Method for manufacturing a gear

A method for manufacturing a gear includes providing a rim gear, a hub and a core wherein the core is annular and has a core forging temperature below a hot hardness temperature of the rim gear and the hub. The rim gear and the hub are rotated about an axis relative to the core. During the relative rotation, the rim gear and the hub are in contact with the core to generate friction heat to raise an interface temperature of the core to the core forging temperature. The hub is driven into the core to upset a first portion of the core into an outer annular groove defined in a first faying surface of the hub. The rim gear is driven over the core to upset a second portion of the core into an inner annular groove defined in a second faying surface of the rim gear.

BACKGROUND

Transmissions for Class 6 through 8 commercial line haul and off road trucks are rugged and reliable. Some such transmissions provide more than one million miles of service; however the transmissions can be heavy. Some heavy duty (HD) truck transmissions weigh from about 500 to about 800 pounds. Thirty percent of the weight of typical existing HD transmission is attributed to the gears. Some currently made gears are fabricated from one piece of solid, carburized steel (e.g., AISI 8620). First, a solid steel billet is forged into a steel pancake. Second, the gear teeth are machined into the pancake. More than 10 percent of the steel is machined away from the pancake and ultimately discarded or recycled. The machined gear is carburized for as long as 13 hours in a furnace that runs continuously. The carburized gear is hardened and tempered in another furnace. Gears fabricated in this existing manner can weigh from several pounds to about 32 pounds depending on the pitch diameter and axial length. Heavy gears can be a factor that limits fuel economy in large commercial trucks. Gear weight in a transmission can also limit the performance of military and commercial helicopters.

The production of gears fabricated in the traditional manner described above may contribute to the consumption of energy by carburizing and heat treating/tempering furnaces that operate continuously. Some heat treating/tempering furnaces may emit carbon dioxide into the environment.

SUMMARY

A method for manufacturing a gear includes providing a rim gear, a hub and a core wherein the core is annular and has a core forging temperature below a hot hardness temperature of the rim gear and the hub. The rim gear and the hub are rotated about an axis relative to the core. During the relative rotation, the rim gear and the hub are in contact with the core to generate friction heat to raise an interface temperature of the core to the core forging temperature. The hub is driven into the core to upset a first portion of the core into an outer annular groove defined in a first faying surface of the hub. The rim gear is driven over the core to upset a second portion of the core into an inner annular groove defined in a second faying surface of the rim gear.

DETAILED DESCRIPTION

As disclosed herein, Friction Plunge Welding (FPLW) is a solid state welding process to join dissimilar materials. FPLW combines solid state welding with mechanical interlocking. FPLW is accomplished with the base materials remaining in a solid state with little or no melting. As disclosed herein, the dissimilar materials may include a base metal couple with one base metal having a significantly higher hot hardness, higher melting temperature and higher forging temperature than the other base metal. As used herein, hot hardness means a property of a material to retain a hardness at an elevated temperature. The hardness of a metal varies with temperature. As stated by Merchant et al, the hardness-temperature relationship is given as H=A EXP (−BT) where H is a hardness equivalent to the mean compressive stress and T is temperature in Kelvin. A is an extrapolated “intrinsic hardness” i.e. hardness at T=0 and constant B is the softening coefficient of hardness. The constants A and B have one set of values (A1, B1) at low temperatures and another set (A2, B2) at higher temperatures, suggesting a change of mechanism. The transition between the low- and high-temperature behaviors may occur at one temperature or over a range of temperatures. In most metals and alloys, the transition temperature (Tt) is about half the melting temperature (Tm). (Hardness- temperature relationships in metals, Merchant et al, Journal of Materials Science 8, 1973, 437-442.)

