NDT Capability for AM Aerospace Applications: the MTC ...

NDT Capability for AM Aerospace

Applications: the MTC Perspective

Ben Dutton12th International Symposium

on NDT in Aerospace

6 Oct-2020

Virtual

Contents

Additive Manufacturing

Defect morphology

Post built NDT (XCT limits & less-conventional methods)

Standards

Post built Metrology

In-process NDT

CFRP NDT

AFRCAdvanced Forming Research Centre

CPICentre for Process Innovation

NAMRCNuclear Advanced ManufacturingResearch Centre

AMRCAdvanced Manufacturing Research Centre

MTCManufacturing Technology Centre

WMGWarwick Manufacturing Group

NCCThe National Composites Centre

MTC also hosts the European Space Agency (ESA) AM Benchmarking Centre since May 2017

HIGH VALUE MANUFACTURING CATAPULT

MTC has become the first ASTM AM Center of Excellence (CoE) in Europe since July 2018

MANUFACTURING INNOVATION

Dimensional & surface Metrology and NDT

M&NDT: TECHNOLOGY COVERAGE HIGHLIGHTS

High-precision tactile instruments High-precision optical instruments Portable tactile instruments Portable optical Instruments

Tactile surface measurement Optical surface measurement Portable surface measurement Microscopes

3D Computed Tomography Computed Radiography

Portable NDT (phased array ultrasound, eddy current flexible array, x-ray backscatter and GPR)

Non-contact laser ultrasound inspection

Dimensional Metrology

Surface Metrology

Non-destructive Testing

NDT Challenges from Additive Manufacturing (AM)

Additive manufacturing generates challenges for NDT due to inherent freedom to manufacture:Complex shapes (internally and externally)

Rough surface finish

Part courtesy of 3T RPD Ltd: www.3trpd.co.uk Part courtesy of MTC’s National Centre for AM

AM Defects

Complexity of Defect Generation

• This flowchart gives an idea of the complexity of “defect” generation within the laser PBF process.

• The generation of one “defect” type can in fact result in a processing condition which generates a second.

• To aid understanding, an outline of laser PBF is given, definitions for each of the inputs are outlined.

Leach, R. (Ed.), Carmignato, S. (Ed.). (2020). Precision Metal Additive Manufacturing. Boca Raton: CRC Press, https://doi.org/10.1201/9780429436543 (Chapter 9: Non-destructive evaluation for additive manufacturing)

AM Defects

Non-unique to AM defects

• Defects, not AM unique - lack of dimensional accuracy or warping, inclusions, process-induced voids, gas-induced porosity, cracks and delamination:

Gas porosity Process void Crack

Delamination

InclusionDimensions/warping

Courtesy ISO/ASTM JG59 DTR 52905, ‘Additive Manufacturing — Non-Destructive Testing and Evaluation — Standard Guideline for Defect Detection in Metallic Parts’, Submitted for balloting.

AM Defects

AM unique defect

• Specific AM defects – Layer defects (horizontal LOF), cross-layer defect (vertical LOF), unconsolidated powder and trapped powder:

Trapped powder

Layer defect (horizontal LOF)

Cross-layer defect (vertical LOF)Unconsolidated powder


AM Defects

DED & PBF defects potentially covered by standards and unique to AM

• Certain AM flaws (for example, voids and porosity) can occur in most or all AM parts (non-process specific), and can be characterized using existing methods for welded or cast parts.

• Other AM flaws (for example layer, cross layer, unconsolidated and trapped powder) are unique to PBF, and new or better NDT detection methods are needed.

Develop

new or

better

NDT

methodsCourtesy ISO/ASTM JG59 DTR 52905, ‘Additive Manufacturing — Non-Destructive Testing and Evaluation —Standard Guideline for Defect Detection in Metallic Parts’, Submitted for balloting.

