Method for manufacturing magnetic composite materials

Abstract

This invention provides a method for manufacturing magnetic composite materials that can increase density by reducing the voids between magnetic material particles contained within the magnetic composite material. [Solution] A first compression step P1 is performed in which a pressing member is moved in a straight line to apply a compressive load L to the mixture filled in the storage section until a preset intermediate load Lm is reached. Following the first compression step P1, a torsional operation step T is performed in which at least one of the pressing member and the shaft-shaped member is rotated back and forth at least once within a set angular range around the axis while maintaining the intermediate load Lm. A second compression step P2 is performed in which a target load Lt, which is higher than the intermediate load Lm, is applied to the mixture by moving the pressing member in a straight line.

Description

[Technical Field]

[0001] The present invention relates to a method for producing a magnetic composite material. [Background Art]

[0002] Patent Document 1 describes, as a method for producing a magnetic composite material, a production method in which a mixture of a particulate magnetic material and a binder is compression-molded at a set press pressure, and also describes a process of rotating and reversing a punch during the compression molding. [Prior Art Literature] [Patent Literature]

[0003] [Patent Document 1] Japanese Patent Laid-Open Publication No. 2001-35714 [Summary of the Invention] [Problem to be Solved by the Invention]

[0004] It is known that for magnetic composite materials (including not only magnets (hard magnetic materials) but also soft magnetic materials such as cores), increasing the pressure applied to a mixture of a particulate magnetic material and a binder during compression molding can increase the density of the magnetic material contained in a magnetic component, increase the magnetic flux density of the magnetic composite material in a magnetized state or an excited state, and improve the performance as a magnetic component.

[0005] For example, in an apparatus where a housing portion is formed inside a cylindrical die and upper and lower punches are provided to sandwich the housing portion, simply increasing the pressure applied from the upper and lower punches has a limit in increasing the density of the magnetic material. Further, even in the apparatus that rotates and reverses the punch during pressing as described in Patent Document 1, there is still a limit to the increase in density.

[0006] In other words, simply increasing the pressure applied to the mixture filled in the containment unit would cause many of the magnetic material particles in the mixture to become tightly packed, but there was a limit to how much the gaps between the particles could be reduced, and therefore a limit to how much the density could be increased.

[0007] For these reasons, there is a need for a method of manufacturing magnetic composite materials that can increase density by reducing the voids between the magnetic material particles contained in the magnetic composite material. [Means for solving the problem]

[0008] The characteristic configuration of the method for manufacturing a magnetic composite material according to the present invention is a method for manufacturing a magnetic composite material in which a compressive load is applied from a pressing member to a mixture of particulate magnetic material and a binder filled in a mold housing to form the mixture, wherein the method comprises: a first compression step in which the pressing member is moved in a straight line to apply a compressive load to the mixture filled in the housing until a preset intermediate load is reached; a torsional operation step following the first compression step in which, while maintaining the intermediate load, at least one of the pressing member and an axial member positioned opposite the pressing member with the mixture filled in the housing in between is rotated back and forth at least once within a set angular range, with the pressing member and the intermediate load being sandwiched between the pressing member and the intermediate load being maintained; and a second compression step in which the straight line operation of the pressing member is used to apply a target load to the mixture that is higher than the intermediate load.

[0009] According to this configuration, a mixture of particulate magnetic material and binder is filled into the housing of the mold, and in the first compression step, an intermediate load is applied to the mixture filled into the housing of the mold by the straight-line movement of the pressing member, thereby increasing the density of the mixture filled into the housing. Next, in the twisting step, at least one of the pressing member and the shaft-shaped member is rotated back and forth at least once around its axis while maintaining the intermediate load acting on the mixture. This allows a portion of the mixture filled into the housing to flow, and some of the flowing magnetic material particles can be fitted into the gaps between the magnetic material particles. Therefore, the density of the mixture can be increased. Furthermore, in the second compression step, by increasing the load to a target load higher than the intermediate load, it is possible to further increase the density of the magnetic material contained in the mixture. Thus, a method for manufacturing a magnetic composite material that can increase the density by reducing the gaps between the magnetic material particles contained in the magnetic composite material has been realized. [Brief explanation of the drawing]

[0010] [Figure 1] This diagram shows an overview of the configuration of a molding unit used to manufacture magnetic composite materials. [Figure 2] This is a flowchart showing the steps involved in the manufacturing method of magnetic composite materials. [Figure 3] This graph shows the relationship between the stroke amount of the upper punch and the compression load during the first compression process, the torsional action process, and the second compression process. [Figure 4] This diagram schematically illustrates the relationship between magnetic material particles and the voids between them. [Figure 5] This is a list of analytical photographs showing the state of plastic strain generated in magnetic material particles when the upper punch operates differently under two different pressures during the compression of a mixture. [Figure 6] This graph shows the relationship between different pressure application methods and the density of the molded body. [Figure 7] This graph shows the relationship between the stroke amount of the upper punch and the compressive load in each of the two types of pressurization configurations. [Figure 8] This graph shows the relationship between the stroke amount of the upper punch and the compressive load in a pressurized configuration with multiple intermediate loads set in another embodiment (a). [Figure 9] This graph shows the relationship between the stroke amount of the upper punch and the torque acting on the upper punch when multiple intermediate loads are applied, as in another embodiment (a). [Figure 10] This figure shows an overview of the configuration of a molding unit for manufacturing a magnetic composite material according to another embodiment (b). [Modes for carrying out the invention]

[0011] The following describes embodiments of the method for manufacturing a magnetic composite material according to the present invention, based on the drawings. The present invention is not limited to the following embodiments, and various modifications are possible without departing from the spirit of the invention. The magnetic composite material includes not only magnets (hard magnetic materials) but also soft magnetic materials such as cores.

