Abstract:
A load control mechanism for use with a pull type tool (also called a riveter), wherein the mechanism includes a telescopic housing and a compressible element, such as a polyurethane compression spring, which works to limit the ultimate load which is applied by the pull type tool during operation, such as during removal of a rivetless nut plate from a hole in parent material. Also provided is a method of removing a rivetless nut plate by using a pulling head which includes a shock absorber and load limiting device, a resetion cup and a mandrel. The load control mechanism provides that a riveter can be used to safely remove a rivetless nut plate without causing damage or undue wear on components of the tool. This load control mechanism also absorbs operating shocks, protecting expensive work parts (ex: aircraft structure) and the operator during operation, resulting in a safe and ergonomic operation.

Description:
RELATED APPLICATION 
   Priority Claim 
   This application claims the benefit of U.S. Provisional Application Ser. No. 60/745,107, file Apr. 19, 2006, which is hereby incorporated by reference in it entirety. 

   BACKGROUND 
   The present invention generally relates to pull type tools, and more specifically relates to a load control mechanism for pull type tools, such as a pull type tool for removing a rivetless nut plate. 
   Fasteners used in association with fluid tanks, such as fuel tanks or water tanks, for aircraft or the like present a problem in preventing leakage through the openings for the fasteners. Fasteners used in such installations may include a nut plate and a nut which are part of an assembly. There are many different design configurations of nut plates being used today. Two major classes are riveted nut plates and rivetless nut plates. 
   In riveted nut plates, two rivets are employed for attaching the body of the nut plate to the workpiece. To eliminate the potential for leakage, sealant is used between the structure and the nut plate. 
   With regard to rivetless nut plates, some designs provide that a sleeve is flared against a workpiece. One example of this type of rivetless nut plate is disclosed in U.S. Pat. No. 4,732,518, which is hereby incorporated herein by reference in its entirety. The &#39;518 patent illustrates the insertion of a sleeve inside a workpiece against heavy interference forces and then deformation of the sleeve to produce flaring of the end of the sleeve. The sleeve has a serration/lobe configuration thereon with the serration/lobe configuration being long and tapered such that the serrations/lobes extend into the walls of the workpiece. The tapered feature, length and specific geometry are necessary to make installation possible with the method of installation which was chosen for its application. The main object of the &#39;518 patent with its tapered and extended serration/lobe configuration was to enhance the fatigue life of the workpiece by distributing the load throughout the workpiece and providing expansion due to the insertion of the sleeve into the workpiece, and to cold work the material adjacent the perimeter of the workpiece aperture. 
   Other nut plate designs do not rely on flaring of the sleeve. U.S. Pat. Nos. 5,096,349, 5,245,743, 5,405,228 and pending U.S. application Ser. No. 10/272,721 (filed Oct. 17, 2002) and Ser. No. 10/929,701 (filed Aug. 30, 2004) disclose rivetless nut plate designs which do not rely on flaring of the sleeve, and these five items are hereby incorporated herein by reference in their entirety. While some rivetless nut plate designs rely on adhesive for attaching the nut plate to the structure, the designs disclosed in the five items cited above rely on heavily cold-worked holes and high interference engagement utilizing a hardened pin as the installation tool to expand a sleeve element into engagement with a workpiece structure. Because of high level expansion, the friction forces created are intended to retain the nut plate and provide expected mechanical properties. 
   Once installed, most rivetless nut plates are removed by drilling out the flared sleeve portion, or by drilling out the rivets while holding the nut plate. Drilling out the rivets and the sleeve from the holes requires a special skill. The procedure, aside from being cumbersome and time consuming, leaves behind contaminating metal chips. Additionally, it often enlarges the hole size requiring an oversized nut plate for replacement. Safety considerations, for drilling out the old nut plate, are required to prevent damage to surrounding structure and the operator. 
   U.S. patent application Ser. No. 11/218,076 discloses a plurality of tools which can be used to remove rivetless nut plates. Some of the designs disclosed in U.S. patent application Ser. No. 11/218,076 provide that a pull type power tool, such as a riveter, can be used to remove a rivetless nut plate. However, the actual working load necessary to complete the removal operation is much lower than the load provided by the riveter. Unfortunately, there is typically no way to control and limit the load that is applied. 
   Riveters are typically used to install break-stem fasteners. In such case, the load which is ultimately applied by the riveter during operation is effectively limited by the breakage of the stem at a certain load, thereby preventing the tool from overload. However, in applications where a riveter is not being used to install a break-stem fastener, such as where the riveter is being used to remove a rivetless nut plate, there is no such inherent load control feature, and there exists a critical need to control the working load in order to provide means for safe operation and prevent tool breakage. 
