Abstract:
Methods for coining or forging powdered metal parts are disclosed. One example method uses a press including a first rod, a first ram surrounding the first rod, a die plate having a die cavity, a second rod opposite the first rod, and a second ram surrounding the second rod wherein the first rod and the second rod are dimensioned to fit within the inside diameter of the part. In the method, the part is positioned within the die cavity, one of the first rod and the second rod is located as a core rod within the inside diameter of the part, and at least one of the first ram and the second ram is moved toward the other of the first ram and the second ram such that both the first ram and the second ram contact and coin or forge the wall of the part.

Description:
CROSS-REFERENCES TO RELATED APPLICATIONS  
       [0001]     Not Applicable.  
       STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH  
       [0002]     Not Applicable.  
       BACKGROUND OF THE INVENTION  
       [0003]     1. Field of the Invention  
         [0004]     This invention relates to methods for coining or forging powdered metal parts, particularly cylindrical parts.  
         [0005]     2. Description of the Related Art  
         [0006]     Powder metal processing involves transforming powdered metal in the compaction process into a sintered product at a given density. The compacting process utilizes presses with a variety of motions to distribute the powder into various sections of the die and when compacted has a relatively even density distribution throughout the part. These motions are essential in distributing the right amount of material within the part. Coining processes, that requalify the sintered dimensions and in some cases further densify the part, are presently done in unsophisticated presses. To alter material flow in these coining processes, complex tooling is required and in most cases is part specific.  
         [0007]     Metal forming has improved over the years with the introduction of CNC (Computer Numerical Controlled) hydraulic presses. These presses have a wide range of adjustability to increase the precision of the formed part and are able to make a wider range of complex geometries. No longer are manufacturers bound by the limitations of most mechanical presses. Example CNC presses are described in U.S. Pat. Nos. 5,435,216, 4,721,028 and 4,116,122. However, secondary presses for coining and forging have not kept pace with these developments as it applies to powder metal processing. This is where the need for a CNC forging/coining press becomes essential.  
         [0008]     Thus, there is still a need for improved methods for coining and forging powder metal parts.  
       SUMMARY OF THE INVENTION  
       [0009]     The invention provides a method wherein a CNC forging/coining press is used to integrate processing steps. A part can be cold worked to increase the overall density while simultaneously burnishing the inner or outer profile. Pressing from the lower and upper rams simultaneously can be obtained in such a press. Another feature is the ability to vary pressing rates. Small features require a slower rate to reach a desired density as compared to a larger feature on the same part. Now the two features could be programmed so that at the final density both portions would reach a uniform density at the same time. Also in forging, if an area becomes fully dense in the center of the cross section of the part, there will be little material movement below the central dense area and the lower portion of the part due to the top down direction of the forging process. Balancing the pressing rates can reduce this limitation.  
         [0010]     One feature of the new method is to balance the press motion requirements for powder metal processing. Material needs to be redistributed in almost all cases in pressing operations. The later operations, forging/coining, require the same movements as required in the compacting operation. Where they differ is the need to use portions of the tooling to aid other portions of the tooling such as ejecting cores. The timing of the closed-loop systems is critical to insure no tooling is damaged.  
         [0011]     As stated above, current methods for forging and coining incorporate relatively simple, unsophisticated machines for producing powdered metal parts. The present invention is a press with programmable features that would allow a variety of motions to forge and/or coin complex powdered metal parts. Having a press with advanced capabilities gives manufacturers the ability to combine processes that are currently done in separate machinery, for example, burnishing. The press would also allow users to program varying pressing rates for flanged parts to maintain even material flow while cold or hot working the part. The advanced functions would also reduce the complexity of the tooling required by adding programmable rotary motions for processing products with helical features.  