Post built NDT Potential

Methods capability: selector tool output for a simple block with machined surface finish

Courtesy AMAZE EU project

Class Type Sub-type Including… Surf

ace

brea

king

crac

ks /

lack

-of-

fusi

on

Surf

ace

brea

king

void

s

Inte

rnal

cra

cks

/

lack

-of-

fusi

on /

laye

r def

ects

Isol

ated

/

clus

tere

d

poro

sity

Inte

rnal

voi

ds,

incl

. cro

ss-l

ayer

defe

cts

Incl

usio

ns

Trap

ped

pow

der

(Pow

der B

ed

Fusi

on o

nly)

Nea

r sur

face

mic

rost

ruct

ure

vari

atio

n

Sub-

surf

ace

mic

rost

ruct

ure

vari

atio

n

Nea

r sur

face

resi

dual

str

ess

Sub-

surf

ace

resi

dual

str

ess

Contact or near-contact (a i r-

coupled)

Single / twin / array probe,

Time of Fl ight Di ffraction

Immers ion

Vibration analysis Resonance testing

Acoustic pattern

recognition

SimpleAids such as l ighting /

boroscope etc.

Dye-penetrant Fluorescent / vis ible

Conventional , 2D

Fi lm / Computed / Real -

time / Digi ta l

Computed Tomography

2D (fan beam) / 3D (cone

beam) CT / Laminography

Diffraction

Flash

Laser

Electrically excited Induction-heated

Vibrationally excited Thermosonics

Eddy current Single / array probe

Magnetic particle

Barkhausen

Alternating Current Field

Measurement

Eletromagnetic-MechanicalElectromagnetic Acoustic

Transducer Ultrasound

Laser Ultrasound

Spatia l ly Resolved Acoustic

Spectroscopy

Shearography

Electronic speckle pattern

interferometry

Laser Speckle Photometry

Grazing Incidence

Ultrasound MicroscopyOptical-MechanicalMixed

Electromagnetic Magnetic field

Thermal

Optically excited

Radiographic X-ray

Optical / visible

light

Mechnical

Ultrasonic


The tool shows that commonly used NDT methods such as Contact/immersion UT and die penetrant for bulk and surface breaking defects respectively, would be capable.

Post built NDT PotentialMethods capability: selector tool output for a complex lattice structure and as built surface condition


The tool shows that the most appropriate NDT method for the majority of defects is X-ray computed tomography and resonance testing.

Class Type Sub-type Including… Surf

ace

brea

king

crac

ks /

lack

-of-

fusi

on

Surf

ace

brea

king

void

s

Inte

rnal

cra

cks

/

lack

-of-

fusi

on /

laye

r def

ects

Isol

ated

/

clus

tere

d

poro

sity

Inte

rnal

voi

ds,

incl

. cro

ss-l

ayer

defe

cts

Incl

usio

ns

Trap

ped

pow

der

(Pow

der B

ed

Fusi

on o

nly)

Nea

r sur

face

mic

rost

ruct

ure

vari

atio

n

Sub-

surf

ace

mic

rost

ruct

ure

vari

atio

n

Nea

r sur

face

resi

dual

str

ess

Sub-

surf

ace

resi

dual

str

ess

Contact or near-contact (a i r-

coupled)

Single / twin / array probe,

Time of Fl ight Di ffraction

Immers ion

Vibration analysis Resonance testing

Acoustic pattern

recognition

SimpleAids such as l ighting /

boroscope etc.

Dye-penetrant Fluorescent / vis ible

Conventional , 2D

Fi lm / Computed / Real -

time / Digi ta l

Computed Tomography

2D (fan beam) / 3D (cone

beam) CT / Laminography

Diffraction

Flash

Laser

Electrically excited Induction-heated

Vibrationally excited Thermosonics

Eddy current Single / array probe

Magnetic particle

Barkhausen

Alternating Current Field

Measurement

Eletromagnetic-MechanicalElectromagnetic Acoustic

Transducer Ultrasound

Laser Ultrasound

Spatia l ly Resolved Acoustic

Spectroscopy

Shearography

Electronic speckle pattern

interferometry

Laser Speckle Photometry

Grazing Incidence

Ultrasound MicroscopyOptical-MechanicalMixed

Electromagnetic Magnetic field

Thermal

Optically excited

Radiographic X-ray

Optical / visible

light

Mechnical

Ultrasonic


Post build NDT: Current method

XCT limits of detection example on a on L-PBF calibration sample

Microscope image of cut-up and polished sectionL-PBF of a calibration sample X-ray CT image (slice) using 225 kV XCT

system

• X-ray CT (XCT) and cut-ups

comparison where defects that

are present in both are circled in

green and defects that are

present only on cut-up are

circled in red.

• The limits of detection, for this

particular sample and X-ray CT

settings, which provided a voxel

resolution of 41 µm, is expected

to be at least twice the voxel

resolution (82 µm). No defects

were found at 82 µm, the closest

was 132 µm.


