Method of producing composite components using sinter fit

Abstract

A method of sinter fitting a powder metal compact around a core forms a composite component. By exploiting the shrinkage associated with the sintering of a powder metal compact, a sintered powder metal section may be dimensionally shrunk onto a core to create a mechanical interference fit between a core section and a sintered powder metal section. This method may be used to join materials such as aluminum and steel together, which traditionally have been difficult to join to one another.

Claims

1. A method of sinter fitting an aluminum powder metal compact around a steel core to form a composite component, the method comprising the sequential steps of: compressing an aluminum powder metal to form an aluminum powder metal compact having an opening formed therein, wherein the aluminum powder metal is a pure aluminum powder metal or is an aluminum alloy powder metal; inserting the steel core in the opening of the aluminum powder metal compact whereby an inter-component clearance is initially established in a space between the aluminum powder metal compact and the steel core; and sintering the aluminum powder metal compact with the aluminum powder metal compact in place around the steel core to form the composite component, the composite component including a sintered aluminum powder metal section that is formed by sintering the aluminum powder metal compact and further including a steel core section comprising the steel core, whereby the sintering step results in a dimensional shrinkage of the aluminum powder metal compact as the sintered aluminum powder metal section is formed by sintering such that the sintered aluminum powder metal section of the composite component shrinks onto the steel core section to cause a mechanical interference fit between the sintered aluminum powder metal section and the steel core section to join the sections together; wherein the steel core is a rivet having a flange on one end.

2. The method of claim 1, wherein the steel core section of the composite component structurally reinforces the sintered aluminum powder metal section of the composite component.

3. The method of claim 1, wherein the steel core section of the composite component inhibits distortion of the sintered aluminum powder metal section of the composite component during sintering.

4. The method of claim 1, wherein the sintered aluminum powder metal section of the composite component provides a skin for the steel core section of the composite component that provides improved protection from corrosion of the steel core section.

5. The method of claim 1, wherein the steel core is magnetic.

6. The method of claim 1, wherein the sintered aluminum powder metal section provides a bearing surface.

7. The method of claim 1, wherein the composite component has electrical properties or thermal properties that combined differ from each of the separate sections.

8. The method of claim 1, wherein the aluminum powder metal compact and sintered aluminum powder metal section are a metal matrix composite and further includes a ceramic reinforcement phase.

9. The method of claim 1, wherein the steel core is fully dense when the steel core is inserted into the opening of the aluminum powder metal compact such that, during the sintering of the aluminum powder metal compact, there is no dimensional change of the steel core due to densification.

10. The method of claim 1, wherein the opening in the aluminum powder metal compact extends from one face of the aluminum powder metal compact to another face of the aluminum powder metal compact and the step of inserting the steel core involves inserting the steel core such that the steel core extends through the opening.

11. The method of claim 1, wherein the inter-component clearance established between the aluminum powder metal compact and the steel core is between facing surfaces of the aluminum powder metal compact and the steel core.

12. The method of claim 11, wherein at least one of the facing surfaces includes a surface feature selected from the group consisting of a key and D-shaped flattened faces.

13. The method of claim 11, wherein a measured dimension defined by points on the facing surface of the aluminum powder metal compact dimensionally shrinks between 1 and 5 percent during sintering.

14. The method of claim 1, wherein the aluminum powder metal compact includes alloying additions other than aluminum.

15. The method of claim 1, wherein the flange on the steel core mates with a generally correspondingly shaped recess on the aluminum powder metal compact.

16. The method of claim 1, further comprising the step of locating another component on an available end of the rivet and riveting the available end of the rivet in order to join the composite component to the other component.

17. The method of claim 1, wherein the steel core has an axially extending opening thereby reducing the weight of the steel core.

18. The method of claim 11, wherein at least one of the facing surfaces includes a surface feature selected from the group consisting of threads and splines.

19. The method of claim 15, wherein the aluminum powder metal compact is a plate.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 is a flowchart illustrating the sequential steps of a method of making a composite component according to one aspect of the present invention.

(2) FIGS. 2A through 2C illustrate exemplary steps in which a core is inserted into a powder metal compact and sinter fit in accordance with the method of FIG. 1 to produce a composite component.

(3) FIGS. 3A through 3C provide side cross-sectional views of the exemplary steps of illustrated FIGS. 2A through 2C, respectively, taken through the central axis of the various components.

