WO2021258192A1

WO2021258192A1 - Additive manufactured landing gear brace using preformed extruded metal as base material

Info

Publication number: WO2021258192A1
Application number: PCT/CA2021/050838
Authority: WO
Inventors: Joseph LAN; Ian MCCLUSKEY; Max LAW
Original assignee: Safran Landing Systems Canada Inc.
Priority date: 2020-06-26
Filing date: 2021-06-18
Publication date: 2021-12-30

Abstract

A hybrid additive manufacturing method includes the steps of obtaining a metallic source material and one or more base materials. The method further includes adding a first feature to the base material with an additive manufacturing process using the metallic source material. When more than one base material is used, the base materials are coupled together with the additive manufacturing process using the metallic source material.

Description

TITLE OF INVENTION

ADDITIVE MANUFACTURED LANDING GEAR BRACE USING PREFORMED EXTRUDED METAL AS BASE MATERIAL

BACKGROUND

Additive manufacturing is a type of three-dimensional (3D) printing where material is solidified in a pattern controlled by computer-aided design (CAD) instructions, and the part being produced is built on a layer-by-layer basis. Unlike a conventional machining process, where material is removed from stock to produce a part, additive manufacturing builds the part by adding layers, where each layer is solidified by a computer-controlled source, such as a laser or an electron-beam, before the tray moves incrementally to allow a new layer to be solidified adjacent the previous layer, or by adding solid stock material directly. Additive manufacturing is capable of producing parts from a wide variety of materials, including metals, polymers, and minerals.

One type of additive manufacturing, powder bed fusion, can be used to produce high fidelity, complex metal parts having relatively tight tolerancing, and a wide variety of alloys are compatible with the powder bed fusion process. However, parts made by the powder bed fusion technique generally lack strength in certain aspects of the part, and the part size capability is constrained by the size of the plate (or material/powder operating bed) and the freedom of movement within the operating envelope of the laser.

Another type of additive manufacturing, direct energy deposition (DED) additive manufacturing, is used to produce complex metal. The DED uses focused thermal energy to melt a source material as it is being deposited on a work piece. The thermal energy is typically provided by a laser, electron beam, or plasma arc. The source material, which is typically a metal powder, wire, or rod, is deposited on the work piece through a feed nozzle. Both the feed nozzle and the thermal energy source are mounted on a controlled drive mechanism, such as a multi-axis Computer Numerical Control (CNC) head or an articulated arm to selectively control the direction from which the source material is deposited. When a 5-axis or 6-axis machine is used, the source material can be deposited from nearly any angle.

DED processes are able to produce metal parts with strength approximately equivalent to forged metal parts, but can only produce in near net shape (i.e., looser tolerances than some other additive manufacturing processes) and generally must be post-machined to gain a high tolerance part. Manufacturing large parts using DED is also time consuming and can be expensive as compared to traditional manufacturing processes.

SUMMARY

This summary is provided to introduce a selection of concepts in a simplified form that are further described below in the Detailed Description. This summary is not intended to identify key features of the claimed subject matter, nor is it intended to be used as an aid in determining the scope of the claimed subject matter.

In accordance with one embodiment of the present disclosure, a hybrid additive manufacturing method is provided. The hybrid additive manufacturing method generally includes obtaining a metallic source material; obtaining a base material; and adding at least a first feature to the base material with an additive manufacturing process using the metallic source material.

In accordance with another embodiment of the present disclosure, a hybrid additive manufacturing method is provided. The hybrid additive manufacturing method generally includes obtaining a metallic source material; obtaining first and second base materials; and coupling the first base material to the second base material with an additive manufacturing process using the metallic source material.

In accordance with any of the embodiments described herein, the first base material may be an extruded metal and/or a forged metal.

In accordance with any of the embodiments described herein, the second base material may be an extruded metal and/or a forged metal.

In accordance with any of the embodiments described herein, the base material may be an extruded I-beam.

In accordance with any of the embodiments described herein, the additive manufacturing process may be a direct energy deposition process.

In accordance with any of the embodiments described herein, the additive manufacturing process may be a powder bed fusion process.

In accordance with any of the embodiments described herein, the metallic source material may be a wire or a rod.

