Patent Publication Number: US-7216520-B1

Title: Cross-threading prevention apparatus for installing nut inserts

Description:
BACKGROUND OF THE INVENTION 
   The present invention relates to an apparatus for installing nut inserts to a workpiece, the workpiece having a first side and a second. Usually the first side is a visible side and the second side is a blind side, meaning there is no access to the second side. More particularly, this invention relates to a modified installation tool which reduces incidents of cross-threading of the nut insert and/or damage to the installation tool. 
   It is known to use threaded rivet nuts, threaded inserts, and threadable inserts (generally, “anchor devices”) as anchors for threaded fasteners in a number of different applications, including thin wall applications, such as sheet metal, which may be too thin to be tapped with threads. In many such cases there is access only to one side of the workpiece. In general, the workpiece is drilled or punched and the anchor device is placed within the resulting hole. The anchor device is either threaded onto a threaded mandrel of the installation tool and placed within the hole by the installation tool, or the threaded mandrel is made up onto the threads of the anchor device after the anchor device has been placed in the hole. When the installation tool is activated, a portion of the anchor device on the blind side of the workpiece, such as a sleeve portion, is deformed to create an enlargement or bubble which prevents removal of the insert from the hole. After the installation tool is removed, a threaded fastener may be inserted into a threaded portion of the insert. 
   Installation tools for setting nut inserts, particularly in blind applications, are generally known. These tools generally comprise a tool body from which extends a mandrel having external threads. The mandrel typically extends through a nose piece which is connected to the front of the tool body. Rotational means are operationally connected to the rear of the mandrel for rotating the threaded mandrel to make up the threaded mandrel within the nut insert prior to deformation of the sleeve portion. The threads of the mandrel are made up into the threads of the nut insert until a flange on the end of the insert abuts the front end surface of the nose piece. If not already placed within an aperture of the work piece, the insert is thereafter placed within the aperture until the flange abuts the first side of the workpiece. 
   A linear force is applied to the mandrel by partially pulling the mandrel into the tool body with reciprocation means. The linear force applied to the insert causes the sleeve of the insert to plastically deform, such that the resulting enlargement or bubble is larger than the diameter of the aperture, preventing withdrawal of the insert from the aperture. Examples of such tools may be found in U.S. Pat. Nos. 4,070,889; 4,368,631; 4,612,793; 4,574,612; 5,605,070; and 6,272,899. 
   On occasion, the threads of the insert are cross-threaded as the male threaded mandrel is inserted into the female threaded insert. Cross-threading can occur with a threaded insert when the threaded mandrel is engaged with the female insert and the threads are not properly aligned when the threads of the mandrel and the threads of the insert first engage. If the threads of the mandrel and the threads of the insert are not properly aligned at the start, the external thread tends to cross over the crest of the internal thread which can produce deformation of the threads and can also cause binding of the mandrel and insert before the desired makeup of the mandrel into the insert is achieved. Unless the mandrel and nut insert are manually realigned at this point, the external thread will wedge against the internal thread and prevent the proper makeup of the mandrel into the nut insert and/or cause damage to the threads of either the insert or the mandrel. 
   It has been found by the inventor herein that in addition to improper alignment, another cause of cross-threading is that the threads of the insert adjacent to the opening, including the root thread, can be damaged by the tip of the mandrel as the mandrel is inserted into the opening of the insert by the operator or operating machinery. The tip of the mandrel may impact the crests of the threads of the insert as the tip is inserted into the opening of the insert. With the existing installation tools, there is little give by the mandrel, such that the resulting impact load is absorbed almost entirely by the threads of the insert. 
   SUMMARY OF THE INVENTION 
   The present invention is directed to an improved installation tool which meet the needs identified above. The improved insert installation apparatus comprises a housing having a body section and a nose piece. The nosepiece comprises a forward end and a rearward end, where the rearward end of the nose piece is attached to the body section. 
   A rotary power source and reciprocating means are contained within the housing. The rotary power source has an extension member which connects the rotary power source to the first end of a drive shaft which is received by the extension member. 
   The improved insert installation apparatus further comprises a mandrel. The mandrel is connected on one end, referred to herein as the “drive end”, to a drive shaft which connects the mandrel to the rotary power source. The drive shaft further comprises a circumferential shoulder member. The opposing end of the mandrel is a threaded shaft which extends out the forward end of the nose piece. 
