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Ausform Gear Finishing for Increased Strength and Durability Nagesh Sonti Drivetrain Technology Center ARL Penn State. Requirements for Aircraft Gearing. High profile accuracy and surface finish to minimize vibration and fatigue loading.

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Ausform Gear Finishing

for Increased Strength and Durability

Nagesh Sonti

Drivetrain Technology Center

ARL Penn State


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


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


  • 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




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


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


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


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


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



  • 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


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


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


Induction Heating and

Marquenching Process Model

Roll Finishing

Process Model

Integrated Model of Multi-tooth Ausforming Process


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


Process Results validated

  • Ausforming Process




Hobbed and shaved 24-30 µin Ra validated

Ground 12-16 µin Ra

Honed 8-10 µin Ra

Ausform finished 4-6 µin Ra

  • Surface Finish Comparison


Ausformed Gear Tooth Profile Charts validated

Before Ausforming

After Ausforming


Ausformed Gear Lead Charts validated

Before Ausforming

After Ausforming


Ausformed Gear Index Charts validated

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”


Root Ausform Finishing of Gears validated

Goal

• Apply ausforming to root/fillet region to enhance bending strength

Status

• Root ausforming of spur and helical gears developed


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


Gear Bending and Surface Durability Testing processing the test gears including Boeing planet gears

  • Performance Testing


Performance Testing Status processing the test gears including Boeing planet gears

  • 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


Phase 1: Ausform test rig gears - active profile only processing the test gears including Boeing planet gears

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


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