Medical Design Briefs - June 2022 - 17

O
ver the last few decades, additive
manufacturing (AM)/
3D printing has fundamentally
changed the way that
manufacturers approach
product development. Industry is now
almost universally aware of the term
rapid prototyping, using AM to convert 3D
CAD data into physical models in a matter
of hours. The role of AM in prototyping
has become embedded across all
industrial sectors.
AM has enabled concurrent engineering
- where all relevant departments
can be engaged early in the product development
process. Concurrent engineering
replaces traditional over-thewall
product development, where design
iterations could be delayed by weeks to
accommodate tooling and machining
considerations. The benefi ts are dramatic
time-to-market reductions and cost
savings in product development.
AM is a uniquely disruptive technology.
About 25-30 years ago, it changed the
manufacturing paradigm by altering the
way that manufacturers produced prototypes.
Today, it is disrupting the way that
manufacturers produce end-use parts
and components and is increasingly seen
as a truly viable production technique.
Now the conversation among manufacturers
is around the most judicious use
of AM for production, its advantages,
the sweet spot is in terms of production
volumes, key opportunities, and barriers
to entry. Many of these barriers relate to
precision quality control of AM parts,
which challenge traditional methods of
surface metrology.
Good Enough?
With the focus today being on the use
of AM for production, the analysis of
the accuracy and repeatable tolerance
attainment of AM has become a far
more critical issue. When used as a prototyping
technology, absolute adherence
to tolerances and precise design
intent is not always necessary, and a
" good enough " approach can be taken.
Hence the proliferation of quite inexpensive
desktop 3D printing machines
that provide suffi ciently accurate rapid
prototypes that do the job without
needing to be pitch perfect.
For production applications, however,
" good enough " is no longer suffi cient. If
an AM part is integral to a safety critical
aerospace or medical application, it is
Medical Design Briefs, June 2022
Cov
MDB Zygo Additive Feature 0622_CC_1.indd 17
A metal AM part with intricate geometries.
essential to achieve dimensional and material
tolerance targets consistent with
design intent. It is here that the role of
metrology to validate the quality of fi nished
parts is so important. It is also an
area where providers like ZYGO, which
makes 3D optical metrology instruments,
can make a difference.
Industry Response
Legacy manufacturing processes for
metals and plastics have established quality
control methods for validating and
measuring parts. The production processes
are understood, as are the most
critical dimensional and surface fi nish
requirements. AM, however, does exactly
what the name implies - it produces
parts layer by layer additively, and this
opens an array of unique issues that can
affect the integrity of a fi nished product,
and also a unique set of surface characteristics
that make the job of measuring and
validating that much more diffi cult.
How the sector is responding to the
metrology and validation conundrum was
highly visible at the recent (and largest)
AM-related event - Formnext in Frankfurt,
Germany. At various learning events
on-site, metrology issues featured prominently,
acknowledging the fact that measurement
and validation of AM parts is a
big deal today. In addition, AM technology
providers are now developing inprocess
metrology (IPM) solutions
to
overcome the specialized challenges
of verifying the integrity of AM processes.
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ToC
5/25/22 2:48 PM
Research in AM Metrology
In the search for relevant metrology
critical to process control, industry is still
trying to understand what to look for on
and under the surface of an AM produced
part, and how these relate to part
functionality. Surfaces of AM parts challenge
existing surface topography measurement
and defy characterization using
standardized texture parameters
because of high surface slopes, voids,
weld marks, and undercut features.
Research into new and improved metrology
for AM is advancing through a
wide range of industry and academic
partnerships, many in cooperation with
ZYGO. An example is work at the University
of Nottingham, where the Manufacturing
Metrology Team (MMT) led by
Prof. Richard Leach is investigating the
full range of solutions, from highprecision
interference microscopy to
x-ray tomography of the internal structure
of completed parts.
In just the past four years, the MMT
has published 43 research papers on AM,
ranging from methods to optimize
17
AM technologies and metrology techniques
have also captured the attention
of professional societies that organize
conferences and symposia worldwide.
These include the American Society of
Precision Engineering (ASPE), the International
Society of Optics and Photonics
(SPIE), and the International Academy
for Production Engineering (CIRP).
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Medical Design Briefs - June 2022

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