65.4 mm

Post build NDT: Emerging method

Process Compensated Resonance Testing (PCRT)

• PCRT demonstrated capability to differentiate between seeded (S1 & S2) and the non-seeded defect (S0) star artefacts.



Resonant Acoustic Method (RAM)

700 µm cylinder defects show highest frequency response compared to all

smaller defects which had lower resonance frequencies. Cube defects had

similar results.Samples courtesy of LNE (France), results courtesy of The Modal Shop

CAD showing sample with CAD seeded

cylindrical and cube defects (1000 µm

long by 10 to 1000 µm diameter/side)

Inconel 625 built sample 26 x 5 mm

(L x D) with a 1 mm diameter

seeded defect

After removal of support: 20 x 5 mm

Also removed the lettering to avoid

interference.

CAD seeded defects

Cylinder

Cube


RAM Tests on Lattice Parts

All parts that displayed visible defects (broken struts) failed with RAM method, others passed.

Part 15 did not display visible defect but also failed. After XCT tests a broken strut was found.

Courtesy ICWAM, Metz 5-6 June 2019, A-F. Obaton


Non-linear acoustic (NLA)

Non-linear acoustics

testing showing

identifiably different

responses for a

‘good’ and a ‘bad’

part (tests performed

by Theta Tech)

Corresponding non-linear responsesaPod 2 ‘good’ (top) and ‘bad’ (bottom) builds


Post build NDT: Hybrid

Automated hybrid NDT methods assessment

Courtesy RASCAL IUK project

Robotic cell demonstrator capabilities• Detection of internal tight cracks via NLR• Detection of external open cracks and notches via Thermography + ADR• Automatically indicate PASS/FAIL, generate a report and data can be accessed through the network.System is used to demo at the MTC and/or other events.

+ADR


Post-Processing: effect of HT, HIP and part separation


Build 1287 Workflow: HIP Only

Build plate

bent inwardsBuild plate

bent outwards

Build 1289 Workflow: HT and Part Separation

Build plate

bent inwardsBuild plate bent

outwardsNo part

distortion

Build 1377 Workflow: Heat Treatment and HIP

Build plate bent

inwards

Build plate bent

outwards

No part

distortion

No part

distortion


Post-Processing: Defect geometrical effect from HIPing

Defect before HIP Defect after HIP

Source: Brown, A., Jones, Z. Tilson, W., Classification, Effects, and Prevention of Build Defects in Powder-bed Fusion Printed Inconel 718, NASA Marshall Space Flight Center, 2016.

Effect of HIPing to a defect: after HIP a defect becomes a line crack which may be more detrimental to the part integrity (potentially fatigue).

NDT Standard

For AM

ISO TC261/ASTM F42 JG59 DTR 52905, ‘Additive Manufacturing — Non-Destructive Testing and Evaluation — Standard Guideline for Defect Detection in Metallic Parts’ (Lead by B. Dutton) Balloting

ISO TC261/ASTM F42 JG60 DTR 52906, ‘Additive Manufacturing — Non-Destructive Testing and Evaluation — Standard Guideline for Intentionally Seeding Flaws Metallic Parts’ (Lead by B. Dutton) Balloting

ASTM E3166 (E07 WK47031), ‘New Guide for Nondestructive Testing of Metal Additively Manufactured Metal Aerospace Parts After Build’ (Lead by Jess Waller and I contributed) Published

ASTM E07 WK62181, ‘New Guide for Standard Guide for In-Situ Monitoring (IPM) of Metal Additively Manufactured Aerospace Parts’, (Lead by Surendra Singh and I am contributing) Draft

NDT Standard

ISO TC 261/ASTM F42 JG59 DTR 52905

ISO/ASTM joint group activity led by MTC through British Standards Institute (BSI).

Ben Dutton, Technical Specialist at MTC is the convener.

This standard is to provide a best practice guide presenting NDT methods potential to detect defects which are not covered by current standards.

Post-built NDT

In-process NDT

Balloting version submitted for review.

Expect to be issued by end of 2020.

MTC


NDT Standard

Star Artefact to test NDT general capabilities

• Star artefact (design S1) with seeded defects representing:• Layer

• Cross-layer

• Unconsolidated/trapped powder

• Designs diameters are based on 10% X-ray transmission depending on material.

