Abstract:
A workholding apparatus including a body and a drive member carried by the body, so that the drive member and body partially define a fluid chamber therebetween for containing a fluid. The drive member includes an annular flange that axially abuts and that attaches to the body to resist torsional twisting of the drive member relative to the body. A driven member is also carried by the body and includes multiple displacement reliefs therein. Interengagement features are provided between the driven member and other components of the workholding apparatus, such as the drive member, to resist torsional twisting of the driven member.

Description:
FIELD OF THE INVENTION  
       [0001]     This invention relates generally to machine tools and more particularly to hydrostatic workpiece holders.  
       BACKGROUND OF THE INVENTION  
       [0002]     Various hydrostatic workpiece holders are known, such as that disclosed in U.S. Pat. No. 6,015,154, which has one or more chambers containing a fluid which, when pressurized, displace one or more polymeric rings which in turn displace one or more metal sleeves into engagement with a workpiece. While such hydrostatic tool holders are effective and reliable under most conditions, the performance and durability can be improved upon for high performance applications.  
       SUMMARY OF THE INVENTION  
       [0003]     In some high performance applications, a more robust workpiece holder is required because cutting tool forces are abnormally high due to the extreme hardness of the workpiece material. The more robust workpiece holder should have a collet with interengagement features that resist twisting of the collet under such conditions.  
         [0004]     A workholding apparatus, such as an arbor, includes a body and a drive member carried by the body, so that the drive member and body partially define a fluid chamber therebetween for containing a pressurized fluid. A driven member is likewise carried by the body, and includes a displacement relief therein. In an exemplary embodiment, the driven member is disposed about the exterior of the body so that the pressure or force of the pressurized fluid in the fluid chamber acts radially outwardly on the driven member to displace or expand the driven member into engagement with the inner surface of a workpiece. In any case, the force of the pressurized fluid is transferred through the drive member to displace the driven member. Uniquely, the driven member is equipped with interengagement features that serve to fix the driven member to another relatively fixed member of the workpiece holder to resist or prevent twisting of the driven member under high torsional loads due to high cutting forces. It is contemplated that the principles of the exemplary embodiment apply equally well to a chuck-type workpiece holder.  
         [0005]     Objects, features, and advantages of this invention include providing a workpiece holder which has a driven member that is interengaged to other relatively fixed members of the workpiece holder, is resistant to twisting, can be used to firmly hold and locate workpieces composed of exceptionally hard material that undergo exceptionally high cutting forces, provides a better finish of the machined workpiece, repeatably and reliably holds and locates workpieces, reliably centers each workpiece, can be displaced generally radially inwardly or radially outwardly, and is of relatively simple design and economical manufacture and assembly and has a relatively longer useful life in service. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0006]     These and other objects, features and advantages of this invention will be apparent from the following detailed description of the preferred embodiments and best mode, appended claims, and accompanying drawings in which:  
         [0007]      FIG. 1  is a cross-sectional view of an arbor embodying the present invention;  
         [0008]      FIG. 2  is an end view of the arbor of  FIG. 1 ;  
         [0009]      FIG. 3  is an enlarged view of a portion  3 - 3  of the arbor of  FIG. 2 ;  
         [0010]      FIG. 4  is a cross-sectional view of an arbor according to an alternative embodiment of the present invention;  
         [0011]      FIG. 5  is an end view of an arbor according to another alternative embodiment of the present invention;  
         [0012]      FIG. 6  is a cross-sectional view of an arbor according to an alternative embodiment of the present invention;  
         [0013]      FIG. 7  is an end view of the arbor of  FIG. 6 ;  
         [0014]      FIG. 8  is a cross-sectional view of an arbor according to an alternative embodiment of the present invention; and  
         [0015]      FIG. 9  is an end view of the arbor of  FIG. 8 . 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0016]     Referring in detail to the drawings,  FIG. 1  illustrates a hydrostatic workpiece holder, and more specifically, a hydrostatic arbor  10  for holding a workpiece W. The arbor  10  includes a body  12  having a cylindrical shaft or mandrel portion  14  and a radially extending mounting flange portion  16 . The body  12  includes a main fluid passage  22  and branch fluid passages  24 ,  26  that are constructed to be filled with a pressurized fluid. As is well known in the art, the main fluid passage  22  is supplied with pressurized fluid from a remote pump (not shown). An external annular recess  28  in an outer surface  30  of the mandrel portion  14  of the body  12  partially defines a fluid chamber  32  that is sealed by resilient polymeric rings  34 , such as O-rings, that are disposed within annular grooves  36  in the mandrel portion  14 .  