(4) FIGS. 4A through 4F show some exemplary alternative cross-sectional views of cores taken on a plane perpendicular to the central axis of the respective cores.

(5) FIGS. 5A and 5B provide two cross sections through a composite component made according to the inventive method in which the core is hollow.

(6) FIG. 6 illustrates one embodiment of a composite component made according to the method in which both the core and the powder metal sections are rings.

(7) FIG. 7 shows another embodiment in which a plurality of slender cores (for example, wires) are received in a powder metal compact.

(8) FIGS. 8A and 8B illustrate a rivet with a flange on one end thereof in which the rivet has either a solid body or has an axially-extending opening formed through the body, respectively.

(9) FIGS. 9A through 9C illustrate various usage configurations of a rivet that is used to join multiple parts together including at least one part which is made from a powder metal.

(10) FIGS. 10A through 10C illustrate the sequential steps of placing a powder metal shroud over a support for production of a planetary gear carrier and then riveting a separate plate to the top.

(11) FIG. 10D illustrates an alternative arrangement for a planetary gear carrier in which, instead of riveting, the plate may be welded to the exposed top of the posts.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

(12) Referring first to FIGS. 1, 2A through 2C, and 3A through 3C, a method 100 of making a composite component 108 is illustrated. Because the order of the method steps is significant to the manner in which the composite component 108 is constructed, the described steps should be performed sequentially.

(13) First, according to step 102, a powder metal is compacted to form a powder metal (PM) compact 110a. As is known to those having ordinary skill in the art, a powder metal compact 110a can be formed by compressing loose powder metal with some amount of lubricant and/or binder to a tool and die set. Typically, this compaction is done in a uniaxial press in which powder metal is fed into a die cavity having a lower tool or tools received therein and then lowering the upper tool or tools and applying a sufficiently high pressure to form a semi-stable powder metal compact. By use of a core rod or other tooling arrangements, an opening 112 (or multiple openings) can be formed in an axial direction of the powder metal compact 110a. Once the powder is compacted, then the compacted powder metal component or preform is ejected from the press by virtue of tool movement.

(14) According to many forms of this invention, the powder metal may be an aluminum powder metal in which the powder metal is purely aluminum or may be an aluminum alloy powder in which one or more alloying elements are added to the powder metal, either as a separate elemental powder or powders, as part of a master alloy, or as pre-alloyed constituents in an aluminum powder (or combinations thereof). It is also contemplated that the powder metal may include ceramic inclusions, such as would be the case in a metal matrix composite material (MMC). If the powder metal compact 110a is an MMC, up to 20 volume percent of the powder metal compact may be ceramic (for example, a SiC ceramic addition). Other powder metal compositions might also be used other than aluminum; although for reasons that will become more apparent below, the powder metal compact 110a should be sinterable at a temperature that is less than a temperature that could structurally compromise the material of the core 114a.

(15) It should be appreciated that aluminum powder metal is a viable manufacturing process for the substitution of die cast aluminum materials or cast aluminum or forged aluminum articles. Aluminum has a lighter weight than steel and, inherently, a lower density than steel. Aluminum typically has a density of approximately 2.7 g/cm.sup.3 whereas steel has a density of 7.87 g/cm.sup.3. However, aluminum also has a lower strength than steel. Typically (although it depends on particular alloying compositions), aluminum has a strength that is less than 50 percent of steel. The modulus of aluminum is also lower than that of steel.

(16) It should also be appreciated that powder metal processes allow the formation of net shape or near net shape of articles, and facilitates the manufacture of parts with potential joining features such as holes for dowels, screws, bolts, clips, bushings, rivets, tennons, dovetails, and so forth. Traditional powder metallurgy exploits these features to allow joining with other parts to increase the function and/or strength of an article. This invention, as will be appreciated from the description that follows, offers the ability to utilize the advantages of powder metal features with novel joining and/or strengthening techniques through formation of a composite component.

(17) Returning now to the method 100, with the compact 110a made and then according to step 104, a core 114a is inserted into the opening 112 of the powder metal compact 110a. This insertion is depicted across FIGS. 2A, 2B, 3A, and 3B, in which the core 114a is illustrated first being outside of the powder metal compact 110a (as in FIGS. 2A and 3A) and is then illustrated as being received entirely through the opening 112 of the core 110a (as in FIGS. 2B and 3B).

