ROTOR PRODUCTION METHOD

Abstract

A rotor production method includes: a first step of arranging a plurality of sintered bodies side by side with an insulating lubricant applied to an interface of at least one of the sintered bodies adjacent to each other, and then housing the sintered bodies in a cavity of a molding die such that the sintered bodies are arranged side by side in the cavity, the sintered bodies being precursors of a plurality of split magnets constituting one rare-earth magnet; a second step of turning the sintered bodies into the split magnets by performing hot working to impart magnetic anisotropy to the sintered bodies arranged in the cavity, and producing an integrated magnet in which the split magnets are integrated together with the lubricant interposed therebetween; and a third step of producing a rotor of a motor by inserting the integrated magnet into a magnet slot of the rotor.

Claims

1. A rotor production method comprising: arranging a plurality of sintered bodies side by side with an insulating lubricant applied to an interface of at least one of the sintered bodies adjacent to each other, and then housing the sintered bodies in a cavity of a molding die such that the sintered bodies are arranged side by side in the cavity, the sintered bodies being precursors of a plurality of split magnets constituting one rare-earth magnet; turning the sintered bodies into the split magnets by performing hot working to impart magnetic anisotropy to the sintered bodies arranged side by side in the cavity, and producing an integrated magnet in which the split magnets are integrated with each other with the lubricant interposed between the split magnets; and producing a rotor of a motor by inserting the integrated magnet into a magnet slot of the rotor.

2. The rotor production method according to claim 1, wherein the lubricant contains boron nitride.

3. The rotor production method according to claim 1, wherein a pre-forging coating thickness of the lubricant is equal to or more than 10 m.

4. The rotor production method according to claim 1, wherein each of the sintered bodies has a NdFeB-based main phase with a nanocrystalline structure, and a grain boundary phase of a NdX alloy, where X is a metal element, the grain boundary phase being present around the main phase.

5. The rotor production method according to claim 4, wherein: the NdX alloy constituting the grain boundary phase is any one of NdCo, NdFe, NdGa, NdCoFe, and NdCoFeGa, or is a mixture of at least two of NdCo, NdFe, NdGa, NdCoFe, and NdCoFeGa; and the NdX alloy is in a Nd rich state.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Features, advantages, and technical and industrial significance of exemplary embodiments of the invention will be described below with reference to the accompanying drawings, in which like numerals denote like elements, and wherein:

[0032] FIG. 1 is a perspective view illustrating a first step of a rotor production method according to an embodiment of the invention;

[0033] FIG. 2 is a perspective view illustrating a part of a second step of the rotor production method;

[0034] FIG. 3 is a perspective view illustrating another part of the second step subsequent to the part in FIG. 2;

[0035] FIG. 4 is a perspective view illustrating a third step of the rotor production method;

[0036] FIG. 5A is a photographic view illustrating two sintered bodies and a lubricant on interfaces of the sintered bodies before hot working (forging); and

[0037] FIG. 5B is a photographic view illustrating an integrated magnet after hot working.

DETAILED DESCRIPTION OF EMBODIMENTS

[0038] Hereinafter, a rotor production method according to an embodiment of the invention will be described with reference to the accompanying drawings. An integrated magnet illustrated in the drawings is formed by subjecting two sintered bodies to hot working. Alternatively, three or more sintered bodies may constitute an integrated magnet. In a rotor illustrated in the drawing, one integrated magnet forms one magnetic pole. Alternatively, two integrated magnets in a generally V-shape may form one magnetic pole.

[0039] The rotor production method according to the embodiment will be described below. FIG. 1 is a perspective view illustrating a first step of the rotor production method according to the embodiment. FIGS. 2 and 3 are perspective views sequentially illustrating a second step of the rotor production method. FIG. 4 is a perspective view illustrating a third step of the rotor production method.

[0040] First, a molding die M is provided. As illustrated in FIG. 1, the molding die M includes a die D, and an upper punch Pu and a lower punch Ps that slide inside the die D. A cavity C is defined by the die D, the upper punch Pu, and the lower punch Ps.

[0041] Two sintered bodies 1, 2 are arranged side by side and housed in the cavity C (the sintered bodies 1, 2 are housed in the cavity C in a direction X1) (first step).

[0042] The sintered bodies 1, 2 are produced by subjecting magnet powder to pressure-forming in a molding die (not illustrated) under a high temperature atmosphere of about 700 C.