Material: Inconel

Manufactured using laser PBF

Material: Titanium

Manufactured using Electron Beam Melting (EBM) PBF


NDT Standard

Star Artefact X-ray Computed Tomography example

Ø200 mm is very faint

Artefact due to scattering effect

• Build limitations were found to be about 200 µm

• XCT shows capability limitations due to scatter effect artefacts.


NDT StandardÀ la carte artefact example which demonstrates the procedure to follow for a specific AM design

• Since AM can be very diverse, no specific geometry can thoroughly cover such requirements in a standard. Therefore, the approach in this standard is to provide a generic procedure that will include the following main steps:

• Identify structurally critical defect locations and sizes to be required for detection, ideally through modelling or mechanical test; (MTC currently working on a project on this to ideally enable more targeted inspections.)

• Seed those defects into a NDT test/calibration part to be built;

• Test with NDT methods (UT, XCT, resonance, any other novel NDT method that may have become available) to qualify it as capable for the part requirements.

Material: Inconel

Manufactured using laser PBF.

The aerofoil contains through holes of various diameter and at various locations.


New project to support further development of NDT standards

Probability of detection (PoD)

Robust quality assurance

In-process monitoring / inspection

PoD experimental / modeling

Post build AM NDT

Project: Robust Quality Approach for AM via In-process and NDT (RAMPID)

Aims:1. Develop a robust way to measure AM NDT reliability through

Probability of Detection (PoD: XCT and PCRT)2. Pursue links between in-process monitoring (Sigma Labs) and

post build NDT for AM parts.3. Develop and validate PoD models.

MTC supporting members:Parker Aerospace, BAE Systems, GKN Aerospace, Rolls-Royce Plc, Renishaw, Sigma Labs, Materialise, Hoganas, Diondo.

External supporting partners: NIST, LNE, NASA, ESA, BAM

Initial results will be presented at ASTM CoE ICAM conference, Nov. 2020

In-process NDT

Laser Ultrasound (LU) introduction

• As with other manufacturing processes, AM inspection has typically relied on post-process/post build NDT, but due to AM’s geometrical complexity, surface finish and material density, ideally NDT would be better placed at an earlier stage.

• AM process has a unique advantage due to its build process: layer-by-layer or bead-by-bead, hence both process monitoring and inspection may be exploited.

• Current additive manufacturing (AM) in-process monitoring relies mainly on surface measurements, potentially missing subsurface defects. Additionally AM processes are at high temperatures. NDT methods such as Laser Ultrasound Testing (LUT) have the potential to detect both surface and sub-surface defects making it ideal for AM.

Rayleigh (surface wave) Skimming pressure (surface wave)

Shear (bulk wave)

Longitudinal (bulk wave)

In-process NDT calibration samples

Laser Ultrasound (LU) highlights on a L-PBF Aluminium part


Calibration and real samples tested

• Calibration samples consisted of Ti64 cuboids with dimensions (10 x 10 x 30 mm) with Electric Discharge Machining (EDM) through holes (400 µm diameter) representing subsurface defects.

• AM part with process subsurface isolated 200 µm and 300 µm gas pores.

Why LUT

• Laser Ultrasound Testing (LUT), being a non-contact ultrasound testing method, is capable to work at elevated temperatures of at around 1000 C, and the system at the MTC is capable to work on rough samples which are expected to be generated from the AM process.

• Research based unit with capability for integration to industrial applications

• MTC has been working on projects showing LUT capability for some AM industrial applications.

In-process NDT calibration sample

Laser Ultrasound on a DED AM Titanium sample with LOF defects

Capable to detect fusion irregularities between side by side and top and bottom beads.

Sample and scan details A-Scans B-ScansCourtesy AMAZE EU project

In-process NDT: LUT detection of isolated bulk pores in laser powder DEDLaser Ultrasound on a DED AM Titanium sample with isolated pores

Courtesy OpenHybrid EU project

Scan

dir

ecti

on

15

mm

Rayleigh wave

Diameter: 0.270 mmDepth: 0.330 mm



XCT vertical slice

LUT B-scan

Sample picture

LUT showing capability to detect isolated pores in a Ti DED as built sample

In-process NDT: LUT on laser welding

Welding and inspection configurations

Schematics of parts to be welded (a) welding/inspection set-up (b).

