby be arranged regularly or irregularly spaced. FIG. 3B and 3C schematically illustrate this principle.

[0082] FIG. 3B illustrates an embodiment where the distances (di-1,i) between neighbouring crack stoppers (c1, . . . , cn) are not all equal. In FIG. 3B, the distances between the crack stoppers 34 are irregular. The specific location of the different crack stoppers 34 may be determined by e.g. manufacturing possibilities, such as by locations where no other features are present in the direct vicinity of the weld line 30, such that it is easy to perform e.g. metal deposition across the weld line 30. In FIG. 3B, the propagation of the crack 42 is limited by the crack stoppers 34 denoted c2 and c3. Thereby, the crack 42 cannot grow longer than the distance d2, 3.

[0083] FIG. 3C illustrates an embodiment with regularly spaced crack stoppers 34. In FIG. 3C, all crack stoppers 34 are positioned at equal distances from each other.

[0084] As can be seen in FIG. 3A to 3C, each crack stopper 34 has a limited extension along the weld line 30. The extension of the crack stopper 34 may be of the same order of magnitude as the width of the weld line 30, or of the heat affected zone extending over the weld line 30 and adjacent areas of the first and second components 26, 28. The crack stoppers 34 may thereby be seen as singular, discrete features along the weld line 30. If a plurality of crack stoppers 34 are positioned along the weld line 30, the sum of the extension of each crack stopper 34 may comprise less than 25% of the length of the weld line 30.

[0085] In FIG. 3A to 3C, the crack stoppers 34 may span across the weld line 30, and extend onto the first and second components 26, 28. The crack stoppers 34 are dimensioned such as to provide a mechanical strength which is high enough to prevent crack propagation. Additionally, if due to the geometry and/or structural construction of one or both of the first and second components 26, 28 additional strengthening would be advantageous, for example due to features (not shown) arranged on the first and/or second components 26, 28, the crack stopper may be arranged such as to extend further onto the first and/or second component 26, 28, eventually onto these features.

[0086] Independent of whether the crack stoppers 34 are arranged at regular distances or not, the distance between adjacent crack stoppers 34 should preferably not be larger than a predetermined maximum allowable crack length along the specific weld line, as this distance limits the crack propagation. The maximum allowable crack length is determined by at least one predetermined strength and/or functionality criteria, as described above.

[0087] Also the dimensions of the crack stopper 34 may be determined by the predetermined strength and/or functionality criteria. Especially, a thickness and/or size of the crack stoppers 34 may be determined by the predetermined strength and/or functionality criteria. The thickness can also be referred to as the height of the crack stopper 34 over the surface on which it is formed, that is, over the first and second components 26, 28. The height of the crack stopper 34 may typically of the same order of magnitude as the thickness of the first and second components 26, 28. Thus, the height of the crack stopper 34 may be approximately equal to the thickness of the structural elements, or it may be a few multiples of the thickness of the structural elements. The size of the crack stopper 34 is related to the area of its attachment to the first 26 and second 28 component and the weld line 30. Ideally, the crack stopper 34 is completely attached to the underlying surface 26, 28, 30.

[0088] Strength criteria are related to preventing sudden, rapid crack propagation, or burst. Crack stoppers 34 should preferably be positioned within such distances from each other that they can prevent a rapid, uncontrolled growth of a crack 42 propagating along the weld line 30.

[0089] Functionality criteria are criteria relating to maintaining the function of the component on which the crack stoppers 34 are provided in spite of the crack 42. Thereby, cracks 42 should not be allowed to grow longer than that so an acceptable functioning of the component is maintained. For example, if the crack stoppers 34 are positioned on an engine component, air leakage through the crack 42 should be limited such that the functionality of the engine is maintained.

[0090] Although, for illustration, in FIG. 3A-3C the crack stoppers 34 are illustrated as having substantially rectangular shape with their main axis extending substantially perpendicular to the weld line 30, the crack stoppers 34 may have basically any shape. The shape can be determined e.g. by ease of manufacturing, for example by geometrical restrictions in the area where it is to be positioned.

[0091] For example, the crack stoppers 34 may have an elongated shape, extending in a direction of a main axis 44, such as substantially rectangular, elliptical or oval. The crack stoppers 34 may be oriented with their main axis 44 oriented in any direction to the weld line 30. For example, the main axis 44 may be oriented perpendicularly to the weld line 30, as shown in FIG. 3A. Further, the main axis 44 may be oriented at an oblique angle to the weld line, or the crack stoppers 34 may be oriented with their main axis 44 extending along the weld line 30, as illustrated by crack stopper 70 in FIG. 5.

