(19)
(11)EP 3 246 124 B1

(12)EUROPEAN PATENT SPECIFICATION

(45)Mention of the grant of the patent:
10.07.2019 Bulletin 2019/28

(21)Application number: 17169938.2

(22)Date of filing:  08.05.2017
(51)International Patent Classification (IPC): 
B23Q 3/06(2006.01)

(54)

FIXTURE FOR HOLDING A COMPLEX-SHAPED PART DURING A MACHINING OPERATION

BEFESTIGUNG ZUM HALTEN EINES KOMPLEX GEFORMTEN TEILS WÄHREND EINES BEARBEITUNGSVORGANGS

DISPOSITIF DE MAINTIEN D'UNE PIÈCE DE FORME COMPLEXE PENDANT UNE OPÉRATION D'USINAGE


(84)Designated Contracting States:
AL AT BE BG CH CY CZ DE DK EE ES FI FR GB GR HR HU IE IS IT LI LT LU LV MC MK MT NL NO PL PT RO RS SE SI SK SM TR

(30)Priority: 17.05.2016 GB 201608639

(43)Date of publication of application:
22.11.2017 Bulletin 2017/47

(73)Proprietor: Rolls-Royce plc
London SW1E 6AT (GB)

(72)Inventors:
  • DURRANT, George
    Derby, Derbyshire DE24 8BJ (GB)
  • BUCHANAN, Alistair
    Derby, Derbyshire DE24 8BJ (GB)
  • GIBSON, Christopher
    Derby, Derbyshire DE24 8BJ (GB)

(74)Representative: Rolls-Royce plc 
Intellectual Property Dept SinA-48 PO Box 31
Derby DE24 8BJ
Derby DE24 8BJ (GB)


(56)References cited: : 
FR-A1- 2 976 203
FR-A1- 2 984 788
  
      
    Note: Within nine months from the publication of the mention of the grant of the European patent, any person may give notice to the European Patent Office of opposition to the European patent granted. Notice of opposition shall be filed in a written reasoned statement. It shall not be deemed to have been filed until the opposition fee has been paid. (Art. 99(1) European Patent Convention).


    Description


    [0001] The present invention is concerned with accurate machining of surfaces of a complex shaped part, more specifically an aerofoil, in particular a turbine blade. More particularly, the invention is concerned with a fixture for holding such a part securely in position whilst leaving the surface to be machined accessible.

    [0002] In the turbine stages of a gas turbine engine there are considerable efficiency losses associated with the aerodynamics of the trailing edges of the aerofoils. It is known that these losses can be greatly reduced if the trailing edge can be made consistently with a thinner profile, which improves the turbine efficiency and therefore decreases the specific fuel consumption.

    [0003] Turbine aerofoil components are conventionally manufactured by an investment casting process. This process inherently has limits on how thin sections can be cast due to surface tension effects. Typically, the smallest trailing edge thickness which can be reliably cast using the process is around 0.6 mm. To reliably manufacture trailing edge thicknesses of less than 0,6 mm it is desirable to carry out an operation such as machining of the cast component. To preserve the aerodynamic properties of the convex surface of the aerofoil it is further desirable that the material is removed from the concave surface during the thinning operation.

    [0004] It is known to use fully adaptive machining processes to thin the trailing edge of the cast aerofoil. One example of such an adaptive machining process is disclosed United States patent application publication no. US 2014/373503 A1. Such processes are very effective, but very expensive adding significantly to unit cost of manufacture.

    [0005] Fixtures for holding aerofoils during machining processes are known. For example, a 6 point location nest is described in United States patent application publication no. US 2014/191455 A1. Whilst such arrangements can secure a part, they do not align a trailing edge for accurate machining with respect to the suction surface of the aerofoil. Also, these known arrangements do not provide unencumbered access to a machine tool along the entire length of the trailing edge.

    [0006] Another example of a known fixture arrangement is described in the applicant's own United States patent application publication US 2013/318773 A1. Whilst the described arrangement allows good access to the trailing edge, the arrangement does not provide for accurate alignment of the trailing edge for machining by a conventional machine tool, an accurate result would require an adaptive machining solution.

