Abstract:
The disclosed method provides a way to fabricate a powder metal compact implementing a top fill through one or more of the upper tool members. The top fill step allows for pre-compaction chamber, defined at least in part by at least one of the upper tool members, to be filled with a powder metal after the upper tool member is initially lowered, but before compaction of the powder metal. The manner in which the pre-compaction chamber is filled allows for the formation of complex geometries in powder metal compacts that are not obtainable using conventional lower tool powder transfer motions and further minimizes or avoids unacceptable variations in powder fill to final part ratios across the powder metal compact.

Description:
CROSS-REFERENCES TO RELATED APPLICATIONS 
     This application represents the national stage entry of PCT International Application No. PCT/US2010/035095 filed on May 17, 2010 and claims the benefit of U.S. provisional patent application No. 61/179,125 entitled “Powder Metal Die Filling” filed on May 18, 2009, and U.S. provisional patent application No. 61/225,799 entitled “Powder Metal Die Filling” filed on Jul. 15, 2009. The contents of both of these applications are hereby incorporated by referenced as if set forth in their entirety herein. 
    
    
     STATEMENT CONCERNING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT 
     Not applicable. 
     BACKGROUND OF THE INVENTION 
     This invention relates to powder metal components and the process used to make them. In particular, this invention relates to a method of making parts having complex shapes using powder metal compaction. 
     Powder metallurgy provides a method of forming metallic parts. Making a part from powder metal typically includes the steps of filling a tool and die set with a powder metal powder, uni-axially compacting the metal powder using the tool and die set to form a powder metal compact, and sintering the powder metal compact to bond the particles of the powder metal compact together to form a final powder metal part. Although the final powder metal part is usually less than fully dense, a powder metal part has exceptional dimensional accuracy in comparison to parts made using other metal fabrication techniques. 
     To form the top side features in a powder metal compact, between the fill and compaction step, powder metal from the lower portion of the die is transferred upward by the relative movement of the lower tool members. If properly done, this powder transfer moves the powder to the appropriate location within the die cavity for compaction while simultaneously maintaining a powder fill to final part ratio of approximately 2:1 over the different vertical columns of the die cavity in the direction of compaction. If the powder fill to final part ratio is not maintained across the various features of the part, then the final part may have unacceptable variations in density. 
     Even though some parts having complex shapes can be made using powder metallurgy, certain geometries cannot be produced as a single part using the above-described techniques. To make powder metal parts having these geometries, two or more sections of the part need to be separately compacted and then joined together after compaction. However, two or more separate compaction steps and a joining step is time consuming, costly, and is likely to require significant post-sintering secondary operations. 
     Hence, a need exists for a way to form powder metal parts having complex geometries. 
     SUMMARY OF THE INVENTION 
     A method of forming a powder metal compact is disclosed. A tool set is utilized including a die having a die cavity, at least one lower tool member, and at least one upper tool member. At least one powder feed chute extends through one of the upper tool members. The lower tool member or members are inserted into the die cavity. The die cavity is filled with a powder metal in a first fill step. An upper tool member or members are then lowered to define a pre-compaction chamber. The pre-compaction chamber includes a filled section that was filled with the powder metal during the first fill step and an unfilled section that is not yet filled with the powder metal. The unfilled section of the pre-compaction chamber is filled with powder metal in a second fill step via the at least one powder feed chute that extends through the at least one upper tool member into the pre-compaction chamber. The powder metal is compacted along an axis of compaction to form a powder metal compact. The powder metal compact is then ejected from the die cavity. 
     The second fill step may include shuttling the powder metal from a hopper system to the upper tool member using a feed plate assembly. The feed plate assembly may include a sliding plate that has at least one powder cavity of a metered volume formed in the sliding plate. The sliding plate may be moveable between a first position and a second position. In the first position, the powder cavity or cavities are located beneath the hopper system to receive a charge of powder metal equal in volume to the powder cavity or cavities. In the second position, the powder cavity or cavities are placed in communication with the powder feed chute or chutes in the upper tool member to allow the charge of powder metal to be fed to the pre-compaction chamber. 
     There may also be a support block between the feed plate assembly and the upper tool member. The feed plate assembly may be positioned on a top side of the support block and the upper tool member may be attached to a bottom side of the support block. The support block may include at least one powder feed chute that places the powder cavity or cavities of the sliding plate in communication with the powder feed chute or chutes of the upper tool member when the sliding plate is in the second position. 
