Abstract:
The provided process creates a fully flanged interlocked bushing by feeding a metal strip into a stamping assembly having a plurality of tool stations. The stations blank a workpiece from the metal strip, and trim the workpiece&#39;s two opposing ends forming a triangular shaped tab and a puzzle locking feature on either end. The workpiece is then formed into an annular shape, wherein the triangular shaped tabs are overlapped as the opposing ends are abutted and interlocked. A flange is then imparted into the side wall of the workpiece relieving the tab&#39;s overlapping condition, causing the tabs to abut one another and become co-planar with the flange. This creating a fully flanged part with a tightly fitted parting line. This invention also includes products formed by the aforementioned process.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application, filed under 37 C.F.R. 1.53(b), is a divisional of earlier filed and still pending U.S. non-provisional patent application entitled, “PROCESS FOR MAKING AN INTERLOCKING GLANGED BUSHING AND PRODUCTS MADE BY THIS PROCESS,” assigned Ser. No. 13/599,223, and filed on Aug. 30, 2012, the contents of which are incorporated herein by reference. 
    
    
     BACKGROUND OF THE INVENTION 
     Field of the Invention 
     This invention relates to a method for making a tubular bushing from flat stock, and particularly to a method for making a fully flanged bushing with interlocking features. 
     Description of the Related Art 
     Bushings, including flanged bushings, may be formed by processes such as roll forming, draw forming, spinning, or stamping, however, a major disadvantage experienced with many of these processes is the extensive material stretching which the workpiece must undergo in order to achieve its final form. Some processes, such as draw forming in particular, deform the workpiece so extensively that they grossly alter or deform the material&#39;s grain structure creating a part with internally dissimilar material properties due to work (strain) hardening. 
     Another disadvantage of these processes occurs when a closed annular form is flanged in a radial direction. Since the area of a circular flanged region is related to its radius through the formula: Area=Pi*Radius 2 , the flange material must necessarily stretch to cover an ever increasing area as the flange&#39;s radial distance increases. This causes excessive stretching in flanged region which may be exhibited by thinning, wrinkling, or even rupture of the material in the flanged portion of the annular form. 
     To avoid this issue, a portion of the annular form may be severed prior to formation of the flange. This creates a discontinuity in the flanged material that progressively enlarges with the increase in the flange&#39;s radius. This discontinuity appears as a ‘V’ shaped gap shown in  FIG. 1  (Prior Art) which serves to relieve the excessive stretching by reducing the area of material coverage in the flange. However, the use of a discontinuous form in this manner has in inherent drawback, since the discontinuity lacks adjacent material support, it will tend to concentrate stresses and loads directly into the root of the discontinuity. This in turn may cause the separation or decoupling of the bushing, and release of any part contained therein. 
     The invention described herein provides a solution to the problems described above. 
     SUMMARY OF THE INVENTION 
     The present invention provides a method and apparatus for transforming a metal sheet into a fully flanged bushing with adjacent support by providing a metal strip into a stamping assembly. The metal strip is trimmed and punched to create a workpiece with a first trimmed end and a tab. The workpiece is formed into an annular shape by abutting a portion of the first trimmed edge with the workpiece&#39;s second opposing end, overlapping the tab with the annular form. The annular form is then flanged creating a radial flange, and the tab is positioned to lie co-planar with the flange. 
     The present invention also includes a method for transforming a metal sheet into a fully flanged bushing by providing a metal strip having a first and second exterior edge into a stamping assembly containing a plurality of tool stations. The tool stations trim the metal strip&#39;s first exterior edge creating a first end, a first tab, and a male interlocking feature. The second exterior edge of the metal strip is also trimmed creating a second opposing end, a second tab, and a female interlocking feature. A workpiece is then blanked from the metal strip and deformed to create an initially formed workpiece containing a first curvature in the workpiece&#39;s first end and a second curvature in the workpiece&#39;s second end. The workpiece is further formed into an annular interlocked workpiece by abutting the first and second ends of the workpiece causing the male interlocking feature to engage the female interlocking feature and causing the first tab to overlap the second tab. The workpiece is then flanged and the first and second tabs are positioned to lie adjacent and co-planar to one another on the flange. 
