Abstract:
A method for performing operations on a workpiece. The method comprises the steps of: contacting the workpiece with a tool; moving the tool along any of multiple axes; moving a clamp along at least a first axis independent of the movement of the tool; and, clamping the workpiece using the clamp. Contacting the workpiece with the tool may comprise plunging a friction stir welding pin tool into the workpiece while the workpiece is being clamped. The tool may be moved by moving a spindle housing over the workpiece, and the clamp may be moved by rotating the clamp around the first axis as the spindle housing moves over the workpiece. The method may further comprise the step of coordinating the movement of the clamp with the movement of the tool.

Description:
This application is a divisional of application Ser. No. 11/771,188, filed Jun. 29, 2007, now U.S. Pat. No. 7,774,910, issued Aug. 17, 2010. 
     CROSS REFERENCE TO RELATED APPLICATIONS 
     This application claims the benefit of Provisional U.S. Patent Application No. 60/849,689 filed Oct. 5, 2006. 
    
    
     FIELD 
     This disclosure generally relates to manufacturing tools having integrated clamping fixtures, and deals more particularly with a tool having a workpiece clamp that can be moved along an axis independent of the direction of tool movement. 
     BACKGROUND 
     A variety of clamping devices are available for applying clamping force to a workpiece in an area near a manufacturing tool operating on the workpiece. The application of clamping forces near the manufacturing tool may reduce the need for complicated or cumbersome external clamping tools that may be needed in processes such as friction stir welding (FSW), to locate the parts being welded, prevent part separation during welding and react to process loads generated during the welding process. 
     One clamping device suitable for use with a FSW machine is disclosed in US Patent Application Publication Number 2005/0092817 published May 5, 2005, and assigned to The Boeing Company. In this prior patent application, the clamping device is mounted on a spindle head that carries the FSW tool. The clamping device is constrained to mechanically follow the path of the FSW tool spindle. The spindle head is mounted on a machine tool arm that moves along any of 3 orthogonal axes in which the weld path, and thus the movement of the clamping device, is straight. In some applications, however, complex curvatures of workpieces require more complicated movements of the FSW tool as well as the clamping device. In these more complicated workpiece geometries, the tool path may vary with the changing slope and contours of the workpiece. As a result, the clamping device may not always “track” with the FSW tool to apply clamping force when and where it is required. 
     Accordingly, there is a need for a workpiece clamping apparatus that is mounted on a common support with a tool, but yet can be moved independently of the tool so that clamping force can be applied at the desired workpiece locations regardless of the orientation of the tool or the support. It would also be desirable to provide a clamping apparatus and related method that coordinates the independent movement of the clamping device with movement of the tool. Embodiments of the disclosure are intended to satisfy these needs. 
     SUMMARY 
     Embodiments of the disclosure provide a clamping apparatus that may be mounted on a common support with a tool, such as a spindle housing, but which may be moved independently of the tool in order to closely follow the contour of a workpiece. The clamping apparatus may be mounted on a spindle housing for movement along at least one axis that is independent of the movement of the tool. The apparatus may include clamping rollers that roll along the surface of the workpiece in order to reduce friction, and apply programmable amounts of clamping force to the workpiece. 
     According to one disclosed embodiment, a manufacturing apparatus is provided, comprising: a spindle support moveable along multiple axes; a tool mounted on the spindle support for performing a manufacturing operation on the workpiece; and, a clamping assembly mounted on the spindle support for movement along at least one axis independent of the movement of the spindle. The clamping assembly includes clamping devices for applying clamping pressure to the workpiece. The clamping assembly may include a rotary drive mounted on the spindle support for rotating the clamping devices around the independent axis. The clamping devices may comprise clamping packs that include a clamping roller mounted on a pneumatically driven slide for applying a programmable amount of pressure to the workpiece. The rotary drive includes a stationary portion secured to the spindle support, and a rotating portion driven by a motorized gear drive. 
     According to another disclosed embodiment, apparatus is provided for performing operations on a workpiece, comprising: a tool assembly including a tool moveable along multiple axes; and a clamping assembly mounted on the tool assembly, the clamping assembly including at least one clamping device for applying clamping pressure to the workpiece, and means for mounting at least one clamping device for movement along at least a first axis independent of the movement of the tool. The tool assembly may include a spindle support and the mounting means may include a rotary mount for mounting at least one clamping device on the spindle support for rotation around the first axis. The mounting means may further include a slide assembly coupled with rotary mount for mounting the clamping device for movement along a second axis, toward and away from the workpiece. The rotary mount may include a stationary portion secured to the spindle, a rotatable portion, and a motorized drive for driving the second portion relative to the first portion. The motorized drive may include an electric motor and a gear drive coupling the motor with the rotatable portion of the rotary mount. The clamping device may include a roller clamp for engaging workpiece and means for biasing the roller clamp against the workpiece. The biasing means may comprise a fluid driven motor, such as a pneumatic cylinder. The clamping device may include a clamping pack and a releasable connection for releasably securing the clamping pack on the mounting means, thereby permitting the use of interchangeable clamping elements. 
