Patent Publication Number: US-9421609-B2

Title: Method for manufacturing rotor

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application is based on and claims the benefit of priority from Japanese Patent Application No. 2013-251323, filed Dec. 4, 2013, the disclosure of which is incorporated herein in its entirety by reference. 
     BACKGROUND 
     1. Technical Field 
     The present invention relates to a method for manufacturing a rotor of a rotating electric machine that is, for example, mounted in a vehicle, and used as a motor or a generator. 
     2. Related Art 
     A motor with a squirrel-cage rotor is known in related art as a type of rotating electric machine used to be mounted in a vehicle or the like. The squirrel-cage rotor has a squirrel-cage structure with conductors having both axial ends that are short-circuited together. The squirrel-cage rotor includes a rotor core and a conductive member. 
     The rotor core is composed of a plurality of steel plates that are stacked in an axial direction of the rotor. The plurality of steel plates have a center shaft hole and a plurality of through holes. The center shaft hole passes through the steel plates in the axial direction. The plurality of through holes pass through the steel plates in the axial direction and are arrayed in a circumferential direction of the rotor. 
     The conductive member has a pair of end rings and a plurality of connection bars. The pair of end rings are disposed on both axial ends of the rotor core in the axial direction. The plurality of connection bars connect the pair of end rings through the through holes. The conductive member is integrally formed by casting. 
     A method for manufacturing a squirrel-cage rotor in related art such as that described above involves a setting step and a casting step. At the setting step, a plurality of steel plates configuring a rotor are stacked in an axial direction of the rotor and set in a predetermined position in a mold. At the casting step, molten metal is fed into a molten metal introduction passage, thereby forming a conductive member. The molten metal introduction passage has a gate that opens onto one axial end side of the stacked steel plates that are set in the mold. 
     In this method, as shown in  FIG. 24 , the molten metal is introduced from a gate  124   a  of a molten metal introduction passage  124  into an end ring cavity  123   a  on one axial end side of the set stacked steel plates. The introduced molten metal then flows into the plurality of through holes  113  provided in the stacked steel plates  111   a , in the order from a through hole  113   a , which is located at a position nearest to the gate  124   a  in a radial direction D2, to a through hole  113   b  which is located at a position furthest from the gate  124   a  in the radial direction D2. Therefore, the molten metal flowing into the through hole  113   a  reaches an end ring cavity  123   b  on the other axial end side of the set stacked steel plates first. 
     The molten metal flowing from the through hole  113   a  then reaches, via the other axial end side, the through hole  113   b  ahead of the molten metal that flows into the through hole  113   b  from the one axial end side. As a result, the flow of molten metal from the other axial end side merges with the flow of molten metal from the one axial end side. A problem occurs in that a cold shut may be thereby formed. 
     In addition, as shown in section A in  FIG. 25 , a problem also occurs in that a blowhole may be formed as a result of air within the mold becoming trapped in a connection bar  117  that is formed within the through hole  113   b . When the blowhole and the above-described cold shut are formed in this way, properties, such as strength and conductivity, of the conductive member are significantly affected. 
     Therefore, JP-A-563-73852 proposes improving the balance of flow of the molten metal that flows through the through holes in the rotor core. The improvement is made by a cylindrical ring being provided at the axial end portion of the pair of end rings disposed on both axial end sides of the rotor core. The cylindrical ring has a radial-direction thickness that is thinner than the end ring. 
     In addition, JP-A-S60-204244 proposes a technique for improving the balance of flow of the molten metal that flows through the through holes in the rotor core. The technique involves providing a plurality of gates in the circumferential direction. The gates each open into the end ring cavity on the one axial end side of the stacked steel plates that are set in the mold. 
     However, in the case of above-described JP-A-S63-073852, a casting defect caused by solidification shrinkage of the molten metal easily occurs in areas in which the thickness of the end ring is increased. In addition, when a cutoff process is performed to ensure product shape after completion of the casting step, a problem occurs in that the casting defect is exposed on the surface. 
