METHOD OF MANUFACTURING MULTI-MATERIAL GEARS

Abstract

A method of manufacturing a multi-material gear is disclosed. The method comprises the steps of (a) heating a first pre-form element of a first material to a temperature at which the first material can be formed; (b) heating a second pre-form element of a second material to a temperature at which the second material can be formed; and (c) forming the first and second pre-form elements in a die at least towards the shape of the gear, thereby providing bonding between the elements.

Claims

1.-12. (canceled)

13. A method of manufacturing a multi-material gear comprising the steps of: (a) in a first furnace, heating a first pre-form element of a first material to a first temperature at which the first material can be formed; (b) in a second furnace, heating a second pre-form element of a second material to a second temperature at which the second material can be formed; and (c) forming the first and second pre-form elements in a die at least towards the shape of the gear, thereby providing bonding between the elements.

14. A method according to claim 13, wherein the temperature at which the first material can be formed is substantially different from the temperature at which the second material can be formed.

15. A method according to claim 13 and comprising the step of juxtaposing the heated pre-form elements.

16. A method according to claim 13 and comprising applying a force to the elements to deform at least part of each element.

17. A method according to claim 16, wherein the deformation is such as to provide mechanical bonding between the elements; and/or the deformation is such as to provide diffusion bonding between the elements; and/or the deformation is such as to provide adhesion between the elements.

18. A method according to claim 17, wherein the bonding and/or adhesion is to resist relative angular movement of the elements.

19. A method according to claim 16, wherein the force is a substantially axial force to cause substantially radial deformation.

20. A method according to claim 13, comprising deforming the elements by different radial amounts at different angular positions.

21. A method according to claim 13, comprising deforming the elements more at angular positions that correspond to the angular positions of gear teeth of the gear.

22. A method according to claim 15, wherein the step of juxtaposing the heated pre-form elements includes placing the heated pre-form elements one inside the other.

23. A method according to claim 17, wherein the deformation by mechanical bonding includes mechanical keying between the elements.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0022] FIG. 1 is a perspective view of a gear formed from three different materials;

[0023] FIG. 2 is a schematic diagram of a method of manufacturing the gear; and.

[0024] FIG. 3 shows two views of a gear made by a method according to an embodiment, the gear being formed of two materials.

SPECIFIC DESCRIPTION OF CERTAIN EXAMPLE EMBODIMENTS

[0025] An example of a multi-material gear manufactured in accordance with a method that amounts to an embodiment is shown in FIG. 1. As can be seen from the figure, the higher performance gear material is applied to the high stress regions, whereas lighter weight material is applied in low stress core regions.

[0026] The forging method to produce this gear depends on the materials chosen. For example, if two metals are chosen, which have similar melting temperatures, such as titanium (1725 C.) and steel (1500 C. ) [12], then the heating may be carried out within one furnace. However, if dissimilar metals, such as magnesium (685 C.) and steel (1500 C.) are chosen, different heating facilities may be required to heat individual materials to their required forging temperatures.

[0027] A description of the forming process is outlined below: [0028] Prepare pre-forms for each of the materials to be used. For example, a 3-material gear requires pre-forms for an outer ring, inner core and inner ring. More layers can be added if necessary. [0029] Heat the individual pre-forms to their required forming temperatures in furnaces. For example, the furnace for steel is heated to about 1100 C., whereas the furnace for aluminium or magnesium could be approximately 500 C. [0030] Place the pre-forms sequentially onto the die set. [0031] Form the gear using a press or other type of forming machine. Lubricant can be applied to the materials or forging tool set as appropriate to reduce friction, or reduce surface degradation, or promote diffusion bonding. [0032] Eject the forged gear from the die. [0033] FIG. 3 shows cross sections of formed lightweight bi-metal gears with a steel outer ring and an aluminium inner core. As shown in FIG. 3, the gear exhibits a strong mechanical lock between the materials used due to the extensive deformation of all materials as they flow to form the gear teeth. Additional locking is obtained due to diffusion bonding between the two materials as has been observed. [0034] If magnesium or magnesium core material is used, the material has low formability and an outer steel ring could provide compressive forces to prevent cracking of the lightweight material during the forming process,

[0035] It is envisaged that, in embodiments: [0036] Gears can be made from various materials ranging from metals alloys including steel and nickel super-alloys, and plastics such as nylon. [0037] All gears require materials which exhibit certain mechanical properties such as high strength, high stiffness and good wear resistance. However, these properties usually come at the expense of either being heavy or of high cost. [0038] It is unnecessary to use the same high performance gear material throughout the entire gear. Certain regions of the gear, such as the contact line between two meshing gears, the root of the tooth, and possibly a keyway or splines attaching the gear to the shaft experience larger stresses than material located in the core of the gear. [0039] A multi-material gear is proposed in which high performance gear materials are used in critical areas of the gear, and lower performance materials are used for less critical regions. The materials can be chosen depending on the particular application, whether it is to produce a low cost gear, or a lightweight gear etc. [0040] These multi-material gears will be produced essentially through a forming/forging process. A forging process produces better overall mechanical properties compared to casting. In the document, use the word forming instead of forging process in order to widen the scope of possible deformation modes. [0041] The different materials can be joined by one or more methods, such as mechanical bonding, diffusion bonding and adhesion.