JP6354684B2 - Plastic working method - Google Patents

Description

  The present invention relates to a plastic processing method in which a workpiece is sandwiched between a pair of punches and the punch is pressed to plastically process the workpiece.

  Rare earth magnets using rare earth elements such as lanthanoids are also called permanent magnets, and their uses are used in motors for driving hard disks and MRI, as well as drive motors for hybrid vehicles and electric vehicles.

  Residual magnetization (residual magnetic flux density) and coercive force can be cited as indicators of the magnet performance of this rare earth magnet. However, in response to increased heat generation due to miniaturization of motors and higher current density, rare earth magnets used also The demand for heat resistance is further increasing, and how to maintain the magnetic properties of the magnet under high temperature use is one of the important research subjects in the technical field.

  As rare earth magnets, in addition to general sintered magnets with a crystal grain (main phase) scale of 3 to 5 μm constituting the structure, nanocrystal magnets with crystal grains refined to a nanoscale of about 50 nm to 300 nm are available. is there.

  An example of a rare earth magnet manufacturing method is outlined. For example, a Nd-Fe-B metal melt is rapidly solidified to produce a fine powder (magnet powder), and an upper punch that slides inside the die and the lower die. A mold body is manufactured while filling a mold cavity constituted by a punch with magnet powder and press-molding it. Next, the compact is compressed in a high temperature atmosphere and densified to produce a sintered body, which is subjected to hot plastic processing to impart magnetic anisotropy to the rare earth magnet (orientated magnet). It is a method of manufacturing. In addition, extrusion processing such as backward extrusion processing and forward extrusion processing, upsetting processing (forging processing), and the like are applied to the hot plastic processing.

  When the forging process is applied as the hot plastic processing described above to introduce processing strain into the sintered body (work), the processing strain introduced into the sintered body differs depending on the location of the sintered body and becomes non-uniform. There is a problem. This is due to the frictional force generated between the sintered body and the punch. The surface of the sintered body in contact with the punch is restrained from plastic deformation by the frictional force, while the inside of the sintered body is from the punch. As a result of plastic deformation relatively freely since there is no direct constraint, processing strain distribution occurs in the sintered body.

  As the processing strain distribution is generated in this way, the degree of orientation of the rare earth magnet formed by hot plastic processing is lowered, leading to a decrease in magnetic characteristics such as residual magnetization.

  By the way, the technique which eliminates the above-mentioned process distortion distribution is disclosed by patent document 1. FIG. The manufacturing method of the warm-working magnet disclosed here is a bulge phenomenon (workpiece that is virtually inevitable in the production of warm-working magnets by densification and plastic working of magnetic powder for RTB permanent magnets. This is a manufacturing method in which the shape is adjusted at the stage of a dense body (sintered body) in consideration of the phenomenon in which the end edge portion is deformed into a barrel shape in advance.

  More specifically, in the densification step, the straight line or the curved part excluding the corner part included in the surface in contact with the upper and lower dies of the dense body shape in advance is more similar to the straight line or curved part than the similar shape of the product shape after the final plastic working. Molded into a shape that is 15% or less concave with respect to the length, and the other dense body has a side that is parallel to the compression direction toward the center of the dense body or 15% or less with respect to the height of the side. After that, plastic working is performed.

  According to this manufacturing method, it is possible to provide a magnet that can be plastically deformed substantially uniformly and has good magnetic properties without cracks. However, since it is necessary to process the shape of the sintered body (work) before hot plastic processing (forging) into a very special shape, the processing is not easy, the processing efficiency is poor, Is hard to say.

JP-A-3-290906

  The present invention has been made in view of the above-described problems. When a workpiece is sandwiched between a pair of punches and the workpiece is plastically processed by pressing the punch, a processing strain is efficiently and substantially uniformly introduced into the workpiece. It is an object of the present invention to provide a plastic working method that can be used.

  In order to achieve the above object, a plastic working method according to the present invention includes an outer punch and an inner punch that slides in the hollow of the outer punch, and a molding die composed of a pair of outer punch and inner punch. When the outer punch and the inner punch are provided with plate material on the end surface, and the plate material is fixed to the outer punch end surface, the inner punch slides in the hollow and the inner punch moves relative to the outer punch. The first step of preparing a molding die in which the portion corresponding to the inner punch of the plate material is plastically deformed to follow the movement of the inner punch, the work is disposed between the pair of inner punches, and the pair of inner punches By pressing and forging the workpiece, the workpiece plastically deforms to the side and corresponds to the end face of the inner punch of the plate material Where also is made of the second step of plastic deformation to the side.