[0012] [Configuration of the molding unit] As shown in Figure 1, the forming unit A comprises a cylindrical mold 1, an axial upper punch 2 (pressing member / example of a first punch) and an axial lower punch 3 (axial member / example of a second punch) inserted into the cylindrical space of the mold 1, a press operating unit 4 that moves the upper punch 2 (first punch) in a straight line, and a torsional operating unit 5 that reciprocates the lower punch 3 (second punch) around the axis X. In this forming unit A, high-strength materials such as steel are used for the mold 1, the upper punch 2, and the lower punch 3.

[0013] Furthermore, the molding unit A can be configured to torsionally actuate the upper punch 2 and linearly actuate the lower punch 3. In this configuration, the lower punch 3 corresponds to the pressing member (first punch), and the upper punch 2 corresponds to the shaft-shaped member (second punch). Alternatively, the molding unit A can also be configured such that one of the upper punch 2 and the lower punch 3 performs linear operation and torsional operation, and the other is fixed to the die 1. In this configuration, of the upper punch 2 and the lower punch 3, the one that performs linear operation corresponds to the pressing member, and the other corresponds to the shaft-shaped member.

[0014] In the molding unit A, when the center line of the cylindrical space in the die 1 is defined as the axis X, the central axis of the upper punch 2 and the central axis of the lower punch 3 are arranged coaxially with the axis X. The molding unit A enables the upper punch 2 to linearly move along the axis X, and allows the lower punch 3 to reciprocally rotate around the axis X.

[0015] In this molding unit A, the lower end portion of the upper punch 2 and the upper end portion of the lower punch 3 are inserted into the cylindrical space of the die 1. Accordingly, in the cylindrical space of the die 1, the accommodating portion 1s is formed in a region sandwiched between the upper punch 2 and the lower punch 3 in the molding unit A. The accommodating portion 1s functions as a pressurizing space, and is filled with a mixture C of a magnetic material Mp and a resin which will be described later.

[0016] The press operating unit 4 is configured as a mechanism that linearly moves the upper punch 2 along the axis X, and realizes adjustment of the load acting on the mixture C from the upper punch 2. Further, the torsional operating unit 5 is configured as a mechanism that torsionally operates the lower punch 3 around the axis X, and realizes torsional operation within a set angle range at any timing.

[0017] In the molding unit A shown in Fig. 1, the die 1, the upper punch 2 and the lower punch 3 are arranged such that the axis X extends along the vertical direction, but the molding unit A can also be used in any posture.

[0018] This molding unit A fills a housing portion 1s with a mixture C obtained by mixing particulate magnetic material Mp having a particle diameter of about several micrometers (see FIG. 4) and a resin (such as epoxy resin) at a predetermined ratio, and achieves compression molding of the mixture C through the operation of an upper punch 2 in the compression direction. The diameter D of the housing portion 1s can be any value, for example, 9 mm. The diameters of the upper punch 2 and the lower punch 3, which are arranged in a fitted state with respect to the housing portion 1s, are also substantially equal to the diameter D of the housing portion 1s.

[0019] Samarium iron nitrogen (SmFeN) is assumed as the magnetic material Mp, but for example, the use of neodymium iron boron (NdFeB)-based, samarium cobalt (SmCo)-based, or alnico-based materials is also conceivable.

[0020] The molding unit A can apply a compressive load L to the mixture C to increase the density of the particulate magnetic material Mp contained in the mixture C. Specifically, in the molding unit A of the present embodiment, with the lower punch 3 arranged at the position shown in FIG. 1 with respect to the die 1 (the position where the lower end of the lower punch 3 is flush with the lower end of the die 1), the driving force of a press operation unit 4 causes the upper punch 2 to move straight downward along the axis X, whereby a compressive load L (see FIG. 3) is applied to the mixture C, and the density of the particulate magnetic material Mp (see FIG. 4) can be increased.

[0021] Further, the molding unit A applies a torsional force to the mixture C by a torsional operation in which the driving force of a torsional operation unit 5 causes the lower punch 3 to rotate reciprocatingly around the axis X. In this torsional operation, a plurality of grooves or a plurality of uneven portions are formed on the lower end surface 2a of the upper punch 2 and the upper end surface 3a of the lower punch 3 so that the rotational operation of the upper punch 2 can efficiently act on the mixture C.

[0022] [Method for Producing Magnetic Composite Material] The process of producing a magnetic composite material using the molding unit A is referred to as the "method for producing a magnetic composite material", and a flowchart of this production method is shown in FIG. 2.

[0023] In this manufacturing method, a mixture C is created by mixing particulate magnetic material Mp (see Figure 4) and a resin (such as epoxy resin) in a predetermined ratio, and this mixture C is then filled into a containment section 1s (pressurized space) (steps #01 and #02).

[0024] In the next step, #03, the mixture C is molded. In this molding process, (a) the first compression step P1, (b) the torsional operation step T, and (c) the second compression step P2 are performed in this order. In other words, in this molding process, an intermediate load Lm is applied to the mixture C by the linear movement of the upper punch 2 (first compression step P1), and then a torsional operation is performed in which the lower punch 3 is reciprocated around the axis X while maintaining the intermediate load Lm (torsional operation step T). After this, the compression load L is increased on the mixture C by the linear movement of the upper punch 2 until the target load Lt is reached (second compression step P2). The relationship between the stroke amount S of the upper punch 2 and the compression load L in this manufacturing method is shown as the third characteristic line C3 in the graph of Figure 3. This third characteristic line C3 represents the process by the manufacturing method of the magnetic composite material described in the embodiment. Details of this molding process (#03 step) will be described later. The mixture C molded by pressurization is sometimes referred to as a molded body.