     According to a method embodiment, manufacturing operations are performed on a workpiece, comprising the steps of: contacting the workpiece with a tool; moving the tool along any of multiple axes; moving a clamp along at least a first axis independent of the movement of the tool; and, clamping the workpiece using the clamp. Contacting the workpiece with the tool may comprise plunging a friction stir welding pin tool into the workpiece while the workpiece is being clamped. The tool may be moved by moving a spindle housing over the workpiece, and the clamp may be moved by rotating the clamp around the first axis as the spindle housing moves over the workpiece. The method may further comprise the step of coordinating the movement of the clamp with the movement of the tool. 
     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 functional block diagram illustrating a friction-stir welding head assembly, including a clamping assembly according to an embodiment. 
         FIG. 1   a  is an isometric illustration of a friction-stir welding head assembly. 
         FIG. 2  is an isometric illustration of a friction-stir welding spindle housing and workpiece clamping apparatus according to one embodiment of the disclosure. 
         FIG. 3  is a sectional illustration taken along the line  3 - 3  in  FIG. 2 . 
         FIG. 4  is an enlarged illustration of the area designated as “FIG.  4 ” in  FIG. 2 . 
         FIG. 5  is an enlarged, sectional illustration of the area designated as “FIG.  5 ” in  FIG. 3 . 
         FIG. 6  is an exploded illustration of the FSW spindle and clamping apparatus shown in  FIG. 2 . 
         FIG. 7  is an enlarged illustration of the area designated as “FIG.  7 ” in  FIG. 6 . 
         FIG. 8  is a broad block diagram illustrating a system for performing manufacturing operations on a workpiece. 
         FIG. 9  is a block diagram illustrating a method for performing operations on a workpiece. 
         FIG. 10  is a flow diagram of aircraft production and service methodology. 
         FIG. 11  is a block diagram of an aircraft. 
     
    
    
     DETAILED DESCRIPTION 
     Referring first to  FIGS. 1-7 , a FSW head  10  ( FIG. 1   a ) includes a tool support comprising a spindle housing  12  pivotally mounted on a yolk  18  by a pair of mounting arms  24  received in pivots  16  on the yolk  18 . The mounting arms  24  form part of a saddle attachment  22  that may be secured to the spindle housing  12 . Arms  24  mount the spindle housing  12  for rotation about the “A” axis. 
     The spindle housing  12  may contain a dual spindle drive  15  configured to separately drive, advance and retract an FSW welding pin tool  46 , and a shoulder tool  48  concentrically surrounding the tip of the welding pin tool  46 . Mounting of the spindle housing  12  on the pivot  16  enables the angle of the spindle housing  12 , and thus that of the tools  46 ,  48  to be adjusted with respect to a workpiece  13  ( FIG. 1   a ). The spindle housing  12  may also be mounted on a track  22  ( FIG. 1   a ), permitting the tools  46 ,  48  to be advanced toward and away from the workpiece  13 . It should be noted here that while a FSW tool  46  and shoulder tool  48  have been illustrated, various other tools may be employed for performing operations on a workpiece  13  where clamping of the workpiece  13  may be necessary or desirable. 
     In order to clamp the workpiece  13  during an FSW welding operation, a clamping assembly generally indicated by the numeral  26  may be mounted on the spindle housing  12 . The clamping assembly  26  broadly comprises a stationary portion  28 , a rotatable portion  30 , and a pair of opposing roller clamp packs  44  disposed on opposite sides of the FSW tool  46 . The stationary portion  28  may surround the spindle housing  12  and includes a pair of brackets  28   a  respectively secured to the saddles  22 . The rotatable portion  30  may include a generally cylindrical housing  30   a  mounted, as by bearings (not shown) on the stationary portion  28  for rotation about an axis  60  that may be independent of the axes of movement of the FSW tool  46 , and shoulder tool  48 . Housing  30   a  may be also connected to the stationary portion  28  by a rack and pinion gear assembly  34  which may be driven by a motor  32  mounted on the stationary portion  28 . The motor  32  may comprise, for example, without limitation, an AC electric stepper motor including an incorporated encoder (not shown) that generates signals representing the rotational position of the housing  30   a  about the independent axis  60 . 
     The lower portion of the housing  30   a  may include a circumferential conduit  40  which may house electrical lines and pneumatic control lines (not shown). A ring shaped, removable plate  38  may be mounted on the bottom of the housing  30   a , as for example and without limitation, by screws to allow access to the conduit  40 . 
     A pair of downwardly depending, spaced apart flanges  42  may be secured to the bottom of the plate  38 , and provide a support for mounting the roller clamp packs  44 . Ball lock pins  58  releasably attach the roller clamp packs  44  on the flanges  42 . The ball lock pins  58  provide a quick release means of mounting the roller clamp packs  44  so that they may be easily removed and replaced with any of a variety of interchangeable clamping member configurations. 
