Abstract:
An inner metal link bushing is formed by providing flat steel stock having a chamfered edge disposed at an angle relative to the surfaces such that, when the flat stock is reshaped to a tubular formation, the edges forming a longitudinal seam will initially contact one another at the outer surfaces thereof leaving slight gap between such edges in the area adjacent the inner surface. The tubular formation is placed in a die having a rigid interior wall surface in close relationship with the outer surface of the tubular formation and a mandrel is positioned inside the tubular formation in slightly spaced relationship therewith. Presses impose compressive forces on the opposing ends of the tubular formation sufficient to squeeze the ends of the tubular formation toward one another and to cause the inner and outer surfaces of the tubular formation to be homogeneously plastically deformed into firm contact respectively with the inner surface of the partible die and the outer surface of the mandrel. The reshaping caused by such compressive forces also forces the edges into sealing engagement with one another.

Description:
CROSS REFERENCE TO RELATED APPLICATION 
   This application is based upon and claims the benefit of U.S. Provisional Application No. 60/475,855 filed Jun. 4, 2003. 

   BACKGROUND OF THE INVENTION 
   Currently there are two common ways to manufacture rubber vibration isolators. Each involves a steel tube or inner metal link bushing surrounded by vulcanized rubber. The steel tube gives the isolator rigidity and provides the means to attach the device. The first method, method A, utilizes a preformed and cured rubber piece. The metal link bushing is coated with a rubber adhesive and pressed into the rubber piece. The adhesion sometimes breaks down and tends to separate the bushing from the rubber. The second and preferred method of manufacturing, method B, places the adhesive coated metal link bushing inside of a mold. The rubber is injected under pressure into the mold and the vibration isolator is cured as one unit. The benefit of this technology, method B, is the bond between the bushing and the rubber is much stronger than under method A. Under method B, the rubber will typically tear before the adhesive gives way. 
   Each of these methods uses a different raw product for the bushing. Method A uses a flat steel stock which, as described below, is progressively formed into a tube. Heretofore, method B has used “drawn over mandrel” (DOM) tubing or welded seam tubing. The raw material cost for DOM tubing is roughly 3–4 times that of flat stock used in forming tubing. The main reason for not heretofore using tubing formed from flat stock for method B, under which rubber is injection molded around tubing positioned in a mold, is seepage of rubber through the seam of the tubing due to the high pressure. Removing this material after curing is troublesome and not cost effective. 
   SUMMARY OF THE INVENTION 
   The present invention permits the use of flat metal stock for forming tubing to be used as a metal link bushing in manufacturing a vibration isolator using the feature of method B of injection molding rubber around the tubing and to do so without seepage of rubber into the interior of such tubular bushing. As a result, it permits the manufacture of a vibration isolator at a cost which is significantly lower than the cost of manufacturing one using DOM tubing according to method B but has the benefits of method B with the strong bond between the injection molded rubber and the metal tubing. 
   According to the present invention, a vibration isolator is formed by providing a substantially flat metal sheet which is deformed by a progressive die or other suitable equipment into a tubular formation. The flat metal sheet is provided with edges which, upon forming to a tubular formation, adjoin one another. The edges are tapered at an angle such that, upon the forming to form the tubular formation, the portions of such edges adjacent the outer surface of the tubular formation will come into contact with one another but portions of the opposing edges adjacent the inner surface of the tubular formation will be spaced from one another leaving an inwardly facing longitudinal gap in the tubular formation. The tubular formation is then positioned in a die having a rigid interior wall in close proximity or contact with the outer surface of the tubular formation. A mandrel is positioned in the interior of the tubular formation. While the tubular formation is thus positioned in the die, presses engage opposing ends of the tubular formation and apply compressive forces, on the order of 40 tons or more, to force the ends closer to one another and thereby causing the tubular formation to deform inwardly into conformity with the mandrel, expand into tight engagement with the rigid wall of the die and cause the edges to deform into firm contact with each other thereby closing the gaps. The compressive force is sufficiently high to cause the steel to flow and form a seal at such edges sufficiently tight to resist any inflow of rubber during injection molding of the rubber. Such cold flow of the steel is believed to create an intermolecular bond between the opposing edges to form such seal. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a schematic view showing reshaping flat steel stock with a progressive die to form a tubular formation. 