     The sliding plate may include a slot through which other upper tool member or members extend in both the first position and the second position of the sliding plate. The sliding plate may have a plurality of powder cavities that are not co-axial with the upper tool member or members that extend through the slot in the sliding plate. 
     The powder feed chute or chutes in the upper tool member may extend through the upper tool member at an angle relative to the axis of compaction. 
     The tool set may include an upper inner punch, an upper middle punch surrounding at least a portion of the upper inner punch, and an upper outer punch surrounding at least a portion of the upper middle punch. The step of lowering the upper tool member or members to define the pre-compaction chamber may include lowering the upper outer punch. The step of lowering the upper tool member or members to define the pre-compaction chamber may further include lowering the upper inner punch to form a cylindrical cavity or the like over the die cavity. During the second fill step, the upper middle punch may be in a retracted position to place the powder feed chute or chutes of the upper outer punch in communication with the pre-compaction chamber. During the step of compacting the powder metal, the upper middle punch may be lowered such that a surface of the upper middle punch slides past an opening of the powder feed chute or chutes in the upper outer punch to remove the powder feed chute or chutes from communication with the pre-compaction chamber. 
     The powder metal compact formed by the method may have at least two different cross sections taken perpendicular to the axis of compaction of the powder metal compact. Each of the two cross sections may have a first filled powder area that is not included in the other of the cross sections. Each of the two cross sections may also have a second filled powder area that is included in the other of the cross sections. This part geometry may be achieved using a top fill during the second fill step and not by a conventional powder transfer motion of the lower tool member or members. A ratio of a powder fill to a final powder metal compact may be approximately 2:1 across the various vertical columns of the die cavity. 
     The first fill step may be performed by placing a feed shoe over the die cavity. 
     The second fill step may be performed by gravity. 
     The step of lowering the upper tool member or members to define a pre-compaction chamber may include moving a lower surface or surfaces of the upper tool member or members flush with a powder metal fill surface of the powder metal from the first fill step. 
     The method may further include the step of sintering the powder metal compact to form a sintered powder metal part. Thus, a sintered powder metal part made by the method is also disclosed. 
     Likewise, a powder metal compact made by the method is disclosed. As stated above, the powder metal compact may have at least two different cross sections taken perpendicular to the axis of compaction of the powder metal compact. Each of the different cross sections have a first filled area of powder metal that is included in the other of the different cross sections and a second filled area of powder metal that is not included in the other of the different cross sections. 
     Thus, the disclosed method provides a way to fabricate a powder metal compact using a top fill step through one or more of the upper tool members. The top fill step allows for pre-compaction chamber, formed at least in part by the upper tool members, to be filled with a powder metal in a manner that is not possible using conventional lower tool powder transfer motions without complex lower tooling members. Further, the manner in which the pre-compaction chamber is filled avoids unacceptable variations in powder fill to final part ratios across the powder metal compact. 
     These and still other advantages of the invention will be apparent from the detailed description and drawings. What follows is merely a description of some preferred embodiments of the present invention. To assess the full scope of the invention, the claims should be looked to as these preferred embodiments are not intended to be the only embodiments within the scope of the claims. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a top perspective view of a segment gear showing a hub side of the gear; 
         FIG. 2  is a bottom perspective view of the segment gear of  FIG. 1  showing the axially-facing gear teeth; 
         FIG. 3  is a top plan view of the segment gear of  FIG. 1 ; 
         FIG. 4  is a cross-sectional side view of the segment gear taken along line  4 - 4  of  FIG. 3 ; 
         FIG. 5  is a flow chart outlining a set of steps for the fabrication of a complex part such as the segment gear; 
         FIGS. 6-10  are cross-sectional views of a tool and die set in a compaction press in which the upper and lower tool members are in the first fill position before the first fill, the first fill position after the first fill, the second fill position after the upper tool members have been lowered but before the second fill, the second fill position after the second fill, and the compaction position, respectively; 
         FIG. 11  is a perspective view of a feed plate assembly attached to a support block; 
         FIG. 12  is a top perspective view of a support block without the feed plate assembly or the upper outer punch attached; and 
         FIG. 13  is a top perspective view of the upper outer punch. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Referring first to  FIGS. 1-4 , a one piece segment gear  100  is shown. The segment gear  100  is fabricated as a single powder metal compact using the powder metal processes according to a process  200  described below. However, the structure of the segment gear  100  is now described to provide context for the steps of the process  200 . 
