Certification of Additive Manufactured and Repaired Aircraft Structures … · · 2017-10-01Certification of Additive Manufactured and Repaired Aircraft Structures and Components

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UNCLASSIFIED – Cleared for Public Release

Certification of Additive Manufactured and Repaired Aircraft Structures and Components

Presenter : Kevin Walker, DST Group Australia

Co-authors: Qianchu Liu, DST Group Australia

Milan Brandt, Centre for Advanced Manufacturing, RMIT University Australia

ADF Aircraft Structural Integrity Symposium

16-18 November 2016

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Presentation Outline

Introduction

Additive Manufacture (Ti-6Al-4V)

Laser Cladding Repairs (Geometry Restoration)

Laser Cladding Repair (Structural)

Certification and Acceptance Strategy

Conclusions

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Introduction

Additive manufacturing offers significant potential benefits including:

– Rapid prototype and manufacture

– Complex geometry, including shapes not possible with conventional subtractive manufacturing

– Minimal waste

– Eliminates need for tools, moulds, dies

– Improved logistics

– Can be used for both manufacture itself, but also for repair

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Cost of Additive versus Traditional Manufacturing

Adapted from A.J. Pinkerton / Optics & Laser Technology 78 (2016) 25–32

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AM for Manufacture and Repair

Manufacture

– Powder Bed Selective Laser Melting (SLM)

Repair

– Powder Blown Laser Melting Direct Metal Deposition

– Two important categories • Geometry restoration (laser cladding, SPD/Cold Spray)

• Structural repair (laser cladding)

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Two Types of AM for Metallic Materials

Generic illustration of an AM

Powder-Bed based system

(Source: William E. Frazier, Metal Additive Manufacturing: A Review, JMEPEG (2014) 23:1917–1928)

Generic illustration of an AM

Powder-Feed based system

(Laser-based systems)

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AM of Ti-6Al-4V

Ti-6Al-4V test samples manufactured using SLM Solutions 250HL system

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Laser Cladding Process

(Source: http://en.wikipedia.org/wiki/Laser_cladding)

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Laser Cladding Set-Up

Laser cladding facility at RMIT University, Australia

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Additive Manufacture of Ti-6Al-4V

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Additive manufacture of Ti-6Al-4V Need to better understand and characterise mechanical properties,

including fatigue

Very large variations in fatigue performance have been reported

Ref: Li, P., et al., Critical assessment of the

fatigue performance of additively

manufactured Ti–6Al–4V and perspective

for future research. International Journal of

Fatigue, 2016. 85: pp. 130-143.

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Sources of Variability

Variability in fatigue may be due to a very large number of parameters including:

– Layer thickness

– Laser power

– Beam profile

– Power density

– Focal distance

– Build direction

– Hatch spacing

– Scan speed

– Scan pattern

– Many more

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Test Specimen Manufacture Details SLM Solutions SLM250HL System

Gas atomised, pre-alloyed powder, 43 µm average spherical particle size

175 W laser power

Scan speed 710 mm/s

Hatch spacing 0.125 mm

Layer thickness 30 µm

Vertical and horizontal build directions

Vertical Build Horizontal Build

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Results – Traditional S-N Plot

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92 µm below surface

SEM Images – Fatigue Origins in Horizontal Build Specimens

267 µm below surface

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Crack growth results

4 – 40 µm

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In-situ martensite decomposition – very strong potential

In-situ martensite decomposition into ultrafine lamellar (α+β) microstructure offers significant potential for superior fatigue crack growth rate properties

Ref: Xu, W. etal, “Additive manufacturing of strong and ductile Ti-6Al-4V by selective laser melting via in situ martensite decomposition”, Acta

Materialia 85 (2015) 74-84

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Laser Cladding Repairs – Geometry Restoration

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Repair Objectives

Repairs required to achieve the following

– Good metallurgical bond

– Low porosity

– No micro-cracking

– Match the hardness of the substrate

– Improve the corrosion resistance

– Recover the full geometrical features of the original item including surface finish

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Australian Air Force Laser Cladding Repair Examples (Geometry Restoration)

High strength aluminium alloys-7000 series

(7075-T7 & T6 series alloys

Titanium Alloys - Ti-6Al-4V

Low carbon steels > 260 ksi. The specific

materials in this category are :

- M300/AISI4140/AISI4340 Steels

- AerMet 100 replacement of AISI4340

Stainless steels – 17-4 PH etc

Components Original Material

Repair Material

Restoration Requirements

F/A-18 Engine Mount Bracket

Ti-6Al-4V Ti-6Al-4V

Geometric restoration to restore wear

F/A-18 Rudder Anti-Rotation Bracket

17-4PH *SS316 & SS420


F/A-18F AIM9X Missile Forward Hanger Assembly

Cast PH13-8 steel

*17-4PH & SS420


C-130J Shelf Bracket Forged 4140 steel

*17-4PH & SS420

Resurface with Stainless steel to reduce corrosion.