As used herein, “hot hardness temperature” means the transition temperature Ttas defined by Merchant et al. AISI (American Iron and Steel Institute) H13 is an example of a steel that maintains its hardness up to temperatures beyond 900° C. (degrees Celsius). However, conventional carburizing gear steels like SAE 8620 start to temper back in hardness at temperatures of 177° C. AISI H13 can be used as forging die base material to forge 8620 steel. Aluminum has no hot hardness. It is soft at all temperatures. All steels have higher hot hardness than aluminum. In FPLW, the frictional heating from steel in rotational contact with aluminum immediately elevates the interface temperature. The aluminum softens, becoming pliable and easily displaceable by the steel. In examples of FPLW disclosed herein, steel pushes the heated soft aluminum away. As disclosed herein, a groove is disposed along the path of aluminum movement, and the aluminum fills the groove.

An example of a base metal couple for FPLW is a steel alloy to be joined to an aluminum alloy. Steel alloy AISI 4150 has a hot hardness to about 800° C., a melting temperature over 1400° C. and a forging temperature over 900° C. In contrast, aluminum alloy 6061 has very low hardness at any temperature, a melting temperature of 600° C. (800° C. lower than steel) and a forging temperature of 450° C. (450° C. lower than steel).

After a short duration frictional heating of the 4150 steel/6061 aluminum interface, the steel is able to bore easily into the aluminum. The aluminum near the interface is displaced to form “ram's horns” of upset aluminum metal or to fill a designed cavity. The FPLW disclosed herein differs from Friction Welding (FW). For example, FW relies only on the development of a solid state weld bond between two materials; however, FPLW relies on both the development of (a) a solid state weld bond and (b) a mechanical interlock. Breaking a friction weld, although a difficult task, requires breaking only the solid state weld. To break a friction plunge weld, the solid state weld bond must be broken first and then, in addition, the mechanical interlock must be broken. Thus, FPLW provides redundant joining modes.

Another example of a difference between FW and the FPLW of the present disclosure is in the weld angles. FW creates welds generally perpendicular to the longitudinal plane of the work pieces; however, FPLW produces welds that occur at several angles in addition to perpendicular to the longitudinal axis of the work pieces. The multiple angle weld bonds are associated with creating the mechanical interlock.

Yet another example of a difference between FW and the FPLW of the present disclosure is in the diversion of displaced metal to mechanically interlocking structures. With FW, the material upset during the welding process is displaced to the outside of the weld joint interface. This FW “ram's horn” material can be removed by a subsequent machining operation and discarded as scrap metal. As disclosed herein, with FPLW, a portion of the metal displaced during the welding process is forced into a cavity to be filled by the back or reversed upsetting of metal. The upset metal is driven into the cavity to become a mechanical interlock. The mechanical interlock reinforces the solid state weld.

As disclosed herein, FPLW forms a lightweight gear from dissimilar metals. Examples of the method of the present disclosure form gears by using FPLW to join three elements. As depicted inFIGS. 1A-1C, a hub10′ and a rim gear14may be formed from steel. A core12may be formed from aluminum or an aluminum alloy. The hub10′, core12, and rim gear14may be combined to form a gear20having an interlocking cross section as depicted inFIG. 2A.

FIG. 2Adepicts a semi-schematic cross-sectional perspective view of an example of a gear20″ according to the present disclosure. The example is described in detail below in the detailed description ofFIGS. 5A-5D.

FIG. 2Bis a graph depicting an example of temperature and hardness relationships for a core12, hub10and rim gear14for friction plunge welding according to the present disclosure. A common log of hardness (H) is depicted on the ordinate axis71and absolute temperature is depicted on the abscissa72. The rim gear/hub trace73depicts a relationship between temperature and hardness of the rim gear14and hub10. The rim gear14and hub10are presumed to be formed from similar materials. In an example, the rim gear14and hub10may be formed from steel.

