PRODUCTS AND SERVICES
q&a: brett muehlhauser
r&d technical fellow, north star imaging
3D scanning has become an integral part of employing additive
manufacturing processes in the production of aircraft components
WHERE IS THE NEED FOR BETTER
QUALIFICATION OF ADDITIVE
MANUFACTURING (AM) PROCESSES?
Flight-critical aerospace AM products are
being used on aircraft today. With the rapidly
accelerating development and application of
AM processes, it’s vital that we continue to
stay grounded in the requirements of
process and product qualification for all
critical AM products.
WHAT IS COMPUTED TOMOGRAPHY’S
ROLE IN THE DEPLOYMENT OF AM
PROCESSES IN AEROSPACE?
All of our aerospace customers are using CT
to develop and validate the AM
Processes then inspect
production AM parts. CT is also being
used to provide metrology data of AM
products. Another rapidly growing area
of use is in dealing with aging aircraft.
CT is being used to reverse engineer
obsolete parts and to provide a 3D
model which can be analysed and
then 3D printed.
HOW DO YOU QUALIFY A CT PROCESS
FOR AM PARTS?
Anytime an inspection method is used it
should first be qualified. It is very common to
have multiple known defect standard parts
printed and CT scanned to qualify the CT
process. These parts are also used for
process control checks to assure CT quality
requirements continue to be met.
WHAT STANDARDS ARE APPLICABLE TO
There are industry standards in use such as
ASTM, ISO and others in development for AM
and Inspection of AM products. The larger
Aerospace companies aren’t waiting around.
They have already begun to implement their
own standards specific to their building and
inspection of production AM products.
96 SEPTEMBER 2019 \\ AEROSPACETESTINGINTERNATIONAL.COM
In general, for a given geometry, it is typically much easier
to perform CT on polymers and other low-density materials
simply because it is easier to penetrate them with x-ray. The
higher density, thicker materials require much higher x-ray
energies to be able to adequately penetrate the product to
produce a quality CT scan.
WHAT AM PROCESSES HAVE BEEN LOOKED AT AND
WHICH PRODUCES THE LEAST DEFECTS?
In our multiple Inspection Service labs, we scan more metal
AM parts than anything else. Most of these AM parts are built
using the Powder Bed Fusion (PBF) AM process but we are
also doing more work with other metal processes such as
plasma deposition and powder-fed processes.
All of the processes have been capable of producing high
quality parts with minimal discontinuities. The fun part for us
at NSI is working with some of the new AM technologies and
see them improve in consistency of product quality as the
specific process evolves. CT has been a big part of the
acceleration of that process improvement. It sure beats
having to do literally thousands of metallography crosssections
to get the same amount of data about the internal
integrity of a part.
CAN YOU EXPLAIN IN-SITU 4D CT?
Bascially 4D is simply 3D over time. Normally we would
always recommend a CT scan of a tensile coupon from an AM
build to create a correlation to the material properties
and the percentage and location of the discontinuities
within the coupon. With In-situ 4D CT we can place the
same load cell within a CT system and perform multiple,
fast CT scans of the tensile coupon while it was under
load. This can provide the same information relative to the
percentage of discontinuities and location while also
providing a 3D view of the initiation and propagation of the
fracture to the point
of failure. \\
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// CT Scan
DO AM METAL OR PLASTIC PARTS HAVE
MORE DEFECTS AND WHICH MATERIAL
IS EASIER TO USE CT ON?
It’s not necessarily just a material question
but a combination of material, product
geometry and the AM process used. Complex
geometries with substantial material
thickness variations can provide more AM
challenges for just about any material.