         [0012]     In the hot forging process, the invention allows users to program a variety of motions to reduce the time a tool member comes in contact with the hot part increasing the core rod tool life. Tool members could also be used in combination to aid in ejection of forms that have a high ejection force, for example, large core rods. This would reduce the stress on bolts currently used to hold such tool members further increasing the life of the tooling.  
         [0013]     One advantage of the invention is to off-load the complexities in the tooling arrangements and add them as features to the machine. Off-loading the tooling complexities to the press has three distinct advantages: (1) changes in tooling operation can be made by adjusting the program, not by expensive tooling modifications, (2) the material flow can be modified in a number of ways for a given set of tools, and (3) the overall cost of the tooling is less since there is no need for costly specialized adapters. These factors can reduce the development time and cost associated when launching new products.  
         [0014]     Thus, the invention provides a method for coining or forging a part having a wall with an inside diameter. In one form, the part is a powder metal part. The method uses a press including a first rod, a first ram surrounding the first rod, a die plate having a die cavity, a second rod opposite the first rod, and a second ram surrounding the second rod wherein the first rod and the second rod are dimensioned to fit within the inside diameter of the part. In the method, the part is positioned within the die cavity, one of the first rod and the second rod is located as a core rod within the inside diameter of the part, and at least one of the first ram and the second ram is moved toward the other of the first ram and the second ram such that both the first ram and the second ram contact and coin or forge the wall of the part. The one of the first rod and the second rod acting as the core rod is then ejected from the inside diameter of the part by pushing the one of the first rod and the second rod acting as the core rod with the other of the first rod and the second rod.  
         [0015]     In one version of the method, the first rod is a lower rod, the second rod is an upper rod, the first ram is a lower ram, and the second ram is an upper ram. The first ram and the second ram are dimensioned to fit within the die cavity, and the first ram and the second ram both move toward each other such that both the first ram and the second ram contact and coin or forge the wall of the part.  
         [0016]     In another version of the method, the first rod is a lower rod, the second rod is an upper rod, the first ram is a stationary lower ram, and the second ram is an upper ram. The first ram and the second ram are dimensioned to fit within the die cavity, and the second ram moves toward the first ram such that both the first ram and the second ram contact and coin or forge the wall of the part.  
         [0017]     In yet another version of the method, the part has an outwardly extending flange on an end of the part. In this version of the method, the first rod is a lower rod, the second rod is an upper rod, the first ram is a stationary lower ram, and the second ram is an upper ram having an outside diameter substantially equal to an outside diameter of the flange. The first ram and the second ram are dimensioned to fit within the die cavity, and the second ram moves toward the first ram such that both the first ram and the second ram contact and coin or forge the wall of the part.  
         [0018]     In still another version of the method, the part is a gear having an inside surface with helical teeth. In this version of the method, the first rod is the core rod, the first rod is rotatable, and the first rod has an outer surface with helical ribs dimensioned to be slidingly complementary to the helical teeth of the gear. In this version of the method, the first rod is oscillated within the gear before ejecting the first rod from the gear in order to rotary burnish the helical teeth of the gear.  
         [0019]     In yet another version of the method, the part is a gear having an inside surface with helical teeth. In this version of the method, the first rod is the core rod, the first rod is rotatable, and the first rod has an outer surface with helical ribs dimensioned to be slidingly complementary to the helical teeth of the gear. The second rod is an upper rotatable rod having an outer surface with helical ribs dimensioned to be slidingly complementary to the helical teeth of the gear. In this version of the method, the first rod is oscillated within the gear before ejecting the first rod from the gear with the second rod in order to rotary burnish the helical teeth of the gear.  