     The present invention further includes a method for transforming a metal sheet into a fully flanged bushing by providing a metal strip having a uniform thickness, first, and second exterior edges into a stamping assembly having a plurality of tool stations. Material is trimmed from the first exterior edge of the metal strip creating a first end with a first triangular shaped tab and a male puzzle locking member. Material is also trimmed from a second exterior edge of said metal strip creating a second opposing end with a second triangular shaped tab and a female puzzle locking recess. The metal strip is cut creating a workpiece with a slight radial cutout along the sides of the first and second triangular shaped tabs. The workpiece is further formed into an initially formed workpiece by imparting a first curvature into the first end of the workpiece, and imparting a slightly differing curvature to the second end of the workpiece. The workpiece is also deformed over a mandrel forming the workpiece into substantially U shaped form which is then formed into an annular interlocked workpiece by abutting the first and second ends of the workpiece, interlocking the male puzzle locking member with the female puzzle locking recess, and overlapping the first and second triangular shaped tabs. The workpiece is flanged creating a radial flange, wherein the first tab and second tabs are positioned to lie adjacent and co-planar to one another on the flange. The flanged part is then re-struck, expanding the male puzzle locking member and causing the first and second triangular tabs to abut one another on the radial flange. 
     It is also anticipated the invention may be performed in a stamping assembly which is purely a progressive die, purely a transfer die, or preferably a combination hybrid progressive/transfer die wherein the progressive portion is removable and interchangeable to allow for the sizing of different annular diameters. The present invention also covers and includes the products created by the processes described above. 
     These and other advantages will become readily apparent to the reader from the detailed description of the different forms of the invention, particularly when considered in combination with the drawing figures accompanying this application wherein: 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWING FIGURES 
         FIG. 1  is a perspective view of a prior art flanged bushing containing a ‘V’ shaped discontinuity along its parting line; 
         FIG. 2  is an elevation view of a simplified die assembly; 
         FIG. 3  is a bottom view of a upper portion of a die assembly for use with the inventive process; 
         FIG. 4  is a plan view of a lower portion of a die assembly for use with the inventive process; 
         FIG. 5  is a cross sectional view of the upper and lower portions of the die assembly shown in  FIGS. 3 and 4  taken along its midline; 
         FIG. 6  is a detail view of area  6  as shown in  FIG. 5 ; 
         FIG. 7  is a plan view of a metal strip showing the progression of forming operations according to one form of the invention; 
         FIG. 8  is a perspective view of an exemplary workpiece formed by the initial formation station; 
         FIG. 9  is a perspective view of an exemplary workpiece formed by the intermediate formation station; 
         FIGS. 10 and 11  are perspective views of an exemplary workpiece formed by the interlocking and annular formation station; 
         FIG. 12  is a perspective view of an exemplary workpiece formed by the inventive process; 
         FIG. 13  is a perspective view of a second exemplary workpiece formed by the inventive process including a locking feature on the flange&#39;s parting line. 
         FIG. 14  is a plan view of a metal strip showing the progression of forming operations according to a second form of the invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     For the express purpose of the following description, the terms “upper,” “lower,” “right,” “left,” “rear,” “front,” “vertical,” “horizontal,” and derivatives thereof shall relate to the invention as oriented in  FIG. 2 . It should be understood the invention may assume different orientations and/or alternative steps or sequences unless it is expressly specified to the contrary. It should also be understood that the specific structures, devices, and processes illustrated in the accompanying drawing figures and described in the following specification are simply exemplary embodiments of the concepts and which are limited or restricted as defined in the appended claims. 
     The following description refers to tooling and apparatus used with the inventive process in their simplest terms. Those having at least some minimal understanding of the stamping and the tool and die industry will readily understand the implementation of the inventive steps and how they may be utilized with the inventive process. For example, we will not describe in detail the intricacies of general stamping principles such as placement and orientation of the individual die stations, gapping, offsets, and load balancing within the die tool, as these are well known to those skilled in the art of metal stamping. 
       FIG. 2  illustrates a simplified example of a die assembly  30  that may be used to perform the inventive process, comprising an upper die  32  and a lower die  34 . The upper die is shown in greater detail in  FIG. 3 , and the lower die is shown in greater detail in  FIG. 4 . 
     The die assembly  30  comprises one or more of the following stations, each of which will be discussed in further detail below: trim station  36 ; annular forming station  38 ; flange forming station  40 ; and an optional finish station  42  which repacks and ejects the workpiece. Each station is further comprised of a complimentary tool half in the upper  32  and lower dies  34  which progressively forms the metal strip into a flanged bushing.  FIG. 5  of the exemplary tool, further details the die assembly  30  via a cross section cut along the midline of the tool shown in  FIGS. 3 and 4 .  FIG. 6  shows a detail view of the flange forming station  40  as shown at  6  in  FIG. 5 . 
     The product of the exemplary process is shown in  FIG. 7  as a series of steps performed on a metal strip  44 , progressively forming the strip into a flanged bushing  46 . Perspective views of the workpiece during the intermediate forming steps are shown in  FIGS. 8-11  and the flanged bushing itself  46  is shown in  FIGS. 12 and 13 , wherein  FIG. 13  further details a flanged bushing  46  containing an optional flange locking feature  48 . 