   The apparatus further comprises mandrel shock absorbing means which allow the mandrel to reciprocate with respect to the nose piece from a first position to a second position, where the mandrel shock absorbing means operates independently from the reciprocating means which are employed to apply the linear force to the threaded insert. The mandrel shock absorbing means allows the threaded shaft to “give” if the tip of the mandrel impacts the crests of the threads of the insert as the tip is inserted into the opening of the insert. It is to be appreciated that one embodiment of the reciprocating means utilizes the application of hydraulic pressure to a piston inside the housing, where a large spring or springs bias the piston (and thus the threaded shaft) forward. In the known tools of this type, there is little or no axial “give” in the threaded shaft because of the strength of the biasing means pushing forward on the piston. That is, with the known tools of this type, the threaded shaft is not easily pushed into the tool body. Thus, the tip of the shaft has little give and is capable of imposing a hard impact on the threads of an insert. However, the mandrel shock absorbing means of the present invention allow the mandrel to be pushed a small amount, approximately 0.7 inch, into the tool body. While a small spring or other biasing means are used to bias the threaded shaft forward (i.e. extending outside of the tool), the threaded shaft may be partially pushed back into the nose piece upon contact with the threads of the insert, thus preventing impact damage to the root thread of the insert and preventing cross-threading. The shaft may further comprise a tip which assists in proper alignment of the threaded mandrel with the threads of the insert. For example, the tip may be chamfered or rounded. 
   These and other features, aspects, and advantages of the present invention will become better understood with regard to the following description, appended claims, and accompanying drawings. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  shows an internal view of an installation tool comprising the improvements disclosed herein. 
       FIG. 2  is a side view of a mandrel which may be utilized in an embodiment of the disclosed invention. 
       FIG. 3  is a side view of a nose piece which may be utilized in an embodiment of the disclosed invention. 
       FIG. 4  is a sectional view of the nose piece shown in  FIG. 3 . 
       FIG. 5  is a front view of the nose piece shown in  FIG. 3 . 
       FIG. 6  is a rear view of the nose piece shown in  FIG. 3 . 
       FIG. 7  is a side view of a drive shaft which may be utilized in an embodiment of the disclosed invention. 
       FIG. 8  is a front view of the drive shaft shown in  FIG. 7 . 
       FIG. 9  is a rear view of the drive shaft shown in  FIG. 7 . 
       FIG. 10  is a side view of an extension member which may be utilized in an embodiment of the disclosed invention. 
       FIG. 11  is a front view of the extension member shown in  FIG. 10 . 
       FIG. 12  is a rear view of the extension member shown in  FIG. 10 . 
       FIG. 13  is a side view of a piston which may be utilized in an embodiment of the disclosed invention. 
       FIG. 14  is a sectional view of the piston shown in  FIG. 13 . 
       FIG. 15  is a front view of the piston shown in  FIG. 13 . 
       FIG. 16  is a rear view of the piston shown in  FIG. 13 . 
       FIG. 17  is a side view of a cover member which may be utilized in an embodiment of the disclosed invention. 
       FIG. 18  is a sectional view of the cover member shown in  FIG. 17 . 
       FIG. 19  is a front view of the cover member shown in  FIG. 17 . 
       FIG. 20  is a rear view of the cover member shown in  FIG. 17 . 
       FIG. 21  shows a quarter-sectional view of a type of threaded insert which may be used with the disclosed threaded insert installation apparatus, before the insert is installed. 
       FIG. 22  shows a quarter-sectional view of the threaded insert of  FIG. 21  after the insert has been installed in a work piece. 
   

   DETAILED DESCRIPTION OF THE EMBODIMENTS 
   Referring now specifically to the drawings,  FIG. 1  shows a cross-section of an embodiment of the threaded insert installation apparatus. The apparatus  10  comprises a housing  12  which may, as shown in  FIG. 1 , be configured in a pistol form, or in other configurations such as a straight housing. The housing  12  may comprise a body section  14  and a nose piece  16 . The body section  14  may comprise a handle section  18  and an intermediate section  20 . The nose piece  16  may comprise a forward end  22  and a rearward end  24 . As shown in  FIG. 1 , rearward end  24  of the nose piece  16  is attached to the body section  14 . 
