Panel assembly and method for its manufacture

Description

BACKGROUND

[0001] The present invention concerns a panel assembly comprising a ceramic matrix composite or ceramic body, as well as a method for forming the panel assembly. Generally, the invention relates to mounting of ceramic and ceramic matrix composite (CMC) structures in engines, for example used for aerospace propulsion.

[0002] The mounting of ceramic and ceramic matrix composite parts in the hot sections of gas turbine engines has involved a variety of difficulties. These have included a number of issues involving differential thermal expansion of the metallic and non-metallic components involved.

[0003] In some situations, metallic fasteners pass entirely through the non-metallic component. One example is as seen in US Patent 8,607,577, of Ruberte Sanchez et al., December 17, 2013.

[0004] US Patent 7,832,972, of Jarmon, November 16, 2010, discloses a system involving slotting the non-metallic panel and inserting the asymmetric heads of fasteners followed by rotating the fasteners to backlock the heads.

[0005] WO 2014 / 187659 A1 discloses a prior art panel assembly as set forth in the preamble of claim 1.

[0006] US 2009 / 226279 A1 discloses a prior art internal pocket fastener system for ceramic matrix composites.SUMMARY

[0007] From one aspect of the invention, there is provided a panel assembly as recited in claim 1.

[0008] There is also provided a gas turbine engine as recited in claim 8.

[0009] There is also provided a method for forming a panel assembly as recited in claim 10.

[0010] Features of embodiments of the invention are set forth in the dependent claims.

[0011] The details of one or more embodiments are set forth in the accompanying drawings and the description below. Other features, objects, and advantages will be apparent from the description and drawings, and from the claims.BRIEF DESCRIPTION OF THE DRAWINGS

[0012] FIG. 1 is a view of a gas turbine engine panel. FIG. 2 is a radial sectional view of an assembly of the panel and fasteners mounted to mounting structure in a gas turbine engine. FIG. 3 is a radial sectional view of the panel during securing of the fasteners in compartments in the panel. FIG. 4 is a radial sectional view of the panel during compartment drilling. FIG. 5 is a radial sectional view of the panel upon insertion of a grinding or machining bit. FIG. 6 is a radial sectional view of the panel after a transverse shift of the bit. FIG. 7 is a radial sectional view of the panel during an orbiting of the bit. FIG. 8 is a radial sectional view of the panel after compartment formation. FIG. 9 is a radial sectional view of an assembly of the panel and alternate fasteners mounted to mounting structure in a gas turbine engine.

[0013] Like reference numbers and designations in the various drawings indicate like elements.DETAILED DESCRIPTION

[0014] FIG. 1 shows a panel 20. The exemplary panel 20 comprises a ceramic or ceramic matrix composite (CMC) body having a first face 22 and a second face 24. The exemplary first face 22 is a gaspath-facing face in a gas turbine engine (broadly inclusive of engines used in propulsion via thrust, other propulsive engines, industrial gas turbines, and the like). Particular applications include combustor panel liners (including as segments thereof), blade outer air seals (BOAS), exhaust nozzle flap liners, and the like. Other applications include ramjet and rocket engine use, aerodynamic thermal tiles, and the like.

[0015] In a typical combustor panel application, BOAS, or flap liner, the panel is generally a frustoconical segment with a leading end / edge 26, a trailing end / edge 28, a first lateral end / edge 30, and a second lateral end / edge 32. In an annular combustor, there may be a longitudinal end-to-end plurality of annular lateral end-to-end arrays of such panels.

[0016] The second face 24 (backside) faces, and may in some implementations contact, an adjacent surface 40 of mounting structure 42. Typically, the mounting structure 42 will be metallic such as a portion of an engine case or a metallic panel carrier structure. As is discussed below, the panel 20 is mounted to the mounting structure via a fastening system. The exemplary fasteners 50 are threaded fasteners having a shank or shaft 52 extending to an end 54 and bearing, along at least a portion, an external thread 56. In the installed condition, the threaded shank is received by a complementary internally-threaded member 60 such as a nut along a backside surface 44 of the mounting structure with the shank passing through a hole 62. Various washers 63, and the like, may also be used.

[0017] The fastener 50 has a head 70 (shown as a protuberant head) at one end of the shank captured in a compartment (e.g., a blind compartment) 80 (FIG. 1) open to the backside 24 so that the shank protrudes from the backside. To backlock the head 70, the compartment has a first portion 82 (FIG. 2) receiving the protuberance of the head and a narrower second portion 84, the second portion outboard of the first portion. As is discussed below, the fastener head protuberance results from an in situ deformation.