     The segment gear  100  is a powder metal part which is formed by compression along an axis of compaction which is parallel to axis A-A and B-B. The segment gear  100  includes a pie-shaped body section  102  having a top surface  104  and a bottom surface  106  which are generally parallel to one another and which are both perpendicular to axis A-A. The body section  102  extends from a central hub  108  at an axis A-A to an arcuate wall  110  at an outer periphery of the segment gear  100 . 
     The central hub  108  is generally cylindrically-shaped and extends downward from the bottom surface  106  of the body section  102 . The central hub  108  and has a lower axial surface  112 , a radially-outward facing surface  114 , and an axially-extending through hole  116  which extends from the top surface  104  to the lower axial surface  112 . The axially-extending through hole  116  has radially-inward facing splines  118  formed therein. 
     The arcuate wall  110  extends downward from the bottom surface  106  of the body section  102 . The arcuate wall  110  includes a radially-inward facing surface  120  and a radially-outward facing surface  122 . On the downward facing surface between the radially-inward facing surface  120  and the radially-outward facing surface  122  of the arcuate wall  110 , a plurality of gear teeth  124  are formed. In the form shown, the gear teeth  124  extend in a generally radially direction relative to axis A-A although the planes defining the tips of the gear teeth  124  are non-perpendicular to the axis A-A. 
     A top side hub  126  is formed on the top surface  104  of the body section  102  and extends along axis B-B which is parallel to, but spaced from, axis A-A. The top side hub  126  is generally cylindrically-shaped having a radially-outward facing surface  128 , a radially-inward facing surface  130 , and an upper axial surface  132 . The radially-inward facing surface  130  defines a cylindrically-shaped cavity  134  in the top side hub  126 . A lower surface  136  of the cavity  134  is essentially parallel with the top surface  104  of the body section  102 . 
     As best shown in  FIGS. 1 and 4 , the top surface  104  also includes a step  138  proximate the arcuate wall  110 . The step  138  is offset from the rest of the top surface  104 . As the top side hub  126  straddles the step  138  and the rest of the top surface  104 , vertical columns of material having varying thicknesses are provided in the region of the top side hub  126  and the arcuate wall  110 . 
     It should be appreciated that a part having this geometry could not be formed as a unitary powder metal compact by a conventional powder metal compaction process. Typically, attempts to form top features, such as the hub  126 , are made by transferring powder metal within the die cavity by a powder transfer motion of the lower tool members. As the powder is transferred, the powder fill to final part ratio along the vertical columns of the part must be approximately 2:1 to provide a part that is relatively uniformly dense after the compaction process. 
     However, a comparison of a horizontal cross section through the hub  126  and a horizontal cross section through the arcuate wall  110  with gear teeth  124  would reveal that there are areas of powder metal in the hub  126  which are not found in the arcuate wall  110  with gear teeth  124  and areas of powder metal in the arcuate wall  110  with gear teeth  124  that are not found in the hub  126 . Thus, conventional tool and die sets are incapable of performing a powder transfer motion that provides an acceptable powder fill to final part ratio over a component having this final geometry. Instead, to fabricate a part of this type, the different sections are conventionally separately compacted and then joined afterwards. 
     Referring now to  FIG. 5 , a process  200  is outlined that allows for the formation of a single powder metal compact, and ultimately a sintered powder metal part, for a component having a geometry similar to the segment gear  100 . With additional reference to  FIGS. 6-10 , which show specific steps of the filling and compaction steps, the steps of the process  200  will be described. 
     In order to form the powder metal compact, a tool and die set must be provided and installed in a compaction press. As shown in  FIGS. 6-10 , the tool and die set includes a die  300  having a die insert  302  that defines a portion of the die cavity  304 . The die insert  302  is typically made of a hard tool material and is formed to have a shape similar to the outline of the periphery of the part. The lower tool members includes a lower core rod  306  which forms the through hole  116 , a lower outer punch  308  surrounding the lower core rod  306  which forms the lower axial surface  112 , and a lower tool member  310  which form the gear teeth  124 . The lower tool members are inserted upward into the die cavity  304  so as to provide a bottom floor in the die cavity  304  and to provide side walls in locations which the die insert  302  would be incapable of forming side walls during compaction (e.g., the radially outward facing surfaces of the lower core rod  306  to form the splines  118  of the through hole  116 ). A number of upper tool members are also provided including an upper outer punch  312  sized to fit into a periphery of an upper portion of the die cavity  304 , an upper middle punch  314  that is at least in part surrounded by the upper outer punch  312 , and an upper inner punch  316  that is at least in part surrounded by the upper middle punch  314 . 
