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Non-destructive testing methods are not up to the job of inspecting parts produced by 3D printing or additive layer manufacturing, according to the head of the Manufacturing Technology Centre’s metrology group.
Katy Milne said the issue would pose a barrier to the uptake of emerging ALM technology in safety-critical areas such as aerospace and nuclear. “Additive manufacturing gives you new design freedoms to create complicated geometries, and that is a big challenge for NDT methods, which have been designed for simpler shapes,” she said.
Traditionally, metal parts are inspected using ultrasound or X-rays, but these techniques cannot cope with the complicated shapes typically produced by ALM, according to Milne. She believes that one solution could lie in developing X-ray computed tomography (CT), a scanning technique used in hospitals to take cross-sections and 3D images of body parts.
But further work would be needed before this could become a viable alternative to existing methods. The process is likely to be more time-consuming than conventional techniques, as inspectors would have to sift through many different slice images, she said. In the future, automatic defect recognition systems may be required, she added.
“X-ray CT may not have enough resolution when you go to larger parts, so you might not be able to find the smaller defects.”
Another solution could lie in developing inline inspection, where each layer is inspected as it is built. This technique could be “game-changing”, said Milne.
Understanding and characterising the types of defect that may be found in 3D printed parts poses further challenges. Defects could include blemishes within the layers that make up the product created during production, or powder that gets trapped within the nooks and crannies of a part.
Creating a library of standard defects, as exists for other manufacturing techniques, could take up to five years, Milne added.