ARLPenn State

Ausform Gear Finishing

for Increased Strength and Durability

Nagesh SontiDrivetrain Technology Center

ARL Penn State

ARLPenn State 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

ARLPenn State

Steps eliminated by Ausform Finishing

Blank Machineand Hob Gear

Conventional Rotorcraft Gear Manufacture

Heat TreatCarburize, harden,

Cryogenic treat,temper

Grind GearNital Etch

Inspect

HIGH procurement cost

HoneShotPeen

ARLPenn State 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

ARLPenn State RCF Life of Ausformed Bars

ARLPenn State Endurance of Ausformed Bearings

ARLPenn State

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

ARLPenn State

• 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

ARLPenn State

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

ARLPenn State

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

Team Boeing Mesa, Honeywell, Purdy, Penn State, Duration January 2000 to July 2003

ONR / Boeing DUS&T Project

ARLPenn State

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

ARLPenn State

Process Modeling

ARLPenn State

Die development requires process modeling to account for the effects of thermal history, metallurgical transformations, and deformation gradients

Ausform Finishing Process

InductionHeat

Pre-formGear

FinalQuench

FinishedGear

Roll Finish

RollingDie

Marquench

Finished gear Accuracy of ±0.00015” (4 µm) for precision rotorcraft gears

ARLPenn State Conventional Tooling Development

StartAusform

FinishGears

Meet Specs

Finish

Modify Die Tooth Form

Grind Dies

GuessDie Tooth

Form

Heat Treat Dies

Hob Gears

Heat TreatGears

HobDies

Inspect Gears

Does notMeet

Specs

Die development can take many regrind iterations

ARLPenn State Process Modeling to Develop Tooling

StartAusform

FinishGears

Meet Specs

Finish

Modify Die Tooth Form

Grind Dies

PredictDie Tooth

Form

GuessDie Tooth

Form

Heat Treat Dies

Hob Gears

Heat TreatGears

HobDies

Inspect Gears

Does notMeet

Specs

ModelAusformProcess

Goal is to reduce hardware regrind iterations to 2-3

ARLPenn State

Induction Heating and

Marquenching Process Model

Integrated Model of Multi-tooth Ausforming Process

Roll FinishingProcess Model

Ausform Finishing Process Models

ARLPenn State

• 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

ARLPenn State

Process Results

Ausforming Process

ARLPenn State

Micro-hardness comparison at mid tooth

0

10

20

30

40

50

60

70

0 0.02 0.04 0.06 0.08 0.1 0.12

Distance from surface (in)

Har

dn

ess

(HR

C)

Ausform finished

Standard heat treat

Microhardness Comparison

ARLPenn State Induction Heating Pattern on Planet Gear

ARLPenn State

• 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

ARLPenn State Ausformed Gear Tooth Profile Charts

Before Ausforming After Ausforming

ARLPenn State Ausformed Gear Lead Charts

Before Ausforming After Ausforming

ARLPenn State 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”

ARLPenn State 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

ARLPenn State

• 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

ARLPenn State

Gear Bending and Surface Durability Testing

Performance Testing

ARLPenn State 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

ARLPenn State

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