Patent Publication Number: US-2011076175-A1

Title: Punch die for powder compacting, powder compacting equipment equipped with punch die, and forming method with an equipment

Description:
FIELD OF THE INVENTION 
     The present invention relates to a punch die for powder compacting, a powder compacting equipment equipped with the punch die, and a forming method with the equipment which are used to manufacture a cylindrical member, having a protrusion portion formed on the inner peripheral side or the outer peripheral side of a cylindrical structure to protrude in the axial direction, by powder compacting. 
     DESCRIPTION OF RELATED ART 
     A powder compacting body having a protrusion portion formed on the inner peripheral side or the outer peripheral side thereof is used in a motor core or the like as a powder magnetic core. For example, in the motor core, a three dimensional powder magnetic core is used having protrusion portions discretely formed in the circumferential direction on an inner peripheral portion of a ring structure. An increase in the density of the powder compacting body contributes to the improvement in motor output power and motor torque. JP-A-2007-124884 discloses a rotating electrical machine in which a stator core is formed by compressing magnetic powder. 
       FIG. 2A  is a perspective view of a cylindrical powder compacting body  200  formed by powder compacting disclosed in JP-A-2007-124884, and  FIG. 2B  is an enlarged perspective view showing a part A in  FIG. 2A  on an inner peripheral surface side. The cylindrical powder compacting body  200  includes a donut-shaped or cylindrical body portion  210 , where a protrusion portion  220  is formed on the inner peripheral side of the body portion  210  to protrude in the axial direction, or a stepped portion or a concave portion is formed in the radial direction between the outer surface and the inner surface of the body portion  210 . 
     Hereinafter, an example of the related art of a punch die for powder compacting, a powder compacting equipment with the punch die, and a forming method with the equipment for manufacturing the cylindrical powder compacting body  200  will be described. 
       FIGS. 4A and 4B  show a shape of an upper punch die  400  of a punch die for powder compacting for manufacturing the powder compacting body  200  of FIG.  2 A., where  FIG. 4A  is a perspective view of the upper punch die  400  when obliquely seen from the upper side thereof, and  FIG. 4B  is a perspective view of the upper punch die  400  when obliquely seen from the lower side thereof. The upper punch die  400  includes a ring portion  410  and a protrusion portion  420  which is formed on the inner peripheral side of the ring portion  410  to protrude in the radial direction. An upper surface  211  of the ring portion of the powder compacting body is pressed by a bottom surface  411  of the ring portion  410 , and an upper surface  221  of the protrusion portion of the powder compacting body is pressed by a lower surface  421  of the protrusion portion  420 . It is noted that in  FIG. 2B , reference number  222  denotes an outer surface of the protrusion portion  220 . 
       FIGS. 12A and 12B  are cross-sectional views showing a structure of a main part of a powder compacting equipment  1200  with the upper punch die when taken along the line B-B′ of  FIG. 4A , and a forming method thereof. The powder compacting equipment  1200  includes an inner peripheral core die  1210 , an outer peripheral die  1220 , an upper punch die  1230  for pressing powder  1201  from the upside thereof to apply a pressure thereto, and a lower punch die  1240  for pressing the powder from the downside thereof to apply a pressure thereto. A powder compacting body  1202  is formed by relatively moving the upper punch die  1230  and the lower punch die  1240 . 
     In the above-described configuration, a problem arises in that cracking occurs due to stress concentration in a corner portion  430  of the upper punch die  400 . During a powder compacting operation, a pressure applied by a press machine is added to the lower surface  421  of the protrusion portion of the upper punch die  400 , and a lateral pressure is added to the inner peripheral surface  412  of the ring portion of the upper punch die  400  in accordance with the compacting of the powder. Accordingly, strong tensile stress occurs in the corner portion  430 . For this reason, in the past, the stress concentration was alleviated by forming a curved surface in the corner portion  430 . Meanwhile, as shown in  FIGS. 2A and 2B , the same curved surface is formed at the corresponding position of the powder compacting body  200 . Likewise, in the method of the related art, a degree of freedom in design of the powder compacting body is restricted in that the unnecessary curved surface is formed in the powder compacting body. For example, when the powder compacting body is used in the motor core shown in JP-A-2007-124884, the iron amount of the protrusion portion is reduced. For this reason, motor output power or motor torque is reduced, and hence sufficient characteristics cannot be obtained in some cases. 
     BRIEF SUMMARY OF THE INVENTION 
     Therefore, an object of the invention is to provide a punch die for powder compacting, a powder compacting equipment equipped with the punch die, and a forming method with the equipment, which are capable of suppressing stress concentration in a punch die without changing a shape of a powder compacting body. 
