JP2006278533A - Manufacturing method of magnetic core - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a manufacturing method of a magnetic core capable of reducing costs in manufacturing (magnetic core manufacturing cost and polishing cost), without substantially requiring polishing after calcination with less deformation upon calcination even in the magnetic core having different thickness portions. <P>SOLUTION: The method can manufacture the magnetic core 2 having the thickness of a portion 12 thinner than other portions by integrally subjecting the core to press working. The method comprises a process of forming a compressed molding structure 2a by disposing a first mold 26 for forming the relatively thin portion 12, and a second mold 28 for forming relatively thick portions relatively movably in a press direction and press molding powder filled in a cavity of a mold composed of the first mold 26 and the second mold 28; and a process of calcining the compressed molding structure 2a. press forces are applied independently to the first mold 26 and the second metal 28 so that the maximum variation of density is reduced in the thin portion 12 and the thick portions in the compressed molding structure 2a. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a method of manufacturing a magnetic core used for a transformer, a choke coil, or the like.

  In recent years, various electronic devices have been demanded to be smaller, thinner, higher performance, etc., and the shape of switching power supplies, transformers, magnetic cores, etc. have been reduced in size, thickness, complexity, and high dimensional accuracy. It has been. With the downsizing, thinning, and high dimensional accuracy of magnetic cores, problems arise when manufacturing magnetic cores. For example, in a magnetic core configured such that a part of the thickness is thinner than the other part, deformation or the like is likely to occur during firing, and sufficient dimensional accuracy cannot be obtained. As a means for preventing this, it is conceivable to reduce the deformation at the time of firing by forming the core core so as to have the same thickness. However, in the case of such a means, the sintered magnetic core must be polished to form a portion that is thinner than other portions, and the manufacturing cost (magnetic core material cost, polishing cost, etc.) ) Will increase.

Specifically, the shape of the magnetic core shown in the following Patent Document 1 is known, and the frame-shaped magnetic core shown in this document is described as being less likely to be deformed during firing because of its vertical and horizontal symmetry. If an attempt is made to integrally mold including the mounting groove, deformation during firing becomes a problem.
Japanese Patent Laid-Open No. 7-230919

  The present invention has been made in view of such a situation, and even a magnetic core having a portion having a different thickness has little deformation at the time of baking, and almost no polishing is required after baking, and the cost at the time of manufacturing (magnetic core material cost, An object of the present invention is to provide a method of manufacturing a magnetic core that can reduce polishing costs and the like.

In order to achieve the above object, a method of manufacturing a magnetic core according to the present invention includes:
It is a method that can be manufactured by integrally pressing a magnetic core that is configured so that the thickness of one part is thinner than the other part,
A first mold part for forming a relatively thin part and a second mold part for forming a relatively thick part are arranged so as to be relatively movable in the pressing direction, and the first mold part Forming a compression molded body by press-molding a powder filled in a mold cavity constituted by a portion and the second mold portion;
Firing the compression molded body,
A pressing force is separately applied to the first mold part and the second mold part so that the maximum variation in density between the thin part and the thick part in the compression molded body is reduced.
In the present invention, “relatively movable” means that one of them can be fixed and the other can be moved, the other can be fixed and one can be moved, or both of these can be moved. It means that you may let them.

Preferably, the magnetic core is
An elongated rectangular ring-shaped frame core that forms a closed magnetic circuit core in combination with a rod-shaped I-shaped core having a rectangular cross section;
A pair of long side portions extending in parallel along the longitudinal direction;
A pair of short side portions arranged in parallel so as to integrally connect both ends of the long side portion, and
At the upper part of each short side portion, an attachment groove is formed in which both ends of the I-type core are detachably fitted, and the thickness of the short side portion where the attachment groove is formed is the length of the long side portion. It is configured to be thinner than the thickness.

