Abstract:
A marking system includes a fixture having a base and means for receiving a pair of jaws in an installed condition. The fixture includes means for articulating the installed jaws relative to the base with at least first and second rotational degrees of freedom. A pair of the jaws includes a first jaw having a surface portion generally concave and complementary to a suction side portion of an airfoil of a first turbine engine element. A second jaw has a surface portion generally convex and complementary to a pressure side portion of the airfoil.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     The invention relates to the manufacture and repair of turbine engine components. More particularly, the invention relates to the identification marking of turbine engine elements.  
         [0002]     Identification marking of turbine engine components has drawn much recent attention. Although the purposes and uses of such marking may vary, key examples are seen during engine manufacture, repair and, more particularly, engine component repair. It has become standard practice for some manufacturers and repair/refurbishing operations to mark each component as it is received for repair or refurbishing. The markings may be identification markings (e.g., operator-readable alphanumeric serial markings or machine-readable codes (e.g., 2-d dot matrix codes)). The markings may, themselves, contain further information (e.g., date/time of repair, place of repair, repair kind code, or the like) or such information may be stored in a database accessible based upon the markings.  
         [0003]     An exemplary marking technique is dot peen indentation marking. Other techniques include laser and/or chemical etching. Dot peen marking has advantages of speed, low cost, and an extreme degree of robustness.  
         [0004]     Typical components have a limited portion of surface area suitable for marking. For example, the airfoils of turbine and compressor blades may be off-limits as may other surfaces exposed to the gas path or to high stresses. For such blades, marking at particular locations along the blade platform underside and/or the ends of the blade attachment root may be appropriate. Thus, for a given component, a manufacturer may specify a finite number of accepted marking locations/sites.  
         [0005]     With typical marking apparatus, the marking location on the component must have a predetermined spatial relationship to a marking head (i.e., the location must be in an operative marking position). Custom fixtures may be used to hold the components. For example, due to different airfoil and other shapes, different fixtures may be required to hold airfoils of each blade stage in the engine. Staying with the example of blades, the fixtures may have surfaces complementary to the particular shape of the airfoils of the associated stage. A given fixture positions a given one of the permitted locations in the operative marking position. To address the various permitted locations, multiple fixtures may be required for the given component, which is expensive and accommodates valuable work cell space.  
         [0006]     Thus, to mark the components as they come in or go out, an operator must inspect each component to see which permitted location(s) have not already been marked. The operator then selects the appropriate unmarked location and selects the fixture or adapter for that specific location from the various fixtures/adapters for that specific component.  
       SUMMARY OF THE INVENTION  
       [0007]     One aspect of the invention involves a system including a fixture having a base and means for receiving a pair of jaws in an installed condition. The fixture includes means for articulating the installed jaws relative to the base with at least first and second rotational degrees of freedom. A pair of the jaws (e.g., a first of several pairs) includes a first jaw having a surface portion generally concave and complementary to a suction side portion of an airfoil of a first turbine engine element. A second jaw has a surface portion generally convex and complementary to a pressure side portion of the airfoil.  
         [0008]     In various implementations, there may be additional sets of jaw pairs, each having first and second jaws whose surface portions are complementary to suction and pressure sides of different airfoils from different turbine engine elements. The means for articulating may further provide articulation in a third rotational degree of freedom.  
         [0009]     The apparatus may be used in a marking operation. For example, the first turbine engine element may be received and installed to the first pair of jaws. The first pair of jaws may be installed to the fixture. A first marking site may be selected on the first turbine engine element. The fixture may be articulated to bring the first marking site to a first spatial relationship with a marking device. The marking device may be used to mark the first marking site.  
         [0010]     The details of one or more embodiments of the invention are set forth in the accompanying drawings and the description below. Other features, objects, and advantages of the invention will be apparent from the description and drawings, and from the claims. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0011]      FIG. 1  is a view of a marking station.  
         [0012]      FIG. 2  is a side view of a fixture of the station of  FIG. 1 .  
         [0013]      FIG. 3  is a front view of the fixture of  FIG. 2 .  
         [0014]      FIG. 4  is a back view of a back mounting block of the fixture of  FIG. 2 .  
         [0015]      FIG. 5  is a back view of an upper portion of a back upright of the fixture of  FIG. 2 .  
         [0016]      FIG. 6  is a isolated bottom view of a mated jaw pair of the fixture of  FIG. 2 . 
     
    
       [0017]     Like reference numbers and designations in the various drawings indicate like elements.  
       DETAILED DESCRIPTION  
       [0018]      FIG. 1  shows a marking station  20  for marking a blade  22 . The exemplary station  20  includes a marking apparatus or head  24  such as a dot-peen marker. The blade  22  is held in a fixture assembly  26 . The exemplary fixture  26 , is, in turn, mounted to the upper surface or top  28  of a base  30  of the station. The head  24  may be mounted relative to the base  30  such as by an arm structure  32 . The exemplary head  24  may be vertically movable along the arm under computer control. The exemplary head carries a marking bit  34  with a lower marking tip  36 . The head or the bit may be movable horizontally under computer control. For example, the bit may be movable fore and aft (away from and toward the arm) and left and right by motors (not shown) in the head.  
