Difference between revisions of "NDE for AM"

Revision as of 09:00, 20 October 2020

Motivation

Additive manufacturing offers a paradigm shift in engineering as previous design constraints, such as tooling paths in matching are removed. The ability to create novel free form structures, such as lattices, clearly offers vast potential benefits for high performance industries including aerospace, medical and tooling. However, the uptake of AM components has been hindered as the process are prone to a variety of defects, such as porosity and cracking, which due to the variation in length scales, 10 µm to 500 µm, and the number of processing parameters, >150, make predicting and optimising against these defects near-impossible.

As such, our optics group is currently working on a number of ways to perform non-destructive evaluation on additive manufactured (AM) parts; currently, XCT is widely used in industry for part validation but is a strictly post-process ex-situ technique and has both time and safety implications. Our aim is to take advantage of the layer-by-layer nature of the AM process to inspect during the build to create a volumetric dataset and validate the part in real-time. Further to real-time validation of the component in-situ inspection offers opportunities to adjust build parameters during the build based on processing signal, analogous with the closed-loop feedback used in conventional machining. Alongside the management of components defects in AM significant research in the field is also dedicated to understanding the microstructure and subsequent mechanical properties of the AM components; in future it is envisaged that the processes can be adapted as such to tailor the component microstructure for a given role, as such a technique which can both verify a components integrity and interrogate the microstructure will be well placed to meet the demands, both current and future, of the AM industry,

SRAS on Additive Manufacturing

Our existing laser ultrasound technique SRAS has previously been used to image the microstructure of metallic samples, giving both grain size and orientation, making it an interesting tool for investigation of SLM samples. Furthermore, In addition to this useful information, the loss of signal or a drastic change in signal amplitude/frequency can be used to measure the presence of both defects on the surface and in the near-surface region. These capabilities combined with the fact SRAS is a non-contact, non-destructive technique makes it an ideal candidate for AM components.

The first SRAS data from AM samples were obtained using the O-SAM system in 2011. The two figures below illustrate the SAW velocity across a blown powder and wire deposited samples with the SAW propagating in the direction of the white arrows. These initial data sets paved the way for the following generations of SRAS system to further investigate the capabilities of SRAS as an NDE tool for AM.

SRAS SAW velocity images of blown powder deposited MERL76 sample.

SRAS SAW velocity images of wire deposited waspaloy sample.

In 2016 a more modern SRAS system was used on Selective Laser Melting (SLM) samples. This system demonstrated a relationship between the mean SAW velocity and laser power used to build eleven cubes using Ti64 powder. As the laser was power increased, an increase in the mean SAW velocity was measured. It was also shown how an in-process SRAS inspection could provide closed-loop feedback to improve the SLM process as a whole. When specifically considering pores, it was shown that alongside detecting, counting and sizing the surface pores, the system was also able to detect subsurface pores. This was in the form of a drastic change in the SAW velocity by ~300 ms-1, wherein the thin plate-like region above the pores, the SAW transformed into a Lamb wave.

(top) A selection of optical maps and (bottom) velocity maps from the central region on the samples. Pores are present on all samples, the velocity variation is similar for the first 3 samples presented, and the 140 W sample shows a drop in mean velocity. Scale bar 0.5 mm.

Defect data used to calculate the normalised circularity and aspect ratio (left) and the number of defects found as ranked by their area (right).

Average acoustic amplitude and velocity data presented for each SLM specimen. The velocity decreases with build power and is not dependant on the acoustic amplitude as the 190 W and 200 W samples had similar acoustic amplitude to the lower power samples, yet their velocity was as expected for well-consolidated material.

