JP2006205219A - Forming method and forming device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To realize a proper pressure control corresponding with an amount of spring-back. <P>SOLUTION: Material powder 10 of a rare earth metal magnet is compressed and formed by means of an upper punch 2 and a lower punch 4 in a forming space C inside a metallic die (die 1). After that, a formed body 11 is taken out from the forming space C in the state that the formed body 11 is gripped by means of the upper and lower punches 2, 4. When the formed body 11 is taken out, the pressing force of the upper and lower punches 2, 4 applied on the formed body 11 is controlled by gas pressure (pneumatic pressure in a pneumatic cylinder 8) so as to gradually decrease with the movement of the taking-out. By this method, the pressure control corresponding with the amount of the spring-back can be carried out, and collapse cracks, flaking cracks, etc. in the formed body 11 can be eliminated. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a molding method and a molding apparatus for pressure-molding rare earth magnet raw material powder, and more particularly to a technique for suppressing the occurrence of cracks during removal of a molded body.

  When manufacturing rare earth sintered magnets such as neodymium iron boron and samarium cobalt, the rare earth magnet raw material powder is pressed into a predetermined shape and sintered to obtain a rare earth sintered magnet having a predetermined shape. I am doing so. In this case, the pressure molding is generally performed by powder compaction in a uniaxial direction using a die and a punch of a mold. For the purpose of obtaining high orientation and high magnetic properties, a molding method in a magnetic field is performed in which the compacting is performed while applying a magnetic field.

  By the way, the pressure molding of the rare earth magnet raw material powder is usually performed by pressing the rare earth magnet raw material powder at a predetermined pressure by the upper and lower punches in the molding space of the mold. The molded body is taken out in a state where the is sandwiched. At this time, the problem is peeling cracks and crushing cracks that occur during the removal. When the molded body is taken out, for example, a springback phenomenon occurs in which the molded body tends to expand in accordance with the taper shape of the molding space of the mold. If the pressure applied by the upper and lower punches is too strong against this springback phenomenon, it will cause crushing cracks. Conversely, if the pressure applied by the upper and lower punches is too weak, it causes peeling cracks.

  Under such circumstances, various studies have been made in various directions, and various techniques for preventing peeling cracks and crushing cracks that occur when a molded body is extracted have been proposed (for example, Patent Documents 1 to 5). (See 3 etc.).

  Specifically, in Patent Document 1, after the magnetic powder is compression-molded by the first and second punches, the interval between the first punch and the second punch is expanded, and the first and second punches are After the pressure applied to the molded body is reduced and the pressure decrease occurs, the die (die) starts to drop before the pressure decrease stops, and the molded body is extracted from the die before the pressure reaches zero. Thus, it is disclosed to prevent peeling and crushing of the molded body.

  In Patent Document 2, the holding pressure of the green compact is controlled so as to be equal to or lower than the crushing cracking limit pressure and higher than the peeling cracking limit pressure according to the height of the green compact in the middle of extracting the die. Thus, it is disclosed that a green compact having good moldability without occurrence of peeling cracks and crushing cracks is produced.

In Patent Document 3, the piston head side hydraulic pressure and the piston rod side hydraulic pressure of a compression cylinder of a hydraulic press device are measured by a pressure sensor, and the green compact holding pressure or load converted from the differential pressure is held slightly larger than the peeling occurrence pressure. It is disclosed that when a pressure adjustment scale on the piston rod side is adjusted so as to be a pressure, a molded product of any molding condition can be stably manufactured without defects with almost no trial and error.
Japanese Patent Laid-Open No. 2001-300790 Japanese Patent Laid-Open No. 10-8102 Japanese Patent Laid-Open No. 10-152702

  However, in the inventions described in the above-mentioned patent documents, the pressure mechanism for taking out the molded body is hardly taken into consideration, and the actual situation is that effective pressure control is difficult. For example, in the invention described in Patent Document 1, the pressure on the compact is controlled by slightly raising the upper punch and enlarging the distance between the upper punch and the lower punch. In the control, even a slight change in the interval leads to a large pressure difference, and it is almost impossible to control the pressure appropriately in accordance with the amount of springback.

