A method for predicting demagnetization rate of neodymium-iron-boron permanent magnet based on physical field simulation

Abstract

The application discloses a method for predicting demagnetization rate of a Nd-Fe-B permanent magnet based on physical field simulation and simulation, and comprises the following steps: establishing a three-dimensional model of a magnetic circuit of the permanent magnet and calculating magnetic field distribution data; obtaining H field intensity of N sampling points in a magnetization direction and obtaining H / Jr ratio through normalization processing; arranging H / Jr ratios of the N sampling points in ascending order to obtain an H / Jr data set, and distributing an overall volume of the Nd-Fe-B permanent magnet to the N sampling points on average; constructing a V(H / Jr) cumulative volume distribution curve; constructing a new relationship curve V(H / Jr*(1-V)); testing Hk and Jr of a Nd-Fe-B permanent magnet blank actually produced at a demagnetization holding temperature, and substituting Hk / Jr ratio as an abscissa value into the new relationship curve V(H / Jr*(1-V)) to obtain a predicted value of the demagnetization rate. The method has good universality, can quantitatively characterize the demagnetization rate of the Nd-Fe-B permanent magnet with a specific geometric shape and a magnetic circuit design, and realizes quantitative and numerical accurate prediction of the demagnetization rate.

Description

TECHNICAL FIELD

[0001] The application belongs to the field of neodymium-iron-boron permanent magnets, and particularly relates to a method for predicting demagnetization rate of a neodymium-iron-boron permanent magnet based on physical field simulation. BACKGROUND

[0002] The neodymium-iron-boron permanent magnet has a tendency of self-demagnetization due to the effect of internal demagnetizing field, and the ability of resisting self-demagnetization is usually represented by coercivity Hcj or Hk as a key performance index. It is worth noting that the distribution of the internal demagnetizing field (i.e. H field) of the neodymium-iron-boron permanent magnet is usually non-uniform, and the relationship between the distribution and strength of the H field is relatively complex, and has great difference with the shape design of the neodymium-iron-boron permanent magnet and the actual magnetic circuit, which is difficult to be directly solved by simple calculation. The uncertainty of the internal demagnetizing field strength makes it difficult to determine what ability of resisting demagnetization the neodymium-iron-boron permanent magnet needs to have to meet the design requirements, which becomes a key problem to be solved in engineering design. At present, two solutions are mainly used in practice: one is to refer to the experience data of similar specifications of neodymium-iron-boron permanent magnet products, and the other is to give a reasonable evaluation by preparing samples for actual measurement. SUMMARY

[0003] The application aims to solve the technical problems of the prior art, and provides a method for predicting demagnetization rate of a neodymium-iron-boron permanent magnet based on physical field simulation, which has good universality and can quantitatively represent the demagnetization rate of the neodymium-iron-boron permanent magnet with a specific geometric shape and magnetic circuit design, and realize quantitative and numerical accurate prediction of the demagnetization rate.

[0004] The technical scheme adopted by the application to solve the above technical problems is as follows: a method for predicting demagnetization rate of a neodymium-iron-boron permanent magnet based on physical field simulation, comprising the following steps:

[0005] S1, a three-dimensional model of a magnetic circuit of a permanent magnet is established by using a physical field simulation software, the three-dimensional model is given a condition that the material is a neodymium-iron-boron permanent magnet, and an initial magnetization condition in a magnetization direction of the designed neodymium-iron-boron permanent magnet is given as saturation magnetization, and then the physical field simulation software is used to calculate magnetic field distribution data, including distribution data of magnetic polarization intensity J, magnetic field intensity H and magnetic induction intensity B inside and outside the neodymium-iron-boron permanent magnet;

[0006] S2, performing finite element analysis on the three-dimensional model of the Nd-Fe-B permanent magnet by a physical field simulation software to obtain H field intensity of N sampling points uniformly distributed inside the Nd-Fe-B permanent magnet in the magnetization direction, N≥50000; performing normalization processing on the H field intensity of the N sampling points, i.e. dividing H value representing the H field intensity of each sampling point by residual magnetic polarization intensity Jr of the Nd-Fe-B permanent magnet to obtain dimensionless H / Jr ratio reflecting the H field intensity of each sampling point; arranging the H / Jr ratio of the N sampling points in order from small to large to obtain H / Jr data set, and equally distributing the total volume of the Nd-Fe-B permanent magnet to the N sampling points so that the H field intensity of each sampling point represents the H field size in the equal volume unit; constructing V(H / Jr) cumulative volume distribution curve, which takes H / Jr as abscissa and cumulative volume V as ordinate, wherein the cumulative volume V is the volume percentage of all volume units with H / Jr ratio higher than the corresponding H / Jr ratio on the abscissa in the total volume of the Nd-Fe-B permanent magnet, and the value range is 0% to 100%;