[0025] In particular, in the graph of Figure 3, the first characteristic line C1 shows the relationship between stroke amount and compressive load when the compressive load L is increased on the mixture C until the target load Lt is reached by the linear motion of the upper punch 2, for comparison with the present manufacturing method (manufacturing method for magnetic composite material). Similarly, for comparison with the present manufacturing method, the second characteristic line C2 shows the relationship between stroke amount and compressive load when the compressive load L is increased on the mixture C until the target load Lt is reached by performing a torsional motion in which the lower punch 3 is reciprocated around the axis X simultaneously with the linear motion of the upper punch 2.

[0026] Next, the molded mixture C is removed from the container 1s, heat-treated (step #04), and then post-processed (step #05). The post-processing also includes magnetization at the required timing, and this magnetization completes the magnetic composite material.

[0027] [Manufacturing method for magnetic composite materials: #03 Step details] (a) In the first compression step P1, as shown by the third characteristic line C3 in Figure 3, the upper punch 2 is driven in a straight line downward along the axis X by the driving force of the press operating unit 4, and the load acting on the mixture C is increased to an intermediate load Lm. This intermediate load Lm is set to 20% or less of the target load Lt shown in Figure 3.

[0028] (b) In the torsional operation process T, the load acting on the mixture C is maintained at an intermediate load Lm, and the lower punch 3 is rotated back and forth a set number of times around the axis X by the driving force from the torsional operation unit 5.

[0029] In the torsional operation process T of this embodiment, a reciprocating rotation is repeatedly performed in which the torsional angle reaches +5° due to a torsional operation in the positive direction from a reference rotational position, and then reaches -5° due to a torsional operation in the negative direction. The range between +5° and -5° is the set angle range. In this embodiment, this torsional operation is performed multiple times by repeatedly moving the lower punch 3 in both forward and reverse directions, but it may also be performed only once (one reciprocating operation).

[0030] Torsional action can be performed at any rotational speed, but it is best to perform it at a rotational speed of, for example, around 1 rpm.

[0031] If only the first compression step P1 is performed, in which an intermediate load Lm is applied to the mixture C by the straight-line movement of the upper punch 2, relatively large voids v exist between the particles of the magnetic material Mp that constitute the mixture C, as shown in Figure 4. Therefore, in this manufacturing method, a torsional action step T is performed. By performing the torsional action step T, a twist is applied to the particles of the magnetic material Mp while maintaining the load as the intermediate load Lm, so that the relative positions of the many particles of magnetic material Mp change so that they flow laterally (for example, in the direction indicated by the arrow in the same figure). Due to this change in the positions of the particles of magnetic material Mp, some of the particles of magnetic material Mp near the voids v become embedded in the voids v, reducing the size of the voids v and increasing the density of the mixture C.

[0032] In other words, when a predetermined compressive load L is applied to the particles of magnetic material Mp, relatively large voids v exist between the particles of magnetic material Mp. In this situation where relatively large voids v are created between the particles of magnetic material Mp, when the particles are in close contact, the particles of magnetic material Mp in the areas where they are in close contact are solidified and have low fluidity. In contrast, in areas where voids v exist between the particles, the particles of magnetic material Mp in the areas surrounding the voids v have fluidity. Therefore, by performing a torsional operation process T, the particles of magnetic material Mp move in a flowing manner, and some of the moving particles of magnetic material Mp fit into the voids v, thereby increasing the density of the mixture C.

[0033] The phenomenon in which some of the particles of the magnetic material Mp flow into the void v by performing the torsional action process T is desirable because it suppresses situations where an excessive load is acting on the particles of the magnetic material Mp in the compressive direction, and it is desirable that an appropriate load is applied. For this reason, in this embodiment, the intermediate load Lm during the torsional action process T is set to 20% or less of the target load Lt.

[0034] Furthermore, in the torsional operation process T, in order to maintain the intermediate load Lm, the upper punch 2 operates slightly in the compression direction as the density of the mixture C increases.

[0035] (c) In the second compression step P2, with the reciprocating rotation stopped, the upper punch 2 is driven in a straight line by the driving force from the press operating unit 4, and the compression load L is increased on the mixture C until the target load Lt is reached.

[0036] In other words, even after the torsional action process T is performed, the compressive load L acting on the mixture C is maintained at an intermediate load Lm, so there are regions where the particles of the magnetic material Mp are slightly separated from each other. Therefore, by increasing the compressive load L acting on the mixture C from the intermediate load Lm to the target load Lt, the particles in the regions where the particles of the magnetic material Mp were separated due to this pressure increase are brought into contact with each other, thereby achieving a further increase in the density of the mixture C.

[0037] In particular, the first feature line C1, the second feature line C2, and the third feature line C3 in the graph of Figure 3 indicate that the stroke amount of the upper punch 2 when the compressive load L reaches the target load Lt is largest in the order of the first feature line C1, the second feature line C2, and the third feature line C3. This stroke amount correlates with the density of the press-formed mixture C (molded body), with a larger stroke amount resulting in a higher density of the molded body. Therefore, it can be understood that the mixture C formed according to the process of the third feature line C3 has the highest density.

[0038] The higher the density of the magnetic material, the higher the magnetic flux density after magnetization or during excitation. Therefore, by molding mixture C according to this manufacturing method, which includes (a) a first compression step P1, (b) a torsional action step T, and (c) a second compression step P2, it is possible to obtain a high-performance magnetic composite material.

