GRINDING MACHINE CALIBRATION

Abstract

A device and method for the setup, alignment and calibration of grinding machines is disclosed. A tool (42c) is described, comprising a bar (44) and a first location feature (48) located on the bar (44) and configured to engage with a first location of a machine. The tool also provides a datum (66) located at a known but variable distance parallel to the bar (44) from the first location feature (48). A method for calibrating a grinding machine using the tool (42c) is also described.

Claims

1. A machine calibration tool, the tool comprising: a bar which has a longitudinal axis; a first location feature which is located on the bar and configured to engage with a first location of the machine; and, a datum having a location adjacent to the bar at a known but variable distance parallel to the longitudinal axis from the first location feature.

2. A machine calibration tool according to claim 1, wherein the perpendicular distance of the datum from the longitudinal axis of the bar is known at all distances of the datum parallel to the longitudinal axis from the first location feature.

3. A machine calibration tool according to claim 1, wherein the datum comprises one or more reference features.

4. A machine calibration tool according to claim 3, wherein one or more of the reference features are tapered along the longitudinal axis of the bar.

5. A machine calibration tool according to claim 3, wherein one or more of the reference features are parallel to the longitudinal axis of the bar.

6. A machine calibration tool according to claim 3, wherein one or more of the reference features are perpendicular to the longitudinal axis of the bar.

7. A machine calibration tool according to claim 3, wherein one or more of the reference features comprise one or more knife-edges.

8. A machine calibration tool according to claim 1, wherein the bar comprises a reference face which is parallel to the longitudinal axis of the bar, to which the datum is engaged.

9. A machine calibration tool according to claim 1, wherein the bar is comprised of one or more of a metal, alloy, ceramic, stone or polymer.

10. A machine calibration tool according to claim 1, wherein the datum is fixedly attached to the bar at any one of two or more locations parallel to the longitudinal axis of the bar.

11. A machine calibration tool according to claim 1, wherein the datum is slidably attached to the bar and is selectively movable parallel to the longitudinal axis of the bar.

12. A machine calibration tool according to claim 1, wherein the datum is configured within an arm arrangement.

13. A machine calibration tool according to claim 12, wherein the datum is configured to pivot about a pivotable attachment feature within the arm arrangement.

14. A machine calibration tool according to claim 12, wherein the arm arrangement is comprised of one or more of a metal, alloy, ceramic, stone or polymer.

15. A machine calibration tool according to claim 1, further comprising a clocking mandrel located on the bar and aligned with the first location feature. 25

16. A machine calibration tool according to claim 15, wherein the clocking mandrel is movable relative to the bar.

17. A method of calibrating a grinding machine comprising the steps of: securing the first location feature of a machine calibration tool according to claim 1 to a grinding machine, setting the datum of the machine calibration tool at a known position relative to a fixed machine datum feature, and using a measurement device and the datum of the machine calibration tool to determine the position of one or more further datum features mounted to the grinding machine relative to the machine datum feature.

18. A method according to claim 17, wherein the measurement device comprises an optical sensor associated with the grinding machine.

19. A method according to claim 17, wherein the one or more further datum features comprise machine mounted datum knife-edges.

20. A method according to claim 17, wherein the grinding machine is a blade tip grinding (BTG) machine, and wherein the machine datum feature comprises a rotational axis of the BTG machine.

Description

[0031] Embodiments will now be described by way of example only, with reference to the Figures, in which:

[0032] FIG. 1 is a sectional side view of a gas turbine engine;

[0033] FIG. 2 is a schematic view of a compressor drum in a BTG machine;

[0034] FIG. 3 is a schematic view of a calibration tool held in the chuck of a BTG machine;

[0035] FIG. 4 is a schematic view of the calibration tool of FIG. 3 in isolation;

[0036] FIG. 5 is a schematic view of an alternative calibration tool;

[0037] FIG. 6 is a schematic view of a further alternative calibration tool;

[0038] FIG. 7 is a schematic view of a further alternative calibration tool; and

[0039] FIG. 8 is a schematic view of a further alternative calibration tool.