The rim gear/hub trace73demonstrates the transition temperature Ttand the hot hardness temperature70as described above. The core trace74shows that the core12is made from a material that has a hardness significantly below the hardness of the material of the rim gear14and hub10. In an example, the core12may be formed from an aluminum alloy. In the example depicted inFIG. 2B, the core forging temperature69is between a minimum core forging temperature68and the core melting temperature67. It is to be understood that the core melting temperature67is a theoretical boundary for the core forging temperature69, but is not reached. The core melting temperature67is indicated by a dashed line by convention indicating that the core forging temperature69is less than the core melting temperature67. Therefore, the core12does not melt in examples of the present disclosure. In the example depicted inFIG. 2B, the hot hardness temperature70is greater than the core melting temperature67. If the hot hardness temperature70were less than the core melting temperature67, the upper temperature limit for the core forging temperature69would be the hot hardness temperature70. In the example shown inFIG. 2B, the minimum rim gear/core forging temperature77is much higher than the core forging temperature69. Therefore, since the FPLW of the present disclosure does not exceed the core forging temperature69, the rim gear14and hub10will remain solid and will not flow.

FIG. 3Adepicts a semi-schematic cross-sectional view of an example of a rotating rim gear14and hub10aligned with a core12prior to FPLW according to the present disclosure.FIG. 3Bdepicts a semi-schematic cross-sectional view of the example depicted inFIG. 3Aafter being formed into a gear20by FPLW according to the present disclosure. Examples of the method disclosed herein include driving a steel component (e.g., the hub10and the rim gear14) into an interference fit bore or outside diameter of an aluminum component (e.g., the core12). The amount of interference may range from about 0.1 mm (0.004 inch) to about 2.5 mm (0.100 inch) or more. In an example, for a lightweight steel-aluminum gear20with a pitch diameter of about 203 mm (8 inches), the interference fit can be about 2.25 mm (0.090 inch).

As depicted inFIG. 3A, the hub10has a cylindrical wall21having a central axis22. The cylindrical wall21defines a bore23. In an example, the bore23may be smooth as depicted inFIG. 3A. In the example depicted inFIG. 1A, however, the bore23′ has inward projecting teeth24to engage complementary structures on a shaft (not shown). The hub10has a chamfered hub end25to penetrate the core12. The hub10has a hub chamfer29defined at the hub outer diameter28on the chamfered hub end25. A hub flange end26is opposite the chamfered hub end25. The hub flange end26has an annular hub flange27defined thereon. The annular hub flange27extends radially outward from the hub outer diameter28. An outer annular groove30is defined in a first faying surface59of the hub10. As used herein, a “faying surface” means a surface to be joined to another surface by welding. The outer annular groove30is defined in the cylindrical wall21between the hub chamfer29and the annular hub flange27. In the example depicted inFIG. 3A, the outer annular groove30is V-shaped with a fillet31between flat sides32.

Still referring toFIG. 3A, the core12has a cylindrical barrel33defined about the central axis22. The cylindrical barrel33defines a cylindrical barrel wall34. The core12has a chamfered core end35to penetrate the rim gear14. The core12has a core chamfer39defined at the core outer diameter38on the chamfered core end35. The core12has a core inner diameter40smaller than the core outer diameter38. A core flange end36is opposite the chamfered core end35. The core flange end36has an annular core flange37defined thereon. The annular core flange37extends radially outward from the core outer diameter38.

As depicted inFIG. 3A, the rim gear14has an annular wall41about the central axis22. The annular wall41defines a cylindrical surface43having a rim gear inner diameter48. In the example depicted inFIG. 1C, the annular wall41has outward projecting gear teeth44. The rim gear14has a first rim gear end45to receive the core12. A second rim gear end46is opposite the first rim gear end45. An inner annular groove50is defined in a second faying surface60of the rim gear14. The inner annular groove50is defined in the annular wall41between the first rim gear end45and the second rim gear end46. In the example depicted inFIG. 3A, the inner annular groove50is V-shaped with a fillet31′ between flat sides32′.

Prior to driving the hub10into the core12, the core12has a core inner diameter40smaller than the hub outer diameter28. Prior to driving the rim gear14over the core12, the core12has a core outer diameter38larger than a rim gear inner diameter48of the rim gear14. In an example, the core inner diameter40may interfere with the hub outer diameter28with an amount of interference ranging from about 0.1 mm (0.004 inch) to about 2.5 mm (0.100 inch). Similarly, in an example, the core outer diameter38may interfere with the rim gear inner diameter48with an amount of interference ranging from about 0.1 mm (0.004 inch) to about 2.5 mm (0.100 inch).

