Abstract:
A unified head for a staked fastener wherein the unified head is made from a first member in combination with a supplemental member, and the two members have at least one shared fiber. In a staking operation that forms the unified head, the operation is conducted in such a manner that a portion of a fiber, initially within the first member or the supplemental member, crosses the boundary therebetween creating the shared fiber, i.e., a segment of a single fiber is embedded in the first member and a segment is embedded in the supplemental member.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a divisional of U.S. application Ser. No. 10/955,174, filed on Sep. 30, 2004, now U.S. Pat. No. 7,351,002. The entire disclosure of this application is hereby incorporated in its entirety by reference. 
    
    
     FIELD OF THE INVENTION 
     The present invention relates to fasteners and more specifically to fasteners formed by staking, such as studs and rivets. 
     BACKGROUND 
     Staked fasteners, such as studs and rivets, are a well-known fastening technology. Studs are typically used to secure a body, such as a circuit board, to a foundation. Rivets, on the other hand, are typically used to fasten two bodies, such as sheet materials, together at an overlapping seam. For either a stud or a rivet, fastening is accomplished by the creation of a head on a shank. In the case of a stud having two ends, a head is formed on one end of the shank with the other end fixed to the foundation with the body therebetween. In the case of a rivet, heads are formed on both ends of the shank with the bodies therebetween. 
     A staked fastener can be made from many materials, such as steel, aluminum and plastic. Where weight is a concern, such as in an airplane, helicopter, or spacecraft, materials with high strength-to-weight ratios, such as plastic, are preferred. Unfortunately, plastic rivets simply do not have the ultimate strength of rivets made from other materials. As a result, plastic rivets, though desirable for many applications, cannot be practicably used, or in some cases used at all. 
     There have been many advances in the plastic rivet. From an initial beginning when plastic rivets were simply all plastic, such as a thermoplastic (e.g., polyetheretherketone (more commonly known as “PEEK”)), newer composite plastic rivets have some type of reinforcement added to the plastic. For example, many composite plastic rivets are reinforced with fibers, such as carbon or glass. 
     Rivets are typically formed in a two step process. First, an initial head is formed with a shank extending therefrom. Generally, the initial head is formed in a factory setting by a machine, by molding or staking an end of a rod, which tends to make a high quality initial head with a properly contoured contact surface (the surface of the head that will abut the body). Also, additional fabrication of the initial head, such as cleanup of the contact surface, can be performed relatively easily. 
     Then in an application, a second head is formed in situate on the end of the shank. More specifically, when a rivet is used in an application, such as connecting two bodies, a hole is made in each of the two bodies. The diameter of the holes is sized such that when the holes are aligned with each other the shank can pass through, but the initial head can not pass through the first hole that the shank passed through. The second head is then formed on the other end of the shank, thereby securing the two bodies together. 
     Unlike the initial head, the second head is formed at the job site, typically using a hand held tool, thus the conditions are not as controlled as those during the formation of the initial head. Additionally, cleanup of its contact surface is impossible, as it is abutting the body. As a result, the precision of the contact surface of the second head is generally not to the level of that of the contact surface of the initial head. This discrepancy results in a second head with less strength than the initial head. 
     More specifically, many processes used on plastic rivets to form the second head create voids in the contact surface of the rivet head. As a result, the head has a local weakness at its parameter edge. If pressure is applied thereto, it will cause a local failure of the head. These local failures result in “play” between the rivet and body, thereby creating the unacceptable amount of movement between the head and the shaft, causing the rivet to fail. 
     What is needed in the art is a staked fastener head and way to make the head such that the resulting rivet, or stud, is stronger than it otherwise would be. 
     SUMMARY OF THE INVENTION 
     This invention is a unified head and a method for making it for a staked fastener, such as a rivet. In an exemplary embodiment of a rivet employing the unified head, a shank with two ends has an initial head formed at one end. Proximate the other end is at least one fiber embedded in the shank. In an application, the shank is passed through a body and a unified head is formed by staking the shank&#39;s other end, thereby trapping the body between the heads. In forming the unified head, a first member is created from a clinch portion of the shank (which has at least a portion of the at least one fiber therein), and a supplemental member placed proximate the first member such that the supplemental member is trapped during staking between the forming first member and the body. Additional sufficient energy is applied during staking such that at least one of the at least one fibers will become a shared fiber (a fiber having one segment embedded in the supplemental member and another segment embedded in the first member). 
     These and other features, aspects, and advantages of embodiments of the present invention will become apparent with reference to the following description in conjunction with the accompanying drawings. It is to be understood, however, that the drawings are designed solely for the purposes of illustration and not as a definition of the limits of the invention. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  shows a side view of a rivet connecting two bodies having a unified head of the present invention. 
