Patent Application
20230405736
The disclosure relates generally to repair of aircraft fan blades. More specifically, the disclosure relates to repairing hollow fan blades of aircraft.
The following presents a simplified summary of the invention in order to provide a basic understanding of some aspects of the invention. This summary is not an extensive overview of the invention. It is not intended to identify critical elements of the invention or to delineate the scope of the invention. Its sole purpose is to present some concepts of the invention in a simplified form as a prelude to the more detailed description that is presented elsewhere herein.
One innovative aspect of the subject matter described in this disclosure can be implemented as a method of repairing a hollow fan blade that includes a first portion and a second portion secured together by a joint. An interior cavity of the hollow fan blade is under a vacuum. The method includes obtaining a replacement portion having a unitary construction, removing a portion from a cutback region of the hollow fan blade to form a weld foundation, and welding the replacement portion to the weld foundation. The welding is at a temperature at the joint that does not exceed a distortion temperature of the joint.
In an aspect, according to any one of the preceding aspects, welding the replacement portion to the weld foundation includes first welding the replacement portion to the weld foundation using a first welding technique and subsequently operably welding the replacement portion to the weld foundation using a second welding technique.
In an aspect, according to any one of the preceding aspects, the first welding technique includes tungsten inert gas (TIG) welding.
In an aspect, according to any one of the preceding aspects, the second welding technique includes electron beam welding.
In an aspect, according to any one of the preceding aspects, a width of the replacement portion is greater than a width of the weld foundation.
In an aspect, according to any one of the preceding aspects, the method includes arranging a thermocouple on at least one of the first portion and the second portion.
In an aspect, according to any one of the preceding aspects, the method includes monitoring a temperature of at least a portion of the hollow fan blade during the welding.
In an aspect, according to any one of the preceding aspects, the method includes securing the hollow fan blade within a purge box prior to the welding.
In an aspect, according to any one of the preceding aspects, welding the replacement portion includes situating the hollow fan blade in a vacuum chamber.
In an aspect, according to any one of the preceding aspects, a length of the replacement portion is at least 20% of a length of a leading edge of the hollow fan blade.
In an aspect, according to any one of the preceding aspects, the interior cavity further includes a honeycomb structure.
In an aspect, according to any one of the preceding aspects, the method includes applying a finishing process after the welding.
In an aspect, according to any one of the preceding aspects, the joint includes a braze joint.
In another aspect, a system for repairing a leading edge of a hollow fan blade including a first portion and a second portion secured together by a joint is disclosed. The hollow fan blade has an interior cavity under a vacuum. The system includes a purge box having a mount for securing the hollow fan blade during a first welding step. The system includes a vacuum chamber for retaining the hollow fan blade during a second welding step. The first welding step is different from the second welding step.
In an aspect, according to any one of the preceding aspects, the system includes an electron beam welding apparatus.
In an aspect, according to any one of the preceding aspects, the system includes a temperature monitoring device disposed on the hollow fan blade.
In another aspect, a method of repairing a hollow component is disclosed. The hollow component has at least two portions secured to each other by a joint and a cavity under a vacuum. The method includes removing a damaged section of the hollow component and obtaining a replacement portion of unitary construction. The method includes initially securing the replacement portion to the hollow component, and securing the replacement portion to the hollow component after the replacement portion is initially secured to the hollow component.
In an aspect, according to any one of the preceding aspects, the hollow component is a fan blade.
In an aspect, according to any one of the preceding aspects, securing the replacement portion to the hollow component after the replacement portion is initially secured to the hollow component includes electron beam welding the replacement portion to the hollow component.
In an aspect, according to any one of the preceding aspects, initially securing the replacement portion to the hollow component includes tungsten inert gas (TIG) welding the replacement portion to the hollow component.