(18) In the form illustrated, the core 114a is steel although it is contemplated that the core 114a might be formed of other materials. Typically, this core 114a will be formed of a non-powder metal material and may be, for example, a cast and/or worked (for example, drawn, rolled, and so forth) part. The core 114a is to be nearly fully dense such that, during the subsequent sintering step 106, the core 114a is not prone to dimensional change at the sintering temperatures for the powder metal compact 110a.

(19) It is important to note that during the step of insertion 104, there is an inter-component clearance 118 present between the facing surfaces 120 and 122 of the powder metal compact 110a and the core 114a, respectively. This inter-component clearance 118 is small, but means that the step 104 of insertion does not involve forming an immediate interference fit between the compact 110a and the core 114a during insertion. Rather, the un-sintered powder metal compact 110a and the core 114a are potentially movable with respect to one another during insertion, such the powder metal compact 110a can be positioned relative to the core 114a.

(20) Once the powder metal compact 110a has been inserted onto the core 114a, then the powder metal compact 110a is sintered around the core 114a in step 106 as illustrated in FIGS. 2C and 3C. This sintering may be done, for example, by placing the compact 110a and the core 114a into a sintering furnace at a sintering temperature for a time duration that will cause the powder metal compact 110a to sinter. Notably, the materials for the powder metal compact 110a and the core 114a and the sintering conditions are selected such that the compact 110a sinters and shrinks (typically in the range of 1 to 3 percent in a linear dimensionally, depending on the particular material composition, compacted densities, and sintering conditions) and such that the core 114a remains dimensionally stable (that is, does not significantly bend, warp, or shrink during sintering).

(21) In this way, the compact 110a can be sinter fitted onto the core 114a. During this sinter fitting, the dimensions of the compact 110a shrink while the dimensions of the core 114a remain stable. As this shrinkage of the compact 110a occurs, the facing surface 120 of the powder metal compact 110a is brought toward the facing surface 122 of the core 114a. Because the inter-component clearance 118 is engineered or selected to be small, as the sintering proceeds, the facing surfaces 120 and 122 are brought into mechanical interference with one another such that the compact 110a is shrunk onto the core 114a so that the two components are mechanically joined together. It should be observed that little or no diffusion bonding between the compact 110a and the core 114a is contemplated during sinter fitting of this type and the primary mechanism for joining is the dimensional change of the compact 110a relative to the core 114a. Indeed for certain materials, diffusion bonding may be undesirable and so one or both of the facing surface might potential be treated or coated to prevent diffusion bonding across the compact and core from occurring.

(22) It will be appreciated the shape and form of the facing surfaces 120 and 122 should be engineered in such a manner as to permit free insertion during step 104, but to cause mechanical interference after sintering in step 106 preventing movement of the components relative to one another. Further, it should be appreciated that the dimensions of the facing surfaces should be selected in such a manner that the sintering step 106 does not cause the compact 110a to be over-stressed as the compact 110a shrinks around the core 114a. That is to say, if the compact 110a is expect to shrink 4 percent (a relatively shrinkage value), then it may be best to provide adequate inter-component clearance 118, as an extremely small amount of initial clearance may place significant internal stress on the compact 110a as it sinters and potentially damage the component(s) during sintering.

(23) In any event, after the sintering step 106 is completed, then a composite component 108 has been formed as is illustrated in FIGS. 2C and 3C. This composite component includes a sintered powder metal portion 110b (which is the sintered version of the powder metal compact 110a) and a core portion 114b (which corresponds to the core 114a).

(24) Although a cylindrically-shaped core 114a and tubular-shaped powder metal compact 110a are illustrated in FIGS. 2A through 2C and 3A through 3C such that the facing surfaces 120 and 122 are made to contact one another substantially over their entire area after sintering, it is observed that nothing so limits the components to these geometries. Indeed, a sinter fit may be obtained in parts having non-cylindrically shaped facing surfaces or having additional features supported thereon.

(25) Some examples of these alternative geometries are illustrated in FIGS. 4A through 4F, which provide cross-sectional views taken through cores such that the core is viewed down its central axis. Although the features are illustrated on the core in these figures, one having ordinary skill in the art will appreciate that these features may have matching profiles on the powder metal compact. These matching profiles may interlock with some or all of the features. Alternatively, in some instances, these features might be made to mechanically interfere with an oppositely facing surface (that is to say, for example, a cylindrical surface of the compact might be shrunk onto, for example, a threaded core). Still yet, the illustrated features on the facing surface of the core might instead be transferred to the facing surface of the powder metal compact and the core may be comparably featureless.

