Abstract:
A method of forming a crankshaft bushing or similar component is provided. A compaction die is provided having an axial, generally cylindrical internal opening. An upper and a lower punch are provided with exterior surfaces corresponding to the internal opening of the compaction die. An upper core rod passes through an axial opening in the upper punch. A lower core rod passes through an axial opening in the lower punch. The upper core rod and the lower core rod each may have a generally flat external surface section. A metal powder is compacted in the compaction die by the combined action of the upper and lower punches and the upper and lower core rods.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    The present invention relates to a method of forming a crankshaft bushing and, more particularly, a method of forming a crankshaft bushing using a powder metal process with a compaction die combined with punches and core rods. 
         [0002]    Ordinary powder metal procedures and methods for forming crankshaft bushings and similar components having a generally cylindrical axial internal opening are useful. However, if a modification is necessary to the internal axial opening within the bushing, such as the forming of a slightly convex surface, such traditional powder metal methods require further finishing. Such further finishing is usually in the form of machining wherein the external cylindrical geometry of the outer diameter is ground such that the slightly convex surface is accurately oriented to the outer geometry. Such additional machining steps are not desirable from a cost point of view and from a productivity point of view. 
         [0003]    Accordingly, is an object of the present invention to provide an improved method for forming a crankshaft bushing or similar component utilizing powder metal methods. 
         [0004]    It is another object of the present invention to provide a method of forming a crankshaft bushing or similar component using powder metal procedures wherein an internal surface of the bushing includes a generally flat or slightly convex surface. 
       SUMMARY OF THE INVENTION 
       [0005]    A method of forming a crankshaft bushing or similar product using powder metallurgy techniques is provided. 
         [0006]    Typically, a compaction die having a generally cylindrical axial internal opening is provided. A lower punch is provided having an exterior surface that corresponds to the internal opening of the compaction die. An upper punch is provided having an exterior surface that also corresponds to the internal opening of the compaction die. 
         [0007]    The lower punch itself further has an internal opening that is generally cylindrical and axial. A lower core rod has an exterior surface that corresponds to the internal opening of the lower punch. 
         [0008]    The upper punch also has a generally cylindrical axial internal opening. An upper core rod is provided that has an exterior surface that corresponds to the internal opening in the upper punch. 
         [0009]    A metal powder is introduced into an internal opening of the compaction die. The metal powder is compacted to form a powder metal blank by having the lower punch and upper punch enter the internal opening of the compaction die. Further the lower core rod passes through the axial opening in the lower punch and the upper core rod passes through the opening in the upper punch to also enter the compaction die in a manner such that a top surface of the lower core rod and a bottom of the upper core rod approach each other. Accordingly, a powder metal blank in the general form of the bushing or similar product is formed. 
         [0010]    Further, the lower core rod includes a generally flat or slightly convex section on its exterior surface which section is tapered from the top surface of the lower core rod downwardly to an intersection with an exterior wall section of the lower core rod. Similarly, the upper core rod includes a generally flat or slightly convex section on its exterior surface which section is tapered from the bottom surface of the upper core rod upwardly to an intersection with an exterior wall section of the upper core rod to form the generally flat or slightly convex section on the powder metal blank. 
         [0011]    Further, the lower core rod itself includes a generally cylindrical axial internal opening. Upon compaction of the metal powder in the internal opening of the compaction die, excess metal powder can exit the internal opening of the compaction die through the internal opening in the lower core rod. 