         [0020]     In still another version of the method, the first ram and the second ram are dimensioned to fit within the die cavity, and the method further comprises oscillating the first ram and the second ram when the first ram and the second ram coin or forge the wall of the part to aid in material movement and to provide for burnishing of the outer surface of the part. Preferably, the oscillation is at a high frequency  
         [0021]     In yet another version of the method, the part is a gear having an inside surface with helical teeth, and the first rod is the core rod and the first rod is an upper rotatable rod having an outer surface with helical ribs dimensioned to be slidingly complementary to the helical teeth of the gear. In this version of the method, the first rod, the first ram and the die table are moved toward the second ram such that both the first ram and the second ram contact and coin or forge the wall of the part. The gear may include a second inside surface having a diameter less than a diameter of the inside surface with helical teeth of the gear, and accordingly the second rod is dimensioned for sliding fit within the second inside surface of the gear to rotary burnish the second inside surface of the gear.  
         [0022]     In still another version of the method, the part is a gear having an inside surface with helical teeth, and the second rod is the core rod and the second rod is a lower rotatable rod having an outer surface with helical ribs dimensioned to be slidingly complementary to the helical teeth of the gear. This version of the method includes the step of moving the first rod, the first ram and the die table toward the second ram such that both the first ram and the second ram contact and coin or forge the wall of the part.  
         [0023]     In yet another version of the method, the method provides for locating the part within the die cavity. In this version of the method, the first rod is an upper rod, the second rod is a lower rod, the first ram is an upper ram, and the second ram is a lower ram. This version of the method includes the steps of extending a lower end of the first rod beyond a lower end of the first ram, locating the lower end of the first rod within the inside diameter of the part, positioning the part within the die cavity by way of the first rod, locating the second rod as the core rod within the inside diameter of the part, and moving the first ram and the die table toward the second ram such that both the first ram and the second ram contact and coin or forge the wall of the part. The part may be a gear having an inside surface with helical teeth, and the second rod may be a lower rotatable rod having an outer surface with helical ribbing dimensioned to be slidingly complementary to the helical teeth of the gear to rotary burnish the helical teeth. Also, the first rod may have an outside diameter less than an outside diameter of the second rod to avoid contact of the first rod with the helical teeth.  
         [0024]     In still another version of the method, the first rod is an upper rod, the second rod is a lower rod and the second rod has an outside diameter greater than an outside diameter of the first rod, the first ram is an upper ram, and the second ram is a lower ram. This version of the method includes the steps of locating the second rod as the core rod within the inside diameter of the part, and moving the first rod, the first ram and the die table toward the second ram such that both the first ram and the second ram contact and coin or forge the wall of the part The part may be a gear having an inside surface with helical teeth, and accordingly, the second rod is a rotatable rod having an outer surface with helical ribs dimensioned to be slidingly complementary to the helical teeth of the gear to rotary burnish the helical teeth. This version of the method may further include the step of moving the die plate downward to eject the coined or forged part.  
         [0025]     In yet another version of the method, the method includes the step of providing the press with means for varying pressing rates of the first ram and the second ram to maintain even material flow while cold or hot working the part. The means for varying pressing rates may include a processor in communication with a hydraulic system for controlling downward and upward movement of the first ram and the second ram.  
         [0026]     In still another version of the method, the method includes the step of providing the press with means for varying downward and upward movement rates of the first rod and the second rod to maintain even material flow while cold or hot working the part. The means for varying downward and upward movement rates may include a processor in communication with a hydraulic system for controlling downward and upward movement of the first rod and the second rod.  
         [0027]     In another aspect, the invention provides a method for coining or forging a part. In one embodiment, the part is a powdered metal part. The method uses a press including a core rod, a ram surrounding the core rod, and a die plate having a die cavity wherein the core rod is dimensioned to fit within an inside diameter of the part. The part is positioned within the die cavity, and the core rod is located within the inside diameter of the part. The ram is moved such that the ram contacts and coins or forges the part, and the core rod is oscillated axially back and forth within the part before removing the core rod from the part to burnish the inside diameter of the part.  