Illustrative aspects of the present disclosure are described in detail below with reference to the attached drawing figures and wherein:
Fan blades direct air through and around the engine of the aircraft. Fan blades are generally attached to a fan disk, which may be rotated by a shaft driven by a gas turbine engine of the aircraft. Fan blades are the outermost rotating components of an aircraft engine. Because the fan blades are exposed to outside air, they may encounter foreign objects (e.g., birds, pebbles, volcanic ash, and sand particles), resulting in damage such as, but not limited to, grooves, nicks, scratches, cracks, tears, and the like. Such damage may adversely affect operational characteristics of a fan blade. One section of a fan blade that is particularly susceptible to damage is the fan blade leading edge. The leading edge is often worn down and shortened with use, thus reducing fan blade chord length (i.e., length of the fan blade cross section measured tip-to-tip). Such may undesirably impact fan blade efficiency, and in some cases, may render the fan blade unsuitable for use.
In aspects, a damaged leading edge of a hollow fan blade may be repaired using a welding process. A hollow fan blade may be typically made of two shells brazed together. The interior of a hollow fan blade may be under a vacuum, which aids in the structural integrity of the fan blade. Hollow fan blades have heretofore been considered unrepairable because conventional repair processes, such as welding, degrade the braze joint and eliminate the vacuum, rendering the blade unfit for repair or use. In an aspect, a portion of the leading edge is removed and rebuilt via a welding process. Care is taken to ensure that the innermost surface of the portion of the leading edge that is removed is at least a minimum safe distance away from the braze joint. Performing weld repair at the minimum safe distance (or a greater distance) ensures that the braze joint does not reach a temperature at which it is compromised. The damaged leading edge may therefore be repaired without impacting the braze joint and discharging the vacuum. In implementations, the temperature at and about the leading edge may be monitored during welding to confirm that the braze joint does not heat up to a temperature at which it is compromised.
Bypass ratio is one aspect of classifying an aircraft engine. Bypass ratio of an aircraft engine is the ratio between mass flow rate of the bypass stream to mass flow rate entering the core. For the same thrust, increasing bypass ratio may result in decreased fuel consumption. Bypass ratio may be increased by increasing size of fan blades. However, increasing size of fan blades may detrimentally increase weight of the engine. To keep this weight down, fan blades may be made of relatively lightweight material. More recently, one or more hollow cavities may be introduced in fan blades to minimize concerns associated with increased weight.
Aircraft fan blades that have incurred damage may be replaced. Alternately, and depending on the type of damage, fan blades may be repaired. Where the fan blades are solid in construction, they may be repaired using one or more conventional processes. For example, a solid fan blade may be repaired using glass bead blasting or peening, application of weld repair patches, etc. Hollow fan blades, which are less common than solid fan blades, may not be readily repaired using these conventional techniques. Such repair techniques may compromise the vacuum within hollow fan blade and render it unfit for use.
A hollow fan blade may be made from two shell halves and an intermediate supporting structure. The two shell halves may include a concave half and a convex half, and the intermediate supporting structure may be a honeycomb structure. The two shell halves may be arranged around the supporting structure and may be affixed to each other via a braze joint. Supporting structure may also be brazed to interior surfaces of the two shell halves. The hollow space which resides between the two shell halves alongside the supporting structure may be under a vacuum, creating a pressure differential across the fan blade and atmosphere. As pressure of the atmosphere outside the two shells substantially exceeds pressure inside the two shells, atmospheric pressure pushes on the shells with a compressive force that is proportional to the pressure differential inside and outside the shells. In effect, vacuum between the two shells may cause the shells to mimic Magdeburg hemispheres. The hollow fan blade may be thus held together not only by mechanical strength of the braze joints securing the two shells but also by the pressure differential between the inside of the hollow fan blade and the atmosphere.
If a braze joint securing the two shells is compromised, it may compromise the vacuum and destabilize the fan blade, rendering it unsuitable for repair or use. Commonly employed techniques usable to repair solid fan blades and comparable gas turbine parts, such as patch welding, may damage the braze joint of a hollow fan blade due to excessive heat associated with these techniques. Such conventional techniques may therefore eliminate the vacuum seal and damage the blade permanently. For at least this reason, hollow fan blades have heretofore been considered unrepairable. Embodiments of the disclosure may allow for repair of hollow fan blades without compromising braze joints thereof.