   While riveters are available in different power ratings, the load provided by the available selection of riveters is too high to be used to remove rivetless nut plates. The high load leads to overloading of the parent material (i.e., the workpiece in which the rivetless nut plate is installed), or certain tool components. It is disadvantageous to overload the tool during operation, as overloading will cause critical failure of the tool. 
   OBJECTS AND SUMMARY 
   An object of an embodiment of the present invention is to provide a load control mechanism for pull type tools. 
   Another object of an embodiment of the present invention is to provide a load control mechanism which provides that a riveter can be used to remove a rivetless nut plate without breaking a mandrel and without causing undue wear on components of the tool. 
   Briefly, and in accordance with at least one of the foregoing objects, an embodiment of the present invention provides a load control mechanism for use with a pull type tool, wherein the mechanism includes a telescopic housing and a compressible element, such as a polyurethane compression spring, which works to limit the ultimate load which is applied by the pull type tool during operation, such as during removal of a rivetless nut plate. As such, another aspect of the present invention provides a method of removing a rivetless nut plate by using a pulling head which includes a telescopic housing and a compressible element. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The organization and manner of the structure and operation of the invention, together with further objects and advantages thereof, may best be understood by reference to the following description, taken in connection with the accompanying drawings, wherein like reference numerals identify like elements in which: 
       FIG. 1  is cross-sectional view of an installed rivetless nut plate which needs to be removed; 
       FIG. 2  is an exploded perspective view of a pulling head which is in accordance with an embodiment of the present invention; 
       FIG. 3  is a view showing a mandrel being pushed through a reaction cup and through the middle of the rivetless nut plate of  FIG. 1 ; 
       FIG. 4  is a view showing the reaction cup being pushed against the workpiece; 
       FIG. 5  is a view showing the mandrel being inserted into the pulling head of  FIG. 2 ; 
       FIG. 6  is a view showing a front of the pulling head being inserted into the hole in which the rivetless nut plate is installed; 
       FIG. 7  is a view showing the riveter, to which the pulling head is attached, being actuated causing jaws of the pulling head to grip the mandrel; 
       FIG. 8  is a view showing the riveter being further actuated, causing a front of the pulling head to push the rivetless nut plate out of the hole, during which time a collapsible element of the pulling head is collapsing; 
       FIG. 9  is a view showing the riveter being further actuated, causing the front of the pulling head to push the rivetless nut plate completely out of the hole, during which time the collapsible element of the pulling head further collapses; 
       FIG. 10  is a view showing the pulling head after a trigger of the riveter has been released, causing a housing of the pulling head to retract to its initial position; 
       FIG. 11  is a view showing the pulling head at the end of the return, at which time the jaws of the pulling head release the mandrel; 
       FIG. 12  is a view showing the front of the pulling head being removed from the hole in which the rivetless nut plate was installed; 
       FIG. 13  shows the mandrel and the reaction cup being pulled away from the workpiece and rivetless nut plate; and 
       FIG. 14  shows the rivetless nut plate being discarded. 
   

   DESCRIPTION 
   While the present invention may be susceptible to embodiment in different forms, there is shown in the drawings, and herein will be described in detail, an embodiment thereof with the understanding that the present description is to be considered an exemplification of the principles of the invention and is not intended to limit the invention to that as illustrated and described herein. 
   One embodiment of the present invention provides a load control mechanism which can be used in association with pull type tools. For example, the load control mechanism can provide that a riveter can be used to remove a rivetless nut plate without breaking a mandrel and without causing undue wear on components of the tool. 
     FIG. 1  illustrates a rivetless nut plate  10  which is installed in a hole  12  in a workpiece (i.e., parent material)  14  and needs to be removed. The rivetless nut plate  10  may be as disclosed in U.S. application Ser. No. 10/272,721 (filed Oct. 17, 2002) and Ser. No. 10/929,701 (filed Aug. 30, 2004), both of which have been incorporated herein by reference in their entirety. 
     FIG. 2  illustrates a pulling head  16  which includes a load control mechanism which is in accordance with an embodiment of the present invention. The pulling head  16  is configured for use with a power tool (i.e., a pull type tool such as a riveter) such as described in U.S. Pat. No. 5,425,164, which is hereby incorporated herein by reference in its entirety. Such a tool is available from Textron as Hand Hydraulic Riveter Model G750A, and includes a housing and a piston for pulling. Alternatively, Textron&#39;s Lightweight CherryMax® Power Tool Model G704B may be used, or some other appropriate power tool. Operation of the pulling head  16  with regard to the power tool will be described in more detail hereinbelow. 
   As shown in  FIGS. 2 and 3 , the pulling head  16  includes a compressible element  18 , such as a polyurethane element. This element  18  is generally cylindrical having a throughbore  20 . Proximate each end  22 ,  24  of the compressible element  18  is a load transfer washer  26 ,  28 . At the back end  30  of the pulling head  16  is a jam nut  32 . The jam nut  32 , which controls pre-load, is adjustable thereby effectively facilitating load adjustment. 