InFIG. 3A, hub rotation arrow51indicates relative rotation between the hub10and the core12. In the example depicted inFIG. 3A, the core12is held stationary. Rim gear rotation arrow52indicates relative rotation between the rim gear14and the core12. It is to be understood that the rotation may be clockwise or counterclockwise. Further, the hub10may rotate in an opposite direction to the rotation of the rim gear14. Hub plunge direction arrow53indicates that the hub10is forced into the core12. Rim gear plunge direction arrow54indicates that the rim gear14is forced over the core12.

In an example, the hub10is rotated relative to the core12in contact with the core12to produce friction heat to raise the hub interface temperature of the core12to the core forging temperature69. As used herein, the “core forging temperature” means a temperature between the minimum core forging temperature68of the core12and a lower of the hot hardness temperature70of the rim gear14and the hub10or a core melting temperature67of the core12. In an example with the hub10and rim gear14both made from AISI 4150 and the core12made from aluminum alloy 6061, the core forging temperature69may be from about 450° C. to about 600° C. based on the temperature properties of the materials provided above. The time to raise the interface temperature of the core12to the core forging temperature69may range from about two seconds to about 30 seconds, depending on the mass of the parts. The time to raise the interface temperature of the core12to the core forging temperature69may also depend on the force applied to the parts and the speed of rotation. The temperature of the hub10and the rim gear14rise correspondingly to the interface temperature of the core12. However, since the hub10and rim gear14have a hot hardness temperature70above the core forging temperature69, the rim gear14and the hub10do not reach the hot hardness temperature70according to the method of the present disclosure.

In the example of the present disclosure depicted inFIGS. 3A and 3B, the hub10is driven into the core12until the annular hub flange27contacts the core12. A first solid state weld55and a first mechanical lock56are formed between the hub10and the core12. The first solid state weld55also joins the annular hub flange27to the chamfered core end35of the core12. The rim gear14is driven over the core12until the annular core flange37contacts the rim gear14. A second solid state weld57and second mechanical lock58are formed between the core12and the rim gear14. The second solid state weld57also joins the annular core flange37to the rim gear14.

The first solid state weld55and the second solid state weld57each have portions (i.e., at the annular hub flange27and at the annular core flange37) that are perpendicular to the central axis22. The perpendicular solid state weld portions complement the portions of the first solid state weld55and the second solid state weld57that develop at the faying surfaces59,60parallel to the central axis22. The mechanical strength of the FPLW joints between the steel driver components (e.g., the hub10and the rim gear14) and the aluminum receiver component (e.g., the core12) is determined by a combination of three factors: (1) the strength of the solid state weld bond parallel to the central axis22; (2) the strength of the solid state weld bond at the flange27,37and perpendicular to the central axis22; and (3) the strength of the mechanical interlock formed with aluminum upset metal filling the inner annular groove50and the outer annular groove30.

In the example depicted inFIGS. 3A and 3B, the core12is held stationary, and the free diameter (diameter farthest away from the rim gear14or the hub10) is constrained from growth by a collet (not shown) or another work piece. Constraining the free diameter of the softer, lower hot hardness material guides the movement of the upset material along a path adjacent to the faying surfaces59,60. This guidance of the upset aluminum metal causes the inner annular groove50and the outer annular groove30to be filled by upset material. The inner annular groove50and the outer annular groove30are to be positioned along the path of movement of the upset aluminum metal. In an example, the driving of the rim gear14over the core12, and the driving of the hub10into the core12may be executed simultaneously. The simultaneous plunging constrains both the core outer diameter38and the core inner diameter40so the upset aluminum is guided into the inner annular groove50and the outer annular groove30.