[0092] Other possible shapes of crack stoppers 34 are circular or polygonal shape.

[0093] Even more, it is not necessary that all crack stoppers 34 along a weld line 30 have similar shape, but the shape may be determined by local requirements, and/or local geometrical and/or constructional restrictions.

[0094] As mentioned above, the method disclosed herein has a wide area of applications. For example, the method may be applied to jet engines or components thereof, such as a fan case, a fan structure, a compressor structure, turbine structure or an engine mount structure. The method of welding presented herein is particularly suitable for being used on compressor structures and on engine mount support structures (EMSS), such as engine mount attachment lugs or similar structures on the engine casing as well as portions of the engine structures which are critical to the engine mount load path. These structures may be known under different terminology depending on the specific engine construction and the engine manufacturer. In examples described below, as a general terminology we refer to such structures as engine compressor structures. Such structures are referred to using different terminology. For example, it may be referred to as primary structural element (PSE), intermediate compressor case (ICC), intermediate case (IMC), and fan hub frame (FHF), all referring to constructions located between the low pressure compression section and the high pressure compression section, mounting the engine to a pylon, which in turn is mounted to the wing of the aircraft. These structures are the direct primary load path transmitting the engine thrust force to the aircraft structure, through the pylon and the wing. The crack stopper technique may be applied to welds comprised in any of the above listed engine mount support structures. In this area, a critical crack length is a length that can just support limit loads.

[0095] Another example where the method described herein is particularly useful are bleed bosses that are exposed to vibration, and stress across the welds joining the bleed boss to the outer case. These cracks, which grow due to HCF loading, may grow beyond critical crack lengths within a few hours of flying, if not stopped. Thereby, it is normally impossible to detect emerging cracks during the regular inspections. In this case, by the presence of crack stoppers across the weld lines, the crack can be stopped early enough to prevent dysfunction during flight.

[0096] FIG. 4 shows a compressor structure 10 according to any of the types described above with reference to FIG. 1. The compressor structure 10 is provided with a plurality of crack stoppers 34 formed by the method described above. The compressor structure 10 comprises a first component 46 and a second component 48 joined by a weld line 30. A plurality of crack stoppers 34 are arranged along this weld line 30. As can be seen in FIG. 4, one of the crack stoppers 34, indicated as crack stopper 34′, extends over the weld line 30 and onto further features 50, 52 located on the first 46 and second 48 components, respectively. The compressor structure 10 shown in FIG. 4 further comprises bosses 54, 56 welded onto the compressor structure 10 by weld lines 58, 60. Crack stoppers 34 are provided over these weld lines 58, 60.

[0097] FIG. 5 shows another view of a compressor structure 10 of the type described above with reference to FIG. 1, in the area of an engine mount support structure. Here a first component 62 and a second component 64 joined by a weld line 66 are shown. The weld line 66 will be exposed to high loads during flight. The second component 64 comprises thrust lugs 22, as described above, forming part of the force path transmitting the thrust from the engine to the air craft body. The weld line 66 has been provided with a plurality of crack stoppers 68, 70. This figure also shows an example of different shapes of crack stoppers 68, 70 arranged along a weld line 66. In FIG. 5, four rectangular crack stoppers 68 are illustrated, oriented with their main axis 44 perpendicular to the weld line 66. A crack stopper 70 is illustrated as having elliptical shape, oriented with its main axis 44 along the weld line 66.

[0098] The compressor structure 10 illustrated in FIGS. 4 and 5 may be arranged in an aircraft engine, for example according to the illustration of FIG. 1.

[0099] The crack stoppers described herein can be applied either during manufacturing of the engine components, but also on already existing engine components.

[0100] It is not excluded from the present method that material is removed at the location of the crack stopper before adding material to produce the crack stopper. However, the method is simplified if merely adding material on top of the earlier made weld line, without removing any material underneath. A method which does not initially remove material is hence preferred at present time.

[0101] The method described herein is not limited to components for the type of aircraft engine illustrated in FIG. 1, but can be used for applications also in other types of aircraft engines. Further, it is not limited to the field of aircraft engines, but can be used also for any type of application requiring high strength welds with limitation of crack propagation.

[0102] Further modifications of the welding method and products and components resulting from application of the welding method within the scope of the claims will be apparent to the skilled person.