       FIG. 2A  is a perspective view of a partially formed length of tubing at an area within the progressive die following initial contact of opposing edges in a prior art process. 
       FIG. 2B  is a view similar to  FIG. 2A  showing a length of tubing formed in the prior art process following its exit from a progressive die. 
       FIG. 3A  is a perspective view of a length of tubular formation formed in a progressive die from flat steel stock having tapered edges as shown in  FIG. 4  according to the present invention. 
       FIG. 3B  is a view similar to  FIG. 3A  showing a length of tubular formation formed according to the present invention following further processing as described with reference to  FIGS. 5A and 5B  to form a metal link bushing. 
       FIG. 4A  is a plan view of a blank of steel used for forming a tubular formation according to the present invention. 
       FIG. 4B  is a sectional view taken through line  4 — 4  of  FIG. 4A . 
       FIG. 4C  is a side view of the blank of steel shown in  FIG. 4A . 
       FIGS. 5A and 5B  are schematic views in section showing the further processing of a length of tubular formation of  FIG. 3A  to form a metal link bushing as shown in  FIG. 3B . 
       FIGS. 6A and 6B  are schematic views showing injection molding rubber around the metal link bushing. 
       FIG. 7  is a view showing the metal link bushing formed according to the present invention. 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
   The steel tubes utilized in method A are made from flat stock material  10  fed through a progressive die set. This process cuts the flat stock to length and through a series of progressions, forms a tube like product as shown in  FIG. 1 . The end product or tube  12  retains a minimum of 50% seam closure with a visible gap on the outer diameter. This is a result of squared edges disposed at 90 degrees to the upper and lower surfaces of the flat stock material  10  and the fact that during the final progressions, the material edges are forced to flow from the inner diameter out. In an open die set localized work hardening stalls the material flow toward the outer diameter. This prevents full closure of the seam thereby providing a gap  22  between the edges  14  at the outer surface and a means for the rubber to breach the interior of the tube  12  during injection of the rubber according to method B as will be discussed in greater detail with reference to  FIGS. 2A and 2B . Additionally, the outer diameter surface condition is heavily marked from multiple striking and inconsistent in form and appearance. Residual stress is an additional side effect of progressive striking or forming. Localized regions of stress within the steel will result in movement of such steel when it is exposed to dynamic or thermal stress as is encountered by injection molding rubber therearound under method B. Such movement also contributes to the inability to obtain a leak-proof seal at the joined edges  14  thereby allowing rubber to seep through the seam 
   The process of the present invention allows the cost effective production of a bushing and vibration isolator in which the tubular formation for the bushing can be formed from flat stock fed through a progressive die set while permitting the injection molding of rubber therearound as described with reference to method B without encountering seepage of rubber into the interior. Furthermore, all product sizes will meet the process requirements of method B. 
   The process, features and advantages of the present invention include the following: 
   1. Coiled steel is slit to the required width to form a sheet of flat stock for a product family.
         Processing from mother coils lowers raw material cost.   Material wall thickness of the tubular formation is approximately 75% of final product.       

   2. Slit coils are processed through a roll former producing a continuous tubular formation.
         Roll forming process reduces local stress regions.   High volume/low maintenance.       

   3. A 25 degree angle chamfer is formed on edges. 
   4. Tubular formation is cut to length in a flying shear.
         High volume and accuracy.       

   5. The respective tubular formations are inserted in a die set with a mandrel positioned in the tubular formation and then cold formed from each end simultaneously with compression members applying compressive loads in the range of 40 tons.
         Eliminates the necessity of costly phosphate coated materials typically found in cold heading processes.   Produces a part with uniform and homogeneous plastic deformation.   Material flows from the outer diameter inward.   Near seamless appearance with exceptional resistance to breach by injection molded rubber.       

