N102-122 TITLE: Gear Hobbing Predictive Model

TECHNOLOGY AREAS: Air Platform, Space Platforms

ACQUISITION PROGRAM: Joint Strike Fighter - Propulsion

OBJECTIVE: Develop a predictive model for analyzing forces, temperatures and residual stresses during hobbing of propulsion transmission gears for process and component improvement.

DESCRIPTION: Gear hobbing is a complex machining process involving fabrication of fatigue critical components with stringent dimensional and surface finish requirements. The hobbing or material removal process can induce stresses that are beneficial (compressive) or detrimental (tensile). Residual tensile stresses work to open up flaws after numerous load cycles are applied, which degrades the maximum life of the part. It is desired to modify the manufacturing process to improve the residual stress state in the gears resulting in improved fatigue life while reducing cycle time and cost.

Develop a physics-based modeling capability to provide detailed analysis of the gear hobbing process including forces, temperatures and residual stresses. The model should be able to capture details of the cutting tool edge and chip formation (e.g., with finite element models) and also analyze the process over the entire part program level. Full three-dimensional representation of the cutting tool and work piece should be provided for both detailed and tool path level analyses.

PHASE I: Determine the feasibility of innovative approach for modeling gear hobbing operations. Provide correlation between predicted and measured forces for gear-specific work piece material.

PHASE II: Develop, demonstrate and validate prototype gear hobbing modeling capability with fully three-dimensional analysis of gear hobbing at the detailed tool-chip (finite element) level as well as the full tool path gear hobbing analysis.

PHASE III: Transition validated full gear hobbing modeling tool to acquisition program and integrate with existing engineering analysis tools.

PRIVATE SECTOR COMMERCIAL POTENTIAL/DUAL-USE APPLICATIONS: Complex machining process involving fabrication of fatigue critical components with stringent dimensional and surface finish is a requirement in gear manufacturing for commercial producers. The innovative gear hobbing modeling tool developed in this program will have equal benefits to the private sector such as the automotive, trucking and heavy equipment companies that utilize gears and gearboxes in their designs. The benefits to the private sector would be lower failure rates/warranty costs and enhanced fuel savings via greater power densities (HP per gearbox pound).

REFERENCES:
1. Gimpert, D. (1994, January-February). The Gear Hobbing Process. Gear Technology, 11 (1), 38-44.

2. Maiuri, T. J. (2009, March-April). Hob Tool Life Technology Update. Gear Technology, 26(2), 50-59.

KEYWORDS: Modeling; Fatigue; Machining; Gear Hobbing; Residual Stress; Gear Life

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