     On the other hand, in the case of above-described JP-A-S60-204244, the plurality of gates that open into the end ring cavity are evenly disposed in the circumferential direction. However, there is a limit to the number of gates that can be disposed. Although the balance of flow is improved compared to when the molten metal flows in from the end portion of the end ring as in the past, described above, the flow is not completely even. 
     Furthermore, in the case of JP-A-S60-204244, when the gates are cut off after completion of the casting step, tensile stress between the gate portion and the product part is used to cut off the gates. Therefore, a large load is also applied to the product part. The gate portion is required to be made smaller to prevent the large load from being applied to the product part. However, when the gates are made smaller, the fluidity of the molten metal becomes extremely poor. A problem occurs in that casting defects easily occur because casting pressure becomes difficult to apply. 
     SUMMARY 
     It is thus desired to provide a method for manufacturing a rotor in which the fluidity of molten metal is improved and the occurrence of casting defects can be suppressed. 
     An exemplary embodiment of the present disclosure provides present invention that has been achieved to solve the above-described problems is a method for manufacturing a rotor. 
     The rotor includes a rotor core and a conductive member. The rotor core is composed of a plurality of steel plates that are stacked in an axial direction of the rotor. The steel plates have a center shaft hole and a plurality of through holes. The center shaft hole passes through the steel plates in the axial direction. The plurality of through holes pass through the steel plates in the axial direction and are arrayed in a circumferential direction of the rotor. The conductive member has a pair of end rings and a plurality of connection bars. The pair of end rings are disposed on both axial ends of the rotor core. The plurality of connection bars connect the pair of end rings through the through holes. The conductive member is integrally formed by casting. 
     The method for manufacturing a rotor includes a setting step, a casting step, a cutoff step, and a mold-releasing step. The setting step includes setting, in a predetermined position in a mold, the plurality of steel plates configuring the rotor core stacked in the axial direction. The mold can be opened and closed by relative movement in the axial direction. The casting step includes feeding molten metal into a molten metal introduction passage such that the conductive member is formed. The molten metal introduction passage has a ring-shaped gate that is opened so as to oppose one axial end surface of the plurality of steel plates set in the mold. The cutoff step includes cutting off the molten metal in the molten metal introduction passage so as to be separated into a gate side and a molten metal introduction opening side. The mold-releasing step includes opening the mold such that a casting configuring the rotor is removed from the mold. 
     In the method for manufacturing a rotor of exemplary embodiment, the mold used at the casting step is provided with the molten metal introduction passage that has the ring-shaped gate. The gate is opened so as to oppose the one axial end surface of the plurality of steel plates set in the mold. Therefore, the molten metal that has been fed into the molten metal introduction passage can be sent to flow evenly in a radiating direction from the ring-shaped gate. 
     As a result, the molten metal can be sent into a cavity in the mold so as to flow evenly in the circumferential direction. The molten metal can therefore flow into each through hole in the plurality of steel plates set in the mold, in a well-balanced manner. As a result, fluidity of the molten metal is improved. The occurrence of casting defects, such as blowholes, can be suppressed. 
