Patent Abstract:
A reconfigurable clamping system is disclosed. An example clamping system for securing a workpiece comprises a retention assembly and an inflatable bladder. The retention assembly comprises a plurality of links, each pair of adjacent links having a pivotal connection to enable the retention assembly to be configured to the general shape of a workpiece, and each pair of adjacent links having a locking mechanism to selectively lock an angular relationship between the pair. The inflatable bladder is coupled between the retention assembly and the workpiece and is to apply a clamping force to the workpiece.

Full Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This patent arises from a continuation of U.S. patent application Ser. No. 11/764,304, filed Jun. 18, 2007, and claims the benefit of Provisional U.S. Patent Application Ser. No. 60/849,688, filed Oct. 5, 2006, the entireties of which are incorporated by reference herein. 
    
    
     TECHNICAL FIELD 
     This disclosure generally relates to systems for clamping workpieces, and deals more particularly with a clamping system that can be reconfigured to match the contours of workpieces having differing shapes. 
     BACKGROUND 
     Various types of known clamping systems may be used to hold workpieces during manufacturing operations such as machining, routing, cutting and welding. These systems may include combinations of toe-clamps, spring clamps, hold-down bars, constant mold-line bladder tools and set screws that are configured to clamp the workpiece to a base. For example, one such clamping system is disclosed in US Patent Application Publication No. US 2006/0237888 A1 owned by The Boeing Company in which an inflatable bladder is held against a workpiece by a rigid retaining bar fastened to a base. Inflation of the bladder applies a clamping force to the workpiece. 
     While clamping systems of the type described above provide satisfactory results, they may be limited in their use to workpieces having a particular configuration or surface contour. These clamping systems are often custom-made to match the configuration of the particular workpiece to be clamped, and thus may not be readily adaptable to clamp workpieces having other configurations. 
     Accordingly, there is a need for an adaptable clamping system that may be readily reconfigured for clamping workpieces having a variety of configurations, thereby avoiding the cost of fabricating clamping elements that are unique to a particular workpiece configuration. Illustrated embodiments of the disclosure are intended to satisfy this need. 
     SUMMARY 
     The disclosed embodiments provide a reconfigurable clamping system in which a flexible retention assembly can be reconfigured for use with any of multiple workpieces having differing feature configurations, or a single workpiece having varying surface contours. The retention assembly may be reconfigured easily and quickly without the need for special tools or clamping elements that are unique to a particular workpiece configuration. 
     According to one embodiment of the disclosure, a clamping system is provided for securing a workpiece comprising: a retention assembly that may be positioned over the workpiece, including a plurality of links; a pivotal connection between each of the links allowing the retention assembly to be configured to the general shape of the workpiece; and, an inflatable bladder positioned between the retention assembly and the workpiece for applying a clamping force to the workpiece. The links may be Z-shaped and arranged in overlapping, nested relationship with each other. A locking mechanism is provided for locking the configuration of the retention assembly to match the configuration of a particular workpiece. The locking mechanism may include spline gears on opposing faces of adjacent links, and fasteners which clench the gears together to lock the links in a desired configuration. A spring may be used between the links for biasing the opposing spline gears away from each other, to allow free rotation of the links during a reconfiguration process. A recess may be provided in the bottom of the links which forms a channel for holding the bladder assembly. 
     According to another disclosed embodiment, a reconfigurable clamping system is provided for securing a workpiece, comprising: a retention assembly reconfigurable to generally match the shape of differing workpieces; a locking device for locking the retention assembly in a desired configuration generally matching the shape of a workpiece; and, an inflatable bladder positioned between the retention assembly and the workpiece for applying a clamping force to the workpiece. The retention assembly may include a chain of pivotally connected links, and locking elements for locking the links against pivotal movement relative to each other. The locking device may include interlocking elements respectively on opposing faces of the links for locking the links against pivotal movement in order to fix the configuration of the retention assembly to match the configuration of a particular workpiece. 