         [0017]     A circumferentially continuous expansible sleeve or diaphragm  38  is adjacent to and circumscribes the mandrel portion  14  of the body  12  and thereby partially defines the fluid chamber  32 . The diaphragm  38  includes an inner cylindrical surface  40  that cooperates with the outer surface  30  of the mandrel portion  14  of the body  12  and further includes an oppositely disposed outer cylindrical surface  42 . The diaphragm  38  may be manufactured by injection molding, machined from a solid block, and the like, and may be composed of a polymeric material such as Delrin®, Nylon®, polyurethane, or the like. In any case, the diaphragm  38  is composed of any material that permits radially outward displacement of a mid-section  44  of the diaphragm  38  under the fluid pressure force acting thereon, yet enables the diaphragm  38  to retain surface contact with the polymeric rings  34 . An annular flange  46  is integrally provided on the diaphragm. The annular flange  46  axially abuts a stepped portion  48  of the body  12  and is fastened thereto by countersink screws  50 . Accordingly, the annular flange  46  prevents or at least resists torsional twisting of the diaphragm  38  relative to other components and provides a rigid foundation for mounting other components thereto.  
         [0018]     A stepped ring  52  radially circumscribes a rearward portion of the diaphragm  38  and is provided for rigidly trapping the diaphragm  38  to the body  12  to resist blowout or leakage of fluid therebetween. The stepped ring  52  is rigidly secured to the body  12  by a stop ring  54  and cap screws  56  as shown.  
         [0019]     A split sleeve or collet  58  is adjacent to and circumscribes the diaphragm  38 . Accordingly, the collet  58  and diaphragm  38  are in a relatively lapped relationship. The collet  58  includes an inner surface  60  that engages the outer surface  42  of the diaphragm  38 . The collet  58  further includes an oppositely disposed outer surface  62  and is generally tubular or cylindrical in shape. As shown in  FIG. 3 , the collet  58  includes a plurality of circumferentially spaced and longitudinally extending through slots or displacement reliefs  64  formed therein such as by milling or electro-discharge machining. The reliefs  64  are formed into a free end  66  of the collet  58  and are bounded by bearing sections  68  as shown, as is well known in the art of collet design. The reliefs  64  sufficiently weaken the collet  58  for facilitating radial displacement of at least the bearing sections  68  of the collet  58 . The collet  58  may be composed of a metal such as hardened SAE 4130 or any other suitable metal. Nevertheless, the collet  58  is composed of a material and constructed in a manner to permit outward radial displacement thereof. In any case, a predefined number of axially extending slots  70  are provided through respective bearing sections  68  of the collet  58 .  
         [0020]     Likewise, a predefined number of interengagement elements or drive pins  72  extend radially through the slots  70  and radially into radial holes  74  of the annular flange  46  of the diaphragm  38 , as shown most clearly in  FIG. 1 . The slots  70  are elongated in an axial or longitudinal direction with respect to the longitudinal axis of the arbor  10 . Accordingly, the bearing sections  68  are restrained from displacement in a circumferential direction, but are somewhat free to move in an axial direction. Such a configuration accommodates the normal displacement action of a collet  58 , and prevents the collet  58  from binding. Preferably, the number of slots  70 , drive pins  72 , and holes  74  is twenty-four, but any reasonable number will suffice. The interconnection or interengagement of the collet  58  to the diaphragm  38  serves to substantially resist or prevent the collet  58  from twisting relative to the diaphragm  38 . Absent such an interengagement element, the collet  58  will twist relative to the diaphragm  38  under high-load conditions such as when using the arbor  10  in the machining of extremely rigid or hard workpieces.  