         [0019]      FIG. 2  shows further details of the blade  22  and fixture  26 . The blade has an airfoil  40  extending outboard from a root  42  to a tip  44 . The airfoil base  42  is attached to a platform  45  (e.g., unitarily formed therewith). An attachment root  46  extends from the inboard end of the platform  45  to a terminus  48 . The exemplary root  46  has a convoluted “fir tree” profile for mating with a complementary slot in a disk (not shown) to secure the blade to the disk. The blade  22  is held between removable jaw elements  50  and  52  of the fixture  26 .  
         [0020]     The exemplary fixture  26  is a vise mechanism having a fixture base  60 . The exemplary base  60  may be mounted to the station base  30  (e.g., with an underside  62  of the base  60  contacting the top  28  and secured thereto by means of fasteners  64 . The upper surface  66  of the base  60  includes a concave surface  68 . In the exemplary fixture  26 , the surface  68  is singly concave having an essentially fixed radius of curvature R 1 . An axis  500  ( FIG. 3 ) of said curvature is near terminus  48 . An exemplary R 1  is  — 0.3 m, more broadly 0.1-2.0 m or 0.2-0.6 m. The surface  68  is engaged by a complementary convex surface  70  of a fixture main body  72 . The main body  72  includes a base portion  74  along which the surface  70  is formed. The main body  72  includes fore and aft upright structures  76  and  78  extending upward from the main body base  74 .  
         [0021]     The main body  72  serves as the body of a vise or clamping structure to which the jaws  50  and  52  act as jaw inserts. In the exemplary fixture  26 , the fore upright  76  serves as a screw carrier having an internally threaded portion  90  along a screw axis  510  ( FIG. 3 ). The internally threaded portion  90  threadingly receives an externally threaded body  92  of a screw  94 . At an outboard end  96 , the screw  94  is engaged to a handle  98  and secured thereto against relative rotation about the axis  510 . At an inboard end  100 , the screw  94  engages a mounting block  102 . The mounting block  102  acts as a movable jaw carrying the insert  52 . In the exemplary fixture  26 , a forward flange  110  of the jaw  52  sits atop an upper surface  112  of the block  102  and is secured thereto by one or more screws  114 . The connection of the screw  94  to the block  102  advantageously permits relative rotation about the axis  510  so that the block may maintain its orientation as it translates along the axis  510 . However, the connection advantageously permits transmission of force along the axis  510  at least in a direction  512  moving the block  102  toward the jaw  50 . Rotation of the handle in a direction  514  ( FIG. 3 ) about the axis  510  drives the block  102  and jaw  52  in the direction  512 . Opposite rotation moves them in an opposite direction. The jaw  50  may similarly be mounted to an aft mounting block  120  carried by the aft upright structure  78 . Mounting of the block  120  to the upright structure  78  advantageously permits a lockable relative rotation about the axis  510  (e.g., as is discussed below).  
         [0022]      FIG. 2  shows exemplary means for providing the lockable relative rotation about the axis  500 . One or more locking members  150  selectively lock the main body base  74  to the fixture base  60 . The exemplary locking members  150  are formed as screws (e.g., a transverse array of three screws  150  shown in  FIG. 3 ). Each of the exemplary screws  150  passes through an associated hole  152  in the body base  74 . In an inserted condition, the screws may further extend into one of an associated group of holes  154 ,  156 , and  158  in the fixture base  60 . In an exemplary embodiment, the hole  152  is unthreaded whereas the holes  154 ,  156 , and  158  are threaded to engage the screw threads to enable a tight securing in the inserted/engaged condition of the screw  150 . With the screws disengaged (i.e., out of the holes  154 ,  156 , and  158 ) the fixture body  72  may be rotated about the axis  500  to bring the hole  152  into alignment with one of the holes  154 ,  156 , and  158 . In the exemplary implementation, the hole  154  corresponds to a neutral condition (e.g., wherein the axis  510  is horizontal). The hole  156  corresponds to a slightly inclined orientation (e.g., with the axis  510  rotated counterclockwise by about 5° as viewed in  FIG. 2 . The hole  158  corresponds with a declined orientation (e.g., the axis  510  rotated clockwise by about 20° as viewed in  FIG. 2 ). For example, with the terminus  48  faceted, the identified rotations can bring each of the facets into the operative position and appropriate orientation (e.g., horizontal). The marking site need not be exactly horizontal. For small transverse marker excursions (e.g., up to about 6 mm) small off-horizontal angles (e.g., up to about 5°) may be acceptable (i.e., the maker can still effectively mark, especially if the head height is fixed). The smaller such angle, the greater the permitted transverse excursion (e.g., dimension of the marking).  