    [0007] French patent application FR 2984788 A1 discloses a method of calibrating a turbine blade. The method involves making a first calibration while the blade is held in a coating block and making a second calibration while the blade is held in a support.

    [0008] French patent application FR 2976203 A1 discloses a method for machining a composite turbine blade. The method involves using a device that includes vices for holding the blade in position and a mechanism for measuring the profile of the blade.

    [0009] The invention seeks to provide a fixture which sets a cast aerofoil in an orientation which is suitable for machining by a direct machining process such as milling.

    [0010] The invention provides a fixture and a use of a fixture as set out in the appended claims.

    [0011] In accordance with the present invention there is provided a fixture for locating a straight edge of a curved surface of an aerofoil, in particular a turbine blade, and holding the aerofoil in a fixed position during performance of a machining operation on a concave side surface adjacent the straight edge of the curved surface of the aerofoil, the fixture comprising: two or more elongate supports that are spaced apart from each other to form a seat for the convex curved surface of the aerofoil, each elongate support extending straightly and in parallel with a chord of the convex curved surface of the aerofoil; two or more detachable end stops arranged to extend in a plane orthogonal to that in which the elongate supports extend and against which, in use, the straight edge of the curved surface of the aerofoil is aligned; and a clamp; the clamp being arranged, in use, to push the convex curved surface of the aerofoil against the elongate supports such that the straight edge of the curved surface of the aerofoil contacts the elongate supports and upon removal of the one or more detachable end stops the concave side surface adjacent the straight edge is exposed for machining.

    [0012] In use, a convex surface of the aerofoil is laid against the elongate supports and tilted such that the straight edge lies against the elongate support(s). The detachable end stops are positioned in the orthogonal plane and the straight edge is slid along the elongate support until the straight edge is aligned with the end stops. With the straight edge in the desired position, the clamp is applied to hold the aerofoil in the desired position. The detachable end stops may then be removed exposing the concave side edge surface for machining.

    [0013] The detachable end stop may comprise a flat plate. Alternatively, the end stop comprises two or more spaced apart rods. The rods may have a rounded cross section. Alternatively the rods may present an angled edge to the straight edge of the aerofoil. Alternatively, the rods may present a narrow flat surface to the straight edge.

    [0014] The fixture may further comprise a convex surface counter-support for countering any undesirable load from the clamp which may cause slippage and/or tilting of the aerofoil after it has been positioned. The counter support may, for example, comprise a wedge or a bar whose position is slidably adjustable to accommodate various degrees of curvature. The counter-support may comprise part of the clamp. The counter-support may comprise part of the support.

    [0015] The clamp and the counter support may comprise a pivoted clamp.

    [0016] The fixture may further comprise one or more additional stops arranged in a third plane orthogonal to both the plane in which the support(s) sits, to control the location of the blade in the direction of which the detachable end stops extend

    [0017] The skilled person will appreciate that except where mutually exclusive, a feature described in relation to any one of the above aspects may be applied mutatis mutandis to any other aspect. Furthermore except where mutually exclusive any feature described herein may be applied to any aspect and/or combined with any other feature described herein.

    [0018] Embodiments of the invention will now be further described with reference to the accompanying Figures in which;

    Figure 1 shows a cast turbine blade having a curved surface and a straight trailing edge of the surface;

    Figure 2 illustrates how the turbine blade of Figure 1 might be machined to provide a thinner trailing edge for a more aerodynamic performance;

    Figure 3 shows a view from a leading edge of the turbine blade of Figure 1 arranged in tooling in accordance with a first embodiment of the invention;

    Figure 4 shows the arrangement of Figure 3 with the blade clamped in the desired position and orientation;

    Figure 5 shows points at which the concave and convex surfaces of the blade of Figure 4 are supported;

    Figure 6 shows material being removed from the trailing edge of a blade aligned and held using tooling in accordance with an embodiment of the invention.

    Figure 7 shows the loading applied to the blade by the clamp of the tooling of Figure 8;

    Figure 8 illustrates a second embodiment of tooling in accordance with the invention applied to a blade which is the same as the blade of Figure 1;

    Figure 9 illustrates a second embodiment of the tooling with the clamp shown in Figure 7 and 8 removed.



