Abstract:
A tool-in-tool device driven by a single power spindle performs multiple operations on a workpiece. The device includes a first tool holder for holding a tool such as a drill, and a second tool holder surrounding mounted on the first tool holder. The second tool holder may hold a second tool such as clamp for clamping the drill to the workpiece, a guide bushing for guiding the drill and a chip breaker for breaking workpiece chips generated by a drilling operation. Multiple interchangeable bushings allow matching the bushing to the size of the drill.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application claims the benefit of Provisional U.S. Patent Application No. 60/849,669 filed Oct. 5, 2006 incorporated by reference in its entirety herein. 
    
    
     TECHNICAL FIELD 
     This disclosure generally relates to machining operations, and deals more particularly with a device and related method for performing clamping and machining operations on a workpiece using a coaxial spindle assembly. 
     BACKGROUND 
     A variety of tool holders are available for holding interchangeable tools used to perform machining operations on workpieces. In some cases, it may be necessary to perform multiple operations simultaneously, using more than one tool, such as clamping and drilling a workpiece. The desired drill is normally loaded into a tool holder which is driven by a rotating spindle, such as those found on multi-axis machining centers, and a separate clamping mechanism is used to clamp the drill to the workpiece and/or to clamp the workpiece to an underlying structure. Some clamping mechanisms may include portions that are required to be positioned between the tool holder and the workpiece, thus requiring a longer drill to reach the workpiece. However, drilling accuracy may suffer when using longer drills because of possible drill run-out and the reduced ability to maintain concentricity of the drill bit relative to target hole locations on the workpiece. 
     Accordingly, there is a need for a device and a related method that allows both clamping and machining of a workpiece that overcomes the problems discussed above. Embodiments of the disclosure are intended to satisfy this need. 
     SUMMARY 
     The disclosed embodiments provide a tool-in-tool device that allows multiple operations to be performed on a workpiece, such as clamping and drilling, using a coaxial spindle assembly. The spindle assembly includes a pair of tool holders coaxial arranged to perform coordinated clamping and drilling operations. In addition to a clamping assembly, one of the tool holders includes a guide bushing that both guides the drill to improve hole accuracy, and breaks up workpiece chips as they are created by the drilling operation. The bushing is replaceable with any of multiple, interchangeable bushings sized to match the drill or other tool used for a particular application. 
     According to one disclosed embodiment, a device for clamping and machining a workpiece device is provided comprising: a clamp for applying a clamping force to the workpiece; a first tool holder adapted to be coupled with a first drive spindle for holding the clamp; a tool passing through the first tool holder for performing machining operations on the workpiece; and a second tool holder adapted to be coupled with a second drive spindle for holding the tool. The first tool holder may include a bushing which guides a shaft of the first tool during a machining operation. The bushing may include a chip breaker for breaking workpiece chips generated by the machining operation. The bushing may be slideably mounted on the first workpiece holder and may be coupled with a spring for biasing a foot on the bushing to apply a clamping force to the workpiece. 
     According to another disclosed embodiment, a tool-in-tool device is provided for performing operations on a workpiece. The device comprises: a first tool for performing a first operation on the workpiece; a second tool for performing a second operation on the workpiece; a first tool holder for holding the first tool; and, a second tool holder for holding the second tool. The second tool passes through and is guided by the first tool holder. The first tool may include a clamp for clamping the device against the workpiece, and the second tool may include a drill for drilling a hole in the workpiece. The clamp may further include a foot for engaging the workpiece, a slide assembly slideably mounting the foot on the second tool holder, and a spring for biasing the foot against the workpiece. 
     According to a disclosed method embodiment, drilling a workpiece comprises the steps of: installing a drill in a first tool holder; installing a clamp in a second tool holder; coaxially feeding the first and second tool holders toward the workpiece; clamping the workpiece with the clamp; and, drilling the workpiece after the workpiece has been clamped. The step of feeding the tool holders may include: attaching the first and second tool holders to first and second coaxial spindles, respectively, and linearly displacing first and second coaxial spindles toward the workpiece. The method may further comprise the steps of biasing the clamp against the workpiece after the clamp engages the workpiece, and displacing the drill relative to the clamp after the clamp has engaged the workpiece. 