         [0028]     In one version of this method, the part is a gear having an inside surface with helical teeth, the core rod is rotatable, and the core rod has an outer surface with helical ribs dimensioned to be slidingly complementary to the helical teeth of the gear to burnish the part. In another version of this method, the press includes a second core rod, the second core rod being rotatable and having an outer surface with helical ribs dimensioned to be slidingly complementary to the helical teeth of the gear. The second core rod is located within the inside diameter of the part and oscillated axially back and forth within the part before removing the second core rod from the part to burnish the inside diameter of the part. The second rod may have an outside diameter less than an outside diameter of the core rod. The press may include a second ram such that the ram and the second ram can move toward each other to coin or forge the part.  
         [0029]     In yet another version of this method, a lower end of the core rod is extended beyond a lower end of the ram, and located within the inside diameter of the part. The part is then positioned within the die cavity by way of the first rod. In still another version of this method, the press includes a second core rod, and the part includes a second inside surface having a diameter less than a diameter of the inside surface of the part, and the second core rod is dimensioned for sliding fit within the second inside surface of the part.  
         [0030]     In yet another aspect, the invention provides a method for coining or forging a part. In one embodiment, the part is a powdered metal part. The method uses a press including a ram and a die plate having a die cavity. In the method, the part is positioned within the die cavity, and the ram is moved such that the ram contacts the part, and the ram is oscillated back and forth when the ram contacts the part to coin or forge the part.  
         [0031]     In one version of this method, the press has a second ram. The second ram is moved such that the second ram contacts the part, and the second ram is oscillated back and forth when the second ram contacts the part to coin or forge the part. In one form, the ram and the second ram are dimensioned to fit within the die cavity. In another form, the part has an outwardly extending flange on an end of the part, and the second ram has an outside diameter substantially equal to an outside diameter of the flange, and the second ram moves toward the ram such that both the ram and the second ram contact and coin or forge the part. In another version of this method, the press has a core rod dimensioned to fit within an inside diameter of the part, and the core rod is located within the inside diameter of the part before coining.  
         [0032]     In still another aspect, the invention provides a method for coining or forging a part. In one embodiment, the part is a powdered metal part. The method uses a press including a ram, a die plate having a die cavity, and means for varying pressing rates of the ram. The part is positioned within the die cavity, and the ram is moved such that the ram contacts the part. The pressing rate of the ram is varied after the ram contacts the part to coin or forge the part. The means for varying pressing rates may be a processor in communication with a hydraulic system for controlling downward and upward movement of the ram.  
         [0033]     The press may include a core rod dimensioned to fit within an inside diameter of the part, and means for varying downward and upward movement rates of the core rod. The core rod is located within the inside diameter of the part before or after positioning the part within the die cavity, and downward and upward movement rates of the core rod are varied within the inside diameter of the part. The means for varying downward and upward movement rates may be the processor in communication with a hydraulic system for controlling downward and upward movement of the core rod.  
         [0034]     In one version of this method, the press has a second core rod opposite the core rod and has a second ram surrounding the second core rod wherein the core rod surrounds the ram, and the core rod and the second rod are dimensioned to fit within the inside diameter of the part. The core rod and the second core rod are located within the inside diameter of the part, and the ram and the second ram are moved toward each other such that both the ram and the second ram contact and coin or forge the wall of the part. The ram and the second ram may be dimensioned to fit within the die cavity. The core rod and the second core rod may also be rotatable.  
         [0035]     These and other features, aspects, and advantages of the present invention will become better understood upon consideration of the following detailed description, drawings, and appended claims. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0036]      FIGS. 1   a  to  1   j  are front cross sectional views on a vertical plane containing the axis of the lower rod, lower ram, upper rod, and upper ram of a press executing a sequence of steps for a first example embodiment of a method for coining or forging a part according to the invention.  
         [0037]      FIGS. 2   a  to  2   i  are front cross sectional views on a vertical plane containing the axis of the lower rod, lower ram, upper rod, and upper ram of a press executing a sequence of steps for a second example embodiment of a method for coining or forging a part according to the invention.  