  Similarly, in the invention described in Patent Document 2, the holding pressure is controlled by a mechanical press or a hydraulic press. However, with these mechanical press and hydraulic press, it is difficult to finely adjust the pressure, which is also commensurate with the amount of spring back. Proper pressure control is nearly impossible. Even if it is possible to finely adjust the pressure, a large adjustment mechanism is required for that purpose, which requires a large cost in terms of capital investment. The invention described in Patent Document 3 also assumes a hydraulic press device and has the same problems as the invention described in Patent Document 2.

  The present invention has been proposed in view of such a conventional situation, and can realize an appropriate pressure control corresponding to the amount of springback, and absorbs the springback phenomenon and does not generate cracks. It aims at providing the shaping | molding method and shaping | molding apparatus which can obtain a body. Another object of the present invention is to provide a molding method and a molding apparatus that can perform the pressure control with a simple mechanism, do not require a large-scale apparatus configuration, and can minimize equipment investment.

  In order to achieve the above-described object, the molding method of the present invention is a method in which the rare earth magnet raw material powder is compression-molded by a pair of punches in a molding space in a mold, and then the molded space is sandwiched between these punches. A molding method for removing the molded body, wherein the pressure applied to the molded body by the pair of punches is controlled by a gas pressure when the molded body is removed, and the pressure is controlled so as to gradually decrease with the removal. Features.

  Further, the molding apparatus of the present invention includes a mold having a molding space and a pair of punches for compressing and molding rare earth magnet raw material powder in the molding space, and sandwiching a molded body molded by these punches, the molding space. A molding apparatus for taking out the molded body from the first pressure, wherein the pressing force of the punch is controlled by the gas pressure so that the pressing force applied to the molded body by the punch gradually decreases with the removal of the molded body. The pressurizing mechanism is provided.

  When the rare earth magnet raw material powder is compression molded and then taken out, it is necessary to suppress the occurrence of cracks due to the springback phenomenon. Therefore, in the present invention, the molded body is pulled out while being held at a pressure corresponding to the springback amount, and the molded body is extracted from the mold after the springback amount becomes zero.

  In taking out the molded body as described above, the control of the pressing force by the punch sandwiching the molded body is an important key, and it is indispensable to appropriately control this in accordance with the springback amount. In the present invention, the pressure applied to the punch at the time of taking out the molded body is controlled by gas pressure (pneumatic pressure), the pressure control can be easily and properly performed, the spring back phenomenon is absorbed reliably, and cracks are generated. It is possible to take out the molded body without any problem. Such pressure control is difficult with a hydraulic press device or a mechanical press device, and proper pressure control corresponding to the amount of spring back is almost impossible.

  According to the present invention, when the molded body is taken out, it is possible to perform appropriate pressure control corresponding to the amount of springback, so it is possible to reliably suppress the occurrence of cracks due to the springback phenomenon, peeling cracks, crushing cracks, etc. It is possible to obtain a molded body without any. Further, in the present invention, since the pressure control is performed by the gas pressure, a complicated pressure control mechanism and a large pressure control mechanism are unnecessary, and a significant cost increase is caused in terms of capital investment and the like. Nor.

  Hereinafter, a molding method and a molding apparatus to which the present invention is applied will be described in detail with reference to the drawings.

  FIG. 1 schematically shows a configuration example of a molding apparatus to which the present invention is applied. This forming apparatus includes a die (die) 1 having a predetermined forming space C, and an upper ram 3 provided with an upper punch 2 inserted into the forming space C and sandwiching rare earth magnet raw material powder from above and below. And a lower ram 5 having a lower punch 4.

Here, the shape of the molded body is determined by the opening shape of the molding space C of the die 1 and the tip shape of the upper punch 2 and the lower punch 4, and the opening shape of the molding space C is rectangular or rectangular, If the tip surfaces of the upper punch 2 and the lower punch 4 are flat surfaces, the shape of the molded body to be molded is a rectangular parallelepiped shape. If the opening shape of the molding space C is circular, the shape of the molded body to be molded is a cylindrical shape. In addition, the opening shape of the molding space C includes a fan shape, a tile shape, and the like. Molding space C is for example planar area of the aperture shape ² about ～10000Mm ² about 10 mm, a thickness (depth) and about 1.0mm approximately 100 mm.

  In addition, the molding space C has a slight taper in shape in order to facilitate removal of the molded body to be molded. For example, when the rare earth magnet raw material powder is compression-molded by the upper punch 2 and the lower punch 4 and then the upper punch 2 and the lower punch 4 are moved upward in the drawing relative to the die 1 to take out the molded body. Are tapered on the wall surface forming the molding space C so that the opening area of the molding space C gradually increases upward.

