The quest to optimise metal 3D printing is now moving at light-speed in the UK. At the core of the research is a £260 million facility that has previously helped researchers to read the Dead Sea Scrolls, advance understanding of HIV and unwrap the complex 3D structure of protein receptors.
Now the Diamond Light Source in Oxfordshire is helping Rolls Royce improve the quality of additively manufactured parts.
Working with AMAZE – a consortium of 26 European institutions from academia and industry – the project uses the national synchrotron science facility at Harwell, Oxfordshire to observe the high energy conditions inside a metal 3D printer.
The x-ray technology of the synchrotron allows Rolls Royce and AMAZE to analyze the regularity and uniformity of the metal layers being deposited by lasers. The aim of the project is collect the vast amount of data that will assist in creating an algorithm to further the use of additive manufacturing.
Regulating laser metal deposition technology
Rolls Royce are no strangers to 3D printing.
For manufacturing in aerospace, Rolls Royce has successfully used additive manufacturing more than a decade. One technique employed is direct energy deposition (DED) – this involves metal powder carried by an inert sheath gas into the focal point of a laser.
Rolls Royce uses the blown powder technique to create blisks (bladed disks) for engines. If a blisk is damaged under intense heat pressure, a repair can be made with DED. After the damaged area is repaired it can be milled back to the required finish.
In a recent interview, Peter Lee, Professor of Materials Imaging at the University of Manchester says that “the controllable point [of laser metal deposition is] just above the surface, where the laser hits the powder. No one actually knows what happens from then on. We are not really sure whether the laser is melting it on the surface or melting the powder in the air.”
Alex Leung, a scientist at The Manchester X-Ray Imaging Facility the adds that “you can see molten pools forming and also defects developing during the melt track evolution. We also see lots of powders that are blowing off – ejecting away from – the powder bed.”
A number of phenomena occur around the position that the metal melts which may cause cracks, partial sintering and uneven surfaces.
Non-destructive testing and data based optimisation
To understand metal printing better and the particle-level reactions occurring inside the build chamber, the x-ray synchrotron captures a slowed down image and analyse the process at 10,000 frames per second. This is done by circulating electrons around a storage ring close to the speed of light, producing a light ten billion times brighter than the sun.
The technique means scientists can then analyse the uniformity and regularity of metal layers being deposited, and detect when, how and eventually why surface fluctuations, irregularities, and imperfections occur during the process. The data gathered during the synchrotron scan process annually amounts to 5 terabytes.
The long-term aim for the project is to use this huge amount of data to create a closed loop system, where the 3D printer corrects itself to avoid faults in the components from happening in the first place.
A necessity to test throughout the UK
I recently visited the National Physical Laboratory (NPL) in Teddington to see how NDT is handled. Working with enterprises such as Renishaw, NPL offers metrology and x-ray tomography services.
In the U.S. the National Institute of Standards and Technology (NIST) makes use of extensive experimental data and multi-physics high fidelity modelling for surface texture analysis, and understanding the chemical and physical processes occurring during additive manufacturing processes.
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Featured image shows the Harwell syncrotron site. Photo by Diamond Light Source.