     In order to achieve the above-described object, according to an aspect of the invention, there is provided a punch die for powder compacting, which is used to form a cylindrical member by powder compacting, the cylindrical member having a substantially cylindrical shape and having a protrusion portion formed on the inner peripheral side or the outer peripheral side thereof to protrude in the axial direction or a stepped portion or a concave portion formed on the inner peripheral side or the outer peripheral side thereof in the radial direction, wherein the punch die has a substantially cylindrical shape and has a protrusion portion formed on at least a part of the inner peripheral surface or the outer peripheral surface thereof to protrude toward the center axis, and wherein the punch die is divided into two upper and lower parts at a surface forming the same surface as a lower surface of the protrusion portion, and the divided surfaces are mechanically connected to each other or adhered to each other by adhesive. 
     In addition, in the punch die for powder compacting of the invention, the upper and lower divided punch dies may be connected to each other at the division surfaces by bolt fastening, screw fastening, or fitting performed by forming a concave portion in one punch die and forming a convex portion in the other punch die. 
     Further, in the punch die for powder compacting of the invention, the lower punch die of the two upper and down divided punch dies may be exchangeable to correspond to the shape of the cylindrical member formed by powder compacting. 
     Furthermore, in the punch die for powder compacting of the invention, a corner portion as a connection portion connecting the lower surface of the protrusion portion to the inner peripheral surface of the down punch die may have at least one of an angular shape with a non-curved surface, a shape which satisfies R/δ&lt;0.2 mm where a curvature radius of the corner portion is denoted by R and a radial width of the protrusion portion is denoted by δ and a shape which satisfies R&lt;0.2 mm where a curvature radius of the corner portion is denoted by R. 
     Moreover, the punch die for powder compacting of the invention may further include: the above mentioned punch die for powder compacting as an upper punch; a lower punch die which is disposed to face the upper punch die in the axial direction; a die which is disposed on the outside of the upper punch die and the lower punch die; and a core die which is disposed on the inside of the upper punch die and the lower punch die, wherein powder filled between the upper punch die and the lower punch die is subjected to powder compacting by relatively moving the upper punch die and the lower punch die. 
     Further, in the invention, by using the above mentioned punch die for powder compacting, the lower punch die may be divided into an inner punch die and an outer punch die to have a diameter substantially corresponding to the outer diameter of the protrusion portion of the cylindrical member. The powder is subjected to powder compacting by relatively moving the upper punch die, the inner punch die, and the outer punch die. 
     Further, in order to achieve the above-described object, according to still another aspect of the invention, there is provided a method of forming a cylindrical member by powder compacting comprising of the steps: disposing a lower punch die to face an upper punch die in the axial direction, which upper punch die has a protrusion portion formed on at least a part of the inner peripheral surface thereof to protrude toward the center axis, is divided into two upper and lower parts at a surface forming the same surface as a lower surface of the protrusion portion, and is mechanically connected to each other or adhered to each other by adhesive; disposing a die on the outside of the upper punch die and the lower punch die; disposing a core die on the inside of the upper punch die and the lower punch die; and, subjecting powder filled between the upper punch die and the lower punch die to powder compacting by relatively moving the upper punch die and the lower punch die, to thereby form a cylindrical member having a substantially cylindrical shape and having a stepped portion or a concave portion formed on the inner peripheral side thereof. 
     Furthermore, in the method of forming the cylindrical member of the invention, the upper and lower divided punch dies may be connected to each other at the division surfaces by bolt fastening, screw fastening, or fitting performed by forming a concave portion in one punch die and forming a convex portion in the other punch die. 
     Moreover, in the method of forming the cylindrical member of the invention, the down punch die of the two upper and down divided punch dies may be exchangeable to correspond to the shape of the cylindrical member formed by powder compacting. 
     In addition, in the method of forming the cylindrical member of the invention, a corner portion as a connection portion connecting the lower surface of the protrusion portion to the inner peripheral surface of the down punch die may have at least one of an angular shape with a non-curved surface, a shape which satisfies at least any one of R/δ&lt;0.2 where a curvature radius of the corner portion is denoted by R and a radial width of the protrusion portion is denoted by δ, and a shape which satisfies R&lt;0.2 mm where a curvature radius of the corner portion is denoted by R. 
