Abstract:
A method for locating a work piece for multiple treatment operations includes identifying six-point datum positions upon a work piece, defining six-point datum contacts on a work piece holder and securing said six-point datum positions upon said work piece into contact with said six-point datum contacts on said work piece holder. A work piece datum transfer apparatus includes a work piece shuttle having a six-point datum nest defining its position in three dimensions corresponding to a work piece six-point datum nest and means for locking said work piece shuttle into contact with said work piece shuttle to transfer said datum nest from said work piece to said shuttle.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     This invention relates generally to the field of tooling and systems for precision metalworking operations, and more particularly, to a datum transfer system to facilitate multiple precision metalworking steps to be performed on a work piece.  
         [0002]     Metalworking frequently involves precision machining of work pieces, often within tolerances of a few mils. (One mil is 0.001 of an inch, or 25 micrometers.) Essential prerequisites of precision machining include rigid support of the work piece and exact movement of the work piece during machining. In conventional metalworking practice, dedicated tooling to hold a particular work piece for each metalworking operation is provided. Such dedicated tooling must provide rigid support for the work piece.  
         [0003]     A metalworking operation can involve the machining of families of work pieces of the same general, proportional shape, but different in size and dimensions. Typically, a family of dedicated holding devices is required for a family of work piece members. While some parts in a work piece family can be very small, and the assorted dedicated tooling can be manipulated and carried by hand, other work pieces and their dedicated tooling can be much larger, requiring mechanical assistance (e.g., a crane) to lift, carry and position the dedicated tooling devices.  
         [0004]     Dedicated tooling is designed to hold one work piece family member in a precise location and position for a metalworking operation. The alignment of the dedicated tooling and the work piece it holds to the metalworking machine must be exact, and often requires significant setup time to ensure proper alignment with the metalworking machine. Achieving such alignment is a trial-and-error process, generally requiring repeating steps of tapping the tooling to move it a small distance, tightening the bolts used to secure it in place, and then checking the alignment using dial indicators or the like. The critical nature of this process typically requires attention by the most highly skilled workers in a manufacturing facility. Often, trial parts of the work piece must be test worked, with minute adjustments of the dedicated tooling to the worktable, to ensure the metalworking operation machines the work piece properly.  
         [0005]     When a metalworking facility needs to machine a variety of members of a work piece family, there can be significant amounts of production time lost in tooling changeover, in disassembling tooling used on the first work piece, retrieving the dedicated tooling for the next work piece, and then installing and aligning the retrieved dedicated tooling for each work piece to be worked. Changing the tooling from that required for one work piece to that required for another similar work piece is frequently a major factor in the cost for operating a metalworking facility, particularly when business conditions in the industry can necessitate small production lot sizes.  
         [0006]     In addition, to machine a family of work pieces that are similar in size but different in detail, equivalent families of dedicated tooling are often required to complete the manufacture. Because each set of dedicated tooling must accept and secure the work piece in generally two or more places for proper positioning and alignment, these dedicated tools can be complex and expensive.  
       BRIEF DESCRIPTION OF THE INVENTION  
       [0007]     One aspect of the present invention relates to an improved fixture for accurately positioning a work piece requiring precision machining, such as a turbine blade. A work piece support system includes locating a six-point datum on a work piece shuttle, locking supports for securing a work piece relative to the shuttle, and datum transfer arms for positioning the shuttle relative to a plurality of V-block work piece supports.  
         [0008]     Another aspect of the invention is a method for locating a work piece for multiple treatment operations. A work piece is secured in a shuttle in a particular orientation with respect to a six-point datum nest on the shuttle, and locked into position by spring loaded work supports.  
