Additive manufacturing of bonded NdFeB, process parameters evaluation on magnetic properties

Abstract

Bonded NdFeB magnets were fabricated by an additive manufacturing (AM) technique known as selective laser sintering (SLS). A mixture of spherical isotropic powders of a NdFeB based alloy and polymeric binder (PA 12) was used as process feedstock. The amount of binder used was varied to optimize mechanical resistance and magnetic properties. Besides that, two parameters were evaluated: layer thickness and hatch spacing. In order to enhance binder activity, fabrication temperature was kept between 368K and 373K. Scanning speed and laser power were constant, 1300 mm/s and 42W, respectively. For magnetic properties evaluation, cylindrical samples with diameter and height of 10mm were produced. Magnetic properties measured in a hystograph (Brockhaus EM 1800 model) indicate that lower SLS parameters combined with lowest binder content (6 wt. %) showed higher magnetic properties, with average values for remanence (B <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">r</sub> ) of 0,33T, intrinsic coercivity (H <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">cj</sub> ) of 696 kA/m and maximum energy-product (BH) <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">max</sub> of 17,1 kJ/m <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sup> . The obtained results were compared with those obtained for bonded magnets fabricated by pressing, using the same feedstock, for which the highest remanence and maximum energy-product were, 0,38 T and 24,1 kJ/m <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sup> . In conclusion, the study showed that magnetic properties can be improved by reducing hatching space and layer thickness and also AM by SLS technique can be used to produce complex magnet shapes.