Metal additive manufacturing (AM) involves complex physical phenomena that need to be quantified in order 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 molten bath, is the idea of CEA-List researchers to understand the mechanisms at play in this increasingly widespread industrial process.
Bragg gratings are patterns etched into the axis of an optical fiber, reflecting light sent by a laser in a wavelength dependent on temperature and surrounding deformations. The integration of such gratings into the core 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 metallic FA, CEA-List researchers, in partnership with the CEA's Energies Division via the Samanta metal additive manufacturing platform, have 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. In this way, the 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 burying of the sensors, the researchers were able to measure temperatures approaching 700°C at a distance of just a few tens of microns from the melting bath, and this at a rate of 5 kHz, enabling in-situ, dynamic monitoring of a part's manufacturing process. The sensors are also interrogated throughout the life of the part to monitor changes in its state of health (exposure to vibrations, high temperatures, presence of deformations, etc.).
The technology has proven its worth for monitoring parts in critical environments such as aeronautics, nuclear power, Oil&Gas...
Visit the site: