Abstract:
An automotive engine component and method of producing the same. The method uses dynamic magnetic compaction to form components, such as camshaft lobes, with non-axisymmetric and related irregular shapes. A die is used that has an interior profile that is substantially similar to the non-axisymmetric exterior of the component to be formed such that first and second materials can be placed into the die prior to compaction. The first material is in powder form and can be placed in the die to make up a first portion of the component being formed, while a second material can be placed in the die to make up a second portion of the component. The second material, which may possess different tribological properties from those of the first material, can be arranged in the die so that upon formation, at least a portion of the component&#39;s non-axisymmetric exterior profile is shaped by or includes the second material.

Description:
BACKGROUND OF THE INVENTION 
     The present invention relates generally to the manufacture of automotive engine components possessing non-round exterior shapes using a powder metallurgy process, and more particularly to the manufacture of camshaft lobes using a modified dynamic magnetic compaction (DMC) process. 
     Automotive engine camshaft lobes must endure significant and repeated mechanical loading under high-speed, high-temperature and tribologically-varying conditions. The use of conventional manufacturing processes, such as casting, forging or the like, tends to produce components which, while satisfactory from a load-bearing perspective, result in heavy, inefficient structures. Likewise, the use of conventional manufacturing approaches is not conducive to tailoring a particular material&#39;s desirable properties to discreet locations on a camshaft lobe. Furthermore, the use of DMC, which is taught in U.S. Pat. Nos. 5,405,574, 5,611,139, 5,611,230 and 5,689,797 (all of which are hereby incorporated by reference), while a valuable way to compact both metallic and non-metallic powders to achieve high-density components, has not hitherto been extended to camshaft lobes, gears or other non-axisymmetric (i.e., non-cylindrical) or otherwise irregularly-shaped components. 
     Camshaft lobes and other highly-loaded engine components could benefit from the strategic placement of materials into the lobe that can be tailored to the lobe operating environment. For example, surface portions (for example, the generally planar eccentric surfaces) of the lobe that are exposed to higher loads may benefit from harder or other more load-bearing materials that would not be needed in the generally axisymmetric portion of the lobe. Likewise, such materials could be used in the DMC process to give a particular shape to a formed component. Because such more robust materials may involve greater expense, weight or detrimental features, they may only be used sparingly. As such, it would be advantageous to develop ways to combine the efficient manufacturing attributes of DMC with the tailored structural properties of disparate constituent materials to fabricate structurally efficient components. 
     BRIEF SUMMARY OF THE INVENTION 
     These advantages can be achieved by the present invention, wherein improved engine components and methods of making such components are disclosed. According to a first aspect of the invention, a method of fabricating an automotive engine component using DMC is disclosed. Under the present method, an exterior profile of the component can be made non-axisymmetric (i.e., such that its external shape deviates from a cylindrical form). The method includes providing a die or related tool with an interior profile that is substantially similar to the exterior profile of the component being formed. Furthermore, a first material in powder form is placed within a first part of the die interior profile such that the first material defines at least a first portion of the component being formed. In addition, the method includes placing within a second part of the die interior profile a second material, and then forming the automotive engine component using dynamic magnetic compaction to compact or otherwise densify the two materials together. In the present context, the term “substantially” refers to an arrangement of elements or features that, while in theory would be expected to exhibit exact correspondence or behavior, may, in practice embody something slightly less than exact. As such, the term denotes the degree by which a quantitative value, measurement or other related representation may vary from a stated reference without resulting in a change in the basic function of the subject matter at issue. 
     In one form, the second material is placed within the region that defines the non-axisymmetric exterior profile, while the first material is placed in the region that defines the axisymmetric exterior profile, non-axisymmetric profile or both. In a more specific form, the first powder can be used to form a majority of the component, with the second material being placed in a location such that upon formation of the component, the second material occupies a portion of the surface of the component that can be expected to be exposed to increased load, wear or related mechanical requirements. In one optional form, the method further includes making the automotive component into a camshaft lobe. In another option, the second material comprises a second powder, which in a more particular optional form, may possess different wear, friction or related tribological properties from the powder of the first material. In an even more particular form, the second powder is harder or otherwise more wear-resistant than the first powder. In another option, at least one of the first and second powders are selected from the group consisting of metal powders, ceramic powders and a combination of both. 