     Further, according to still another aspect of the invention, there is provided a powder compacting equipment for a cylindrical member, including: the punch die used in the above mentioned method of forming the cylindrical member by powder compacting as an upper punch die; a lower punch die which is disposed to face the upper punch die in the axial direction; a die which is disposed on the outside of the upper punch die and the lower punch die; and a core die which is disposed on the inside of the upper punch die and the lower punch die, wherein powder filled between the upper punch die and the lower punch die is subjected to powder compacting by relatively moving the upper punch die and the lower punch die. 
     Furthermore, in the powder compacting equipment of the invention, the lower punch die is divided into an inner punch die and an outer punch die to have a diameter substantially corresponding to the outer diameter of the protrusion portion of the cylindrical member. The powder is subjected to powder compacting by relatively moving the upper punch die, the inner punch die, and the outer punch die. 
     In the punch die of the invention, since the protrusion portion is divided into two parts, it is difficult to damage the corner portion due to the following reasons: 
     1) Since the inner peripheral surface of the cylindrical portion and the lower surface of the protrusion portion of the punch die are not integrated with each other in a view of material, stress of the lower surface and the inner peripheral surface is not applied to the corner portion. 
     2) Although a large load is applied to the protrusion portion of the punch die, tensile stress of the protrusion portion becomes weak due to the structure in which the punch die is divided at the surface forming the same surface as the lower surface of the protrusion portion of the punch die, and the divided punch dies are connected to each other. 
     3) Since the punch die is divided at the protrusion portion, cracking does not develop. 
     For these reasons, it is possible to reduce stress concentration in the corner portion which is the connection portion connecting the lower surface of the protrusion portion of the punch die to the inner peripheral surface of the cylindrical portion connected thereto. 
     Other objects, features and advantages of the invention will become apparent from the following description of the embodiments of the invention taken in conjunction with the accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING 
         FIG. 1A  is a perspective view showing a powder compacting body formed by a powder compacting equipment of a first embodiment according to the invention, and  FIG. 1B  is an enlarged perspective view showing an outer peripheral surface of a part F in  FIG. 1A . 
         FIG. 2A  is a perspective view showing a powder compacting body formed by a conventional powder compacting equipment, and  FIG. 2B  is an enlarged perspective view showing an outer peripheral surface of a part A of  FIG. 2A . 
         FIGS. 3A and 3B  show a structure of a punch die of the first embodiment, and  FIG. 3A  is a perspective view of a punch die of which upper and down punch dies are connected to each other, and  FIG. 3B  is a perspective view of the punch die of which the upper and down punch dies are separated from each other. 
         FIGS. 4A and 4B  show a shape of a conventional punch die, and  FIG. 4A  is a perspective view when obliquely seen from the upside of the punch die, and  FIG. 4B  is a perspective view when obliquely seen from the downside of the punch die. 
         FIGS. 5A and 5B  are cross-sectional views of a structure of a main part of a powder compacting equipment with an upper punch die of a second embodiment according to the invention when taken along the line C-C′ in  FIG. 3A . 
         FIGS. 6A and 6B  show a conventional example. 
         FIGS. 7A and 7B  are cross-sectional views of a structure of a main part of a powder compacting equipment of a fourth embodiment according to the invention. 
         FIG. 8A  is a perspective view showing a powder compacting body formed by the powder compacting equipment of the third embodiment, and  FIG. 8B  is an enlarged perspective view showing an outer peripheral surface of a part I in  FIG. 8A . 
         FIGS. 9A and 9B  show a structure of a punch die of the third embodiment, and  FIG. 9A  is a perspective view of the punch die of which the upper and down punch dies are connected to each other, and  FIG. 9B  is a perspective view of the punch die of which the upper and down punch dies are separated from each other. 
         FIG. 10  is a perspective view showing a powder compacting body formed by the powder compacting equipment of the fourth embodiment. 
         FIGS. 11A and 11B  are cross-sectional views of a structure of a main part of the powder compacting equipment with the upper punch die of the first embodiment when taken along the line C-C′ of  FIG. 3A . 
         FIGS. 12A and 12B  are cross-sectional views of a structure of a main part of the powder compacting equipment with the upper punch die of the conventional punch die when taken along the line B-B′ of  FIG. 4A . 
         FIGS. 13A and 13B  are cross-sectional views of a structure of a main part of a powder compacting equipment of a fifth embodiment according to the invention. 
         FIGS. 14A to 14C  are perspective views showing an example in which the powder compacting body formed by the powder compacting equipment of the fourth embodiment is applied to a stator of a motor. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Hereinafter, embodiments according to the invention will be described with reference to the accompanying drawings. 