         [0023]      FIG. 2  shows further details of the means for providing lockable rotation of the jaws and blade relative to the fixture body  72  about the axis  510 . In the exemplary fixture  26 , the block  120  has a circular boss  170  received in a circular aperture  172  in the upright  78  centered on the axis  510 . Sliding interaction of the boss  170  and surface of the aperture  172  guide the relative rotation about the axis  510 . The rotation may be locked by locking means. Exemplary locking means include one or more locking members  180  and  182 . An exemplary locking member  180  is formed as a pin. An exemplary pin is shown having a spring-loaded ball detent  94  for detent locking the pin in an inserted position extending through apertures or holes in the upright  78  and block  120 . An exemplary hole  186  is shown in the block  78 .  FIG. 2  also shows an exemplary hole  188  in the block  120 .  FIG. 4  is an aft view of the block  120  showing the hole  188 .  FIG. 4  further shows additional holes  190 ,  192 , and  194  of like size and at like radius from the axis  510 . The exemplary holes  186 ,  188 ,  190 ,  192 , and  194  are unthreaded.  
         [0024]     With the locking members  180  and  182  in disengaged conditions, the block  120  may be rotated about the axis  510  relative to the upright  78 . This rotation may be of both blocks  120  and  102 , their mounted jaws  50  and  52 , and the blade  22  as a unit. The rotation may bring any of the holes  188 ,  190 ,  192 , and  194  into alignment with the hole  186  of  FIG. 2 . For example, relative to the hole  188 , the holes  192  and  194  may represent respective 90 degree rotations of the block counterclockwise and clockwise, respectively as viewed in  FIG. 4 . The hole  190  may be at a different angle. An exemplary angle involves a counterclockwise rotation of 17°30′ which facilitates marking on the underside  196  ( FIG. 2 ) of a platform tongue  198 . Such tongues are common blade features having undersides within a few degrees of the exemplary underside orientation. Thus the 17°30′ angle is a good approximation, allowing the fixture to be used for a variety of blades.  
         [0025]     The exemplary locking members  182  are cap screws (e.g., hex-head). In the exemplary fixture  26 , the shafts of these cap screws pass through slots  200  ( FIG. 5 ) in the upright  78 . The exemplary slots  200  are formed essentially as annular segments of slightly more than 90 degree extent about the axis  510 . Each of the slots  200  has a pair of circumferential ends  202  which determine ends of a rotational range of motion with the screws  182  installed in a given set of corresponding holes in the block  120 .  FIG. 4  shows four such corresponding holes  210 ,  212 ,  214 , and  216  evenly spaced about the axis  510  exactly out of phase with the holes  188 ,  192 , and  194 . In the exemplary fixture, these holes  210 ,  212 ,  214 , and  216  are threaded to receive the shafts of the screws  182 . Accordingly, when these screws  182  are tightened, the block  120  is firmly secured to the upright  78 . By changing the particular pair of these holes engaged by the screws  182 , a full range of rotation about the axis  510  may be obtained subject to the lockouts provided by the pin  180 .  
         [0026]     The exemplary jaws  50  and  52  of  FIG. 4  are each assemblies of a metallic structural member  250  and  252  with a polymeric blade-engaging member  254  and  256 . The exemplary structural members  250  and  252  are identical to each other. The blade-engaging members have internal surfaces  258  and  260  for engaging the blade. These surfaces  258  and  260  include respective convex and concave portions generally complementary to the pressure and suction sides  270  and  280  of the airfoil. The exemplary polymeric members  254  and  256  are heat bonded to their associated metallic members  250  and  252 .  FIGS. 2 and 6  further show a pair of pins  280  press fit in bores  282  in the polymeric member  256  and slidingly extending into bores  284  in the mating polymeric member  254 . The pins  280  serve an alignment function. As the jaw  52  is driven in the direction  512 , there is a degree of float in the mounting of the block  102  to the screw  94 . Engagement of the pins  280  with the bores  284  provides proper alignment of the two jaws  50  and  52  as the jaws are closed around the blade.  
         [0027]     In operation, the fixture is installed to the base and remains fixed. To mark a blade, the operator installs the jaws for that blade if they are not already installed. The operator then inserts the blade and clamps the jaws. The operator then orients the desired marking site in the marking orientation. The operator then manually or semi-manually brings the head to the correct height (e.g., so that the tip is at the appropriate height). In this height the tip may be slightly above the marking site, height but has a reciprocal range of motion effective to provide the indentation. Then, under automatic control, the marker provides the desired marking. This may involve motors in the head moving the tip to a given location along the site, indenting to provide a first indentation or pixel, moving the tip transversely to the location of the next pixel and so on.  
         [0028]     The use of an articulating fixture may have several advantages. First, for processing any given part configuration (e.g., a given blade) only a single pair of jaws are required. this may be distinguished from several fixtures for each part configuration. This reduction saves cost and changeover time. Furthermore, large scale processing may be facilitated. The parts may be installed to the associated jaw pairs without reference to which site on the part will ultimately be marked. Then the fixture may be articulated to bring the desired unmarked marking site into the proper position and orientation. The need to change fixtures for different parts is also reduced or eliminated.  
         [0029]     One or more embodiments of the present invention have been described. Nevertheless, it will be understood that various modifications may be made without departing from the spirit and scope of the invention. For example, details of the particular parts and the particular marking apparatus used may influence details of any particular implementation. Accordingly, other embodiments are within the scope of the following claims.