In accordance with any of the embodiments described herein, the first feature may be of a stiffening rib, a lug, or a clevis. In accordance with any of the embodiments described herein, the hybrid additive manufacturing method may further include a step of machining a portion of the base material and/or the first feature with a tool to provide a finished part.

In accordance with any of the embodiments described herein, the hybrid additive manufacturing method may further include a step of adding at least a first feature to the coupled first and second base materials with the additive manufacturing process using the metallic source material.

In accordance with another embodiment of the present disclosure, a hybrid additive manufacturing method for manufacturing an aircraft landing gear brace is provided. The aircraft landing gear brace has an elongate body with a clevis formed on at least one end. The method includes obtaining a metallic source material and obtaining an extruded I-beam base material, wherein the I-beam base material has first and second flanges and a central web. The method further includes adding a first lug to the first flange at an end of the I-beam material with an additive manufacturing process using the metallic source material; and adding a second lug to the second flange at the end of the I-beam material with the additive manufacturing process using the metallic source material, wherein the first and second lug define the clevis.

In accordance with another embodiment of the present disclosure, a hybrid additive manufacturing method for manufacturing an aircraft landing gear brace is provided. The aircraft landing gear brace has an elongate body with a clevis formed on at least one end. The method includes the steps of obtaining a metallic source material and obtaining first and second T-shaped base materials, each of the first and second T-shaped base materials having a leg and a cap. The method further includes arranging the first and second T-shaped base materials on an operating bed of an additive manufacturing process so that the legs of the first and second T-shaped base materials are aligned and coupling the first base material to the second base material with a web extending from the leg of the first T-shaped base material to the leg of the second T-shaped base material, the web being formed with the additive manufacturing process using the metallic source. The method also includes adding a first lug to an end of the cap of the first T-shaped base material with the additive manufacturing process using the metallic source material and adding a second lug to an end of the cap of the second T-shaped base material with the additive manufacturing process using the metallic source material, wherein the first and second lugs define a clevis. In accordance with any of the embodiments described herein, the hybrid additive manufacturing method may further include a step of machining a portion of at the first base material, the second base material, and/or the first feature with a tool to provide a finished part. DESCRIPTION OF THE DRAWINGS

The foregoing aspects and many of the attendant advantages of the claimed subject matter will become more readily appreciated as the same become better understood by reference to the following detailed description, when taken in conjunction with the accompanying drawings, wherein: FIGURE 1 is a front, left, top perspective view of a representative embodiment of a part manufactured from a hybrid manufacturing method in accordance with an aspect of the present disclosure, wherein the part is shown during a first manufacturing phase;

FIGURE 2 is a front, left, top perspective view of the part of FIGURE 1 during a second manufacturing phase; FIGURE 3 is a front, left, top perspective view of the part of FIGURE 1 during a third manufacturing phase;

FIGURE 4 is a flow diagram describing a representative embodiment of a method of manufacturing a part, such as the part of FIGURES 1-3, in accordance with another aspect of the present disclosure; FIGURE 5 is a front, left, top perspective view of a second representative embodiment of a part manufactured from a hybrid manufacturing method in accordance with another aspect of the present disclosure, wherein the part is shown during a first manufacturing phase;

FIGURE 6 is a front, left, top perspective view of the part of FIGURE 5 during a second manufacturing phase; and

FIGURE 7 is a flow diagram describing a representative embodiment of a method of manufacturing a part, such as the part of FIGURES 5 and 6, in accordance with another aspect of the present disclosure.

DETAILED DESCRIPTION The detailed description set forth below in connection with the appended drawings, where like numerals reference like elements, are intended as a description of various embodiments of the present disclosure and are not intended to represent the only embodiments. Each embodiment described in this disclosure is provided merely as an example or illustration and should not be construed as precluding other embodiments. The illustrative examples provided herein are not intended to be exhaustive or to limit the disclosure to the precise forms disclosed.

In the following description, specific details are set forth to provide a thorough understanding of exemplary embodiments of the present disclosure. It will be apparent to one skilled in the art, however, that the embodiments disclosed herein may be practiced without embodying all of the specific details. In some instances, well-known process steps have not been described in detail in order not to unnecessarily obscure various aspects of the present disclosure. Similarly, any steps described herein may be interchangeable with other steps, or combinations of steps, in order to achieve the same or substantially similar result. Moreover, some of the method steps can be carried serially or in parallel, or in any order unless specifically expressed or understood in the context of other method steps. Further, it will be appreciated that embodiments of the present disclosure may employ any combination of features described herein.