     The disclosed apparatus was developed with the Tool in tool concept in mind. A standard drill is clamped into the small (second) tool holder and a compliant spring loaded bushed clamp device is clamped into the first tool holder. The device is maneuvered to the surface of a part and overdriven by the machine controller in order push against and allow the spring device to engage and comply to the part surface. This clamp up is to hold the skin tightly against the substructure. The skin is held in place allowing for the drill pass. By tight clamping of the skin to the substructure, chips from the process, cannot migrate in between the skin and substructure. The drill is advanced through the part eliminating burrs between the two prices. 
     When drilling with the disclosed FSW system, the small tool holder is utilized in the Tool in Tool Concept which is the second tool. Because of the physical characteristics of the spindle, the second tool requires a longer drill bit which resides in the high speed section of the spindle. (100 to 8000 rpm) The shoulder tool or first tool can only attain a speed of 2000 rpm which may be inefficient for drilling aluminum. This system uses the force control of the machine and the clamp mechanism residing on the first tool to clamp the two work pieces (skin and structure) together. 
     The disclosed embodiment is a tool in tool based drill clamp concept that uses both holding fixtures in the coaxial FSW spindle design to secure skin to structure while concurrently drilling that structure in a one pass operation. The coaxial spindle design integrates the technological advances of the FSW machine and the force control loop to engage the skin with the structure clamp (first tool), assuring proper clamp pressure, before the drill pass (second tool). The force produced by the clamping device reduces the amount of chips that could otherwise migrate between the skin and the structure and the constant clamp-up pressure from the bushed clamp should improve concentricity. 
     The disclosed embodiment is a tool in tool based drill clamp that uses both holding fixtures in the coaxial FSW spindle design to secure skin to structure while concurrently drilling that structure in a one pass operation. The coaxial spindle integrates the technological advances of the FSW machine and the force control loop to engage the skin with the structure clamp (first tool), assuring proper clamp pressure, before the drill pass (second tool). 
     The disclosed apparatus utilizes the FSW machine coaxial spindle and the force control feature of the FSW system along with the two piece drill clamp apparatus to clamp to structure, sense load and drill structure minimizing run-out and improving drilled hole concentricity. 
     The disclosed apparatus allows the use of coaxial spindle features and the force loop to, drill concentric holes with the two set-up as opposed to a drill pass with the higher speed spindle only. The interchangeable bushings in the first tool reduces the predicted run-out of the drill pass for any drill required. If the second tool was used by itself the run-out would be more significant because of the extended lengths of the drill bits and the exclusion of the bushing feature. 
     Other features, benefits and advantages of the disclosed embodiments will become apparent from the following description of embodiments, when viewed in accordance with the attached drawings and appended claims. 
    
    
     
       BRIEF DESCRIPTION OF THE ILLUSTRATIONS 
         FIG. 1  is a block diagram illustration of a tool-in-tool device for performing clamping and drilling operations on a workpiece. 
         FIG. 2  is a perspective illustration of the tool-in-tool device. 
         FIG. 3  is an elevational illustration of the device shown in  FIG. 2 , during a drilling operation on a workpiece. 
         FIG. 4  is a sectional illustration taken along the line  4 - 4  in  FIG. 3 . 
         FIG. 5  is an exploded, sectional illustration of the tool holders and clamping assembly. 
         FIG. 6  is an enlarged sectional illustration of the clamping assembly. 
         FIG. 7  is a side illustration of the lower portion of the device immediately before contacting a workpiece to be drilled. 
         FIG. 8  is an illustration similar to  FIG. 7  but showing the workpiece having been clamped and the drill having penetrated the workpiece. 
         FIG. 9  illustrates in elevation, a slide tube forming part of the clamping assembly. 
         FIG. 10  is a sectional illustration taken along the line  10 - 10  in  FIG. 9 . 
         FIG. 11  is a sectional illustration taken along the line  11 - 11  in  FIG. 10 . 
         FIG. 12  is a plan illustration of a clamp member. 
         FIG. 13  illustrates one side of a tube body forming part of the clamping assembly, and the crescent shape members separated from the tube body. 
         FIG. 13   a  is an exploded, bottom plan illustration showing how the crescent shaped members attach to the ears on the tube body. 
         FIG. 14  illustrates another side of the tube body shown in  FIG. 13 . 
         FIG. 15  is a perspective illustration of a guide bushing forming part of the clamping assembly. 
         FIG. 16  illustrates one side of the guide bushing shown in  FIG. 15 . 