     The upper tool members are configured such that a powder metal can be fed through at least one of the upper tool members. Referring now to  FIGS. 11-13 , a support block  318  is shown to which the upper outer punch  312  and a feed plate assembly  320  are attached. The support block  318  is mounted to a portion of the upper press assembly such that the support block  318 , the upper outer punch  312 , and the feed plate assembly  320  move together regardless of the positioning of the other upper tool members. 
     The feed plate assembly  320  shuttles charges of the powder metal from an axially offset hopper system  322  to powder feed chutes  324  and  326  that run through the support block  318  and the upper outer punch  312 , respectively. The feed plate assembly  320  includes a sliding plate  328  that has a guide slot  330  and three powder cavities  332  which extend through the sliding plate  328 . The linear path of the sliding plate  328  is guided by a track system that slidably connects sliding plate  328  to the support block  318 . The track system includes front guides  334  and rear guides  336  that engage the lateral sides of the sliding plate  328  and a middle guide  338  that engages the walls of the guide slot  330 . 
     The feed plate assembly  320  includes an actuation mechanism that moves the three powder cavities  332  of the sliding plate  328  back and forth between the hopper system  322  and the powder feed chutes  324  and  326 . In the form shown, the actuation mechanism includes a set of cylinders  340  (shown retracted in  FIG. 11 ), which can be extended and retracted to move a connecting bar  342  that is connected to the sliding plate  328  via a pair of linkages  344 . Of course, other actuation mechanisms could be used to move the sliding plate  328 . As will be described in more detail below, the particular timing of the shuttling of the powder metal from the hopper system  322  to the powder feed chutes  324  and  326  is timed with the press cycle. 
     The track system and actuation mechanism allows the sliding plate  328  to be movable between a first position (not shown) and a second position (shown in  FIG. 11 ). In the first position, the powder cavities  332  are located under the hopper system  322  to receive a charge of powder metal. In the second position, the powder cavities  332  are slid over the support block  318  such that the bottom of the powder cavities  332  align with the upper openings of the powder feed chutes  324  in the support block  318  and are placed in communication with the powder feed chutes  324  and  326  of the support block  318  and upper outer punch  312 , respectively. When the powder cavities  332  are in any position other than over the powder feed chutes  324  in the support block  318 , a lower surface beneath the powder cavities  332  supplied by a support plate  345  (which also has holes aligning with the powder feed chutes  324 ) prevents the powder metal charge from dropping out of the bottom of the powder cavities  332 . 
     Referring now to  FIG. 12 , the details of the support block  318  are shown. The support block  318  is generally cylindrically shaped with a number of bolt holes  346  for mounting the support block  318  to the upper press assembly. A number holes and/or chutes extend through the support block  318 . A through hole  348  axially extends through the support block  318  to accommodate for the passage of the upper middle punch  314  and the upper inner punch  316  through the support block  318 . Additionally, three powder feed chutes  324  or channels are situated about the through hole  348 . As can be best seen in  FIGS. 8 through 10 , the three powder feed chutes  324  extend axially inward as the powder feed chutes  324  extend downward. 
     Referring now to  FIG. 13 , the details of the upper outer punch  312  are shown. The upper outer punch  312  has an opening  350  extending axially there through. When the upper outer punch  312  is mounted to the support block  318 , the opening  350  has three powder feed chutes  326  which align with the exit ends of the three powder feed chutes  324  on the bottom face of the support block  318 . These powder feed chutes  326  direct the powder metal downward and axially inward. Further, three walls  352  separate the feed chutes  326  from one another and guide the upper middle punch  314  (which has a complementary sliding fit with the inner diameter of the opening  350  as provided by the three walls  352 ) as the upper middle punch  314  extends through the upper outer punch  312 . 
     Looking at the feed plate assembly  320 , the support block  318 , and the upper outer punch  312  in combination with the rest of the upper tool members, it should be observed that the particular design of the sliding plate  328  and powder feed chutes  324  and  326  is made to accommodate the extension of the upper middle punch  314  and the upper inner punch  316  through the other components. The slot  330  in the sliding plate  328 , the through hole  348  in the support block  318 , and the opening  350  of the upper outer punch  312  accommodate the passage and axial movement of the upper middle punch  314  and the upper inner punch  316  there through during the press cycle. 