   6. Formed tubes are machined to final length and deburred.
         Minimal material loss.   Squares the end faces to protect against extruded rubber seepage or flashing.       

   As used herein, the term “tubular formation” means the product exiting the progressive die set before or after cutting to the desired length but before being subjected to the compressive forces forming the tube with a leak-proof seam. 
   Detailed Part Process 
   Steps 1, 2, 3 and 4 of the above process provide a rough dimensioned tubular formation suitable for forming a part conforming to the desired specifications. Each edge of the flat stock is shaped with a chamfer of 25 degrees plus or minus 10 degrees, such that the edges which abut one another following passing through the progressive die set will make contact with the opposing edge in the area adjacent the outer surface of the tubular formation. The tubular formation is formed in one continuous operation and cut to length. The application of compressive forces to the ends of such tubular formation when positioned in a die with a mandrel inside the tubular formation creates a smooth outer surface on the finished tube. This alleviates the problem of material being pushed through the seam during injection molding of rubber in method B processing. 
   The cold forming or pressing operation is based on the weight/mass of the finished tube. Forming is done by a dual action cold forming process. The rough sized tubular formation is placed into a die,  FIGS. 5A and 5B , to hold the outer diameter to the tolerances necessary. A mandrel is placed through the tubular formation to create the inside dimension of the finished tube. Applying compressive force on both ends of the tubular formation causes the steel flow into the void spaces between the tubular formation and (1) the die and (2) the mandrel and to fill in gaps between the joined edges. It also shortens the length such that the length of the finished tube is within 0.005″ of the specified length. Carbide milling heads may be used to trim the tube to size. 
   Referring to  FIGS. 1 ,  2 A and  2 B, there is shown forming a blank of flat stock steel  10  by means of a progressive die into a tubular shape which can be trimmed by a cutter  13  to form a tubular formation  12 A of desired length. The flat stock  10  of the prior art had edges  14  which were perpendicular to the opposing sides or surfaces  16 ,  18  of the sheet  10 .  FIG. 2A  shows schematically the positioning of the edges  14  of a section of nearly formed tubing at the area of the progressive die when the opposing edges  14 ,  14  initially come into contact with one another. As can be seen in  FIG. 2A , since the edges  14 ,  14  of the original flat blank  10  were cut at 90° to the flat surface  16  intended to become the inner surface and the opposing surface intended to become the outer surface  18  of the partially formed tubular formation  12 A, the edges  14 ,  14  will initially contact one another at an interior line of contact  20  at the inner surface  16 . As the partially formed length of tubing (tubular formation  12 A) continues to be processed, the edges  14 ,  14  are squeezed together resulting in a squeezing together initially at the interior surface  16  and flowing outwardly. However, as the length of tubing  12  exits the progressive die, there will remain a gap  22  between the edges  14 , 14  at the outer surface  18 . As previously discussed, when a length of tubing  12  such as that shown in  FIG. 2B  is utilized as an inner metal link bushing according to method B previously described in which rubber is injected under pressure into a mold containing such metal link bushing, the rubber will seep through the gap  22  and be forced into the interior surface  16  between the joined edges  14 . 
   Under the present invention, a blank  30  of steel (see  FIGS. 4A ,  4 B and  4 C) having a flat first side  32  intended to form the inner surface of the tubing and a flat second side  34  intended to form the outer surface of the tubing is provided. The blank  30  has side edges  36  which will be joined together following forming in the progressive die or other reshaping mechanism to form a tubular formation  40  as shown in  FIG. 3A . The side edges  36  are each disposed at an included angle of 65°±10° to the outer surface  34 . This is shown in  FIG. 4B  as an angle of 115°±10° to the extended planes of the first side  32  and edges  36 . Each of the edges  36  forms a line of juncture  37  with the second side  34 . Third and fourth edges  38 ,  38  intended to become the ends of the length of the tubular formation  40  and the formed tubing extend between the angled edges  36  and are disposed at right angles to the first and second sides  32  and  34 . 
