Metal additive manufacturing (AM) involves complex physical phenomena that need to be quantified to control the quality of the finished product. Placing sensors at the heart of metal parts undergoing additive manufacturing as close as possible to the melting bath is the idea of cea-list researchers to understand the mechanisms involved in this increasingly widespread industrial process.
Bragg gratings are patterns engraved in the axis of an optical fiber, which reflect the light sent by a laser in a wavelength depending on the temperature and surrounding deformations. The integration of such networks at the heart of metal structures therefore provides valuable insights into the effects of the stresses they undergo, such as their local deformation during the manufacturing process and beyond.
To apply the technique to metal AM, CEA-List researchers, in partnership with the CEA's energy department, via the Samanta metal additive manufacturing platform, used Bragg gratings that are particularly resistant to high temperatures: the glass is structured by a so-called "femtosecond" laser, used to form strings of microbubbles inside the fiber. Thus, diffraction gratings do not fade with temperature, as is the case with conventional Bragg gratings. The structured fibers are then positioned at the heart of the part during the manufacturing process.
Thanks to this burial of the sensors, the researchers were able to measure temperatures approaching 700 ° C at a distance of only a few tens of microns from the melting bath, and this at a rate of 5 kHz which allows the in situ and dynamic monitoring of the manufacturing process of a part. The sensors are also interrogated throughout the life of the room to monitor the evolution of its state of health (exposure to vibrations, high temperatures, presence of deformations ...).
The interest of the technology is proven for the monitoring of parts in critical environments such as aeronautics, nuclear, Oil & Gas ...
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