     In another option, instead of a powder, the second material may be in the form of a substantially rigid insert. Such insert may be made from a different material from the alloy used to make up the remainder of the component. In one form, the different material may be a hardenable steel alloy, ceramic material or other long-wearing, high load-bearing composition. Such an insert defines a profile such that can be placed over at least a portion of the first material such that the second material forms an outer surface of a part of the component that is expected to be exposed to higher levels of load, wear, friction or the like. For example, in situations where the component includes an eccentricity or related non-axisymmetric shape and such non-axisymmetric shape corresponds to the part of the component in need of additional structural properties, the second material can be placed in such a way that it makes up at least a majority of the non-axisymmetric exterior profile, or takes a majority of the loading when the load is at a maximum. The substantially rigid insert may be made from either a reusable or non-reusable. In the case of the latter, the insert may remain with the formed component upon completion of the compaction. In the case of the former, such as when being used to shape the outer profile of the component of interest, the insert does not remain with the automotive engine component upon the fabrication such that it may be re-used. In one configuration, during the forming process, the one or more substantially rigid insert cooperates with one or more reusable inserts such that an outer shape of the component is defined by such cooperation. In a more particular form, numerous such reusable segments can be placed within a die so that their inner surfaces compact the first and second materials in response to the DMC process. In this way, the reusable segments can press the non-reusable segments into place in a particular location in the component to be formed. 
     According to another aspect of the invention, a method of fabricating a camshaft lobe is disclosed. The method includes providing a die with an interior profile that substantially defines an exterior surface of the lobe, placing a first material within a first part of the interior profile of the die, placing a second material within a second part of the interior profile of the die such that the second material is used to form at least a portion of the exterior surface of the lobe that corresponds to the lobe eccentricity, and forming the lobe using dynamic magnetic compaction. As with the previous aspect, one significant advantage over the prior art DMC process is that non-axisymmetric and related irregular component shapes can be formed. 
     Optionally, the second material occupies a majority of the exterior surface of the lobe that corresponds to the lobe eccentricity. In this way, the use of materials with tribologically superior properties can be tailored to corresponding surface regions of the lobe. This can be an advantageous way of supplementing the tribological or related structural properties of heavily-loaded parts of the lobe, such as its eccentric region, where conventional DMC may not be capable of producing a part with the necessary structural attributes. In another option, at least one of the first and second materials is made of a powder that can be compacted via the DMC process. In a further option, the second material can be made from a different composition than the first material. In this way, metal alloys, ceramic precursors or related materials can be strategically placed on portions of the exterior surface of the lobe to tailor the material properties to the load-bearing needs of the lobe. In yet another option, the second material is made from a substantially rigid non-reusable insert that may be operated upon by a reusable insert. The interior profile of the die used to form the lobe may be made up of reusable inserts that cooperate with the one or more non-reusable inserts so that the second material that makes up the non-reusable insert is pressed together with the first material. In this way, the lobe is formed as a substantially unitary structure that can be further processed. 
     According to yet another aspect of the invention, a camshaft lobe for an internal combustion engine is disclosed. The lobe can be made by the DMC process discussed in the previous aspects, and includes a camshaft-engagable interior surface made up of a first material and an exterior surface made up of one or more eccentric portions at least a portion of which is formed by a second material. In this way, the interior surface defines an axial bore thought the lobe. 