     According to a method embodiment of the disclosure, clamping a workpiece during a manufacturing operation comprises the steps of: configuring a flexible retention assembly to generally match the shape of the workpiece; fixing the configuration of retention assembly to form a rigid retention assembly; bridging at least a portion of the workpiece with the rigid retention assembly; placing a bladder between the rigid retention assembly and the workpiece; and, inflating the bladder. The retention assembly is configured by placing a flexible chain of links over the workpiece to generally conform to the workpiece. The configuration of the retention assembly may be fixed by locking the position of the links relative to each other. The method may include reconfiguring the retention assembly to match the shape of multiple workpieces having differing contours or feature configurations. 
     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 an exploded, isometric illustration of a workpiece and a substructure on which the workpiece is to be clamped. 
         FIG. 1A  is a functional block diagram illustrating a clamping system for clamping the workpiece on the substructure. 
         FIG. 2  is a view similar to  FIG. 1  but showing the workpiece clamped on the support structure using the clamping system according to an embodiment of the disclosure. 
         FIG. 3  is an enlarged, perspective illustration of the reconfigurable clamping system shown in  FIG. 2 . 
         FIG. 4  is a cross sectional illustration of the clamping system, shown in relation to the workpiece and a tool. 
         FIG. 5  is a sectional illustration showing details of the clamping system. 
         FIG. 6  is a side illustration of a portion of one of the links, better depicting a spline gear. 
         FIG. 7  illustrates the bottom of one of the links, better showing a recess channel for retaining an inflatable bladder. 
         FIG. 8  is a block diagram illustration of a method for clamping a workpiece according to a method embodiment of the disclosure. 
         FIG. 9  is a flow diagram of an aircraft production and service method. 
         FIG. 10  is a block diagram of an aircraft. 
     
    
    
     DETAILED DESCRIPTION 
     Referring to  FIGS. 1-7 , the disclosed embodiments relate to a clamping system generally indicated at  20  for clamping a workpiece  10  on a substructure  12 . As shown in  FIG. 1A , the clamping assembly  20  broadly comprises a retention assembly  22  and an inflatable bladder  30  for applying a clamping force  17  the workpiece  10 . The retention assembly  22  includes a plurality of links  22  coupled together by pivotal connections  19 . The retention assembly  22  retains the inflatable bladder  30  in position over the workpiece  10 . Inflation of the inflatable bladder  30  results in the application of the clamping force  17  to the workpiece  10 . The substructure  12  applies a reactive force  21  to the workpiece  10 , causing the workpiece  10  to be clamped between the substructure  12  and the clamping assembly  20 . 
     In the illustrated embodiment, the workpiece  10  comprises a skin that is intended to be fastened, as by welding, to a substructure  12  that may form, for example, part of an aircraft. A series of spaced mounting post assemblies  16  are positioned on opposite sides of the substructure  12  and each include a mounting plate  18 . The mounting plates  18  have a common hole pattern allowing any of identical clamping assemblies  20  to be secured to the mounting post assemblies  16  using mounting blocks  23  and hold down fasteners  24 . An adjustment screw such as a set screw  25  may be used to adjust the attitude of the mounting blocks  23  on the plates  18 . Mounting post assemblies  16  along with the substructure  12  are supported on a common base  14 . 
     In the illustrated example, the workpiece  10  has a cross section that is generally bell shaped which changes in contour from the front to the rear, as viewed in  FIGS. 1 and 2 . For sake of simplicity, only a single clamping system  20  is shown in  FIG. 2 , however in practice it should be understood that a plurality of the clamping systems  20  may be employed to clamp the workpiece  10  to the substructure  12  along its length. In the embodiment illustrated in  FIGS. 1 and 2 , four clamping systems  20  may be used which bridge the width of the workpiece  10  and are respectively supported on the mounting post assemblies  16 . 
