Patent Application
20210205896
The present invention relates to a machining tool for internal machining of a shaft with an inner bore, such as an aircraft engine turbine shaft.
US patent publication U.S. Pat. No. 8,839,699 discloses a long shaft inner surface machining apparatus. A long shaft support device fixes a long shaft in order to prevent bending, the long shaft having an inner bore into which a machining head can be positioned axially using a head support device from one end of the long shaft. A blade drive device is coupled with the machining head from the other end of the long shaft to rotary drive a blade of the machining head. As the blade drive device and head support device are at opposite parts of the long shaft, this arrangement requires much space. Furthermore, the inner surface of the long shaft may be damaged by the support rollers of the support device, and it cannot be applied to axially varying diameter bores.
German patent publication DE-A-1086110 discloses a machining tool for internal machining of a shaft with an inner bore. The tool comprises a boring bar, a cutting insert, and an end part rotatable connected to a main part of the boring bar. An end part of the boring bar is provided with one or more radially moveable guiding pads.
US patent publication U.S. Pat. No. 6,394,710 discloses a tool having a base body on which at least one cutter holder, preferably a rocker-type cutter holder, is mounted such that it can be adjusted transversely with respect to the axis of the tool.
European patent publication EP-A-2136962 discloses a tool for working an internal bore, wherein a tube wear pad is used an pressed against the inside of a workpiece for pushing a spindle head against the opposing side.
US patent publication U.S. Pat. No. 8,839,699 discloses an apparatus to cut an inner surface of a long shaft, comprising a boring bar utilizing three or more sets of radially moveable free rollers that can rotate so as to permit and support movement in axial direction and rotation of the boring bar.
The present invention seeks to provide an improved machining tool and machining method, which is particularly suited for machining an inner bore of an elongate shaft, even if the inner diameter profile of the inner bore comprises narrow openings on one or both sides of the shaft.
According to the present invention, a machining tool as defined above is provided, comprising an external boring bar support device, a boring bar having a diameter smaller than a smallest opening on one side of the inner bore of the shaft, the boring bar comprising a radially extensible cutting insert, and an end part of the boring bar rotatably connected to a main part of the boring bar, wherein the end part is provided with one or more radially moveable guiding pads. More specifically, a method is provided as defined in claim 1. This allows to very accurately machine the internal surface of an inner bore of an elongate shaft.
The present invention will be discussed in more detail below, with reference to the attached drawings, in which
The present invention is discussed below with reference to a number of exemplary embodiments, and in general relates to machining of an inner bore of a shaft. Such a shaft with an inner bore is e.g. applied as an aircraft engine turbine shaft (fan mid shaft), more specifically to remove any possible internal corrosion in the shaft.
Specific problems encountered when trying to machine the inner bore 3 of a shaft 2 are that a normal machining operation cannot be performed due to lack of proper and suitable tooling support. Without tooling support the required surface finish of the inner bore 3 and dimensional accuracy is impossible to meet. Because of this limitation a special machining tool has been developed, as described herein with reference to a number of exemplary embodiments.
Other factors that makes this type of machining operation hard to perform are that in certain applications, the material to be machined is very hard (e.g. hardened steel 54 HRc), and as mentioned above that the inner bore 3 of the shaft 2 has small diameter areas at both sides of the shaft 2, which hinders machining operation.
According to a first aspect of the present invention, a machining tool is provided for internal machining of a shaft 2 with an inner bore 3, wherein the machining tool comprises an external boring bar support device 5 and a boring bar 6 as shown in the cross sectional view of
It is noted that as shown in the exemplary embodiment of
As the cutting insert 7 is radially extensible, the boring bar diameter db can be selected as high as possible for a specific type of shaft 2 with inner bore 3, in order to obtain sufficient rigidity over the long length of the shaft 2. In an exemplary embodiment, the operational machining length is 2130 mm, and a minimum diameter is 92 mm, so a ratio of operational machining length to diameter of the boring bar (6) can be in the order of 20 (more specifically 23), and is possibly within a range of 10-30.
By having the support pads 8 in the end part 6b of the boring bar 6, wherein the end part 6b can rotate with respect to the main part 6a of the boring bar 6, it is possible to have a non-rotating support of the machining tool (with respect to the surface of the inner bore 3). This also makes it possible to machine internal areas of the shaft 2 which otherwise cannot be machined at all with existing solutions. These support pads 8 can follow the internal diameter variation of the inner bore 3 in axial direction (e.g. using a continuously monitored extension pressure, see further below). Without these support pads 8 the boring bar 6 of a machining tool could bend as much as at least 10 mm downwards because of its mass. This makes machining impossible and causes collisions between the machining tool and the shaft 2.
Because of the rotating end part 6b of the boring bar 6, which holds the support pads 8 there is no damage of the internal surface of the inner bore 3 of the shaft 2. The support pads 8 are only sliding in an axial direction with respect to the internal surface of the inner bore 3. In further exemplary embodiments, the end part 6b is provided with at least three radially moveable guiding pads 8, e.g. at 120° intervals (i.e. evenly distributed around the circumference of the end part 6b). This allows a precise axial alignment of the boring bar 6 in the inner bore 3. The guiding pads 8 may comprise a plastic material, even further lessening the chance of damage to the inner bore 3.