F/A-18 NLG Piston 300M 4140 or 4340

Geometric restoration to restore corrosion & wear

F/A-18 MLG Housing Forged AA2014 Al Alloy Geometric restoration to restore corrosion

* Mixed powder

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Repair of F/A-18 Anti-Rotation Bracket

• Unserviceable damage due to wear

• Precipitation-hardened stainless steel

• Geometrical restoration (No post heat treatment)

• Clad hardness to match component

Problem & Requirements:

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Repair of F/A-18 Rudder Anti-Rotation Bracket

Before Repair

After Repair (as-clad)

After Repair (machined)

Repair & Certification:

• Machine damaged area

• Develop a laser cladding repair (mixed powders)

• Clad & machine to tolerance

• TRL 9 (Certification approved, applied to aircraft)

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Repair of F/A-18F Forward Hanger Assembly AIM-9X Missile Attachment Lug



• Dampeners causing flange wear damage

• Allowable flange tolerance 0.25 mm

• Geometry restoration

Dampeners

Wear Damage

FHA Block

AIM-9X

CATM Tube

FWD

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Repair of F/A-18F Forward Hanger Assembly

Damaged by Wear

Material: Cast PH13-8 stainless steel

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Repair of F/A-18F Forward Hanger Assembly During Repair

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Repair of F/A-18F Forward Hanger Assembly

(a)

(d) (c)

(b)

Damaged surface Grind out

LC repair Machining

Process developed:

* Matched on hardness

* Awaiting certification

Shoulder depth,

6.62-6.81 mm

Recess depth

~4.92 mm FWD

Flange

thickness

4.87-4.98 mm

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Repair of F/A-18 Engine Mount


• Titanium Alloy (Ti-6Al-4V)

• Geometrical restoration (No post heat treatment)


Damaged area

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Repair chamber at Swinburne University, Australia

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Set-up for repair at Swinburne University

Laser nozzle

Engine mount

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Repaired area in Engine mount (at Swinburne University)

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Laser Cladding Repair C-130J Landing Gear Shelf Bracket Corrosion

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C-130J Landing Gear Shelf Bracket Details 4140 steel forging

Corrosion in drag pin holes

Corrosion damage depth limit is very conservative – maximum allowable depth 12 µm, 0.0005 in

Typically find 3 out of 4 brackets need to be replaced at 6 yearly depot servicing

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Shelf Bracket Function (1 of 2)

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Shelf Bracket Function (2 of 2)

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C-130 Landing Gear Shelf Bracket Repair Development Strategy

Develop system to clad internally

Match hardness using a mixture of stainless steel powders – also provides improved corrosion resistance

Conduct trials on steel tube specimens

Conduct trials on scrapped shelf brackets

Cut sections from trial repairs and evaluate microstructure, hardness, adhesion

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Internal Cladding System

Schematic of a cladding nozzle for the internal repair,

designed by Fraunhofer Institute of Laser Technology

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Powder characteristics

AISI 420 Stainless Steel • 17-4 PH Stainless Steel

AISI 420 stainless steel 17-4 PH stainless steel

+75 µm 1.8 0.0

45-75 µm 95.2 99.0

-45 µm 3.0 1.0

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Trials on Tube Samples Clad layer

HAZ Substrate

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Trials on Tube Samples

Clad

Machined

Original

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Optimised Process Parameters for the Repair

Laser processing parameters Value

Laser focus distance (mm) 8 mm

Laser power (W) 950

Laser traverse speed (mm/min) 900

Powder flow rate (g/min) 8 (2.5 RPM)

Step-over width (mm) 0.45

Nozzle carrier gas flow rate (L/min) 5 (Helium)

Shielding gas flow rate (L/min) 10 (Argon)

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Set-up for Repair of C-130J Shelf Bracket

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Assessment on Repaired Shelf Bracket

As-built (clad) As machined

200

µm

Transition

Cross-section

Cutting

Clad

Substrate

Clad Clad

Substrate Substrate

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Laser Cladding Repairs – Structural

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Repair Material (RS & Fatigue):

Research on Structural Repair

• Repair on round bars

• AerMet powder

(High Strength Steel – AerMet 100)

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Fatigue Fracture Surface of the Repair:

Repair of AerMet 100

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Crack Behaviour & Prediction:

- Slow fatigue crack growth due to the compressive residual stress in clads

- Restore strength (promising) & further research work

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Certification and Acceptance

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Judgement of

Significance

Hazard

Analysis

Design

Analysis

Design

Certification Deviation Acceptance

*Acceptance strategy for Structural repair is being developed

Certification and Acceptance Strategy

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Judgement of Significance

Addresses the consequence and risk of incorporating the proposed repair.

The scope of the proposed laser cladding repair is determined to be geometrical only.

The effect of the design change in terms of form, fit or function is also assessed and possible failure of the component is considered.

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Hazard Analysis

Investigates the risk associated with laser cladding repairs as opposed to replacing the component. Any hazard description, effects, risk and risk mitigation are addressed.

For example, dimensional tolerance is restored, structural integrity is not compromised, material hardness remains the same, quality control of the process and powder used is established and the consequence of failure is no worse than leaving the component in its current worn stage.

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Design Analysis

Investigates the in-service loading conditions acting on the repaired region and its structural integrity due to material loss.

Repair criteria are established in which the maximum allowable or acceptable damage is identified.

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Design Certification

Formal approval or acceptance of the repair is established based on the three preceding criteria.

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Deviation

The repair method or standard operating procedure documentation is established for conducting future repairs.

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Conclusions Additive manufacturing offers significant potential benefits, but

significant issues including variability in properties needs to be addressed

Laser cladding has been demonstrated to be a very effective repair method for geometrical restoration

Further work is needed to extend the range of materials and geometries for laser cladding repairs

Further work is needed to extend laser cladding repairs to structural cases

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QUESTIONS?

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Certification of Additive Manufactured and Repaired Aircraft Structures … · · 2017-10-01Certification of Additive Manufactured and Repaired Aircraft Structures and Components