     First Embodiment 
       FIGS. 3A and 3B  show a structure of a punch die  300  of a first embodiment, where  FIG. 3A  is a perspective view of the punch die  300  of which an upper punch die  310  and a down punch die  320  are connected to each other, and  FIG. 3B  is a perspective view of the punch die  300  of which the upper punch die  310  and the down punch die  320  are separated from each other. 
     As shown in  FIG. 3A , the punch die of the first embodiment is used to form a shape of a protrusion portion in a body portion of a powder compacting body, and is formed in a substantially cylindrical shape, and three protrusion portions  330  formed in the upper inner peripheral surface of the punch die to protrude toward the center axis are arranged in the circumferential direction. 
     As shown in  FIG. 3B , a punch die  300  is divided into two parts at the surface forming the same surface as the lower surface of the protrusion portion  330 . That is, the punch die  300  is divided into an upper punch die  310  and a down punch die  320 , and the division surface of the punch die forms the same surface as the lower surface of the protrusion portion. 
     The upper and down punch dies are connected to each other at the division surface in accordance with a dividable connection method. For example, the upper and down punch dies can be strongly connected to each other in such a manner that a bolt (not shown) is attached to the down punch die, a nut (not shown) is attached to the upper punch die corresponding to the down punch die, and then the upper and down punch dies are connected to each other by bolt fastening. 
     The method of fastening the upper and down punch dies is not limited to the bolt fastening. For example, a concave portion is formed in one of the division surfaces of the upper and down punch dies, and a convex portion is formed in the other thereof, and the concave and convex portions are fitted to each other, so as to connect the upper and down punch dies by press fitting or the like. 
     In addition, the connection of the upper and down punch dies may be performed by adhesive or the like, or screw fastening. 
     As described above, the punch die has a structure in which the upper and down punch dies are connected to each other at the flat division surface formed by the lower surface of the upper punch die and the upper surface of the down punch die. 
     For this reason, a corner portion  340  (not shown) formed by the inner peripheral surface  321  and a lower surface  331  of the protrusion portion, to be provided with a step of the punch die, can be formed in a non-curved shape, for example, substantially at a right angle. 
       FIGS. 11A and 11B  are cross-sectional views of a structure of a main part of a powder compacting equipment  1100  with the upper punch die when taken along the line C-C′ of  FIG. 3A  thereof as an upper punch die  1130 .  FIG. 11A  shows the structure of the equipment when the upper punch die is moved up before the powder compacting operation.  FIG. 11B  shows the structure of the equipment immediately after the powder compacting operation of moving down the upper punch die  1130 , and moving down the lower punch die  1140  to press powder  1101  and to form a powder compacting body  1102 , and before the extraction operation of extracting the powder compacting body  1102 . 
       FIGS. 11A and 11B , on the left side with respect to the central axis D, show the structure of the punch die portion with the protrusion portion in the equipment, and on the right side with respect to the central axis D, show the structure of the punch die portion without the protrusion portion in the equipment. 
     As shown in  FIG. 11A , in the powder compacting equipment  1100 , a lower punch die  1140  is disposed at the outside portion of the outer peripheral surface of the core die  1100  to apply a pressing force from the downside. In addition, a die  1120  is disposed at the outside portion of the outer peripheral surface of the lower punch die  1140 . An upper punch die  1130  is disposed above a space E formed by the die  1120 , the core die  1110 , and the lower punch die  1140  to apply a pressing force from the upside. 
     In the powder compacting equipment  1100  with this configuration, as shown in  FIG. 11A , the powder  1101  is filled into the space E formed by the die  1120 , the core die  1110 , and the lower punch die  1140 . Then, as depicted by the white arrow of  FIG. 11B , the upper punch die  1130  is moved down to apply a load to the powder  1101  from the upside thereof, and the lower punch die  1140  is moved down to apply a load to the powder  1101  from the downside thereof. As described above, the powder compacting body  1102  is formed by performing the powder compacting operation of pressing the powder  1101  by the use of the die  1120 , the core die  1110 , the lower punch die  1140 , and the upper punch die  1130 . 
     In addition, the powder compacting body having a structure shown in  FIG. 1  is formed in such a manner that a powder magnetic core material is used as powder, and a load is applied from the powder compacting equipment of the press machine thereto to have the total density of the powder compacting body in which the powder magnetic material constituting the powder is not less than 92% of true density. 
     Further,  FIG. 1A  is a perspective view showing a powder compacting body  100  formed by the powder compacting equipment  1100 , and  FIG. 1B  is an enlarged perspective view showing an outer peripheral surface of a part F of the powder compacting body  100  shown in  FIG. 1A . 