  Note that the taper is not a visible taper in practice, and a taper with a very small dimensional difference may be added. Specific numerical values are, for example, about 0.02 mm to 0.5 mm per 100 mm taken out length of the molding space C. The design of the taper is not limited to this, and may be set as appropriate according to the dimensions of the closed space of the mold, the material to be molded, and the like.

  The upper punch 2 and the lower punch 4 function as a pressurizing unit when the rare earth magnet raw material powder is compression-molded in the molding space C, and also functions as a taking-out unit when taking out the molded body after molding. Therefore, the upper ram 3 and the lower ram 5 are provided with hydraulic presses 6 and 7 that apply pressure to the upper punch 2 and the lower punch 4 during compression molding as a second pressurizing mechanism, and the upper ram 3 Is provided with a gas pressure press (here, air cylinder 8) as a first pressurizing mechanism for applying an appropriate pressurizing force to the molded body at the time of removal.

  Here, the hydraulic presses 6 and 7 are for applying a large pressure necessary for compression molding, and may be any one that can apply a predetermined pressure. A control mechanism that gradually changes is not necessary. In addition, as a 2nd pressurization mechanism for providing the pressure required for compression molding, not only the said hydraulic press but a mechanical press etc. may be sufficient, for example.

  On the other hand, as the first pressurizing mechanism for applying pressure to the molded body at the time of taking out, it is necessary to control the pressure corresponding to the amount of spring back, and the pressurizing mechanism that can easily and appropriately adjust the pressure Is preferred. From such a viewpoint, in the present invention, a gas pressure press (air cylinder 8) that performs pressure control by gas pressure is employed as the first pressurizing mechanism. In the air cylinder 8, by controlling the internal gas pressure, it is possible to control the pressure appropriately in accordance with the amount of spring back.

  The air cylinder 8 is provided with an electropneumatic valve 9, and the electropneumatic valve 9 is configured to change the pressure applied by the air cylinder 8 linearly. The electropneumatic valve 9 adjusts the pressure according to the opening degree of the control valve. By changing the opening degree of the control valve with an electric signal, for example, the pressure can be varied linearly. In the pressure control at the time of taking out, it is important to control the amount of spring back, and considering that the amount of spring back decreases linearly with taking out, the pressure can be linearly varied by the electropneumatic valve 9. The air cylinder 8 that can be used is optimal as the first pressurizing mechanism.

  The basic configuration of the molding apparatus is as described above. The molding apparatus of the present invention is applied to a molding process in manufacturing a rare earth magnet, for example, a rare earth sintered magnet. Then, next, the manufacturing process of a rare earth sintered magnet is demonstrated and the shaping | molding method is demonstrated in it.

  First, a rare earth sintered magnet to be manufactured is mainly composed of a rare earth element R, a transition metal element T, and boron B, and is extremely excellent in magnetic properties. And high performance can be realized.

  The magnet composition of the rare earth sintered magnet to be manufactured is not particularly limited, and may be arbitrarily selected according to the application. For example, the rare earth element R specifically means Y, La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb or Lu. 1 type (s) or 2 or more types can be used. Among these, it is preferable that the main component as the rare earth element R is Nd because it is abundant in resources and relatively inexpensive. Moreover, as the transition metal element T, any conventionally used transition metal element can be used. For example, one or more of Fe, Co, Ni and the like can be used. Among these, Fe and Co are preferable from the viewpoint of sinterability, and it is particularly preferable to mainly include Fe from the viewpoint of magnetic characteristics. In addition to the rare earth element R, transition metal element T, and boron B, for the purpose of improving characteristics such as coercive force, an element such as Al may be added. In addition to these elements, for example, carbon and oxygen may be contained as inevitable impurities or trace additives.

  For the production of the rare earth sintered magnet as described above, a powder metallurgy method is used. The manufacturing process includes, for example, an alloying process, a coarse pulverization process, a fine pulverization process, a forming process in a magnetic field, a sintering process, and an aging process , A machining process, a film forming process, and the like.