   Referring to  FIG. 3A , there is shown a length of tubular formation  40  as trimmed following its exit from the progressive die or other reshaping mechanism. The lines of juncture  37  of the respective tapered edges  36  are shown as having made contact with one another along a line of contact  42  at the outer surface  34  but are also shown as having a gap  44  along the inner surface  32 . 
     FIG. 3B  shows the finished length of tubing  40 A after processing as shown in  FIGS. 5A and 5B  with the edges  36 A engaged to one another throughout their complete surface areas. The tubing  40 A is suitable for use as an inner metal link bushing. 
   As shown in  FIGS. 5A and 5B , the tubular formation  40  is enclosed within the sections of a partible die  50 , with the inner surface  52  of each die section being rigid and slightly spaced from the outer surface  34  forming a gap  55 . The gap  55  is quite small, being only large enough to accommodate irregularities at the outer surface  34  to permit the sections of the partible die  50  to close therearound. A mandrel  54  is positioned in the tubular formation  40  in spaced relationship with the inner surface  32  leaving a gap  57 . First and second punches  56 , each of which is substantially equal in size to the size of the ends  38  of the tubular formation  40 , are engaged to the opposing ends  38  of the tubular formation  40 . A compressive force on the order of 40 tons or more is applied to the punches  56  and by the punches  56  to the ends  38  to thereby force the ends  38  closer to one another and thereby causing the steel of tubular formation  40  to flow into the gap  55  between the outer surface  34  and inner surfaces  52  of the partible die  50  and into the gap  57  between the inner surface  32  and the mandrel  54 . The steel will flow inwardly to a greater extent than outwardly as the gap  57  is wider than the gap  55 . Such flowing of the steel under the high compressive forces also causes the opposing edges  36  to become firmly joined together throughout their length and breadth as joined edges  36 A as shown in  FIG. 3B  forming a tube  40 A defining a metal link bushing with a longitudinal seam S. As will be appreciated, the compressive forces will cause the ends  38 A to be closer together than the ends  38  of the tubular formation  40 . The compressive force and flowing of the steel form a seam S which is sealed sufficiently tight to resist any inflow of rubber during injection molding of the rubber as previously described according to method B. The compressive force causes the steel to be homogeneously plastically deformed thereby resulting in such leak-proof seal at the seam S. 
   Referring to  FIGS. 6   a  and  6 B, there is shown schematically injection molding of rubber around the tube  40 A which was formed in accordance with the present invention with the seam S. The tube  40 A is positioned between the open halves  60 A and  60 B of a partible mold. Following such positioning, the mold halves  60 A and  60 B are closed around the tube  40 A as shown in  FIG. 6B . The closed mold halves  60 A and  60 B define a cavity  62  larger in peripheral size than the tube thereby leaving a space in which rubber may be injection molded. 
   As is well known in the art, rubber is processed in an extruder  64  and delivered/injected under pressure through a passageway  66  leading to one of the mold halves  60 A. As shown in  FIG. 6B  the mold half  60 A is provided with an inlet passageway  68  for receiving the heated rubber from the extruder  64  and its passageway  66  and delivering it to the cavity  62  to thereby form a rubber member R. As shown in  FIG. 6B , the rubber encircles the circumferential periphery of the tube  40 A in a bonding relationship. However, as a result of the tube  40 A being formed in accordance with the present invention, the seam S is sealed sufficiently tight to be able to resist any in-flow of rubber into the interior of the tube  40 A during the injection molding operation. 
   Referring to  FIG. 7 , there is shown a bushing  70  for use as a component of a vibration isolator. It could be used with a variety of vibration isolators widely available in the art. The bushing  70  comprises (1) the metal tube  40 A formed in accordance with the teachings and descriptions of  FIGS. 3 through 5A  and  5 B, and (2) the injection molded rubber member R formed as shown and described with respect to  FIGS. 6A and 6B . Additionally, the bushing  70  may have an outer metal layer  72  encircling the rubber member R. 
   Modifications will be readily apparent to those skilled in the art. Accordingly, the scope of the present invention should be limited only by the scope of the claims appended hereto.