[0043] A method of producing magnet powder for forming the sintered bodies 1, 2 will be described below. By a melt spinning method performed by using a single roll, a quenched thin strip (a quenched ribbon) is produced by subjecting an alloy ingot to high-frequency melting in a furnace (not illustrated) in which the pressure is reduced to 50 kPa or less, and then injecting a molten metal onto a copper roll. The molten metal has a composition that provides a rare-earth magnet. Then, the produced quenched thin strip is roughly crushed to produce the magnet powder. The particle size of the magnet powder is adjusted to be within a range from 75 m to 300 m.

[0044] The sintered bodies 1, 2 each have, for example, a NdFeB-based main phase (in which the average particle size is equal to or less than 300 nm, and the grain size is, for example, about 50 nm to 200 nm) with a nanocrystalline structure, and a grain boundary phase of a NdX alloy (where X is a metal element). The grain boundary phase is present around the main phase. The NdX alloy constituting the grain boundary phase is an alloy containing Nd and at least one of Co, Fe, Ga, and the like. The NdX alloy is, for example, any one of NdCo, NdFe, NdGa, NdCoFe, and NdCoFeGa. Alternatively, the NdX alloy is a mixture of at least two of NdCo, NdFe, NdGa, NdCoFe, and NdCoFeGa. Thus, the NdX alloy is in the Nd rich state.

[0045] Before the sintered bodies 1, 2 are housed in the cavity C, an insulating lubricant 3 is applied to a side surface of the sintered body 1, the side surface facing the sintered body 2.

[0046] The application amount of the lubricant 3 is set such that, when the sintered bodies 1, 2 are plastically deformed through forging in the molding die M, the lubricant 3 is spread all over the interfaces of both the sintered bodies 1, 2 and a predetermined coating thickness of the lubricant 3 is achieved.

[0047] A coating thickness t of the lubricant 3 in the stage in FIG. 1 before forging is set to 10 m or more. The coating thickness t is set in this manner based on the results of verification made by the present inventor. The coating thickness t is a coating thickness before forging, which ensures good insulation between two split magnets constituting the integrated magnet that is finally produced.

[0048] As the lubricant 3 having an insulating property, slurry formed by mixing boron nitride with an appropriate solvent (an organic solvent, water, or the like) is used.

[0049] After the two sintered bodies 1, 2 are arranged side by side with the lubricant 3 interposed therebetween and then housed in the cavity C, hot working (forging) is performed. Specifically, the molding die M is placed in an atmosphere with a temperature of about 600 C. to 900 C., and then the upper punch Pu and the lower punch Ps are slid in the cavity C in directions (a direction X2 and a direction X3) in which the sintered bodies 1, 2 are pushed by the upper punch Pu and the lower punch Ps, as illustrated in FIG. 2.

[0050] Hot working with a high working degree (a high compression ratio, or a high rolling reduction ratio), such as hot working with a compression ratio equal to or higher than about 10%, may be referred to as hot hard working or referred simply to as hard working. It is preferable that hot hard working with a compression ratio of 60% to 80% be performed.

[0051] After hot working is completed, as illustrated in FIG. 3, the lower punch Ps is moved upward (in a direction X4), so that a product produced through hot working comes out of the cavity C (second step).

[0052] The product is an integrated magnet 6 including split magnets 4, 5 and the insulating lubricant 3. The split magnets 4, 5 are formed by imparting magnetic anisotropy to the sintered bodies 1, 2 illustrated in FIG. 1 and plastically deforming the sintered bodies 1, 2 through forging. The insulating lubricant 3 is interposed between the interfaces of the split magnets 4, 5.

[0053] In the integrated magnet 6, the split magnets 4, 5 are lightly connected to each other to such a degree that the split magnets 4, 5 are not separated from each other during subsequent handling, instead of being firmly connected to each other.

[0054] After the integrated magnets 6 are produced, as illustrated in FIG. 4, the integrated magnets 6 are sequentially inserted into magnet slots S of a rotor R that has been already produced.

[0055] The rotor R is formed by stacking a plurality of annular magnetic steel sheets up to a predetermined height and then integrating the magnetic steel sheets by, for example, crimping. Each magnetic steel sheet has an opening Ra for a rotor shaft, and the opening Ra is at the center of the magnetic steel sheet. The number of the magnet slots S formed in the rotor R corresponds to the number of magnetic poles.