[0039] [Plastic deformation] Taking the example of applying a compressive load L to a mixture C using the molding unit A shown in Figure 1, it has been confirmed that in multiple configurations in which a mixture C of particulate magnetic material Mp and resin is filled into a housing 1s and a compressive load L is applied from the upper punch 2, plastic strain is induced in the particles of magnetic material Mp at a predetermined ratio after the load is applied. This plastic strain is difficult to explain simply by the load alone, and it is necessary to consider the effect of reciprocating rotation in order to explain it.

[0040] This plastic strain alters the properties of the magnetic material Mp, leading to a decrease in coercivity and ultimately a degradation in the performance of the magnetized or excited magnetic composite material.

[0041] Figure 5 shows a list of magnified analytical photographs of the mixture C after pressurization in each of the following pressurization configurations: when a mixture C of particulate magnetic material Mp and resin is filled into the housing 1s and two surface pressures, 300 MPa and 1000 MPa, are applied as molding surface pressures, the upper punch 2 is in "straight-line operation", the lower punch 3 is in "one-way rotation", the lower punch 3 is in "reciprocating rotation (±5°)" around the axis X, and the lower punch 3 is in "reciprocating rotation (±15°)" around the axis X.

[0042] Specifically, the analysis focused on the portion of the molded body produced using molding unit A, where approximately 0.1 mm of the outer circumference was removed near the lower punch 3, exposing the surface. In the analysis photograph shown in Figure 5, the particles of the magnetic material Mp are shown in gray, and the regions where plastic strain occurred within these particles are shown in a lighter gray than the particle gray.

[0043] In other words, as shown in Figure 5, in both cases where the molding surface pressure is 300 MPa and 1000 MPa, the area where plastic strain occurs (the area of ​​lighter gray than the particle gray) is larger in the pressurizing configuration where the lower punch 3 is "rotated in one direction" (the left and right photographs in the second row from the top of the figure) compared to the pressurizing configuration where the upper punch 2 is "operated in a straight line" without rotating the lower punch 3.

[0044] In contrast, when observing the pressurized state in which the lower punch 3 is "reciprocated (±5°)" (the left and right photos in the third row from the top of the figure) and the pressurized state in which the lower punch 3 is "reciprocated (±15°)" (the left and right photos in the bottom row of the figure), it can be confirmed that the pressurized state with "reciprocated (±5°)" reduces the region in the magnetic material Mp that undergoes plastic strain compared to the pressurized state with "reciprocated (±15°)".

[0045] From this, it can be seen that if the angular range of the reciprocating rotation of the upper punch 2 in the torsional operation process T is too high, plastic strain is likely to occur in the magnetic material Mp. Therefore, in this embodiment, the angular range of the reciprocating rotation of the lower punch 3 in the torsional operation process is set to ±5°.

[0046] Figure 6 shows the relationship between the density of the molded body (the density of mixture C molded by pressurization) and the pressurization method, which was determined experimentally. In the figure, from left to right, the densities of molded bodies produced under each pressurization method are shown: "linear operation" where the upper punch 2 moves in a straight line without rotating the lower punch 3; "unidirectional rotation" where the lower punch 3 rotates in one direction; "constant speed compression + reciprocating rotation ±5°" where the lower punch 3 is reciprocated within an angular range of ±5° while the pressure is increased at a constant speed; and "constant speed compression + reciprocating rotation ±15°" where the lower punch 3 is reciprocated within an angular range of ±15° while the pressure is increased at a constant speed.

[0047] The density of molded bodies produced by these four pressure modes is lowest for "linear operation" and highest for "constant speed compression + reciprocating rotation ±15°".

[0048] Furthermore, Figure 6 shows the density of molded bodies produced using three pressure configurations corresponding to this manufacturing method, in addition to the four pressure configurations already described. Specifically, it shows the density of molded bodies produced using three pressure configurations, each with a modified pressure configuration in the torsional operation process: "pressure maintained at 50 MPa + reciprocating rotation ±5°", "pressure maintained at 150 MPa + reciprocating rotation ±5°", and "pressure maintained at 50 MPa and 150 MPa + reciprocating rotation ±5°".

[0049] "Maintaining pressure at 50 MPa + reciprocating rotation ±5°" is a pressurization method in which, during the torsional operation, the compressive load is temporarily maintained so that the surface pressure is 50 MPa, and the lower punch 3 is reciprocated within an angular range of ±5°. "Maintaining pressure at 150 MPa + reciprocating rotation ±5°" is a pressurization method in which, during the torsional operation, the compressive load is temporarily maintained so that the surface pressure is 150 MPa, and the lower punch 3 is reciprocated within an angular range of ±5°. Furthermore, "Maintaining pressure at 50 MPa and 150 MPa + reciprocating rotation ±5°" is a pressurization method in which, during the torsional operation, the compressive load is temporarily maintained so that the surface pressure is 50 MPa, the lower punch 3 is reciprocated within an angular range of ±5°, and then the compressive load is temporarily maintained so that the surface pressure is 150 MPa, and the lower punch 3 is reciprocated within an angular range of ±5°.

[0050] As can be seen from Figure 6, all three pressurization methods result in a higher density of the molded body than the "linear operation," "unidirectional rotation," "constant speed compression + reciprocating rotation ±5°," and "constant speed compression + reciprocating rotation ±15°" methods. From this, it can be understood that, as a method of pressurizing mixture C, it is effective to temporarily stop the pressure increase during the pressure-raising process and reciprocate the lower punch 3 within an angular range of ±5°. In other words, it can be understood that performing a torsional operation is effective in increasing the density of the molded body.