         [0021]     In assembly, the polymeric rings  34  are stretched over the mandrel portion  14  of the body  12  and positioned into the annular grooves  36 , as shown in  FIG. 1 . The diaphragm  38  is then telescoped or assembled coaxially over the end of the mandrel portion  14  into axial abutment with the flange portion  16  of the body  12  and in circumferential sealing engagement with the resilient polymeric rings  34  to compress the rings  34  and seal the fluid chamber  32 . The annular flange  46  of the diaphragm  38  abuts the stepped portion  48  of the mandrel portion  14  of the body  12  and is attached thereto, such as by the screws  50 , but may otherwise be attached in any other manner. The stepped ring  52  is then assembled over the diaphragm  38  and located against the flange  16  of the body  12 . The collet  58  is then assembled over the diaphragm  38  into abutment with the stepped ring  52 . The drive pins  72  are then inserted through the collet  58  and preferably press fit into the diaphragm  38 , such that the drive pins  72  are recessed below the outer surface  62  of the collet  58 . The stop ring  54  is then assembled over the above-mentioned components and fastened to the flange  16  of the body  12  by the cap screws  56 . Accordingly, the mandrel portion  14  of the body  12  carries thereon the various assembled components described above to constitute the arbor  10 .  
         [0022]     In use, the workpiece W is disposed over the outer surface  62  of the collet  58  until the workpiece W axially engages a portion of the stop ring  54 . The workpiece W may be a cast iron sleeve, a gear blank, or any other workpiece suitable for mounting on an arbor. In the machining of rigid and hard workpieces, such as those made from INCONEL and other hard materials, the workpieces often undergo substantially high cutting forces, such that workpieces tend to twist or spin on conventional arbors. This is because collets, or bearing sections thereof, circumferentially flex under the strain of the high cutting forces and, thus, tend to release their hold on the workpieces. Thus, the interengagement configurations of the present invention are required to firmly hold and accurately locate such workpieces on the arbor  10 .  
         [0023]     To firmly hold the workpiece W on the arbor  10 , fluid under pressure is provided from an external or internal source through the main fluid passage  22  and branch fluid passages  24 ,  26  and into the fluid chamber  32 . The force of the pressurized fluid radially outwardly displaces the resilient diaphragm  38  which firmly engages and radially outwardly displaces the collet  58  to urge the collet  58  into firm engagement with an inner surface of the workpiece W to firmly hold and accurately locate the workpiece W for machining operations to be performed thereon. To remove the workpiece W after machining operations, the pressure of the fluid supplied to the fluid chamber  32  is decreased, thereby decreasing the pressure of the fluid in the fluid chamber  32  to thereby relax the diaphragm  38  and collet  58 . Thus, the diaphragm  38  acts as a drive member to radially outwardly urge a driven member (collet  58 ) into engagement with the workpiece W.  
         [0024]     Referring now to a second embodiment,  FIG. 4  illustrates a hydrostatic workpiece holder, and more specifically, a hydrostatic arbor  110 . The arbor  110  is similar to the embodiment of  FIGS. 1 through 3  except for the interengagement structure between a diaphragm  138  and a collet  158 . Accordingly, for brevity and clarity, details in common between the two embodiments will be omitted from further discussion of the arbor  110 . The diaphragm  138  includes a threaded outer surface  142 , while the collet  158  includes a threaded inner surface  160  that threadingly engages the outer surface  142  of the diaphragm  138 . The assembly of the arbor  110  is largely the same as the previous embodiment with one exception. The collet  158  is threaded onto the diaphragm  138  in a circumferential direction that is the same as the circumferential direction of the cutting forces acting on the workpiece W or, in other words, in a circumferential direction that is opposite of the rotation of the arbor  110  and workpiece W under cutting conditions.  
