This invention relates to methods and devices for shaping edges of aerofoils. In particular it relates to devices and methods for refurbishing the leading edges of service-worn aerofoils of gas turbine engines.
Aerofoils, especially fan blades, are subjected in use to impacts from airborne debris. Although generally such debris is very small and will not cause significant damage to the aerofoils or to the engine, one effect of the impacts is to flatten or blunt the leading edges of the aerofoils. This is detrimental to the engine's performance and is undesirable. It is therefore common for aerofoil leading edges to be refurbished to restore a more acceptable profile.
It is known to refurbish leading edge profiles of such aerofoils by hand dressing, using a hand-held mechanical abrasive tool. Inspection with profile gauges is used to determine when the correct profile shape has been achieved. This method requires very highly skilled operators, and it is difficult to achieve consistency in material removal and in the profile shape. Also, hand dressing is not approved by aviation authorities for use on installed engines and so the engine must be removed from the aircraft to enable the blades to be removed and dressed individually. This is time-consuming and expensive, and very disruptive to airlines' operations.
Automated methods for leading edge shaping are known, which can more easily achieve repeatable profile shapes. However, these methods also require the blades to be removed from the engine and individually mounted in a machining station, which in turn requires the engine to be removed from the aircraft. As noted above, this is costly and disruptive.
There is therefore a need for a device and method for shaping the edges of aerofoils that can achieve accurate and repeatable profiles without requiring high levels of operator skill, and which can be used on blades in situ in an engine, with the engine still on-wing.
Accordingly, the invention provides a device and method for shaping an edge of an aerofoil as set out in the claims.
In a first aspect the invention provides a portable device for shaping an edge of an aerofoil, the device comprising a housing, a cutting tool mounted in the housing, the cutting tool having a cutting edge to remove material from the edge, and a plurality of guides mounted in the housing, so that in use the aerofoil engages with the guides to locate the edge of the aerofoil relative to the cutting edge and to permit movement of the housing in a cutting direction so as to remove material from the edge of the aerofoil. The device is characterised in that the cutting tool is mounted so that in use the cutting edge can move relative to the edge of the aerofoil in a direction generally perpendicular to the cutting direction.
The guides allow the aerofoil to be repeatably located in the housing so that the edge of the aerofoil is brought into the correct relationship with the cutting edge. Because the cutting tool can move relative to the edge of the aerofoil, it can more readily follow the contour of the edge thereby ensuring that the edge profile is smooth along the entire length to be shaped.
The cutting tool may be pivotably mounted. This allows the cutting tool to rotate slightly about an axis in order to follow the contour of the edge. In a preferred embodiment, the cutting edge can move through an angle of about 5 degrees to each side of its central position.
The device may further comprise at least one spring which in use can apply a restoring force tending to centre the cutting tool. This helps to locate the cutting edge in the correct position relative to the edge of the aerofoil, and may help in reducing vibration of the cutting tool in use. In a preferred embodiment, a titanium sheet spring is mounted at each side of the cutting tool.
The cutting tool may have a plurality of cutting edges. For example, a triangular cutting tool may have a cutting edge at each vertex. This permits quicker replacement of a worn cutting edge by a fresh one, simply by rotating the cutting tool. The plurality of cutting edges may have different properties, for example different profiles or different cutting characteristics. In this way a single cutting tool may be used for successive cutting operations to bring an edge profile from an initial, damaged state to a final or near-final state.
The cutting tool may be angled with respect to the cutting direction. This may facilitate quicker or cleaner material removal and may lengthen the life of the cutting edge. In a preferred embodiment, the cutting edge may be angled at about 60 degrees to the cutting direction.
The guides may comprise rollers. These provide a positive and repeatable engagement with the aerofoil, and also facilitate smoother movement of the device along the aerofoil in the cutting direction than would pads or similar stationary guides.
A leading roller may be provided that engages, in use, with the edge of the aerofoil. This roller may be V-shaped to engage more securely with the edge.
A pair of side rollers may be provided that engage, in use, with opposing (pressure and suction) surfaces of the aerofoil. These rollers provide accurate positioning of the aerofoil so that the edge of the aerofoil is kept in a consistent relationship with the cutting edge.
The side rollers may be resiliently mounted. This helps to ensure consistent location of the aerofoil in the housing by ensuring that the rollers are always in contact with the aerofoil surfaces. Furthermore, it helps the device to follow more accurately the profile of the aerofoil in use, thereby improving the positioning of the cutting edge relative to the aerofoil edge. In a preferred embodiment, the side rollers are mounted on titanium sheet springs.