         FIG. 2  is a series of three drawings, individually identified as A, B, and C, each taken along cross-section  2 - 2  of  FIG. 1 , showing the creation of a unified head of the present invention. 
         FIG. 3  shows a perspective view of a style of supplemental member for use in the present invention. 
         FIG. 4  shows a perspective view of another style of supplemental member for use in the present invention. 
         FIG. 5  is a cross-sectional view of the supplemental member shown in  FIG. 4  taken along line  5 - 5 . 
         FIG. 6  is a perspective view of another style of supplemental member for use in the present invention. 
         FIG. 7  is a side view of the supplemental member depicted in  FIG. 6 . 
         FIG. 8  is a cross-sectional view of the supplemental member depicted in  FIG. 6  used in an application. 
         FIG. 9  is an expanded perspective view of another embodiment of a supplemental member. 
         FIG. 10  is an expanded perspective view of another embodiment of a supplemental member. 
         FIG. 11  is a side view of another embodiment of a supplemental member. 
         FIG. 12  is a side view of the supplemental member depicted in  FIG. 11  having another orientation. 
         FIG. 13  is yet another style of supplemental member for use in the present invention. 
         FIG. 14  is a cross-sectional side view of another shape of a first member of the present invention. 
         FIG. 15  is a top view of the first member depicted in  FIG. 14 . 
         FIG. 16  is a cross-sectional view of a stud employing a supplemental member. 
     
    
    
     DETAILED DESCRIPTION 
     Referring to  FIG. 1 , a rivet, generally referred to by reference number  10 , secures a first body  12 , such as a sheet material, to a second body  14 , such as a sheet material. The rivet  10  has an initial head  16  having a contact surface  18 , a unified head (generally referred to by reference number  20 ) having a contact surface  22 , and a grip member  24 . The unified head  20  has a first member  26 , which is formed from a clinch portion  28 , and a supplemental member (not easily seen in this view, discussed below). 
     The grip member  24  and the clinch portion  28  are separate segments of a shank  30 , which extends outwardly from the initial head  16 . In the embodiment depicted in  FIG. 1 , the grip member  24  is that segment of the shank  30  passing through holes  32 ,  34 , which are defined by the first and second bodies  12 ,  14 . The clinch portion  28  (depicted by dotted lines) is the segment of the shank  30  extending outwardly beyond a surface  35  of the second body  14 . As those skilled in the art will appreciate, the precise demarcation between the grip member  24  and the clinch portion  28  of the shank  30  is a function of the style of head (flush, as shown, or countersunk), which determines the contact surface of the head. Thus, the demarcation point should not be strictly construed to begin at the surface of the body from which the shank extends, as shown in this exemplary embodiment. Additionally, the use of additional elements, such as washers, may alter the demarcation point. Also, it should be appreciated that the initial head  16  could be formed from another clinch portion of a rod (not shown), thereby creating the shank  30  with the initial head  16 . It should also be appreciated that the initial head  16  could be of the same structure as the unified head  20 . 
     Referring to the series of Figures that comprise  FIG. 2 , the rivet  10  has the unified head  20  formed in the following manner. As shown in  FIG. 2A , the rivet  10  originally has the initial head  16  and the shank  30 , with the grip member  24  and the clinch portion  28 , which has an end  36 . An enlarged view of the clinch portion  28  of  FIG. 2A , shows at least one fiber  38  contained therein. The at least one fiber  38  in the clinch portion  28  is oriented generally parallel to the centerline of the shank  30 . 
     A supplemental member  40  is collocated with the clinch portion  28  of the shank  30  proximate the second body  14 . Further discussion of the supplemental member  40  is presented below. 
     Continuing with  FIGS. 2B and 2C , the first member  26  is formed by staking the end  36  of the clinch portion  28  with a staking tool (not shown). The staking operation continues over a distance d, until the unified head  20  is formed. 
     As shown in the expanded view of  FIG. 2B , the staking operation, which may utilize a staking tool, such as one having a semi-hemispherical shape (not shown), tends to bend the at least one fiber  38  in the first member  26  toward a perimeter segment  42 , which will eventually abut the supplemental member  40 . A void  44  defined by the perimeter segment  42  of the first member  26  may be formed during the staking operation. 
     As shown in  FIGS. 2B and 2C , the staking operation brings the first member  26  into contact with the supplemental member  40 . The energy from the staking operation enters the supplemental member  40  causing it to deform to the contour of the perimeter segment  42 , entering the void, and forming at least part of the contact surface  22  of the unified head  20 . In other words the clinch portion  28  is substantially enveloping the supplemental member  40 . 