[0007] S3, giving a simplified assumption that the H field intensity of the permanent magnet is attenuated by 1% synchronously with each demagnetization of 1%, introducing a new factor (1-V) based on the simplified assumption to modify H / Jr, and constructing a new relationship curve V(H / Jr*(1-V)) taking H / Jr*(1-V) as abscissa and cumulative volume V as ordinate, wherein the value of H / Jr*(1-V) when V is zero is taken as the critical value;

[0008] S4, testing Hk and Jr of the Nd-Fe-B permanent magnet blank actually produced at the demagnetization holding temperature, if the ratio Hk / Jr falls between zero and the critical value, then the ratio Hk / Jr is taken as the abscissa value to be substituted into the new relationship curve V(H / Jr*(1-V)) to obtain the value of the corresponding cumulative volume V, i.e. the predicted value of the demagnetization rate.

[0009] The magnetic polarization intensity J, the magnetic field intensity H and the magnetic induction intensity B correspond to three magnetic fields usually involved inside the Nd-Fe-B permanent magnet, wherein the magnetic polarization intensity J is the body magnetic moment magnetization result, representing the magnetic strength of the permanent magnet; the magnetic field intensity H is the derived field of J, which is the origin of demagnetization of the Nd-Fe-B permanent magnet, and is therefore also called demagnetization field Hd; the magnetic induction intensity B is the real magnetic field intensity after superposition of J field and H field, and the magnetic field intensity H as the source power of demagnetization is the main analysis object of the method.

[0010] The application is based on finite element analysis, and the H field intensity of N sampling points uniformly distributed in the interior of a Nd-Fe-B permanent magnet in the magnetization direction is obtained by physical field simulation software, and the H / Jr ratio is used to reflect the H field intensity of each sampling point. The H / Jr ratio only depends on the shape of the Nd-Fe-B permanent magnet and the magnetic circuit design, so it is universal and suitable for any brand of Nd-Fe-B permanent magnet. The number N of sampling points in the interior of the Nd-Fe-B permanent magnet is more than 50,000, and tens of thousands can be selected. The number of sampling points is large enough to simply consider that the H field intensity of each sampling point represents the H field size of one N-th volume in the interior of the Nd-Fe-B permanent magnet. There is a difference from the actual completely smooth real magnetic field distribution, but when the number of sampling points is sufficient, the difference is small enough to be ignored.

[0011] The application constructs a V(H / Jr) cumulative volume distribution curve. Since it is considered that the H field intensity of each sampling point represents a part of the micro volume, the V actually reflects the proportion of the sampling points in the Nd-Fe-B permanent magnet whose H / Jr value is higher than a certain value. At a certain H / Jr value, the Nd-Fe-B permanent magnet can be divided into two parts, one part with H field intensity higher than the certain value, accounting for V, and the other part with H field intensity lower than the certain value, accounting for 1-V. The magnetic decay of the Nd-Fe-B permanent magnet starts from the highest H field position and gradually spreads to the lower H field position. After the highest occupied volume V part decays, the remaining part of the H field intensity will be (1-V) times of the pre-decay. The actual demagnetization is a dynamic decay process, that is, as the demagnetization proceeds, the magnetization degree of the permanent magnet decreases, and the derived self-demagnetizing field decays synchronously. This process is actually very complex. In the method of the application, Hk is regarded as the critical demagnetizing field allowed in the interior of the Nd-Fe-B permanent magnet blank in the demagnetization test. In the performance test of the Nd-Fe-B permanent magnet, one of the most obvious characteristics is that when the H field intensity is lower than a certain value, the magnetism of the Nd-Fe-B permanent magnet hardly decays or decays very low, and when the H field intensity crosses a certain range, the magnetism of the Nd-Fe-B permanent magnet quickly and completely disappears in a very short H field increase range. The Hk value can approximately represent the turning point of the demagnetization curve from almost no decay to rapid decay. The whole dynamic decay process can be simplified as follows: the part of the Nd-Fe-B permanent magnet whose H field intensity is higher than Hk has exceeded the anti-demagnetizing ability of the Nd-Fe-B permanent magnet, so the magnetic decay continues until the part of the volume is completely demagnetized, and the H field intensity value of the remaining part of the volume decays to the Hk level. Therefore, we make a simplified assumption that the H field intensity of the permanent magnet decays by 1% for every 1% demagnetization, and based on this simplified assumption, a new factor (1-V) is introduced to correct H / Jr, and a new relationship curve V(H / Jr*(1-V)) is constructed with H / Jr*(1-V) as the horizontal coordinate and the cumulative volume V as the vertical coordinate, which approximately describes this process. The curve considers the dynamic process of the Nd-Fe-B permanent magnet starting from the highest H field position, and has high consistency with the actual demagnetization process.