   The pulling head  16  includes a housing  34  housing which includes two components  36 ,  38  which telescope relative to each other during operation of the pulling head  16 , as will be described in more detail hereinbelow. Each housing component  36 ,  38  is generally cylindrical having a longitudinal throughbore  40 ,  42 . A rear housing component  36  includes an externally threaded portion  44  proximate its back end  46  for threaded engagement with the housing of a pull type tool, such as a riveter as discussed above. Proximate a front end  48  of the rear housing component  36  are two slots  50  which are configured to receive a dowel pin  52 . Specifically, the dowel pin  52  extends through holes  54  provided in a sidewall  56  of the front housing component  38  as well as through the slots  50  in the rear housing component  36 . As such, the front housing component  38  and the rear housing component  36  are effectively attached to each other, but can telescope relative to each other. 
   A front end  58  of the front housing component  38  includes an internally threaded section  60  (i.e., a front end  58  of the longitudinal bore  42  is threaded) for threaded engagement with a corresponding external threaded portion  62  of a nose insert  64 . The nose insert  64  includes an extending front portion  66  which defines the front  68  of the pulling head  16 , and a longitudinal throughbore  70  into which a mandrel  72  extends during operation of the pulling head  16 , as will be described in more detail hereinbelow. 
   Inside the two-part telescopic housing  34  is a drawbolt assembly  74 , which includes a drawbolt  76 , a compression spring  78 , a jaw follower  80 , a set of jaws  82  which are configured to grip the mandrel  72  during operation of the pulling head  16 , and a collet  84 . The drawbolt  76  is generally cylindrical with a bore  86  provided at its front end  88  and a threaded bore  90  provided at its rear end  92 . The threaded bore  90  is provided at the rear end  92  of the drawbolt  76  so the drawbolt  76  can be threaded onto a piston of the pull type tool. Additionally, an externally threaded portion  94  is provided proximate the front end  88  of the drawbolt  76  for threading into a rear end  96  of the collet  84 . The collet  84  is generally cylindrical having an opening  98  in its front end  100 . Like the rear housing component  36 , the drawbolt  76  includes a pair of slots  102  which receive the dowel pin  52 . 
   As shown in  FIG. 5 , a rear end  104  of the compression spring  78  sits in a recess  106  which is provided proximate the front end  88  of the drawbolt  76 , and a front end  108  of the compression spring  78  engages a shoulder  110  of the jaw follower  80 . A rear end  112  of the jaw follower  80  extends into the bore  86  which is provided in the front end  88  of the drawbolt  76 , and a front, facing surface  114  of the jaw follower  80  contacts a back surface  116  of the jaws  82 . But for the shoulder portion  110  of the jaw follower  80  and the front, facing surface  114 , the jaw follower  80  is generally cylindrical having a longitudinal throughbore  118 . 
   As shown in  FIG. 2 , the pulling head  16  may be provided as having a pair of internal jaws  82 , where each jaw  82  has a tapered surface  120  for engaging a corresponding tapered internal wall  122  (see  FIG. 6 ) inside the collet. As discussed above, the compression spring  78  is disposed between the drawbolt  76  and the shoulder  110  of the jaw follower  80 . As such, the compression spring  78  tends to push the jaw follower  80 , and the jaws  82  forward in the pulling head  16 . The pushing of the compression spring  78  on the jaw follower  80  and the contacting engagement of the tapered surface  120  of the jaws  82  with the corresponding tapered internal wall  122  inside the collet  84 , tends to force the jaws  82  closed. An inner surface  124  of each of the jaws  82  provides serrations for gripping a mandrel  72 . 
   Although the spring bias of the jaws  82  and the engagement of the tapered surface  120  of the jaws  82  with the corresponding tapered internal wall  122  inside the collet  84  tends to force the jaws  82  closed, preferably each jaw  82  also includes a front surface  126  (identified in  FIG. 7 ) which is tapered inwardly. When the jaws  82  are most forward in the pulling head  16 , such as is shown in  FIG. 5 , the inwardly tapered surface  126  of each of the jaws  82  engages a corresponding tapered surface  130  (identified in  FIG. 8 ) which is provided at the back end  62  of the nose insert  64 , said engagement tending to force the jaws  82  open for easy insertion of a mandrel  72  as shown in  FIG. 6 . Due to the jaws  82  being effectively held open by the back end  62  of the nose insert  64 , it is easier to insert a mandrel  72  into the pulling head  16 , and there is reduced wear associated with doing so. 
   Also provided, for operation of the pulling head  16 , is the mandrel  72  which has a head portion  132  which is provided at the end of a shaft  134 . Ribs  136  are provided on the shaft  134  for gripping by the jaws  82 . Also provided is a reaction cup  140  which is generally hollow and cylindrical, having a hole  142  large enough to receive the shaft  134  of the mandrel  72 , but being too small to allow the head  132  of the mandrel  72  to pass through. 