The present application may include references to directions, such as "forward," "rearward," "front," "rear," "upward," "downward," "top," "bottom," "right hand," "left hand," "lateral," "medial," "distal," "proximal," "in," "out," "extended," etc. These references, and other similar references in the present application, are only to assist in helping describe and to understand the particular embodiment and are not intended to limit the present disclosure to these directions or locations.

The present application may also reference quantities and numbers. Unless specifically stated, such quantities and numbers are not to be considered restrictive, but exemplary of the possible quantities or numbers associated with the present application. Also in this regard, the present application may use the term "plurality" to reference a quantity or number. In this regard, the term "plurality" is meant to be any number that is more than one, for example, two, three, four, five, etc. The terms "about," "approximately," "near," etc., mean plus or minus 5% of the stated value. For the purposes of the present disclosure, the phrase "at least one of A and B" is equivalent to "A and/or B" or vice versa, namely "A" alone, "B" alone or "A and B.". Similarly, the phrase "at least one of A, B, and C," for example, means (A), (B), (C), (A and B), (A and C), (B and C), or (A, B, and C), including all further possible permutations when greater than three elements are listed.

The following description provides several examples that relate to methods for additive manufacturing. In these examples, additive manufacturing processes are described in conjunction with hybrid manufacturing methods of the present disclosure. The present disclosure generally relates to hybrid manufacturing methods that utilize DED manufacturing processes; however, the disclosure should not be construed as limited to the specific processes referenced herein. Embodiments of the present disclosure are suitable for use with any powder bed or direct deposition technology (additive manufacturing) using the melting of rods/wire/powder. In some embodiments, the methods include optional post machining. In these regards, the methods of the present disclosure are suitable for use with hybridization of any additive manufacturing process.

As previously noted, each type of additive manufacturing possesses various advantages and disadvantages relating to processing speed, part size and weight, geometric freedom, aerodynamic properties, finished material strength, material and machine cost, availability of source materials, machine service intervals, machine size, part tolerance capabilities, and other considerations. For example, some additive manufacturing processes produce parts quickly and cheaply, but with rough manufacturing tolerances and low material strength. Other additive manufacturing processes can be slower to produce a part, or more expensive to operate and maintain, but produce parts with closer tolerances and higher strength.

The present disclosure contemplates methods that are suitable to create hybrid parts by applying an additive manufacturing process to a base material. Further, different additive manufacturing processes can be applied to areas, components, or features of parts according to benefit from the advantages of the processes in order to meet operational requirements of the parts while reducing manufacturing costs. In some examples, a part may have functional requirements best suited for one additive manufacturing process, while other parts are best suited for a different additive manufacturing process. In these examples, the hybrid manufacturing methods of the present disclosure are suitable to allow a designer to design parts to take advantage of the strengths and to mitigate the weaknesses of each additive manufacturing process in order to produce parts having the requisite quality, strength, and finish designed by the designer; while reducing cost, weight, and processing time to increase throughput.

In one representative example, aerospace components generally include complex structures with very tight tolerance, strength, and weight requirements. In the ensuing description, one example of a group of aerospace components — aerospace landing gear structural members — will be used. It should be noted that the use of aerospace landing gear parts herein is exemplary, and does not limit the scope of the present disclosure. The hybrid manufacturing methods disclosed herein are suitable for use with any part benefiting from the hybridization of different additive manufacturing processes.

For the example of a landing gear structural member, optimizing strength, weight, and acoustic properties is critical, among consideration of other aspects and properties. In some examples of other parts produced by aspects of the present disclosure, strength and fatigue properties may be less critical, so other characteristics, such as cost and manufacturing time may be accommodated by using different additive manufacturing techniques.

In some embodiments, features are added to a single base material using a DED manufacturing process. In some embodiments, multiple base materials are joined together using a DED manufacturing process. In some embodiments, additional features are added to the joined multiple base materials. In some embodiments, the additional features are one or more of mounting points, interfacing features, stiffening ribs, and other designed components of the part. Sections of the base material or materials and additional features requiring tighter tolerances can be post-machined to final dimensions.

