CEIT is a research center located in San Sebastian, Spain, affiliated to the University of Navarra, with 230 employees working on multi-disciplinary applications in the fields of materials, manufacturing, transportation, energy, water, health and ICT.
The Advanced Powder Metallurgy and Laser Manufacturing group of CEIT leads the center’s activity in Additive Manufacturing and laser cladding. The CEFAM project, sponsored by the Spanish Government, supports the development of novel processing routes for Ni alloys using the Directed Energy Deposition (DED) laser process to make solid parts. In the DED laser process, a constant flow of powder is directed to a target spot where it is melted by a high-power laser beam, creating a melt pool that solidifies rapidly creating a layer of new material.
Due to its excellent mechanical strength and resistance to corrosion, wear and oxidation, Ni-based superalloys are commonly used in high-temperature applications in the aerospace and energy sectors. Among the objectives of the CEFAM project is the optimization of the process parameters of Ni-based alloys and superalloys, including height control of deposited layers, the optimization of the microstructure and the absence of porosity and defects.
Large residual stresses generated in the DED process often lead to cracking. The preheating of the substrate is an effective way of reducing residual stresses and may become key to success in the processability of some Ni-based alloys and superalloys, especially those with low weldability. Induction heating is the preferred option to produce fast and consistent preheating.
CEIT’s objective is to attain a target preheating temperature at the precise location of the laser spot. In laboratory tests, preheating of the whole base plate is efficient, simple and easy to implement, but this approach cannot be applied to larger parts with more complex shapes. In such cases, preheating of the whole part is either impractical or undesirable and, therefore, heat must be concentrated around the region to be processed and must travel with the same scanning velocity as the nozzle. The precise determination of the induction power needed to attain the target temperature is a challenging task that needs a powerful simulation tool like CENOS Induction Heating.
Prof. Alejo Avello has carried out detailed simulations of the heating process to determine the temperature history of each point in the substrate, which is an essential information to control the necessary amount of heating. A hairpin inductor with a flux concentrator scans the surface of the substrate and rapidly heats a short strip of material. As the inductor travels forward, the material left behind radiates and diffuses heat, quickly loosing temperature. Since the DED nozzle trails behind the inductor by a few centimeters, the exact temperature on the surface can be determined in this way.
Temperature field on the surface and inside the material during the scanning process.
Temperature variation over time in a point on the surface.