     Optionally, the first material is made from different than the second material. In a more specific option, both the first and second materials comprises a powder such that each is tailored to particular portions of the lobe. In another option, the second material can be made from a substantially rigid insert selected from the group consisting of reusable inserts and non-reusable inserts. In the case of re-usable inserts, the second material is used to form a portion of the finished lobe, but does not remain with it. In the case of non-reusable inserts, the second material, by virtue of the DMC process, is formed into at least a portion of the lobe exterior surface and remains with it. In this way, the second material can (in the case of a re-usable insert) help to define the shape during DMC or (in the case of a non-reusable insert) be used to actually occupy a portion of the lobe exterior surface once co-formed with the first material during DMC. 
    
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS 
       The following detailed description of the present invention can be best understood when read in conjunction with the following drawings, where like structure is indicated with like reference numerals and in which: 
         FIGS. 1A through 1C  shows a the various steps used in the DMC process of the prior art for making a cylindrical-shaped powder component; 
         FIG. 2  shows a top-down view of a cylindrical part and the various parts used to form such part using a conventional DMC process of the prior art; 
         FIG. 3  shows a cutaway view of a camshaft lobe and associated tooling of the modified DMC process according to an aspect of the present invention; 
         FIG. 4  shows a cutaway view of a camshaft lobe and associated tooling of the modified DMC process according to another aspect of the present invention; 
         FIG. 5  shows a camshaft lobe as produced by the tooling of  FIG. 3 ; and 
         FIG. 6  shows a partial cutaway view of an automotive engine with a camshaft employing one or more lobes made by the modified DMC process of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Referring initially to  FIGS. 1A through 1C , the DMC process according to the prior art is shown, where a generally cylindrical-shaped component is produced.  FIG. 1A  shows a powder material  10  placed within an electrically conductive cylindrical armature  20 . A coil  30  is connected to a direct current power supply (not shown) such that electric current can be passed through the coil  30 . The powder material  10  substantially fills the electrically conductive armature  20  (also called a sleeve). Referring with particularity to  FIG. 1B , a large quantity of electrical current  40  is made to flow through the coil  30 ; this current induces a magnetic field  50  in a normal direction that in turn sets up magnetic pressure pulse  60  that is applied to the electrically conductive container  20 . This radially inward pressure acts to compress the container  20 , causing the powder material  10  to become compacted and densified into a full density parts in a very brief amount of time (for example, less than one second) and at relatively low temperatures. In addition, this operation can (if necessary) be performed in a controlled environment to avoid contaminating the consolidated material. By way of example, the current flow through the coil  30  may be in the order of 100,000 amperes at a voltage of about 4,000 volts, although it will be appreciated that other values of current and voltage may be employed, depending on the characteristics of the container  20  and the powder material  10  inside. Referring with particularity to  FIG. 1C , once the DMC process is complete, the armature  20  and powder material  10  are shown compressed, occupying a smaller transverse dimension than previous size of  FIG. 1A . 
     Referring next to  FIG. 2 , a top-down view of a notional cylindrical DMC containment structure according to the prior art is shown. A loosely held powder  10  is placed in an electrically conductive round container  20 . The sudden passage of a large amount of current through the coil  30  produces a magnetic field, which in turn induces a current in the container  20 . This induced current produces a second magnetic field which, by its magnitude and direction, repels the first magnetic field. This mutual repulsion causes container  20  to be compressed, which in turn applies pressure on the powder  10 , causing its compaction. A top-down view of a notional cylindrical DMC containment structure is shown. Coil  30  is placed inside an external containment shell  70  to restrain the coil  30  against radially-outward expansion when repelled by the second magnetic field. 