[0012] Preferably, in step S1, the three-dimensional model is established according to the actual specifications of the permanent magnet product and the actual demagnetization application conditions, and the three-dimensional model is divided into fine three-dimensional grids by designing a finite element grid.

[0013] Preferably, in step S4, Hk is obtained by demagnetization curve testing, wherein Hk represents the H field strength corresponding to the 5% decay of the magnetic polarization intensity in the demagnetization test.

[0014] Preferably, the physical field simulation software is Comsol software.

[0015] Compared with the prior art, the present application has the following advantages: the present application proposes a method for predicting the demagnetization rate of a neodymium-iron-boron permanent magnet based on physical field simulation, which can quantitatively characterize the demagnetization rate of a neodymium-iron-boron permanent magnet with a specific geometric shape and magnetic circuit design, and realize quantitative and numerical accurate prediction of the demagnetization rate. The method of the present application is good in universality, and is suitable for neodymium-iron-boron permanent magnets of any brand and performance, and can provide reliable theoretical basis and technical support for product design, process development and performance optimization of neodymium-iron-boron permanent magnets. BRIEF DESCRIPTION OF DRAWINGS

[0016] Figure 1 is the V(H / Jr) cumulative volume distribution curve in the example;

[0017] Figure 2 is the V(H / Jr*(1-V)) new relationship curve in the example. DETAILED DESCRIPTION

[0018] The present application will be further described in detail below with reference to the embodiments combined with the accompanying drawings.

[0019] A method for predicting the demagnetization rate of a neodymium-iron-boron permanent magnet based on physical field simulation, comprising the following steps:

[0020] S1, a three-dimensional model of the magnetic circuit of the permanent magnet is established by a physical field simulation software Comsol according to the actual specifications of the permanent magnet product and the actual demagnetization application conditions, the three-dimensional model is divided into fine three-dimensional grids by designing a finite element grid, the three-dimensional model is given the condition that the material is a neodymium-iron-boron permanent magnet, and the initial magnetization condition in the designed magnetization direction of the neodymium-iron-boron permanent magnet is given as saturation magnetization, and then the physical field simulation software Comsol is used to calculate the magnetic field distribution data, including the distribution data of the magnetic polarization intensity J, the magnetic field intensity H and the magnetic induction intensity B inside and outside the neodymium-iron-boron permanent magnet;

[0021] S2, perform finite element analysis on a three-dimensional model of the Nd-Fe-B permanent magnet by a physical field simulation software Comsol, to obtain H field intensity of N sampling points uniformly distributed inside the Nd-Fe-B permanent magnet in a magnetization direction, N≥50000; perform normalization processing on the H field intensity of the N sampling points, that is, divide H value representing H field intensity of each sampling point by residual magnetic polarization intensity Jr of the Nd-Fe-B permanent magnet to obtain dimensionless H / Jr ratio reflecting H field intensity of each sampling point; arrange the H / Jr ratio of the N sampling points in ascending order to obtain an H / Jr data set, and evenly distribute the total volume of the Nd-Fe-B permanent magnet to the N sampling points, so that the H field intensity of each sampling point represents H field size in an equal volume unit; construct a V(H / Jr) cumulative volume distribution curve, which takes H / Jr as the horizontal coordinate and cumulative volume V as the vertical coordinate, wherein the cumulative volume V is a volume percentage of all volume units with an H / Jr ratio higher than the corresponding H / Jr ratio on the horizontal coordinate in the H / Jr data set in the total volume of the Nd-Fe-B permanent magnet, and the value range is 0% to 100%;