    [0019] As can be seen the blade of Figure 1 has a concave surface 1 on an opposite face to a convex surface 2. The two surfaces 1, 2 meet at a trailing edge 3. The blade has a tip platform 4 and a root platform 5. Figure 2 shows the blade of Figure 1 in the process of having a surface of the trailing edge 3a machined by a tool 6. For example, the machine tool 6 may be of a milling or grinding machine.

    [0020] Figure 3 shows the blade of Figure 1 arranged in a fixture according to an embodiment of the invention. As can be seen, the fixture comprises a pair of support bars 10a, 10b onto which the convex surface 2 of the blade is seated. Extending in an orthogonal plane is a pair of detachable end stops in the form of rods 11. The trailing edge 3 of the blade is aligned against the end stops 11. Desirably, the convex surface 2 adjacent the trailing edge 3 is positioned flat against the supports 10a, 10b. This may be facilitated by means of a pivoted convex surface support 12. The tooling may further include a stop 13 in a third orthogonal direction against which the tip platform is aligned. In alternatives, the position of this stop could be on the opposite face of the tip platform 4, or on either face of the root platform 5. The stop 13 may be fixedly connected to a frame which also comprises the support bars 10a, 10b.

    [0021] As can be seen in Figure 4, once the trailing edge 3 is aligned with the detachable rods 11, the blade is secured in position by a pivoted clamp 14. The pivoted convex surface support 12 serves to counter any load from the clamp 14 which might push the trailing edge out of alignment with the rods 10a and 10b. This is better illustrated with the schematic cross-sectional view of the blade in Figure 5.

    [0022] In the fixture shown in Figures 4 and 5, the centrally pivoted clamp 14, is located approximately 1/3 of the way along the chordal length of the blade from the trailing edge 3 to the leading edge. This clamp 14 acts on the concave surface to force the aerofoil firmly against the supports 10a, 10b and the centrally pivoted counter-support 12, but without excessive force so as to cause distortion of the trailing edge. The blade is thus firmly gripped as a result of the reactionary forces from the clamp 14, the supports 10a, 10b and the centrally pivoted convex support 12. The trailing edge end stops 11 can now be retracted (e.g. vertically) away from the remainder of the tooling to allow access for the cutting tool 6 as shown in Figures 2 and 6. It is important to note that the detail of the tooling design will depend on the specific geometry of the aerofoil to be machined, and in particular the relative distances and angles between the clamp 14 and the counter-support 12 and the trailing edge supports 10a and 10b, to ensure that the aerofoil is held firmly in position during the machining operation. Following clamping of the aerofoil and retraction of the trailing edge stops 11, the trailing edge 3 can be machined along the concave surface side of the trailing edge to form the desired thinner trailing edge profile. To ensure an accurate trailing edge profile is generated, a measurement process, such as a scanning probe or a laser system, may be used to measure the trailing edge thickness from the tip platform 4 to the root platform 5, or visa-versa, to make allowances for any part distortion, such as trailing edge bow, during the machining operation.

    [0023] In an alternative embodiment as shown in Figure 8, the tip and root platforms 4, 5 of the blade are supported in compliant gripping fixtures 15, 16. The compliant gripping fixtures may be rotated and locked into position once the convex surface adjacent the trailing edge is in contact with the support bars 10a, 10b and the detachable end stops 11. Before the gripping fixtures 15, 16 are locked in position the clamp 14 (which in this embodiment is positioned closer to the trailing edge 3) pushes the convex surface intimately against the supports 10a, 10b. With the blade properly positioned for subsequent machining, the compliant gripping fixtures 15, 16 are locked to maintain the position and the clamp 14 can be removed providing access to the concave side trailing edge for machining.

    [0024] In this embodiment, the clamp 14 can be dispensed with once compliant gripping fixtures 15, 16 have been locked in position. For example, in Figure 7, the clamp 14 is arranged such that there is negligible force in a plane parallel to the support bars 10a, 10b. Thus, the position of the blade can be maintained whilst compliant gripping fixtures 15, 16 are locked in position.