  The forming apparatus and the forming method of the present invention are applied to the forming step in a magnetic field, and form rare earth magnet raw material powder into a predetermined shape in a state of being oriented in a predetermined direction. The formed molded body is subjected to the next sintering step, and sintering is performed. 2a to 2d schematically show a procedure for forming rare earth magnet raw material powder using the forming apparatus of this embodiment.

  When forming the rare earth magnet raw material powder, first, as shown in FIG. 2a, the upper ram 3 is raised, and the feeder box (illustration omitted) in which the rare earth magnet raw material powder is accommodated and the bottom surface is opened is reciprocated. By moving, the rare earth magnet raw material powder 10 is filled in the molding space C of the die 1.

  Next, as shown in FIG. 2 b, the upper punch 2 is lowered to form a closed space surrounded by the upper punch 2, the lower punch 4, and the die 1. The rare earth magnet raw material powder 10 filled in the above process is accommodated in this closed space.

  Subsequently, in this state (the state in which the rare earth magnet raw material powder 10 is accommodated in the closed space), a magnetic field is applied to the rare earth magnet raw material powder 10 in the horizontal direction in the figure, for example, by the magnetic field applying means (magnetic field applying coil or the like). To do. Then, the rare earth magnet raw material powder 10 is compression molded by the upper punch 2 and the lower punch 4 while applying a magnetic field. In this example, the direction in which the magnetic field is applied is performed perpendicularly to the pressurizing direction (horizontal direction in the figure).

  In the compression molding, the pressure applied by the upper and lower punches 2 and 4 may be appropriately set according to the type, particle size, shape, and the like of the rare earth magnet raw material powder 10 to be used, but is usually about 30 MPa to 200 MPa. This pressing force is applied by hydraulic presses 6 and 7 provided on the upper punch 2 and the lower punch 4. Similarly, the strength of the magnetic field to be applied may be appropriately set according to the rare earth magnet raw material powder 10 to be used, for example, about 0.8T to 2.0T.

  After the compression molding, as shown in FIG. 2 c, the molded body 11 is moved upward in the drawing while being sandwiched between the upper punch 2 and the lower punch 4, and is taken out from the molding space C of the die 1. At this time, as the molded body 11 is taken out, a springback phenomenon occurs in which the molded body 11 tends to expand according to the taper of the molding space C. When the springback phenomenon occurs, cracks are caused in the molded body 11. For example, if the pressure applied to the molded body 11 is too strong, the molded body 11 is crushed to generate crushing cracks and press the molded body 11. If the pressure is too weak, cracks due to peeling (peeling cracks) occur.

  Therefore, when the molded body 11 is taken out, it is necessary to press the molded body 11 with an appropriate pressure corresponding to the springback amount. Therefore, in the present invention, the pressing force at the time of taking out the molded body 11 is obtained by the air cylinder 8, and the opening degree of the control valve of the electropneumatic valve 9 is controlled by an electric signal, whereby the molded body is obtained. In synchronization with the change in the amount of spring back at the time of removal, an appropriate pressure corresponding to the amount of spring back is applied.

  FIG. 3 shows a pressure profile from compression molding to removal of the molded body 11. 3A shows the movement (position) of the upper ram 3, FIG. 3B shows the pressure change applied to the compact 11 (rare earth magnet raw material powder 10), and FIG. The change of the quantity (filling quantity) of the molded object 11 accommodated in FIG.

  In FIG. 3, the compression molding process is performed up to point A, and a pressing force T <b> 1 (for example, about 30 MPa to 200 MPa) necessary for molding is applied to the molded body 11 by hydraulic presses 6 and 7. When compression molding is completed, a process called depressurization is performed, and the pressure applied by the hydraulic presses 6 and 7 is released to a predetermined pressure T2 (for example, about 7 MPa to 50 MPa) (point B). The pressure T2 is not less than the maximum pressure obtained by the air cylinder 8.

  After the pressure release of the hydraulic presses 6 and 7 is finished, the upper ram 3 is slightly raised (points C to D), and the pressure applied to the upper punch 2 is switched from the hydraulic press 6 to the air cylinder 8. During the compression molding, pressure is applied to the upper punch 2 and the lower punch 4 by the hydraulic presses 6 and 7, and at this time, the air in the air cylinder 8 is crushed and functions as a pressurizing mechanism. Not. When the upper ram 3 is slightly raised after the pressure release, the air in the air cylinder 8 expands, and the air pressure T3 (for example, 0.7 MPa) of the air in the air cylinder 8 is applied to the upper punch 2 at the point D. About 10 MPa).