[0022] S3, give a simplified assumption that the H field intensity of the permanent magnet is attenuated by 1% synchronously with each demagnetization of 1%, introduce a new factor (1-V) based on the simplified assumption to modify H / Jr, and construct a new relationship curve V(H / Jr*(1-V)) taking H / Jr*(1-V) as the horizontal coordinate and cumulative volume V as the vertical coordinate, wherein the value of H / Jr*(1-V) when V is zero is taken as the critical value;

[0023] S4, test Hk and Jr of the Nd-Fe-B permanent magnet blank actually produced at the demagnetization holding temperature, wherein Hk is obtained by a demagnetization curve test, and Hk represents H field intensity corresponding to a magnetic polarization intensity attenuation of 5% in the demagnetization test; if the ratio Hk / Jr falls between zero and the critical value, then the ratio Hk / Jr is taken as the horizontal coordinate value and substituted into the new relationship curve V(H / Jr*(1-V)) to obtain the value of the corresponding cumulative volume V, that is, the predicted value of the demagnetization rate.

[0024] Taking a Nd-Fe-B permanent magnet with a designed magnetic circuit condition of open circuit and a specification of D20*1.84 as an embodiment, the demagnetization rate of the Nd-Fe-B permanent magnet is predicted by the method. The remanence Br=14.700 kGs is set by the physical field simulation software Comsol to analyze and calculate the H field distribution inside the Nd-Fe-B permanent magnet. The calculation shows that the maximum value of the H field intensity inside the Nd-Fe-B permanent magnet is obtained at the center point, and the specific value is 1018050 A / m, that is, 12.793 kOe. The H field intensity is proportional to Br, and in order to be applicable to different grades of Nd-Fe-B permanent magnets with different remanences, normalization is performed, that is, H / Jr is used to represent the maximum H field intensity. In this embodiment, H / Jr is highest at 12.793 / 14.700=0.8703.

[0025] By simulation analysis through the physical field simulation software Comsol, the H field intensity of each sampling point inside the Nd-Fe-B permanent magnet can be obtained, the H / Jr ratio of each sampling point is arranged in order from small to large, and the total volume of the Nd-Fe-B permanent magnet is evenly distributed to N sampling points, so that the H field intensity of each sampling point represents the H field size in the equal volume unit, and a V(H / Jr) cumulative volume distribution curve is further constructed, as shown in Figure 1 The V(H / Jr) cumulative volume distribution curve is a characteristic curve reflecting the H field distribution inside the Nd-Fe-B permanent magnet based on the simulation results. This curve also needs to be corrected based on the dynamic decay assumption, that is, the variable H / Jr on the horizontal axis is multiplied by an additional factor (1-V), and a new relationship curve V(H / Jr*(1-V)) is constructed. The new relationship curve V(H / Jr*(1-V)) is used for demagnetization analysis. For convenience of description, we adopt the fitting quadratic function of the curve for subsequent calculation. As shown in Figure 2 The V(H / Jr*(1-V)) new relationship curve finally obtained in this embodiment can be fitted as:

[0026] V=0.1235*(H / Jr*(1-V)) 2 -1.2231*(H / Jr*(1-V))+0.9764

[0027] Figure 2 In the formula, x represents (H / Jr*(1-V)), and y represents V.

[0028] When applied to actual analysis, the ratio Hk / Jr is the horizontal coordinate value in the new relationship curve V(H / Jr*(1-V)).

[0029] Application Case 1: The Nd-Fe-B permanent magnet blank with the grade A has the following performance test results at 60°C: the measured Jr is 13.863 kGs, the measured Hk is 9.722 kOe, and the measured demagnetization rate is 18.48%. The relevant calculation results based on the method of Embodiment 1 are as follows:

[0030] The Hk / Jr is calculated to be 0.7013;

[0031] The demagnetization rate V is calculated to be 0.1235*0.7013*0.7013-1.2231*0.7013+0.9764=0.1794=17.94%, which has a difference of 0.54% compared with the measured value 18.48% of the demagnetization rate. It can be seen that the matching of the predicted value of the demagnetization rate obtained according to the method of the present application and the measured value is good, and the accuracy of the prediction of the method of the present application is high.