  In the plastic working method of the present invention, a molding die in which the inner punch is configured to be slidable with respect to the outer punch and the outer punch and the inner punch are paired is used. One feature is that a plate material is disposed on the end surface (the end surface facing the other of the pair of outer punches and the inner punch), and a molding die in which the plate material is fixed to the outer punch is used. Therefore, the work is directly sandwiched between the pair of upper and lower plate members, not the pair of upper and lower inner punches.

  And when this plate material slides the inner punch with respect to the outer punch, moves the inner punch relative to the outer punch to forge the workpiece, and plastically deforms the workpiece to the side, The plate material also has deformation performance and rigidity that cause plastic deformation to the side.

  Here, “the plate material is fixed to the end surface of the outer punch” means that the plate material disposed between the outer punch and the end surface of the inner punch is fixed to the end surface of the outer punch, and the end surface of the inner punch is It means not fixed. By adopting such a configuration, when the inner punch moves relative to the outer punch and protrudes from the outer punch, the portion corresponding to the end surface of the outer punch of the plate material is plastically deformed laterally and protruded. The inner punch can extend to a length extending from the side surface (side surface protruding from the outer punch) to the end surface.

  In this way, the location where the plate material comes into contact with the workpiece according to the plastic deformation to the side of the workpiece (the location corresponding to the end face of the inner punch of the plate material) is also plastically deformed to the side, so that between the workpiece and the plate material. The influence of the frictional force on the plastic deformation of the workpiece can be greatly reduced.

  In addition, since the influence of the frictional force that the workpiece receives from the plate material during plastic deformation to the side of the workpiece becomes extremely low, the amount of processing strain on the surface portion where the workpiece contacts the plate material and the amount of processing strain inside the workpiece The difference is reduced, and it is possible to introduce machining strain that is as uniform as possible throughout the workpiece.

  Here, as the plate material that is plastically deformed by the movement of the inner punch, a metal plate material can be applied, and for example, a SUS plate material can be applied.

  In the second step, it is desirable to control the moving speed of the inner punch so that the flow speed when the workpiece is plastically deformed laterally approaches the flow speed when the workpiece is plastically deformed laterally. .

  If the moving speed of the inner punch is too slow, the plastic deformation to the side of the plate does not catch up with the plastic deformation to the side of the workpiece, and as a result, the influence of the frictional force from the plate on the plastic deforming workpiece increases. .

  Therefore, the workpiece is pressed while varying the moving speed of the inner punch for each workpiece material (rigidity, deformation performance) and shape, and the plastic deformation to the side of the plate material occurs during plastic deformation to the side of the workpiece. It is preferable that the moving speed of the following inner punch is specified, and the inner punch is pressed at the specified moving speed.

  Moreover, although a workpiece | work is not specifically limited, The sintered compact which is a rare earth magnet precursor can be mentioned as embodiment of a workpiece | work.

  The sintered body is manufactured by filling a molding die with magnet powder and press-molding, and the sintered body is manufactured by compressing and densifying the manufactured molded body in a high-temperature atmosphere. . When the sintered body is subjected to hot plastic working to introduce processing strain and impart magnetic anisotropy to produce a rare earth magnet, the hot plastic working (forging) is applied to the plastic working method of the present invention. Applies.

  The rare earth magnet formed by imparting magnetic anisotropy to the sintered body by the plastic working method of the present invention introduces processing strain as evenly as possible to the entire rare earth magnet and has a high degree of orientation. For this reason, it becomes a rare earth magnet excellent in magnetic characteristics represented by residual magnetization.

  As can be understood from the above description, according to the plastic working method of the present invention, the inner punch is configured to be slidable with respect to the outer punch, and a molding die in which the outer punch and the inner punch are paired is used. In this use, a plate material is arranged on the end surfaces of the outer punch and the inner punch and fixed to the outer punch, a work is disposed between the pair of inner punches, and the work is forged by pressing the pair of inner punches. . By this method, when the workpiece is plastically deformed to the side, the plate material is also plastically deformed to the side, so that the influence of the frictional force between the workpiece and the plate material becomes extremely low during the plastic deformation of the workpiece. It is possible to introduce as much processing strain as possible to the whole.