         [0025]      FIG. 5  illustrates a third embodiment of a hydrostatic arbor  210 . Again, the arbor  210  is similar to the arbor  10  embodiment of  FIGS. 1 through 3  except for the interengagement structure between a diaphragm  238  and a collet  258 . The diaphragm  238  includes a splined outer surface  242 , while the collet  258  includes a complementary splined inner surface  260  that interengages the outer surface  242  of the diaphragm  238 . The assembly of the arbor  210  is essentially the same as the first embodiment.  
         [0026]      FIGS. 6 and 7  illustrate a fourth embodiment of a hydrostatic arbor  310 . The arbor  310  is similar to the first embodiment of  FIGS. 1 through 3 , except that a stepped ring  352  and a collet  358  are provided with an equidistantly spaced plurality of holes  353  and  359  therein and therethrough respectively. Also, a plurality of interengagement elements or drive pins  372  are slidably received within the holes  359  and preferably press fit into the holes  353 , thereby affixing the collet  358  relative to the stepped ring  352  to resist twisting of the collet  358 . The assembly of the arbor  310  is similar to the first embodiment, except that it may be desirable to sub-assemble the stepped ring  352 , drive pins  372 , and collet  358 , and then slide the resultant sub-assembly over the diaphragm  38 .  
         [0027]      FIGS. 8 and 9  illustrate a fifth embodiment of an arbor  410  that is similar to the previously described embodiment. In this embodiment, however, a nose piece  480  is attached to the body  12 . Again, the stepped ring  352  and collet  358  are provided with an equidistantly spaced plurality of holes  353  and  359  therein and therethrough respectively. Also, a plurality of interengagement elements or drive pins  472  are received within the holes  359  and preferably press fit into the holes  353  to fix the collet  358  relative to the stepped ring  352 , and thereby resist twisting of the collet  358 . The nose piece  480  is also provided with a plurality of holes  482  into which the drive pins  472  extend for additional support and resistance against twisting of the collet  358 . The nose piece  480  is attached to the body  12  by a plurality of equidistantly spaced cap screws  484 , which have a bolt pattern that is clocked with respect to the bolt pattern of countersink screws  50 . The assembly of the arbor  410  is similar to the previously described embodiment, wherein it may be desirable to sub-assemble the stepped ring  352 , drive pins  472 , and collet  358  and then slide the resultant sub-assembly over the diaphragm  38 . Subsequently, the nose piece  480  is assembled to the body  12  such that the drive pins  472  align with and insert into the holes  482 . Then the cap screws  484  are fastened through the nose piece  480  and into the body  12 . The nose piece  480  has an outer diameter  486  that is slightly smaller than the outer diameter  362  of the collet  358 , whereby the nose piece  480  acts as an assembly aid to facilitate the quick and reliable location of the workpiece W to the arbor  410 .  
         [0028]     The drive pin and hole interengagement features of the above-described embodiments need not involve individual components that are separately assembled to the arbor. Rather, the drive pins and holes can be integrated into one or more of the collet, stepped ring, diaphragm, and nose piece. For example, such integrated drive pins could take the form of tab and slot, or tongue and groove configurations. More specifically, the collet could be provided with castellations formed in one or both axial end thereof that interengages with similar castellations formed in the stepped ring, diaphragm, and/or nose piece. In any case, the drive pin or interengagement element designs of the above described arbor embodiments add a unique and unobvious feature to the art of workpiece holders. Under high performance applications where a workpiece undergoes abnormally high cutting forces, the interengagement concept of the present invention provides a simple, inexpensive, and effective way to resist or prevent the collet from twisting and failing to hold the workpiece, and thereby bolsters the maximum clamping or gripping force of the arbor. Accordingly, the arbor will achieve longer tool life and can handle extremely high cutting force conditions to provide greater holding power without twisting and failure of the collet.  
         [0029]     While the forms of the invention herein disclosed constitute a presently preferred embodiment, many others are possible. It is not intended herein to mention all the possible equivalent forms or ramification of the invention. It is understood that terms used herein are merely descriptive, rather than limiting, and that various changes may be made without departing from the spirit or scope of the invention.