     The staking procedure imparts to at least one of the at least one fibers  38  and the supplemental member  40  sufficient energy such that a portion of those fibers cross the boundary and become embedded in the supplemental member  40 . As a result, at least one of the at least one fibers  38  will become a shared fiber  45 . The shared fiber  45  being a fiber that is simultaneously embedded in the first member  26  and the supplemental member  40 . In other words, the shared fiber  45  will have a segment embedded in the first member  26  and a segment embedded the in supplemental member  40 . As shown in  FIG. 2C  in the expanded view, a shared fiber  45   a  could cross the perimeter segment  42  more than once. 
     The staking method employed depends upon the materials selected for the clinch portion  28  and the supplemental member  40 . For example, where the clinch portion  28  and the supplemental member  40  are plastic, such methods as ultrasonic and/or induction could be used. 
     The staking procedure to create a shared fiber  45 , however, is different than conventional procedures. In a standard ultrasonic procedure, the staking procedure is controlled by the distance d s  the staking tool must travel to accomplish the formation of the relevant head. More specifically, sufficient energy is applied to the clinch portion  30  via the staking tool to cause the clinch portion to flow thereby allowing the staking tool to act on the clinch portion to travel the distance d s  to deform the clinch portion into a desired head shape. Once the desired head shape is accomplished, i.e., the travel distance d s  has been accomplished, the energy is removed, but the staking tool is held in position for some hold time. The hold time allows the head, which is under the staking tool and still fluid enough to flow, to cool sufficiently so that the staking tool can be removed without the clinch portion further flowing. In the procedure of the invention, there is a fixer step in the staking procedure that occurs after the travel distance d s  has been accomplished prior to the hold. In the fixer step, energy is still applied, generally at the level previously used, to the pre-head (the head as it exists immediately after the travel distance d s  has been reached). The fixer step adds additional energy to the pre-head to create the shared fiber  45 , thereby converting the pre-head to a unified head  20 . The amount of energy is application dependent depending on such factors as the materials used in the pre-head and their associated masses. Depending upon the degree of additional energy added during the fixer step and the materials used, the supplemental member  40  and the first member  26  may merely be welded to each other or may form a coherent mass. 
     If induction staking is used, materials that generate heat when exposed to induction energy would most likely have to be present in the clinch portion  30 , but could be present elsewhere, such as in the supplemental member  40 . 
     The supplemental member  40  can be of almost any shape, such as a rectangular solid ( FIG. 3 ), a washer ( FIG. 4 ), a keyed structure ( FIG. 6 ), or a graduated structure ( FIG. 11 ). Typically these types of structures have a hole  46 ,  48 ,  50  and  71 , which is defined by the supplemental member  40 , sized to allow the clinch portion  28  of the shank  30  to pass through. 
     The supplemental member  40  should have a sufficient initial volume V 1 , V 2 , V 3 , V 4  to permit it to at least fill the void  44 . The supplemental member  40  may have a greater volume than that necessary to fill the void  44  that will simply flow out during the staking operation. As those skilled in the art will appreciate, some material of the first member  16  may also flow out from under the staking tool as it travels the distance d s , causing a decrease in the density of the first member  16 . Therefore, the volume V 1 , V 2 , V 3 , V 4  of the supplemental member  40  may be sufficiently increased above that required to fill the void  44  to compensate for this loss in density. 
     As depicted in  FIG. 5 , at least one fiber  54  could be incorporated in the supplemental member  40 . It is, therefore, within the scope of the invention if at least one of the at least one fibers  54  from the supplemental member  40  becomes a shared fiber  45  regardless of whether the clinch portion  28  of the shank  30  has fibers or not. 
     Referring to  FIGS. 6 ,  7 ,  8 ,  9  and  10 , the supplemental member  40  may be a keyed structure. As shown in  FIGS. 6 and 7 , a supplemental member  40  has a keyed structure of a top-hat design having a brim  56  with a crown  58  extending therefrom. In one application, the crown  58  is inserted into the hole  34  of the second body  14 , and the shank  30  of the rivet  10  is inserted through the hole  54  such that the clinch portion  28  extends outwardly from the brim  56 . As shown in  FIG. 8 , in a keyed structure, a portion, i.e., a key, of the supplemental member  40 , such as the crown  58 , can be positioned between the grip member  24  of the shank  30  and the second body  14  and even into the first body  12 . 
