Methods for Fabricating Strain Wave Gear Flexsplines Using Metal Additive Manufacturing

Patent metadata

Field	Value
Publication number	US-2018257141-A1
Application number	US-201815918831-A
Country	US
Kind code	A1
Filing date	Mar 12, 2018
Priority date	Mar 10, 2017
Publication date	Sep 13, 2018
Grant date	—

Abstract

Methods for the fabrication of metal strain wave gear flexsplines using a specialized metal additive manufacturing technique are provided. The method allows the entire flexspline to be metal printed, including all the components: the output surface with mating features, the thin wall of the cup, and the teeth integral to the flexspline. The flexspline may be used directly upon removal from the building tray.

First claim

1 . A method for fabricating a strain wave gear flexspline comprising using a metal additive manufacturing system to form an entirety of the strain wave gear flexspline as a single piece, wherein the strain wave gear flexspline is a cylindrical cup comprising:
a bottom defining a circumference, a cup wall disposed atop the bottom and defining a cylindrical volume, and gear teeth disposed on an upper outer surface of the cup wall's edge, wherein
the cup wall has a thickness of between 0.05 and 2 mm, and
the cup wall having a height that is at least 50 times larger than the smallest thickness of the cup wall; and
wherein the strain wave gear flexspline is fabricated in a vertical orientation, such that the bottom is disposed on a build platform and the cup wall is oriented perpendicularly to the build platform of the metal additive manufacturing system at all times during fabrication, and the properties of the strain wave gear flexspline in any single deposition layer are the same and are axially symmetric.

2 . The method of claim 1 , wherein the strain wave gear flexspline is attached to the building platform for support during fabrication only at the bottom and no supporting material is added to the cup wall during fabrication.

3 . The method of claim 1 , wherein the feature sizes of the strain wave gear flexspline are less than 1 mm in dimension.

4 . The method of claim 1 , wherein the metal additive manufacturing system is selected from the group consisting of: powder bed fusion printing, powder bed selective laser melting, direct energy deposition printing, metal extrusion, fused filament modeling, metal binder jetting, wire arc additive manufacturing, ultrasonic additive manufacturing, thermal spray additive manufacturing, liquid jetting, laser sintering, electron beam freeform, laser melting, or any combination thereof.

5 . The method of claim 1 , wherein the thickness of the cup wall is within 15% of the spot size of the laser of the metal additive manufacturing system.

6 . The method of claim 1 , wherein the cup wall is fabricated using a single width of the laser scanning of the metal additive manufacturing system or a single wire deposition extrusion process.

7 . The method of claim 1 , wherein at least one of the properties, composition, or microstructure of the strain wave gear flexspline are uniform in the direction parallel to the building platform but vary in the directing perpendicular to the building platform.

8 . The method of claim 1 , wherein the strain wave gear flexspline has a horizontally laminated structure such that the strain wave gear flexspline has a 10% higher fracture toughness than a strain wave gear flexspline made of monolithic metal.

9 . The method of claim 1 , wherein the strain wave gear flexspline is fabricated from a material with a fracture toughness between 30 and 150 MPa m 1/2 .

10 . The method of claim 9 , wherein the fracture toughness of the material is variable along the direction perpendicular to the building platform.

11 . The method of claim 1 , wherein the elastic limit of the strain wave gear flexspline ranges from 0.1-2%.

12 . The method of claim 1 , wherein-the strain wave gear flexspline comprises at least two regions with the same chemical composition but distinct physical properties disposed along the direction perpendicular to the building platform.

13 . The method of claim 1 , wherein the strain wave gear flexspline comprises at least two regions of distinct chemical compositions disposed along the direction perpendicular to the building platform.

14 . The method of claim 1 , wherein a gear teeth region of the strain wave gear flexspline comprising the gear teeth comprises a material that is chemically, physically, or both, distinct from the rest of the strain wave gear flexspline, and wherein the gear teeth region is more resistant to wear than the rest of the strain wave gear flexspline.

15 . The method of claim 1 , wherein a gear teeth-less region of the strain wave gear flexspline that excludes gear teeth comprises a material that is chemically, physically, or both, distinct from the gear teeth region of the strain wave gear flexspline, and wherein the gear teeth-less region is more resistant to fracture than the rest of the strain wave gear flexspline.

16 . The method of claim 1 , wherein a material used in the fabrication of the strain wave flexspline is introduced from the building head rather than from a bed of metal.

17 . The method of claim 1 , wherein the metal additive manufacturing system utilizes a material in one of the forms chosen from the group consisting of: powder, wire, molten metal, liquid metal, metal in a binder, metal in dissolvable inks, metal bound in polymer, sheet metal, any other printing form allowing vertical printing, or any combination thereof.

18 . The method of claim 1 , wherein the gear teeth have a vertically oriented curvature.

19 . The method of claim 1 , wherein the strain wave gear flexspline undergoes a post-fabrication process selected from the group consisting of:
chemical treatment to smooth the surface of the gear teeth and the inner surface of the cup wall; mechanically grinding, sanding or polishing to reduce surface roughness; coating with another metal; heat treating to alter one or more properties chosen from the group consisting of physical properties, porosity, temper, precipitate growth, other properties as compared to the as-fabricated state; and any combination thereof.

20 . The method of claim 1 , wherein the strain wave gear flexspline is fabricated from an alloy, a bulk metallic glass or metallic glass composite based on one or more elements chosen from the group consisting of: Fe, Ni, Zr, Ti, Cu, Al, Nb, Ta, W, Mo, V, Hf, Au, Pd, Pt, Ag, Zn, Ga, Mg, or any combination thereof.

21 . The method of claim 1 , wherein the strain wave gear flexspline is fabricated from a metal matrix composite, and wherein the volume fraction or the chemical composition of the metal matrix composite, or both, is uniform in the direction parallel to the building platform but variable in the directing perpendicular to the building platform.

22 . The method of claim 1 , wherein the strain wave gear flexspline is fabricated from both a crystalline metal alloy and a metallic glass alloy, and wherein the two materials are interchanged in the directing perpendicular to the building platform.

23 . The method of claim 1 , wherein the strain wave gear flexspline is fabricated from a high melting temperature alloy with a melting temperature greater than 1,500 Celsius.

24 . The method of claim 23 , wherein the high melting temperature alloy is Inconel or an alloy based on one of the elements chosen from the list: Nb, Ta, W, Mo, V, any combination thereof.

25 . The method of claim 1 , wherein the gear teeth can have a curved or arbitrary shape so that the performance of the stain wave gear can be enhanced or modified for a particular application.

Assignees

• California Inst Of Techn

Inventors

• Hofmann Douglas C
• Pate Andre M

Classifications

• B22F10/14

  by jetting of binder onto a bed of metal powder · CPC title

• B22F10/22

  Direct deposition of molten metal · CPC title

• B22F10/16

  by embedding the binder within the powder bed · CPC title

• B22F10/18

  by mixing binder with metal in filament form, e.g. fused filament fabrication [FFF] · CPC title

• B22F10/66

  by mechanical means · CPC title