   A rotary power source, such as a pneumatic motor  26 , is contained within housing  12 . The rotary power source provides rotary motion to mandrel  28 , which is connected to the rotary power source by drive shaft  30 . An extension member  32  couples the drive shaft  30  to the rotary power source. In addition to rotational motion, mandrel  28  is also configured to be stroked in a reciprocating motion by reciprocating means operationally attached to the mandrel, such as piston assembly  34 . Piston assembly  34  may be biased in a forward position, that is, biased toward the front of the apparatus  10  (i.e. toward the nose piece  16 ) by spring  36 . As shown in greater detail in  FIGS. 13–16 , piston assembly  34  may comprise a piston body  38  and piston shaft  40 . The piston assembly  34  may be reciprocated to a rearward position, that is, axially away from the nose piece  16 , by the application of a force, such as hydraulic force, sufficient to overcome the bias of spring  36  or other biasing means. When reciprocated rearward, piston shaft  40  pulls mandrel  28  rearward as well because piston shaft  40  is connected to cover member  62 , and the end plate  68  of the cover member engages the drive end  48  of the mandrel, thus pulling the mandrel and drive shaft  30  rearward. 
   Drive shaft  30  is free to float with respect to extension member  32 , that is, the end of the drive shaft inserted in the extension member is, subject to the biasing means described below, free to move axially within the extension member over the length C indicated in  FIG. 1 . For example, the inventor herein has found that if length C is approximately 0.75 inches, there is sufficient length for the adequate stroke of drive shaft  30  to allow for the operation of the reciprocating means and for the operation of the mandrel shock absorbing means. Drive shaft  30  is biased in a forward position, that is, biased toward the front of the apparatus  10  by biasing means, such as spring  42 , such that mandrel  28 , which is operationally attached to drive shaft  30 , is also biased forward. 
   The length B denotes the stroke length of piston assembly  34 . The stroke length is the amount the piston assembly  34  moves in an axial direction when the reciprocation means is activated. The inventor herein has found that a stroke length B of 0.50 inches is sufficient stroke length to collapse the sleeve of an insert as discussed below. 
   It is to be appreciated that if mandrel  28  impacts against an object, such as the root thread of a fastener, the mandrel shock absorbing means of the apparatus allow the mandrel to be depressed into the nose piece  16  if the force applied by the biasing means is exceeded. The biasing means, such as spring  42 , will typically be sized to require a very small load to depress the mandrel. As shown in  FIG. 1 , mandrel  28  may be depressed a length A into the nose piece without engaging the front of piston shaft  40 . The inventor herein has found that a suitable dimension for length A, that is the stroke length of the mandrel shock absorbing means, is approximately 0.70 inches. As mandrel  28  is depressed into the nose piece  16 , drive shaft  30  cooperatively moves in a rearward direction into the extension member  32 . However, reciprocation of the mandrel  28  and the drive shaft  30  into the housing  12  does not require a simultaneous reciprocation of the piston assembly  34  unless the mandrel is depressed more than length A. In other words, the mandrel shock absorbing means operates independently of the reciprocation means for the stroke length of the mandrel shock absorbing means. 
     FIG. 2  shows an embodiment of a mandrel  28  which may be utilized in an embodiment of the disclosed apparatus. Mandrel  28  comprises a shaft  44 . The mandrel  28  further comprises threads  46  and a drive end  48 . The drive end  48  is operably coupled to one end of the drive shaft  30  either directly or by means of coupling member  60 . As shown in  FIG. 1 , a portion of mandrel  28  is disposed in nose piece  16  such that the threads  46  extend beyond the forward end  22  of the nose piece. In an embodiment of the device where length A is 0.70 inches, length B is 0.50 inches, and length C is 0.75 inches, the length of L 1  of shaft  44  may be configured to a length of approximately 1.750 inches. Mandrel  28  may further comprise a chamfered or rounded end  50 , which facilitates the insertion of the of the threads  46  into a threaded insert, such as the type of insert  52  shown in  FIG. 21 . As shown in  FIG. 2 , the tip  50  may comprise a “dog point” where a portion of the tip has, beginning at the tip, a reduced diameter which transitions into the larger thread diameter. For example, for a mandrel having a M6 size shaft  44 , there may be a section of approximately 0.350 inch in length having a diameter of about 0.189 inch which transitions to the actual thread diameter of approximately 0.236 inch. 
     FIGS. 3 through 6  show an embodiment of a nose piece  16  which may be utilized in an embodiment of the disclosed invention. The nose piece comprises a forward end  22  and a rearward end  24 . As shown in  FIG. 1 , nose piece  16  may further comprise a front member  54  which retains the mandrel  28  within the nose piece. Front member  54  may be retained within nose piece  16  by insertion of a pin through aperture  17 . As shown in  FIG. 4 , nose piece  16  has an opening  19  extending axially through which mandrel  28  operates. As shown in  FIGS. 5 through 6 , the opening may be in a hexagonal configuration. In an embodiment of the device where length A is 0.70 inches, length B is 0.50 inches, and length C is 0.75 inches, the length of L 2  of nose piece  16  may be configured to a length of approximately 2.92 inches. 