     In the present disclosure, a well-known technique, such as die casting, gravity casting, or sand-mold casting, can be used at the casting step. In addition, the material of the conductive member formed by casting can be, for example, aluminum, copper, zinc, magnesium, or a combination of two or more of such materials. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       In the accompanying drawings: 
         FIG. 1  is a flowchart of a method for manufacturing a rotor according to a first embodiment; 
         FIG. 2  is a planar view of the rotor manufactured by the method for manufacturing a rotor according to the first embodiment; 
         FIG. 3  is a cross-sectional view taken along III-III in  FIG. 2 ; 
         FIG. 4  is a front view of the rotor manufactured by the method for manufacturing a rotor according to the first embodiment; 
         FIG. 5  is a cross-sectional view taken along V-V in  FIG. 4 ; 
         FIG. 6  is an explanatory diagram of a setting step in the method for manufacturing a rotor according to the first embodiment; 
         FIG. 7  is a cross-sectional view of stacked steel plates in a direction perpendicular to a shaft, the stacked steel plates being held by a holding pin, at the setting step in the method for manufacturing a rotor according to the first embodiment; 
         FIG. 8  is an explanatory diagram of a casting step in the method for manufacturing a rotor according to the first embodiment; 
         FIG. 9  is a flowchart of the casting step in the method for manufacturing a rotor according to the first embodiment; 
         FIG. 10  is an explanatory diagram of the flow of molten metal in an axial direction from a gate at the casting step in the method for manufacturing a rotor according to the first embodiment; 
         FIG. 11  is an explanatory diagram of the flow of molten metal in a radial direction from the gate at the casting step in the method for manufacturing a rotor according to the first embodiment; 
         FIG. 12  is an explanatory diagram of a state immediately before a cutoff step in the method for manufacturing a rotor according to the first embodiment; 
         FIG. 13  is an explanatory diagram of the cutoff step in the method for manufacturing a rotor according to the first embodiment; 
         FIG. 14  is an explanatory diagram of a mold-releasing step in the method for manufacturing a rotor according to the first embodiment; 
         FIG. 15  is an explanatory diagram of a cutoff state by a cutoff portion of the holding pin in a first variation example; 
         FIG. 16  is an explanatory diagram of a cutoff state by the cutoff portion of the holding pin in a second variation example; 
         FIGS. 17A to 17F  are explanatory diagrams of a method for connecting the holding pin and a driving unit in a third variation example; 
         FIGS. 18A to 18C  are explanatory diagrams of a method for connecting the holding pin and the driving unit in a fourth variation example; 
         FIGS. 19A to 19C  are explanatory diagrams of a method for connecting the holding pin and the driving unit in a fifth variation example; 
         FIG. 20  is a schematic cross-sectional view of a casting apparatus that includes a driving mechanism of the holding pin in a sixth variation example; 
         FIG. 21  is an explanatory diagram of the holding pin in a seventh variation example; 
         FIG. 22  is an explanatory diagram of the holding pin in an eighth variation example; 
         FIG. 23  is an explanatory diagram of the holding pin in a ninth variation example; 
         FIG. 24  is an explanatory diagram of a problem in a common conventional manufacturing method; and 
         FIG. 25  is an explanatory diagram of another problem in the common conventional manufacturing method. 
     
    
    
     DESCRIPTION OF THE EMBODIMENTS 
     A method and an apparatus for manufacturing a rotor according to an embodiment of the present disclosure will hereinafter be described in detail with reference to the drawings. 
     First Embodiment 
     The method for manufacturing a rotor according to the present embodiment will be described with reference to  FIGS. 1 to 14 . First, a rotor  10  that is manufactured by the manufacturing method according to the present embodiment will be described. The rotor  10  is a squirrel-cage rotor that is mounted in a rotating electric machine (not shown). The rotating electric machine is used as, for example, a squirrel-cage three-phase motor for a vehicle. In the following descriptions, an axial direction, a radial direction, and a circumferential direction of the rotor  10  and an apparatus (including a casting apparatus) for manufacturing the rotor  10  are respectively denoted by D1, D2, and D3. 
     As shown in  FIGS. 2 to 5 , the rotor  10  includes a rotor core  11  and a conductive member  15 . The rotor core  11  is composed of a plurality of steel plates that are stacked in the axial direction D1. The conductive member  15  has a pair of end rings  16  and a plurality of connection bars  17  (see  FIG. 3 ). The plurality of connection bars  17  connect the two end rings  16 . The conductive member  15  is integrally formed by casting. 