     As best seen in  FIG. 7 , each of the roller clamp packs  44  may include a generally rectangular housing  50  in which a slide member  52  is mounted for confined sliding movement within housing  50  along an axis  62  that is inclined with respect to the central axis  60  of the FSW tool  46 . The movement of the slide member  52  along axis  62  may be independent of the axes of movement (not shown) of the FSW tool  46  and shoulder tool  48 . A bifurcated arm  54  may be secured to the bottom of the slide member  52 . A clamping roller  56  may be rotatably mounted on the bottom of each of the arms  54 . 
     It should be noted here that although a pair of opposing roller clamp packs  44  have been illustrated, fewer or a greater number of the roller clamp packs  44  may be employed, depending on the operation to be performed on the workpiece  13 . The housing  50  may include a pneumatic cylinder (not shown) which may be connected to drive the slide members  52  using pressurized air delivered from a source (not shown) to the roller clamp packs  54  via pneumatic connections  14  (see  FIGS. 4 ,  5  and  7 ). The delivery of this pressurized air to the roller clamp packs  44  causes slide members  52  to move downwardly, thereby extending the arm  54  until the clamping roller  56  engages the workpiece  13  and applies a controlled amount of clamping pressure to the workpiece  13 . 
     Referring now also to  FIG. 8 , the operations performed on the workpiece  13  by the FSW head  10 , including workpiece clamping, may be operated by a controller  70  which may comprise, without limitation, a programmed computer or PLC (programmable logic controller). Controller  70  may control a machine tool  72  that moves the FSW head  10 . Controller  70  may also control the operation of the FSW tools  46 ,  48  which performs the FSW welding operation on the workpiece  13 . 
     The controller  70  may further control a source of pressurized air, (not shown) as well as pneumatic logic (not shown). The pneumatic logic controls the roller clamp packs  48 , by controlling the pressure of the air supplied to the cylinders in the roller clamp packs  44 . The controlled air pressure regulates the amount of clamping pressure applied to the workpiece  13  by the clamping rollers  56 . The controller  70  may send control signals to the motor  32 , which may in turn control the rotational position of housing  30   a , and thus the rotational position of the clamping rollers  56  on the workpiece  13 . Controller  70  may coordinate the movement of the machine tool  72 , the operation of the FSW tool  46  and shoulder tool  48 , the rotational position of the clamping rollers  56  and the pressure applied to the workpiece  13  by the roller clamp packs  44 . 
     Attention is now also directed to  FIG. 9  which illustrates the basic steps of a method for performing manufacturing operations on a workpiece  13 . Beginning at step  74 , controller  70  issues control signals that result in movement of the spindle housing  12  into proximity to a target location on a workpiece  13 . Next, at step  76 , the controller  70  controls motor  32  to rotate the roller clamp packs  44  into position, following which the roller clamp packs  44  are actuated at  78 , causing clamping rollers  56  to apply clamping force to the workpiece  13 . 
     With the workpiece  13  having been clamped, the FSW tool  46  is plunged into the workpiece  13  as shown at step  80 . The FSW head  10  moves the tool  46  over the workpiece  13  as shown at step  82 . As the tool  46  is being moved through a pre-programmed path, the controller  70  coordinates movement of the roller clamp packs  44  around the independent axis  60  with movement of the tool  46 , as shown at step  84 . In order to coordinate these movements, motor  32  is controlled to rotate the rotatable portion  30  of the clamping assembly  26 , so that the clamping rollers  56  properly track movement of tool  46  and the contours of the workpiece  13 . If required, the air pressure applied to the roller clamp packs  44  is adjusted at step  88  so that the desired level of clamping force is maintained regardless of the position of the tool  46  on the workpiece  13 . When the FSW operation is ended at step  90 , the roller clamp packs  44  may be deactuated at step  92 , thereby unclamping the workpiece  13 . 
     Referring now to  FIGS. 10 and 11 , embodiments of the disclosure may be used in the context of an aircraft manufacturing and service method  94  as shown in  FIG. 10  and an aircraft  96  as shown in  FIG. 11 . During pre-production, exemplary method  94  may include specification and design  98  of the aircraft  96  and material procurement  100 . During production, component and subassembly manufacturing  102  and system integration  104  of the aircraft  96  takes place. Thereafter, the aircraft  96  may go through certification and delivery  106  in order to be placed in service  108 . While in service by a customer, the aircraft  96  is scheduled for routine maintenance and service  110  (which may also include modification, reconfiguration, refurbishment, and so on). 
     Each of the processes of method  94  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. 11 , the aircraft  96  produced by exemplary method  94  may include an airframe  112  with a plurality of systems  114  and an interior  116 . Examples of high-level systems  114  include one or more of a propulsion system  124 , an electrical system  118 , a hydraulic system  120 , and an environmental system  122 . 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  94 . For example, components or subassemblies corresponding to production process  102  may be fabricated or manufactured in a manner similar to components or subassemblies produced while the aircraft  96  is in service. Also, one or more apparatus embodiments, method embodiments, or a combination thereof may be utilized during the production stages  102  and  104 , for example, by substantially expediting assembly of or reducing the cost of an aircraft  96 . Similarly, one or more of apparatus embodiments, method embodiments, or a combination thereof may be utilized while the aircraft  96  is in service, for example and without limitation, to maintenance and service  110 . 
     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.