Images for the 190 W AM test sample (a) Optical image (scale bar 1 mm) (b) Optical zoom (scale bar 250 um), (c) SEM micrograph of the corresponding area (scale bar 250 um) and inset zoom of large pore (scale bar 25 um). (d) Acoustic velocity map (scale bar 1 mm) (e) zoom of acoustic data (scale bar 250 ?m) (f) XCT subsurface (with no surface) data of zoomed region up to an approximate depth of 60 ?m (scale bar 250 um)

The next set of experiments carried out in 2017 were aimed at understanding the capability of SRAS to detect changes to build process, specifically the scan strategies used. Four 10mm cubes were manufactured using a nickel superalloy power (CM247LC) on a Realizer SLM machine. The cubes were made up of four small 5 mm square islands. One sample was used as a control (0°) and the islands were rotated on the other three samples relative to the previous layer. The rotation angles were set to 15°, 30° and 45° across the tree samples. Using SRAS data and verified by optical microscopy several trends were identified between the crack and pore distribution relative to the island rotation angle. Furthermore, the island boundaries were identified using SRAS based on their distinctly different drop in the group SAW velocity.

Schematic plan view of: (a) 00°; and (b) 45° hatch angle samples with equally sized square islands, illustrating how the scan lines are consistently aligned to the set angle across each layer.

Optical images of SRAS scans of varying hatch angle samples showing some variations in porosity (top row) and velocity maps of varying hatch angle samples showing clear indications of island boundaries as regions of low velocity (bottom row) (0.5 mm scale bar).

Plan view of the overall scan strategy for a 30° sample. The region in which the scan lines overshoot the assigned island is highlighted with green arrows alongside both SRAS optical and velocity maps of the same region. Outlined in black, the optical image shows no indication of the scan lines, whereas the velocity map clearly illustrates a change in this region.

Some further work was carried out towards understanding the data obtained using SRAS from form AM samples. In this case, both the cross-section and sidewall of Wire–arc additive manufacturing (WAAM) samples were inspected using SRAS. Here we are able to identify the differences between undeformed and rolled samples.

SLM manufactured Ti-6Al-4V sample. (left)n Optical micrograph showing the as-deposited 'rough surface'. (right) SRAS velocity map of the as-deposited surface, captured using a Speckle Knife Edge Detector (SKED)

SLM build platform adapted for SRAS optical train, with beam deliver through galvanometer scanning mirrors and f-theta lens.

By incorporating the SRAS instrument into the SLM build machine, it shall be possible to image 3D renders both defects and the microstructure on a layer-by-layer basis. The challenges in this project are both in the optical setup, such as measuring signals off rough surfaces, as well as mechanical integration, where atmosphere, temperature, small envelope and interfering particles are all factors to overcome. Furthermore, for the technology to be commercially applicable the quality of data must be balanced against the impact on the manufacturing time. In order to assess this, we have developed a framework for comparing the spatial capability and temporal penalty of various inspection systems.

Research Team

Adam Clare, Matt Clark, Richard Smith, Wenqi Li, Rikesh Patel, Rafael Fuentes Dominguez, Don Pieris and Paul Dryburgh are actively working on this project. Previous contributors include Steve Sharples, Matthias Hirsch and Samuel Osei Achamfuo-Yeboah.

Related Publications and Talks

Publications

Journal of Materials Processing Technology 236:93--102,2016

https://www.sciencedirect.com/science/article/pii/S0924013616301352
Bibtex

Author : R. J. Smith, M. Hirsch, P. Patel, W. Li, A. T. Clare, S. D. Sharples
Title : Spatially resolved acoustic spectroscopy for selective laser melting
In : Journal of Materials Processing Technology -
Address :
Date : 2016

Additive Manufacturing 13:135--142,2017

https://www.sciencedirect.com/science/article/pii/S2214860416301877
Bibtex

Author : M. Hirsch, R. Patel, W. Li, G. Guan, R. K. Leach, S. D. Sharples, A. T. Clare
Title : Assessing the capability of in-situ nondestructive analysis during layer based additive manufacture
In : Additive Manufacturing -
Address :
Date : 2017

Proc. R. Soc. A 473(2205):170--194,2017

http://rspa.royalsocietypublishing.org/content/473/2205/20170194
Bibtex

Author : M. Hirsch, S. Catchpole-Smith, R. Patel, P. Marrow, W. Li, C. Tuck, S. D. Sharples, A. T. Clare
Title : Meso-scale defect evaluation of selective laser melting using spatially resolved acoustic spectroscopy
In : Proc. R. Soc. A -
Address :
Date : 2017

