Abstract:
A device for holding a turbine engine blade for purposes of machining, the device including a support including at least one housing in which at least one block is removably mounted, the block including two jaws presenting an opening for mounting an airfoil of a blade. The block further includes six presser points for pressing against the airfoil, and a movable presser finger for pressing against a pressure side surface or a suction side surface of the blade, the finger being moved by an actuation mechanism such that in a blade clamping position, the presser finger presses the blade against the presser points of the block, which itself is pressed against the support.

Description:
BACKGROUND OF THE INVENTION 
     Field of the Invention 
     The present invention relates to a device for holding a turbine engine blade for the purposes of machining. 
     Description of the Related Art 
     A turbine engine blade comprises an airfoil that is to be placed in a gas-flow passage, and a root that is to be engaged in a slot in a disk. The airfoil and the root are separated by a platform defining a portion of the inside wall of the gas-flow passage. 
     When fabricating a blade, it is conventional to use forging or casting to make an un-finished part having dimensions that correspond to the finished dimensions, so far as the airfoil-forming portions is concerned. In contrast, the portion that is to form the root is no more than a blank that needs to be machined in order to give it its final shape and dimensions. 
     Once machined, the blade root still has projecting edges of angles that need to be rounded or smoothed during an operation referred to as fitting or radiusing. 
     A blade root is generally radiused manually by an operator who machines the projecting edges using a carbide bur or a brush, for example. Since that radiusing operation is manual, dimensional differences can appear from one blade to another or from one operator to another. 
     If the radiusing of a blade root is performed in insufficient or inaccurate manner (e.g. because the projecting edge is not sufficiently rounded), fabrication operations further downstream may suffer. This happens in particular when shot blasting a poorly-radiused blade root, since some of the beads of shot can be deformed by an edge that projects too much. A projecting edge also gives rise to stress concentrations that lead to premature cracking of the blade root. 
     Dimensional differences between the blade roots can also complicate assembling the roots in the slots of disks. 
     Finally, manual radiusing operations are complex and expensive. 
     Patent application FR 10/57384, in the name of the applicant and not yet published, discloses a method of radiusing blade roots with the help of a numerically-controlled machine. While they are being radiused, the blades are held in tooling comprising a support having housings formed therein. The airfoil of the blade is clamped between two jaws that are hinged together at one end and fastened together at the other end with the help of a first screw. The jaws have presser studs for pressing against the blade. Once the blade is in place between the jaws, a second screw provided on one of the jaws serves to press the blade against the above-mentioned presser points. The jaws and the blade are then mounted in a housing of the support and they are held therein with the help of latches. 
     A plurality of blades can thus be mounted simultaneously on the support of the tooling in different housings, in order to be subjected to radiusing. 
     Nevertheless, installing and removing the blades is time-consuming. Specifically, after radiusing, for example, when it is desired to remove a blade, it is necessary to move the latches, to withdraw the jaws together with the blade from the housing in the support, and to unscrew the second screw in order to be able to withdraw the airfoil from the jaws. 
     Also, such a mounting does not make it possible to know accurately the position of the blade relative to the support. Specifically, the jaws are mounted in the housing of the support with a small amount of mounting clearance such that, even if the blade is correctly positioned on its presser points, it is not possible to know exactly the position of the jaws (and thus of the blade) relative to the support that constitutes a known frame of reference. 
     BRIEF SUMMARY OF THE INVENTION 
     A particular object of the invention is to provide a solution to those problems that is simple, effective, and inexpensive. 
     To this end, the invention proposes a device for holding a turbine engine blade for the purposes of machining, the device comprising a support having at least one housing in which at least one block is mounted in removable manner, said block presenting an opening for mounting an airfoil of a blade and having at least six presser points for pressing against the airfoil, the device being characterized in that it has a movable presser finger for pressing against a pressure side surface or a suction side surface of the blade, the finger being moved by actuation means in such a manner that in a blade clamping position, the presser finger presses the blade against the presser points of the block, which itself is pressed against the support. 
     This makes it easier to install and remove a blade. Specifically, for mounting purposes, it suffices to insert the blade in the opening in the block (which may already be mounted in the housing in the support), and then to actuate the presser finger so that the blade and the block are pressed respectively against the presser points and against the support in such a manner as to fasten them on the support. To remove the blade, it suffices to actuate the presser finger in the opposite direction so that the blade can be withdrawn from the block. 