Preferably, the maximum variation in density between the thin portion and the thick portion in the compression molded body is within 0.16 Mg / m ³ , more preferably within 0.08 Mg / m ³ , and particularly preferably 0.02 Mg / m ^3. The pressing force is separately applied to the first mold part and the second mold part so as to be within the range.

  Preferably, the polishing treatment is not performed on any surface of the fired molded body, but only a relatively thin portion of the fired molded body may be polished.

Preferably, the powder filled in the cavity of the mold is a MnZn-based ferrite material,
More preferably, the MnZn-based ferrite is
_{Fe 2 O 3: 50.0 ~ 70.0} mol% and ZnO: includes 0 ~ 30.0 mol%, the balance being substantially MnO.

  In order to achieve the above object, the inventors of the present invention have intensively studied to reduce deformation in the magnetic core after firing without performing polishing. It has been found that by molding the part so as to have a uniform density, it is possible to manufacture a magnetic core with a small deformation amount and high dimensional accuracy even after firing, and the present invention has been completed.

  According to the present invention, even a magnetic core having portions with different thicknesses can be manufactured with a high dimensional accuracy with little deformation without being polished after firing. It is possible to reduce the amount of energy, equipment, members, etc. required for polishing, and the material generated by polishing.

In the present invention, the pressing force is separately applied to the first mold portion and the second mold portion so that the maximum variation in density between the thin portion and the thick portion in the compression molded body is within 0.16 Mg / m ^3. By adding to the above, deformation after firing is within 0.20 mm at the maximum. Further, by applying a pressing force separately to the first mold part and the second mold part so that the maximum variation in density with the thick part is within 0.08 Mg / m ³ , deformation after firing can be reduced. The maximum is within 0.08 mm. Furthermore, by applying a pressing force separately to the first mold part and the second mold part so that the maximum variation in density with the thick part is within 0.02 Mg / m ³ , deformation after firing can be reduced. The maximum is within 0.01 mm.

Hereinafter, the present invention will be described based on embodiments shown in the drawings.
FIG. 1 is a perspective view of a magnetic core according to an embodiment of the present invention,
FIG. 2 is a perspective view of an I-shaped magnetic core used in combination with the magnetic core shown in FIG.
3A is a cross-sectional view of a main part of a mold for forming a compression molded body before firing in the magnetic core shown in FIG.
FIG. 3B is a partial perspective view of the mold shown in FIG.
FIG. 4 is a plan view of the compression molded body,
FIG. 5 is a schematic view showing the amount of deformation of the sintered body after firing.

  As shown in FIG. 1, a magnetic core 2 according to an embodiment of the present invention is combined with a rod-shaped I-shaped core (magnetic core) 4 having a rectangular cross section shown in FIG. 2 to form a closed magnetic circuit core. Specifically, a conducting wire is wound around the I-type core (magnetic core) 4, and both ends of the core 4 are fitted into the mounting grooves of the magnetic core 2.

  A magnetic core 2 shown in FIG. 1 has a rectangular through-hole 6 formed at the center, and is a frame core having an elongated rectangular ring shape as a whole, and a pair of parallel extending along the longitudinal direction X. It has a long side portion 8. The magnetic core 2 has a pair of short side portions 10 and 10 arranged in parallel along the width direction Y so as to integrally connect both ends of the long side portions 8 and 8 respectively.

  At the center upper part of each short side portion 10, there are formed mounting grooves 12, 12 into which both ends of the I-shaped core shown in FIG. 2 are detachably fitted, and the short side on which the mounting grooves 12, 12 are formed. The thickness of the portion 10 is made thinner than the thickness of the long side portion 8. The width w1 of the mounting groove 12 is substantially the same as or wider than the width w2 of the I-type core 4. Further, the depth d1 of the mounting groove 12 is substantially the same as or thicker than the thickness d2 of the I-type core 4.

  For this reason, the thickness (vertical direction Z) of the short side portion 10 in which the mounting groove 12 is formed is about 10 to 90% as compared with other portions (the remaining short side portion 10 and the long side portion 8). It becomes thinner.