         [0038]      FIGS. 3   a  to  3   f  are front cross sectional views on a vertical plane containing the axis of the lower rod, lower ram, upper rod, and upper ram of a press executing a sequence of steps for a third example embodiment of a method for coining or forging a part according to the invention.  
         [0039]      FIGS. 4   a  to  4   f  are front cross sectional views on a vertical plane containing the axis of the lower rod, lower ram, upper rod, and upper ram of a press executing a sequence of steps for a fourth example embodiment of a method for coining or forging a part according to the invention.  
         [0040]      FIG. 5  shows a helical gear that may be forged using the method shown in  FIGS. 3   a  to  3   f.    
         [0041]      FIG. 6  shows a helical gear that may be forged using the method shown in  FIGS. 4   a  to  4   f.    
         [0042]      FIGS. 7   a  to  7   d  are front cross sectional views on a vertical plane containing the axis of the lower rod, lower ram, upper rod, and upper ram of a press executing a sequence of steps for a fifth example embodiment of a method for coining or forging a part according to the invention. 
     
    
       [0043]     Like reference numerals will be used to refer to like parts from Figure to Figure in the following description of the drawings.  
       DETAILED DESCRIPTION OF THE INVENTION  
       [0044]     Referring first to  FIGS. 1   a  to  1   j , there are shown front cross sectional views on a vertical plane containing the axis of the lower rod, lower ram, upper rod, and upper ram of a press executing a sequence of steps for a first example embodiment of a method for coining or forging a part according to the invention. The press, indicated generally at  10 , includes an upper core rod  20 , an upper ram  30 , a die plate  40 , a lower core rod  50 , and a lower ram  60  all having a common axis A.  
         [0045]     The upper core rod  20  is mounted for rotational movement on the piston (not shown) of a cylinder (not shown). The piston and the cylinder are part of an upper core rod hydraulic system for controlling downward and upward movement of the upper core rod  20 . The upper core rod hydraulic system is controlled by a processor which is in communication with the upper core rod hydraulic system. The processor is a microprocessor, computer, microcomputer or other circuit capable of handling inputs and outputs to control the upper core rod hydraulic system in accordance with a programmed routine. An example control system for a hydraulic cylinder can be found in U.S. Pat. No. 4,721,028 which is incorporated herein by reference along with the other patents cited herein.  
         [0046]     The upper ram  30  is mounted on a piston (not shown) of a cylinder (not shown). The piston and the cylinder are part of an upper ram hydraulic system for controlling downward and upward movement of the upper ram  30 . The upper ram hydraulic system is also controlled by the processor.  
         [0047]     The die plate  40  is mounted on a piston (not shown) of a cylinder (not shown). The piston and the cylinder are part of a die plate hydraulic system for controlling downward and upward movement of the die plate  40 . The die plate hydraulic system is also controlled by the processor. The die plate  40  has a cylindrical die cavity  42 .  
         [0048]     The lower core rod  50  is mounted on a support shaft  52  for rotational movement. The support shaft  52  is mounted on a lower rod support  54  which is mounted on the piston (not shown) of a cylinder (not shown). The piston and the cylinder are part of a lower core rod hydraulic system for controlling downward and upward movement of the lower core rod  50 . The lower core rod hydraulic system is controlled by the processor.  
         [0049]     The lower ram  60  is mounted on a support  62  which is mounted to a piston (not shown) of a cylinder (not shown). The piston and the cylinder are part of an lower ram hydraulic system for controlling downward and upward movement of the lower ram  60 . The lower ram hydraulic system is also controlled by the processor.  