Frictional heating requires from two to 30 seconds, depending on mass of the work pieces. The rim gear interface and the hub interface of the core12are raised to the core forging temperature69, at which the core material flows easily and is readily pushed out of the way by the hub10and the rim gear14. Following the brief frictional heating period, the rotating hub10and rim gear14are driven into the core12. Force for driving the hub10and rim gear14into the core12is obtained from a hydraulic cylinder (not shown). The steel driver (e.g., the hub10or the rim gear14) initially encounters the interfering aluminum material, penetrates the aluminum and creates pressure in the interfering aluminum that causes the aluminum to extrude along the faying surfaces59,60. A portion of the upset aluminum may move ahead of the steel driver, and another portion may back extrude opposite to the respective hub plunge direction arrow53or the rim gear plunge direction arrow. An amount of the upset aluminum may emerge from between the faying surfaces59,60and out beyond the ends of the faying surfaces59,60as a “ram's horn”47. However, when the advancing or back extruding upset material encounters a groove (e.g., the inner annular groove50or the outer annular groove30) defined in the steel driver component, the groove is filled with the upset aluminum, creating a mechanical lock. The amount of the upset aluminum that emerges beyond the ends of the faying surfaces59,60depends on an interference volume and on a portion of the interference volume that gets diverted into the inner annular groove50or the outer annular groove30. The ram's horns47may be removed, for example by grinding or machining; however, it may not be necessary to remove the ram's horns47.

FIG. 4Adepicts a semi-schematic cross-sectional view of another example of a rotating rim gear14′ and hub10′ aligned with a core12′ prior to FPLW according to the present disclosure.FIG. 4Bdepicts a semi-schematic cross-sectional view of the example depicted inFIG. 4Aafter being formed into a gear20′ by FPLW according to the present disclosure.

As depicted inFIG. 4A, the hub10′ has a barrel wall64having a central axis22. The barrel wall64defines a bore23. In an example, the bore23may be smooth or may have a contour that is complementary to a shaft (not shown). The hub10′ has a frustoconical outer surface61with a smaller hub end65to penetrate the core12′. A larger hub end66is opposite the smaller hub end65. In examples of the present disclosure, a largest hub diameter62at the larger hub end66may be larger than a smallest hub diameter63at the smaller hub end65by about 0.1 mm (0.004 inch) to about 2.5 mm (0.100 inch). Unlike the example depicted inFIG. 3A, the example depicted inFIG. 4Adoes not have a flange defined on the hub. An outer annular groove30′ is defined in a first faying surface59′ of the hub10′. The outer annular groove30′ is defined in the frustoconical outer surface61between the smaller hub end65and the larger hub end66. In the example depicted inFIG. 4A, the outer annular groove30′ is V-shaped with a fillet31′ between flat sides32′.

Still referring toFIG. 4A, the core12′ has a cylindrical barrel33′ defined about the central axis22. The cylindrical barrel33′ defines a cylindrical barrel wall34′. The core12′ has a first core end75to penetrate the rim gear14′. The core12′ has a core inner diameter40′ smaller than a core outer diameter38′. A second core end76is opposite the first core end75.

As depicted inFIG. 4A, the rim gear14′ has an annular wall41′ about the central axis22. The annular wall41′ defines an interior surface85defining a frustoconical space81. Similar to the example depicted inFIG. 1C, the annular wall41′ may have outward projecting gear teeth44. The rim gear14′ has a first rim gear end45′ to receive the core12′. A largest rim gear inner diameter83is at the first rim gear end45′. A second rim gear end46′ is opposite the first rim gear end45′. A smallest rim gear inner diameter84is at the second rim gear end46′. An inner annular groove50′ is defined in a second faying surface60′ of the rim gear14′. The inner annular groove50′ is defined in the annular wall41′ between the first rim gear end45′ and the second rim gear end46′. In the example depicted inFIG. 4A, the inner annular groove50′ is V-shaped with a fillet31′ between flat sides32′.

Prior to driving the hub10′ into the core12′, the core12′ has a core inner diameter40′ smaller than the smallest hub diameter63. In an example, the core inner diameter40′ may interfere with the smallest hub diameter63with an amount of interference ranging from about 0.1 mm (0.004 inch) to about 2.5 mm (0.100 inch). Prior to driving the rim gear14′ over the core12′, the core12′ has a core outer diameter38′ larger than the largest rim gear inner diameter83at the first rim gear end45′. Although the frustoconical space81is largest at the first rim gear end45′, there is an interference to generate friction when the rim gear14′ is rotated relative to the core12′. In an example, the core outer diameter38′ may interfere with the largest rim gear inner diameter83with an amount of interference ranging from about 0.1 mm (0.004 inch) to about 2.5 mm (0.100 inch).