     There is therefore no need to remove the block from the housing in the support, nor is there any need to tighten or loosen one or more screws, as is necessary in the prior art. 
     Also, the position of the block relative to the support is known exactly since the block is pressed against a reference surface of the support. The positions of the airfoil and of the blade root can therefore be determined with great accuracy, thereby improving the quality of the radiusing that is performed. Consequently, the airfoils of the blades as radiused in this way can be correctly positioned inside the gas-flow passage. 
     According to another characteristic of the invention, the presser points are formed by studs, e.g. removable studs, having ends for coming into contact with the blade that do not have any sharp edges, and that are hemispherical, for example. 
     This characteristic makes it possible to avoid the airfoil being subjected locally to stresses that are too great and that could cause its material to recrystallize, which would degrade its mechanical characteristics. 
     When it is desired to radius another type of blade, it is possible merely to change the presser points while conserving the same block, thereby adapting the positions of the presser points to the shape of the airfoil. Naturally, it is also possible to change the block, should that be found to be necessary. 
     Advantageously, the block has an internal wall defining the opening for mounting the airfoil, from which wall there project: first, second, and third mutually spaced-apart studs for pressing on a leading edge of the blade or close thereto; a fourth stud for pressing on a trailing edge of the blade or close thereto; a fifth stud for pressing in register with the movable presser finger; and a sixth stud for pressing against a platform of the blade. 
     It should be observed that none of the studs presses against the blade root, thereby making it easier to radius. The position of each of the above-mentioned studs also makes it possible to hold the blade in position effectively and accurately. 
     Preferably, the block has two studs for pressing against the platform of the blade before the blade is clamped by the movable presser finger, the platform being spaced apart from said studs after the blade has been clamped. 
     The two above-mentioned studs serve to pre-position of the blade before clamping and they make it possible to avoid the airfoil pivoting into a wrong position during clamping by means of the movable presser finger. 
     In an embodiment, the block includes a hole for passing the movable presser finger. 
     By way of example, the block is formed of two jaws that are hinged to each other at one end and fastened to each other at another end. 
     Also, the means for actuating the movable presser finger may comprise a cam fitted with an actuation handle, and turning the cam with the help of the handle causes the movable presser finger to move. 
     Under such circumstances, the device may include an abutment suitable for limiting the angular stroke of the actuation handle. 
     In advantageous manner, the support includes a plurality of housings, each for mounting a respective block and blade. 
     A plurality of blade roots can then be radiused in a single operation. 
     According to another characteristic of the invention, the support includes means for retaining the block inside the corresponding housing, such as latches. 
     The block can thus be held in the housing of the support even when the bearing finger is in the release position. 
     The invention can be better understood and other details, characteristics, and advantages invention appear on reading the following description made by way of nonlimiting example and with reference to the accompanying drawings, in which: 
    
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS 
         FIG. 1  is a perspective view of a blade holder device of the invention; 
         FIG. 2  is a perspective view on a larger scale of a portion of the support; 
         FIG. 3  is a view on a larger scale and in perspective of a housing of the support in which two jaws are mounted; 
         FIG. 4  is a perspective view of one of the jaws; 
         FIG. 5  is a perspective view of the other jaw and of a presser finger; 
         FIG. 6  is a perspective view of the machine and of the presser finger of  FIG. 5 , together with the cam for actuating said presser finger; 
         FIGS. 7 and 8  are diagrammatic plan views showing a portion of the device and of a blade, respectively before and after clamping the blade; 
         FIGS. 9 and 10  are perspective views showing a portion of the device, respectively before and after clamping; 
         FIGS. 11 and 12  show the positions of the presser studs relative to the blade; and 
         FIG. 13  is a view on a larger scale also showing the position of two temporary presser studs of the platform of the blade, before clamping the blade with the movable presser finger. 
     
    
    
       FIG. 1  shows a device for holding a turbine engine blade for machining purposes, in particular for radiusing. The device comprises a support  1  of generally rectangular shape that is movable in rotation about its longitudinal axis A. The support  1  is mounted in bearings at its two ends  2 ,  3 , one of these ends  2  being driven in rotation by an electric motor  4  and control means. 