     The trim station  36 , shown in  FIGS. 3 and 4 , further comprises an end trim tool  50 , and a blanking tool  52 . The end trim tool  50  comprises an end trim punch  54  ( FIG. 3 ) and a complimentary punch support  56  ( FIG. 4 ) which are used to trim excess material from a first  58  and second edge  60  of a metal strip  44  ( FIG. 7 ). This creates a first and second end  59 ,  61  on the eventual work piece  62 . The end trim punch  54  and complimentary punch support  56  ( FIGS. 3 and 4 ) are shaped to create at least one tab  64  located on the first and/or second ends  59 ,  61  of the work piece  62 , and may also include the shapes necessary to create interlocking features  66 , such as puzzle locks. The tabs  64  created by the end trim punch  54  are ideally sized to represent and fill in roughly one half of the prior art&#39;s V′ shaped material gap  68 , ( FIG. 1 ) which is formed when a prior art annular form with a discontinuity is flanged. It is preferred that tabs  64 , ( FIGS. 7-13 ) are shaped to be roughly triangular and extend away from the first and second ends  58 ,  60  of the metal strip  44  beginning at an initiation point  70  corresponding to the initiation of the flange&#39;s radius  72  ( FIGS. 12 and 13 ). 
     The trim station further comprises a blanking tool  52 , including a blanking punch  74  ( FIG. 3 ), and a complimentary blanking support  76  ( FIG. 4 ). The blanking tool  52 , creates individual workpieces  62  ( FIG. 7 ) by placing a spacing between the workpieces creating two sidewalls  78 . The blanking tool  52  also preferably cuts a slight radius  80  into the sidewall  78  adjacent to the tabs  64  on the first and second ends  59 ,  61  of work piece. 
     The annular formation station  38  preferably comprises three individual tools in the embodiment shown in  FIGS. 3 and 4 , including initial forming tool  82 , intermediate formation tool  84  and an annular formation tool  86 . The initial formation tool  82  comprises an upper formation die  88 , and a lower formation support  90  which deforms the first and second ends of the workpiece  59 ,  61  (Shown in  FIG. 7 ) in a downward direction and preferably imparts a radius  92  to both ends of the workpiece. The amount of the deflection is varied slightly from the first end  59  to the second end  61  so that when the annular form is created, tab  64  overlaps the annular form  94  (See  FIGS. 10 and 11 ). An exemplary initially formed workpiece  96  is shown in  FIG. 8 . 
     The intermediate formation tool  84  ( FIGS. 3 and 4 ) forms the workpiece  62  into a substantially U-shaped form  98  ( FIG. 11 ) by using an upper forming die  100  and a lower forming support  102  to deflect the workpiece about a mandrel  104 . An exemplary intermediate formed workpiece  106  is shown in  FIG. 9 . 
     The annular formation tool  86  ( FIGS. 3 and 4 ) performs the final shape of the annular form of the workpiece  62  and comprises an upper forming die  108 , a mandrel  110 , and a lower formation die  112  which brings the first and second ends  59 ,  61  of the workpiece  62  together, overlapping the tab  64  on the annular form  94 . This creates an overlapped annular workpiece  114  as shown in  FIGS. 10 and 11 . 
     The flange formation station  40 , shown in  FIGS. 3 and 4 , and detailed in  FIG. 6 , preferably comprises a lower support  116 , an upper support  118 , and at least one cam die  120 , wherein the annular overlapped workpiece  114  is placed onto the lower support  116 , secured by the upper support  118 , and the cam die  120  is driven into the side  78  of the workpiece  62 , imparting a flange  124  thereto. The flange is preferably formed to lie perpendicular to the annular form  94 , and includes material from the overlapping tab  64 , which is repositioned to lie co-planar with the flange  124 , creating a fully flanged part  126 , filling in the ‘V’ shaped discontinuity  68  shown in the prior art ( FIG. 1 ), thereby providing adjacent material support  128  to the flange  124 . 
     In the preferred form of the invention, radii  130  are placed into sides  78  the workpiece  62  ( FIG. 7 ) by the blanking tool  52  ( FIGS. 2 and 3 ). These radii  130  assist in the formation of the fully flanged part  126  ( FIGS. 12 and 13 ) by allowing the tabs  64  to freely transition to their co-planar orientation in the flange  124  by allowing the tabs to freely transition across the annular form  94 . 