In order to manufacture the magnetic core 2 shown in FIG. 1, a mold apparatus 20 shown in FIGS. 3A and 3B is used in the present embodiment. The mold apparatus 20 has a frame mold 22, and an intermediate rod mold 6 a shown in FIG. 3B is arranged at the center of the hollow portion 24 of the frame mold 22. The middle bar mold 6a is arranged so as to be movable in the vertical direction Z simultaneously with the frame mold 22 shown in FIG. 3A. In FIG. 3B, the frame mold 22 is not shown.
A lower punch 28 and a mounting groove forming mold 26 are arranged in the space between the middle bar mold 6 a and the frame mold 22. The lower punch 28 is fixedly arranged with respect to the mold apparatus 20. The mounting groove forming mold 26 is arranged so as to be movable in the vertical direction Z with respect to the lower punch 28.
Above these mounting groove forming mold 26 and lower punch 28, a square ring-shaped upper punch 30 is disposed so as to be movable in the vertical direction Z on the inner surface of the hollow portion 24. In the present embodiment, the space between the middle bar mold 6a and the frame mold 22 is a cavity 32 for molding the compression molded body 2a, and the middle bar mold 6a is a through hole of the compression molded body 2a. 6 is a part forming 6.

The cavity 32 of the mold apparatus 20 is prefilled with a ferrite material for forming the magnetic core 2. Although it does not specifically limit as a ferrite material, For example, a MnZn type ferrite material is used. The MnZn-based ferrite generally contains Fe ₂ O ₃ : 50.0 to 70.0 mol% and ZnO: 0 to 30.0 mol%, with the balance being substantially made of MnO 2. The average particle diameter of the ferrite material (granules) before being compression-molded is, for example, about 50 to 200 μm.

3A and 3B, the upper punch 30 is moved downward, and the ferrite material is compression-molded between the upper punch 30 and the lower punch 28 and between the upper punch 30 and the mounting groove forming mold 26. Thus, a compression molded body 2a having a shape in which the magnetic core 2 shown in FIG. 1 is turned upside down is obtained. A mold upper surface 12b for forming the mounting groove 12 shown in FIG. 1 is formed on the upper part of the mounting groove forming mold 26 shown in FIG. 3A.
When the upper punch 30 moves downward, the lower punch 28 does not move, but the mounting groove forming mold 26 moves according to the downward movement of the upper punch 30. However, the downward movement of the mounting groove forming mold 26 is not the same as the downward movement of the upper punch 30, but the pressure applied to the ferrite material positioned on the mounting groove forming mold 26 and the upper punch 28. The pressure applied to the ferrite material located at is controlled to be the same.

  The material positioned on the upper surface 12b of the mounting groove forming mold 26 is compression-molded to form a pre-firing short side portion 10a where the pre-firing mounting groove 12a is formed, and is positioned above the lower punch 28. The material to be compressed is compression-molded to form a pre-firing long side portion 8a in which the pre-firing mounting groove 12a is not formed (including the pre-firing short side portion 10a in a portion where the pre-firing mounting groove 12a is not formed). The lower punch 28 is fixedly disposed on the apparatus 20, and only the portion (groove portion) where the mounting groove forming mold 26 is disposed so as to be movable downward is subjected to pressure control separately from the other portions. It is possible to separately control the pressing force at the time of compression molding in the other portions.

In this embodiment, the density of the thin part (part in which the attachment groove 12 shown in FIG. 1 is formed) and the thick part (the long side part 8 shown in FIG. 1) in the compression-molded body molded by the mold apparatus 20. The upper punch 30 is moved, the lower punch 28 is fixed, and the mounting groove forming mold 26 is moved with respect to the lower punch 28 so that the maximum variation of the portion is 0.16 Mg / m ^{3 or} less. The pressing force can be controlled separately. Then, the upper punch 30 and the mounting groove are set so that the pressure applied to the ferrite material positioned on the mounting groove forming mold 26 is the same as the pressure applied to the ferrite material positioned on the lower punch 28. The movement of the forming mold 26 is controlled. As a result, pressure is uniformly applied to each part of the compression molded body.