     The rotor core  11  is formed by a plurality of ring plate-shaped steel plates  11   a  being stacked in the axial direction D1. The steel plates  11   a  have a center shaft hole  12  and a plurality (16 according to the present embodiment) through holes  13  (see  FIG. 5 ). The center shaft hole  12  passes through the steel plates  11   a  in the axial direction D1. The plurality of through holes  13  pass through the steel plates  11   a  in the axial direction D1 and are arrayed in the circumferential direction D3. 
     The pair of end rings  16  configuring the conductive member  15  are disposed on both axial ends of the rotor core  11 . The connection bars  17  configuring the conductive member  15  connect the pair of end rings  16  via the through holes  13 . According to the present embodiment, 16 connection bars  17  are provided. 
     Next, the method for manufacturing the rotor  10  according to the present embodiment will be described. The manufacturing method according to the present embodiment manufactures the rotor  10  by aluminum die casting. As shown in the flowchart in  FIG. 1 , a setting step S 10 , a casting step S 20 , a cutoff step S 30 , and a mold-releasing step S 40  are performed in sequence. 
     At the setting step S 10 , the plurality of steel plates  11   a  configuring the rotor core  11  are stacked in the axial direction D1 and set in a predetermined position of a mold  21  in a casting apparatus  20  that is used for manufacturing the rotor  10 . The mold  21  can be opened and closed by relative movement in the axial direction D1. As shown in  FIG. 6 , the mold  21  used herein is mounted in the casting apparatus  20 . The mold  21  includes a fixed mold  22  and a movable mold  23 . The fixed mold  22  has a cavity  22   a  in which the plurality of steel plates  11   a  configuring the rotor core  11  are set. The movable mold  23  is provided so as to be capable of relative movement (approaching and separating) in the axial direction D1 (the left/right direction in  FIG. 6 ) in relation to the fixed mold  22 , by a driving unit (not shown). 
     The movable mold  23  is provided with a molten metal introduction passage  24 . The molten metal introduction passage  24  feeds molten metal into the cavity  22   a . The molten metal introduction passage  24  has a ring-shaped gate  24   a . The gate  24   a  opens so as to oppose one axial end surface (the right end surface in  FIG. 6 ) of the plurality of steel plates  11   a  set in the cavity  22   a  of the fixed mold  22 . The gate  24   a  according to the present embodiment is formed into a ring shape that makes a single continuous circuit in the circumferential direction D3. A cylindrical sloped passage  24   b  is disposed on the gate  24   a  side of the molten metal introduction passage  24 . The sloped passage  24   b  is sloped so as to gradually increase in diameter towards the gate  24   a.    
     In addition, the plurality of steel plates  11   a  that are set in the cavity  22   a  of the fixed mold  22  are held by a holding pin  25  in a state in which the steel plates  11   a  are stacked in the axial direction D1. The holding pin  25  includes a shaft portion  25   a  and a blocking portion  25   b . The shaft portion  25   a  is inserted into the center shaft hole  12  of the steel plates  11   a . The blocking portion  25   b  is disposed on one axial end portion of the shaft portion  25   a . The blocking portion  25   b  blocks an opening of the center shaft hole  12  on the molten metal feeding side. 
     As shown in  FIG. 7 , a positioning portion is provided in the shaft portion  25   a  of the holding pin  25 . The positioning portion performs positioning in a rotation direction (circumferential direction D3) of the plurality of steel plates  11   a  that are fitted onto the shaft portion  25   a . According to the present embodiment, the positioning portion is composed of an engaging recessing portion  26   a  and an engaging projecting portion  26   b . The engaging recessing portion  26   a  is provided in the center shaft hole  12  of the steel plates  11   a . The engaging projecting portion  26   b  is disposed on the outer peripheral surface of the shaft portion  25   a . The engaging projecting portion  26   b  is capable of engaging with the engaging recessing portion  26   a . The projecting/recessing relationship between the engaging recessing portion  26   a  and the engaging projecting portion  26   b  may also be reversed. 
