Abstract:
A simplified method for producing internally threaded blind fasteners includes cold forming of the thin deformable walls of the fastener into bowed out sections by reverse extrusion to form deep grooves, and subsequent further cold forming to increase the diameter of this thin walled portion of the fastener to form it into bowed out sections. Three or more or even five or more sections may be formed, to increase the “pull-out” resistance by increasing the “footprint” of the deformed sections of the blind fastener.

Description:
FIELD OF THE INVENTION  
         [0001]    This invention relates to a method for making blind threaded fasteners, and to the resultant fastener.  
         BACKGROUND OF THE INVENTION  
         [0002]    Blind threaded fasteners are known, and they involve fasteners which are intended for use on metal or plastic sheets or panels, particularly where one side of the sheet or panel is not readily accessible. The fasteners often involve an enlarged head, an internally threaded outer end, and an intermediate, thin-walled hollow tube interconnecting the head and the threaded outer portion. The fastener is mounted into a hole in the panel. A drive screw extends through the thin walled hollow tube and the drive screw is rotated to pull the threaded portion of the fastener toward the panel, with the result being that the thin walled tubular part of the fastener collapses, extending outward beyond the hole, and the fastener is securely held in the panel by the head on the accessible side of the panel, and the enlarged collapsed portion of the fastener on the inaccessible side of the panel.  
           [0003]    It has previously been proposed to manufacture blind fasteners of this type by initial cold forming steps in a header type machine, subsequently cutting four longitudinally extending slits in the thin tubular material, using inwardly directed blades, and in a further step, bowing the resultant sections of the tube slightly outward.  
         SUMMARY OF THE INVENTION  
         [0004]    However, the foregoing method and the resultant fasteners have certain shortcomings. For example the various steps required in separate machines makes the fasteners unduly expensive; and excessive time and space are needed to manufacture the completed blind fastener. In addition, the tube slitting step may form burrs which may interfere with a subsequent plating process, resulting in incomplete plating, so that the fasteners may corrode and fail. In addition, it is not convenient to form more than four slits in the separate slitting process, and the resultant fastener has concentrated forces which may damage thin plastic sheets into which the fasteners may be secured.  
           [0005]    In accordance with one aspect of the invention, the longitudinal slitting and the outward bowing of the tubular section of the fastener are all accomplished by cold metal forming, preferably in machines of the general type used to make conventional threaded bolts with heads. These machines are known as “headers” and they are expensive, noisy and may cost several hundred thousand dollars. One well known manufacturer of multi-station header type machines is Sacma, based in Italy near Milan.  
           [0006]    Returning to the process, the longitudinal splits in the tubular intermediate portion of the fastener are formed in part by inwardly directed protrusions on the header die and backward extrusion of the metal from the deepening central opening in an intermediate step of cold forming the fastener. In a later step included in a multiple station header, the head of the fastener is more completely formed and the tubular sections are fully separated and are bowed slightly outward.  
           [0007]    The resultant fastener body is fully cold formed, and may have as many outwardly extending sections, such as 5 or 6, as may be desired, to spread the area of the retention portion of the fastener. In addition, in the absence of the cutting burrs, the fastener is smoothly formed and shaped to receive a complete plating coating thereby avoiding possible corrosion and failure.  
           [0008]    In accordance with one preferred method illustrating the principles of the invention, a blind threaded fastener may be formed from coils or rods of heavy cylindrical stock by the following steps:  
           [0009]    1. Cut off slug of generally cylindrical configuration.  
           [0010]    2. Cold forming slug to size while starting a central recess.  
           [0011]    3. Deepening the central recess and initial formation of flange or head of fastener.  
           [0012]    4. The knurling and vertical slits are accomplished by inwardly directed portions of the header die, and backward extrusion of the metal as the central opening through the fastener is enlarged.  
           [0013]    5. The final cold forming step punches out the small central slug of metal closing the end of the fastener, completes the flange or head of the fastener, and bows out the previously formed sections of the tubular portion of the fastener.  
           [0014]    It is noted in passing that the length of the completed fastener may be double the length of the initial cylindrical slug, for example, a ⅜ inch long cylindrical slug may be formed into a ¾ inch long fastener.  
           [0015]    Following the cold forming steps outlined above, the fasteners may be annealed to reduce or eliminate work hardening in the side walls which are to be deformed, and internal threads at the outer end of the fastener are roll formed to provide some work hardening. Subsequently, depending on the material of the fasteners, they may be plated. Concerning materials, the fasteners may typically be formed of steel, brass, monel or other metals; and they may be plated with zinc, tin, gold, or in some cases nickel. A zinc coating on steel fasteners, to avoid corrosion, is commonly employed.  