Turning initially to FIGURES 1-3, an embodiment of a part 100 manufactured using a hybrid manufacturing method according to aspects of the present disclosure is shown. The part 100 includes a metallic base material 102, shown in FIGURE 1, to which other features are added by one or more additive manufacturing processes. In the illustrated embodiment, the base material is in the form of an I-beam having parallel flanges 104 and 106 connected by a central web 108. In some embodiments, the base material 102 is extruded. In some embodiments, the base material is forged. In some embodiments, the base material is a flat plate, a solid or hollow bar, a "T," a "Z," a "U,"an angle, a closed box, or any other suitable shape. In still other embodiments, the one or more features have been formed in base material 102 prior to being modified by one or more additive manufacturing processes. It should be appreciated that the metallic base material 102 may be made from any material by any processes suitable to provide the strength, durability, and performance characteristics required of the part 100. Such suitable processes may include, for example, casting, milling, extruding, additive manufacturing, forging, etc.

FIGURE 2 shows the base material 102 with additional features added by one or more additive manufacturing processes. In the illustrated embodiment, circular segments 110 are added to opposite edges of each flange 104 and 106. On each flange 104 and 106, the opposing circular segments are sized and positioned so that the circular segments have a common center point and radius. A plurality of stiffening ribs 112 are also added to the base material 102. The stiffening ribs 112 extend in a perpendicular direction from the web 108, from one flange 104 to the other flange 106. In the illustrated embodiment, additional circular segments 114 are added to the edges of the flanges 104 and 106 where the larger circular segments 110 meet the edge of the flange.

Referring now to FIGURE 3, material is removed from the base material 102 and added features 110, 112, 114. In the illustrated embodiment, a portion of the web 108 is removed between the circular segments 110, and concentric holes 116 are formed in the corresponding flanges 104 and 106 to define a pair of lugs on the end of the part 100. Holes 118 are also formed in the additional circular segments 114 to form additional lugs. In some embodiments, lightening holes 120 are added to reduce the weight of the part 100 and to provide access and/or routing paths for electrical or other systems. In some embodiments, additional material is added around the lightening holes 120 prior to or after the lightening holes 120 are formed in the part 100.

Material removal can be accomplished by any suitable process or combination of processes. In some embodiments, material is removed by milling machine, lathes, drill presses, or other known manufacturing equipment. In some embodiments, material is removed by chemical milling, e.g., industrial etching. In still other embodiments the material removal is followed by post-machining processes such as peening, coldworking, heat treating, chemical treating, priming, painting, or any other suitable process or combination of processes.

Turning to FIGURE 4, one representative embodiment of a method 200 of hybrid manufacturing of a part, such as a landing gear part, is shown. The method generally includes obtaining a metallic base material; placing the metallic base structure on an operating bed or other structure of an additive manufacturing process; manufacturing one or more features, i.e., structural or nonstructural elements, coupled to the metallic base material with the additive manufacturing; and machining a portion of the structure with a tool to provide a finished part.

In some embodiments, the step of manufacturing one or more features is performed using a DED additive manufacturing process. In some embodiments, the metallic source material for the DED additive manufacturing process is a wire source material. In other embodiments, the metallic source material for the DED additive manufacturing process is a rod source material. In still other embodiments, the metallic source material for the DED additive manufacturing process is a powder source material.

In block 202, a metallic base material, such as an extrusion, forging, or plate is obtained. The metallic base material is used in the additive manufacturing of the part, and is suitably any metallic base material.

In block 204, a metallic source material for the additive manufacturing process is obtained. The metallic source material is used in the additive manufacturing of the part, and is suitably any metallic source material.

In block 206, the metallic base material is placed on, for example, an operating bed or a support structure suitable for the additive manufacturing process or processes utilized in the method 200.

In block 208, one or more features are manufactured on the metallic base material with the metallic source material using an additive manufacturing process. In some embodiments, the additive manufacturing process is a DED additive manufacturing process using a wire or rod as a source material. In some embodiments, the additive manufacturing process is a DED additive manufacturing process using a metallic powder as a source material. The DED thermal energy source, e.g., laser, electron beam, plasma arc, etc., heats the metallic source material to solidify it in a pattern defined by CAD data, and builds the added features of the part on a layer-by-layer basis. In some embodiments, the one or more features are lugs, clevises, stiffeners, attachment interfaces, mounting features, or any other suitable feature or parts thereof, or combinations thereof.