[0040] With reference to FIG. 1, a gas turbine engine is generally indicated at 10, having a principal and rotational axis 11. The engine 10 comprises, in axial flow series, an air intake 12, a propulsive fan 13, an intermediate pressure compressor 14, a high pressure compressor 15, combustion equipment 16, a high pressure turbine 17, an intermediate pressure turbine 18, a low pressure turbine 19 and an exhaust nozzle 20. A nacelle 21 generally surrounds the engine 10 and defines both the intake 12 and the exhaust nozzle 20.

[0041] The gas turbine engine 10 works in the conventional manner so that air entering the intake 12 is accelerated by the fan 13 to produce two air flows: a first air flow into the intermediate pressure compressor 14 and a second air flow which passes through a bypass duct 22 to provide propulsive thrust. The intermediate pressure compressor 14 compresses the air flow directed into it before delivering that air to the high pressure compressor 15 where further compression takes place.

[0042] The compressed air exhausted from the high pressure compressor 15 is directed into the combustion equipment 16 where it is mixed with fuel and the mixture combusted. The resultant hot combustion products then expand through, and thereby drive the high, intermediate and low pressure turbines 17, 18, 19 before being exhausted through the nozzle 20 to provide additional propulsive thrust. The high 17, intermediate 18 and low 19 pressure turbines drive respectively the high pressure compressor 15, intermediate pressure compressor 14 and fan 13, each by suitable interconnecting shaft.

[0043] Other gas turbine engines to which the present disclosure may be applied may have alternative configurations. By way of example such engines may have an alternative number of interconnecting shafts (e.g. two) and/or an alternative number of compressors and/or turbines. Further the engine may comprise a gearbox provided in the drive train from a turbine to a compressor and/or fan.

[0044] FIG. 2 shows an intermediate pressure (IP) compressor drum, generally indicated 14, in a blade tip grinding (BTG) machine, which is generally designated 24. The IP compressor drum 14 is mounted on a central axis 26 between a headstock spindle 28 and a tailstock spindle 30 of the BTG machine 24. A grinding wheel 32 and an optical sensor 34 are aligned with one stage 36 of the compressor drum 14. As the compressor drum 14 is rotated about the axis 26, the grinding wheel 32 is moved into contact with the ends of individual compressor blades in a particular stage 36, while the optical sensor 34 measures the location of the blade tips, and thereby determines their radii from the axis 26.

[0045] It will be understood that in order for the BTG machine 24 to ensure that the rotor/blades are machined to the required finished size, and thus ensure the correct tip clearance when the drum 14 is received in its compressor casing, the optical sensor 34 must be aligned and positioned correctly relative to the axis of rotation 26 and other datum features of the BTG machine 24.

[0046] Machine mounted calibration edges such as datum knife-edges 38, 40 are also provided at known radial and axial distances from the datum features forming part of the BTG machine 24 structure, such as the rotational axis 26 of the workhead spindle 28 and/or the tailstock spindle 30, and are used during machining of blades on the rotor/drum 14.

[0047] FIG. 3 shows a calibration tool 42 mounted in the BTG machine 24 of FIG. 2. The calibration tool 42 will be described more fully below, but briefly comprises a gauge bar 44, a gauge arm 46 extending at right angles to the gauge bar 44, and a mounting spigot 48 via which the calibration tool 42 can be mounted to the headstock spindle 28. The optical sensor 34 is aligned with a free end portion of the gauge arm 46, which represents the position of the tip of a machined compressor blade.

[0048] The optical sensor 34 is capable of measuring in the plane perpendicular to its optical axis, which is into the page as shown, so can detect datum features provided on the gauge arm 46. Through use of the calibration tool 42, the position of the machine mounted datum knife-edges 38, 40 may be reliably established relative to the datum features forming part of the BTG machine structure.

[0049] An optical sensor, such as a ZIMMER gauge, may be aligned axially and radially relative to datum features on the BTG machine using the described calibration tool. Some blade stages have Hade angles ground on their tips, and therefore any axial positioning error can affect the measured radii of individual blade stages.