As shown in
In some aspects, hollow fan blade 50 may be repaired using the same or similar material that constitutes fan blade 50. In an implementation, a bulk composition analysis of hollow fan blade 50 may be performed to determine constituent(s) of blade 50. Hollow fan blades, including braze joints thereof, are typically formed of Titanium or a Titanium alloy (e.g., Ti64 alloy). Hollow fan blade 50 may be formed of Titanium or a Titanium alloy. Hollow fan blade 50 may additionally or alternately include aluminum or stainless steel. One having skill in the art will thus understand that techniques described herein are applicable to fan blades formed of any suitable metal(s). Further, techniques described herein may be usable to fix other components having a braze or other such joint securing two or more walls defining a cavity under a vacuum.
Braze joint 70 of hollow fan blade 50 may not be heated beyond a certain temperature, as such may unduly alter the physical characteristics of braze joint 70 and damage blade 50. For example, Applicant has discovered that the structural integrity of braze joint 70 including Titanium degrades beyond repair at or around 720° C. (around 993.2K). At or around this temperature, physical change in joint 70 may compromise the vacuum within hollow fan blade 50. For this reason, it may be prudent to ensure that braze joint 70 does not reach this temperature. The temperature at which a joint of a hollow fan blade, such as the braze joint 70 of the hollow fan blade 50, distorts beyond repair and discharges the vacuum therein, may also be referred to herein as the “distortion temperature.” One having skill in the art will understand that the distortion temperatures of joints of different hollow fan blades may differ based on the construction of these blades and joints.
Welding temperatures may easily exceed the distortion temperature for the braze or other joint of a particular blade. For example, TIG welding temperatures may reach 3,000° C. (3,723.2K) or more—far greater than the distortion temperature of joint 70 of hollow fan blade 50. Conventional wisdom therefore counsels against repairing hollow fan blades using welding processes, such as patch welding or welding in layers of material, as exorbitant welding temperatures may destruct braze joint 70 and discharge the vacuum, rendering the fan blade 50 unfit for use.
As shown in
In an aspect, minimum safe distance 102 is between about 0.125 inches (about 3.175 mm) and about 0.375 inches (about 9.525 mm). For example, a user may safely remove material approximately 0.25 inches (approximately 6.35 mm) away from braze joint 70. In aspects, cut back region 104 may encompass an area of fan blade 50 up to about 0.200 inches (about 5.08 mm), e.g., between 0.1 inches (2.54 mm) and 0.3 inches (7.62 mm) below the type certificate holder (TCH) minimum chord dimension for a given hollow fan blade 50 to be repaired. One having skill in the art will understand that the minimum safe distance may vary from blade to blade depending, e.g., on the constitution of the blade and the location of the braze joint.
In some aspects, to ensure that braze joint 70 is not compromised during the welding process, a plurality of thermocouples 118 (
In the illustrated embodiment, thermocouples 118A-118E are disposed on the convex or suction shell 66 and thermocouples 118F-118I are located on the concave or pressure shell 68. Temperature of thermocouples 118A-118I may be monitored during the weld repair process. If any thermocouple 118A-118I indicates that the temperature is approaching the distortion temperature, the welding process may be halted or otherwise modified to prevent breakage of joint 70.
The distance between a thermocouple 118A-118I and bond line 70 may impact usefulness of the temperature readings. For example, if a thermocouple is too far away from joint 70, the temperature reading may not correlate to or indicate temperature at joint 70. In an implementation, thermocouples 118A-118I may be spaced about an inch from each other in a radial or y-axis direction, and may be aligned anywhere from about 0.240 inches (6.096 mm) to 0.783 inches (19.888 m) circumferentially, or in the x-axis direction, from leading edge 60. Table 1 below outlines the position of thermocouples 118A-118I, in one example.
Of course, values in Table 1 are merely exemplary and are not intended to be independently limiting. One having skill in the art will understand that thermocouples 118A-118I may be arranged differently (e.g., distance between two successive thermocouples 118A-118I may be greater or less than about one inch, and depending on the particular fan blade, may be further away or closer to the leading edge). In some implementations, thermocouples 118A-118I may be secured (e.g., temporarily) to fan blade 50 using any suitable method, such as with an adhesive or via spot welding.