     FIGS. 7 through 9  show an embodiment of a drive shaft  30  which may be utilized in an embodiment of the disclosed invention. As shown in  FIG. 7 , the drive shaft  30  comprises a circumferential shoulder member  41 . Drive shaft  30  further comprises a first end  56  and a second end  58  opposite the first end. First end  56  is received by extension member  32 . Second end  58  is either coupled directly to mandrel  28  or, as shown in  FIG. 1 , connected to coupling member  60  which in turn is connected to the mandrel. In an embodiment of the device where length A is 0.70 inches, length B is 0.50 inches, and length C is 0.75 inches, the length of L 3  of drive shaft  30  may be configured to a length of approximately 4.62 inches. 
     FIGS. 10 through 12  shown an embodiment of an extension member  32  which may be utilized in an embodiment of the disclosed invention. Extension member  32  receives first end  56  of the drive shaft. As shown in  FIG. 1 , the opposite end of extension member  32  is coupled to a rotary power source, such as a pneumatic motor  26 . As shown in  FIG. 10 , extension member  32  may have an opening  33  extending axially through the part, or alternatively may have openings on either side for receipt of the first end  56  of the drive shaft and a drive member from the rotary power source. As shown in  FIGS. 11 through 12 , the opening may be in a square configuration. In an embodiment of the device where length A is 0.70 inches, length B is 0.50 inches, and length C is 0.75 inches, the length of L 4  of extension member  32  may be configured to be a length of approximately 0.92 inches. 
     FIGS. 13 through 16  show an embodiment of a piston assembly  34  which may be utilized as reciprocating means in an embodiment of the disclosed invention. Piston assembly  34  may comprise a piston body  38  and piston shaft  40 . As shown in  FIG. 14 , piston assembly  34  has an opening  35  extending axially through the entire assembly, through which opening drive shaft  30  may partially be disposed. Piston body  38  may have a counter-sunk opening  39  for seating of spring  36  which biases the piston assembly  34  forward. A second spring  43  may be utilized to provide additional bias to the piston assembly  34 . 
     FIGS. 17 through 20  show cover member  62 . As shown in  FIG. 1 , cover member  62  is attached to piston shaft  40 . Cover member  62  has an open end  64  which may axially attach to piston shaft  40  such as with threads  66 . Cover member  62  further comprises a closed end comprising an end plate  68 , the end plate having aperture  70  through which mandrel  28  operates. Aperture  70  is sized such that mandrel shaft  44  is free to reciprocate through the aperture, but drive end  48  is larger than the aperture. As shown in  FIGS. 19 through 20 , cover member  62  may be hexagonal in shape. 
   The reciprocation means and the rotary power source may be activated by trigger  72 . The reciprocation means may be activated by the application of hydraulic pressure to piston assembly  34 . 
   The disclosed apparatus is used in the same manner as known insert installation tools. An embodiment of a threaded insert which may be utilized with the disclosed apparatus is depicted in  FIGS. 21 through 22 . Threads  46  of mandrel  28  are made up into the threads  74  of the insert  52 . The insert  52  is placed within an aperture in a work piece  76 . As the mandrel  28  is withdrawn into housing  12  of the apparatus  10 , the insert  52  is prevented from moving by the nose piece  16  engaging the face of flange  78 . As the mandrel  28  is withdrawn further into housing  12 , a portion of the tubular sleeve  80  of the insert  52  on the second side (or blind side)  82  of workpiece  76  is plastically deformed into a bubble  84  or secondary flange larger than the diameter of the hole in the workpiece. The bubble  84  prevents withdrawal of the insert  52 ′ from the hole.  FIG. 22  shows an insert  52 ′ after it has been installed in workpiece  76  and the bubble  84  has been formed on the second side  82  of the workpiece. 
   These and other features, aspects, and advantages of the present invention will become better understood with regard to the following description, appended claims, and accompanying drawings. While the above is a description of various embodiments of the present invention, further modifications may be employed without departing from the spirit and scope of the present invention. For example, the size, shape, and/or material of the various components may be changed as desired. Thus the scope of the invention should not be limited by the specific structures disclosed. Instead the true scope of the invention should be determined by the following claims.