[0051] Furthermore, comparing the pressurization methods of "maintaining pressure at 50 MPa + reciprocating rotation ±5°", "maintaining pressure at 150 MPa + reciprocating rotation ±5°", and "maintaining pressure at 50 MPa and 150 MPa + reciprocating rotation ±5°", the density of the molded body is highest in the case of "maintaining pressure at 50 MPa + reciprocating rotation ±5°". From this, it can be seen that it is preferable to perform a torsional operation process only once during compression molding, and in particular, it is preferable to perform the torsional operation process in the initial stage of compression molding. In particular, in the experiment shown in Figure 6, when the surface pressure is maintained at 50 MPa, the compressive load is maintained at 3.2 kN, and the compressive load is set to 19.1 kN so that the surface pressure is finally 300 MPa. Therefore, it can be seen that it is preferable that the load maintained in the torsional operation process is 20% or less of the target load.

[0052] Furthermore, Figure 6 shows the density of molded bodies produced using three additional pressure configurations related to this manufacturing method, in addition to the seven pressure configurations already described (the three on the far right in the horizontal direction). Specifically, it shows the density of molded bodies produced using three different pressure configurations: "pressure maintained at 50 MPa + reciprocating rotation ±15°", "pressure maintained at 150 MPa + reciprocating rotation ±15°", and "pressure maintained at 50 MPa and 150 MPa + reciprocating rotation ±15°", which are variations in the pressure configuration during the torsional operation process.

[0053] Thus, the three pressure configurations on the far right in the horizontal direction have a twist angle of ±15° around the axis X of the lower punch 3 during the twisting operation process T. These three pressure configurations differ from the three pressure configurations adjacent to them on the left side in the horizontal direction in that the twist angle of the twisting operation process T is set to ±15°.

[0054] As can be seen from Figure 6, among the molded bodies produced using the three pressure settings on the far right in the horizontal axis direction, the density of the molded body produced using the "pressure maintained at 50 MPa + reciprocating rotation ±15°" pressure setting is the highest. Following this, the density of the molded bodies decreases in the order of "pressure maintained at 150 MPa + reciprocating rotation ±15°" and "pressure maintained at 50 MPa and 150 MPa + reciprocating rotation ±15°". Furthermore, when comparing pressure settings with the same maintained pressure, the density of the molded bodies is higher for the pressure setting with a torsional angle of ±15° in the torsional operation process T than for the pressure setting with a torsional angle of ±5°.

[0055] According to this experiment, molded bodies produced with a torsion angle of ±5° showed relatively few cracks and chips, while molded bodies produced with a torsion angle of ±15° showed shear and cracks in the upper and lower uneven surfaces. In order to efficiently apply torsional force to mixture C, multiple grooves and multiple uneven surfaces are formed on the lower end surface 2a of the upper punch 2 and the upper end surface 3a of the lower punch 3, resulting in the formation of uneven surfaces on the upper and lower surfaces of the molded bodies. Therefore, it is inferred from the experiment that molded bodies produced with a torsion angle of ±15° show shear connected to the upper and lower uneven surfaces, as well as cracks in the horizontal direction (direction intersecting the axis X).

[0056] These experimental results indicate that setting the torsion angle to ±15° makes it possible to increase the density of the molded body compared to setting the torsion angle to ±5°. However, the molded body produced with a torsion angle of ±15° exhibits shear and horizontal cracks, resulting in low quality and making it unsuitable as a material for magnetic composites. This suggests that if the angular range of the reciprocating rotation of the upper punch 2 in the torsion operation process T is too high, the quality of the molded body tends to deteriorate. Therefore, in this embodiment, as explained in the section on [plastic strain], the angular range of the reciprocating rotation of the upper punch 2 in the torsion operation process T is set to ±5°.

[0057] Figure 7 shows two graphs for different holding pressure conditions, illustrating the relationship between the stroke amount S of the upper punch 2 and the compressive load L in a pressurizing configuration of "pressure maintenance + reciprocating rotation ±5°". The solid line in this graph shows the change in stroke amount S (corresponding to density) when the pressure (surface pressure) applied to the mixture C is increased to 150 MPa, the pressure (surface pressure) is maintained, the lower punch 3 is reciprocated within an angular range of ±5°, and then the pressure (surface pressure) is increased to 300 MPa.

[0058] Furthermore, the dashed line in this graph shows the change in stroke length S (corresponding to density) when the pressure (surface pressure) applied to mixture C is increased to 50 MPa, the lower punch 3 is rotated back and forth within an angular range of ±5° while maintaining the pressure (surface pressure), and then the pressure (surface pressure) is increased to 300 MPa.

[0059] As shown in Figure 7, when the surface pressure is maintained at 50 MPa, the stroke amount S is larger by the stroke difference St compared to when the surface pressure is maintained at 150 MPa, resulting in a higher density of the molded body. This also shows that performing the torsional operation process in the initial stage when the compressive load is small results in a higher density of the molded body.

[0060] [Application of a magnetic field] In the manufacturing method of the magnetic composite material, during the molding process in step #03 of Figure 2, an external orientation magnetic field is applied to the mixture C in at least one of the following steps: the first compression step P1, the torsional operation step T, and the second compression step P2.

[0061] Furthermore, the process of applying an external orientation magnetic field to mixture C may be performed in all steps: the first compression step P1, the torsional operation step T, and the second compression step P2. Alternatively, the process of applying an external orientation magnetic field to mixture C may be performed in at least one of the first compression step P1 and the torsional operation step T.

[0062] The process of applying an externally oriented magnetic field to mixture C may be performed before, during, or after step #03 in Figure 2. However, when performing the molding in step #03, it is preferable to perform it in one of the three steps: the first compression step P1, the torsional operation step T, and the second compression step P2.