    [0025] As can be seen in Figure 9, once the blade has been positioned and secured into position, the detachable rods 11 are removed allowing a machine tool 6 to remove material 17 from the trailing edge on the concave surface side.

    [0026] In the tooling arrangement shown in Figures 7 and 8 the centrally pivoted clamp 14 is positioned much closer to the apex of the trailing edge 3. This allows the trailing edge to be located more intimately against the supports 10a, 10b, thereby improving the accuracy of the setting and thus the final profile of the trailing edge. With this arrangement, the blade is clamped in position after it has been appropriately positioned and oriented. As an alternative to the counter support 12 of the previously described embodiment, the compliant gripping fixtures 15, 16 can be arranged to hold a platform 4, 5 of the blade in a given orientation. Once the blade and compliant gripping fixtures 15, 16 are in the desired position and orientation, the ends of the fixtures 15, 16 are firmly clamped. The end stops 11 and clamp 14 are retracted away from the trailing edge 3 to allow access for the cutting tool 6 to machine the trailing edge 3. The material removal 17 is carried out relative to the datum system of the tool, in particular the supports 10a, 10b and the position of the trailing edge end stops 11 (prior to their removal).


    Claims

    1. A fixture for locating a straight edge (3) of a curved surface (2) of an aerofoil, in particular a turbine blade, and holding the aerofoil in a fixed position during performance of a machining operation on a concave side surface adjacent the straight edge of the curved surface of the aerofoil, the fixture comprising:

    two or more elongate supports (10a, 10b) that are spaced apart from each other to form a seat for the convex curved surface (2) of the aerofoil, each elongate support (10a, 10b) extending straightly and in parallel with a chord of the convex curved surface (2) of the aerofoil;

    two or more detachable end stops (11) arranged to extend in a plane orthogonal to that in which the elongate supports (10a, 10b) extend and against which, in use, the straight edge (3) of the curved surface (2) of the aerofoil is aligned; and

    a clamp (14);

    the clamp being arranged, in use, to push the convex curved surface (2) of the aerofoil against the elongate supports (10a, 10b) such that the straight edge (3) of the curved surface (2) of the aerofoil contacts the elongate supports (10a, 10b) and upon removal of the detachable end stops (11) the concave side surface adjacent the straight edge (3) is exposed for machining.


     
    2. A fixture as claimed in claim 1 wherein each elongate support (10a, 10b) has a rounded cross section.
     
    3. A fixture as claimed in claim 1 or 2 wherein each detachable end stop (11) comprises two or more spaced apart rods.
     
    4. A fixture as claimed in claim 3 wherein each rods has a rounded cross section.
     
    5. A fixture as claimed in any preceding claim wherein the clamp (14) comprises a pivoted clamp.
     
    6. A fixture as claimed in any preceding claim further comprising a convex surface counter-support (12) for countering any undesirable load from the clamp (14) which may cause slippage and/or tilting of the part after it has been positioned.
     
    7. A fixture as claimed in claim 6 wherein the convex surface counter support (12) comprises a wedge or a bar whose position is slidably adjustable to accommodate various degrees of curvature.
     
    8. A fixture as claimed in claim 6 wherein the convex surface counter-support (12) comprises a pivoted support.
     
    9. A fixture as claimed in any preceding claim further comprising one or more additional stops (13) arranged in a plane orthogonal to both the plane in which each elongate support (10a, 10b) sits and the plane in which the detachable end stops (11) extend.
     
    10. A fixture as claimed in any one of claims 1 to 5 further comprising a pair of compliant gripping fixtures (15, 16) configured to receive opposing ends of the part in a manner which does not permit the part to rotate relative to the pair of compliant gripping fixtures (15,16).
     
    11. Use of a fixture according to any preceding claim to align and secure an aerofoil with its trailing edge (3) accessible to a machine tool and performing a machining operation with the machine tool to remove material from the trailing edge on a concave surface side of the aerofoil.
     