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0009]      FIG. 1  is a schematic illustration of one embodiment of a work piece mounting shuttle for providing a six-point datum nest and a work piece to be secured;  
         [0010]      FIG. 2  is a schematic illustration of a work piece having identified datum points for defining structure of the work piece for machining;  
         [0011]      FIG. 3  is a schematic illustration of work piece positioning features of the embodiment of a work piece shuttle of  FIG. 1 ;  
         [0012]      FIGS. 4 and 5  are schematic illustrations of a holding fixture showing a work piece in position to be secured for machining;  
         [0013]      FIG. 6  is a schematic illustration of a spring mounting assembly for maintaining a work piece in position during machining; and  
         [0014]      FIGS. 7 and 8  are schematic illustrations of features of one clamp arrangement for securing a work piece in position for machining while clamped in the datum nest. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0015]      FIG. 1  is a schematic illustration of one embodiment of a work piece holder  40  aligned with a work piece  10  to be machined, polished, finished or treated by other manufacturing techniques. Work piece holder  40  includes shuttle  50  and a pair of transfer arms  42 ,  44  having respective notches  46 ,  48  for engagement by clamping and transfer mechanisms and locator surfaces  47 ,  49  at the ends of respective transfer arms  42 ,  44 . The transfer arms  42 ,  44  extend through respective holes  14 ,  16  in a work piece ID pocket web  18  to engage the base (not shown) of a work piece holder.  
         [0016]      FIG. 2  is a schematic illustration of one embodiment of a work piece  10  having a six-point datum nest in an ID pocket  12  which includes a work piece six-point datum including datum positions  20 ,  22 ,  24 ,  26 ,  28  and  32  which together precisely define the work piece position in three dimensions in reference to a precision casting standard. ID pocket  10  includes ID pocket web  18  which contains datum positions  20 ,  22  and  24  which define a plane within work piece  10 . Vertical wall  30  of the ID pocket  12  includes two work piece datum positions  26 ,  28  which define a line  32  through work piece  10 , and end surface  38  of ID pocket  12  includes one datum position  34  of the cast work piece  10 . ID pocket  12  is located in a portion of the work piece  10  that requires no machining or finishing following casting of the work piece  10 . This allows a fixture to engage the work piece datum positions throughout all machining, finishing or other processes required to complete manufacturing of the work piece  10 , so that a single step of positioning and locking work piece  10  into holding fixtures is needed, thereby reducing set-up time and opportunity for introduction of errors in the fixturing.  
         [0017]      FIG. 3  is a schematic illustration of the work piece shuttle  50  which is designed and made to include datum contacts  52 ,  54 ,  56 ,  58 ,  60  and  64  which constitute a shuttle six-point datum nest which is a precise indicator of the position in three dimensions of work piece shuttle  50 . The datum contacts  56 ,  58  are located to engage work piece datum positions  26 ,  28 , respectively, datum contacts  52 ,  54  are located to engage work piece datum positions  20 ,  22 , respectively, datum contact  60  on projection  62  is located to engage datum position  24  and datum contact  64  on pin  66  which projects from end  68  of work piece shuttle  50  is located to engage datum position  34 . A tapered, spring-loaded lever  84  projects from the work piece shuttle  50  to contact end wall of one surface of hole  36  through ID pocket web  18 . When the six-point work piece datum positions are in secure contact with the respective work piece datum positions, the location of the shuttle  50  precisely defines the location of work piece  10 . Since the ID pocket  12  requires no machining or finishing, the work piece datum positions may be engaged throughout all machining and finishing of other surfaces. This avoids the possibility of introducing errors in machining or finishing the work piece due to variances in work piece holders.  
         [0018]      FIG. 4  is a schematic illustration of the work piece  10  in contact with work piece shuttle  50  and lever  84  to align the work piece  10  to ensure that the shuttle six-point datum nest accurately engages the work piece six-point datum positions. Transfer arm  42  has faces  43 ,  45  each shown at an angle of approximately forty-five degrees to the surface  53 , and transfer arm  42  has faces  55 ,  57  each shown at an angle of approximately forty-five degrees to the surface  59 .  FIG. 5  schematically illustrates the v-block locators  72 ,  74  in the support structure  76  that engage the respective angled surfaces  43 ,  45  and  55 ,  57  on the transfer arms  42 ,  44  to lock the work piece  10  against the work piece shuttle  50 . The specific angle of surfaces  43 ,  45  to surface  53  and of surfaces  55 ,  57  to surface  59  is not critical, so long as the transfer arms  42 ,  44  are centered with the respective v-block locators  72 ,  74 .  