     The blocking portion  25   b  of the holding pin  25  is formed into a circular truncated cone shape. The blocking portion  25   h  gradually decreases in diameter as the blocking portion  25   b  becomes farther away from the shaft portion  25   a . The diameter of the bottom surface on the large diameter side of the blocking portion  25   b  is a predetermined dimension that is larger than the diameter of the shaft portion  25   a.    
     As shown in  FIG. 8 , the holding pin  25  is set together with the plurality of steel plates  11   a  in the cavity  22   a  of the fixed mold  22 . The end portion of the holding pin  25  on the opposite side of the blocking portion  25   b  is connected to a driving unit  31 . The driving unit  31  is configured by an air cylinder or the like. The holding pin  25  is thereafter pulled towards the left side in  FIG. 8  by the driving unit  31 . 
     As a result, the bottom surface of the blocking portion  25   b  on the large diameter side comes into contact with the one direction end of the steel plates  11   a . The opening of the center shaft hole  12  on the molten metal feeding side is blocked. Inflow of molten metal into the center shaft hole  12  is prevented. The holding pin  25  and the driving unit  31  are connected by, for example, connection methods described in third to fifth variation examples, described hereafter. 
     The blocking portion  25   b  is fitted into the sloped passage  24   b  of the movable mold  23  when the mold  21  is closed. The mold  21  is closed by the fixed mold  22  and the movable mold  23  being moved so as to approach each other in the axial direction D1. 
     As a result, the cylindrical sloped passage  24   b  is formed between the outer peripheral wall of the sloped passage  24   b  and the outer peripheral surface of the blocking portion  25   b . The sloped passage  24   b  is sloped so as to gradually increase in diameter towards the gate  24   a  side. The slope angle of the outer peripheral wall surface of the sloped passage  24   b  and the slope angle of the outer peripheral surface of the blocking portion  25   b  in relation to a center axial line L1 of the shaft portion  25   a  are substantially the same. 
     Therefore, the sloped passage  24   b  is formed into a cylindrical shape having a substantially fixed thickness. The ring shaped gate  24   a  is formed in the end portion of the sloped passage  24   b  on the large diameter side. The gate  24   a  makes a single continuous circuit in the circumferential direction D3. In other words, the inner peripheral surface side of the sloped passage  24   b  is partitioned by the outer peripheral surface of the blocking portion  25   b.    
     From the state after completion of the setting step S 10  shown in  FIG. 6 , the subsequent casting step S 20  is performed based on the flowchart shown in  FIG. 9 . In other words, molten aluminum is injected into the molten metal introduction passage  24  in the mold  21  under predetermined pressure, and then, filling is started (step S 21 ). At this time, as shown in  FIG. 10 , the molten metal that has been injected into the molten metal introduction passage  24  flows through the sloped passage  24   b . The molten metal then flows from the gate  24   a  into the cavity  23   a  of the movable mold  23 . 
     According to the present embodiment, the sloped passage  24   b  is formed into a cylindrical shape that is sloped so as to gradually increase in diameter towards the gate  24   a . The gate  24   a  is also formed into a ring shape. Therefore, as shown in  FIG. 11 , the molten metal that flows from the gate  24   a  into the cavity  23   a  flows evenly in a radiating direction (radial direction D2). 
     As shown in  FIG. 10 , the molten metal within the cavity  23   a  then flows through each through hole  13  in the stacked steel plates  11   a  into the cavity  22   a  of the fixed mold  22 . As a result, the molten metal fills each through hole  13  and the interior of both cavities  22   a  and  23   a . In this state, filling is completed (step S 22 ). Then, when the molten metal filling the through holes  13  and the cavities  22   a  and  23   a  starts to solidify (step S 23 ), shrinkage occurs with temperature decrease. Therefore, the through holes  13  and the cavities  22   a  and  23   a  are refilled with molten metal, and then, solidification of the filled molten metal is completed (step S 24 ). After the elapse of a predetermined amount of time, the subsequent cutoff step S 30  is performed. 