         [0050]     Thus, downward and upward movement of the upper core rod  20 , the upper ram  30 , the die plate  40 , the lower core rod  50 , and the lower ram  60  of the press  10  can be operated in accordance with a routine programmed in the processor. In this regard, a commercially available CNC hydraulic press may be suitably modified to operate in accordance with the method of the present invention. User initiated control inputs may be provided to processor to set the operating parameters of the hydraulic press. For example, the processor may permit the user to select the up and down stroke speed of each hydraulic cylinder, the position at which the stroke is reversed, or the tonnage at which the stroke will reverse. Other user controlled inputs may also be provided to processor depending on the particular features desired with the press. For instance, rotational movement of the upper core rod  20  and the lower core rod  50  can be controlled by the processor.  
         [0051]     Still referring to  FIGS. 1   a  to  1   j , the sequence of steps for a first example embodiment of a method for coining or forging a part according to the invention is shown. In  FIG. 1   a , a hollow cylindrical part  70  is loaded into die cavity  42  and lower core rod  50  is inserted in the hollow interior of the part  70 . The upper ram  30  then moves into the die cavity  42  to close off the die plate  40  as shown in  FIG. 1   b . The upper core rod  20  and the lower core rod  50  then come into contact as shown in  FIGS. 1   b  and  1   c . In  FIGS. 1   d  to  1   h , the upper ram  30  and the lower ram  60  move into equal amounts in opposite directions to compact the part  70  while the upper core rod  20  and the lower core rod  50  move down at a faster rate to start burnishing the inside surface  74  of the wall  72  of the part  70 . The upper ram  30  and the lower ram  60  keep moving in equal amounts to densify the part  70 .  
         [0052]     While the densification process is taking place, the upper core rod  20  and the lower core rod  50  are making an upward and downward motion during the process until the part  70  reaches its finished dimension. This upward and downward motion of the upper core rod  20  and the lower core rod  50  serves to densify and burnish the inside surface of the part  70 . When the part  70  is a gear having helical teeth on the inside surface of the gear, the outer surface of the upper core rod  20  may have helical ribs dimensioned to be slidingly complementary to the helical teeth of the gear. Also, the outer surface of the lower core rod  50  may have helical ribs dimensioned to be slidingly complementary to the helical teeth of the gear. Because the upper core rod  20  and the lower core rod  50  are mounted for rotational movement, the upper core rod  20  and the lower core rod  50  rotate and serve to burnish the helical teeth of the gear during upward and downward motion. The upper ram  30  and the lower ram  60  also have the capability of small upward and downward high frequency motion while compacting the part  70  to aid in material movement during forging and to provide for burnishing of the outer surface of the part  70 .  
         [0053]     In  FIG. 1   i , the upper core rod  20  and the upper ram  30  move up to their home positions while the die plate  40  moves down to expose the finished part  70 . After removal of the finished part  70 , the press  10  is in the loading position shown in  FIG. 1   j  so that another part  70  may be loaded into the die cavity  42  for processing.  
         [0054]     Turning now to  FIGS. 2   a  to  2   i , there are shown front cross sectional views of the press  10  executing a sequence of steps for a second example embodiment of a method for coining or forging a part according to the invention. In  FIG. 2   a , the cylindrical part  70  is placed near the die cavity  42 . Looking at  FIG. 2   b , upper core rod  20   a  is moved down to line up the cylindrical part  70  with the die cavity  42 . It can be seen that upper core rod  20   a  has a diameter smaller than lower core rod  50  and the inside diameter of the part  70 . Next, as shown in  FIG. 2   c , the upper core rod  20   a  is moved up and the upper ram  30  is moved down to capture the part  70 . Then, as shown in  FIG. 2   d , the upper core rod  20   a  and the upper ram  30  move down to place the part  70  into the die cavity  42 .  