In a second aspect the invention provides a method of shaping an edge of an aerofoil, the method comprising the steps of providing a portable shaping device comprising a housing, a cutting tool having a cutting edge, and a plurality of guides, mounting the cutting tool in the housing so that the cutting edge can move relative to the edge of the aerofoil in a direction generally perpendicular to a cutting direction, locating the housing over the edge of the aerofoil so that the aerofoil engages with the guides and the edge of the aerofoil engages with the cutting edge, and moving the device along the aerofoil in the cutting direction so as to remove material from the edge of the aerofoil and thereby to shape it.
The guides allow the aerofoil to be repeatably located in the housing so that the edge of the aerofoil is brought into the correct relationship with the cutting edge. Because the cutting tool can move relative to the edge of the aerofoil, it can more readily follow the contour of the edge thereby ensuring that the edge profile is smooth along the entire length to be shaped.
Embodiments of the invention will now be described in more detail, with reference to the attached drawings, in which
Referring first to
A block 20, attached to one side wall 28 of the housing 12, supports a leading roller 22 which is mounted on a spindle 24 so it can rotate freely. The leading roller has a V-shaped profile, which will be further described below.
A sheet-metal support plate 26 is attached to opposite side walls 28, 30 of the housing 12 and spans the width of the housing. Mounted to the support plate is a cutting tool 32, which will be further described below.
In use, the device 10 is located on a fan blade 34 of a gas turbine engine, so that the leading edge 36 of the fan blade lies within the channel 18. The leading edge 36 is supported by the leading roller 22. The V-shaped profile of the leading roller 22 engages with the leading edge 36 to ensure its correct positioning.
Two side rollers (not shown in
At each vertex of the cutting tool 32 is formed a cutting edge 44. When the cutting tool 32 is mounted in the housing 12, one cutting edge 44 will extend into the channel 18 so as to engage with the leading edge 36 of the fan blade 34, as will be explained presently. The other two cutting edges are not in use. This arrangement means that a worn cutting edge 44 can very easily be replaced by a fresh one simply by rotating and re-securing the cutting tool 32.
The shape of the cutting edge 44 is designed to produce the desired leading edge profile for the fan blade, as recorded in the CAD model for the blade. In use, the leading roller 22 (
It is clear from
In use, only the leading roller 22 and the cutting edge 44 are in contact with the leading edge 36. The leading roller 22, as well as supporting the fan blade in the correct position, maintains the correct angle of the cutting tool relative to the blade leading edge. This arrangement enables the cutting edge 44 to remain constantly in contact with the leading edge 36 of the blade, and consistently at the correct angle, even though the geometry of the leading edge along its length is complex.
It will be appreciated that the shape of the cutting edge 44 may need to be modified to take account of the cutting tool angle to be used, so that the resulting blade profile is as desired.
In the embodiment shown in
Two side rollers 52 are mounted to the side walls 28, 30 of the housing 12 via sheet titanium springs 54. Each side roller 52 is mounted on a spindle 56 so it can rotate freely.
In use, the side rollers 52 engage with the pressure and suction surfaces of the fan blade 34 to guide it through the housing and to ensure that the cutting edge 44 is kept in the correct relationship with the leading edge of the fan blade. The springs ensure that the rollers always maintain contact with the surfaces of the fan blade.
To use the device, it is first positioned on the leading edge 36 of the fan blade 34, using the location features (the leading roller 22 and the side rollers 52) to centralise it against the cutting edge 44. The device is then moved manually along the fan blade 34 in a cutting direction shown by the arrow A. For a fan blade installed in an engine this would be in a generally radial direction. As this happens the cutter shaves the leading edge, removing material from it until it has the same profile as the cutting edge. If necessary, several passes of the device may be performed until the profile of the leading edge matches the desired profile. Finally, the leading edge is manually polished with a standard polishing cloth to attain a surface finish comparable with the surrounding area.
An arrangement may be provided to collect and contain the removed material so that it can be safely removed from the engine. This ensures that it cannot pass through the engine (potentially causing damage), and that it can be recycled or disposed of appropriately. Such an arrangement may, for example, include a vacuum removal device.