    Ansprüche

    1. Befestigung zum Positionieren einer geraden Kante (3) einer gekrümmten Oberfläche (2) eines Leitflügels, insbesondere eines Turbinenflügels, und Halten des Leitflügels in einer festen Position während der Ausführung von Maschinenbearbeitung an einer konkaven Seitenfläche, angrenzend an die gerade Kante der gekrümmten Oberfläche des Leitflügels, wobei die Befestigung umfasst:

    zwei oder oder mehr längliche Stützen (10a, 10b), die voneinander beabstandet sind, um einen Sitz für die konvexe gekrümmte Oberfläche (2) des Leitflügels zu formen, wobei jede längliche Stütze (10a, 10b) gerade und parallel zu einer Flügeltiefe der konvexen gekrümmten Oberfläche (2) des Leitflügels verläuft;

    zwei oder mehrere abnehmbare Endanschläge (11), die angeordnet sind, um in einer Ebene zu verlaufen, die rechtwinklig zu der ist, in der die länglichen Stützen (10a, 10b) verlaufen und auf die, in Gebrauch, die gerade Kante (3) der gekrümmten Oberfläche (2) des Leitflügels ausgerichtet ist;

    und eine Klemme (14);

    wobei die Klemme, in Gebrauch, angeordnet ist, um die konvexe gekrümmte Oberfläche (2) des Leitflügels gegen die länglichen Stützen (10a, 10b) zu drücken, so dass die gerade Kante (3) der gekrümmten Oberfläche (2) des Leitflügels die länglichen Stützen (10a, 10b) kontaktiert und nach dem Entfernen der abnehmbaren Endanschläge (11) die konkave Seitenfläche angrenzend an die gerade Kante (3) zur Maschinenbearbeitung freigelegt ist.


     
    2. Befestigung nach Anspruch 1, wobei jede längliche Stütze (10a, 10b) einen abgerundeten Querschnitt aufweist.
     
    3. Befestigung nach Anspruch 1 oder 2, wobei jeder abnehmbare Endanschlag (11) zwei oder mehrere beabstandete Stangen umfasst.
     
    4. Befestigung nach Anspruch 3, wobei jede Stange einen abgerundeten Querschnitt aufweist.
     
    5. Befestigung nach einem der vorstehenden Ansprüche, wobei die Klemme (14) eine schwenkbare Klemme umfasst.
     
    6. Befestigung nach einem der vorstehenden Ansprüche, ferner umfassend eine konvexe Oberflächen-Konterstütze (12) zum Kontern von unerwünschten Lasten von der Klemme (14), die zu Gleiten und/oder Kippen des Teils nach seiner Positionierung führen können.
     
    7. Befestigung nach Anspruch 6, wobei die konvexe Oberflächen-Konterstütze (12) einen Keil oder einen Balken umfasst, dessen Position gleitbar eingestellt werden kann, um unterschiedlichen Krümmungsgraden Rechnung zu tragen.
     
    8. Befestigung nach Anspruch 6, wobei die konvexe Oberflächen-Konterstütze (12) eine schwenkbare Stütze umfasst.
     
    9. Befestigung nach einem der vorstehenden Ansprüche, ferner umfassend einen oder mehrere zusätzliche Anschläge (13), die in einer Ebene angeordnet sind, die rechtwinklig zu der Ebene, in der jede längliche Stütze (10a, 10b) sitzt, und zu der Ebene, in der die abnehmbaren Endanschläge (11) verlaufen, ist.
     
    10. Befestigung nach einem der Ansprüche 1 bis 5, ferner umfassend ein Paar nachgiebige Greifbefestigungen (15, 16), die konfiguriert sind, um gegenüberliegende Enden des Teils auf eine Art und Weise aufzunehmen, die nicht zulässt, dass das Teil relativ zum Paar nachgiebiger Greifbefestigungen (15, 16) rotiert.
     
    11. Verwendung einer Befestigung nach einem der vorstehenden Ansprüche, um einen Leitflügel so auszurichten, dass seine Hinterkante (3) für ein Maschinenwerkzeug zugänglich ist, und Ausführen eines Maschinenbearbeitungsvorgangs mit dem Maschinenwerkzeug, um Material von der Hinterkante an einer konkaven Oberflächenseite des Leitflügels zu entfernen.
     