     Referring next to  FIGS. 3 and 4 , camshaft lobes  110  ( FIG. 3) and 210  ( FIG. 4 ) are shown, as well as the tooling used to form them. The use of non-axisymmetric tooling results in a modified DMC process in that the axisymmetric limits of the traditional DMC process have been overcome. Referring with particularity to  FIG. 3 , an electrically-conducting coil  130  is wound around a sleeve  125  that is placed between the coil  130  and die  120 . As shown, a gap (for example, and air gap)  135  is situated between coil  130  and sleeve  125 . As with conventional DMC, the present DMC-based process exploits the electric current flowing through coil  130  in order to impart a magnetically-compressive force onto the sleeve  125 , die  120  and the precursor materials within. The die  120  is generally axisymmetrically-shaped around its outer surface  121 , while its inner surface  122  is similar to the desired outer shape of the lobe  110  being formed. The die  120  is formed from four reusable segments  120 A,  120 B,  120 C and  120 D, where the portion of the inner surface  122  that is used to form the axisymmetric part of the lobe  110  corresponds to die segments  120 A and  120 B and the portion of the inner surface  122  that is used to form the non-axisymmetric eccentric part of the lobe  110  corresponds to die segments  120 C and  120 D. A central bore  101  can be formed in the lobe  110  through the inclusion of an appropriately-shaped mandrel (not shown) during the lobe-forming process. Sleeve  125  is compressed by the magnetic forces generated by coil  130 , as is die  120 ; this in turn causes the precursor materials to be deformed by the compressive forces to compact the precursor powder materials. This results in formation of a “green” or un-sintered lobe  110  that may undergo conventional sintering, machining and related finishing steps (none of which are shown). 
     As can be seen in the figure, lobe  110  has at least two distinct portions  110 A and  110 B. The first portion  110 A forms a base circle portion of lobe  110  and is preferably made from a material such as an alloy steel powder possessive of mechanical properties suitable for camshaft lobe applications. In addition to occupying the substantial entirety of the axisymmetric portion of the lobe  110 , the first portion  110 A can form the underlying (i.e., interior) surface of the non-axisymmetric part, and a first material can be used to define or otherwise occupy this first portion  111 A. By contrast, a second material can be used for the second portion  110 B where additional structural (including tribological) properties may be desired. Unlike the first portion  111 A, the second portion  110 B is preferably limited to parts of the lobe  110  that require the enhanced properties associated with the second material. As with the first material, the second material may be a metal powder specifically formulated to meet the specific needs for an application where the lobe surface would experience at least one of rolling loads, sliding loads or a combination thereof. In one example, the powder may be made from a ferrous alloy with chemical composition formulated in a way so as to improve wear resistance, friction reduction or the like of the second material. Because the second material is tailored to meet particular performance needs, and is typically at least one of more expensive, heavier or more difficult to fabricate with, it should be used sparingly. As such, it may be advantageous to only have it occupy as much surface area of lobe  110  as necessary. By having this structurally-enhanced second material occupy the outer surface of portion  110 B of lobe  110 , it can, with subsequent compaction with the first material of the first portion  110 A by DMC, form lobe  110  into a substantially unitary structure with composite properties: a low-cost, lightweight, readily manufacturable first portion  110 A and a durable, tribologically-enhanced second portion  110 B. 
     Referring with particularity to  FIG. 4 , lobe  210  can be formed by the operation of the die  220 , coil  230  and sleeve  225 . Lobe  210  can define a slightly different shape than that of lobe  110 , including a reduced use of a second material in first portion  210 A in a region that makes room for an insert in the form of second portion  210 B. Unlike the lobe  110  of  FIG. 3 , the first portion  210 A may have an exposed outer surface in the non-axisymmetric portion of the lobe  210 . As with the lobe  110  of  FIG. 3 , a first material may be used to occupy the first portion  210 A. Also, as with the lobe  110 , lobe  210  includes discrete locations on the outer surface of the second portion  210 B where a second material insert can be used to enhance local structural properties. Also as with the device of  FIG. 3 , the die  220  with inner and outer surfaces  222 ,  221  can be segmented into reusable segments  220 A,  220 B,  220 C and  220 D and include the shaped cutouts on the inner surface  222  thereof to promote ease of component assembly. Also as with the configuration depicted in  FIG. 3 , a gap  235  may be formed between the coil  230  and the die  220 . 
