(1 Metal Industries Research & Development Centre, Kaohsiung, Taiwan,
2 Department of Mold and Die Engineering, National Kaohsiung University of Applied Sciences, Kaohsiung, Taiwan)
Abstract:
1. Introduction
Studies had shown that through hot deformation, the texture of Nd-Fe-B magnets would be elongated, which would contribute to the enhancement of magnetic properties. In 2003, Hinz et al. studied the influence of backward extrusion process upon the hot-deformed Nd-Fe-B magnets made by different nanocrystalline powders. Inhomogeneous magnetic properties were obtained on top and bottom of the hot-deformed ring magnets. Those inhomogeneous parts should be cut off in order to obtain ring magnets with uniform magnetic properties. Judging from the distribution of remanence values, engineers could decide the cut-off area of the backward-extruded ring magnets. However, it would be very time-consuming to verify the cut-off area of each set of parameters by experiments and magnetic property examinations. Therefore, a method which can shorten the time for evaluating cut-off area should be established.
Studies had shown that through hot deformation, the texture of Nd-Fe-B magnets would be elongated, which would contribute to the enhancement of magnetic properties. In 2003, Hinz et al. studied the influence of backward extrusion process upon the hot-deformed Nd-Fe-B magnets made by different nanocrystalline powders. Inhomogeneous magnetic properties were obtained on top and bottom of the hot-deformed ring magnets. Those inhomogeneous parts should be cut off in order to obtain ring magnets with uniform magnetic properties. Judging from the distribution of remanence values, engineers could decide the cut-off area of the backward-extruded ring magnets. However, it would be very time-consuming to verify the cut-off area of each set of parameters by experiments and magnetic property examinations. Therefore, a method which can shorten the time for evaluating cut-off area should be established.
2. Main text
In this study, packaged finite element software DEFORM-3D is applied to establish simulation model for hot-deformed Nd-Fe-B magnets. Fully-dense hot-compaction specimens purchased from MQI Company (MQ2-16-125) were used for hot deformation experiments in this study. Flow stress data and friction coefficient used for establishing simulation model were obtained by upsetting and ring compression tests. In order to predict the texture of hot-deformed Nd-Fe-B magnets, the flake size and orientation of hot-compaction specimen were observed by OM inspection. By using digital image processing technique and CAD software, the pattern of flakes could be plotted digitally, and input into DEFORM-3D to simulate for the flake pattern after hot deformation. After simulation is accomplished, the deformed flake pattern would be exported and compared with experimental results. Thickness-to-length ratio of the flakes before and after hot deformation is used for evaluating the texture prediction capability of simulation model. Before hot deformation, average thickness-to-length value of the flake measured from hot-compaction specimen is 0.20, with a standard deviation of 0.0045. For die-upsetting hot-deformed magnets, the thickness-to-length ratio of the deformed flakes in simulation ranged from 0.081 (center) to 0.116 (corner), while the experimental results ranged from 0.096 to 0.118. For backward extruded magnets, the thickness-to-length observed in simulation ranged from 0.190 (top) to 0.252 (corner), while the experimental results ranged from 0.198 to 0.232. The thickness-to-length ratio could be used for indexing if the examining area has elongated flakes. From the results, the area with thickness-to-length ratio less than 0.150 all located on high effective strain area plotted by simulation. Since high strain value may correlate with enhanced remanence, it could be inferred that area with higher thickness-to-length ratio could be determined as the cut-off area.
In this study, packaged finite element software DEFORM-3D is applied to establish simulation model for hot-deformed Nd-Fe-B magnets. Fully-dense hot-compaction specimens purchased from MQI Company (MQ2-16-125) were used for hot deformation experiments in this study. Flow stress data and friction coefficient used for establishing simulation model were obtained by upsetting and ring compression tests. In order to predict the texture of hot-deformed Nd-Fe-B magnets, the flake size and orientation of hot-compaction specimen were observed by OM inspection. By using digital image processing technique and CAD software, the pattern of flakes could be plotted digitally, and input into DEFORM-3D to simulate for the flake pattern after hot deformation. After simulation is accomplished, the deformed flake pattern would be exported and compared with experimental results. Thickness-to-length ratio of the flakes before and after hot deformation is used for evaluating the texture prediction capability of simulation model. Before hot deformation, average thickness-to-length value of the flake measured from hot-compaction specimen is 0.20, with a standard deviation of 0.0045. For die-upsetting hot-deformed magnets, the thickness-to-length ratio of the deformed flakes in simulation ranged from 0.081 (center) to 0.116 (corner), while the experimental results ranged from 0.096 to 0.118. For backward extruded magnets, the thickness-to-length observed in simulation ranged from 0.190 (top) to 0.252 (corner), while the experimental results ranged from 0.198 to 0.232. The thickness-to-length ratio could be used for indexing if the examining area has elongated flakes. From the results, the area with thickness-to-length ratio less than 0.150 all located on high effective strain area plotted by simulation. Since high strain value may correlate with enhanced remanence, it could be inferred that area with higher thickness-to-length ratio could be determined as the cut-off area.
3. Conclusions
The results showed that the simulation could be used for predicting the flake size and orientation after hot deformation. The methodology could be used on evaluating die-upsetting and backward extrusion processes. By using the proposed analytical technique, cut-off area of hot-deformed Nd-Fe-B magnet could be determined.
The results showed that the simulation could be used for predicting the flake size and orientation after hot deformation. The methodology could be used on evaluating die-upsetting and backward extrusion processes. By using the proposed analytical technique, cut-off area of hot-deformed Nd-Fe-B magnet could be determined.