     As shown in  FIGS. 1A ,  1 B,  11 A, and  11 B, the powder compacting body  100  having three protrusion portions  120  formed on the upper surface of the donut-shaped body portion  110  in the circumferential direction is formed by using the powder compacting equipment  1100 . 
     The powder compacting body  100  has a substantially cylindrical shape, and has the protrusion portion  120  formed on the inner peripheral side thereof to protrude in the axial direction or the stepped portion or the concave portion formed in the radial direction, that is, the stepped portion or the concave portion formed in the radial direction to form the protrusion portion  120 . 
     However, in the punch die  400  shown in  FIG. 4 , cracking occurs due to stress concentration in the corner portion  430  during the powder compacting operation, and hence the punch die is damaged after a short period of time. 
     Since the load applied to the punch die becomes larger as the true density of the powder of the powder compacting body becomes higher, the life span of the punch die becomes shorter. 
     On the contrary, since the punch die  300  of the first embodiment has a structure in which the punch die  300  is vertically divided into two parts, that is, the upper punch die  310  and the down punch die  320  at the surface forming the same surface as the lower surface of the protrusion portion, as shown in  FIG. 3 , stress concentration does not occur in the corner portion (not shown) formed by the inner peripheral surface  321  and the lower surface  331  of the protrusion portion of the punch die  300  because of the forming of the corner portion by the separate upper punch die  310  and the separate down punch die  320 , and excessive stress is prevented from being applied to the punch die  300 , thereby preventing the damage thereto. 
     In addition, in this embodiment, the powder compacting body  100  shown in  FIGS. 1A and 1B  may have a structure in which a curvature radius  123  in a connection portion of a front end surface  121  and an outer peripheral surface  122  of the protrusion portion  120  is almost zero. 
     On the other hand, in the case of  FIG. 2 , since a corner portion  223  of the powder compacting body  200  shown in  FIG. 2B  has a curved shape, the area of the flat region of the front end surface  221  becomes small. 
     Likewise, when the flatness of the front end surface of the protrusion portion of the powder compacting body is improved, the following effects can be obtained. 
     1) In the case where the front end surface of the protrusion portion of the powder compacting body is overlapped, when the front end surface of the protrusion portion is flat, it is possible to further improve the adhesion force. 
     2) It is desirable that all end surfaces constituted by the front end surface of the powder compacting body are flat on the ground so that the powder compacting body for the equipment having a narrow width can be decreased in thickness. 
     3) In the application of forming a motor core or the like using a powder magnetic core material, since the iron amount is increased in the same physical shape by avoiding the unnecessary curved shape, the motor output power or motor torque is increased. 
     In addition, in the first embodiment described above, as shown in  FIG. 1 , the case is shown in which the number of the protrusion portions of the powder compacting body is three, but the same effect is exhibited even when the number of the protrusion portions is not three. 
     Second Embodiment 
     A second embodiment will be described with reference to  FIGS. 5A and 5B .  FIGS. 5A and 5B  are cross-sectional views showing a structure of a main part of powder compacting equipment  500  of the second embodiment.  FIG. 5A  shows the structure of the equipment when an upper punch die  530  is moved up before the powder compacting operation, and  FIG. 5B  shows the structure of the equipment immediately after the powder compacting operation of moving down the upper punch die  530 , and moving down a lower outer punch die  540  and a lower inner punch die  550  to press powder  501  and to form a powder compacting body  502 , and before the extraction operation of extracting the powder compacting body  502 . It is noted that in  FIG. 5A , reference numeral  510  denotes a core die, and  520  denotes a die. 
     As shown in  FIG. 5A , in this embodiment, the lower punch die pressing the lower surface of the powder compacting body is divided into two parts, that is, the lower inner punch die  550  and the lower outer punch die  540 . When the lower outer punch die  540  is moved up before the powder compacting operation, it is possible to allow the height of the powder of the body portion  110  of the powder compacting body shown in  FIG. 1  to be lower than the height of the powder of the protrusion portion  120  of the powder compacting body. 
     In the state of  FIG. 5A , the upper punch die  530  is moved down to press the powder  501 . Simultaneously, the lower outer punch die  540  is moved down, while applying a load upward, up to a position at which an upper surface  541  of the lower outer punch die  540  is substantially aligned to an upper surface  551  of the lower inner punch die  550 . 
     With the above-described configuration, it is possible to allow the compression amount of the powder in the body portion  110  of the powder compacting body to be substantially equal to the compression amount of the powder in the protrusion portion  120 . That is, it is possible to perform the powder compacting operation while uniformizing the densities of the protrusion portion  120  and the body portion  110  of the powder compacting body. 