     
    
     
       BRIEF OF THE DESCRIPTION OF THE DRAWINGS 
         [0012]    In the drawings,  FIG. 1  is a side, cross sectional view of an apparatus for carrying out the method of the present invention; 
           [0013]      FIG. 2  is a side, cross sectional view at a 90° angle from the view of  FIG. 1  of an apparatus for carrying out the method of the present invention; 
           [0014]      FIG. 3  is a perspective view of an upper punch and upper core rod in accordance as part of the apparatus for carrying out the method in accordance with the present invention; 
           [0015]      FIG. 4  is a bottom view of a lower punch and lower core rod and compaction die of an apparatus for carrying out the method of the present invention; 
           [0016]      FIG. 5  is a perspective view of a bushing made in accordance with the method of the present invention, and 
           [0017]      FIG. 6  is a side view in cross section of a bushing made in accordance with the method of the present invention. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
       [0018]    Referring to  FIGS. 1 and 2 , compaction die  12  is seen to be a generally cylindrical structure having an internal cylindrical surface  13 . Compaction die  12  usually comprised of a tool steel and is usually between 5 and 10 inches (12.7 and 25.4 centimeters) in diameter and about 5 to 10 inches in height (12.7 and 25.4 centimeters). Internal opening  13  is obviously tied to the desired shape of the bushing or other product being formed, but such internal diameter is usually 1 to 2 inches with a height of 2 to 4 inches (2.54 to 5.08 to 2.54 to 10.16 centimeters). 
         [0019]    Lower punch  14  is again seen to be a generally cylindrical structure with an outer diameter corresponding to internal opening  13  of compaction die  12 . Lower punch  14  has a usually cylindrical outer surface  16 , with again a usually cylindrical axial internal opening  18 . Lower punch  14  again is usually comprised of a tool steel, and is usually about 4 to 6 inches in length (10.16 to 15.24 centimeters). 
         [0020]    Lower core rod  20  is seen to comprise a generally cylindrical structure having an outer surface  22  that corresponds to internal opening  18  of lower punch  14 . Lower core rod  20  also includes an axial, usually cylindrical internal opening  24  that extends from the top surface  26  of lower core rod  22  to the bottom  25  of lower core rod  20 . Again lower core rod  20  is usually comprised of tool steel and is generally 6 to 8 inches in length (15.24 to 20.32 centimeters). 
         [0021]    Upper punch  30  is seen to be generally cylindrical structure having an outer generally cylindrical surface  32  and an internal generally cylindrical axial opening  34 . Again the dimensions of upper punch  30  would be similar to the dimension of lower punch  14  in that outer surface  32  of outer punch  30  would enter internal opening  13  in compaction die  12  from the top; whereas lower punch  14  enters opening  13  of compaction die  12  from the bottom. Upper punch  30  is also seen to have an internal generally cylindrical axial opening  34  of a similar dimension to the internal opening  18  of lower punch  14 . Upper punch  30  is usually comprised of tool steel and usually has a length of 2 to 3 inches (5.08 to 7.62 centimeters). 
         [0022]    Upper core rod  36  is seen to be generally cylindrical structure having an outer surface  38  that is generally cylindrical and sized to fit into internal opening  34  of upper punch  30 . Upper core rod  36  is also seen to have a bottom surface  40  which is seen to approach and align with top surface  26  of lower core rod  20 . Bottom surface  40  of upper core rod  36  is also seen to include a protrusion  42  which is usually of a tapered cylindrical or pyramidal type structure. Such protrusion  42  is seen to align with and enter a corresponding depression  44  in the top surface  26  of lower core rod  20 . 
         [0023]    Further, lower core rod  20  is seen to have a flattened or slightly concave surface  48  that extends from outer surface  22  of lower core rod  22  to the top surface  26  of lower core rod  20 . Similarly, upper core rod  36  is seen to have a flattened surface  46  that extends from the outer surface  38  of upper core rod  36  to the bottom surface  40  of upper core rod  36 . 
         [0024]    Referring now to  FIG. 3 , a detailed view of upper punch  30  is shown, with outer surface  32  of upper punch  30  clearly being shown as a cylindrical surface. Further, upper core rod  36  is also shown with bottom surface  40  and protrusion  42 . Protrusion  42  is here shown to be a tapered cylindrical surface, but could be a pyramidal tapered surface as well. Upper core rod  36  is also seen to comprise a flat surface or slightly concave  46  extending from bottom  40  of upper core rod  36  upwardly to an intersection with outer surface  38  of upper core rod  36  in a tapering fashion. 