         FIG. 17  is a plan illustration of the guide bushing shown in  FIG. 16 . 
         FIG. 18  illustrates one side of a spacer body. 
         FIG. 19  illustrates the bottom of the spacer body shown in  FIG. 18 . 
         FIG. 20  illustrates the top of the spacer body shown in  FIG. 18 . 
         FIG. 21  illustrates the top of a clamping foot. 
         FIG. 22  illustrates one side of the clamping foot shown in  FIG. 21 . 
         FIG. 23  illustrates one end of the clamping foot shown in  FIG. 20 . 
         FIG. 24  is a block diagram illustration of a method for clamping and machining a workpiece according to a method embodiment of the disclosure. 
         FIG. 25  is a flow diagram of an aircraft production and service methodology. 
         FIG. 26  is a block diagram of an aircraft. 
     
    
    
     DETAILED DESCRIPTION 
     Referring first to  FIG. 1 , a tool-in-tool clamping and drilling device  30  is powered by a pair of drives  10 ,  12  through a pair of independent, coaxial spindles  24 ,  26 . Drive  10  displaces the spindle  24  linearly along a central axis  14  (see  FIGS. 4 and 5 ). The device  30  includes a first tool holder  32  which may hold any of various tools. In the illustrated example, tool holder  32  is adapted to hold a clamping assembly  38 . 
     Drive  12  powers spindle  26  to move linearly along the central axis  14 , and to rotate around axis  14 . A second tool holder  34  is coupled with the spindle  26 , and may hold any of various machine tools for performing machining operations. In the illustrated example, tool holder  34  holds a drill  36 . The drive  12  both rotates and feeds the drill  36  to perform drilling operations. The drives  10 ,  12  may form part of a machining center (not shown) for example and may include electric, hydraulic or pneumatic motors. In one exemplary application, the clamping and drilling device  30  may be used on a friction stir welding (FSW) machine (not shown) to drill holes into skins or substructures (not shown) for alignment and probing purposes. In the FSW application, the clamping and drilling device  30  may clamp up to and drill flat or contoured surfaces. 
     Referring now to all of the Figures, the first and second tool holders  32 ,  34  respectively, may perform coordinated clamping and drilling operations on a workpiece  100 . As will be discussed below in more detail, the tool holder  32  concentrically surrounds and is coaxial with tool holder  34 . As best seen in  FIGS. 4 and 5 , tool holder  34  includes a generally cylindrical body  40  having an upper end  35  configured to be coupled with spindle  24 . Tool holder  34  further includes a collet  42  having a central axial opening  37  for holding the shank  39  of a drill  36 . The drill  36  extends downwardly through a guide bushing  69  which functions to guide and stabilize the drill  36  during a drilling operation. 
     Tool holder  32  broadly includes a body  44  having a lower, tube-like extension  45  for holding a tool such as a clamping assembly  38 . The upper end of body  44  includes an opening  41  in which the lower portion of the tool holder  34  is disposed. A collar  43  is secured to the body  44  and defines a ring shaped receptacle  46  for receiving a ring shaped, second spindle  26 . The spindle  26  may be connected to the tool holder  32  by mating threads (not shown) between the second spindle  26  and the inside face of the collar  43 . The outer surface of the collar  43  may include splines  46   a  that form part of a connection between the spindle  26  and the collar  43 . The second spindle  26  displaces tool holder  32  linearly, in the direction of the arrows  28 , toward and away from the workpiece  100 , independent of the movement of second tool holder  34 . 
     Tool holder  32  includes a collet  47  held within the tubular extension  45  of the body  46 . A cylindrical sleeve  60  is held in the collet  47  and slideably receives the upper end of a cylindrical slide tube  48 . The slide tube  48  includes a pair of rectangular, opposing openings  54  that define upper and lower stops  56 ,  58 , respectively. The lower end of the slide tube  48  includes a through-hole  52  which functions as an access port, as will be described in more detail below. The lower end of the slide tube  48  includes an area of increased wall thickness  50  which defines an outer circumferential shoulder  50   a.    
