| Since sintered NdFe B permanent magnet has good magnetic and mechanical properties,it is one of the commonly used permanent magnetic materials. Its cost is low and is widely researched on its development and application by people. The material has high hardness,high brittleness, low Curie temperature and poor thermal stability. The difficult productivity and easy corrosion are two main reasons to affect its application. The topic of this paper is mostly focused on the above issues. Now researchs about forming and surface protections of magnet are a lot, but they are all carried out separately. This paper tried to simultaneity achieves the requirements of the two different aspects in EDM, which is a new method of surface protection. The main research contents and conclusions are as follows:1. Researched on the influencing laws of material removal rate and surface quality of sintered NdFeB in electric discharge machining. Under certain conditions, the MRR and surface roughness all increased with the increase of peak current, and the influence on MRR is significant. The influence of pulse width has the same trend with the peak current,but large pulse width can cause low MRR and high surface roughness. So processing should be avoided in this kind of electric parameters. The influence of pulse interval is opposite. Good surface can be obtained in high pulse interval, but the processing speed is low at the same time.2. By the regression analysis of experimental datas, a processing model of NdFeB in EDM is established. After compared the prediction results with actual results, we found that they are similar and the values are in the range of errors, which made the prediction of process effect reasonable. While a white bright layer appears in the microstructure of NdFeB. Under certain processing time, the thickness of strengthening layer is increased by the increase of peak current and pulse width. But the surface is easy to appear crack at larger peak current, and similarly the strengthening layer is easy to peel at larger pulse width. The effect on strengthening layer of pulse interval is opposite; the thickness of layer is large at low pulse interval. The thickness is decreased by the increase of pulse interval,but the quality is relatively good.3. The surface morphology, microstructure, alloy composition and phase of processed NdFeB are analyzed, and the hardness and corrosion resistance tests are carried. The mainmanners of material removal are melting, gasifying, spray, whole partical removal and removal by micro fracture with large areas; the hardness of NdFeB material is improved by the new amorphous alloy on the surface which changed its mechanical properties; the corrosion potential is increased and the corrosion current density is decreased in electrochemical experiment which showed that it is more difficult to corrosion and the corrosion rate is low after processed, and the corrosion resistance is improved.4. According to the processing model, this paper designed a visual simulation system of sintered NdFeB in EDM, which can effectively predit the results in different machining parameters. For high efficiency and high quality processing, many indicators should be considered such as removal rate and surface quality. So the optimal solution problem in EDM changed into an optimization problem of multi object function. In order to solve this problem, this paper combined the neural network with genetic algorithm and achieved the comprehensive optimization of processing parameters.After the systemic research of sintered NdFeB in EDM by this paper, the conclusion is that there is really a layer of amorphous alloy on the surface of processed material and it can improve the comprehensive performance of magnetic material. The dual role of material removal and surface modification are achieved simultaneously by EDM. |
PDF Full Text Request