         [0025]    Referring now to  FIG. 4 , bottom of compaction die  12  is shown with compaction die  12  clearly seen to be a generally cylindrical structure. Internal opening  13  in compaction die  12  is also clearly shown. Lower core rod  20  is clearly seen to be a generally cylindrical structure protruding from the internal opening in upper punch  30  top surface of  26  of lower core rod  20  is also clearly shown to have an internal opening  24  therein the top of which is a depression  44 . Depression  44  leads to internal opening  24  in lower core rod  20 . Finally, lower core rod  20  is seen to have flat surface  48  that approaches and aligns with flat surface  46  and upper core rod  36 . 
         [0026]    Referring now to  FIGS. 5 and 6 , a crankshaft bushing made in accordance with the method of the present invention is generally shown at  50 . Bushing  50  is seen to have a generally cylindrical outer surface  52 , with a first inner flat surface  54  and a second inner flat surface  56 . Bushing  50  can be comprised of any of the desired metal powder compositions, which will be described further below in examples. First inner flat surface  54  of bushing  50  would be formed by contact with upper core rod flat surface  46 , and bushing second inner flat surface  56  is formed by contact with lower core rod flat surface  48 . 
         [0027]    The material for bushing  50  can be, as mentioned above, any low alloy material that would produce a strong wear resistant metallic structure. 
         [0028]    In general, a method of manufacturing a bushing in accordance with one aspect of the present invention comprises the steps of providing an initial metal alloy powder comprising the desired elemental components, with the balance essentially iron. A suitable lubricant is added in accordance with powder metal practice to form lubricated metal powder. The lubricated metal powder is then injected into the internal opening of compaction die  12 . The metal powder is then compacted, typically at a pressure of between 40 and 65 tons per square inch, to form a die compacted metal blank. The compaction is accomplished by having the upper punch  30  and lower punch  14  enter the opening in compaction die  12  under suitable pressures, while the lower core rod  20  and upper core rod  36  both enter the internal opening of compaction die  12  through the respective openings in lower punch  14  and upper punch  30 . The partial flatten surfaces on bushing  50  are created by the alignment of lower core rod  20  and upper core rod  36 , with top surface  26  of lower core rod  20  and bottom surface  40  of upper core rod  36  approaching and eventually contacting each other with upper core rod protrusion  42  entering depression  44  in lower core rod top surface  26 . 
         [0029]    Examples of the method of carrying out the present invention follow: 
       EXAMPLE 1 
       [0030]    In a method of manufacturing a crankshaft bushing, a metal powder of particle sizes between 45 and 250 micron was provided comprising, by weight, 0.5% C composition and 0.85% Mo composition, with the balance essentially iron. A 0.75 percent of EBS was added as a lubricant to form a lubricated metal powder. The lubricated metal powder was compacted at a pressure of 45 tons per square inch in a compaction die utilizing a lower punch having a lower core rod and an upper punch having an upper core rod. The resulting die compacted metal blank was then sintered at a temperature of 2080° F. for 15 minutes, the sintered metal blank was then quenched from an initial temperature of 1650° F. to a temperature of 150° F. The quenched metal blank was then tempered at a temperature of 380° F. for 120 minutes. The final tempered metal blank was then finish ground to the final bushing dimensions and configurations. 
       EXAMPLE 2 
       [0031]    In a method of manufacturing a crankshaft bushing, a metal powder of particle sizes between 45 and 250 micron was provided comprising, by weight, 0.5% C composition and 1.5% Mo composition, with the balance essentially iron. A 0.75 percent of EBS was added as a lubricant to form a lubricated metal powder. The lubricated metal powder was compacted at a pressure of 45 tons per square inch in a compaction die utilizing a lower punch having a lower core rod and an upper punch having an upper core rod. The resulting die compacted metal blank was then sintered at a temperature of 2080° F. for 15 minutes, the sintered metal blank was then quenched from an initial temperature of 1650° F. to a temperature of 150° F. The quenched metal blank was then tempered at a temperature of 380° F. for 120 minutes. The final tempered metal blank was then finish ground to the final bushing dimensions and configurations.