(26) Six alternative profiles are illustrated in FIGS. 4A through 4F. In FIG. 4A, a threaded outer surface 124 is illustrated on a core 126. In FIG. 4B, the core 128 has a cylindrical radially outward facing surface 130, but the core 128 itself is hollow, making it tubular. Such modification can be made to reduce the weight of the core 128. In FIG. 4C, the core 132 has a plurality of axially-extending splines 134 extending away from its radially outward facing surface 136 while, in FIG. 4D, a core 138 has a plurality of axially-extending negative splines 140 extending into its radially outward facing surface 142. In FIG. 4E, the core 144 has a flat surface 146 formed into the otherwise cylindrical facing surface 148 that creates a D-shape for further inhibiting rotational movement on a matching compact (although it is noted that the mechanical sinter fit should prevent such relative rotation under non-extreme loading circumstances which might induce significant rotational shear stresses). In FIG. 4F, a key 150 is formed onto a radially outward facing surface 152 of a core 154 and this key 150 may be received in a corresponding slot in the compact.

(27) According to the method described above and herein, a composite material can be created from a sintered powder metal material and a non-powder metal component that offers many benefits over a purely powder metal component.

(28) Two such benefits are an improved combined modulus of the composite over a purely powder metal part and a strengthening of the composite over a purely powder metal part, particularly in the instance in which the core is made of steel and the compact is made of aluminum. Effectively, when the core is steel and the PM compact is aluminum, a powder metal article can be made using standard powder metal processes, but can be further made to have a supporting steel core (by virtue of the sinter fit interlocking) to produce a reinforced composite material. The reinforced powder metal compact can have a modulus or strength that exceeds that of the powder metal part alone.

(29) Because there can be a tradeoff between the composite properties and weight of the composite component, it is further contemplated that the reinforcing phase (that is, the core) does not need to be solid. For example, with reference to FIGS. 5A and 5B, it can be seen that a composite component 156 might be made having a tubular steel core portion 158 having a central channel 160 running through it and further having an sintered aluminum powder metal portion 162 sinter fit around the core 158. The absence of material in the channel 160 reduces the weight of the core 158 in comparison to a solid core and, depending on the particular usage situation, may not significant compromise the benefits of having the steel core in the first instance.

(30) Another potential variant is illustrated in FIG. 6 in which a composite component 164 in the form of a ring is made having a steel core portion 166 in the form of a ring and a sintered aluminum powder metal portion 168. Effectively, this configuration and geometry may provide a steel-backed aluminum ring. This arrangement may be beneficial in certain bushing or bearing applications.

(31) Turning now to FIG. 7, it is contemplated that wires or other slender elements 170 may constitute the core or cores and be inserted into corresponding openings in a powder metal section 172 that is sintered around the wires or other slender elements 172. Such a construction may offer desirable electrical or thermal properties. For example, the slender elements 170 may be wires and may be a copper material having particularly good thermal conductivity. This may improve heat transfer into or out of the core in which they are embedded after sinter fitting.

(32) Still yet, one of the potential benefits of a composite part made according to the method may be that the core is made of a magnetic material (such as steel, iron, or a hard magnet) while the surrounding powder metal compact is not magnetic (such as an aluminum or aluminum alloy based powder metal part). In this way, a non-magnetic powder metal part may have an internally-supported magnetic constituent that gives the combined composite part magnetic properties that would be lacking in a component fabricated solely from non-magnetic powder metal.

(33) As another example, it is contemplated that this composite component may be advantageously used in bushing or bearing constructions. Aluminum material is often used in bushings or bearings due to its being a dissimilar material to steel. This reduces heat generation and the probability of a friction weld forming. This disclosed composite component, particularly when MMC material is utilized, may be particularly well-suited for high wear resistance applications.

(34) Additionally, it is contemplated that a composite material of the type described above may be utilized to reduce distortion of the powder metal portion during sintering. As noted above, aluminum powder metal materials tend to have high degrees of shrinkage during sintering and, further, can slump under their own mass during sintering as they are heated to temperatures approaching their melting point. A steel core might be added in order to inhibit slumping or distortion during sintering such that the core effectively provides a dimensionally stable support for the aluminum powder metal material as it is sintered.

(35) Yet another potential benefit is that an aluminum powder metal skin or shell on a composite part can be made to cover the steel core such that the core is more resistant to rusting or corrosion than if the steel was left exposed. Effectively, the aluminum might serve as a cladding and it may be possible to cap any exposed ends of the core using separate aluminum powder metal components or by utilizing a blind hole.