  The compression molded body 2a thus obtained is then subjected to binder removal processing as necessary, and then fired. The binder removal condition and the firing condition are determined by the material of the ferrite constituting the compression molded body 2a. During firing, zirconium oxide or the like having an average particle diameter of about 100 to 200 μm is sprayed on the firing jig to promote slipping during the shrinking process (reducing friction with the firing jig). Then, a plurality of compression-molded bodies are placed thereon and fired.

In this embodiment, a pressing force is separately applied to the lower punch 28 and the mounting groove forming mold 26 with respect to the upper punch 30 so that the maximum density variation is within 0.16 Mg / m ³ (the lower punch 28 is In other words, the deformation of the molded body after firing is at most 0.20 mm.

Further, by applying a pressing force so that the maximum variation in density with the thick portion is within 0.08 Mg / m ³ , the deformation after firing is within 0.08 mm at the maximum. Furthermore, by applying a pressing force such that the maximum variation in density with the thick portion is within 0.02 Mg / m ³ , the deformation after firing is within 0.01 mm at the maximum.

  Therefore, in the method according to the present embodiment, the magnetic core 2 having high dimensional accuracy with little deformation can be manufactured without polishing after firing. Therefore, the amount of magnetic core material can be reduced by eliminating the need for polishing, and the energy required for polishing can be reduced. It is possible to reduce the number of equipment / members and materials generated by polishing.

The present invention is not limited to the above-described embodiment, and can be variously modified within the scope of the present invention.
For example, depending on the state of use in a transformer or the like, the surface of the mounting groove 12 shown in FIG. 1 may require surface accuracy and must be polished. However, the purpose of polishing in this case is different from that for forming the mounting groove.

  Hereinafter, although this invention is demonstrated based on a more detailed Example, this invention is not limited to these Examples.

Example 1

In the present invention, MnZn-based ferrite was used as the magnetic core. Fe ₂ O ₃ , Mn ₃ O ₄ and ZnO were used as starting materials for the main component, and other subcomponents were contained.

  The starting materials were weighed, wet-mixed, dried, and calcined at 900 ° C. for 2 hours in the air. Subcomponents were added to the calcined product obtained in this manner and mixed by pulverization. After mixing, an appropriate binder such as polyvinyl alcohol was added and granulated with a spray dryer or the like to obtain granules having an average particle size of 50 to 200 μm. Next, this granule was filled in the cavity of the mold apparatus 20 shown in FIG. 3A, and compression molded into the shape shown in FIG.

  Further, the obtained compression molded body 2a was fired at about 1250 to 1400 ° C. in an atmosphere in which the oxygen concentration was controlled to obtain a sintered magnetic core 2 shown in FIG. During firing, powder such as zirconium oxide having an average particle diameter of about 100 to 200 μm was sprayed on the firing jig, and a compression-molded magnetic core was placed thereon.

  Table 1 shows the compact density of each part of the magnetic core and the deformation amount of the sintered body. As shown in FIG. 5, the deformation amount of the sintered body was measured by measuring the end dimensions A1 and A2 in the width direction Y of the end in the longitudinal direction X of the magnetic core, and the smaller value among them was Amin. And this Amin. And the difference B-Amin. Represents.

  In Table 1, the difference in the molded body density (maximum variation in density) indicates the density of each part of the compression molding 2a after press molding using the mold apparatus 20 shown in FIG. 3A, as shown in FIG. The magnetic core is divided into 8 parts, and the difference between the maximum value and the minimum value of the density measured in each part is shown.