In a further embodiment, the main part 6a of the boring bar 6 is connected to an axial drive unit 11, to allow machining (and measurement) along a large part of the inner bore 3 by moving the boring bar 6 left and right in the inner bore 3. The axial drive unit 11 may be implemented in various manners, of which one example is shown in the embodiment shown in
The cutting insert 7 as shown in the
It is noted that internal diameters cannot be measured with conventional inspection tooling of a shaft 2 with an inner bore 3. Visibility before, during and after the machining operation might even require custom made vision equipment, and required minimum surface finish may require custom made surface finish measurement tooling. To address these issues, in a further embodiment, the main part 6a of the boring bar 6 further comprising an inner bore diameter measurement device 9, axially positioned near to the radially extensible cutting insert 7. As an example, the inner bore diameter measurement device 9 is a laser based measurement device 9, as shown in the partial perspective view of
As shown in the embodiment of
The inner bore diameter measurement device 9 may comprise a protection cover 9a as shown in
In operation, the (build-in laser) inner bore diameter measurement device 9 measures the internal diameter before and after the machining operation at programmable locations in a further method embodiment of the present invention. Conventional inspection tools to determine internal diameters are not useable.
To this end, the method embodiment as described above, may further comprise measuring an inner bore axial diameter profile before and/or after the machining of the inner bore 3. The measurement before machining can be used to determine an initial profile, match it with a desired profile and determine where e.g. internal corrosion is present. However this is optional, the machining can also be executed using a pre-stored profile. The measurement after machining can then be used to check whether the inner bore 3 is within desired specifications.
In a further embodiment, measuring comprises measuring the inner bore axial diameter profile at a plurality of predetermined axial locations along the inner bore 3. When taking sufficient measurements, or using known parameters of the inner bore 3 profile (e.g. number of straight, tapered, and/or complex form sections of the inner bore 3), it is possible to determine a proper inner bore axial diameter profile.
In an even further embodiment, the method may comprise converting the measured inner bore axial diameter profile to a predetermined machining profile. Such a predetermined machining profile may then e.g. be used for batch processing of a number of shafts 2 in sequence.
The CNC unit may be implemented as a single unit, or as a combination of separate control units (possibly interconnected). This allows to be able to work with tapered diameters of the inner bore 3 and smooth transitions between non-machined and machined areas, possibly using custom made CNC control software.
The radially extensible cutting insert 7 is remotely controlled by a (numerically controlled) cutting diameter setting unit 13 in a further embodiment. An implementation thereof is shown in the cross sectional view of
In a further embodiment, the radially moveable guiding pads 8 are remotely controlled by a (numerically controlled) guiding pad diameter setting unit 14. In the embodiment shown in cross section in
The guiding pad diameter setting unit 14 may further be provided with a torque sensing device in a further embodiment, e.g. at one or more of the radially moveable guiding pads (8). This allows to arrange for a feedback control loop for accurately keeping the boring bar 6 centred within the inner bore 3 during operation.
Alternatively or additionally, the radially moveable guiding pads, or components thereof, may be fitted with force sensors, allowing a continuously monitored extension pressure of the guiding pads 8 (again e.g. using a feedback control loop).
For operational control of the machining tool, a tool control unit 16 is provided in a further embodiment, which is connected to the optionally present axial drive unit 11, cutting diameter setting unit 13, guiding pad diameter setting unit 14, and/or inner bore diameter measurement device 9. This exemplary set-up is shown in the schematic diagram of
It is noted that for the machining operation, the shaft 2 may be rotationally driven, i.e. in a circumferential direction, while the boring bar 6 is only axially moving, and not rotating. To this end, the machining tool may further comprise a rotational drive unit 12 (possibly connected to and controlled by the tool control unit 16).
With machining of an inner bore 3 of a shaft 2, it is possible that produced metal chips and/or further debris will collect inside the shaft 2 and these must be removed before these can disturb the machining operation or damage the machined areas. In a further embodiment of the present invention machining tool, coolant, required for machining, is flushed backward thus preventing being entrapped between guiding pads 8 and inner surface of the inner bore 3 of the shaft 2 which could otherwise result in damages of the inner surface. Construction wise, the machining tool may further comprise a coolant supply device arranged to flush a coolant liquid during operation in a direction from the guiding pads (8) to the radially extensible cutting insert (7), i.e. towards the one end of the inner bore 3.
The present invention has been described above with reference to a number of exemplary embodiments as shown in the drawings. Modifications and alternative implementations of some parts or elements are possible, and are included in the scope of protection as defined in the appended claims.
| Number | Date | Country | Kind |
|---|---|---|---|
| 18174581.1 | May 2018 | EP | regional |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/EP2019/063421 | 5/24/2019 | WO | 00 |
