250 Prakt. Met. Sonderband 52 (2018) 
The SEM micrograph on fig. 1a shows the morphology of melt spun Nd-Fe-B ribbons. The 
ribbons are plate-like with a particle size ranging from 10 to 600 um and average particle 
size about 250 um used for production of polymer bonded magnets. To achieve higher 
loading factors and to decrease the melt viscosity during compounding and 3d printing, the 
melt spun ribbon were grinded to obtain narrower particle size distribution and average 
particle size about 25 um. Additionally, the magnetic powder was sieved after grinding 
through 90 um sieve to eliminate larger particles that could potentially clogged the nozzle 
during 3D printing. 
Fig. 1: SEM micrographs of plate-like Nd-Fe-B ribbons made by melt spinning (a) and 
microstructure of 3D printed polymer bonded magnets (b) 
On the other hand, the SEM micrograph on fig. 1b reveals the microstructure of polymer 
bonded magnet after 3D printing. Its microstructure consists of PA12 matrix (shown grey on 
micrograph on fig. 1b) and homogenously distributes bright plate-like Nd-Fe-B ribbons within 
the matrix. Additionally, the micrograph on fig. 2 reveals also the notable amount of porosity 
in the microstructure of polymer bonded magnets, which is shown as dark regions within the 
PA12 matrix. The results of our research work are showing that the amount of porosity and 
the microstructure homogeneity are strongly dependent on the layer thickness during 3D 
printing. In the microstructure of sample A, that was printed by 300 um layer thickness, the 
highest amount of porosity was determined, which reflects in the worst magnetic properties 
and density (fig. 2a, b and table 2). On the other hand, by reducing the layer thickness from 
300 on 100 um, the microstructure of the 3D printed sample (sample B) become more 
homogenous with reduced amount of porosity and consequently better magnetic properties 
and higher density (fig 2c, d and table 2). 
One would expect the remanence and the energy product of bonded magnets to be directly 
linked to the amount of binder used. However, porosity and internal magnetic shear loss, oo 
also lead to lower the expected B;, values. Pores reduces the magnet density and hence the 
Br. They can be limited by particle morphology, type of binder and consolidation technique. 
Internal shear loss is the effect caused by isolated magnetic particles magnetically shearing An 
with one another within the polymer. The effect increases with higher levels of polymer and Cr 
powders with low rare-earth content or high B/Hgi [1]. ome 
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