     DETAILED DESCRIPTION OF THE INVENTION 
     In the embodiment of  FIG. 1 , the support  1  has four housings  5  of generally square shape opening out on either side of the support  1  in surfaces referred to below as a top surface  6  and a bottom surface  7 , with “top” and “bottom” being relative to their position shown in  FIG. 1 . 
     As can be seen more clearly in  FIG. 2 , the inside walls  8  of the housings  5  have longitudinal projections  9  for forming abutments that are arranged at the bottom ends of the housings  5  and that are situated facing each other. 
     The support  1  is also fitted with latches  10  arranged at the top ends of the housings, the latches  10  being movable between an unlocking position ( FIG. 2 ) in which they are fully received in recesses  11  of the support  1 , and a locking position ( FIG. 3 ) in which they extend across the corresponding housing  5 . 
     The support also includes a cam  12  that is received in a recess  13  of the support  1 . The cam  12  is cylindrical in shape and is mounted to pivot on the support  1  about an axis B that is offset from the geometrical center of the cam  12 . In this way, the cam  12  can pivot between a retracted position ( FIG. 2 ) in which it is fully received in the above-mentioned recess  13 , and a deployed position in which it extends across the housing  5 . 
     The cam  12  has a cylindrical stud  14  extending upwards along the axis B, with the free end thereof including a flat  15  for inserting in a hole  16  of complementary shape in a handle  17  for actuating the cam  12 . 
     The top end of the stud  14  does not project beyond the top plane of the support  1 . A lateral recess  18  is also made in the top surface  6  of the support  1  so as to allow the handle  17  to be mounted on the stud  14  of the cam  12  and also so as to allow the handle  17  to move angularly in order to drive the cam  12 . An abutment  19  ( FIGS. 9 and 10 ) may also be provided on the support  1  so as to limit the stroke of the handle  17 . By way of example, this abutment may be formed by the head  19  of a screw. 
     While it is not in use, the handle  17  may be received in a lateral recess  20  of the support, and it may be held in the recess by means of a latch  21  similar to the latches  10 . 
     The device of the invention also includes at least two jaws  22 ,  23 , that can be seen in  FIGS. 3 to 8 . 
     A first jaw  22  is shown in  FIG. 4 . In plan view, this jaw is generally L-shaped and has a top surface  24 , a bottom surface  25 , two lateral surfaces  26 ,  27  forming substantially a right angle, and first and second lateral ends  28 ,  29 . 
     The lateral ends  28 ,  29  are connected together via an internal wall  30  from which there extend studs that are to come against a suction side surface  33  of an airfoil  34  of a blade  35 . 
     More particularly, there project from the internal wall  30 : first and second mutually spaced-apart studs  31  and  32  for pressing against the suction side surface  33  of the airfoil  34  close to a leading edge  36  of the blade  35 ; a third stud  37  for pressing against said suction side surface  33  close to a trailing edge  38  of the blade  35 ; and a fourth stud  39  for pressing against a middle zone of the suction side surface  33  in register with a movable presser finger that is described below. The stud  39  is not shown in  FIGS. 9 and 10 . A fifth stud  40  projects from the top surface  24  of the first jaw  22  and is for pressing against a platform  41  of the blade  35  ( FIG. 11 ). 
     As can be seen in particular in  FIGS. 5 and 6 , in plan view, the second jaw  23  is also generally L-shaped and has a top surface  24 , a bottom surface  25 , two lateral surfaces  26  and  27  forming substantially a right angle, and first and second lateral ends  28 ,  29 . 
     The lateral ends  28 ,  29  of the second jaw  23  are connected together via an internal wall  30  from which there extends a stud  42  that is to press against the suction side surface  33  of the blade  35 , in the vicinity of the leading edge  36  of the blade  35 . 
     The studs  31 ,  32 ,  37 ,  39 ,  40 , and  42  to form six reference presser points enabling the blade  35  to be properly positioned in the jaws  22  and  23 . 
     The second jaw  23  also has a hole passing therethrough, opening out in the wall  30  and for use in mounting a presser finger  43  that is to press via a first end  44  ( FIG. 6 ) against the cam  12 , and via a second end  45  against the pressure side surface  46  ( FIG. 12 ) of the airfoil  34  of the blade  35 , substantially in register with the stud  39 . The second end  45  of the presser finger  43  presents a rounded surface matching the pressure side surface  46  in the corresponding pressing zone. 