In aspects, hollow fan blade 50 may be situated within a purge box 200 during the repair process.
In some aspects, in addition to purge box 200, gas pads 300 may be employed to facilitate the weld repair process (see
In an implementation, one or more chilling or cooling systems 306 may be arranged along or proximate leading edge 60. These cooling systems 306 may include, for example, copper chill blocks and/or water-cooled blocks which may serve to bring down temperature of fan blade 50 during the welding process. Cooling systems 306 may help ensure that braze joint 70 does not approach distortion temperature during the welding repair process.
At step 408, a plurality of thermocouples (e.g., thermocouples 118A-118I) may be arranged along the braze joint associated with the damaged portion of the blade. The thermocouples may be temporarily affixed, using spot welding or adhesive for example. The thermocouples may allow for the temperature of the fan blade proximate the bond line of the joint to be monitored during the welding repair process, to ensure temperature of the bond line does not reach the distortion temperature.
At step 410, the hollow fan blade may be secured within a purge box (e.g., may be fixed to mount 204 of purge box 200) to minimize the chance that oxidation of the fan blade will occur during the weld repair process. At step 412, gas pads (e.g., gas pads 302 and 304), alone or together with cooling features (e.g., cooling features 306) may be located along the bond line of the blade portion being repaired.
At step 414, any suitable welding technology now known or subsequently developed (e.g., but not limiting of the disclosure, TIG welding, gas metal arc welding, shielded metal arc welding, flux-cored arc welding, electron beam welding, etc.) may be used to weld material to the weld foundation (e.g., welded section 110 may be added via welding to weld foundation 108). In aspects, welded material may be added in layers and each layer may be deposited after some time has elapsed after deposition of the prior layer. In an aspect, the welding process may include forming weld buildup in layers, including between one layer and twelve or more layers, where each layer can be applied in a window of in a range between about four minutes and about six minutes. The application of each layer may be spaced with about a minute or more between each layer. The timing of the application of layers, as embodied by the disclosure, may be provided in any number of layers, with any spacing and time period in between layers. The layers may be built onto the fan blade in any pattern, including but not limited to, starting at the middle of the blade and moving towards the blade tip. Care may be taken to ensure the distortion temperature of the braze joint (e.g., joint 70) is not exceeded during the welding process so as to not compromise the vacuum of the fan blade 50.
At step 416, the blade (e.g., the newly welded material) may undergo finishing to bring the blade within the desired specifications. Finishing the blade may involve, for example, machining down the weld buildup to ensure the shape and size of the repaired blade are within required tolerances, adding a surface coating, etc. In aspects, a machining tool (e.g., a 5-axis machining tool) may be employed for finishing the blade and completing the repair process. At step 418, the repaired blade may be inspected to ensure the blade is fit for operation. For example, the repaired blade may be visually inspected. In implementations, the repaired blade may be evaluated using x-ray scanning, depth profiling, fluorescent penetrant inspection, eddy current inspection, etc. Additional welding may be performed if needed in view of this evaluation to ensure the repaired blade is airworthy.
One having skill in the art will understand that steps of method 400 may be modified, added to, and/or omitted as desired, and that such considerations have been contemplated and are within the scope of the disclosure. For example, one having skill in the art will understand that the step of arranging thermocouples may take place before material is removed from the fan blade to create the cutback region, that thermocouples may be omitted entirely, or that a different temperature sensor(s) may be employed.
As noted, one damaged hollow fan blade may require a solitary layer (or pass) of TIG welding for repair, whereas another blade that has incurred more damage may require multiple welding passes. Each TIG welding pass may require some time to complete, and the blade may need to be cooled down after each welding pass is completed and before the next welding pass is initiated. For example, in practice, it may take up to ten to twelve hours to repair a hollow fan blade using method 400 where a repair requires eight or more welding passes. Where the number of blades being repaired is large, repair of blades may take a considerable amount of time and effort, particularly where the blades require multiple passes (e.g., eight or more passes) of TIG welding for repair.