     The clamping system  20  may be employed to hold down a workpiece  10  during any of a variety of manufacturing operations such as machining, routing, cutting or welding. In the illustrated example, a tool  26  in the form of a friction stir welding (FSW) head is used to weld the skin  10  to the substructure  12 . As will be discussed later in more detail, the clamping system  20  may be readily reconfigured to clamp workpieces  10  having part features, configurations or surface contours other than those illustrated in the drawings. Moreover, a plurality of identical clamping systems  20  may be employed to hold down various areas of a particular workpiece  10  even though the surface contour of the workpiece  10  may vary over its surface. 
     The retention assembly  22  is pivotally connected to the mounting blocks  23 . The inflatable bladder  30  functions as a hold-down intensifier that holds and pushes the workpiece against the substructure  14 . When locked in a rigid, clamping position as described later herein, the retention assembly  22  generally conforms to the shape of the workpiece  10  and functions to retain the inflatable bladder  30  while the inflatable bladder  30  is inflated to apply clamping force to the workpiece  10 . The ends of the retention assembly  22  are secured to the mounting plates  18  by the mounting blocks  23  and hold down fasteners  24 . 
     The retention assembly  22  includes a chain of Z-shaped, pivotally connected links  28  arranged on overlapping, nested relationship. Each end of each of the links  28  includes a through-hole  48  (see  FIGS. 5-7 ) for receiving a fastener which may comprise a bolt  34  having a threaded end for receiving a nut  36 . The bolt  34  forms a pivotal connection between adjacent ones of the links  28 . Washers  38  may be provided to better distribute clamping forces to the links  28 . One end of each of the links  28  may include a counterbore recess  42  in order to recess the nut  36 . A spring  40 , which may be a Bellville washer or a spring washer for example, is sleeved over the bolt  34  and positioned between opposing faces  29  ( FIGS. 5 and 6 ) in order to normally bias the faces  29  away from each other. 
     The opposing faces  29  of the links  28  each include interlocking elements which may comprise circular spline gears  32  circumferentially arranged around the through-hole  48 . The spline gears  32  may be formed in the opposing faces  29  of the links  28  by machining, molding or other common fabrication techniques. The spline gears  32  provide radial features  50  which meshingly engage the corresponding features  50  on an opposing face  29  when the links are clenched together, so as to interlock the links  28  in a desired rotational position, allowing the links  28  to conform to the shape of the workpiece  10 . 
     As best seen in  FIGS. 4 ,  5  and  7 , each of the links  28  includes a recess  46  on the bottom side thereof facing the workpiece  10 . The recesses  46  in the links  28  collectively form a channel  52  that has a width “W” ( FIG. 7 ) and extends substantially the entire length of the retention assembly  22 . The inflatable bladder  30  is retained within the channel  52  and may include a flat rib  44  on the upper side thereof which engages the bottom of the links  28  and thereby better distributes force between the retention assembly  22  and the workpiece  10 . 
     In one particular embodiment, the inflatable bladder may comprise a silicon hose including NOMEX fiber manufactured by Presray Pneuma-seal of Pawling Engineered Products. The inflatable bladder  30  with NOMEX fiber retains approximately 80% of its strength at 400° F., permitting high temperature manufacturing operations to be undertaken on the workpiece  10  in close proximity to the retention assembly  22 . By way of example, but not limitation, in friction stir welding applications of approximately ⅛″ aluminum skin to an underlying substructure, the inflatable bladder  30  is suitably inflated to about between 10 and 80 psi. The friction stir welding tool  26  may then engage the workpiece  10  in the area immediately around the retention assembly  22  while the inflatable bladder  30  maintains clamping pressure on the workpiece  10 , despite the heat generated by the welding tool  26 . 
     Referring now to  FIG. 8 , a method of clamping a workpiece begins at step  54  in which the retention assembly  22  is bridged over the workpiece  10  so that the ends of the retention assembly  22  lie generally over the mounting plates  18 . At this stage, the links  28  freely pivot relative to each other as a result of the outward biasing force imposed by the springs  40  which force the spline gears  32  apart so that they are unlocked. Therefore, the retention assembly  22  is freely flexible and thus may conform to the surface configuration and contours of the workpiece  10 . The retention assembly  22  is configured at step  56  by manually manipulating the links  28  to conform to the surface contours of the workpiece  20 . 