     Likewise, when the densities of the protrusion portion and the body portion of the powder compacting body are uniformized, the following effects can be obtained. 
     1) It is possible to uniformize the strength of the powder compacting body in the body portion and the protrusion portion. 
     2) In the application of forming a motor core or the like using a powder magnetic core, magnetic characteristics such as saturation flux density or iron loss are substantially uniformized in the motor core. 
     Third Embodiment 
     A third embodiment will be described with reference to  FIGS. 8A ,  8 B,  9 A, and  9 B.  FIG. 9A  shows a structure of a punch die  900  of the third embodiment, and is a perspective view of the punch die  900  of which an upper punch die  910  and a down punch die  920  are connected to each other.  FIG. 9B  is a perspective view of the punch die  900  of which the upper punch die  910  and the down punch die  920  are separated from each other. 
     As shown in  FIG. 9A , the punch die  900  of the third embodiment is used to form the shape of the protrusion portion in the body portion of the powder compacting body, and is formed in a substantially cylindrical shape, and three protrusion portions  930  formed on the upper inner peripheral surface of the punch die to protrude toward the center axis are arranged in the circumferential direction. A lower surface  931  of the protrusion portion  930  is formed in a double-stage tapered shape in the axial direction to be inclined downward from the inner peripheral side to the outer peripheral side. 
     As shown in  FIG. 9B , the punch die  900  is vertically divided into two parts at a position where the inclinations of the tapered lower surfaces  931  of the protrusion portions  930  are different. That is, the punch die  900  includes an upper punch die  910  and a down punch die  920  which are separable from each other, and the division surface of the punch die  900  forms the same surface as the lower surface of the protrusion portion. 
     The upper and down punch dies are connected to each other at the division surface in accordance with a dividable connection method. For example, the upper and down punch dies can be strongly connected to each other in such a manner that a bolt (not shown) is attached to the down punch die, a nut (not shown) is attached to the upper punch die corresponding to the down punch die, and then the upper and down punch dies are connected to each other by bolt fastening. 
     The method of fastening the upper and down punch dies to each other is not limited to the bolt fastening. For example, the upper and down punch dies  910  and  920  may be connected to each other in such a manner that a concave portion is formed in one of the division surfaces of the upper and down punch dies, and a convex portion is formed in the other thereof, and the concave and convex portions are fitted to each other so as to connect them by press fitting. 
     In addition, the connection of the upper and down punch dies may be performed by adhesive or the like, or screw fastening. 
     As described above, the punch die  900  has a structure in which the upper and down punch dies  910  and  920  are connected to each other at the division surface having a flat face formed by the lower surface of the upper punch die and the upper surface of the down punch die. 
     In addition,  FIG. 8A  is a perspective view showing a powder compacting body  800  formed by the powder compacting equipment  500  using the punch die  900  of  FIG. 9A  as the upper punch die, and  FIG. 8B  is an enlarged perspective view showing an outer peripheral surface of a part I of the powder compacting body  800  shown in  FIG. 8A . 
     The powder compacting body  800  having three protrusion portions  820  formed on an upper surface of a donut-shaped body portion  810  in the circumferential direction is formed on the upper surface of the body portion  810  having a donut-shaped structure by using the powder compacting equipment  500  shown in  FIG. 8A . 
     The powder compacting body  800  has a substantially cylindrical shape, and has the protrusion portion  820  formed on the inner peripheral side thereof to protrude in the axial direction or the stepped portion or the concave portion formed in the radial direction, that is, the stepped portion or the concave portion formed in the radial direction to form the protrusion portion  820 . The upper surface  821  of the protrusion portion  820  of the powder compacting body  800  is provided with a taper  823  which is formed in the circumferential direction to be inclined downward from the inner peripheral side to the outer peripheral side. The upper surface  821  of the protrusion portion  820  is provided with a taper  824  which is formed in the radial direction to be inclined downward from the inside to the outside. An outer peripheral surface  822  of the protrusion portion  820  is provided with a taper  825  which is formed from the upper end to the lower end to be enlarged toward the outer peripheral side. 
     Likewise, when the taper is formed in the punch die, the following effect can be obtained. 
     1) Since the protrusion portion of the powder compacting body is thinned in the axial direction, it is easy to extract the upper punch die from the powder compacting body after the powder compacting operation. 
     Fourth Embodiment 
     A case of performing a powder compacting operation on a stator core of a three dimension (3D) motor of a fourth embodiment will be described with reference to  FIGS. 7A ,  7 B,  10 , and  14 A to  14 C. 