[0063] Furthermore, it is desirable to apply an external orientation magnetic field to the mixture C as early as possible. For example, this could be done only in the first compression step P1, only in the torsional action step T, or from the first compression step P1 to the torsional action step T.

[0064] [Effects of the Embodiment] In this way, a mixture C of particulate magnetic material Mp and binder is filled into the housing section 1s of the mold 1, and in the first compression step P1, the upper punch 2 is operated in a straight line to apply an intermediate load Lm, thereby increasing the density of the mixture C to an appropriate value. Next, in the torsional operation step T, the lower punch 3 is twisted (reciprocating rotation) while maintaining this intermediate load Lm, thereby actively flowing the mixture C and creating a state in which some of the particles of magnetic material Mp fit into the voids v between the particles of magnetic material Mp, thereby increasing the density of the mixture C. In order to flow the mixture C by the twisting operation (reciprocating rotation) of the lower punch 3, it is desirable that the value of the intermediate load Lm is a value that enables the flow of the particles of mixture C. For this reason, during compression molding, the torsional operation step is performed in the initial stage when the compression load is sufficiently small compared to the target load. Specifically, the intermediate load Lm in the torsional operation step is set to 20% or less of the target load Lt.

[0065] Furthermore, in the subsequent second compression step P2, the upper punch 2 is operated in a straight line to apply a target load Lt that is higher than the intermediate load Lm, thereby reducing the gaps between the particles of the magnetic material Mp in the mixture C and increasing its density.

[0066] Experiments investigating the relationship between the density of molded bodies produced by multiple pressure modes have shown that molded bodies produced by maintaining a set pressure and reciprocating the lower punch 3 within an angular range of ±5° exhibit reduced shear and horizontal cracking, resulting in higher quality compared to molded bodies produced by maintaining a set pressure and reciprocating the lower punch 3 within an angular range of ±15°. For this reason, a pressure mode that reciprocates the lower punch 3 within an angular range of ±5° is employed. As a result, it is possible to manufacture high-quality magnetic composite materials.

[0067] In particular, during the torsional operation process T, as shown in Figure 5, when the lower punch 3 is reciprocated within an angular range of ±5° around the axis X, the proportion of magnetic material Mp that has increased plastic strain is lower than when it is reciprocated within an angular range of ±15°. For this reason, by reciprocating the lower punch 3 within a set angular range (for example, an angular range of ±5°), the coercivity of the molded mixture C can be maintained at a high value.

[0068] Furthermore, since multiple grooves or protrusions are formed on the lower end surface 2a of the upper punch 2 and the upper end surface 3a of the lower punch 3, the torsional force of the torsional operation process T is reliably transmitted to the mixture C, enabling a significant increase in density.

[0069] During the molding process (step #03), applying an external orientation magnetic field to the mixture C aligns the crystal arrangement of the magnetic material Mp contained in the mixture C, enabling an increase in magnetic flux density when the molded mixture C is magnetized or excited.

[0070] [Another embodiment] The present invention may also be configured as follows, in addition to the embodiments described above (parts having the same functions as the embodiments are given the same numbers and reference numerals as the embodiments).

[0071] (a) Before reaching the target load Lt, a torsional operation may be performed in which the lower punch 3 is reciprocated around the axis X while maintaining an appropriate load at multiple different intermediate loads Lm. In other words, multiple torsional operation steps T with different intermediate loads Lm may be performed until the load acting on the mixture C reaches the target load Lt.

[0072] As a specific example of this alternative embodiment (a), as shown in Figure 8, torsional operation steps T1, T2, and T3 are performed with first intermediate loads Lm1, second intermediate loads Lm2, and third intermediate loads Lm3, respectively, that are smaller than the target load Lt. In this alternative embodiment (a), even when the compression load L reaches the target load Lt, a torsional operation is performed to reciprocate the lower punch 3 around the axis X. In other words, the torsional operation is performed after the second compression step P2.

[0073] This alternative embodiment (a) corresponds to the molding process of step #03 in the flowchart of the manufacturing method of the magnetic composite material described in the embodiment. The relationship between the stroke amount S of the upper punch 2 and the compressive load L in the molding process of this alternative embodiment (a) is shown as the third characteristic line C3 in the graph of Figure 8. Furthermore, the torque Tq acting on the lower punch 3 during multiple torsional operations is shown in Figure 9.

[0074] In this alternative embodiment (a), the compressive load L acting on the mixture C is increased to a first intermediate load Lm1 by the straight-line movement of the upper punch 2, and the first torsional operation is performed while maintaining this first intermediate load Lm1 (first torsional operation step T1). Subsequently, the compressive load L acting on the mixture C is increased to a second intermediate load Lm2 by the straight-line movement of the upper punch 2, and the second torsional operation is performed while maintaining this second intermediate load Lm2 (second torsional operation step T2). Furthermore, the compressive load L acting on the mixture C is increased to a third intermediate load Lm3 by the straight-line movement of the upper punch 2, and the third torsional operation is performed while maintaining this third intermediate load Lm3 (third torsional operation step T3).

[0075] Next, the compressive load L acting on the mixture C is increased to the target load Lt (second compression step P2), and while maintaining this target load Lt, the fourth torsional action of the lower punch 3 is performed (fourth torsional action step T4). Note that if the torsional action step is repeated multiple times, the fluidity of the magnetic material Mp particles decreases with each subsequent step (in other words, the particles solidify more), so the amount of straight stroke the upper punch 2 travels decreases. For this reason, as shown in the graph in Figure 9, the duration of the first torsional action step T1, the second torsional action step T2, the third torsional action step T3, and the fourth torsional action step T4 is shortened in this order.