     The sleeve  60  includes four circumferentially spaced openings  62  which allow a tool such as a spanner (not shown) to grip and twist the sleeve  60  in order to disassemble the clamping assembly  38 . The sleeve  60  is provided with a circumferential shoulder  64  having a pair of downwardly depending ears  66 . A pair of opposing, crescent shape members  68  are secured to the ears  66 , as by screws (not shown). Each of the members  68  includes an inwardly facing projection  68   a  which extends through one of the rectangular openings  54  in the slide tube  48 . The projections  68   a  function to engage the stops  56 ,  58  which limit the sliding movement of the slide tube  48  within the sleeve  60 . A biasing device, such as, without limitation, a Belleville washer  90  is sleeved over the slide tube  48  and is trapped between members  68  and the shoulder  50   a  on the slide tube  48 . The Belleville washer  90  biases the slide tube  48  to slide toward its extended position in which the projections  68   a  engage the upper stop  56  of the rectangular opening  54  in the slide tube  48 . 
     A spacer body  76  is secured to the bottom of the slide tube  48  and includes a central opening  78  for receiving the bottom end of the guide bushing  69 . A pair of workpiece engaging feet  80  are secured to the bottom of the spacer body by screws  92  ( FIG. 6 ). 
     As best seen in  FIGS. 16-17 , the guide bushing  69  has an interior diameter “d” closely matched to the diameter of the drill  36  so as to center the drill  36  and minimize run-out of the lower end of the drill  36 . The guide bushing  69  includes a shoulder  70  that engages a ledge  71  on the spacer body  76 . The bottom of the guide bushing  68  includes a plurality of circumferentially spaced, notch-like teeth  72  which function to break up accumulations of workpiece chips as they are generated by the drill  36 . 
     In use, a drill  36  is placed in the collet  42  of tool holder  34 , and a guide bushing  69  is installed in tool holder  32  that is sized to match the selected drill  36 . The drill  36  is rotated by power supplied to the spindle  24  by drive  12 . The guide bushing  68  guides the bottom end of the drill  36  so as to maintain its concentricity relative to a target location on the workpiece  100 . 
     The movement and operation of the spindles  24 ,  26  are independent of each other however, they may be coordinated under computer control. Normally, spindle  26  moves toward the workpiece  100  while spindle  24  remains retracted. As spindle  26  feeds the tool holder  32  toward the workpiece  100 , the foot  80  engages and presses against the workpiece  100 . Continued linear displacement of the spindle  26  (and thus the tool holder  32 ) results in the foot  80  engaging the workpiece  100 . 
     As the tool holder  32  continues to be displaced toward the workpiece  100 , the washer  90  yields to the displacement force applied by the spindle  26 , causing the slide tube  48  to slide within the sleeve  60  until the stop  56  is engaged by the projection  69  on member  68 , or the spindle  26  reaches a programmed stopping point. The pressure applied by the foot  80 , which is determined by the strength of the Belleville washer  90 , clamps the workpiece  100  against a structural member  102  or similar backing plate. With the workpiece  100  securely clamped, spindle  24  then begins linearly displacing tool holder  34  toward the workpiece  100  until the drill  36  contacts the target location where a drill hole is to be formed. Continued displacement of the spinning spindle  24  causes the drill  36  to penetrate the workpiece  100 , as the foot  80  continues to clamp and stabilize the workpiece  100  until the drilling operation is completed. 
     Workpiece chips (not shown) generated by the drilling operation move upwardly through the open interior of the spacer body  76  until they are engaged by the notch-like teeth  72  on the guide bushing  69 . The teeth  72  function to break up accumulations of the chips as they are generated, which allows the chips to be carried away by an air or fluid stream so that they do not clog or interfere with the drilling operation. Due to the fact that the workpiece is tightly clamped between the foot  80  and the structural member  102 , potential burrs around the drilled hole are reduced or eliminated, which might otherwise occur if workpiece  100  and structural member  102  are not tightly clamped together. Moreover, tight clamping of the workpiece  100  to the structural member  102  assures that workpiece chips and other cutting debris do not enter and become lodged between the workpiece  100  and the structural member  102 . 
     In order to further facilitate chip removal during a drilling operation, fluid or air may be supplied to the drill  36  through the access port  52 . Alternatively, a vacuum may be connected to the access port  52  in order to vacuum away cutting debris. The access port  52  also permits visually inspection of the drill  36  during a drilling operation. 
     After a hole has been drilled, spindle  24  is linearly retracted until the drill  36  disengages the workpiece  100 . When the drill  36  has cleared the workpiece  100 , spindle  26  then begins linearly retracting, causing tool holder  32  to move away from the workpiece  100 . As the tool holder  32  moves away from the workpiece  100 , the Belleville washer  90  continues to bias the foot  80  into engagement with the workpiece  100  to maintain clamping pressure until the clamping assembly  38  reaches the end of its travel where stop  58  is engaged. 