     The keyed structure may also have the additional feature of a non-rotational cross-sectional shape such that in cooperation with the cross-sectional shape of the hole the supplemental material will not rotate within the hole defined by the body, or bodies. For example referring to  FIGS. 9 and 10 , the hole  34  and the supplemental member  40  could have a crown  58  with a complementary rectangular cross-sections, or a corresponding protrusion  62  and slot  64 . 
     The supplemental member  40  may also be graduated. Referring to  FIG. 11 , an example of a graduated design for a supplemental member  40  in the form of a top-hat having a brim  66  and a crown  68 . In application, the crown  68  would most likely extend outwardly from the surface  35 ; however as shown in  FIG. 10  the graduated member could have the opposite orientation. Depending upon the application, other graduated shapes, such as frustum of pyramid, could be used. 
     The supplemental member  40  may also be designed to engage the clinch portion. Engagement could be by friction or mechanical fastener. As shown in  FIG. 12 , the fastener could be grips  70  for engaging the clinch portion  28  extending outwardly from a surface  72  that defines the hole  71 . The fastener could be of a one-way design, i.e., the fastener is broken to effectuate removal of the supplemental member  40 . 
     Referring to  FIG. 13 , the supplemental member  40  could also be a wrap  60 , such as a cord or tape, applied around the rivet  10 , most likely the grip member  28  proximate the second body  14 . The cross-section of the wrap  60  could be any shape. 
     While the results of a hemispherical shaped head for a staking tool have been previously depicted, other shapes can be used.  FIGS. 14 and 15  depict a symmetrical unified head  20 . The symmetrical head  20  has a first member  26  where the at least one fibers  38  generally extend radially from the centerline of the clinch portion  28 . This symmetry is accomplished by using a staking tool  74  with a shank center locator  76 . The shank center locator  76  penetrates into the clinch portion  28  of the shank  30  on the longitudinal axis causing the at least one fibers  38  to be splayed radially outwardly therefrom. 
     Materials for the rivet  10  and supplemental member  40  are a matter of design choice. Typical plastics, which include thermoplastics, such as PEEK or polyetherimide (more commonly known as PEI), are particularly well suited for the invention. As discussed above, staking may cause a weld to occur between the material of the rivet  10  and the supplemental member  40  and even between the rivet and/or the supplemental member and the second body  14 . 
     As those skilled in the art will appreciate, the strength of the weld or whether a coherent mass is formed between the first member  26  and supplemental member  40  is, among other things, dependent upon the materials from which the rivet and supplemental member are made. If the rivet and supplemental member are made from compatible or the same material, the weld could be stronger and the coherent mass more uniform than it might otherwise be. 
     Any fibers can be embedded into the plastic of the rivet  10  or supplemental member  40 . Fibers are also a matter of design choice and may include carbon or glass. Carbon fibers are particularly strong and lightweight. 
     The at least one fiber  38  in the shank  30  has been depicted in  FIG. 2  as being oriented generally parallel with the centerline of the shank  30 , but the at least one fibers could have any orientation. Where there are two or more fibers  38  in the shank  30 , they could be randomly oriented one to the other. Additionally, the at least one fibers  38  can be of any length, even running from end to end through the grip portion and clinch portions of a rod (not shown) from which the rivet  10  was created. Also in the case of multiple fibers  38 , fibers of varying lengths could be used. Therefore, depending upon the length of the particular fibers in the first member  26 , a majority of the length of the shared fiber  45  could be in the first member, or in the supplemental member  40 . This is equally true for the at least one fibers  54  incorporated in the supplemental member  40 . 
     Referring to  FIG. 2 , a filler  78  maybe added about the grip member  24  between the two bodies  12 ,  14 . The filler  78  can be of any shape, such as a washer, and be made from any number of materials to meet any particular need. For example, the filler  78  could contain a rubber or neoprene to provide a seal, or an adhesive, such as a 100% solids adhesive, that would be activated, in the case of a 100% solids adhesive melt and flow, as a result of the staking operation for providing additional bonding between the first and second bodies  12 ,  14 . 
     Referring to  FIG. 16 , in the case of a stud  80  having one end affixed to a foundation  82 , it would be beneficial to create a stop  84  to support the filler  78 . The stop  72  could be created in any number of ways such as by a notch in or taper of the shank  30 . 
     While there has been illustrated and described what is at present considered to be preferred and alternative embodiments of the claimed invention, it will be appreciated that numerous changes and modifications are likely to occur to those skilled in the art. For example, while the unified head has been shown for a rivet, it is equally applicable for use with a stud. In addition, the unified head could be used for both heads of a rivet. Also, the use of the singular should be interpreted to mean at least one unless the specification makes such expressly clear. It is intended in the appended claims to cover all those changes and modifications that fall within the spirit and scope of the claimed invention.