       FIG. 7A  is a cross-sectional view showing a structure of a main part of a powder compacting equipment  700  for performing the powder compacting operation on the 3D motor core, and shows the structure of the equipment of which an upper punch die  730  is moved up before the powder compacting operation.  FIG. 7B  shows the structure of the equipment immediately after the powder compacting operation of moving down the upper punch die  730  and moving down the lower punch die to press the powder and to form a powder compacting body  702 , and before the extraction operation of extracting the powder compacting body  702 . 
       FIGS. 7A and 7B , on the left side of the central axis D, show the structure of the punch die portion with the protrusion portion in the equipment, and on the right side of the central axis D, show the structure of the punch die portion without the protrusion portion in the equipment. 
     As shown in  FIG. 7A , in the powder compacting equipment  700 , a lower inner punch die  750  and a lower outer punch die  740  are disposed at the outside portion of the outer peripheral surface of a core die  710  to apply a pressing force from the downside. In addition, a die  720  is disposed at the outside portion of the outer peripheral surface of the lower outer punch die  740 . An upper punch die  730  is disposed above a space K formed by the die  720 , the core die  710 , the lower inner punch die  750 , and the lower outer punch die  740  to apply a pressing force from the upside. 
     In the powder compacting equipment  700  with this configuration, as shown in  FIG. 7A , powder  701  is filled into the space K formed by the die  720 , the core die  710 , the lower inner punch die  750 , and the lower outer punch die  740 . Then, as depicted by the white arrow of  FIG. 7B , the upper punch die  730  is moved down to apply a load to the powder  701  from the upside thereof, and the lower outer punch die  740  is moved down to apply a load to the powder  701  from the downside thereof. As described above, the powder compacting body  702  is formed by performing the powder compacting operation of pressing the powder  701  by the use of the die  720 , the core die  710 , the lower inner punch die  750 , the lower outer punch die  740 , and the upper punch die  730 . 
     In addition, the powder compacting body having a structure shown in  FIGS. 10 and 14A  to  14 C is formed in such a manner that a powder magnetic core material is used as powder, and a load is applied from the powder compacting equipment of the press machine thereto so that the total density of the powder compacting body in which the powder magnetic material constitutes the powder is not less than 92% of true density. 
     Further,  FIG. 10  is a perspective view showing a powder compacting body  1000  formed by the powder compact equipment  700 , and  FIGS. 14A to 14C  are perspective views showing an example in which a powder compacting body  1410  formed by the powder compacting equipment  700  is applied to a stator of a motor. 
       FIGS. 14A and 14C  are respective perspective views of the stator of the motor of the powder compacting body  1410  formed by the powder compacting equipment  700 , and  FIG. 14B  is a perspective view of a coil  1420  which is sandwiched by the stators of the motor of the powder compacting body  1410 , for passing an electric current. 
     In the above-described configuration, a powder magnetic core material of iron is used, and a load is applied to the powder by using the upper and lower punch dies so that the total densities of the powder compacting body and the protrusion portion of the powder compacting body are not less than 92%. 
     In the past, in such a high density state, as shown in  FIGS. 4A ,  4 B described above, stress concentration occurs in the corner portion  430  of the upper punch die  400 , and hence the punch die  400  may be damaged after a short period of time. Since the load applied to the upper punch die becomes larger as the density of the material of the powder compacting body becomes higher, the life span of the upper punch die becomes shorter. 
     However, in the fourth embodiment, since a corner portion  731  of a punch die  730  is formed in the manner that the upper and down punch dies  732  and  733  are separated from each other and then connected to each other, it is possible to suppress the punch die  730  from being damaged. 
     By means of the above-described powder compacting operation, as shown in  FIGS. 10 ,  14 A, and  14 C, a powder compacting body ( 1000  and  1410 ) having twelve protrusion portions  1020  formed on the upper surface of a ring-structured body  1010  in the circumferential direction is formed. 
     The powder compacting body has a substantially cylindrical shape, and has the protrusion portion  1020  formed on the inner peripheral side thereof to protrude in the axial direction, or the stepped portion or the concave portion formed in the radial direction, that is, the stepped portion or the concave portion formed in the radial direction to form the protrusion portion  1020 . 
     In the powder compacting body  1000 , as shown in  FIGS. 7A and 7B , the punch die  730  of the powder compacting equipment  700  for forming the powder compacting body  1000  is divided into two parts, that is, the upper punch die  732  and the down punch die  733 . In addition, a connection portion  1023  of a front end surface  1022  and the outer peripheral surface  1021  of the protrusion portion  1020  of the powder compacting body shown in  FIG. 10  is formed by the inner peripheral surface of the down punch die and the lower surface of the protrusion portion of the upper punch die, as shown in  FIG. 10 . The connection portion  1023  of the powder compacting body can be formed in an angular shape such as a perpendicular surface having a non-curved structure and a non-perpendicular surface, and the front end surface  1022  can be formed as a flat surface. 