     In order to switch to a different size of the drill  36 , the current drill  36  is released from the collet  42 , and a spanner or other wrench (not shown) is inserted into the openings  62  in order to unscrew the clamping assembly  38  so that a guide bushing  69  matching the size of the new drill  36  can be installed. 
     Attention is now directed to  FIG. 24 , wherein the overall steps of a method embodiment are illustrated. Beginning at step  104 , a drill  36  of the desired size is installed in the second tool holder  34 . Next, at step  106 , a bushing  69  is installed in the first tool holder  32  that has an internal diameter matching the size of the selected drill  36 . Then, at step  108 , the first tool holder  32  is displaced by the spindle  26  toward the workpiece  100 , resulting in the workpiece  100  being securely clamped to a structural member  102 , as shown at step  110 . Movement of the first spindle  26  is stopped at step  112  when the workpiece  100  has been clamped. 
     With the workpiece  100  securely clamped, the second tool holder  34  is fed by spindle  24  toward the clamped workpiece  100 , as shown at step  114 . As the tool holder  34  is being advanced toward the workpiece  100 , the spindle  24  is activated, causing the drill  36  to rotate. As the spindle  24  continues to displace the tool holder  34 , the drill  36  is fed into the clamped workpiece  100  resulting in a hole being drilled at step  118 . 
     When the hole has been fully drilled, spindle  24  begins linearly retracting, thereby moving the second tool holder  34  and drill  36  away from the workpiece  100 . When the drill  36  has cleared the workpiece  100 , rotation of spindle  24  may be terminated, as shown at step  122 . As soon as the drill  36  has cleared the workpiece  100  during the retraction stroke, the first tool holder  32  may commence retraction at step  124 , thereby unclamping the workpiece  100 , as shown at step  126 . 
     Finally, with a hole having been drilled in the workpiece  100  at the target location, spindles  24  and  26  can be moved along with their respective tool holders  32 ,  34  to the next target hole location. 
     The embodiments of the disclosure described above may be used in an aircraft manufacturing and service method  130  as shown in  FIG. 25  and an aircraft  160  as shown in  FIG. 26 . During pre-production, exemplary method  130  may include specification and design  132  of the aircraft  160  and material procurement  134 . During production, component and subassembly manufacturing  136  and system integration  138  of the aircraft  106  takes place. Thereafter, the aircraft  160  may go through certification and delivery  140  in order to be placed in service  142  While in service by a customer, the aircraft  160  is scheduled for routine maintenance and service  144  (which may include modification, reconfiguration, refurbishment, and so on). 
     Each of the processes of method  130  may be performed or carried out by a system integrator, a third party, and/or an operator (e.g., a customer). For the purposes of this description, a system integrator may include without limitation any number of aircraft manufacturers and major-system subcontractors; a third party may include without limitation any number of venders, subcontractors, and suppliers; and an operator may be an airline, leasing company, military entity, service organization, and so on. 
     As shown in  FIG. 26 , the aircraft  160  produced by exemplary method  130  may include an airframe  146  with a plurality of systems  148  and an interior  150 . Examples of high-level systems  148  include one or more of a propulsion system  152 , an electrical system  154 , a hydraulic system  156 , and an environmental system  158 . Any number of other systems may be included. Although an aerospace example is shown, the principles of the invention may be applied to other industries, such as the automotive industry. 
     Apparatus and methods embodied herein may be employed during any one or more of the stages of the production and service method  130 . For example, components or subassemblies corresponding to production process  136  may be fabricated or manufactured in a manner similar to components or subassemblies produced while the aircraft  160  is in service. Also, one or more apparatus embodiments, method embodiments, or a combination thereof may be utilized during the production stages  136  and  138 , for example, by substantially expediting assembly of or reducing the cost of an aircraft  160 . Similarly, one or more of apparatus embodiments, method embodiments, or a combination thereof may be utilized while the aircraft  160  is in service, for example and without limitation, to maintenance and service  144 . 
     Although the embodiments of this disclosure have been described with respect to certain exemplary embodiments, it is to be understood that the specific embodiments are for purposes of illustration and not limitation, as other variations will occur to those of skill in the art.