Patent Publication Number: US-2013252012-A1

Title: Powder metal axial and radial retention features for molding applications

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This claims the benefit of the filing date of U.S. Provisional Patent Application No. 61/407,294 filed Oct. 27, 2010, which is hereby incorporated by reference for all purposes. 
    
    
     FIELD OF THE INVENTION 
     This invention relates to sintered powder metal manufacturing and in particular to forming axial and radial locking features in components that will become part of a molded assembly. 
     BACKGROUND OF THE INVENTION 
     The use of sintered powder metal (PM) parts has increased in the recent past as a base component or insert that becomes part of a molded product of multi-materials. These materials may be plastic, rubber, aluminum, or another material as required. The advantage of the multi-material product is lower cost, increased productivity and greater design flexibility. These advantages are achieved in part because PM parts can provide added strength and features for the molded component not achievable as a single material product, and PM parts can be manufactured to net-shape or near net-shape in various alloys which yields little material waste and eliminates or minimizes machining. 
     Typically the PM part will have an inner surface that defines features required for consumer use of the product. This may be a straight through hole, keyway, double D hole, or others as required. The outer surface engages the other component material. This quite often is achieved by molding the material around the PM part often referred to as overmolding. Simple PM parts or inserts might not include any retention features. As such the PM insert may break free and fall out of the component. To address this problem, some inserts may include retaining features to provide a more secure connection to the component. For example, some PM inserts will have a flange to provide retention in one direction, another may have outer surface features such as ribs, a keyway, a polygonal shape and so forth to provide rotary or radial retention. Other designs include knurling, undercuts, or perforations into which the molded material can flow to provide axial retention. 
     However, to achieve both rotary and axial retention, typically additional processing will be required that significantly increases the overall manufacturing time and cost of the multi-material component. For example knurling, turning, undercutting or milling an undercut or side perforations all require an additional processing step. Considering these limitations of previous designs, a need exists for an improved PM part that has both rotary and axial retention features that is easily manufactured. 
     SUMMARY OF THE INVENTION 
     In one aspect the present invention provides a PM part that comprises a first or upper end surface and a second or lower end surface. The distance between the end surfaces defines an axial or longitudinal direction. The PM part further comprises an inner surface that defines a passageway configured as required by consumer use of the product and an outer surface configured to engage a material structure in which the PM part is placed. The distance between the inner and outer surfaces defines a radial direction perpendicular to the axial or longitudinal direction. The PM part further comprises a first set of retention features that project inwardly from the outer surface and longitudinally from the first end surface. A second set of retention features project inwardly from the outer surface and longitudinally from the second end surface. This second set of retention features is angularly located midway between the first set of retention features so that they are angularly offset from one another do not intersect. Both the first and second sets of retention features have at least a portion of the surface that is perpendicular to the tangential direction. Furthermore these features also have a portion of the feature surface that is perpendicular to the longitudinal direction. Thus they provide retention in both the axial or longitudinal direction to resist punch out of the PM part in the axial direction as well as retention in a radial direction so as to resist rotation of the PM part relative to the material surrounding it. 
     In another aspect the present invention provides a method for forming the part from powder metal. This method includes the step of pressing the powder metal in a longitudinal direction. This can be accomplished utilizing a compaction die set including a lower punch, a lower core, a lower die, an upper die, an upper punch, and an upper core. The top surface of the PM part will be formed by the upper punch. The upper outer surface including the upper retention features will be formed by the upper die cavity. The lower outer surface of the part including the lower retention features will be shaped by the lower die cavity. The lower end face of the part will be formed by the lower punch. The inner surface of the part is shaped with the core. This method further includes removal of the part by first raising the upper die and upper punch from the part and final removal by lowering the lower die and core. 
     Other features and advantages of the invention will appear in the detailed description which follows. In the description, reference is made to the accompanying drawings which illustrate a preferred embodiment of the invention. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1   a  is a perspective view of a prior art, powder metal part having knurling and circular undercut features for axial and radial retention; 
         FIG. 1   b  is a sectional view of the same powder metal part of  FIG. 1   a  showing the part  51  overmolded with another material  52  as a multi-material product; 
         FIG. 2   a  is a perspective view of a powder metal part redesigned to incorporate the present invention; 