[0076] When performing the molding process of this alternative embodiment (a), the load increases in the order of first intermediate load Lm1, second intermediate load Lm2, third intermediate load Lm3, and target load Lt. As shown in Figure 9, the value of the torque Tq acting on the lower punch 3 also increases in the first torsional operation process T1, second torsional operation process T2, third torsional operation process T3, and fourth torsional operation process T4.

[0077] By performing multiple torsional twisting processes during the molding process, the density of the magnetic material Mp in the molded product can be further increased. Note that the number of torsional twisting processes is not limited to four; it can be set to fewer than four or more than four. Furthermore, when performing multiple torsional twisting processes, it is preferable that the intermediate load (first intermediate load Lm1) in the first torsional twisting process (first torsional twisting process T1) be set to 20% or less of the target load Lt.

[0078] (b) As shown in Figure 10, a ring-shaped housing portion 1s may be formed by arranging an axial core mold 1a coaxial with the axis X in the central space of a cylindrical mold 1, and a ring-shaped upper punch 2 is inserted into this ring-shaped housing portion 1s from above, and a lower punch 3 is inserted into this housing portion 1s from below to constitute a molding unit A. In this way, the ring-shaped housing portion 1s in the area sandwiched between the upper punch 2 and the lower punch 3 functions as a pressurized space.

[0079] Although not shown in the figure, the molding unit A of this alternative embodiment (b) is equipped with a press operating part 4 and a torsional operating part 5 similar to those described in the embodiment. As a result, the molding unit A applies a compressive load L to the mixture C by moving the upper punch 2 in a straight line along the axis X, and applies a torsional operating force to the mixture C by reciprocating rotation of the lower punch 3 around the axis X.

[0080] By configuring the molding unit A in this way, it becomes possible to mold the mixture C into a ring shape.

[0081] (c) For example, as shown in Figure 3, in a process in which the first compression process P1 and the second compression process P2 are performed at the timing of the torsional operation process T, the torsional operation of the lower punch 3 is performed in at least one of the first compression process P1 and the second compression process P2.

[0082] In this alternative embodiment (c), the torsional operation step T is performed, which is common to the embodiment shown in Figure 3, but it differs from the embodiment in that torsional operation is also performed in the first compression step P1 and the second compression step P2. In other words, in the alternative embodiment (c), in the first compression step P1, the upper punch 2 is operated in a straight line while simultaneously performing a torsional operation that causes the lower punch 3 to reciprocate around the axis X until an intermediate load Lm is reached, or in the second compression step P2, the upper punch 2 is operated in a straight line while simultaneously performing a torsional operation that causes the lower punch 3 to reciprocate around the axis X until a target load Lt is reached, and the torsional operation of the lower punch 3 is performed in at least one of these two steps.

[0083] Furthermore, in this alternative embodiment (c), as described in alternative embodiment (a), a control configuration is set to set multiple intermediate loads Lm and to twist the lower punch 3 so that it reciprocates at each intermediate load Lm. In this configuration, when the load is increased to the multiple intermediate loads Lm, the lower punch 3 is twisted so that it reciprocates around the axis X.

[0084] (d) As a torsional action, the lower punch 3 is rotated back and forth once around the axis X, as partially described in the embodiment. Specifically, it is rotated 5° in one direction (+5°), and then the lower punch 3 is rotated 5° in the opposite direction (-5°). By rotating the torsional action back and forth once in the torsional action step T in this way, changes in the properties of the magnetic material Mp due to the torsional force acting on the particles of the magnetic material Mp (e.g., plastic strain) can be suppressed.

[0085] The twist angle in the torsional action process T is not limited to ±5°. The twist angle may be smaller than ±5° (e.g., ±4°) or larger than ±5° (e.g., ±15°).

[0086] Furthermore, the configurations disclosed in the above embodiments (including other embodiments, the same applies hereinafter) can be applied in combination with configurations disclosed in other embodiments, provided that no inconsistencies arise. Moreover, the embodiments disclosed herein are illustrative, and the embodiments of the present invention are not limited thereto, and can be modified as appropriate without departing from the object of the present invention.

[0087] In the embodiment described above, the following configuration can be envisioned. (1) A method for manufacturing a magnetic composite material, wherein a compressive load L is applied from a pressing member (upper punch 2) to a mixture C of particulate magnetic material Mp and a binder filled in a housing section 1s of a mold 1 to form the mixture C, comprising: a first compression step P1 in which the pressing member (upper punch 2) is moved in a straight line and a compressive load L is applied to the mixture C filled in the housing section 1s until a preset intermediate load Lm is reached; a torsional operation step T following the first compression step P1, in which, while maintaining the intermediate load Lm, the mixture C is rotated at least once in a set angular range between the pressing member (upper punch 2) and an axial member (lower punch 3) positioned opposite the pressing member (upper punch 2) with the mixture C filled in the housing section 1s in between; and a second compression step P2 in which a target load Lt higher than the intermediate load Lm is applied to the mixture C by the straight line operation of the pressing member (upper punch 2).