As shown in Table 1, it is possible to reduce the amount of deformation of the sintered body by reducing the difference in the density of the compacts in each part of the magnetic core, and a high dimensional accuracy magnetic core with little deformation without polishing after firing. It was confirmed that can be manufactured. The difference in the green density of the magnetic core each part, from the results in Table 1, preferably, 0.16 mg / ^{m 3} within, more preferably, 0.08 mg / ^{m 3} within, and particularly preferably, 0.02 mg / ^{m 3} It was confirmed that the deformation after firing was within 0.20 mm, within 0.08 mm, and particularly within 0.01 mm.

FIG. 1 is a perspective view of a magnetic core according to an embodiment of the present invention. FIG. 2 is a perspective view of an I-shaped magnetic core used in combination with the magnetic core shown in FIG. 3A is a cross-sectional view of a main part of a mold for forming a compression molded body before firing in the magnetic core shown in FIG. FIG. 3B is a partial perspective view of the mold shown in FIG. 3A. FIG. 4 is a plan view of the compression molded body. FIG. 5 is a schematic view showing the amount of deformation of the sintered body after firing.

Explanation of symbols

DESCRIPTION OF SYMBOLS 2 ... Magnetic core 2a ... Compression molding 4 ... I-shaped magnetic core 8 ... Long side part 8a ... Long side part before baking 10 ... Short side part 10a ... Short side part before baking 12 ... Mounting groove 12a ... Mounting groove before baking 20 ... Gold Mold device 22 ... Frame die 24 ... Hollow portion 26 ... Mounting groove forming die 28 ... Lower punch 30 ... Upper punch 32 ... Cavity

Claims (8)

It is a method that can be manufactured by integrally pressing a magnetic core that is configured so that the thickness of one part is thinner than the other part,
A first mold part for forming a relatively thin part and a second mold part for forming a relatively thick part are arranged so as to be relatively movable in the pressing direction, and the first mold part Forming a compression molded body by press-molding a powder filled in a mold cavity constituted by a portion and the second mold portion;
Firing the compression molded body,
A magnetic core characterized in that a pressing force is separately applied to the first mold part and the second mold part so that the maximum variation in density between the thin part and the thick part in the compression molded body is reduced. Manufacturing method. The magnetic core is
An elongated rectangular ring-shaped frame core that forms a closed magnetic circuit core in combination with a rod-shaped I-shaped core having a rectangular cross section;
A pair of long side portions extending in parallel along the longitudinal direction;
A pair of short side portions arranged in parallel so as to integrally connect both ends of the long side portion, and
At the upper part of each of the short side portions, there is formed a mounting groove in which both ends of the I-shaped core are detachably fitted, and the thickness of the short side portion where the mounting groove is formed is the length of the long side portion. 2. The method of manufacturing a magnetic core according to claim 1, wherein the magnetic core is made thinner than the thickness. The pressing force is separately applied to the first mold part and the second mold part so that the maximum variation in density between the thin part and the thick part in the compression molded body is within 0.16 Mg / m ^3. The method of manufacturing a magnetic core according to claim 1, wherein the magnetic core is added. Press force is separately applied to the first mold part and the second mold part so that the maximum variation in density between the thin part and the thick part in the compression molded body is within 0.08 Mg / m ^3. The method of manufacturing a magnetic core according to claim 3, wherein the magnetic core is added.   The method for manufacturing a magnetic core according to claim 1, wherein no polishing treatment is performed on any surface of the sintered magnetic core.   The method for manufacturing a magnetic core according to any one of claims 1 to 4, wherein a polishing process is performed only on a relatively thin portion of the magnetic core after firing.   The method of manufacturing a magnetic core according to claim 1, wherein the powder filled in the cavity of the mold is a MnZn-based ferrite material. The MnZn ferrite is
The method for producing a magnetic core according to claim 7, comprising Fe ₂ O ₃ : 50.0 to 70.0 mol% and ZnO: 0 to 30.0 mol%, with the balance being substantially composed of MnO 3.

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