[0018] In an exemplary embodiment, the fastener 50 is initially formed with the head 70 in an at least relatively non-protuberant condition and then the head 70 is expanded. FIG. 3 shows the fastener in this initial condition. The shank 52 and head 70 are hollow. In various embodiments, the head 70 and shank 52 are separately formed and then joined. For example, the shank 52 may be formed from threading and machining tubular stock or from rod stock with a passageway 90 drilled between ends 54 and 58. The head 70 may be machined or stamped in a cup-like form having a sidewall 72 with a rim 74 at one end and a transverse web 76 at the other end. The head 70 and shank 52 may then be attached to each other such as via welding or brazing the rim 74 to the end 58 to form a weld or braze joint.

[0019] Alternative techniques may manufacture the fastener in a single piece unitary structure such as metal injection molding (powder metallurgical (PM)), casting, or additive manufacturing. FIG. 9 shows such a single-piece fastener 50-1 with a head 70-1 in its expanded condition relative to the shank 52-1. Exemplary fastener materials for any of these embodiments include nickel-based superalloys. Exemplary alloys include IN625, IN718, IN617, Waspalloy ™< , and Haynes ™< 230 and 282.

[0020] The unexpanded head 70, 70-1 may then be inserted into the compartment 80. A source 400 of pressurized fluid may then (or already) be connected to the fastener such as by attaching a fitting 402 to the shank 52, 52-1 (e.g., threading a threaded fitting or applying a quick release fitting). An exemplary source 400 is a high pressure gas source (e.g., having a compressor 404 and a storage tank 406). Other systems include hydraulic systems using liquid fluid. High pressure fluid is then delivered from the source 400 to the fastener 50, 50-1 (e.g., via opening a valve), pressurizing the head interior 71 and causing an at least partial plastic deformation to create the protuberance or sufficiently increase the protuberance of the head 70, 70-1 to backlock the fastener 50, 50-1 in the panel. The source 400 may then be disengaged (e.g., closing valve and unscrewing the fitting from the shank), leaving the head 70, 70-1 deformed and protuberant to hold the fastener 50, 50-1 against extraction. To facilitate the plastic deformation, the fastener 50, 50-1 may be heated (via gas torch or oven (not shown)) prior to expansion and then cooled. Other methods of heating the fastener 50, 50-1 are induction (selectively heats the metal relative to non-conductive ceramic and CMCs) or IR to locally heat the ceramic from surface 22, which then heats the metal via conduction.

[0021] The process may be repeated for multiple fasteners 50, 50-1 on a given panel 20.

[0022] The panel 20 may then be installed by engaging the shank(s) 72, 72-1 with the associated holes 62 and installing the washer(s) 63 and installing / tightening the nut(s) 60. During nut tightening, the shank 72, 72-1 may be held against rotation by a respective wrench or key (e.g., hex key (not shown)) holding an end portion of the shank (e.g., respectively externally faceted or internally faceted). In principle, a number of processes may be used to form the compartments 80. In examples not forming part of the present invention, the compartments may be pre-formed such as by molding the ceramic over sacrificial cores having the compartment shape and then chemically or thermally removing the cores. Such cores may also be used when forming a CMC. In an embodiment of the present invention, the compartments 80 are machined into a precursor of the panel 20. The machining technique involves first drilling (drill 420 with axis of rotation 530 of FIG. 4) a straight blind bore of a given diameter (e.g., just large enough to pass the shank 72, 72-1 and head 70, 70-1 pre-deformation) and having an axis 520. This step effectively forms the second portion 84. The portion 82 is formed by inserting a bit (430 of FIG. 5) with a protuberant cutting or grinding portion 432. The bit 430 may be inserted with the protuberant cutting or grinding portion 432 just being accommodated by the initial bore. The bit may be shifted radially outward relative to the axis 520 of the bore until the narrow shaft 434 of the bit 430 contacts or nears the bore surface. The rotating bit 430 may then be orbited (180° completed of 360° in FIG. 7) around the bore axis 520 to complete the machining of the first portion 82. The bit 430 may then be re-centered coaxial with the bore and withdrawn, leaving the compartment 80 with the enlarged first portion 82 (FIG. 8).