     Next, at step  58 , the links  28  are locked in place by tightening the nuts  36 . Tightening of the nuts  36  draws adjacent links  28  together, bringing the opposing spline gears  32  into interlocking engagement which locks the links against pivotal movement. Tightening of the nut  36  effectively clenches the spline gears  32  together, against the biasing influence of the spring  40 . After tightening each of the nuts  36  for all of the links  28 , the retention assembly  22  becomes a rigid assembly having a shape generally matching that of the contour or configuration of the workpiece  10  in the area where the clamping assembly  20  has been installed. 
     With the retention assembly  22  having been configured, the inflatable bladder  30  is then installed within the channel  52 , between the retention assembly  22  and the workpiece  10 , as shown at step  60 . Next, at step  62 , the retention assembly  22  is secured to the mounting post assemblies  16  by fastening the mounting blocks  23  to the plates  18  using the hold down fasteners  24 . The inflatable bladder  30  is then inflated at step  64 , resulting in a clamping force being applied to the workpiece  10  as the retention assembly  22  holds and retains the inflatable bladder  30 . The retainer assembly  22  resists the load imposed by the inflatable bladder  30 , causing the inflatable bladder  30  to hold the workpiece  10  to the substructure  12 . The inflatable bladder  30  also makes up the gap between the retention assembly  22  and the workpiece  10  so that the retention assembly  22  tightly conforms to the contour of the workpiece  10 . 
     With the workpiece  10  securely clamped, any of various operations such as friction stir welding may be performed on the workpiece  10 , as shown in step  66 . When the operations on the workpiece  10  are complete, the inflatable bladder  30  is deflated at step  68  following which the retention assembly  22  is released from the base  14 , as shown in step  70 , by unfastening the mounting blocks  23  from the mounting plates  18 . Next, at step  72 , the links  28  are unlocked so that the retention assembly  22  may be later configured to hold a different workpiece  10 . This unlocking process comprises loosening (unscrewing) the nuts  36  until the springs  40  to force the opposing faces  29  apart, thereby unlocking the spline gears  32 . At this point, the retention assembly  22  is again freely flexible, allowing it to be reconfigured to match the contour of a new workpiece, as shown at step  74 . 
     The embodiments of the disclosure described above may be used in an aircraft manufacturing and service method  76  as shown in  FIG. 9  and an aircraft  106  as shown in  FIG. 10 . During pre-production, exemplary method  100  may include specification and design  78  of the aircraft  106  and material procurement  80  During production, component and subassembly manufacturing  82  and system integration  84  of the aircraft  106  takes place. Thereafter, the aircraft  106  may go through certification and delivery  86  in order to be placed in service  88 . While in service by a customer, the aircraft  106  is scheduled for routine maintenance and service  90  (which may include modification, reconfiguration, refurbishment, and so on). 
     Each of the processes of method  76  may be performed or carried out by a system integrator, a third party, and/or an operator (e.g., a customer), as indicated by the “X” in the grid to the right of the flow diagram of  FIG. 9 . 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. 10 , the aircraft  106  produced by exemplary method  76  may include an airframe  92  with a plurality of systems  94  and an interior  96 . Examples of high-level systems  94  include one or more of a propulsion system  98 , an electrical system  100 , a hydraulic system  102 , and an environmental system  104 . 
     Apparatus and methods embodied herein may be employed during any one or more of the stages of the production and service method  76 . For example, components or subassemblies corresponding to production process  82  may be fabricated or manufactured in a manner similar to components or subassemblies produced while the aircraft  106  is in service. Also, one or more apparatus embodiments, method embodiments, or a combination thereof may be utilized during the production stages  82  and  84 , for example, by substantially expediting assembly of or reducing the cost of an aircraft  106 . Similarly, one or more of apparatus embodiments, method embodiments, or a combination thereof may be utilized while the aircraft  106  is in service, for example and without limitation, to maintenance and service  90 . 
     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.

Technology Classification (CPC): 1