[0050] The calibration tool 42 from FIG. 3 is shown in greater detail in FIG. 4.

[0051] The gauge bar 44 is flat and straight, with the sides square to each other, and is of sufficient rigidity and stability such that it does not distort under its own weight and that of the gauge arm 46. The gauge bar 44 is provided with a number of discrete mounting points, stops or other fixings to allow location of the gauge arm 46 at a number of discrete/defined radial distances 60 from the mounting spigot 48. The gauge bar 44 and arm 46 as illustrated are steel components, but it should be understood that either or both could instead be constructed from an alternative thermally and dimensionally stable material, such as a suitable metal, alloy, ceramic, stone (such as granite) or polymer, or from a combination of such materials.

[0052] The gauge bar 44 is fastened onto the mounting spigot 48. The function of the mounting spigot 48 is to locate the gauge bar 44 and arm 46 onto the spindle face of the BTG machine 24 in place of the hydraulic chuck used during machining operations, and assist with stability and alignment. However, it would be possible instead to provide the gauge bar 44 with suitable features to allow it to be mounted into a chuck, collet or similar work holding feature, or for the mounting spigot 48 to be integrally formed with the gauge bar 44.

[0053] A rear engagement face 50 of the mounting spigot 48 abuts to the front face of the spindle of the BTG machine 24, and a calibrated dimension 52 between the plane of the rear face 50 of the mounting spigot 48 and the front face 54 of the gauge bar 44 can then be established via a suitable measurement method.

[0054] The function of the gauge arm 46 is to provide datum features in known geometric alignment to the face 54 of gauge bar 44 and the rotational axis 26 of the BTG machine workhead spindle 28. For example, taking a corner 56 of the gauge arm 46 as a datum, the axial distance 58 from the face 54 is known, and the radial distance from the rotational axis 26 is the sum of the distance 60 and the radius of the mounting spigot 48, both of which are known.

[0055] Levelling screws may be provided to set the gauge bar 44 parallel to the direction of travel of the optical sensor 34 and the base of the BTG machine. This operation may be performed using an engineer's spirit or electronic level, mounted onto the horizontal surface of the gauge bar 44. The centring of the mounting spigot 48 on the rotational axis 26 can be checked using a Dial Test Indicator (DTI) or similar to measure the runout on its outside diameter (OD).

[0056] In order to account for possible misalignment of the tool 42 when secured to the BTG machine, a clocking mandrel 51 is provided concentrically with the mounting spigot 48 on the opposite side of the gauge arm 44. The alignment of the clocking mandrel 51 can be adjusted independently of the gauge arm 44, and can thus be made precisely coaxial with the rotational axis 26 of the BTG machine. This could be achieved by measuring the runout on the outside diameter of the clocking mandrel 51, for example with a Dial Test Indicator (DTI), and adjusting the alignment of the clocking mandrel 51 so that the runout is minimised. A Total Indicated Runout (TIR) of less than 5 m, for example, would indicate that the outside diameter of the clocking mandrel 51 is concentric to the rotational axis 26 of the machine.

[0057] The clocking mandrel 51 gives greater certainty of the position of the datum point 56 relative to the rotational axis 26. The distance 61 from the outer diameter of the clocking mandrel 51 to the datum point 56 can be readily determined, either by direct measurement or by measurement to a known reference point on the gauge arm 46. The radius of the clocking mandrel 51 is known and, because of the possibility of fine adjustment, is known to precisely correspond to additional distance to the rotational axis 26 of the machine.

[0058] The inclusion of the clocking mandrel 51 additionally provides a readily accessible reference for the machine axis 26, which is an important datum of the BTG machine that is largely obscured or inaccessible once the tool 42 is attached.