(36) Finally, one major benefit of the disclosed method is that it can be employed in more complex joining processes.

(37) For example, and with reference to FIGS. 8A and 8B, the core material may be formed as a steel rivet. As in FIG. 8A, the steel rivet 174 may include a generally cylindrical body 176 having a radially-extending flange 178 formed at one end thereof. In an alternative form illustrated in FIG. 8B, to reduce weight, a steel rivet 180 may again be formed having a flange 182 on one end of a cylindrical body 184, but may also have an axially extending opening 186 passing through the center of the body 184 to eliminate material mass.

(38) This steel rivet may be used to join one or more components in which at least one of the components is composed of a powder metal material.

(39) Turning now to two examples in FIGS. 9A and 9B, the rivet 174 is shown extending through openings in a powder metal compact 188a or 188b and a separate non-powder metal plate 190. In the instance of powder metal compact 188a in FIG. 9A, the powder metal compact 188a has a simple through hole 192a while, in FIG. 9B, the powder metal compact 188b has a counter-bored opening 192b that receives the flanged end 178 of the rivet 174.

(40) With the rivet 174 in place and extending through the components to be joined (i.e., the powder metal compact 188a or 188b and the plate 190), the powder metal compact 188a or 188b is sintered and sinter fit around the rivet 174. In the instance of the powder metal compact 188b of FIG. 9B (with the counter-bored opening 190b), the corresponding sintered powder metal portion 188c is illustrated in FIG. 9C. In FIG. 9C, the opening 192b from FIG. 9B has dimensionally shrunk to capture the rivet 174 in it as well as its flange 178 in the counter-bored section of the hole. This locks the rivet 174 (or core section) in the surrounding powder metal section 188c. At this point, the free end can be riveted to further join the plate 190 to the powder metal section 188c. It is contemplated that the plate 190 might be a fully dense non-powder metal material or may be also be a separate powder metal component that shrinks upon sintering. It is also contemplated that the plate 190 need not be present during the sintering of the powder metal compact around the rivet and, in some instances, it may even be preferred to keep the plate separate from the powder metal compact to prevent diffusion joining of the components 188a, 188b, 188c, and/or 190 to one another or to prevent variances between the variable hole-to-hole distances of the powder metal section as it is sintered and the comparably static hole-to-hole distances in the plate.

(41) Turning now to FIGS. 10A through 10D, an alternative joining form is illustrated for reinforcing aluminum shells on a planetary gear carrier using a steel reinforcement plate.

(42) Looking first at FIG. 10A, a cross section through two support legs of a planetary gear carrier is illustrated in which an un-sintered aluminum shroud 194a is received over a steel reinforcement plate 196 having two spaced posts 198 extending upwardly therefrom. As the view illustrated is a sectional view, it will be appreciated that the aluminum shroud 194a has two tubular legs 200 that are received on the posts 198 (although the tubular nature of the legs is not readily apparent from the sectional view illustrated). This un-sintered aluminum shroud 194a is sintered to form a sintered aluminum shroud 194b, as is illustrated in FIG. 10B. Effectively, this sintering causes the legs 200 of the shroud 194a to dimensionally shrink onto the posts 198 to sinter fit the sintered shroud 194b onto the reinforcement plate 196. At this point with the sinter fit completed, a secondary plate 202 can be placed on the free, exposed end of the steel posts 198 as illustrated in FIG. 10B. This secondary plate 202 can then be attached to the composite component (comprising the reinforcement plate 196 and the sintered shroud 194b) by folding over or riveting the free end of the posts 198 to capture the secondary plate 202 on the ends on the sintered legs 200 as is illustrated in FIG. 10C.

(43) In a modified version of this construction, illustrated in FIG. 10D, the posts 198 may not extend beyond top of the legs 200 of the sintered aluminum shroud 194b, but may instead be generally flush therewith. The secondary plate 204 may be placed on top of the legs 200 and resistance or spot welding may be used to join the secondary plate 204 (which is steel) with the top face of the posts 198 (which are also steel).

(44) One having skill in the art will appreciate that while the sintering of an aluminum powder metal part around a steel core has been described above that, because of the range of temperatures involved in the sintering of the aluminum, the concept would not be applicable to most, if not all, hardened steel components since the sintering temperature for the aluminum powder metal part typically exceed the tempering temperature for steel.

(45) 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.