Improving NdFeB magnet fabrication: In situ observation of powder flow

NdFeB powder is magnetically anisotropic and can provide high performance magnets via compaction in an applied magnetic field. In this study we observe the behavior of the magnetic powder during compaction after applying a magnetic field, with the objective of obtaining guidelines for improved design of the magnet fabrication process. We make a transparent die, fill it with NdFeB powder and locate the assembly at the center of a coil. The coil is separated into two halves, in order to visualize the powder response. A pulsed magnetic field is applied and the punch displaced to compact the powder. Movement of the powder is analyzed by template-matching with corretotion-relaxation-labeting. This is compared to the response obtained without application of a magnetic field. The movement of the powder changes due to column structures formed in the presence of the magnetic field.