As shown in
To prepare hollow fan blade 550 for the welding repair process, a minimum safe distance 602 from bond line 570 may be determined (see
Minimum safe distance 602, in certain embodiments, may be between about 0.125 inches (about 3.175 mm) and about 0.375 inches (about 9.525 mm). For example, a user may safely remove material approximately 0.25 inches (approximately 6.35 mm) away from braze joint 570. In certain exemplary aspects, cut back region 604 may encompass an area of fan blade 550 up to about 0.200 inches (about 5.08 mm), e.g., between 0.1 inches (2.54 mm) and 0.3 inches (7.62 mm) below the type certificate holder (TCH) minimum chord dimension for a given hollow fan blade 550 to be repaired. As noted above, these numerical values are not intended to be independently limiting, and one having skill in the art will understand that the minimum safe distance from the bond line may differ from one hollow fan blade to the next depending, e.g., on the constitution of the blade and the location of the braze joint.
Focus is directed to
Replacement portion 702 may be initially secured to hollow fan blade 550′, i.e., to weld foundation 608 thereof. A first welding technique may be associated with the initial or first securement. In an aspect, initial securement may involve TIG welding replacement portion 702, i.e., inner section 708 thereof, to weld foundation 608. In examples of the disclosure, replacement portion 702 may be initially secured to weld foundation 608 of fan blade 550′ via TIG welding in a single pass, or in a small number of passes. In some examples, another suitable welding technique (such as gas metal arc welding, shielded metal arc welding, flux-cored arc welding, etc.) may be used to initially secure replacement portion 702 to weld foundation 608.
In a non-limiting aspect of the disclosure, replacement portion 702 may be initially secured to weld foundation 608 of fan blade 550′ in a purge box 800 (see
Once replacement portion 702 has been initially secured to weld foundation 608 (e.g., but not limiting of the disclosure, via TIG welding), the hollow fan blade 550″ (which now includes the replacement portion 702) may be situated in a vacuum chamber. For example, hollow fan blade 550″ may be situated in vacuum chamber 850 (
In certain non-limiting aspects of the disclosure, an electron beam welding apparatus 860 having an electronic beam gun may operably weld replacement portion 702 to weld foundation 608. Electron beam welding is a fusion welding process in which a beam of high-velocity electrons is applied to materials to be joined. Kinetic energy of the electrons may cause replacement portion 702 and/or weld foundation 608 to melt and flow together as the kinetic energy is transformed into heat upon impact. The greater width of replacement portion 702 relative to weld foundation 608 may provide for material that may readily be melted during welding to secure replacement portion 702 and weld foundation 608. The vacuum chamber 850 may ensure that welding conditions do not cause or allow for the dissipation of the electron beam.
Once replacement portion 702 is welded to weld foundation 608, fan blade 550″ may be finished as desired to ensure that the repaired area has a smooth finish and the appropriate dimensions. Finishing the blade may involve, for example, machining the weld buildup to ensure the shape and size of the repaired blade are within required tolerances, adding a surface coating, and other such finishing processes. In certain implementations, the repaired blade may be evaluated after finishing, for example using x-ray scanning, depth profiling, fluorescent penetrant inspection, eddy current inspection, or other inspection methods now known or hereinafter developed. Additional welding may be performed if needed in view of this evaluation to ensure the repaired blade is airworthy.
Once repaired blade 550″ is welded in this manner, repair may be complete and fan blade 550″ may be ready for use. Using electron beam welding to secure a relatively large unibody replacement portion to the blade may ensure that defects in locations of the original leading edge, including but not limited to multiple defects at multiple locations, are addressed at the same time quickly and effectively (e.g., relative to effectuating the repair via eight or more TIG welding passes). In some aspects, another suitable welding technique may be utilized to operably secure a replacement portion to a damaged fan blade.