In block 210, a portion of the combined base material/added features is optionally machined with a tool to provide a finished part. The step of machining with a tool may provide improved finish tolerancing to certain features of the part, such as a mounting location, a lug, a clearance feature, or the like.

FIGURES 5 and 6 show an embodiment of a part 300 manufactured using a hybrid manufacturing method of the present disclosure. The part 300 is similar to the previously described part 100 shown in FIGURES 1-3, except that more than one metallic base material 302 is used to form the part 300. In some embodiments, multiple metallic base materials 302 are joined using an additive manufacturing process. In some embodiments, the metallic base materials are identical or are mirror images of each other. In some embodiments, the metallic base materials have different configurations that contribute to various features of the finished part 300.

As best shown in FIGURE 5, the illustrated embodiment of the part 300 includes two metallic base materials 302. Each of the base materials 302 is in the general shape of a "T" section, having a leg 304 and a cap 306 perpendicular to the leg. In the illustrated embodiment, stiffeners 308 extend along the edges of the cap 306. The base materials 302 are arranged relative to each other so that bottoms of the respective legs 304 are proximate to each other, and the corresponding side faces of the respective legs are parallel to each other. In the illustrated embodiment, the base materials are arranged so that the caps 306 are angled relative to each other. In some embodiments, the materials are arranged so that the caps 306 are parallel to each other. In some embodiments, more than two base materials 302 are included. It will be appreciated that various embodiments are possible in which the number and arrangement of base materials differ from the disclosed embodiments, and such variations should be considered within the scope of the present disclosure.

Referring now to FIGURE 6, a web portion 310 is added between the legs 304 of the base materials 302 by an additive manufacturing process. In the illustrated embodiment, the web portion 310 extends from one leg 304 to the other leg so that the legs 304 and the web portion 310 cooperate to form a web that extends from the cap 306 of one base material 302 to the cap of the other base material. A stiffener 312 is formed perpendicular to the web portion 310 at one end, and a lug 314 is formed at the corresponding end of each of the base portions 302.

Turning to FIGURE 7, another representative embodiment of a method 400 of hybrid manufacturing of a part, such as a landing gear part, is shown. The method is generally similar to the previously described method 200, but includes the use of more than one metallic base material. In this regard, the method 400 includes obtaining two or more base source materials; placing the metallic base materials on an operating bed of an additive manufacturing process; coupling the metallic base materials to produce a combined portion; adding additional features to the coupled metallic source materials using an additive manufacturing process; and machining an area of the second portion with a tool to provide a finished part. In some embodiments, the coupling of metallic base materials is performed with one of an adhesive, a welding process, a fastener, an interlocking feature in the more than one first structures/portions, and a second additive manufacturing process prior to being placed, for example, on the operating bed.

In block 402, two or more metallic base materials are obtained. The metallic base materials may be extrusions, forgings, plates or any other suitable material is obtained. In some embodiments, the metallic base materials are identical. In some embodiments, two or more of the metallic base materials are made from different materials, have different shapes, and/or were produced using different manufacturing techniques.

In block 404, a metallic source material for the additive manufacturing process is obtained. The metallic base material is used in the additive manufacturing of the part, and is suitably any metallic source material.

In block 406, the metallic base materials are arranged, for example, on an operating bed of an additive manufacturing process. In some embodiments, the metallic base materials are arranged relative to each other in the same relationship as they will have in the finished part.

In block 408, the metallic base materials are coupled to each other by the additive manufacturing process. In some embodiments, the metallic base materials are coupled to each other prior to the additive manufacturing process, and the additive manufacturing process provides an additional connection between the metallic base materials. In some embodiments, the additive manufacturing process is aDED additive manufacturing process using a wire or rod as a source material. In some embodiments, the additive manufacturing process is DED additive manufacturing process using a metallic powder as a source material. In these embodiments, the DED thermal energy source, e.g., laser, electron beam, plasma arc, etc., heats the metallic source material to solidify it in a pattern defined by CAD data, and builds the added features of the part on a layer-by-layer basis. In some embodiments, the one or more features are lugs, clevises, stiffeners, attachment interfaces, mounting features, or any other suitable feature or parts thereof, or combinations thereof.