Welding laser

(a)

(b)

Direction of rotation

Detection laserGeneration laserWelding laser

Detection laserGeneration laser

Direction of weld

(a)

(b)

Welding laser

Detection laser

Generation laser

Direction of weld

(a)

(b)

CAV TISICSLeonardo MW

Courtesy of OLIVER IUK project

In-process NDT: LUT on laser welding calibration sample

Natural voids in cylindrical butt weld

Three distinct pores visible in the X-ray image and the corresponding parabolic indications on the LUT B-scan.

X-ray showing three distinct internal

pores (~400 µm)

LUT B-Scan with corresponding indications of porosity defectsWeld sample with marks

showing the scanned area

Gen Det


In-process NDT: LUT on laser welding AT PROCESS SPEED

TISICS demonstration Setup

Welding laser

LUT generation laser

LUT detection laser optics

• Mounting of generation and detection lasers• The red spot is the guide laser (shows the point at which the

detection laser hits the part)• Rotation of the part was towards the inspection lasers from

the welding laser

• Video capture of the in-process inspection of the welding part• Bright spot is plasma generated by the generation laser on contact with the surface of

the part



TISICS demonstration Scan Results vs XCT


Data direction

Rotation direction

Start/end weld

Start/end weld

Start/end weld

1. XCT slice (left) of TISCIS weld and LUT B-Scan (right), where the more visible indications, correspond to the larger defects (voids), are highlighted: Red: 480 µm, Purple 400 µm, Blue: 540 µm, Amber: 440 µm, Green: 280 µm. A small indication from the Start/End of weld is also detected as a small undercut.

2. Smaller voids detected by XCT (down to 210 µm) were not clearly identified by LUT at this speed but are not required to be detected even in the most stringiest case which corresponds to 0.3t or 0.3 x 5000 µm = 1500 µm.

3. As validated by XCT the largest defects were well bellow the stringiest requirements.

Courtesy OLIVER IUK project


TISICS demonstration Scan

~6 mm

~5 mm~1 mm

~2 mm

NDT Inspection of CFRP

X-ray Backscatter (reasonable resolution and speed)

Scan time: 3 minutes

Sample dimensionsHeight: 370 mmWidth: 325 mmThickness: 4 mm

NDT Inspection of CFRP

Laser Ultrasound (higher resolution but slower or same resolution & speed)

If scan step is increased to 1 mm then scan time of same small area is estimated to be 20/40 = 0.5 minutes

• Using a 4 kHz laser then 0.125 minutes for small area or 4.25 minutes for the whole part, which is similar to X-ray backscatter

Area Scan area:79 x 44 mm

Sample dimensions: 370 x 325 x 4 mm (Height x Width x Thickness)

Summary

AM

AM defect formation is highly complex and better understanding is required. This is important to both reduce and/or prepare for the adequate NDT method to detect process produced defects.

The added geometrical freedom from AM to build complex geometries continues to challenge the NDT technologies, to both improve current methods and to search/develop novel ones to cope with these new and challenging requirements.

For very complex AM geometries only a few NDT methods are capable, mainly: XCT and resonance, but they also have their limitations. Additionally, more work is required on these methods to assess their capabilities.

MTC have been leading the development of NDT standards for AM, through ISO/ASTM JGs and other ASTM participations, but more work is necessary to expedite the quality assurance of such parts, i.e. POD studies.

Metrology showed good capability detecting geometrical deviations from the original CAD and actual build in addition to post processes effect that HT and HIP have on AM part;

HT and HIP may be useful to reduce residual stresses and increase part density, respectively, but care must be taken that part quality is not reduced due to defects becoming more crack like.

In-process monitoring has the value to monitor and potentially control the process to reduce poor quality issues. In addition, in-process inspection has the added value to inspect the part as it is built, which for some very complex AM parts may be the only NDT capable solution, but also has the potential to reduce or eliminate the need for inspection at the end of the build, reducing both cost for final part inspection and scrap of parts.

CFRP

X-ray backscatter and LUT have shown to have enough or above required capabilities and should be further considered for inspection.

Final thought

In order to reduce the demand for better NDT capability and be more effective, i.e. targeted inspection, it would be very valuable to run structural models to determine critical geometrical locations and defect sizes required for detection in AM parts. The MTC has started working on such a project applicable to AM.

Thank [email protected]

NDT Capability for AM Aerospace Applications: the MTC ...

Documents

Transcript of NDT Capability for AM Aerospace Applications: the MTC ...