     The movement of the upper middle punch  314  relative to the upper outer punch  312 , allows openings  356  of the powder feed chutes  326  to be opened or closed by sliding a radially outward facing surface of the upper middle punch  314  past the openings  356  in the upper outer punch  312 . The position of the powder cavities  332 , and the powder feed chutes  324  and  326  that align with the powder cavities  332  in the second position, are designed to provide a relatively even distribution of powder metal through the upper tooling members into the annular chamber  354 , when the upper middle punch  314  is sufficiently retracted, as will be described in more detail below. 
     The rest of the press and tool members will not be described in detail. However, those of ordinary skill in the art will appreciate that the press can be configured such that the stroke of each of the tool members relative to the die  300  can be controlled independently. Further, those having ordinary skill in the art will appreciate that other combinations of tool members could be substituted to perform similar functions. For example, the upper outer punch  312  could be replaced by two separate punches including a punch used to form the step  138  separate from the rest of the top surface  104 . Likewise one or more lower tool members may be used to form the gear teeth  124 . 
     Referring now to  FIG. 6 , the filling and compaction steps begin with the lower core rod  306 , lower outer punch  308 , and lower tool member  310  being inserted in the die cavity  304  from below to form a bottom of the die cavity  304  and additional interior side walls. Although the lower tool members provides a base or floor of the die cavity  304 , the lower tools are also retracted relative to their compaction position which is illustrated in  FIG. 10 . Prior to the powder filling, all of the upper tool members are initially in a lifted position above the die cavity  304 . 
     With the upper tool members lifted as shown in  FIG. 6 , a feed shoe (not shown) can be moved over the die cavity  304  to fill the die cavity  304  with a powder metal according to the first fill step  202 . When the feed shoe is retracted from over the die cavity  304 , the powder metal fill line in the die cavity  304  is level with an upper surface  358  of the die  300  as illustrated in  FIG. 7 . 
     Next, at least some of the upper tool members are lowered towards the die cavity  304  according to step  204 . As shown in  FIG. 8 , the upper outer punch  312  and the upper inner punch  316  are lowered to a point at which their lower axial faces are flush with (or slightly below) the powder metal fill line which corresponds to the upper surface  358  of the die  300 . The upper outer punch  312  and the upper inner punch  316  may be brought into contact with the powder metal already in the die cavity  304  from the first fill step  202 , but do not significantly compact the powder metal at this point in the process. 
     It is observed that the axial face of the upper outer punch  312  used to form the step  138  is slightly below the powder metal fill line in  FIG. 8 . Depending on the particular dimensions and compactability of powder metal, this slight compaction of the powder metal below the face of the upper outer punch  312  may be acceptable. However, if this slight compaction is not acceptable, then this condition may be remedied by replacing the one-piece upper outer punch with a two-piece upper outer punch having one piece that moves independently of the other piece that forms the step  138 . 
     At some point, either before or after the upper tool members are lowered, the upper middle punch  314  is retracted relative to the upper outer punch  312  and the upper inner punch  316 . This defines an annularly-shaped cylindrical space  354  between the upper outer punch  312  and the upper inner punch  316  that will be used to form the top side hub  126 . It should be noted, however, that the timing and degree of the retraction of the upper middle punch  314  needs to be properly coordinated with the delivery of the powder metal charge by the feed plate assembly  320 . When the upper middle punch  314  is retracted above the powder feed chutes  326  of the opening  350  in the upper outer punch  312 , if powder is present in the powder feed chutes  326 , the powder will be delivered by gravity into the space  354  between the upper outer punch  312  and the upper inner punch  316 . If the upper tool members are not yet descended to a position such as that shown in  FIG. 8 , then the powder metal will be prematurely fed and not captured in the annularly-shaped cylindrical space  354 . 
     When the upper tool members are lowered into the position shown in  FIG. 8 , the upper tool members, the lower tool members, and the die cavity define a pre-compaction chamber. The pre-compaction chamber includes a filled portion, which includes the bottom portion previously filled with powder metal during the first fill step  202 , and an unfilled portion, which is the volume defined by the space  354  between the upper tool members above the powder metal fill line from the first fill step  202 . 
