Ausform Gear Finishing for Increased Strength and Durability Nagesh Sonti

1. Ausform Gear Finishing for Increased Strength and Durability Nagesh Sonti Drivetrain Technology Center ARL Penn State

2. Requirements for Aircraft Gearing High profile accuracy and surface finish to minimize vibration and fatigue loading High surface strength and gradient to maximize tooth fracture strength and surface fatigue resistance High toughness of core material to maximize impact strength

3. Conventional Rotorcraft Gear Manufacture Blank Machine and Hob Gear HIGH procurement cost Heat Treat Carburize, harden, Cryogenic treat, temper Nital Etch Inspect Shot Peen Grind Gear Hone Steps eliminated by Ausform Finishing

4. What is Ausforming? • Process • Modified steel heat treatment process • Plastic deformation of metastable austenite • Benefits • 30-50% increase in strength • Gear finishing time of less than a minute, as compared to over 40 minutes for grinding • Over 60% reduction in manufacturing time due to elimination of operations • Cost-effective integrated in-line manufacturing operation

5. RCF Life of Ausformed Bars

6. Endurance of Ausformed Bearings

7. BULK AUSFORMING 30 to 50% increase in strength without loss in ductility Over 500% improvement in surface fatigue (L10) life of ausformed balls, rollers and bearings as compared to standard heat treatment Aus-forged spur gears performed significantly better than machined gears Limitations Requires large forging capability Requires subsequent finishing operations Applicable to through hardening steels only AUSFORM FINISHING Penn State technique applies ausforming to localized surface layers for precision finishing Does not require large forging capability Applicable to carburizing grade gear steels as well as through hardening steels Cost-effective integrated inline manufacturing operation • Rationale for Surface Ausform Finishing

8. Developed double die ausforming machine Demonstrated ausform finishing of V-22 planetary gears Achieve desired accuracy by using high precision roll finishing Demonstrated potential for enhanced gear strength by inducing ausforming effects in surface layers Demonstrated potential for substantial cost reduction by eliminating expensive and labor-intensive operations • Prior ONR Mantech Project

9. Objective Increase the power density and reduce the lifecycle cost of rotorcraft gearing by implementing ausform gear finishing Approach Develop process models to facilitate tooling and process optimization Qualify ausform finishing process for DoD components Demonstrate and validate gear performance Establish commercial suppliers of ausforming equipment • ONR/Boeing DUS&T Project

10. Objective Qualify ausform finishing process as an acceptable DoD process, as an alternative to hard gear grinding Program Tasks Process modeling to develop tooling, and evaluate variability and sensitivity to tooling/process changes Verify performance enhancement on 9310 and Pyrowear 53 steel test rig gears Develop tooling/process for Apache sun/planet gears, including root/fillet ausform finishing Compare bending fatigue strength of ausform finished and conventionally finished Apache sun/planet gears Conduct transmission tests Deliverables Analytical capability to predict tooling geometry Comparative strength and durability data for test rig gears and Apache sun/planet gears Process specifications for Apache sun/planet gears TeamBoeing Mesa, Honeywell, Purdy, Penn State, Duration January 2000 to July 2003 • ONR / Boeing DUS&T Project

11. Phase 1: Ausform test rig gears - active profile only Process modeling Tooling and test gears manufacture Optimize tooling and process Gear performance testing Phase 2: Ausform test rig gears - active profile and root/fillet Process modeling Tooling and test gears manufacture Optimize tooling and process Gear performance testing Phase 3: Ausform Apache planet/sun gears Tooling and test gears manufacture Optimize tooling and process Process test gears Phase 4: Testing of Apache planet/sun gears Bending fatigue testing at ARL Transmission rig testing at Boeing • ONR / Boeing DUS&T Project - Phases

12. Process Modeling

13. Ausform Finishing Process • Finished gear Accuracy of ±0.00015” (4 µm) for precision rotorcraft gears Rolling Die Pre-form Gear Induction Heat Final Quench Finished Gear Marquench Roll Finish • Die development requires process modeling to account for the effects of thermal history, metallurgical transformations, and deformation gradients

14. Heat Treat Dies Ausform Finish Gears Heat Treat Gears Meet Specs Finish • Conventional Tooling Development Die development can take many regrind iterations Hob Dies Guess Die Tooth Form Modify Die Tooth Form Grind Dies Does not Meet Specs Hob Gears Inspect Gears Start

15. Heat Treat Dies Ausform Finish Gears Heat Treat Gears Meet Specs Finish • Process Modeling to Develop Tooling Goal is to reduce hardware regrind iterations to 2-3 Hob Dies Guess Die Tooth Form Predict Die Tooth Form Model Ausform Process Modify Die Tooth Form Grind Dies Does not Meet Specs Hob Gears Inspect Gears Start

16. Ausform Finishing Process Models Induction Heating and Marquenching Process Model Roll Finishing Process Model Integrated Model of Multi-tooth Ausforming Process

17. Ausforming model methodology development completed and validated Achieved program objective by significantly reducing number of hardware iterations Ausforming models successfully applied to development of various test gears Ausforming models extended to analyze flank and root/fillet finishing Model method has been applied to develop die design for Boeing planet gear • Process Models - Summary

18. Process Results • Ausforming Process

19. Microhardness Comparison

20. Induction Heating Pattern on Planet Gear

21. Hobbed and shaved 24-30 µin Ra Ground 12-16 µin Ra Honed 8-10 µin Ra Ausform finished 4-6 µin Ra • Surface Finish Comparison

22. Ausformed Gear Tooth Profile Charts Before Ausforming After Ausforming

23. Ausformed Gear Lead Charts Before Ausforming After Ausforming

24. Ausformed Gear Index Charts Before Ausforming Total Index Variation Left Flank: 0.0021” Right Flank: 0.0011” After Ausforming Total Index Variation Left Flank: 0.0005” Right Flank: 0.0007”

25. Root Ausform Finishing of Gears Goal • Apply ausforming to root/fillet region to enhance bending strength Status • Root ausforming of spur and helical gears developed

26. Established ausforming tooling and processing conditions for processing the test gears including Boeing planet gears Achieved required metallurgical design specifications for Pyrowear 53 and AISI 9310 steel test gears Achieved required surface finish and gear accuracy specifications for the test gears and Boeing planet gears • Gear Processing Summary

27. Gear Bending and Surface Durability Testing • Performance Testing

28. Performance Testing Status • Baseline Gear Testing Status • Single tooth bending fatigue testing of ground TR-1 gears completed • Rotating Surface fatigue testing of ground TR-2 gears completed • Rotating Surface fatigue testing of ground TR-1 gears - 75% complete • Rotating bending fatigue testing of ground TR-1 gears - 25% complete • Scoring resistance testing of ground TR-2 gears completed • Ausformed Gear Testing Status • Single tooth bending fatigue testing of ground TR-1 gears - 10% complete • Rotating Surface fatigue testing of ground TR-2 gears - initiated • Rotating Surface fatigue testing of ground TR-1 gears - initiated

29. Phase 1: Ausform test rig gears - active profile only Process modeling Tooling and test gears manufacture Optimize tooling and process Gear performance testing Phase 2: Ausform test rig gears - active profile and root/fillet Process modeling Tooling and test gears manufacture Optimize tooling and process Gear performance testing Phase 3: Ausform Apache planet/sun gears Tooling and test gears manufacture Optimize tooling and process Process test gears Phase 4: Testing of Apache planet/sun gears Bending fatigue testing at ARL • Program Status Summary Tasks Completed Tasks yet to be completed