Abstract:
A clamping system for clamping aerofoils. The clamping system has pivotally mounted engagement members that engage the aerofoil mounted on a pivotally mounted arm either side of the pivotal mounting. The arm can pivot as required relative to the item, to accommodate differences in shape in the item, whilst providing a substantially equal clamping force by both engagement members.

Description:
CROSS REFERENCE TO RELATED APPLICATION 
       [0001]    This application is entitled to the benefit of British Patent Application No. GB 0808354.5, filed on May 9, 2008. 
       FIELD OF THE INVENTION 
       [0002]    This invention concerns a clamping system, and particularly, but not exclusively, a clamping system for use in clamping nozzle guide vanes of a gas turbine engine during the carrying out of manufacturing operations on the nozzle guide vanes. 
       BACKGROUND OF THE INVENTION 
       [0003]    Nozzle guide vanes are used for instance in gas turbine engines to guide air therethrough. Nozzle guide vanes generally comprise a pair of aerofoils extending between two spaced plates. The aerofoils have to be orientated in a particular way relative to the other aerofoil in the pair, and also relative to adjacent vanes. During manufacture of nozzle guide vanes, some manufacturing differences invariably occur, such that machining operations such as grinding have to be carried out on the vanes subsequent to casting. 
         [0004]    Nozzle guide vanes have to be held securely during such machining operations to enable the operations to be carried out, and also to provide a reaction to any machining forces applied thereto. Because each guide vane is slightly different, it is necessary for each component to be held slightly differently. 
         [0005]    Previously difficulties have been encountered in holding nozzle guide vanes during machining operations, and in many instances it has been necessary to remount the nozzle guide vanes between different operations. For instance, up to eight separate set ups have been used at times to hold a nozzle guide vane during grinding operations. 
       SUMMARY OF THE INVENTION 
       [0006]    According to the present invention there is provided a clamping system, the system including a support platform upon which an item to be clamped can locate, a clamping assembly selectively movable to a closed position relative to the support platform, with one or more clamping arrangements being provided on the clamping member, the or each clamping arrangement including a pair of engagement members mounted on a pivotally mounted arm either side of the pivotal mounting, such that the engagement members are engageable when the assembly is in a closed position with an item on the support platform to be clamped, and the arm can pivot as required relative to the item, to accommodate differences in shape in the item, whilst providing a substantially equal clamping force by both engagement members, wherein a pair of clamping arrangements are provided, each pivotally mounted to a beam member, the beam member being pivotally mounted on the clamping assembly between the clamping arrangements. 
         [0007]    The beam member may be threadably mounted by a bolt member on the clamping arrangement, such that a predetermined clamping force can be applied thereto. The bolt member may be engageable with the beam member through profiled contact surfaces which permit pivotal movement of the beam member. The contact surfaces may be substantially hemispherical. 
         [0008]    Two beam members may be provided on the clamping arrangement, and the beam members may be arranged adjacent to each other in a parallel alignment. 
         [0009]    The engagement members may include heads with an enlarged cross sectional area relative to the remainder of the engagement member, so as to spread the clamping load on an item. 
         [0010]    The engagement members may have heads which include trapped movable members, which movable members may have one or more generally flat surfaces engageable with a clamped item. 
         [0011]    The clamping assembly may be pivotally mounted relative to the support platform, and locking means may be provided for retaining the clamping assembly in a closed position. 
         [0012]    One or more adjustable supports may be provided engageable with the item, and the adjustable supports may be provided on the clamping assembly and/or the support platform. 
         [0013]    The or each adjustable support may include a projection member extending from a housing, and means for locking the projection member in a required position relative to the housing. The projection member may be spring urged from the housing. 
         [0014]    One or more non adjustable engagement members may be provided on the clamping assembly and/or support platform. 
         [0015]    One or more clamping engagement members may be provided, which clamping engagement members may be threadably mounted on the clamping assembly and/or support platform. 
         [0016]    The invention also provides a clamping system for a nozzle guide vane of a gas turbine engine, the system being according to any of the preceding ten paragraphs. 
         [0017]    The system may be arranged such that the engagement members are engageable with the aerofoil of a nozzle guide vane. 
         [0018]    The system may be arranged such that the clamping arrangement on one side of a beam member engage with a first aerofoil of a nozzle guide vane, and the clamping arrangement on the other side of the beam member engage with a second aerofoil of the nozzle guide vane. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0019]      FIG. 1  is a diagrammatic perspective view of a nozzle guide vane; 
           [0020]      FIG. 2  is a diagrammatic sectional side view through a clamping system according to the invention; 
           [0021]      FIG. 3  is a diagrammatic perspective view of the system of  FIG. 2 ; and 
           [0022]      FIG. 4  is a diagrammatic sectional end view through the system of  FIG. 2 . 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0023]      FIG. 1  shows a nozzle guide vane  10  as used for example in a gas turbine engine of a jet aircraft. The guide vane  10  comprises two spaced aerofoils  12  extending between plates  14 . 
         [0024]      FIGS. 2-4  of the drawings show a clamping system  16  in use clamping a guide vane  10 . The system  16  includes a support platform  18  and a clamping assembly  20 . The assembly  20  is pivotally mounted to the support platform  18  towards the right hand side of the latter as shown in  FIG. 2 , about a horizontal axis  22 . A bolt  24  is extendable through the left hand end of the support platform  18  as shown in  FIG. 2  and threadably engageable in a block  26  on the left hand end of the support platform  18 , for selectively retaining the clamping assembly  20  in a closed position as shown. 