           [0016]    The fastener need not be knurled, but are preferably knurled to resist rotation relative to the panel or wall into which they are mounted. This knurling may be accomplished as part of one step in a multi-station header machine. Also, as mentioned above, the fastener may have 3 or more or even 5 or more separate “back-side” locking sections to increase the “pull-out” or resistance force when an outward force is applied to the fastener.  
           [0017]    Other objects, features and advantages will become apparent from a consideration of the following detailed description and the accompanying drawings. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0018]    [0018]FIG. 1A is sideview of a fastener with the lower half thereof being shown in cross-section, made in accordance with the principles of the present invention;  
         [0019]    [0019]FIG. 1B is a partial cross-sectional view of the fastener of FIG. 1A after it has been installed in an opening through a panel or wall;  
         [0020]    [0020]FIG. 1C is a end view of the installed fastener of FIG. 1B showing how the collapsed side walls of the fastener engage the inaccessible side of the panel;  
         [0021]    [0021]FIG. 2A shows a slug of metal of cylindrical configuration which has been initially formed with a slight indentation on one end;  
         [0022]    [0022]FIG. 2B is a cross-sectional view showing the die configuration by which the slug of FIG. 2A is formed;  
         [0023]    [0023]FIG. 3A shows the slug of FIG. 2A following an additional cold forming step by which the flange of the fastener is initially fully formed, and the central recess is further depressed;  
         [0024]    [0024]FIG. 3B is the die configuration by which the intermediate fastener configuration of FIG. 3A is formed;  
         [0025]    [0025]FIG. 4A is a cross-sectional view of a further intermediate stage of the formation of the fastener;  
         [0026]    [0026]FIG. 4B shows the die configuration by which the fastener configuration of FIG. 4A is formed, involving a backward extrusion step;  
         [0027]    [0027]FIG. 4C is a cross-sectional view taken along plane C-C of FIG. 4A;  
         [0028]    [0028]FIG. 5A represents the next step in the fastener formation, with the central opening being deepened as compared with FIG. 4A, for example;  
         [0029]    [0029]FIG. 5B is the die configuration resulting in the intermediate product of FIG. 5A;  
         [0030]    [0030]FIG. 6A represents the final formed fastener product as it would leave the multi-station header machine;  
         [0031]    [0031]FIG. 6B represents the die configuration resulting in the fastener product shown in FIG. 6A; and  
         [0032]    [0032]FIG. 6C is a cross-sectional view taken along plane C-C of FIG. 6A, and showing the side wall sections being bowed out slightly and separated from adjacent side wall sections. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0033]    While the specification describes particular embodiments of the present invention, those of ordinary skill can devise variations of the present invention without departing from the inventive concept.  
         [0034]    Referring more particularly to the drawings, FIG. 1A shows a fastener  12  in a partial or one quarter cutaway cross-sectional configuration. The fastener  12  includes the head  14  and outer portion  16  which is internally threaded as indicated at reference numeral  17 , and an intermediate knurled section  18  which has been divided into five sections as indicated by the cut  20 . It may also be noted that the side wall sections  18  between the threaded section  16  and the head  14  have been bowed outward to some extent.  
         [0035]    Referring now to FIG. 1B of the drawings, the blind fastener of FIG. 1A has been installed into a panel or wall  22  having an accessible side to the left as shown in FIG. 1B, and an inaccessible side shown to the right FIG. 1B. In practice, to install the fastener  18 , it is initially mounted through a hole in panel  22 . A threaded screw-like part is then threaded into the internal threads  17  at the outer end  16  of the fastener  12 , and is pulled to the left as shown in FIG. 1B so that the outwardly bowed walls  18 ′ collapse and engage the inner, inaccessible side of the panel  22 . The outwardly bowed sections which will be designated by the reference numeral  24  in FIG. 1C are uniformly collapsed outwardly, as shown in FIG. 1C. The view of FIG. 1C is that of the fastener and panel assembly of FIG. 1B as viewed from the right hand side of FIG. 1B.  
         [0036]    In the following portion of the specification, the successive cold forming steps of which the final fastener body is formed will be described. It is noted that the material such as steel wire of a circular cross-section is normally received at the multi-station header machine in the form of rolls or coils of metal, or in some cases for large fasteners, in the form of rods of metal. They are initially cut off into short sections or cylindrical slugs for processing by the heading machine which cold forms the material into the basic fastener configuration.  
         [0037]    Referring now to FIGS. 2A and 2B, the initial station of the cold heading machine forms the short slug of material into the slug  32  as shown in FIG. 2A, with an initial recess  34  in the upper end of the slug.  