It can be seen that the spindles 56 are not vertical, but are inclined slightly, so they are parallel with the pressure and suction surfaces 38, 40 of the blade 34. This ensures better contact and support between the side rollers 52 and the blade surfaces, and also reduces any tendency for the blade to “ride up” between the side rollers.
a) shows a cross-section through the leading edge region of an alternative design of fan blade 134, with an asymmetric leading edge profile. That is to say, the position of the leading edge 136 is displaced from the centre line 160 of the fan blade 134. To refurbish such a leading edge, a cutting tool will be required whose cutting edge is profiled to match the asymmetric leading edge profile, and this can readily be achieved in the same manner explained above for symmetrical leading edges.
b) shows a cross-section through the leading edge region of a further alternative design of fan blade 334, with a drooped tip. The leading edge 336 is substantially elliptical, as in the fan blade shown in
However, for some blade profiles and especially for asymmetric or drooped profiles as shown in
a) shows part of a cutting tool 132 with a cutting edge 144 profiled to refurbish an asymmetric leading edge such as that shown in
An alternative arrangement is shown in
In both the embodiments of
The embodiments of the invention described above are illustrative and are not intended to be limiting. It will be appreciated that various modifications and alternatives may be employed, without departing from the scope of the invention.
The device may be employed to shape the profiles of leading or trailing edges of any type of aerofoil. Although the described embodiments relate to fan blades, the device could be adapted for use on any sort of rotating or static aerofoil within a gas turbine engine, including those on blisks, blings and the like.
The housing may be constructed in any convenient way, and of any suitable material.
Other numbers or configurations of rollers may be used, provided they fulfil the purpose of locating the aerofoil with respect to the cutting edge. Other types of guides may be used instead of rollers, for example pads made from, or coated with, low-friction material.
The spring-loading of the rollers may be achieved by a different type of spring, or indeed by a different type of resilient mounting such as an elastomeric material.
The cutting tool may take a different form, or be made from a different material. The cutting tool may have only a single cutting edge. Where the cutting tool has multiple cutting edges, the different cutting edges may have different properties, for example different profiles or different cutting characteristics. In this way a single cutting tool may be used for successive cutting operations to bring an edge profile from an initial, damaged state to a final or near-final state.
When different cutting edges are used to perform successive cutting operations, the angle of the cutting tool may not be the same for each cutting operation. For example, a first cut may be performed with a cutting tool angle close to 60 degrees to the direction indicated by the arrow A in
To facilitate this, the cutting blade may be mountable at different angles with respect to the support plate, or the support plate may be mountable at different angles with respect to the housing.
Where the leading edge refurbishment is to be achieved by successive cutting operations, a plurality of cutting edges may be provided in sequence, for example by mounting a plurality of cutting tools to the support plate 26 by the same bolt 46, so that they form a “stack”. In use, the plurality of cutting edges will engage with the leading edge of the aerofoil simultaneously as the device is located on the aerofoil. As the device is moved along the blade leading edge, the first cutting edge performs the first cut on a given section of the leading edge, followed by the second cutting edge performing the second cut on the same section, and so on, in the manner of a broach. With such an arrangement, it may be possible to achieve the refurbishment of the leading edge with a single pass of the device along the blade.
The profile of the cutting edge may be taken from the CAD model of the blade as originally manufactured. However, it may alternatively be a different profile, for example to provide a simple means for reprofiling blades if an improved leading edge profile is subsequently identified. As noted before, the profile of the cutting edge may need to be adjusted to take account of the angling of the cutting tool.
The cutting tool may simply be pivoted, without springs to support it. If springs are provided they may be of any suitable type, or may be replaced by a different type of resilient mounting such as an elastomeric material. The range of movement of the cutting tool may be less or greater than in the embodiment described.
To help ensure simple and reliable operation of the device, a visual indication may be provided to show the operator the correct direction of movement for the device in use.
For example, an arrow might be provided on the sides or top of the housing to show the correct direction of travel, or colour-coding might be used (for example, green on the “front” of the housing and red on the “rear”).
The invention therefore provides a device for shaping the edges of aerofoils that is quick to use, and may be used during an aircraft's normal downtime at an airport. The pre-formed profile cutter, shaped according to the CAD model of the ideal leading edge profile, provides accurate and repeatable shaping of the leading edge to a predetermined profile with minimal operator training. The device can be used on-wing with the blades still installed in the engine. The device is lightweight and easily transportable, and requires no external power source.
Number | Date | Country | Kind |
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1306566.9 | Apr 2013 | GB | national |