         [0019]      FIG. 6  is a schematic partial illustration of the rod and spring arrangement which secures the work piece datum positions in engagement with the datum contacts on the work piece shuttle  50 . Rods  90 ,  92 ,  94 ,  96 ,  98  and  100  are spring loaded by springs  102 ,  104 ,  106 ,  108 ,  110  and  112  and held in position in holes in plates  114  and  116 . Springs  102 ,  104 ,  106 ,  108 ,  110  and  112  are placed against plate  118  to bias the rods  90 ,  92 ,  94 ,  96 ,  98  and  100  into contact with the work piece  10 , thereby locking work piece datum positions  20 ,  22 ,  24 ,  26 ,  28  and  32  into contact with shuttle datum contacts  52 ,  54 ,  56 ,  58 ,  60  and  64 , respectively. The rods  90 ,  92 ,  94 ,  96 ,  98  and  100  engage the work piece  10  outside and areas to be machined, finished or treated, facilitating the single loading of work piece  10 .  
         [0020]      FIG. 7  is a schematic elevation illustration of a work piece holder including hydraulic cylinders  120  which engage notches  122  to lock the shuttle transfer arms  42 ,  44  in the horizontal position in contact with the v-block locators shown in  FIG. 5 . Hydraulic cylinders  124  which engage notches  46 ,  48  to pull transfer arms  42 ,  44  down. Surface  47  of transfer arm  42  is pulled down to lock surface  47  into contact with curved end surface  126  on peg  128 , and surface  49  of transfer arm  44  is pulled into contact with a similar curved end surface of a peg (not shown) to secure shuttle transfer arms  42 ,  44  in the vertical direction.  FIG. 8  is a schematic plan view of a v-block locator member  78 . The v-block locator member  78  is moved into engagement with the transfer arms  42 ,  44  by hydraulic actuators  132 ,  134 ,  136 ,  138 ,  140  and  142  which move v-block locator member  78  generally perpendicular to the transfer arms  42 ,  44  to secure work piece  10  against the shuttle  50 .  
         [0021]     In operation an ID pocket  12  is defined in a work piece  10 . The ID pocket and the work piece datum positions within the ID pocket  12  may be secured to a shuttle  50  in a single mounting process, so that it will maintain its exact relationship and transfer the six-point work piece datum to a six point shuttle datum. In the particular process using the apparatus shown in  FIGS. 5-8 , the work piece  10  is loaded in shuttle  50  so that rods  90 ,  92 ,  94 ,  96 ,  98  and  100  loaded respectively by springs  102 ,  104 ,  106 ,  108 ,  110  and  112  locate each of the work piece datum positions  20 ,  22 ,  24 ,  26 ,  28  and  34  of the six-point datum nest to engage respective datum contacts  52 ,  54 ,  56 ,  58 ,  60  and  64  of the shuttle six-point datum nest. The transfer arms  42 ,  44  are drawn into a clamp mechanism and locked against the v-block locators  72 ,  74 . The work piece is now securely locked against the shuttle, and the machining apparatus may perform all grinding, finishing and other metal treatment processes on the surfaces of work piece  10  outside ID pocket  12  without requiring additional positioning and part locating steps. In this process, no sequential reloading of the work piece  10  into separate holding mechanisms is required, so no opportunity is allowed to introduce errors in mounting and securing the work piece  10  to the machining, finishing or other manufacturing apparatus. This represents a significant saving in time and complexity of work piece handling and avoids introduction of errors in multiple work piece handling steps.  
         [0022]     While the invention has been described in terms of various specific embodiments, those skilled in the art will recognize that the invention can be practiced with modification within the spirit and scope of the claims.