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Development of Additive Manufacturing for Aerospace Gear Applications


TECHNOLOGY AREA(S): Materials/Processes


OBJECTIVE: Develop and demonstrate an additive manufacturing process for advanced aerospace gears meeting or exceeding the mechanical properties of SAE AMS 6308.


DESCRIPTION: The lead time for manufacturing gears for testing in Science and Technology (S&T) prototype demonstrators can be several months and requires costly special tooling. Additive manufacturing is a manufacturing technique that can be used to reduce the lead time and cost for prototype hardware. Additive Manufacturing (AM) refers to a process by which digital 3D design data is used to build up a component in layers by depositing material. The goal for this topic is to develop a new or improved AM process for aerospace quality gears in order for them to be used in prototype demonstrator applications. Potential AM processes that could be improved upon includes (but is not limited to) Laser Engineered Net Shaping (LENS) and Electron Beam Melting (EBM). The AM process must be developed to overcome existing challenges that limit the use of AM for gear manufacturing. Some of the common challenges/limitations are: 

  1. Residual stresses can be high in AM parts, which limit the loading of parts. Stress mitigation and optimization strategies must be developed as part of the effort.
  2. Density of the material throughout AM parts can be inconsistent. Density can be influenced by un-melted entrapped powders. Overcoming this challenge needs to be addressed as part of the effort.
  3. The rapid cooling rates associated with AM processes can affect the microstructure of the base material resulting in variations in desired strength, ductility, toughness, and modulus. The new AM processes must mitigate the effects to material properties.

Final components manufactured using the developed process must meet or exceed the mechanical properties of SAE AMS 6308 (Pyrowear 53). Pyrowear 53 may be considered as an Aerospace Grade 3 material, as defined in AGMA 926-C99. Any additional processing steps (such as hardening or surface finishing) must be defined, and should be minimized if possible. A method to vary the properties between the case and core regions of a gear must also be addressed. Specific metrics for the final manufactured gears are:

  • Minimum surface contact stress allowable = 250ksi
  • Minimum bending stress allowable = 40ksi
  • Minimum core hardness = 34 HRC
  • Minimum case hardness = 60 HRC
  • Minimum core yield strength = 140ksi
  • Minimum core ultimate tensile strength = 170ksi
  • Maximum surface finish = 16Ra


PHASE I: Demonstrate the feasibility of the new or improved AM process for use in additive manufacturing. Efforts should show that the formed parts can meet the properties equivalent to SAE AMS 6308 steel by utilizing simple geometric shape test specimens that have been produced using additive manufacturing.


PHASE II: Contractors are encouraged to collaborate with an Army rotorcraft OEM during Phase II. The contractor shall further optimize the AM process based on the Phase I results. This optimization shall include developing methods to reduce additional gear manufacturing processes (such as carburization, peening, surface finishing) by altering the AM process. Coupon level testing shall be performed to demonstrate mechanical properties such as yield and ultimate tensile strength. Several sets of 4 inch diameter spur gears (representative of aerospace quality gears) shall be manufactured using the developed process. Testing and analysis of these final gears shall be performed to demonstrate that each of the topic metrics has been met. Additionally, the microstructure of the final gears shall be analyzed and compared to Pyrowear 53.


PHASE III DUAL USE APPLICATIONS: Transition the new process via aerospace Original Equipment Manufacturers (OEM) and/or qualified suppliers for Army rotorcraft. Demonstrate the AM process for actual aircraft components.


KEYWORDS: Gears, additive manufacturing, rotorcraft, drive system, transmission, Pyrowear

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