         [0055]     Turning to  FIG. 2   e , the lower core rod  50  is inserted in the part  70 , and the upper core rod  20   a , the upper ram  30 , the die plate  40 , and the lower ram  60  move downward. No material movement occurs in the part  70 . Then, as shown in  FIG. 2   f , the upper core rod  20   a , the upper ram  30 , the die plate  40 , and the lower core rod  50  move downward to forge the part. In  FIG. 2   g , the upper core rod  20   a  and the lower core rod  50  move downward to eject the lower core rod  50 . Because the upper core rod  20   a  has a diameter smaller than lower core rod  50 , the upper core rod  20   a  does not contact the part  70  when ejecting the lower core rod  50 . This aids in ejection of the lower core rod  50 . Then, as shown in  FIG. 2   h , the upper core rod  20   a  and the upper ram  30  move up to top-dead-center, and the die plate  40  moves downward to eject the part  70 . In  FIG. 2   i , the die plate  40 , the lower core rod  50  and the lower ram  60  move to their original positions such that location and loading of another part  70  can occur. Thus, the method of  FIGS. 2   a  to  2   i  provides for location of parts in a die cavity. This method is particularly useful for locating out of round parts in a die cavity.  
         [0056]     In  FIGS. 3   a  to  3   f , there are shown front cross sectional views of a press executing a sequence of steps for a third example embodiment of a method for coining or forging a part according to the invention. In particular, the press sequence of  FIGS. 3   a  to  3   f  may be used to forge a helical gear  70   a  as shown in  FIG. 5 . Looking at  FIG. 5 , the gear  70   a  includes a cylindrical wall  72   a  having an inside surface  74   a  with helical teeth  75   a  and an outside surface  76   a  with helical teeth  77   a.    
         [0057]     Referring now to  FIGS. 3   a  to  3   f , in  FIG. 3   a , the press  10  is in the loaded position with gear  70   a  in the die cavity  42 . In  FIG. 3   b , the lower core rod  50  is inserted in the gear  70   a , and the upper core rod  20   a , the upper ram  30 , the die plate  40  and the lower ram  60  move downward with no material movement of the gear  70   a . In  FIG. 3   c , the upper core rod  20   a , the upper ram  30 , the die plate  40  and the lower core rod  50  move downward to forge the gear  70   a . The lower core rod  50  may have an outer surface with helical ribs dimensioned to be slidingly complementary to the helical teeth  75   a  of the gear  70   a  in order to burnish the helical teeth  75   a  of the gear  70   a . The lower core rod  50  is mounted for rotational movement so that the lower core rod  50  may rotate and burnish the helical teeth  75   a  of the gear  70   a  during upward and downward motion. In  FIG. 3   d , the upper core rod  20   a  and the lower core rod  50  move downward to eject the lower core rod  50 . Because the upper core rod  20   a  has a diameter smaller than lower core rod  50 , the upper core rod  20   a  does not contact the part  70   a  when ejecting the lower core rod  50 . In  FIG. 3   e , the upper core rod  20   a  and the upper ram  30  move up to top-dead-center and the die plate  40  moves downward to eject the gear  70   a . Then as shown in  FIG. 3   f , the die plate  40 , the lower core rod  50  and the lower ram  60  move to their original positions such that loading of another gear  70   a  can occur.  
         [0058]     In  FIGS. 4   a  to  4   f , there are shown front cross sectional views of a press executing a sequence of steps for a fourth example embodiment of a method for coining or forging a part according to the invention. In particular, the press sequence of  FIGS. 4   a  to  4   f  may be used to forge a helical gear  70   b  as shown in  FIG. 6 . Looking at  FIG. 6 , the gear  70   b  includes a cylindrical wall  72   b  having an inside surface  74   b  with helical teeth  75   b  and an outside surface  76   b  with helical teeth  77   b . A lower end of the gear  70   b  has an inwardly directed flange  79  on the inside surface  74   b . The flange  79  forms a smooth inside surface of reduced diameter on the end of the gear  70   b.    