     Referring to  FIGS. 10-13 , an optional interlocking feature  132  may also be placed into the overlapped annular workpiece  114  by modifying the trim station  36  ( FIGS. 3 and 4 ), and particularly the end trim tool  50 , to impart a complimentary interlocking feature  132  into the first and second ends  59 ,  61  of the workpiece  62  ( FIG. 14 ). The interlocking feature  132  assists in the retention of the annular form  94  by joining the first and second ends  59 ,  61  of the workpiece  114 . In the preferred form of the invention, the interlocking feature  132  is an ‘puzzle lock’, which comprises a male projection  136  located on the first end  59  of the workpiece  62  and a complimentary female cutout  138  on the second opposite end  61 . The interlocking features  132  are joined, preferably in the annular formation tool  86  of the formation station  38  shown in  FIGS. 3 and 4 , wherein the first and second ends  59 ,  61  of the workpiece  114  are interlocked by mechanically linking the male projection  136  with the female recess  138 . Several exemplary puzzle lock designs are shown in FIGS. 8-11 of the U.S. Pat. No. 4,907,626, which issued to Mori on Mar. 13, 1990 and which is incorporated herein by reference. 
     An optional finish station  42  ( FIGS. 3 and 4 ), comprises a fixed lower support  140 , an upper support  142  and a cam die  144 , similar to that used in first flange forming station  40  ( FIG. 6 ). The finish and repack station  42  compresses the flange  124 , locking features  132  and annular portion  94  of the workpiece ( FIGS. 12 and 13 ) against the tool&#39;s cam die  144 . This compresses the annular form reducing the radius of the annular portion of the workpiece  62 , and increases the part&#39;s material thickness. This increase in thickness creates a tightly fitted seam between the first and second ends  59 ,  61  of the workpiece  62  and causes a slight expansion of the male projection  136  of the locking feature (if present) creating a tightly interlocked form. 
     The inventive process may be carried out in one form of the invention by feeding a metal strip  44  ( FIG. 7 ) of uniform width and thickness into a first end  146  of the die assembly  30  ( FIG. 2 ). The metal strip may be provided from a coil roll which contains a first and second edge  58 ,  60 . As the metal strip  44  is advanced into the assembly  30 , it encounters a trim station  36 , which imparts a first and second end  59 ,  61  to the metal strip  44 , by removing material from the first and second edge  58 ,  60 , preferably creating at least one tab  64 , and an interlocking feature  132 . A blanking tool  52  then forms individual workpieces  62  from the metal strip  144 , creating two side walls  78 . 
     The workpiece  22  ( FIG. 7 ) is then indexed into the annular forming station  38 , wherein the tab  64  is deflected so that it they may readily overlap the workpiece  62  as first and second ends  59 ,  61  are brought proximate to one another. The ends  59 ,  61  of the workpiece  62  are then abutted, creating an overlapped annular workpiece  114 . If the workpiece  62  contains optional interlocking features  132 , these features are also joined as the first and second ends  59 ,  61  are abutted. 
     The overlapped annular workpiece  114  is then indexed to the flange formation station  40 , wherein a flange  124  is formed on the side of the overlapped annular workpiece  114 , the tab  64  is brought co-planar with the flange  124 , and material from the tab  64  is used to fill in the ‘V’ shaped gap  68  ( FIG. 1 —Prior art) caused by the discontinuity  148  between the ends  59 ,  61  of the workpiece. Thus the tab  64 , when repositioned, provides adjacent support to the first and second ends  59 ,  61  located in the flanged region  150  of the fully flanged part  126 . 
     The fully flanged part  126  may optionally be indexed to a finish station  42  ( FIGS. 3 and 4 ), wherein the workpiece&#39;s annular radius is reduced, increasing the material thickness of the part. This increase in material thickness creates a tightly fitted seam at the ends  59 ,  61  of the workpiece and causes a slight expansion of the interlocking feature  132  creating a tightly interlocked form. 
     In an alternate form of the inventive process stated above, the end trim tool  50  may be modified to create a notched cutout  152  in the tab  64  on the first end of the workpiece  59  ( FIG. 13 ), while simultaneous placing a complimentary protrusion  154  on the second end  61  of the workpiece  62  ( FIG. 14 ). In the preferred embodiment, the notched cutouts  152  and complimentary protrusions  154  are oriented to lie perpendicular to the peripheral edge  156  of the strip. The subsequent stations of the die assembly  30  ( FIG. 1 ) are otherwise unmodified, and the flange forming station  40  ( FIG. 6 ) interlocks the flange  124  by joining the notched cutout  152  with the complimentary protrusion  154 . 
     The process and associated parts created by this process are considered that of the preferred embodiments only. Modifications of the invention will occur to those skilled in the art and those who make or use the invention. For instance, one skilled in the art would understand and appreciate that the process described could be performed in either a progressive or a transfer die system; with or without a carrier web. Hence, specific dimensions and other physical characteristics relating to the embodiments or tooling described shall not be considered limiting, unless expressly stated otherwise in the specification or the claims. Therefore, it is understood that the embodiments shown in the drawings and the examples set forth herein are described merely for illustrative purposes and not intended to limit the scope of the invention&#39;s claims as interpreted according to the principles of patent law, including the doctrine of equivalents.