In some aspects of the disclosure, thermocouples 718 (e.g., thermocouples 718A-718F shown in
In some aspects of the disclosure, gas pads 870 may be employed to facilitate the weld repair process (see
In an implementation, one or more chilling or cooling systems 880 may be arranged along or proximate leading edge 560. These cooling systems 880 may include, for example, copper chill blocks and/or water-cooled blocks which may serve to bring down temperature of fan blade 550 during welding. Cooling systems 880 may help ensure that braze joint 570 does not approach distortion temperature during the welding repair process.
At step 906, a region of the leading edge of the blade within a cutback region may be removed to yield a weld foundation. Cutback region 604 may be outboard the braze joint 570, as such, may not enter the hollow interior of fan blade 550. Specifically, the weld foundation may be spaced apart from braze joint at least by minimum safe distance 602. Weld foundation 608 may be machined (e.g., smoothed) to ensure a smooth surface for accepting the replacement portion. A length of the weld foundation may be between about 20% and about 80% of a length of leading edge 560 of blade 550.
At step 908, a plurality of thermocouples may be arranged along braze joint 570 associated with the damaged portion of the blade. The thermocouples may be temporarily affixed, using spot welding or adhesive for example, as discussed above with reference to
At step 910, the hollow fan blade may be secured within a purge box (e.g., may be fixed to mount 804 of purge box 800) to reduce the chance that oxidation of the fan blade will occur during the weld repair process. At step 912, gas pads and/or other cooling features may be located along the bond line of the blade portion being repaired, as discussed above with reference to
At step 914, a replacement portion 702 may be machined in a preform 700. Preform 700, in certain aspects of the disclosure, may have a unitary construction (i.e., may be a unibody piece) and may be made of the same metal or metal alloys as the hollow fan blade being repaired. At step 916, replacement portion 702 may be disassociated from preform 700.
At step 918, replacement portion 702 may be initially secured to weld foundation 608 using a first welding technique. In aspects, replacement portion 702 may be spot welded (e.g., but not limited to using TIG welding) to weld foundation 608 in a purge box 800. In some non-limiting examples, replacement portion 702 may have a width greater than a width of weld foundation 608, and replacement portion 702 may be laterally centered with respect to weld foundation 608 and spot welded to weld foundation 608. This position provide for extra material on either side of weld foundation 608 that may be usable to securely weld replacement portion 702 to weld foundation 608.
At step 920, replacement portion 702 may be operably secured to weld foundation 608 using a subsequent (or second) welding technique. For example, and not limiting of the embodiments, replacement portion 702 may be electron bean welded to weld foundation 608 in a vacuum chamber 850. At step 922, the repaired blade may be finished (e.g., machined as needed). The repaired blade may be evaluated to ensure suitability of repair. In implementations, the repaired blade may be evaluated using x-ray scanning, depth profiling, fluorescent penetrant inspection, eddy current inspection, etc.
As embodied by the disclosure, method 900 may be modified, performed in a different order, added to, and/or omitted as desired, and that such considerations have been contemplated and are within the scope of the disclosure. For example, forming a unibody replacement portion from a unitary preform may occur prior to the cutback region being removed from the fan blade.
Many different arrangements of the various components depicted, as well as components not shown, are possible without departing from the spirit and scope of the present disclosure. Embodiments of the present disclosure have been described with the intent to be illustrative rather than restrictive. Alternative aspects will become apparent to those skilled in the art that do not depart from its scope. A skilled artisan may develop alternative means of implementing the aforementioned improvements without departing from the scope of the present disclosure. It will be understood that certain features and subcombinations are of utility and may be employed without reference to other features and subcombinations and are contemplated within the scope of the claims. Not all steps described herein and/or listed in the various figures need be carried out or need to be carried out in the specific order described.
This application is a continuation-in-part of U.S. patent application Ser. No. 18/156,466 filed Jan. 19, 2023, which claims priority to U.S. Provisional Application No. 63/366,707, filed Jun. 21, 2022. The disclosure of each of these applications is incorporated herein by reference in its entirety.
| Number | Date | Country | |
|---|---|---|---|
| 63366707 | Jun 2022 | US |
| Number | Date | Country | |
|---|---|---|---|
| Parent | 18156466 | Jan 2023 | US |
| Child | 18446923 | US |