[0023] The system may have one or more of several advantages. In several advantages, the head of the fastener is not exposed to the gaspath. This reduces heating of the fastener and helps maintain its integrity. In certain situations such as nozzle flaps, it may reduce RADAR or infrared (IR) signature. There may be reduced likelihood of vibrating loose. Depending upon the nature of the alternative fastener, this may also involve reduced likelihood of the fastener becoming dislodged and potentially damaging other components.

[0024] Although panels are illustrated, other examples include those panels and other structures disclosed in the aforementioned Ruberte Sanchez and Jarmon patents. Non-panel situations may include, for example, the mounting of vane clusters.

[0025] The use of "first", "second", and the like in the following claims is for differentiation within the claim only and does not necessarily indicate relative or absolute importance or temporal order. Similarly, the identification in a claim of one element as "first" (or the like) does not preclude such "first" element from identifying an element that is referred to as "second" (or the like) in another claim or in the description.

[0026] One or more embodiments have been described. Nevertheless, it will be understood that various modifications may be made. For example, when applied to an existing baseline configuration, details of such baseline may influence details of particular implementations. Accordingly, the scope of the present invention is only defined the following claims.

Claims

1. A panel assembly (20) comprising: a ceramic matrix composite or ceramic body (20), the body(20) having a compartment (80), the compartment (80) having a first portion (82) and a second portion (84), the second portion (84) outboard of and narrower than the first portion (82); and a fastener (50;50-1), characterised in that the fastener (50; 50-1) has a hollow expanded portion (70;70-1) within the compartment first portion (82), wherein the expanded portion (70; 70-1) has been deformed in situ within the first portion (82) of the compartment (80), wherein the expanded portion (70; 70-1) is too large to pass through the second portion (84) of the compartment (80), wherein the second portion (84) is a drilled straight blind bore having an axis (520) and the first portion (82) has been machined by a bit (430) having a narrow shaft (434) and a protuberant cutting or grinding portion (432).

2. The panel assembly of claim 1, wherein the compartment (80) is a blind compartment (80).

3. The panel assembly of claim 1 or 2, wherein the fastener (50;50-1) has a threaded shank (52;52-1).

4. The panel assembly of claim 3, in combination with a mounting structure (42), the threaded shank (52;52-1) passing through a hole (62) in the mounting structure (42) and held by a nut (60).

5. The panel assembly of any of claims 1 to 3, wherein the expanded portion interior (71) is continuous with a hollow portion of a or the shank (52;52-1).

6. The panel assembly of any preceding claim, wherein the body (20) is shaped as a segment of a frustoconical shell.

7. The panel assembly of any preceding claim, wherein the hollow expanded portion (70; 70-1) is machined or stamped in a cup-like form having a sidewall (72) with a rim (74) at one end of the sidewall (72) and a transverse web (76) at the other end of the sidewall (72).

8. A gas turbine engine comprising the panel assembly preceding claim, wherein the panel (20) is along a gaspath of the gas turbine engine.

9. The gas turbine engine of claim 8, wherein the panel (20) is selected from the group consisting of combustor panels, blade outer air seals, and exhaust nozzle liners.

10. A method for forming the panel assembly (20) of any of claims 1 to 7, the method comprising: inserting a portion of the fastener (50;50-1) into the compartment (80) of the ceramic matrix composite or ceramic body (20); and delivering a fluid into the fastener (50;50-1) to expand a portion (70;70-1) of the fastener (50;50-1) within the compartment first portion (82).

11. The method of claim 10, wherein: the fastener (50;50-1) has a or the threaded shank (52;52-1), and the method comprises engaging a fluid source (400) to the shank (52) before the delivering and disengaging the fluid source from the shank (52) after the delivering.

12. The method of claim 10 or 11, further comprising heating a portion (70;70-1) of the fastener (50;50-1).

13. The method of claim 10, 11 or 12, further comprising forming the compartment (80) by laterally shifting a rotating bit (430), the rotating bit (430) having a protuberant cutting or grinding portion (432) that forms the compartment first portion (82).

14. The method of claim 14, wherein: the forming the compartment (80) further comprises forming an initial bore; and / or the lateral shifting comprises a circular shift.

15. The method of claim 13 of 14, wherein: the body (20) is a combustor panel body; and / or the method further comprises manufacturing the fastener (50;50-1) via metal injection molding or additive manufacture.