         [0038]    Referring to FIG. 2B, the lower end of the die cavity is formed by the plug  34 . In this die assembly, the punch  36  is actively moved into stamping engagement with the work piece  32  thereby forcing the work piece  32  to move backward and radially, and simultaneously reducing its length to stabilize the diameter and the length of the work piece  32 . The work piece, following the initial forming step, is transferred to the next station of the header machine.  
         [0039]    Reference will now be made to FIGS. 3A and 3B of the drawings. In the die structure of FIG. 3B, the lower end of the die cavity is closed by the plug  38 . The punch  40  supported by the sleeve  42  is actively moved into stamping engagement with the work piece  44 , thereby forcing the upper end of the work piece  44  be moved upward and radially coming into contact with the sleeve  42 . The punch  40  and the sleeve  42  continue to move downward, deepening the recess and forming the flange  46 . The resultant intermediate product is shown in FIG. 3A.  
         [0040]    Referring now to FIGS. 4A through 4C, particularly with reference to  4 B, the lower end of the cold forming die cavity is closed by the plug  50 . In this die assembly, the punch  52  is actively moved into stamping engagement with the work piece  54 . The recess previously formed in the second header station, is deepened by backward extrusion, simultaneously forming the deep axial grooves in the periphery of the work piece  54  by the configuration of the upper inner corners of the die member  56 .  
         [0041]    The resultant part  54  as shown in FIG. 4A includes the relatively shallow knurling of  58  and the deeper grooves  60 . In addition, the central recess  62  has been deepened. FIG. 4C is a cross-sectional view taken along lines C-C of FIG. 4A. The knurling  58  and the deeper grooves  60  may be clearly seen in FIG. 4C. It is also noted that the die part  56  at its upper inner corners has a configuration which is complementary to the sectional configuration of FIG. 4C, as the knurling  58  and deep grooves  60  are formed by this backward extrusion along the inner corners of the die part  56 .  
         [0042]    Reference will now be made to FIGS. 5A and 5B of the drawings. In FIG. 5B, the work piece  64  has been transferred from the prior station of the header machine. The lower end of the die cavity is closed by the plug  66 . In this die assembly  68 , the punch  70  is actively moved into stamping engagement with the work piece  64 . The smaller blind recess, at the bottom of the work piece  64  is formed by backward extrusion, simultaneously forcing the outside diameter of work piece  64  to move radially, filling the die cavity at the lower end thereof, with the die cavity having a somewhat greater diameter than the upper side walls  72  of the work piece  64 .  
         [0043]    Reference will now be made to FIGS. 6A, 6B, and  6 C. FIG. 6B represents the fifth and last station of the multi-station header apparatus. The lower end of the die includes the cylindrical sleeve  82 . In this die assembly  84 , the punch  86 , supported by the sleeve  88 , is actively moved into stamping engagement the work piece  90 . This action forces the punch  86  to pierce the lower end of the blind recess, pushing the small slug  92  through the sleeve  82 . Simultaneously the head  94  is formed from the flange by the sleeve  88  which forces the larger bored recess of the fastener to move radially as indicated by reference numeral  96 , opening up the deep grooves to form controlled axially splits  96 , as seen to advantage in FIG. 6C of the drawings. Incidentally, the reduced diameter opening  98  is subsequently roll formed to produce internal threads, with the roll forming providing some work hardening for the threads. This threading step follows an annealing step which reduces or eliminates work hardening for the thin wall sections  100 , so that they will readily bend as indicated in FIGS. 1B and 1C.  
         [0044]    Incidentally, concerning multi-station heading machines, the work pieces are normally transferred successively from station to station by known arrangements, with successive cold forming steps taking place at successive stations, and with all of the punch members being actuated concurrently.  
         [0045]    It is to be understood that the foregoing detailed description and the accompanying drawings relate to one illustrative preferred embodiment of the method of the present invention. Various changes and modifications may be made without departing from the spirit and scope of the invention. Thus, by way of example and not of limitation, instead of a single multi-station header machine, the cold forming may be done in various successive machines. Further, the particular operations which are accomplished in successive stages may be shifted somewhat with more or less being accomplished at each station and with additional or fewer stations being required for the cold formation process, depending largely on the configuration of the fasteners. Also, depending on the application, the thickness of the panel into which the fasteners are to be secured, and other factors, the length of the thin walled slit section of the fastener may be increased or decreased, or the number of sections modified. In addition, in some cases the threads at the outer end of the fastener may be formed by cutting, using a tap, and an appropriate support for the cylindrical outer surface of the die, if necessary. Accordingly, the present invention is not limited to the exact embodiments shown in the drawings and described in detail hereinabove.