         [0025]    The system  16  is shown clamping the nozzle guide vane  10  with the plates  14  extending behind and in front of the system  16  as shown in  FIG. 2 . The system  16  is engageable with the two aerofoils  12 . 
         [0026]    Two shallow n shaped beams  28  are mounted in a parallel alignment on top of the assembly  20 . Each beam  28  is mounted by a bolt  30  which engages with a hemispherical section block  32 , and through which block  32  the bolt  30  extends. The block  32  locates in a correspondingly shaped recess  34  in the top of the respective beam  28 , to permit limited pivotal movement of the beams  28  relative to the bolts  24 . 
         [0027]    A clamping assembly  36  is pivotally mounted to each of the side limbs of the beams  28 , towards the lower end thereof. Each assembly  36  includes a bar  38  which extends through a recess in the lower end of the respective side limb of the beam  28 , and is pivotally mounted thereto, about a generally mid point of the bar  38 . An engagement member  40  extends downwardly from each end of each bar  38  through an opening in the clamping assembly  20 . A trapped ball bearing  41  is provided at the free end of each engagement member  40 , and the ball bearing  41  may have one or more flattened faces engageable with the respective aerofoil  12 . As can be seen in  FIG. 2 , a shorter engagement member  40  is provided on the left hand side of each bar  38 , to correspond to the inclination of the top surface of the aerofoils  12 . 
         [0028]    A number of other adjustable support members are engageable with the guide vane  10 .  FIG. 4  shows two adjustable support members  42 ,  44 . The upper support member  42  as shown in  FIG. 4  extends forwards as shown in  FIG. 2  out of the clamping assembly  20  to engage with a one of the plates  14 . The lower support member  44  as shown extends rearwards and upwardly as shown in  FIG. 2  to engage with the other plate  14 . Each of the support member  42 ,  44  includes a cylindrical sleeve  46  from which an engagement bar  48  extends. The engagement bar  48  may again have a trapped ball bearing  50  at its free end. The engagement bar  48  is spring urged out of the sleeve  46  by a trapped spring  52 . A locking screw  54  extends laterally into the sleeve  46  to engage with the bar  48  to hold same at a required position extending from the sleeve  46 . 
         [0029]    The support member  44  extends from a block  56  located generally midway along the support platform  18 . A fixed support member  58  also extends from the block  56 , and in this instance the member  58  extends in a forwards direction relative to  FIG. 2 . The support member  58  could be spring urged to reduce vibration. A fixed support member  60  also extends from the clamping assembly  20  in an opposite direction to the support member  42  to engage with the other plate  14 . 
         [0030]    As shown in  FIG. 2  two further fixed support members  62 ,  64  are provided on the platform  18 , and are located to each receive and support a substantially lowermost part of the respective aerofoil  12 . A further adjustable support member  66  is provided extending upwardly and to the right as shown in  FIG. 2  from the block  26 , to be engageable with the underside of an upper part of the left hand aerofoil  12  as shown in  FIG. 2 . 
         [0031]    A further adjustable support member  68  extends upwardly through the block  56  to locate beneath the right hand aerofoil  12  as shown in  FIG. 2  to provide support therefor. A lock screw  72  for the support member  70  extends through the support platform  18  to the right hand side thereof as shown in  FIG. 2 . A pair of spaced adjustable support members  74  are provided extending through a block  76  at the right hand end of the support platform  18  as shown in  FIG. 2 , which block  76  mounts a pair of spaced webs  78  which mount a pin  80  to provide the axis  22 . 
         [0032]    To use the system  16 , the bolt  24  will be undone and the clamping assembly  20  pivoted upwardly. The nozzle guide vane  10  can then be located in position, with the aerofoil  12  resting inter alia on the fixed support member  58 ,  62 ,  64 . A number of the adjustable support members such as  42 ,  52 ,  66 ,  68  and  74  can be adjusted as required. 
         [0033]    The clamping assembly  20  is then pivoted back onto the support platform  18 , and the bolt  24  is tightened. The clamping assembly  20  can then be brought into play by tightening of the bolts  30 , which bolts  30  can be tightened to the same torque setting. As the bolts  30  are tightened, dependent on the precise positioning and shape of the nozzle guide vane  10 , the beams  28  may pivot slightly relative to the alignment of the bolt  30 . Also the bars  38  may pivot so that substantially equal clamping forces are applied by the respective engagement members  40 . 
         [0034]    The nozzle guide vane  10  will then be securely held, and appropriate grinding or other operations can be carried out as required. It has generally been found that all grinding operations can be performed on the nozzle guide vane  10  without removal from the system  16 . The clamping assembly with the pivoted beams and bars means that differences due to manufacturing tolerances can generally be automatically compensated for by the engagement members. The system therefore readily permits a nozzle guide vane to be located thereon, whilst compensating for manufacturing differences in the vane. 
         [0035]    Various modifications may be made without departing from the scope of the invention. For instance a different number and/or arrangement of engagement and support members may be provided as required. The engagement members may take a different form. The engagement members may have heads with an enlarged cross sectional area to spread the clamping load on an item. Whilst the above-described example relates to clamping of guide vanes, such systems could be used with other components or articles.