Investigation For Influence Of Preparing Processes On Magnetic Properties Of Bonded NdFeB Magnet Based On The Least Squares Support Vector Machine Modeling

For the bonded NdFeB magnets with different demand of magnetic properties, it is necessary to chose different manufacture conditions, such as the type of magnetic powder, the binder content, and the process parameters. It has an important significance in reduce experiment cost to establish mathematical model to calculate the dependence of the magnetic properties on the process parameters.The calculating model of relationship between the magnetic properties and the process parameters has been established by using the least squares support vector machines (LS-SVM). The process parameters include binder content, curing temperature, curing time and molding pressure. The magnetic properties are the remanence Br, the intrinsic coercivity Hcj, and the maximum energy product (BH)_m. The sample data is acquired by uniform design. The relationship between preparing processes and magnetic properties has been simulated by the LS-SVM modeling. The dependence of the magnetic properties on the process parameters has been investigated and the optimal manufacture conditions have been obtained. The main conclusions are as follows:(1) The bonded NdFeB magnets are prepared and their magnetic properties are measured based on the experimental scheme designed by uniform design. According to these data of the magnetic properties and the process parameters, the modeling's parametersγandσhave been selected and the optimal LS-SVM modeling has been established.(2) In order to check the precision of the LS-SVM modeling, an artificial neural network (ANN) modeling has been established and the contrast investigations have been carried out. The result shows that the LS-SVM modeling has better precision and lower relative errors. The average relative errors of LS-SVM modeling are 0.6719%, 0.9607%, 1.2288%, and the maximum relative errors are 2.0888%, 2.7089%, 2.4247%. Therefore, the LS-SVM modeling is useful for the prediction of magnetic properties.(3) Using the LS-SVM modeling, the dependences of the magnetic properties on binder content and molding pressure have been obtained. With the increase of binder content, Br and (BH)_m firstly increase, and decrease then. The Br and (BH)_m reach to the maximum for the binder content of 2.75wt%. The effect of molding pressure on Br and (BH)_m is similar to binder content. With the increase of molding pressure, Br and (BH)_m firstly increase due to the increase of density, and decrease then due to the crush of magnetic powder.(4) The dependences of Br and (BH)_m on curing processes is more complicated. The Br and (BH)_m reach the maximums at two conditions: lower curing temperature and longer curing time; higher curing temperature and shorter curing time. The main reasons for magnetic property decrease are the magnetic powder corrosion caused by water, which generated during cross linking reaction, and the magnetic powder oxidation. When the curing temperature is lower than 110℃, the bonded NdFeB magnets have high Br and (BH)_m because the oxidation of magnetic powder is poor and the product of esterification reaction is oligomer, without water , the magnetic powder corrosion does not occur. When the curing temperature is higher than 110℃, the water, which generated from the reaction of oligomer and the hydroxyl of epoxy resin, will cause magnetic powder to corrode, reducing the Br and (BH)_m of bonded NdFeB magnets. While the curing temperature exceeds 160℃, the epoxy will react with the oligomer and the reaction will prohibit the generation of water. Therefore, the bonded NdFeB magnets, especially with low binder content, have high B_r and (BH)_m at high temperature and short time.(5) According to the LS-SVM modeling, two preparing processes have been obtained:â‘ binder content 1.25%, curing time 2h, curing temperature 100℃and molding pressure 509.2MPa;â‘¡binder content 2.75%, curing time 0.5h, curing temperature 180℃and molding pressure 483.7 MPa. Properties of bonded NdFeB magnets are:â‘ Br=0.6351T, H_cj=778.565kA/m, (BH)_m=64.25kJ/m³;â‘¡Br=0.6309T, Hcj=782.21kA/m, (BH)_m=63.47kJ/m³. The LS-SVM modeling prediction results compare with this results, the relative errors are lesser. Therefore, the LS-SVM modeling is good at prediction of Bonded NdFeB magnets.