     At this point, the powder metal from the upper tooling members is delivered to the unfilled portion of the pre-compaction chamber in a second fill step  206 . This delivery is performed by shuttling powder metal via the powder cavities  332  of the sliding plate  328  from the hopper system  322  to the powder feed chutes  324  in the support block  318 . Once the powder cavities  332  are aligned with the powder feed chutes  324  in the support block  318 , gravity causes the powder metal in the powder cavities  332  to drop through the powder feed chutes  324  in the support block  318 , through the powder feed chutes  326  in the upper outer punch  312 , and into the annular space  354  (assuming the upper middle punch  314  is sufficiently retracted to place the powder feed chutes  326  in communication with the annular space  354 ). The charge of powder metal delivered to the unfilled portion of the pre-compaction chamber should provide an appropriate amount of powder metal to the unfilled portion of the pre-compaction chamber to form the top side hub  126 . As the powder cavities  332  are of metered volume, the aggregate metered volume can be selected to be of a volume equal to the amount of powder metal to form the top side hub  126 . Although only one set of powder feed chutes  324  and  326  are shown in the cross section of  FIG. 8 , as can be appreciated from  FIGS. 11-13 , there are, in fact, three powder feed chutes. Depending on the particular design of the tools there may be one or more powder feed chutes within the upper tool members. 
     Once the second fill step  206  is complete as is illustrated in  FIG. 9 , then the powder fill to final part ratio should be approximately 2:1 in each of the vertical columns of powder. Of course, as some powder materials have different compressibilities or targeted compacted apparent densities, and so the exact ratio may differ. 
     After the second fill step  206 , the powder metal is properly distributed within the pre-compaction chamber formed by the tool members and the die. Now the upper middle punch  314  is lowered to seal the openings  356  of the powder feed chutes  326 , completely closing the pre-compaction chamber. At this point, the upper and lower tool members can compress the powder metal in the pre-compaction chamber according to the compaction step  208 . The final tool placement at the end of the compaction step  208  is shown in  FIG. 10 . During compaction, the upper outer punch  312  and the upper inner punch  316  are moved downward into the die insert  302  to form the body section  102 , the upper middle punch  314  is moved downward to form the top side hub  126 , the lower outer punch  308  is extended upward to form the central hub  108 , and the lower tool member  310  is moved upward to form the gear teeth  124 . This forms a one piece powder metal compact having a geometry of the segment gear  100 . 
     After the powder metal compact is formed, the powder metal compact is ejected from the tools and die in an ejection step  210 . During ejection, the upper and lower tool members are retracted in a coordinated sequence to separate the powder metal compact from the surfaces of the upper and lower tools and die. Typically, the upper outer punch  312  and upper inner punch  316  would be retracted first, while the upper middle punch  314  held the upper axial surface  132  of the top side hub  126  in place to prevent the compacted top side hub  126  from fracturing due to upward force on the radially-facing walls. Once the upper tool members are removed from the powder metal compact, the lower tools are raised to an eject position in which the bottom side features are ejected from the walls of the die cavity  304 . Of course, the ejection sequence may vary based on part geometry and the die and tool members used to form the powder metal compact. 
     Finally, the powder metal compact may be sintered according to step  212 , by processes well known in the art. During sintering, the powder metal compact is heated to temperatures below the melting point of the powder metal in a controlled atmosphere to cause the powder metal particles to diffuse, resulting in the particles necking together, and forming a strong solid sintered part. During sintering the part dimensions may shrink as porosity decreases, but the part maintains its general shape. To account for this shrinkage, the powder metal compact is typically engineered to be slightly larger than the final sintered part. 
     Additionally, the sintered part may be subjected to any number of finishing or secondary process. The sintered part could be deburred, machined, heat treated, carburized, coined, forged, or subjected to any of a number other post-sintering operations known to those of ordinary skill in the art. 
     Although a method has been disclosed to create a segment gear having a hub on the top and a central hub and axially-oriented gear teeth on the bottom, the disclosed method is applicable to any part having asymmetric top and bottom features in which lower tool members are incapable of performing a powder transfer motion necessary to achieve sufficient powder fill to final part ratios. 
     It should also be noted that various spacer plates may be incorporated in the tool design and press set up. To the extent necessary, such spacer plates or other support blocks may also be formed to include holes or powder feed chutes to allow for the delivery of powder through the upper tool members. 
     It should further be appreciated that the powder feed chute need not necessarily extend to the lowest upper tool member. For example, the powder feed chute opening which places the chute in communication with the pre-compaction chamber could be formed in the support block  318 , although in the tool setup shown, this would require lifting the upper middle punch  314  past this opening during the top fill step. It will be appreciated that one having skill in the art would recognize that this and other such modifications to the tool set could be made to achieve the same top fill capability. 
     It should be appreciated that various other modifications and variations to the preferred embodiments can be made within the spirit and scope of the invention. Therefore, the invention should not be limited to the described embodiments. To ascertain the full scope of the invention, the following claims should be referenced.