ADDITIVE MANUFACTURING
Learning Every Day Industrial CT scanning for inspection offers a look
at parts that’s unparalleled, and related software shows whether a part veers from its CAD drawing. “There are a lot of people who’ve never even heard of
this technology, but it’s the only way in the world to see internal or full volumetric defects,” Ben Connors, manager of inspection services at North Star Imaging (Rogers, MN), said of his company’s industrial CT scanners. “There’s no other technology that can do what it does, and it’s advanc- ing quickly all the time.”
Personal protective equipment (PPE), such as this powered air- purifying respirator Ed Tackett, director of education programs at the UL Additive Manufacturing Competency Center at the University of Louisville, is displaying, is important for some additive manufacturing processes.
Some of the defects a CT scan can reveal include: voids;
lamination; heat-related defects (specifically, contamination in the powder or issues with the laser); weld-related defects (lack of fusion of one layer to another); and powder that wasn’t melted, is misshapen or doesn’t build out completely. CT offers yet another advantage: a variety of software on
the market can compare the part’s CT scan to its CAD model. “The cool thing about CT scanning is that you’re compar- ing the inside and the outside of that model,” Connors said. CT scanning combined with AM also affects the feedback loop that leads to refinements in design and/or engineering.
North Star does inspection on thousands of parts every
year for aerospace, automotive, medical and defense manufacturers.
Inspection with an industrial CT scanner can take from
seconds up to a few hours, but it’s much faster compared with other methods. That’s because the inspector doesn’t have to cut up the part. Cutting up the part can introduce other problems. “With some of the other methods, there’s a risk of chang- ing the part when you cut it,” Connors explains. “And then some of the measurements can be brought into question.” Also, the CT scan process is unaffected by defects in
the part. “You can see through the entire part volume and not be
inhibited by defects,” he said. “Some other technologies can be inhibited or slowed down by certain defects.”
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The CT scan’s picture into the inside of a part is also a power- ful way to convey information to engineers and designers. “When you combine 3D printing with scanning it makes
that loop so much faster,” Connors said. While North Star and Connors have lots of experience inspecting metal AM parts, he doesn’t have an answer on whether any one of the different methods of metal print- ing (powder with nozzle; extruded wire or powder bed) is associated with any particular quality problems in the parts produced. “The different methods all have some degree of issue with bonding/lack of fusion/voiding from one layer to the next,” Connors said. “What is not clear at this point is the difference in defects from one process to another, but they all have some type of defect or anomaly. “It’s still a new area and we are learning every day.”
Spring 2016
Photo courtesy of UL
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