[0056] FIG. 4 illustrates a state where the integrated magnets 6 have already been inserted into and installed in five magnet slots S, and the integrated magnet 6 is going to be inserted into the remaining magnet slot S (in a direction X5).

[0057] As described above, the two split magnets 4, 5 constituting the integrated magnet 6 are connected to each other via the lubricant 3 to such a degree that the split magnets 4, 5 are not separated from each other during handling from removal of the integrated magnet 6 from the molding die M until insertion of the integrated magnet 6 into the magnet slot S.

[0058] Thus, it is possible to perform work from production of the integrated magnet 6 in the molding die M to insertion of the integrated magnet 6 into the magnet slot S of the rotor R.

[0059] In the integrated magnet 6, the split magnets 4, 5 formed by plastically deforming the two sintered bodies 1, 2 through forging performed in the molding die M are integrated with each other. Thus, the dimensional accuracy of the integrated magnet 6 is high, so that the dimensional accuracy need not be controlled as rigorously as in a production method in which two split magnets are produced independently from each other and then integrated with each other through adhesion. In the latter production method, each split magnet has its own dimensional deviation, and the dimensional deviation of the whole integrated magnet is the sum of the dimensional deviations of all the split magnets. Therefore, the dimensional accuracy of each of the split magnets needs to be rigorously controlled.

[0060] The integrated magnets 6 are inserted into and installed in all of the magnet slots S, so that the rotor R is produced (third step). In the rotor R produced in this way, all the integrated magnets 6 inserted into and installed in the magnet slots S are each constituted by the split magnets 4, 5 connected to each other with the insulating lubricant 3 interposed therebetween. Thus, the rotor R has a good eddy-current loss reduction effect.

[0061] Next, an experiment for defining a pre-forging coating thickness of a lubricant made of boron nitride and the results thereof will be described. The inventor performed an experiment for defining a pre-forging coating thickness of a lubricant made of boron nitride. In this experiment, the pre-forging coating thickness of the lubricant was set to four values, that is, 5 m, 10 m, 20 m, and 50 m. Then, each of the lubricant having a coating thickness of 5 m, the lubricant having a coating thickness of 10 m, the lubricant having a coating thickness of 20 m, and the lubricant having a coating thickness of 50 m was disposed on interfaces of two sintered bodies, and the sintered bodies were subjected to forging to produce an integrated magnet (a test piece). Then, a continuity test was performed three times on each test piece to check whether the test piece is electrically continuous. In this continuity test, CARD HiTESTER 3244 manufactured by HIOKI E. E. CORPORATION was used as a measuring device.

[0062] The dimensions of one sintered body before forging was 4 mm24 mm9 mm. Boron nitride (ABL manufactured by SHOWA DENKO) was used as the lubricant.

[0063] The two sintered bodies with the lubricant applied to their interfaces were forged under the conditions that the temperature of a molding die during forging was 780 C., the rolling reduction ratio was 67%, and the working time was 12.8 seconds. As a result, an integrated magnet having dimensions of 14.5 mm46 mm5 mm as a whole was produced.

[0064] The measurement results are indicated in Table 1. A test piece before forging and the test piece after forging are indicated in photographic views in FIG. 5A and FIG. 5B, respectively.

TABLE-US-00001 TABLE 1 Pre-forging Coating Thickness Insulating Property of Lubricant First Second Third (m) Measurement Measurement Measurement 5 Observed Not observed Observed 10 Not observed Not observed Not observed 20 Not observed Not observed Not observed 50 Not observed Not observed Not observed Not observed: Electrical continuity was not observed. Observed: Electrical continuity was observed.

[0065] As illustrated in FIG. 5B, it was confirmed that, in each of the integrated magnets after forging, the two split magnets were integrated together with the lubricant interposed therebetween and the split magnets were not separated from each other during handling.

[0066] Further, as indicated in Table 1, electrical continuity was observed when the pre-forging coating thickness of the lubricant was 5 m, whereas electrical continuity was not observed when the pre-forging coating thickness was equal to or more than 10 m.

[0067] It is understood from the measurement results that the pre-forging coating thickness of the lubricant is preferably set to 10 m or more when boron nitride is used as the lubricant.

[0068] While one embodiment of the invention has been described in detail with reference the drawings, the specific configurations are not limited to those in the foregoing embodiment, and design changes and the like within the scope of the invention are also included in the scope of the invention.