Medical Design Briefs - June 2022 - 20

ADDITIVE MANUFACTURING
standard for instrument calibration and
traceability. The company is also a member
of the ASME B46.1 working group on
surface texture analysis, which currently
includes a task team concentrating on
AM metrology standards.
Post-Process Metrology
Measurements of AM parts post-process
serve to validate conformance with design
intent and to provide clues into fabrication
problems left by surface signatures.
However, the uniqueness of AM processes
and produced parts lead manufacturers
to use an array of different mechanical
and metrology verifi cation techniques.
They adopt an empirical approach as no
one solution is trusted to provide accurate
enough data.
Gage R&R is used as a stand-in for a
more rigorous measurement uncertainty
approach. Consequently, AM parts are often
overtested to improve confi dence, but
this means extra time and extra cost, areas
that must be addressed to make AM for
production more viable.
The open question is how to improve
this situation for greater effi ciency while
maintaining confi dence. The answer is
for metrology solutions providers to
adapt existing metrology technologies to
better align them with the unique characteristics
of the AM process and end-use
AM parts, which are characterized by irregular,
steeply sloped surface topography
that many measurement technologies
fail to capture.
ZYGO's true-color
interferometric
topography
measurements of
Ti-6Al-4V laser powder
bed fusion sample
provided by the University
of Nottingham illustrates
the unusual and
challenging surface
structure of AM parts.
The height range for the
topography is 150 µm.
Through extensive research and development
of the foundational coherence
scanning interferometry (CSI)
technology in the ZYGO 3D optical profi
lers, high-accuracy AM metrology tools
are now available to industry. Both instruments
use innovative hardware and
software upgrades, the package of improvements
being referred to internally
as " more data technology, " which makes
the instruments much better suited to
AM parts.
" More data " signifi cantly improves the
baseline sensitivity of CSI and enables
high-dynamic range (HDR) operation
making it valuable for a wide range of
parts, from steeply sloped smooth parts
to exceptionally rough textures with
poor refl ectivity. Additionally, HDR measures
parts with a wide range of refl ectance,
often a struggle for other instruments
that use interferometry as a
measurement principle. ZYGO, for example,
was the fi rst to demonstrate
full-color surface topography measurement
of metal additive manufactured
surfaces using interferometry, and
ZYGO engineers actively use AM internally
for instrument prototyping and applications
development.
Summary
AM produces parts layer by layer additively, which opens an array of unique issues that can affect the
integrity of a finished product.
20
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MDB Zygo Additive Feature 0622_CC_1.indd 20
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ToC
5/25/22 2:48 PM
With AM now an established production
technology for certain applications,
there are barriers to mass adoption that
are being addressed, including the need
for in-process and post-process metrology
technologies that can validate the
quality and accuracy of the parts produced.
AM parts have a unique set of
characteristics that render traditional
measuring technologies impotent in
some situations, and today innovative
metrology technologies are being developed
that can provide meaningful measurement
data effi ciently and costeffectively.
Only when such issues are
addressed will the use of AM become
mainstream as a viable production technology
across an array of industry sectors
and applications.
This article was written by Peter de Groot,
PhD, Chief Scientist at ZYGO Corporation,
Middlefi eld, CT. ZYGO, which is owned by
AMETEK, designs and manufactures optical
metrology instruments, high-precision optical
components, and complex electro-optical systems.
The author acknowledges Chris Young,
MicroPR&M, for great discussions and contributions
to this article. For more information,
visit http://info.hotims.com/82322-342.
Medical Design Briefs, June 2022
Credit: Zygo

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Medical Design Briefs - June 2022

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