InFIG. 4A, hub rotation arrow51′ indicates relative rotation between the hub10′ and the core12′. In the example depicted inFIG. 4A, the core12′ is held stationary. Rim gear rotation arrow52′ indicates relative rotation between the rim gear14′ and the core12′. It is to be understood that the rotation may be clockwise or counterclockwise. Further, the hub10′ may rotate in an opposite direction to the rotation of the rim gear14′. Hub plunge direction arrow53′ indicates that the hub10′ is forced into the core12′. Rim gear plunge direction arrow54′ indicates that the rim gear14′ is forced over the core12′. Rim gear plunge direction arrow54′ is opposite hub plunge direction arrow53′. The hub10′ may be driven into the core12′ before the rim gear14′ is driven over a sub assembly of the hub10′ and the core12′.

In the example of the present disclosure depicted inFIGS. 4A and 4B, the hub10′ is driven into the core12′ until the hub10′ is in a predetermined position relative to the core12′. As depicted inFIG. 4B, the predetermined position of the hub10′ relative to the core12′ is characterized by the smaller hub end65and the second core end76lying in the same plane. A first solid state weld55′ and a first mechanical lock56′ are formed between the hub10′ and the core12′. The rim gear14′ is driven over the core12′ until the rim gear14′ is in a predetermined location relative to the core12′. As depicted inFIG. 4B, the predetermined location of the rim gear14′ relative to the core12′ is characterized by the first rim gear end45′ and first core end75lying in the same plane. A second solid state weld57′ and second mechanical lock58′ are formed between the core12′ and the rim gear14′.

In the example depicted inFIGS. 4A and 4B, the core12′ is held stationary, and the free diameter (diameter farthest away from the rim gear14′ or the hub10′) is constrained from growth by a collet (not shown) or the hub10′. Constraining the free diameter of the softer, lower hot hardness material guides the movement of the upset material along the intended path. This guidance of the upset aluminum metal causes the inner annular groove50′ and the outer annular groove30′ to be filled by upset material. The inner annular groove50′ and the outer annular groove30′ are to be positioned along the path of movement of the upset aluminum metal. Ram's horns47may form similarly to the ram's horns47disclosed above in relation toFIG. 3B.

FIG. 5Adepicts a semi-schematic cross-sectional view of an example of a rotating hub10″ aligned with a core12″ prior to FPLW according to the present disclosure.FIG. 5Bdepicts a semi-schematic cross-sectional view of the example depicted inFIG. 5Aafter being formed into a hub core subassembly90by FPLW according to the present disclosure.FIG. 5Cdepicts a semi-schematic cross-sectional view of an example of a rotating rim gear14″ aligned with the hub core subassembly90fromFIG. 5Bprior to FPLW according to the present disclosure.FIG. 5Ddepicts a semi-schematic cross-sectional view of the example depicted inFIG. 5Cafter being formed into a gear20″ by FPLW according to the present disclosure.

As depicted inFIG. 5A, the hub10″ has a barrel wall64′ having a central axis22. The barrel wall64′ defines a bore23′. In an example, the bore23′ may be smooth or may have a contour that is complementary to a shaft, journal, or bearing assembly (not shown). The hub10″ has a chamfered hub end25′ to penetrate the core12″. The hub10″ has a hub chamfer29′ defined at the hub outer diameter28′ on the chamfered hub end25′. A hub flange end26′ is opposite the chamfered hub end25′. The hub flange end26′ has an annular hub flange27defined thereon. The annular hub flange27extends radially outward from the hub outer diameter28′. An outer annular groove30is defined in a first faying surface59of the hub10″. The outer annular groove30is defined in the barrel wall64′ between the hub chamfer29′ and the annular hub flange27. In the example depicted inFIG. 5A, the outer annular groove30is V-shaped with a fillet31between flat sides32.