     As shown in  FIG. 12 , at the cutoff step S 30 , the driving unit  31  moves the holding pin  25  towards the blocking portion  25   b  side (the right side in  FIG. 12 ). The molten metal in the sloped passage  24   b  is locally pressurized. As a result, as shown in  FIG. 13 , the outer peripheral wall of the blocking portion  25   b  of the holding pin  25  comes into contact with the outer peripheral wall surface of the sloped passage  24   b . The molten metal within the sloped passage  24   b  is cut off, and separated into the gate  24   a  side and the molten metal introduction opening side. As a result, casting defects accompanying solidification shrinkage of the molten metal are prevented from occurring. At the same time, cut-off of the molten metal near the gate  24   a  of the sloped passage  24   b  is facilitated. 
     After the cutoff step S 30  is completed and solidification of the molten metal is completed, the subsequent mold-releasing step S 40  is performed. As shown in  FIG. 14 , a driving unit (not shown) relatively moves the movable mold  23  so as to separate from the fixed mold  22  in the axial direction D1 (towards the right side in  FIG. 14 ). The mold  21  is thereby opened. In this state, a casting  10 A (rotor  10 ) is removed from the cavity  22   a  of the fixed mold  22 . The holding pin  25  is pulled out and removed. The mold-releasing step S 40  is completed. Thereafter, post-processing, such as deburring, is performed as required. All steps are then completed. The rotor  10  that is the product shown in  FIG. 2  to  FIG. 5  is thereby completed. 
     As described above, in the method for manufacturing the rotor  10  according to the present embodiment, the mold  21  that is used at the casting step S 20  is provided with the molten metal introduction passage  24 . The molten metal introduction passage  24  has the ring-shaped gate  24   a . The gate  24   a  opens so as to oppose the one axial end surface of the plurality of steel plates  11   a  set in the mold  21 . As a result, the molten metal can be sent into the cavity of a mold in a well-balanced manner, so as to flow evenly in the circumferential direction D3. Therefore, fluidity of the molten metal becomes favorable. The occurrence of casting defects, such as blowholes, can be suppressed. 
     In addition, according to the present embodiment, the molten metal introduction passage  24  has the cylindrical sloped passage  24   b . The sloped passage  24   b  is sloped so as to gradually increase in diameter towards the gate  24   a . As a result, the molten metal that is fed into the molten metal introduction passage  24  can be smoothly sent from the sloped passage  24   b  towards the gate  24   a  so as to flow evenly in the circumferential direction D3. 
     In addition, according to the present embodiment, at the setting step S 10 , the plurality of steel plates  11   a  that are set in the mold  21  are held by the holding pin  25 . The holding pin  25  includes the shaft portion  25   a  and the blocking portion  25   b . The shaft portion  25   a  is inserted into the center shaft hole  12 . The blocking portion  25   b  is provided in the one axial end portion of the shaft portion  25   a . The blocking portion  25   b  blocks the opening of the center shaft hole  12  on the molten metal feeding side. 
     Therefore, risk of the plurality of steel plates  11   a  set in the mold  21  becoming separated by pressure from the molten metal can be prevented. In addition, the blocking portion  25   b  can prevent the molten metal from flowing into the center shaft hole  12  of the plurality of steel plates  11   a . As a result, occurrence of defective products and reduced dimensional accuracy can be prevented. 
     In addition, the holding pin  25  according to the present embodiment has the engaging projecting portion  26   b  (positioning portion). The engaging projecting portion  26   b  performs positioning in the rotation direction of the plurality of steel plates  11   a  fitted onto the shaft portion  25   a . Therefore, when the stacked plurality of steel plates  11   a  are set in the mold  21 , the rotation-direction positions of the mold  21 , the plurality of steel plates  11   a , and the holding pin  25  can be clarified. As a result, occurrence of defective products and reduced dimensional accuracy can be prevented with further certainty. 
     In addition, according to the present embodiment, at the cutoff step S 30 , the molten metal is cut off as a result of the driving unit  31  moving the holding pin  25  in the axial direction D1. The blocking portion  25   b  thereby comes into contact with the outer peripheral wall surface of the sloped passage  24   b . As a result, the cutoff step S 30  can be simply and easily performed using the holding pin  25 . 
