Patent Application
20230405735
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 for repairing a hollow fan blade. The hollow fan blade includes a first portion and a second portion secured together by a joint. An interior cavity of the hollow fan blade is charged with a vacuum. The method includes removing material from a damaged portion of the hollow fan blade and welding the damaged portion such that a temperature of the joint does not exceed a distortion temperature.
An aspect of the method includes arranging a thermocouple on at least one of the first portion and the second portion.
An aspect of the method includes monitoring a temperature of a portion of the hollow fan blade during the welding using a thermocouple.
An aspect of the method includes arranging a plurality of thermocouples on each of the first portion and the second portion.
An aspect of the method includes arranging each of a plurality of thermocouples using at least one item selected from the group consisting of spot welding and adhesive.
An aspect of the method includes securing the hollow fan blade within a purge box prior to the welding.
An aspect of the method includes arranging a gas pad on at least one of the first portion and the second portion for dispersing an inert gas during the welding.
An aspect of the method includes cooling the blade using a cooling system during the welding.
In an aspect of the method, a cooling system includes at least one of a copper block and a water-cooled block.
In an aspect of the method, the welding includes Tungsten Inert Gas (TIG) welding.
In an aspect of the method, the interior cavity further includes a honeycomb structure.
An aspect of the method includes applying a finishing process after the welding.
In an aspect of the method, the joint includes a braze joint.
Another innovative aspect of the subject matter described in this disclosure can be implemented as a system for repairing a leading edge of a hollow fan blade. The hollow fan blade includes a first portion and a second portion secured together by a joint. An interior cavity of the hollow fan blade is charged with a vacuum. The system comprises a purge box having a mount for securing the hollow fan blade. The system includes a thermocouple configured for monitoring of a temperature of the hollow fan blade during welding.
In an aspect of the system, the system further includes a cooling apparatus for cooling the first portion and the second portion of the blade during the welding.
In an aspect of the system, the system further includes at least one gas pad arranged on at least one of the first portion and the second portion for dispensing an inert gas during the welding.
In an aspect of the system, the hollow fan blade further includes a honeycomb structure within the interior cavity.
Another innovative aspect of the subject matter described in this disclosure can be implemented as a method of repairing a hollow fan blade. The hollow fan blade includes a concave portion and a convex portion secured together by a joint. An interior cavity of the hollow fan blade is charged with a vacuum. The method comprises removing material from a damaged portion of the hollow fan blade. The method includes repairing the damaged portion using welding such that a temperature of the joint does not exceed a distortion temperature.
An aspect of the method further includes monitoring a temperature of the joint during the welding using a temperature sensor.
An aspect of the method includes arranging at least one gas pad proximate the joint on at least one of the concave portion and the convex portion for dispersing an inert gas during the welding.
Details of one or more implementations of the subject matter described in this disclosure are set forth in the accompanying drawings and the description below. Other features, aspects, and advantages will become apparent from the description, the drawings and the claims. Note that the relative dimensions of the following figures may not be drawn to scale.
Illustrative aspects of the present disclosure are described in detail below with reference to the attached drawing figures and wherein:
blade.
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 the 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 the fan blade chord length (i.e., the length of the fan blade cross section measured tip-to-tip). Such may undesirably impact the efficiency of the fan blade, 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 that are brazed together. The interior of a hollow fan blade may be charged with 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 the 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.
One aspect of classifying an aircraft engine is the bypass ratio. The bypass ratio of an aircraft engine is the ratio between the mass flow rate of the bypass stream to the mass flow rate entering the core. For the same thrust, increasing the bypass ratio may result in decreased fuel consumption. The bypass ratio may be increased by increasing the size of the fan blades. However, increasing the size of the fan blades may detrimentally increase the 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 the 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, the 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, et cetera. 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 the 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. The supporting structure may also be brazed to the interior surfaces of the two shell halves. The hollow space which resides between the two shell halves alongside the supporting structure may be charged with a vacuum, creating a large pressure differential across the fan blade and the atmosphere. As the pressure of the atmosphere outside the two shells substantially exceeds the pressure inside the two shells, the atmospheric pressure pushes on the shells with a compressive force that is proportional to the pressure differential inside and outside the shells. In effect, the 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 the 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 the 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, the hollow fan blades have heretofore been considered unrepairable. Embodiments of the disclosure may allow for repair of hollow fan blades without compromising the braze joints thereof.