Still referring toFIG. 5A, the core12″ has a cylindrical barrel33″ defined about the central axis22. The cylindrical barrel33″ defines a cylindrical barrel wall34″. The core12″ has a first core end75′ to penetrate the rim gear14″(seeFIG. 5CandFIG. 5D). The core12″ has a core inner diameter40″ smaller than a core outer diameter38″. A second core end76′ is opposite the first core end75′.

Prior to driving the hub10″ into the core12″, the core12″ has a core inner diameter40″ smaller than the hub outer diameter28′. In an example, the core inner diameter40″ may interfere with the hub outer diameter28″ with an amount of interference ranging from about 0.1 mm (0.004 inch) to about 2.5 mm (0.100 inch).

InFIG. 5A, hub rotation arrow51indicates relative rotation between the hub10″ and the core12″. In the example depicted inFIG. 5A, the core12″ is held stationary. It is to be understood that the rotation may be clockwise or counterclockwise. Hub plunge direction arrow53″ indicates that the hub10″ is forced into the core12″.

In the example depicted inFIGS. 5A and 5B, the core12″ is held stationary and the free diameter (diameter farthest away from the hub10′) is constrained from growth by a collet (not shown). Constraining the free diameter of the softer, lower hot hardness material guides the movement of the upset material along the intended path. This guidance of the upset aluminum metal causes the outer annular groove30to be filled by upset material. The outer annular groove30is to be positioned along the path of movement of the upset aluminum metal. Ram's horns47may form similarly to the ram's horns47disclosed above in relation toFIG. 3B.

As depicted inFIG. 5C, the rim gear14″ has an annular wall41″ about the central axis22. The annular wall41″ defines a cylindrical surface43′ having a rim gear inner diameter48′. Similar to the example depicted inFIG. 1C, the annular wall41″ may have outward projecting gear teeth44. The rim gear14″ has a first rim gear end45″ to receive the core12″. A second rim gear end46″ is opposite the first rim gear end45″. The second rim gear end46″ has an annular rim gear flange49defined thereon. The annular rim gear flange49extends radially inward from the rim gear inner diameter48′. An inner annular groove50″ is defined in a second faying surface60″ of the rim gear14″. The inner annular groove50″ is defined in the annular wall41″ between the first rim gear end45″ and the second rim gear end46″. In the example depicted inFIG. 5C, the inner annular groove50″ is V-shaped with a fillet31′ between flat sides32′.

Prior to driving the rim gear14″ over the core12″, the core12″ has a core outer diameter38″ larger than a rim gear inner diameter48′ of the rim gear14″. In an example, the core outer diameter38″ may interfere with the rim gear inner diameter48′ with an amount of interference ranging from about 0.1 mm (0.004 inch) to about 2.5 mm (0.100 inch).

Rim gear rotation arrow52″ indicates relative rotation between the rim gear14″ and the core12″. The rim gear14″ may rotate in an opposite direction to the rotation of the hub10″ or in the same direction as the rotation of the hub10″. Rim gear plunge direction arrow54″ indicates that the rim gear14″ is forced over the core12″.

In the example of the present disclosure depicted inFIGS. 5A-5B, the hub10″ is driven into the core12″ until the annular hub flange27contacts the core12″. A first solid state weld55″ and a first mechanical lock56″ are formed between the hub10″ and the core12″. The first solid state weld55″ also joins the annular hub flange27to the chamfered core end35′ of the core12″.

As depicted inFIGS. 5C-5D, the rim gear14″ is driven over the core12″ until the annular rim gear flange49contacts the core12″. A second solid state weld57″ and second mechanical lock58″ are formed between the core12″ and the rim gear14″. The second solid state weld57″ also joins the annular rim gear flange49to the core12″.