It is the schematic diagram explaining the 1st step of the plastic working method of this invention. It is the schematic diagram explaining the 2nd step of the plastic working method. It is the schematic diagram which showed the 1/4 analysis model, Comprising: (a) is a model figure of a comparative example, (b) is a model figure of an Example. It is the figure which showed the mesh model figure of the sintered compact before and behind forging of a comparative example and an Example. It is the figure which compared the amount of compressive strain in the measurement point of a comparative example and an Example.

  Hereinafter, embodiments of the plastic working method of the present invention will be described with reference to the drawings. In the illustrated example, a sintered body, which is a rare earth magnet precursor, is applied to the workpiece. However, it goes without saying that the workpiece is not limited to the sintered body.

(Embodiment of plastic working method)
FIG. 1 is a schematic diagram explaining the first step of the plastic working method of the present invention, and FIG. 2 is a schematic diagram explaining the second step of the plastic working method.

  The illustrated mold 10 is composed of a pair of outer punch 1 and inner punch 2, and the inner punch 2 is configured to be slidable within the hollow of the outer punch 1. When the mold 10 is operated, the outer punch 1 does not move and only the inner punch 2 slides, or the outer punch 1 moves, and the inner punch 2 moves (slids faster than the outer punch 1). The operation control of the mold 10 can be selected as appropriate.

  In the illustrated example, in a state before operation, the end surface of the inner punch 2 faces the end surface of the outer punch 1 and protrudes toward the inner punch 2 side.

  A plate material 4 made of SUS is disposed on the end surfaces of the outer punch 1 and the inner punch 2, and the plate material 4 is fixed to the end surface of the outer punch 1 by a pressing member 3 and fixed to the end surface of the inner punch 2. It is just touching without being done.

  In this way, a mold 10 comprising the outer punch 1 and the inner punch 2 provided with the plate material 4 on the end face is prepared (first step).

  And the sintered compact S which is a workpiece | work is arrange | positioned between a pair of inner punches 2 and 2. FIG. This sintered body S is a rare earth magnet precursor, and is produced by pressure-molding magnet powder.

  Here, the production method of the magnet powder is outlined. First, in a furnace (not shown) whose pressure is reduced to 50 kPa or less, the alloy ingot is melted at a high frequency by a melt spinning method using a single roll, and a molten metal having a composition that gives a rare earth magnet is prepared. Quenching thin ribbon (quenching ribbon) by spraying on copper roll. Next, the rapidly quenched ribbon is roughly pulverized to produce magnet powder. The particle size range of the magnet powder is adjusted to be in the range of 75 to 300 μm.

  The microstructure of the sintered body S consists of a Nd-Fe-B main phase (average grain size of 300 nm or less, for example, a crystal grain size of about 50 nm to 200 nm) having a nanocrystalline structure and Nd around the main phase. -X alloy (X: metal element) grain boundary phase. The Nd—X alloy constituting the grain boundary phase is composed of Nd and at least one alloy of Co, Fe, Ga, etc., for example, Nd—Co, Nd—Fe, Nd—Ga, Nd— One of Co—Fe and Nd—Co—Fe—Ga, or a mixture of two or more of these, is in an Nd-rich state.

  Next, as shown in FIG. 2, by pressing the pair of inner punches 2 and 2 (X1 direction, X2 direction) and forging the sintered body S, the sintered body S is plastically deformed laterally ( Deformation: δ1), the plastic deformation imparts magnetic anisotropy to the sintered body S, thereby producing a rare earth magnet J.

  In this forging process, when the sintered body S is plastically deformed to the side, the plate material 4 is also plastically deformed. Specifically, the portion corresponding to the end face of the inner punch 2 of the plate member 4 (the portion sandwiching the sintered body S) is plastically deformed to the side in the same manner as the sintered body S (deformation: δ2). The portion corresponding to the side surface of the inner punch 2 protruding relative to the outer punch 1 is plastically deformed in the protruding direction of the inner punch 2 (deformation: δ3). That is, the plate material 4 is in an overhanging state.

  As described above, the portion where the plate member 4 is in contact with the sintered body S (the portion corresponding to the end surface of the inner punch 2 of the plate member 4) is also plastically deformed laterally in accordance with the plastic deformation to the side of the sintered member S. Thereby, the influence which the frictional force between the sintered compact S and the board | plate material 4 has on the plastic deformation of the sintered compact S can be reduced significantly.