[0032] Application Case 2: Nd-Fe-B permanent magnet blank with grade B, the performance test results at 100℃ are as follows: measured Jr=13.120 kGs, measured Hk=8.087 kOe, and measured demagnetization rate is 30.10%. The relevant calculation results based on the method of Example 1 are as follows:

[0033] Hk / Jr is calculated as 0.6164;

[0034] The demagnetization rate V is calculated as 0.1235*0.6164*0.6164-1.2231*0.6164+0.9764=0.2694=26.94%, compared with the measured value of demagnetization rate 30.10%, the deviation is 3.16%. It can be seen that the predicted value of the demagnetization rate obtained according to the method of the application matches well with the measured value, and the accuracy of the prediction of the method of the application is high.

Claims

1. A method for predicting demagnetization ratio of a neodymium-iron-boron permanent magnet based on a physical field simulation analog, characterized in that, The method comprises the following steps: S1, a three-dimensional model of a magnetic circuit of a permanent magnet is established by physical field simulation software, a material condition of neodymium iron boron permanent magnet is given to the three-dimensional model, an initial magnetization condition of saturation magnetization is given in a designed magnetization direction of the neodymium iron boron permanent magnet, and magnetic field distribution data including magnetic polarization intensity J, magnetic field intensity H, and magnetic induction intensity B inside and outside the neodymium iron boron permanent magnet are calculated by using the physical field simulation software; S2, finite element analysis is performed on the three-dimensional model of the neodymium iron boron permanent magnet by using the physical field simulation software, H field intensity of N sampling points uniformly distributed inside the neodymium iron boron permanent magnet in the magnetization direction is obtained, N≥50000; the H field intensity of the N sampling points is normalized, that is, the H value representing the H field intensity of each sampling point is divided by the residual magnetic polarization intensity Jr of the neodymium iron boron permanent magnet to obtain a dimensionless H / Jr ratio reflecting the H field intensity of each sampling point; the H / Jr ratios of the N sampling points are arranged in ascending order to obtain an H / Jr data set, and the total volume of the neodymium iron boron permanent magnet is evenly distributed to the N sampling points, so that the H field intensity of each sampling point represents the H field size in an equal volume unit; a V(H / Jr) cumulative volume distribution curve is constructed, the curve takes H / Jr as the abscissa and accumulative volume V as the ordinate, wherein the accumulative volume V is the volume percentage of all volume units with an H / Jr ratio higher than the corresponding H / Jr ratio on the abscissa in the total volume of the neodymium iron boron permanent magnet in the H / Jr data set, and the value range is 0% to 100%; wherein the H field is the demagnetizing field inside the neodymium iron boron permanent magnet; S3, give a simplified assumption, that is, the H field strength of the permanent magnet is attenuated by 1% synchronously with the demagnetization of 1%, introduce a new factor (1-V) to modify H / Jr based on the simplified assumption, to H / Jr (1-V) as the abscissa and the cumulative volume V as the ordinate, construct a new relationship curve V(H / Jr (1-V)) to obtain the critical value of H / Jr (1-V) when V is zero; S4, test the Hk and Jr of the actual production Nd-Fe-B permanent magnet blank at the demagnetization temperature, Hk represents the H field strength corresponding to the 5% attenuation of the magnetic polarization intensity in the demagnetization test, if the ratio Hk / Jr falls between zero and the critical value, the ratio Hk / Jr is taken as the abscissa value substituted into the new relationship curve V(H / Jr (1-V), to obtain the value of the corresponding cumulative volume V, which is the predicted value of the demagnetization rate.

2. The method for predicting the demagnetization ratio of a Nd-Fe-B permanent magnet based on physical field simulation and modeling according to claim 1, characterized in that, In step S1, the three-dimensional model is established according to the actual specifications and actual demagnetization application conditions of the permanent magnet product, and the three-dimensional model is divided into fine three-dimensional grids by designing finite element grids.

3. The method of claim 1, wherein the method is characterized by: In step S4, Hk is obtained by demagnetization curve testing.

4. The method for predicting the demagnetization ratio of a Nd-Fe-B permanent magnet based on physical field simulation and modeling according to claim 1, characterized in that, The physical field simulation software is Comsol software.

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