In the example depicted inFIGS. 5C and 5D, the hub core subassembly90is held stationary and the free diameter of the core (diameter farthest away from the rim gear14″) is constrained from growth by the hub10″. Constraining the free diameter of the softer, lower hot hardness material guides the movement of the upset material along the intended path. This guidance of the upset aluminum metal causes the inner annular groove50″ to be filled by upset material. The inner annular groove50″ is to be positioned along the path of movement of the upset aluminum metal. Ram's horns47may form similarly to the ram's horns47disclosed above in relation toFIG. 3B.

The first solid state weld55″ and the second solid state weld57″ each have portions (e.g., at the annular hub flange27and at the annular rim gear flange49) that are perpendicular to the central axis22. The perpendicular solid state weld portions complement the portions of the first solid state weld55″ and the second solid state weld57″ that develop at the faying surfaces59″,60″ parallel to the central axis22. The mechanical strength of the FPLW joints between the steel driver components (e.g., the hub10″ and the rim gear14″) and the aluminum receiver component (e.g., the core12″) is determined by a combination of three factors: (1) the strength of the solid state weld bond parallel to the central axis22; (2) the strength of the solid state weld bond at the annular hub flange27, the annular rim gear flange49, and perpendicular to the central axis22; and (3) the strength of the mechanical interlock formed with aluminum upset metal filling the inner annular groove50″ and the outer annular groove30″.

FIG. 6is a flowchart depicting an example of the method of the present disclosure. At reference numeral110,FIG. 6depicts a step of providing a rim gear, a hub and a core wherein the core is annular and has a core forging temperature below a hot hardness temperature of the rim gear and the hub. Reference numeral120depicts the step of rotating, about an axis, the rim gear and the hub relative to the core, the rim gear and the hub in contact with the core to generate friction heat to raise an interface temperature of the core to the core forging temperature. Reference numeral130depicts the step of driving the hub into the core to upset a first portion of the core into an outer annular groove defined in a first faying surface of the hub. Reference numeral140depicts the step of driving the rim gear over the core to upset a second portion of the core into an inner annular groove defined in a second faying surface of the rim gear.

FIG. 7is a flowchart depicting another example of the method of the present disclosure. Reference numeral210depicts the step of providing a rim gear, a hub and a core wherein the core is annular and has a core forging temperature below a hot hardness temperature of the rim gear and the hub. Reference numeral220depicts the step of rotating, about an axis, the hub relative to the core, the hub in contact with the core to generate friction heat to raise a hub interface temperature of the core to the core forging temperature. Reference numeral230depicts the step of driving the hub into the core to upset a first portion of the core into an outer annular groove defined in a first faying surface of the hub. Reference numeral240depicts the step of rotating, about the axis, the rim gear relative to the hub core subassembly, the rim gear in contact with the core to generate friction heat to raise a rim gear interface temperature of the core to the core forging temperature. Reference numeral250depicts the step of driving the rim gear over the core to upset a second portion of the core into an inner annular groove defined in a second faying surface of the rim gear.

It is to be understood that the terms “connect/connected/connection” and/or the like are broadly defined herein to encompass a variety of divergent connected arrangements and assembly techniques. These arrangements and techniques include, but are not limited to (1) the direct communication between one component and another component with no intervening components therebetween; and (2) the communication of one component and another component with one or more components therebetween, provided that the one component being “connected to” the other component is somehow in operative communication with the other component (notwithstanding the presence of one or more additional components therebetween).

Further, it is to be understood that the ranges provided herein include the stated range and any value or sub-range within the stated range. For example, a depth ranging from about 0.1 mm to about 2.5 mm should be interpreted to include not only the explicitly recited limits of 0.1 mm to 2.5 mm, but also to include individual amounts, such as 0.12 mm, 1.5 mm, etc., and sub-ranges, such as from about 0.2 mm to about 0.9 mm, etc. Furthermore, when “about” is utilized to describe a value, this is meant to encompass minor variations (±10% from the stated value (e.g., about 2.5 mm is 2.25 mm to 2.75 mm)).

While several examples have been described in detail, it will be apparent to those skilled in the art that the disclosed examples may be modified. Therefore, the foregoing description is to be considered non-limiting.