Additive Manufacturing 19:127-133,2018

https://www.sciencedirect.com/science/article/pii/S2214860417303925
Bibtex

Author : M. Hirsch, P. Dryburgh, R. Patel, S. Catchpole-Smith, L. Perry, S. D. Sharples, I. A. Ashcroft, A. T. Clare
Title : Targeted rework strategies for powder bed additive manufacture
In : Additive Manufacturing -
Address :
Date : 2018

Applied Sciences 8(10):1991,2018

https://www.mdpi.com/2076-3417/8/10/1991
Bibtex

Author : R. Patel, M. Hirsch, P. Dryburgh, D. Pieris, S. Achamfuo-Yeboah, R. Smith, R. Light, S.D. Sharples, A.T. Clare, Matt Clark
Title : Imaging Material Texture of As-Deposited Selective Laser Melted Parts Using Spatially Resolved Acoustic Spectroscopy
In : Applied Sciences -
Address :
Date : 2018

Insight - Non-Destructive Testing & Condition Monitoring 61(3):132-137,2019

Bibtex

Author : D. Pieris, R. Patel, P. Dryburgh, M. Hirsch, W. Li, S. Sharples, R.J. Smith, A.T. Clare, M. Clark
Title : Spatially resolved acoustic spectroscopy towards online inspection of additive manufacturing
In : Insight - Non-Destructive Testing & Condition Monitoring -
Address :
Date : 2019

Additive Manufacturing accepted,2019

Bibtex

Author : P. Dryburgh, D. Pieris, F.Martina, R. Patel, S. Sharples, W. Li, A.T. Clare, S. Williams, R.J. Smith
Title : Spatially Resolved Acoustic Spectroscopy for Integrity Assessment in Wire-Arc Additive Manufacturing
In : Additive Manufacturing -
Address :
Date : 2019

Conference Papers

3rd International Symposium on Laser-Ultrasonics and Advanced Sensing, Yokohama, Japan 581,2013

http://iopscience.iop.org/article/10.1088/1742-6596/520/1/012004
Bibtex

Author : S. D. Sharples, R. A. Light, S. O. Achamfuo-Yeboah, M. Clark, M. G. Somekh
Title : The SKED: Speckle Knife Edge Detector
In : 3rd International Symposium on Laser-Ultrasonics and Advanced Sensing, Yokohama, Japan -
Address :
Date : 2013

13th Anglo-French Physical Acoustics Conference (AFPAC2014) 581,2014

http://iopscience.iop.org/article/10.1088/1742-6596/581/1/012009/meta
Bibtex

Author : S. O. Achamfuo-Yeboah, R. A. Light, S. D Sharples
Title : Optical detection of ultrasound from optically rough surfaces using a custom CMOS sensor
In : 13th Anglo-French Physical Acoustics Conference (AFPAC2014) -
Address :
Date : 2014

Proceedings of LPM2018 - the 19th International Symposium on Laser Precision Microfabrication ,2018

https://nottingham-repository.worktribe.com/output/1190715/targeted-rework-of-powder-bed-fusion-additive-manufacturing
Bibtex

Author : P. Dryburgh, R. Patel, S. Catchpole-Smith, M. Hirsch, L. Perry, R. J. Smith, M. Clark, I. A. Ashcroft, A. T. Clare
Title : Targeted rework of powder bed fusion additive manufacturing
In : Proceedings of LPM2018 - the 19th International Symposium on Laser Precision Microfabrication -
Address :
Date : 2018

Proceedings of BINDT2018 - the 57th Annual British Conference on Non-Destructive Testing ,2018

https://nottingham-repository.worktribe.com/output/1191130/spatially-resolved-acoustic-spectroscopy-additive-manufacturing-towards-online-inspection
Bibtex

Author : D. M.Pieris, R. Patel, P. Dryburgh, M. Hirsch, W. Li, S. D. Sharples, R. J. Smith, A. T. Clare, M. Clark
Title : Spatially resolved acoustic spectroscopy additive manufacturing: towards online inspection
In : Proceedings of BINDT2018 - the 57th Annual British Conference on Non-Destructive Testing -
Address :
Date : 2018