An entire EOS 3D printing system set up for melt pool
monitoring. Image credit: EOS.
high speed machining – these are all often necessary secondary
processes to additive metal manufacturing,” says Snow.
According to Snow, additive and subtractive technologies
are codependent on each other. “Secondary finishing is often
required to get to a point where the finished product out of the
DMLS or powder bed fusion is going to be at the specifications
of the end user,” he adds.
That being said, there are applications where the surface
quality created from the AM process alone is sufficient for
certain applications. For example, when manufacturing implants
for the human body, surgeons often prefer a rougher finish,
meaning there is greater surface area, and therefore the
opportunity for increased osseointegration, or bone growth.
In-Process Quality Assurance
As the use of metal 3D printing becomes more widespread
across various industries, in-process quality assurance is also
becoming more important.
“One aspect that has been evolving and will continue to
evolve is called ‘in-situ’ monitoring of product quality,” says
Snow. “EOS provides such monitoring in four elements.”
The first is systems monitoring, which basically monitors
control of all systems, settings, process parameters, etc. It
ensures that the system and process conditions are optimized
so that the user can get the highest quality parts.
Then, there is powder bed monitoring, which comes in a
variety of forms. Integrated camera systems in the process
chamber are able to monitor the powder bed as it builds layer
by layer. Innovations in the technology allow users to perform
image recognition of parts internally. Therefore, the improved
error identification along with some closed loop controls allow
for potentially short feeding on recoating.
“Such monitoring allows for the automatic assurance of
recoating quality before exposure. In addition, image recognition
and part error identification is possible, detecting failures to
specific layer and part number during the build process,” says
The third area of in-process quality assurance, melt pool
monitoring, has been developed primarily to meet the needs of
the aerospace community. Extensive hardware helps to separate
the light created by the fusion process from the reflected light,
Optical tomography is the fourth area of monitoring. This
technique uses cameras to continuously monitor the fusion
process. When paired with several sensors that monitor the
general system status, optical tomography is able to precisely
control the exposure process and melting characteristics of the
material at all times.
“The camera platform takes pictures of the powder bed on
an average of about 12 snapshots per second,” explains Snow.
“This allows you to detect a variety of potential failure types
such as cracks, voids, and inclusions within the part being
processed.” The process was co-developed between MTU Aero
Engines and EOS.
Future of Metal 3D Printing
With the help of in-process monitoring, metal 3D printer
manufacturers are constantly striving to improve system
productivity while maintaining part quality.
“Technology issues are always about speed and productivity;
therefore, trying to get the fastest laser will always be something
the industry is chasing to bring to market systems,” says Snow.
Unsurprisingly, one of the main benefits of using metal
3D printing is part consolidation. For example, the fuel
nozzle incorporated in GE’s Leap jet engine was originally
manufactured with about 20 components. Now, the fuel nozzle
is 3D printed as one component. 3D printing took away a variety
of additional manufacturing steps that would be required to
assemble the 20 components.
“You couldn’t do it on a traditional CNC. I think the two
technologies are codependent on one another – it’s all
geometry dependent,” says Snow. “You also need to create a
process chain – almost like a factory of the future. Many people
are working on creating a seamless process chain where you
can go into the secondary processes. I think that’s the way to
the future – fully integrated production cells.”
A single sub plate, additively manufactured via an EOS M 290 system,
bears nine individual parts. The sub plate is bolted onto a macro reference
element (with a matching hole/dowel pattern) and is now ready for final
machining and finishing using such traditional methods as milling, grinding,
EDM, etc. Image credit: Georg Fischer Machine Systems.