     In this embodiment, the punch die is divided only at the position  731  corresponding to the inner peripheral protrusion portion of the powder compacting body, but the punch die may be divided at the stepped portion  734  of the outer peripheral side of the powder compacting body. Further, both of them may be used together. 
     Likewise, when the flatness of the front end surface of the protrusion portion of the powder compacting body is improved, the following effects can be obtained. 
     1) When the front end surface of the protrusion portion of the powder compacting body is overlapped, it is possible to further improve the adhesion force on the flat surface. Since it is possible to maximize the connection surface in the front end surface having a large flat region during the connection between the front end surface and the planar material, it is possible to further improve the adhesion force, and to remove the unnecessary space. 
     2) It is desirable that the front end surface is flat on the ground that the powder compacting body for the equipment having a narrow width can be decreased in thickness. 
     In the fourth embodiment, the case has been described in which the curvature radius R is zero, but even when the curvature radius is not zero, if R/δ&lt;0.2, or R&lt;0.1 mm, the above-described effect can be sufficiently obtained. In addition, as shown in  FIG. 10 , δ indicates the width of the front end surface of the protrusion portion of the powder compacting body. 
     Then, as the value becomes smaller to be R/δ&lt;0.1 and R/δ&lt;0.05, the above-described effect is improved. As the curvature radius becomes a small value to be R&lt;0.1 mm and R&lt;0:05 mm, the above-described effect is improved. 
     When the total density of the powder compacting body becomes high to be not less than 92% of the true density of the material constituting the powder, the following effects can be obtained. 
     1) Since the powder compacting body becomes rigid in accordance with an increase in the density thereof, it is possible to improve the strength of the powder compacting body. 
     2) In the case of mounting the powder compacting body to a restricted space, the present invention is effective. 
     3) The powder compacting body can be formed by net shape manufacture and the productivity is improved. 
     In addition, when the powder compacting body is utilized in a motor core or the like using a powder magnetic core material, the following effect can be obtained. 
     4) Since the powder compacting body can be formed in a more desired shape, the distortion of magnetic flux is suppressed, and the density of magnetic flux is improved. Also, the motor output power or motor torque depending on the magnetic flux becomes large. 
     Then, since the maximum stress is reduced, the following effects are obtained. 
     1) Since the stress applied to the powder compacting body is averaged, it is possible to uniformize the density of the powder compacting body. 
     2) Since it is possible to reduce residual stress concentrating on a part of the powder compacting body, it is possible to reduce hysteresis loss. 
     3) In the case of using the insulatively coated powder magnetic core material as the powder, since the stress applied to the powder compacting body is averaged without concentration, the breakage of the insulating coating is prevented, and hence the eddy current loss is reduced. 
     4) Since the stress concentration in the punch die is prevented, it is possible to prolong the life span of the die without a risk of excessive stress. 
     5) As described above, the present invention is effective in the application to the components of the motor, the components of the actuator, or the loading components. 
     Fifth Embodiment 
     A fifth embodiment will be described with reference to  FIGS. 13A and 13B .  FIGS. 13A and 13B  are cross-sectional views showing a structure of a main part of the fifth embodiment, and  FIG. 13A  shows a structure of an equipment  1300  of which an upper punch die  1330  is moved up before the powder compacting operation.  FIG. 13B  shows the structure of the equipment immediately after the powder compacting operation of moving down the upper punch die  1330 , and moving down a lower inner punch die  1350  to press a powder  1301  and to form a powder compacting body  1302 , and before the extraction operation of extracting the powder compacting body  1302 . 
     The powder compacting body formed in this embodiment has a protrusion portion  1303  formed in the outer peripheral side thereof, but as in the fourth embodiment, the same effect is obtained by dividing the punch die into an upper punch die  1332  and a down punch die  1333  at a protrusion upper end portion or a counter portion  1331 . In addition, the punch die may be divided at a stepped portion  1334  of the inner peripheral portion of the powder compacting body. Further, the same effect can be obtained even when both of them are used in combination. 
     It should be further understood by those skilled in the art that although the foregoing description has been made on embodiments of the invention, the invention is not limited thereto and various changes and modifications may be made without departing from the spirit of the invention and the scope of the appended claims.