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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
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
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
Courtesy AMAZE EU project
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
Courtesy AMAZE EU project
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
Courtesy AMAZE EU project
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.
Courtesy AMAZE EU project
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.
Courtesy ISO/ASTM JG59 DTR 52905, ‘Additive Manufacturing — Non-Destructive Testing and Evaluation — Standard Guideline for Defect Detection in Metallic Parts’, Submitted for balloting.
Post build NDT: Emerging method
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
Post build NDT: Emerging method
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
Post build NDT: Emerging method
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
Courtesy AMAZE EU project
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 built Metrology
Post-Processing: effect of HT, HIP and part separation
Courtesy AMAZE EU project
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 built Metrology
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
Courtesy ISO/ASTM JG59 DTR 52905, ‘Additive Manufacturing — Non-Destructive Testing and Evaluation — Standard Guideline for Defect Detection in Metallic Parts’, Submitted for balloting.
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
Courtesy ISO/ASTM JG59 DTR 52905, ‘Additive Manufacturing — Non-Destructive Testing and Evaluation — Standard Guideline for Defect Detection in Metallic Parts’, Submitted for balloting.
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.
Courtesy ISO/ASTM JG59 DTR 52905, ‘Additive Manufacturing — Non-Destructive Testing and Evaluation — Standard Guideline for Defect Detection in Metallic Parts’, Submitted for balloting.
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.
Courtesy ISO/ASTM JG59 DTR 52905, ‘Additive Manufacturing — Non-Destructive Testing and Evaluation — Standard Guideline for Defect Detection in Metallic Parts’, Submitted for balloting.
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
Courtesy AMAZE EU project
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
Diameter: 0.300 mmDepth: 2.700 mm
Diameter: 0.200 mmDepth: 2.700 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
Courtesy of OLIVER IUK project
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
Courtesy of OLIVER IUK project
In-process NDT: LUT on laser welding AT PROCESS SPEED
TISICS demonstration Scan Results vs XCT
Courtesy of OLIVER IUK project
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
In-process NDT: LUT on laser welding AT PROCESS SPEED
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]