     The movable presser finger  43  is slidably mounted in the second jaw  23  to move between a release position in which it does not press against the pressure side surface  46  of the airfoil  34 , and a clamping position in which it presses against this surface  46 . The movable finger  43  is caused to slide by the cam  12  turning between its retracted and deployed positions. The presser finger  43  may be returned to its release position manually or with the help of resilient return means, e.g. with the help of a spring. 
     In a variant (not shown), the presser finger  43  may be pivotally mounted on the jaw  23  to pivot between a release position and a clamping position. 
     Two mutually spaced-apart studs  48 ,  49  also project from the top wall  24  of the second jaw  23 , and they come to press against the platform  41  of the blade  35 , prior to the blade  35  being clamped by the movable presser finger  43 , as described in greater detail below. These studs  48 ,  49  are not shown in  FIGS. 11 and 12  in order to make the drawings more readable. 
     The studs  31 ,  32 ,  37 ,  39 ,  40 ,  42 ,  48 , and  49  and the presser finger  43  may be removable so as to enable them to be changed in order to adapt to airfoils  34  of different shapes or dimensions. The ends of the studs pressing against the airfoil  34  do not have any sharp edges, and by way of example they may be hemispherical or frustoconical. 
     The first ends  28  of the jaws  22 ,  23  form a hinge enabling the jaws to be opened and closed by pivoting about an axis, which is constituted by a screw  50  ( FIG. 3 ). The second ends  29  of the jaws  22 ,  23  may be fastened to each other via a screw mounted in a hole  51  of the second jaw  23  ( FIG. 5 ) and screwed into tapping  52  in the first jaw  22  ( FIG. 4 ). Once the jaws  22  and  23  have been fastened together they form a block  53  that is shown diagrammatically in  FIGS. 7 and 8 . In these diagrammatic figures, only the presser studs  31  and  37  are shown, and they are not represented pictorially. 
     In a variant, the jaws  22  and  23  may be replaced by a one-piece unit, without that modifying the operation of the invention. 
     The operation of the device is described below. 
     Prior to mounting a blade  35 , a block  53  is mounted in at least one of the housings  5  of the support  1 . The block  53  is made up of two jaws  22  and  23  that are fastened together and that are fitted with presser studs  31 ,  32 ,  37 ,  39 ,  40 ,  42 ,  48 , and  49  and with a movable presser finger  43 . The block  53  rests on the abutments  9  and is retained in the corresponding housing by the latches  10 . The cam  12  is in the retracted position and the presser finger  43  is in the release position. 
     The airfoil  34  of a blade  35  can then be inserted in the space defined between the jaws  22  and  23  of the block  53 , until the platform  41  of the blade  35  presses against the studs  48 ,  49  in provisional manner. 
     The cam  12  is then actuated by an operator using the handle  17  so as to move the presser finger  43  towards its clamping position. The presser finger  43  then presses the blade  35  towards the studs  31 ,  32 ,  37 ,  39 ,  40 , and  42 , thus also pressing the block  53  back against the inside wall of the housing  5  of the support  1 . Thus, in a single clamping action, the airfoil  34  of the blade  35  is held stationary by the presser finger  43  against the block  53 , which itself is held against the support  1 . 
     The blade  35  can then be machined, and in particular the blade root  54  can then be radiused, with the help of a numerically-controlled machine, in the same manner as in document FR 10/57384. The positioning of the presser points, of the jaws  22 ,  23 , and the turning of the support  1  about its axis A give easy access to all of the zones that are to be machined. Also, since the airfoil  34  is positioned accurately relative to the support  1 , it is also possible to perform the radiusing of the blade root  54  accurately and in reproducible manner. 
     Naturally, an airfoil  35  may be mounted in each of the housings  5  of the support  1 , so that a plurality of blades  35  can be radiused in a single operation. 
     The blade  35  is removed by turning the handle  17  and the cam  12  in the opposite direction, thereby moving the presser finger  43  towards its release position. 
     The block  53  and/or the studs  31 ,  32 ,  37 ,  39 ,  40 ,  42 ,  48 , and  49 , and the presser finger  43  may also be changed easily, when it is desired to machine a blade of a different type. Specifically, the positions of the presser points may vary for each type of blade.