   In use, initially as shown in  FIG. 1 , there is provided a rivetless nut plate  10  which must be removed from a hole  12  in a workpiece  14  (i.e., the parent material). As shown in  FIG. 3 , first the shaft  134  of the mandrel  72  is extended through the hole  142  in the reaction cup  140 , and the reaction cup  140  is seated against the parent material  14 , as shown in  FIG. 4 , such that the head  132  of the mandrel  72  contacts the reaction cup  140 . As shown in  FIG. 5 , the shaft  134  of the mandrel  72  is inserted into the end  68  of the pulling head  16  (i.e., into the opening  70  in the nose insert  64 ) and the front end  68  of the pulling head  16  (i.e., the extending portion  66  of the nose insert  70 ) is inserted in the hole  12  in the parent material  14 , in contact with the rivetless nut plate  10  as shown in  FIG. 6 . During this time, the jaws  82  are generally kept open as a result of the jaws  82  being spring-biased forward (viz-a-viz the spring  78  pushing on the shoulder  110  of the jaw follower  80 ) into contact with the nose insert  64 . As discussed above, the rear end  62  of the nose insert  64  is provided with an angled surface  130  which contacts corresponding inwardly tapered surfaces  126  on the jaws  82 , causing the jaws  82  to be forced open. 
   Then, the pull type tool (i.e., riveter) to which the pulling head is engaged (engagement with a riveter is represented in  FIG. 5  using arrows  150 ) is actuated, causing the piston of the riveter to pull the drawbolt  76  back, causing the collet  84  to also move back. Such relative movement between the collet  84  and the jaws  82  causes the jaws  82  to slide up the tapered surface  122  in the collet  84  and grip the mandrel  72  as shown in  FIG. 7 , thereby applying a force which is also applied to the rivetless nut plate  10 . 
   As the riveter continues to be actuated, the drawbolt  76  and collet  84  keep moving back in the housing  34  and the jaws  82  keep pulling on the mandrel  72  as shown in  FIG. 8 . As long as the force is lower than the force necessary to push the rivetless nut plate  10  out of the hole  12  in the parent material  14 , the telescopic housing  34  of the pulling head  16  collapses, forcing the compressible element  18  to compress, and the force continues to build up in the compressive element  18  (i.e., the compressible element  18  continues to be compressed). 
   When the force built up in the compressive element  18  equals the push out force of the rivetless nut plate  10  to be removed, the collapse stops and the nut plate  10  is removed as shown in  FIG. 9 . Additional travel/load will only increase the load incrementally, at a known rate. When the face  152  of the nose insert is pushed against the parent material, or the nut plate riveter  10  is pushed against the back  154  of the reaction cup  140 , as shown in  FIG. 9 , the housing  34  keeps collapsing, increasing the load slightly. However, the compressive element  18  provides that only a portion of the overall load applied by the riveter is actually applied to the active area. For example, depending on the riveter and the properties of the compressive element, out of say 3100 lbs. (depending on the riveter) applied by the riveter, only 500 lbs. (depending on the properties of the compressive element  18 ) is applied to the active area, keeping the parent material  14  from becoming damaged, keeping the mandrel  72  from breaking, and keeping tool components from experiencing undue wear. 
   When the nut plate removal is completed, the trigger of the riveter can be released, thereby causing the piston to push the drawbolt  76  forward and causing the housing  34  to expand, as shown in  FIG. 10 . The drawbolt  76  is pushed forward until the riveter reaches the end of its stroke. At the end of the stroke, the jaws  82  are pushed into the back tapered surface  126  of the nose insert  64 , forcing the jaws  82  open. As such, the mandrel  72  is now free, and the pulling head  16  can be pulled away from the mandrel  72  and parent material  14 , as shown in  FIG. 12 . Then, as shown in  FIG. 13 , the mandrel  72  and reaction cup  140  are pulled away from the parent material  14 , and the removed fastener  10  can thereafter be discarded, as shown in  FIG. 14 . 
   The load control mechanism described hereinabove, i.e., the telescopic housing  34  working together with the compressive element  18 , etc., works to absorb some of the load exerted by a pull type tool during load application, such as while using a riveter to remove a rivetless nut plate. As such, the load control mechanism allows a pull type tool to be used in applications in which the pull type tool would otherwise be overrated. For example, the load control mechanism provides that a riveter, such as a riveter which typically applies 3100 lbs. at 90 p.s.i., can be used to remove a rivetless nut plate without breaking a mandrel, causing undue wear on components of the tool, or damaging the parent material. 
   While embodiments of the present invention are shown and described, it is envisioned that those skilled in the art may devise various modifications of the present invention without departing from the spirit and scope of the disclosure.