[0088] According to this, a mixture C of particulate magnetic material Mp and a binder is filled into the housing section 1s of the mold 1. In the first compression step P1, an intermediate load Lm is applied to the mixture C filled in the housing section 1s of the mold 1 by the straight-line movement of the pressing member (upper punch 2), thereby increasing the density of the mixture C filled in the housing section 1s. Next, in the twisting step T, at least one of the pressing member (upper punch 2) and the axial member (lower punch 3) is rotated back and forth at least once around the axis X while maintaining the intermediate load Lm acting on the mixture C. This allows the mixture C filled in the housing section 1s to flow, and some of the flowing magnetic material Mp particles can fit into the gaps v between the magnetic material Mp particles. Therefore, the increase in the density of the mixture C can be increased. Furthermore, in the second compression step P2, by increasing the load to a target load Lt that is higher than the intermediate load Lm, it is possible to further increase the density of the magnetic material Mp contained in the mixture C. Therefore, a method for manufacturing magnetic composite materials has been realized that allows for an increase in density by reducing the void v between the magnetic material particles contained in the magnetic composite material.

[0089] (2) The pressing member is composed of a first punch (upper punch 2) fitted into one end of the housing portion 1s, and the shaft-shaped member is composed of a second punch (lower punch 3) fitted into the other end of the housing portion 1s, and it is preferable to rotate the shaft-shaped member (lower punch 3) back and forth during the torsional operation process.

[0090] According to this, the first punch (upper punch 2) and the second punch (lower punch 3) are fitted into the housing section 1s in a positional relationship where they face each other. By operating the first punch (upper punch) in a straight line, pressure can be applied to the mixture C, and by operating the second punch (lower punch 3) in a twisting motion, a torsional force can be applied to the mixture C.

[0091] In the method for manufacturing the magnetic composite material according to (3)(2), it is preferable that in at least one of the first compression step P1 and the second compression step P2, a torsional operation is performed in which at least one of the pressing member (upper punch 2) and the axial member (lower punch 3) is reciprocated around the axis X, along with the linear operation of the pressing member (upper punch 2).

[0092] According to this, by performing a torsional action when the compressive load L applied to mixture C increases, it is possible to further increase the density of mixture C.

[0093] (4) In the method for manufacturing magnetic composite materials described in (1) to (3), it is preferable that the intermediate load Lm is set to 20% or less of the target load Lt.

[0094] The torsional operation process T involves torsion of either the pressing member (upper punch 2) or the axial member (lower punch 3) while maintaining an intermediate load Lm. This torsional operation actively causes the mixture C to flow, creating a state in which some of the magnetic material Mp particles fit into the gaps v between the magnetic material Mp particles. In order to cause the mixture C to flow through the torsional operation of either the pressing member (upper punch 2) or the axial member (lower punch 3), it is desirable that the value of the intermediate load Lm be relatively low so as to allow the flow of some of the particles of the mixture C. Therefore, by setting the intermediate load Lm to 20% or less of the target load Lt, the magnetic material Mp particles become easier to flow, making it easier to increase the density.

[0095] (5) In the method for manufacturing magnetic composite materials described in (1) to (4), it is preferable that the torsional operation step T is performed only once.

[0096] According to this, by rotating the torsion mechanism back and forth once during the torsional operation process T, it becomes possible to increase the density of the molded body while suppressing changes in the properties of the magnetic material Mp due to the torsional force acting on the particles of the magnetic material Mp (e.g., plastic strain), and to maintain a high coercivity after magnetization.

[0097] (6) In the method for manufacturing magnetic composite materials according to (1) to (5), it is preferable to apply an external orientation magnetic field to the mixture C in at least one of the first compression step P1 and the torsional operation step T.

[0098] According to this, the crystal arrangement of the particulate magnetic material Mp contained in mixture C is aligned, which allows for an increase in magnetic force when the molded mixture C is magnetized. [Industrial applicability]

[0099] This invention can be used in a method for manufacturing magnetic composite materials. [Explanation of Symbols]

[0100] 1: Mold, 1s: Housing section, 2: Upper punch (pressing member / first punch), 3: Lower punch (shaft-shaped member / second punch), C: Mixture, Lm: Intermediate load, Lm1: First intermediate load (intermediate load), Lm2: Second intermediate load (intermediate load), Lm3: Third intermediate load (intermediate load), Lt: Target load, Mp: Magnetic material, P1: First compression process, P2: Second compression process, T: Torsional process, X: Shaft

Claims

1. A method for manufacturing a magnetic composite material, comprising applying a compressive load from a pressing member to a mixture of particulate magnetic material and a binder filled in a mold housing, thereby forming the mixture, A first compression step involves moving the pressing member in a straight line to apply a compressive load to the mixture filled in the housing until a preset intermediate load is reached. Following the first compression step, while maintaining the intermediate load, a torsional operation step is performed in which at least one of the pressing member and the axial member positioned opposite the pressing member with the mixture filled in the housing in between is rotated back and forth at least once within a set angular range, with the intermediate load maintained. A method for manufacturing a magnetic composite material, comprising a second compression step in which a target load higher than the intermediate load is applied to the mixture by the straight-line movement of the pressing member.

2. The pressing member is composed of a first punch fitted into one end of the housing portion, and the shaft-shaped member is composed of a second punch fitted into the other end of the housing portion. A method for manufacturing a magnetic composite material according to claim 1, wherein the shaft-shaped member is reciprocated in the torsional operation step.

3. A method for manufacturing a magnetic composite material according to claim 1, wherein in at least one of the first compression step and the second compression step, a torsional operation is performed to cause at least one of the pressing member and the axial member to reciprocate around the axis, along with the straight-line operation of the pressing member.

4. A method for manufacturing a magnetic composite material according to claim 1, wherein the intermediate load is set to 20% or less of the target load.

5. The method for manufacturing a magnetic composite material according to claim 1, wherein the torsional operation step is performed only once.

6. A method for manufacturing a magnetic composite material according to any one of claims 1 to 5, wherein an orientation magnetic field is applied to the mixture from an external source in at least one of the first compression step and the torsional operation step.

Images