     Other Embodiments 
     The present disclosure is not limited to the above-described embodiment. Various modifications are possible without departing from the scope of the present disclosure. Hereafter, these modifications are described in detail by first to ninth variation examples. Components and sections in the first to ninth variation examples that are common to the first embodiment are given the same reference numbers. 
     First Variation Example 
     The holding pin  25  according to the first embodiment is configured so that the slope angle of the outer peripheral surface of the blocking portion  25   b  and the slope angle of the outer peripheral wall surface of the sloped passage  24   b  in relation to the center axial line L1 of the shaft portion  25   a  are substantially the same. The molten metal is cut off by the overall outer peripheral surface of the blocking portion  25   b  coming into contact with the outer peripheral wall surface of the sloped passage  24   b.    
     Instead of this configuration, as in a first variation example shown in  FIG. 15 , a cutoff portion  27  may be disposed on an opposing surface of the blocking portion  25   b  that opposes the outer peripheral wall surface of the sloped passage  24   b . The cutoff portion  27  is formed by a corner portion at which two surfaces, i.e., an outer peripheral surface and a tip surface of the blocking portion  25   b  meet (intersect). 
     In the cutoff portion  27  in this instance, the slope angle of the outer peripheral surface of the blocking portion  25   b  in relation to the center axial line L1 is smaller than the slope angle of the outer peripheral wall surface of the sloped passage  24   b  in relation to the center axial line L1. Therefore, the cutoff portion  27  is formed by the corner portion in which the outer peripheral surface and the tip surface of the blocking portion  25   b  meet. 
     In the first variation example, a shape is formed that facilitates the application of localized stress on the outer peripheral wall surface of the sloped passage  24   b . Therefore, cut-off of the molten metal within the sloped passage  24   b  can be easily performed with certainty. 
     Second Variation Example 
     Instead of the above-described first variation example, cutting portions  28  may be provided in two locations of the blocking portion  25   b , as in a second variation example shown in  FIG. 16 . In this instance, the blocking portion  25   b  is formed into a two-step columnar shape composed of a large diameter portion and a small diameter portion. One cutoff portion  28  is formed by a corner portion in which the outer peripheral surface of the large diameter portion and a ring-shaped plane of a stepped portion meet. The other cutoff portion  28  is formed by a corner portion in which the outer peripheral surface of the small diameter portion and the tip surface of the blocking portion  25   b  meet. 
     In the second variation example, the cutoff portions  28  are formed in two locations on the outer peripheral surface of the blocking portion  25   b . Therefore, compared to the first variation example, cut-off of the molten metal within the sloped passage  24   b  can be more easily performed with further certainty. 
     Third Variation Example 
     As shown in  FIGS. 17A to 17F , a third variation example is an example of a connection method for connecting the holding pin  25  and the driving unit  31  in the above-described first embodiment. A lock mechanism actualized by rotation is used.  FIGS. 17D to 17F  show the state at a position shifted by about 90° in the circumferential direction D3 in relation to the position in  FIGS. 17A to 17C . 
     In this instance, a pair of engaging protrusions  41  are provided in the one axial end portion (the right end portion in  FIGS. 17A to 17F ) of a cylinder rod  31 A of the driving unit  31 . The pair of engaging protrusions  41  are provided in positions on the outer peripheral surface that are phase-shifted by 180°. 
     Meanwhile, an insertion hole  42  and a pair of engaging grooves  43  are provided in the end portion on the opposite side of the blocking portion  25   b  (the left end portion in  FIGS. 17A to 17F ) of a shaft portion  251   a  of the holding pin  25 . The one axial end portion of the cylinder rod  31 A is inserted into the insertion hole  42 . The pair of engaging protrusions  41  engage with the pair of engaging grooves  43 . The insertion hole  42  opens onto the end surface on the opposite side of the blocking portion  25   b  of the shaft portion  251   a  and extends in the axial direction D1. 