     Unlike the assembly of  FIG. 3 , the second material used for the second portion  210 B of lobe  210  is in the form of an insert that cooperates with the first material such that upon compaction by the DMC process, forms indentations into the lobe  210  that define the second portion  210 B. In one form, the second portion insert  210 B can be a material (for example, in powder form) that has tribologically different properties than the material making up the first portion  210 A of lobe  210 . Together, the inserts made up of lobe inserts  210 B and die  220  (including its segments  220 A,  220 B,  220 C and  220 D) take on one of two forms. In the first form, inserts in the form of die segments  220 A,  220 B,  220 C and  220 D are reusable, while in the second, the inserts  210 B are non-reusable in that they become a part of the finished lobe  210 , and the two forms can cooperate with one another to form lobe  210 . Die segments  220 A and  220 D are placed such that upon compaction, the non-reusable inserts fill the indents that are formed in the outer surface of the second portion  210 B of lobe  210  that, in addition to being used to help create a desired lobe profile, remain with the lobe  210  upon completion of the compaction process, thereby forming an integral part of the outer surface thereof by occupying the second portion  210 B. As such, it is designed to couple with the powder first material precursor to form a composite lobe  210  in a manner generally similar to that of lobe  110 . Placement of the non-reusable insert (made of, for example, the second material) into the precursor may be simpler than in the case of lobe  110 , where both the first and second materials are in powder form. To facilitate the process (where a dual powder filling operation is employed), a temporary screen (not shown) may be used to keep fill powders in the desired regions until compaction. Appropriate heat treatment may be performed on the compacted lobes. As with the previous aspect of lobe  110 , once DMC has been completed, various additional sintering, machining and related finishing steps may be undertaken. 
     Referring next to  FIGS. 5 and 6 , an as-manufactured lobe  1100  and incorporation into a camshaft  1150  and automotive engine  1000  is shown. Referring with particularity to  FIG. 5 , the two portions  1100 A and  1100 B of lobe  1100  are shown co-formed by the DMC process. As will be understood from the above discussion, first portion  1110 A is generally made up of the first material that occupies the substantial entirety of the axisymmetric part  1110 . Second portion  1110 B is generally made up of the structurally-enhanced second material that occupies the substantial entirety of the non-axisymmetric part  1120 . The central bore  1001  that is used to connect the lobe  1100  to a camshaft  1150  (shown in  FIG. 6 ) may be of any appropriate size. 
     Referring with particularity to  FIG. 6 , portions of the top of an automotive engine  1000  incorporating a lobe  1100  and accompanying camshaft  1150  is shown for a notional direct-acting tappet design. A piston  1300  reciprocates within a cylinder in the engine block (not shown). A cylinder head  1200  includes intake ports  1240  and exhaust ports  1250  with corresponding intake and exhaust valves  1400 ,  1500  to convey the incoming air and spent combustion byproducts, respectively that are produced by a combustion process taking place between the piston  1300  and a spark plug (not shown) in the cylinder. Camshaft  1150  is driven from an external source, such as a crankshaft (not shown), and includes a cam lobe  1100  that defines a non-axisymmetric profile about the longitudinal axis of the camshaft  1150 . Upon camshaft  1150  rotation about its longitudinal axis, the eccentric portion of the lobe  1100  selectively overcomes a bias in valve spring  1600  to force exhaust valve  1500  at the appropriate time. It will be appreciated that similar structure is included for the intake valve  1400 , but is removed from the present drawing for clarity. The lobe  1100  of the present invention includes selective reinforcement in the eccentric portion as discussed above to promote enhanced durability and performance. It will be appreciated by those skilled in the art that the valve train architecture shown associated with engine  1000 , which includes a direct-acting tappet, is merely representative, and that camshaft lobes manufactured using the modified DMC process as described herein are equally applicable to other valve train architectures (not shown). 
     While certain representative embodiments and details have been shown for purposes of illustrating the invention, it will be apparent to those skilled in the art that various changes may be made without departing from the scope of the invention, which is defined in the appended claims.