         FIG. 2   b  is a sectional view of the same powder metal part of  FIG. 2   a  showing the part  53  overmolded with another material  54  as a multi-material product; 
         FIGS. 3   a - 3   f  are sectional schematic views of the tooling for forming the powder metal part of  FIG. 2   a ; and 
         FIG. 4  is a schematic view summarizing which parts of the powder metal part are formed by which parts of the tooling. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     In accordance with the present invention, the axial or longitudinal and radial retention features are created during the pressing cycle. As shown in  FIG. 2   a,  the PM part further comprises an inner surface  90  that defines a passageway configured as required by consumer use of the product, and an outer surface configured to engage a material structure in which the PM part is placed. The distance between the inner and outer surfaces defines a radial direction perpendicular to the axial or longitudinal direction. The PM part further comprises a first set of upper retention features  91  that project inwardly from the outer surface and longitudinally from the upper surface  92 . A second set or lower retention features  93  project inwardly from the outer surface and longitudinally from the lower surface  94 . This second or lower set if retention features  93  are offset angularly so that they are located on the periphery of the part between the upper retention features  91  so that they do not intersect, were they to be extended into the zone of the other set of retention features. Both sets of retention features extend generally parallel to the axial direction of the part and for less in axial length than the length of the part, so that each feature defines a blind end surface  95 , which extends radially and circumferentially and is in a plane that is perpendicular to the axial direction. 
     As illustrated, both the upper and lower retention features have at least a portion of the surface that is perpendicular to the radial direction and also have a portion of the feature surface that is perpendicular to the longitudinal direction. Thus they provide retention in both the axial direction and in the radial direction. 
     The process is illustrated in  FIGS. 3   a - 3   f  being performed to make the retention features. As shown in  FIGS. 3   a - 3   f , a PM insert for overmolding can be made according to the invention using a compaction tooling set that includes as tooling members a lower die  501 , an upper die  502 , an upper punch  601 , an upper pin  701 , a lower punch  201 , and a lower core pin  101 . The tooling members are moved by mechanical, hydraulic or other means of power when installed in a powder metal compacting press. 
     The starting position is shown in  FIG. 3   a . In this position, the die  501  is aligned with the lower tooling members  101  and  201  and the lower tooling members all have their upper surfaces level with one another. The lower punch  201  is tubular and can be retracted relative to the die  501  and core pin  101  so as to surround the core pin  101  below the cavity into which powder metal is filled. 
     The second step, shown in  FIG. 3   b , is moving the tooling members lower core  101  and die  501  relative to lower punch  201  to form a cavity  582 . This may occur by moving the punch  201  down or moving the core  101  and die  501  up. 
     Next in  FIG. 3   c  the third step is to fill the resulting cavity  582  with powder metal. 
     The fourth step,  FIG. 3   d , is to bring the tooling members upper die  502 , upper pin  701  and upper punch  601  down to the position where the upper die  502  is against lower die  501 , and upper pin  701  is against lower core pin  101 . 
     The fifth step,  FIG. 3   e , is to continue down with the upper die  502 , forcing the lower tooling member die  501  to move downward with the powder being held in a relative position by the lower punch  201 . The powder cavity  583  is now formed partially by the upper die  502  and partially by the lower die  501 . 
     The sixth step,  FIG. 3   f  is to continue moving the punches toward each other until the powder is compacted between them. PM compact  585  is formed with the inside shape formed by the core  101  and on the outside shape formed partially by upper die  502  and partially by lower die  501 , with the upper die forming retention features from the top surface and the lower die forming retention features from the bottom surface and the upper die  502  and lower die  501  offset angularly in position with the top to bottom retention features angularly offset so that the features of each set are between the features of the other set, with each set providing both axial and radial retention. The alignment of upper die  502  to lower die  501  can be completed with a setting guide tool or additional tooling features can be utilized to facilitate this alignment. 
     The final or seventh step,  FIG. 3   g , is for the upper die  502  to move upward followed by the upper punch  601 , then the lower die  501 , and lower core  101  moved downward to fully eject the part and return to the starting position. 
     Thereby, referring to  FIG. 4 , the inside surface  90  is formed by the core  101 , the upper surface  92  is formed by the punch  601 , the lower surface  94  is formed by punch  201 , the upper outer section  96  is formed by die  502  and the lower outer section  98  is formed by die  501 . 
     Following compaction the part is sintered in a sintering oven to fuse the powder of the compact and solidify it, making it structurally sound while largely maintaining its shape. 
     Preferred embodiments of the invention have been described in considerable detail, many modifications and variations to the preferred embodiments described will be apparent to a person of ordinary skill in the art. For example the powder metal parts may have various retention shapes or size or the part may have additional levels of complexity. Therefore, the invention should not be limited to the embodiments described.