  Accordingly, the processing strain introduced when the sintered body S is plastically deformed is that the surface of the sintered body S that receives the frictional force from the plate material 4 is not directly affected by the frictional force from the plate material 4. The inside is also at the same level, the degree of orientation of the rare earth magnet after plastic deformation is high, and the magnetic properties are excellent.

  Here, it is desirable to control the moving speed of the inner punch 2 so that the flow speed at the time of the plastic deformation of the plate material 4 approaches the flow speed at the time of the plastic deformation of the sintered body S to the side. .

  If the moving speed of the inner punch 2 is too slow, the plastic deformation to the side of the plate material 4 does not catch up with the plastic deformation to the side of the sintered body S, and as a result, the plate material 4 to the sintered body S that undergoes plastic deformation. The effect of frictional force from is increased. Therefore, the sintered body S is pressed while changing the moving speed of the inner punch 2 for each material (rigidity, deformation performance) and shape of the sintered body S, and the plastic body is deformed laterally. It is preferable that the moving speed of the inner punch 2 in which the plastic deformation to the side of the plate material 4 follows is specified in advance and the inner punch 2 is pressed at the specified moving speed.

(CAE analysis and results)
The present inventors conducted an analysis to verify the effect when forging a sintered body through a plastically deformable plate material. Here, FIG. 3A is a model diagram showing a quarter of the analysis model of the comparative example that does not include a plate material, and FIG. 3B is a quarter of the embodiment that includes the plate material. It is the figure which showed the analysis model.

  In the comparative example, forging was performed by pressing the inner punch into the sintered body at a pressing speed of 0.75 mm / sec. A graphite lubricant was applied to the interface between the sintered body and the inner punch, and the friction coefficient was set to 0.1.

  On the other hand, in the example, a plate made of SUS304 is interposed between the sintered body and the inner punch, the end of the plate is fixed with a die and a holding plate, a force of 50000 N is applied to the die, and the inner punch and the holding plate are pressed. Both plates were forged by pressing at 0.75 mm / sec. The coefficient of friction between the inner punch and the plate material was 0.01.

  The analysis results are shown in FIGS. Here, FIG. 4 shows a mesh model diagram of the sintered body before and after forging of the comparative example and the example, and FIG. 5 is a diagram comparing the amount of compressive strain at the measurement points of the comparative example and the example. .

  FIG. 4 shows that in the comparative example after forging, there is a large difference in the degree of crushing at the measurement points A and B.

  On the other hand, in the example after forging, it can be seen that the crushing condition is approximately the same at the measurement points A and B because the plate material extends sideways.

  Actually, from FIG. 5, the amount of compressive strain before and after forging in the comparative example is 0.59 at the measurement point A affected by the frictional force and 1.07 at the measurement point B hardly affected by the frictional force. There is a gap.

  In contrast, the amount of compressive strain before and after forging in the example is 0.65 at measurement point A and 0.84 at measurement point B, indicating that both values are very close.

  From this analysis result, by forging the sintered body through a plastically deformable plate material, the influence of the frictional force between the plate material and the sintered body is reduced, and as uniform as possible in the entire area of the sintered body. It was found that the amount of processing strain can be introduced.

  The embodiment of the present invention has been described in detail with reference to the drawings. However, the specific configuration is not limited to this embodiment, and there are design changes and the like without departing from the gist of the present invention. They are also included in the present invention.

  DESCRIPTION OF SYMBOLS 1 ... Outer punch, 2 ... Inner punch, 3 ... Holding member, 4 ... Plate material, 10 ... Mold, S ... Sintered body (workpiece), J ... Rare earth magnet

Claims (1)

In a mold having an outer punch and an inner punch that slides in the hollow of the outer punch, and comprising a pair of outer punch and inner punch, a plate material is disposed on the end surface of the outer punch and the inner punch, and the plate material Is fixed to the end face of the outer punch, and when the inner punch slides in the hollow and the inner punch moves relative to the outer punch, the portion corresponding to the inner punch of the plate material is plastically deformed and the inner punch moves. A first step of preparing a mold that follows the movement of the punch;
By placing the workpiece between the pair of inner punches and forging the workpiece by pressing the pair of inner punches, the workpiece is plastically deformed to the side, and the portion corresponding to the end face of the inner punch of the plate is also on the side A plastic working method comprising a second step of plastically deforming in the direction.

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