[0059] FIG. 5 shows an alternative calibration tool 42a. A gauge bar 44, mounting spigot 48 and clocking mandrel 51 are provided as before, but in the alternative tool 42a the gauge arm 46 has been replaced by a shaped extension 46a having a surface 47 provided at an oblique angle to the front face 54 of the gauge bar 44. It will be understood that so long as the position and geometry of the shaped extension 46a and its position relative to the gauge bar 44 are known, the axial position 58 and radial position 60, 61 of any datum point 56a on the angled surface 47 can be readily determined. In other words, the location of the datum 56a perpendicular to the longitudinal axis of the gauge bar 44 is known at all distances of the datum 56a from the rotational axis 26 of the BTG machine 24.

[0060] A further alternative calibration tool 42b is shown in FIG. 6. The tool 42b comprises a gauge bar 44, gauge arm 46, mounting spigot 48 and clocking mandrel 51 similar to the tool 42 of FIG. 4. However, the alternative calibration tool 42b of FIG. 6 additionally comprises a knife-edge square plate 62, which provides a radial knife-edge 64 and an axial knife-edge 66.

[0061] The radial knife-edge 64 and an axial knife-edge 66 provide features which, when measured by the optical sensor 34, are of the same form as the datum features 38, 40 of the BTG machine 24. Both the radial knife-edge 64 and the axial knife-edge 66 can be aligned in a plane that passes through the rotational axis 26, and is parallel to the top face of the gauge bar 44. The optical sensor 34 is designed to see knife-edges, such as the datum knife-edges 38, 40 or compressor blade tips, so the inclusion of the knife-edge square plate 62 helps to ensure that the datum(s) 56b provided on the calibration tool 42b is/are reliably detected. The radial and axial knife-edges 64, 66 provide a good approximation to compressor blade tips.

[0062] As noted above, the optical sensor 34 is capable of measuring in the plane perpendicular to its optical axis, i.e. along axes perpendicular to the radial and axial knife-edges 64, 66, and also of the machine mounted calibration edges 38, 40.

[0063] A further alternative calibration tool 42c is shown in FIG. 7. The tool 42c comprises a gauge bar 44, mounting spigot 48 and clocking mandrel 51 as before. The gauge arm 46c in the tool 42c of FIG. 7 extends at an oblique angle to the gauge bar 44 and is provided, at its free end, with a knife-edge square plate 62 as described in relation to FIG. 6. The axial knife-edge 66 of the knife-edge square plate 62 is aligned to be parallel with the gauge bar 44.

[0064] In this alternative, the radial distance 60c, 61c from the mounting spigot 48 to a datum point is made continuously variable. The front face 54 of gauge bar 44 is provided with a T-slot, and the gauge arm 46c has two ground surfaces which abut to the gauge bar 44. Screws from the gauge arm 46c are received in T-nuts fitted into the T-slot, allowing the gauge bar 46c to slide along the gauge bar 44 as shown at 68. Once in the desired radial position, the ground surfaces of the gauge arm 46c are clamped against the ground surfaces of the gauge bar 44 by tightening the screws into the T-nuts. The sliding adjustment described allows stepless, continuous, adjustment of the gauge arm 46c in the radial direction. The radial distance 60c may be set and measured using any suitable measurement system and method.

[0065] FIG. 8 shows a further alternative calibration tool 42d. The gauge arm 46d in this alternative has a first portion 70 extending from the gauge arm 44, and a second portion 72 mounted to the first portion 70 by a pivot 74, and movable between positions indicated in broken lines. A knife-edge square plate 62, as previously described, is provided on the end of the second portion 72 remote from the pivot 74. The axial and radial positions 58d, 60d, 61d of the datum can both be varied using the pivot 74.

[0066] It will be understood that the invention is not limited to the embodiments above-described and various modifications and improvements can be made without departing from the concepts described herein. Except where mutually exclusive, any of the features may be employed separately or in combination with any other features and the disclosure extends to and includes all combinations and sub-combinations of one or more features described herein.

[0067] For example, the gauge arm 46, 46a, 46b, 46c, 46d may be provided with one of more measurement faces and/or levelling pads for mounting an engineer's spirit or electronic level to ensure that the gauge arm 46, 46a, 46b, 46c, 46d is level relative to the base of the BTG machine 24.