    Revendications

    1. Pièce de fixation destinée à localiser un bord droit (3) d'une surface incurvée (2) d'une surface portante, en particulier une aube de turbine, et à maintenir la surface portante dans une position fixe pendant l'exécution d'une opération d'usinage sur une surface latérale concave adjacente au bord droit de la surface incurvée de la surface portante, la pièce de fixation comprenant :

    deux supports allongés ou plus (10a, 10b) qui sont espacés l'un de l'autre pour former un siège de la surface incurvée convexe (2) de la surface portante, chaque support allongé (10a, 10b) s'étendant droit et en en parallèle à une corde de la surface incurvée convexe (2) de la surface portante ;

    deux butées d'extrémité détachables ou plus (11) agencées pour s'étendre sur un plan orthogonal à celui sur lequel les supports allongés (10a, 10b) s'étendent et contre lequel, en utilisation, le bord droit (3) de la surface incurvée (2) de la surface portante est aligné ;

    et un collier (14) ;

    le collier étant agencé, en utilisation, pour pousser la surface incurvée convexe (2) de la surface portante contre les supports allongés (10a, 10b) de manière à ce que le bord droit (3) de la surface incurvée (2) de la surface portante soit en contact avec les supports allongés (10a, 10b) et au retrait des butées d'extrémité détachables (11) la surface latérale concave adjacente au bord droit (3) soit à découvert pour un usinage.


     
    2. Pièce de fixation selon la revendication 1, dans laquelle chaque support allongé (10a, 10b) a une coupe transversale arrondie.
     
    3. Pièce de fixation selon la revendication 1 ou 2, dans laquelle chaque butée d'extrémité détachable (11) comprend deux tiges ou plus espacées les unes des autres.
     
    4. Pièce de fixation selon la revendication 3, dans laquelle chaque tige a une coupe transversale arrondie.
     
    5. Pièce de fixation selon l'une quelconque des revendications précédentes, dans laquelle le collier (14) comprend un collier pivotant.
     
    6. Pièce de fixation selon l'une quelconque des revendications précédentes, comprenant en outre un contre-support de surface convexe (12) destiné à contrer toute charge indésirable depuis le collier (14) qui pourrait induire un glissement et/ou un inclinaison de la pièce après son positionnement.
     
    7. Pièce de fixation selon la revendication 6, dans laquelle le contre-support de surface convexe (12) comprend une cale ou une barre dont la position est ajustable par coulissement pour s'adapter à divers degrés de courbure.
     
    8. Pièce de fixation selon la revendication 6, dans laquelle le contre-support de surface convexe (12) comprend un support pivotant.
     
    9. Pièce de fixation selon l'une quelconque des revendications précédentes, comprenant en outre une ou plusieurs butées supplémentaires (13) agencées sur un plan orthogonal à la fois au plan sur lequel chaque support allongé (10a, 10b) est assis et au plan sur lequel les butée d'extrémité détachables (11) s'étendent.
     
    10. Pièce de fixation selon l'une quelconque des revendications 1 à 5, comprenant en outre une paire de pièces de fixation aggripantes compatibles (15, 16) configurées pour recevoir des extrémités opposées de la pièce de manière à ne pas permettre à la pièce de pivoter par rapport à la paire de pièces de fixation aggripantes compatibles (15, 16).
     
    11. Utilisation d'une pièce de fixation selon l'une quelconque des revendications précédentes pour aligner et sécuriser une surface portante avec son bord de fuite (3) accessible à une machine-outil et pour exécuter une opération d'usinage avec la machine-outil pour retirer de la matière du bord de fuite sur un côté de surface concave de la surface portante.
     




    Drawing





























    Cited references

    REFERENCES CITED IN THE DESCRIPTION



    This list of references cited by the applicant is for the reader's convenience only. It does not form part of the European patent document. Even though great care has been taken in compiling the references, errors or omissions cannot be excluded and the EPO disclaims all liability in this regard.

    Patent documents cited in the description