  After the applied pressure is switched from hydraulic to pneumatic by the slight rise of the upper ram 3, the removal of the molded body 11 is started. That is, the molded body 11 is sandwiched between the upper punch 2 and the lower punch 4, and the upper punch 2 and the lower punch 4 (that is, the upper ram 3 and the lower ram 5) are raised relative to the die 1. This operation may be performed by raising the upper ram 3 and the lower ram 5 or by lowering the die 1. Alternatively, the upper ram 3 and the lower ram 5 may be raised and the die 1 may be lowered.

When the molded body 11 sandwiched between the upper punch 2 and the lower punch 4 is raised relative to the die 1 as described above, the molded body 11 gradually protrudes from the molding space C to the external space as it rises. Specifically, the molded body 11 is taken out as shown in FIG. 2d. During this time, the spring back phenomenon occurs and causes cracks. Therefore, by using the air pressure of the air cylinder 8, the molded body 11 is placed in the upper punch 2 and the lower punch 4 so as to have an appropriate pressure commensurate with the amount of spring back. The pressure is applied to remove the material (points E to F). In this example, molding was performed using rare earth magnet raw material powder having an average particle size of 2.0 to 10.0 μm, and the compact density was set to 3.5 to 4.8 g / cm ³ .

  By using the air pressure of the air cylinder 8, for example, the opening of the control valve is controlled by the electropneumatic valve 9, and the pressure applied to the molded body 11 is linearly changed following the change of the springback amount. It is possible to prevent crushing cracks due to the pressure being too strong and peeling cracks due to the pressure being too weak.

  By performing the pressure control as described above, it is possible to reliably suppress the occurrence of cracks due to the springback phenomenon, and it is possible to obtain a molded body free from peeling cracks and crushing cracks. Further, the pressure control can be realized only by adding the air cylinder 8, and a complicated pressure control mechanism and a large-scale pressure control mechanism are unnecessary, which is advantageous in terms of equipment investment.

It is a schematic diagram which shows one structural example of the shaping | molding apparatus to which this invention is applied. It is a schematic diagram which shows a shaping | molding process, (a) is a filling process of rare earth magnet raw material powder, (b) is a compression molding process, (c) is a molded object taking-out process, (d) is the completion state of taking-out of a molded object. . It is a figure which shows an example of the pressure profile from compression molding to taking out of a molded object.

Explanation of symbols

1 die, 2 upper punch, 3 upper ram, 4 lower punch, 5 lower ram, 6,7 hydraulic press, 8 air cylinder, 9 electropneumatic valve, 10 rare earth magnet raw material powder, 11 compact

Claims (9)

A molding method in which a rare earth magnet raw material powder is compression-molded by a pair of punches in a molding space in a mold, and is then taken out of the molding space in a state where the molded body is sandwiched between these punches,
A molding method characterized in that, when the molded body is taken out, the pressure applied to the molded body by the pair of punches is controlled by a gas pressure, and the pressure is controlled to gradually decrease with the removal.   The molding method according to claim 1, wherein the pressure is controlled so as to gradually decrease by reducing the gas pressure.   The molding method according to claim 1, wherein the gas pressure is controlled by an electropneumatic valve.   The molding method according to any one of claims 1 to 3, wherein the pair of punches are pressurized by a hydraulic pressure during the compression molding.   The molding method according to any one of claims 1 to 4, wherein the molding space has a tapered shape in which an opening area gradually increases in the take-out direction. A molding apparatus including a mold having a molding space and a pair of punches for compression molding rare earth magnet raw material powder in the molding space, and sandwiching a molded body molded by these punches and taking out from the molding space,
A first pressurizing mechanism for controlling the pressurizing force of the punch with a gas pressure so that the pressing force applied to the formed body by the punch gradually decreases with the removal of the formed body; Characteristic molding device.   The molding apparatus according to claim 6, wherein the first pressurizing mechanism includes an electropneumatic valve for gas pressure control.   The molding apparatus according to claim 6, further comprising a second pressurizing mechanism that pressurizes the punch with hydraulic pressure during the compression molding.   9. The molding apparatus according to claim 6, wherein the molding space has a tapered shape in which an opening area gradually increases in a take-out direction of the molded body.

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