As shown in
In some aspects, the hollow fan blade 50 may be repaired using the same or similar material that constitutes the fan blade 50. In an implementation, a bulk composition analysis of the hollow fan blade 50 may be performed to determine the constituent(s) of the blade 50. Hollow fan blades, including the braze joints thereof, are typically formed of Titanium or a Titanium alloy (e.g., Ti64 alloy). The hollow fan blade 50 may be formed of Titanium or a Titanium alloy. The hollow fan blade 50 may additionally or alternately include aluminum or stainless steel. One having skill in the art will thus understand that the techniques described herein are applicable to fan blades formed of any suitable metal(s).
The braze joint 70 of the hollow fan blade 50 may not be heated beyond a certain temperature, as such may unduly alter the physical characteristics of the braze joint 70 and damage the blade 50. For example, Applicant has discovered that the structural integrity of the braze joint 70 including Titanium degrades beyond repair at or around 720° C. (around 993.2K). At or around this temperature, the physical change in the joint 70 may compromise the vacuum within the hollow fan blade 50. For this reason, it may be prudent to ensure that the 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 ofjoints 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 the joint 70 of the 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 the exorbitant welding temperatures may destruct the braze joint 70 and discharge the vacuum, rendering the fan blade 50 unfit for use.
As shown in
In an aspect, the 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 the braze joint 70. In aspects, the cut back region 155 may encompass an area of the 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 the braze joint 70 is not compromised during the welding process, a plurality of thermocouples 118 or other suitable temperature sensors may be situated proximate the weld joint 70 and the weld foundation 108. Specifically,
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. The temperature of the 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 the joint 70.
The distance between a thermocouple 118A-118I and the weld line 70 may impact the usefulness of the temperature readings. For example, if a thermocouple is too far away from the joint 70, the temperature reading may not correlate to or indicate the temperature at the joint 70. In an implementation, the 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 the leading edge 60. Table 1 below outlines the position of the thermocouples 118A-118I, in one example.
Of course, the values in Table 1 are merely exemplary and are not intended to be independently limiting. One having skill in the art will understand that the thermocouples 118A-118I may be arranged differently (e.g., the 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, the thermocouples 118A-118I may be secured (e.g., temporarily) to the fan blade 50 using any suitable method, such as with an adhesive or via spot welding.
In aspects, the hollow fan blade 50 may be situated within a purge box 200 during the repair process.
In some aspects, in addition to the 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 the 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 the temperature of the fan blade 50 during the welding process. The cooling systems 306 may help ensure that the 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 weld line of the joint to be monitored during the welding repair process, to ensure the temperature of the weld 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 weld line of the blade portion being repaired.
At step 414, any suitable welding technology now known or subsequently developed (e.g., TIG welding, gas metal arc welding, shielded metal arc welding, flux-cored arc welding, etc.) may be used to weld material to the weld foundation (e.g., welded section 110 may be added via welding to the weld foundation 108). In aspects, the welded material may be added in layers and each layer may be deposited after some time has elapsed after the deposition of the prior layer. In an aspect, the welding process may include forming the weld buildup in layers, including six 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 between each layer. The timing of the application of layers 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, et cetera. 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, et cetera. 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 the steps of the 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 has been described, various aspects of the disclosure may allow for the repair of a hollow fan blade while mitigating or eliminating the risk that the braze joint thereof will be destroyed or that the vacuum within the blade will be compromised. By employing a buffer of material and ensuring that the distortion temperature is not reached, the vacuum charge, and thus the structural integrity, of the fan blade may be maintained during the repair process. While the discussion herein largely focused on welding and repairing a leading edge of a hollow fan blade, the artisan will understand that the methods described herein may be adapted to weld any other suitable area of a hollow 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 claims priority to U.S. Provisional Application No. 63/366,707, filed Jun. 21, 2022, the disclosure of which is incorporated herein by reference in its entirety.
| Number | Date | Country | |
|---|---|---|---|
| 63366707 | Jun 2022 | US |
