Different types of recycled NdFeB powders were prepared and analysed and made into different feedstock compositions: These were evaluated in terms of processibility by the SDS Metal Injection Moulding (MIM) and 3D printing processes.
It has been found that the recycled and sieved powder are suitable for the MIM processing route. To compensate for oxidation of EoL magnets, the addition of small percentages of Nd material either in hydrided form or as a master alloy is beneficial for the magnetic properties, allowing to reach properties of non-recycled virgin material.
A main aspect of the work carried out was to develop appropriate debinding and sintering routes, especially due to the fact that the RE powders are very sensitive to picking up oxygen and carbon during the processes. Extensive and detailed investigations in terms of processing parameters of debinding and sintering have been conducted, in order to keep contamination within acceptable ranges. In the sintered state, isotropic magnets were produced showing coercivity up to 95% of the starting material.
The achieved values are competitive to today’s isotropic sintered magnets produced via the conventional pressing and sintering route, which use fresh instead of recycled powders. In order to produce aligned (anisotropic) magnets by the SDS processes, injection moulding test tools with integrated magnets to create suitable alignment fields were simulated, constructed and built. Radial, parallel and multiaxial aligned samples were manufactured, with the strength of the alignment field being optimised for maximum alignment.
For 3D-printing, a printable, debindable and sinterable feedstock system has been developed. The design and setup of a specific ME printer has been successfully accomplished, being tested with stainless steel, Ti and NdFeB material, which led to magnets with minimised C-contents. However, as the printing was done under air, an oxygen contamination of the NdFeB could not be avoided, leading to improvable magnetic properties. Work under protective atmospheres is ongoing.
For the LMM-printing of metals, also a new type of printer and a corresponding feedstock system has been developed. Printing of NdFeB type material could not be achieved, due to a catalytic reaction between the photopolymeric binder and Nd. However, the route has proved to be an excellent method to shape other metals, e.g. stainless steel and Ti with high precision.
An alignment system for the ME-3D-printer was constructed and tested. For NdFeB, the initial alignment looks promising, the work is ongoing.
For corrosion protection of the magnets, an optimized coating which combines a LPPS (low pressure pack sublimation) with electroplating was developed. Comparative mechanical and corrosion testing of samples made by SDS and conventional sintering routes with standard and optimised coatings were carried out.
A comprehensive Life Cycle Analysis (LCA) and Life Cycle Cost (LCC) assessment of SDS processing of RE magnets was carried out.
The consortium was active in dissemination and publication of results, while at the same time carefully protecting generated knowledge and IP, with one patent being filed and a lot of substantial technical know-how was created with all partners.
REProMag was selected as a winner of the German Innovation Price for Raw Material Efficiency 2017 and the EcoTech Award for Resource Efficiency 2017 of the German State of Baden-Württemberg.