In block 410, one or more features are manufactured on the metallic base material with the metallic source material using an additive manufacturing process. In block 412, a portion of the base materials with the added external features is optionally machined with a tool to provide a finished part. The step of machining with a tool may provide improved finish tolerancing to certain features of the part, such as a mounting location, a lug, a clearance feature, or the like.

The principles, representative embodiments, and modes of operation of the present disclosure have been described in the foregoing description. However, aspects of the present disclosure, which are intended to be protected, are not to be construed as limited to the particular embodiments disclosed. Further, the embodiments described herein are to be regarded as illustrative rather than restrictive. It will be appreciated that variations and changes may be made by others, and equivalents employed, without departing from the spirit of the present disclosure. Accordingly, it is expressly intended that all such variations, changes, and equivalents fall within the spirit and scope of the present disclosure as claimed.

Claims

CLAIMS The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. A hybrid additive manufacturing method, comprising: obtaining a metallic source material; obtaining a base material; and adding at least a first feature to the base material with an additive manufacturing process using the metallic source material.

2. The method of Claim 1, wherein the base material comprises at least one of an extruded metal and a forged metal.

3. The method of Claim 1 or 2, wherein the base material is an extruded I- beam.

4. The method of any of Claims 1 through 3, wherein the additive manufacturing process is a direct energy deposition process.

5. The method of Claim 4, wherein the metallic source material comprises one of a wire and a rod.

6. The method of any of Claims 1 through 3, wherein the additive manufacturing process is a powder bed fusion process.

7. The method of any of Claims 1 through 6, wherein the at least first feature includes at least one of a stiffening rib, a lug, and a clevis.

8. The method of any of Claims 1 through 7, further comprising a step of machining a portion of at least one of the base material and the first feature with a tool to provide a finished part.

9. A hybrid additive manufacturing method, comprising: obtaining a metallic source material; obtaining first and second base materials; and coupling the first base material to the second base material with an additive manufacturing process using the metallic source material.

10. The method of Claim 9, wherein the additive manufacturing process is a direct energy deposition process.

11. The method of Claim 10, wherein the metallic source material comprises one of a wire and a rod.

12. The method of Claim 9, wherein the additive manufacturing process is a powder bed fusion process.

13. The method of any of Claims 9 through 12, further comprising a step of adding at least a first feature to the coupled first and second base materials with the additive manufacturing process.

14. The method of any of Claims 9 through 13, further comprising a step of machining a portion of at least one of the first and second base materials and the first feature with a tool to provide a finished part.

15. The method of any of Claims 9 through 14, wherein the first base material comprises one of an extruded metal and a forged metal.

16. The method of any of Claims 9 through 15, wherein the second base material comprises one of an extruded metal and a forged metal.

17. The method of any of Claims 9 through 16, wherein the at least first feature includes one or more of a stiffening rib, a lug, and a clevis.

18. A hybrid additive manufacturing method for manufacturing an aircraft landing gear brace, the aircraft landing gear brace having an elongate body with a clevis formed on at least one end, the method comprising: obtaining a metallic source material; obtaining an extruded I-beam base material, the I-beam base material comprising first and second flanges and a central web, the extruded I-beam material forming a main core of the landing gear brace; adding a first lug to the first flange at an end of the I-beam material with an additive manufacturing process using the metallic source material; and adding a second lug to the second flange at the end of the I-beam material with the additive manufacturing process using the metallic source material, wherein the first and second lug define the landing gear brace clevis.

19. A hybrid additive manufacturing method for manufacturing an aircraft landing gear brace, the aircraft landing gear brace having an elongate body with a clevis formed on at least one end, the method comprising: obtaining a metallic source material; obtaining first and second T-shaped base materials, each of the first and second

T-shaped base materials having a leg and a cap; arranging the first and second T-shaped base materials on an operating bed of an additive manufacturing process so that the legs of the first and second T-shaped base materials are aligned; coupling the first base material to the second base material with a web extending from the leg of the first T-shaped base material to the leg of the second T-shaped base material, the web being formed with the additive manufacturing process using the metallic source; adding a first lug to an end of the cap of the first T-shaped base material with the additive manufacturing process using the metallic source material; and adding a second lug to an end of the cap of the second T-shaped base material with the additive manufacturing process using the metallic source material, wherein the first and second lugs define a clevis.