         [0059]     Referring now to  FIGS. 4   a  to  4   f , in  FIG. 4   a , the press  10  is in the loaded position with gear  70   b  in the die cavity  42 . In  FIG. 4   b , the upper core rod  20 , the upper ram  30 , and the lower core rod  50   a  are moved down to insert the gear  70   b  into the die cavity  42 . The upper core rod  20  may have an outer surface with helical ribs dimensioned to be slidingly complementary to the helical teeth  75   b  of the gear  70   b  in order to burnish the helical teeth  75   b  of the gear  70   b . The upper core rod  20  is mounted for rotational movement so that the upper core rod  20  may rotate and burnish the helical teeth  75   b  of the gear  70   b  during upward and downward motion. The lower core rod  50   a  has a smaller diameter than the upper core rod  20  and therefore, the lower core rod  50   a  can burnish the inside surface of the flange  79  on the end of the gear  70   b . In  FIG. 4   c , the upper core rod  20 , the upper ram  30 , the die plate  40  and the lower core rod  50   a  move downward to forge the gear  70   b . In  FIG. 4   d , the upper core rod  20  moves upward to eject the lower core rod  50   a . Alternatively, the lower core rod  50   a  could eject the upper core rod  20 . In  FIG. 4   e , the upper core rod  20  and the upper ram  30  move up to top-dead-center, and the die plate  40  and the lower core rod  50   a  move downward to eject the gear  70   b . In  FIG. 4   f , the die plate  40  and the lower core rod  50   a  move to their original positions such that loading of another gear  70   b  can occur.  
         [0060]      FIGS. 7   a  to  7   d  are front cross sectional views of a press executing a sequence of steps for a fifth example embodiment of a method for coining or forging a part according to the invention. In particular, the press sequence of  FIGS. 7   a  to  7   f  may be used to forge a part  70   c  including a cylindrical wall  72   c  having an outside surface  76   c  with an outwardly directed flange  81 .  
         [0061]     Referring now to  FIGS. 7   a  to  7   d , in  FIG. 7   a , the press  10  is in the loaded position with part  70   c  in the die cavity  42   c  of the die plate  40   c . The die plate  40   c  has a ledge  44   c  located below the top surface  46   c  of the die plate  40   c . The outwardly directed flange  81  of the part  70   c  rests on the ledge  44   c  when the part  70   c  is loaded in the die plate  40   c . In  FIG. 7   b , the lower core rod  50  is inserted in the part  70   c , and the upper core rod  20   a , the upper ram  30 , the die plate  40   c  and the lower ram  60  move downward with no material movement of the part  70   c . It can be seen that upper core rod  20   a  has a diameter smaller than lower core rod  50 . In  FIG. 7   c , the upper core rod  20   a , the upper ram  30 , the die plate  40   c  and the lower core rod  50  move downward to forge the part  70   c . The lower core rod  50  is dimensioned to be slidingly complementary to the inside surface of the gear  70   c  in order to burnish the inside surface of the gear  70   c . In  FIG. 7   d , the upper core rod  20   a  and the lower core rod  50  move downward to eject the lower core rod  50 . The upper core rod  20   a  and the upper ram  30  may then move up to top-dead-center and the die plate  40   c  may move downward to eject the part  70   c . Because the upper core rod  20   a  has a diameter smaller than lower core rod  50 , the upper core rod  20   a  does not contact the part  70   c  when ejecting the lower core rod  50 . Then, the die plate  40   c , the lower core rod  50  and the lower ram  60  move to their original positions such that loading of another part  70   c  can occur as shown in  FIG. 7   a.    
         [0062]     Although the present invention has been described with reference to certain embodiments, one skilled in the art will appreciate that the present invention can be practiced by other than the described embodiments, which have been presented for purposes of illustration and not of limitation. For example, while the invention has particular utility in coining and/or forging powder metal parts, the invention can also be applied to wrought metal parts. Therefore, the scope of the appended claims should not be limited to the description of the embodiments contained herein.  
       INDUSTRIAL APPLICABILITY  
       [0063]     The invention relates to methods for coining or forging powdered metal parts.