     In addition, the engaging groove  43  is formed so as to bend at a right angle in the circumferential direction D3 after extending for a predetermined distance in the axial direction D1 from the end surface on the opposite side of the blocking portion  25   b  of the shaft portion  251   a.    
     The connection operation in the third variation example is performed as follows. First, as shown in  FIGS. 17A and 17D , the shaft portion  251   a  of the holding pin  25  and the cylinder rod  31 A are disposed in a state in which the respective axial end surfaces oppose each other in the axial direction D1. 
     At this time, positioning of the engaging protrusions  41  of the cylinder rod  31 A and the engaging grooves  43  of the shaft portion  251   a  is performed. From this state, as shown in  FIGS. 17B and 17E , the tip of the cylinder rod  31 A is relatively moved in the axial direction D1 and inserted into the insertion hole  42  of the shaft portion  251   a.    
     Then, after the engaging protrusions  41  reach the innermost end of the engaging grooves  43 , as shown in  FIGS. 17C and 17F , the cylinder rod  31 A is relatively rotated in the circumferential direction D3. As a result, the engaging protrusions  41  are engaged with the engaging grooves  43  that extend in the circumferential direction D3. 
     The cylinder rod  31 A and the shaft portion  251   a  are connected in a state in which relative movement in the axial direction D1 is restricted. 
     In the connection method of the third variation example, the lock mechanism actualized by rotation is used. Therefore, the cylinder rod  31 A and the shaft portion  251   a  can be connected with certainty by a simple and easy operation. 
     Fourth Variation Example 
     A fourth variation example is an example of another connection method for connecting the holding pin  25  and the driving unit  31  in the above-described first embodiment. In the fourth variation example, as shown in  FIGS. 18A to 18C , instead of the lock mechanism actualized by rotation that is used in above-described third variation example, a lock mechanism actualized by an insertion pin  47  is used. 
     In this instance, a first pin hole  44  is provided in a predetermined position on the one axial end portion (the right end portion in  FIGS. 18A to 18C ) of a cylinder rod  31 B of the driving unit  31 . An insertion pin  47  is inserted into the first pin hole  44 . The first pin hole  44  is formed so as to pass through the cylinder rod  31 B in the radial direction D2. The first pin hole  44  intersects with a center axial line of the cylinder rod  31 B at a right angle. 
     Meanwhile, an insertion hole  45  and a second pin hole  46  are provided in the end portion on the opposite side of the blocking portion  25   b  (the left end portion in  FIGS. 18A to 18C ) of a shaft portion  252   a  of the holding pin  25 . The one axial end portion of the cylinder rod  31 B is inserted into the insertion hole  45 . The second pin hole  46  is provided in a position on an extension line of the first pin hole  44  provided in the cylinder rod  31 B when the cylinder rod  31 B is inserted into the insertion hole  45 . 
     The connection operation in the fourth variation example is performed as follows. First, as shown in  FIG. 18A , the shaft portion  252   a  of the holding pin  25  and the cylinder rod  31 B are disposed in a state in which the respective axial end surfaces oppose each other in the axial direction D1. 
     At this time, positioning of the first pin hole  44  of the cylinder rod  31 B and the second pin hole  46  of the shaft portion  252   a  is performed. From this state, as shown in FIG.  18 B, the tip portion of the cylinder rod  31 B is relatively moved in the axial direction D1 and inserted into the insertion hole  45  of the shaft section  252   a.    
     At this time, the tip of the cylinder rod  31 B reaches the innermost end of the insertion hole  45 . The first pin hole  44  and the second pin hole  46  overlap in the radial direction D2. In this state, as shown in  FIG. 18C , the insertion pin  47  is inserted into the first pin hole  44  and the second pin hole  46 . The connection operation is thereby completed. 
     In the connection method of the fourth variation example, the lock mechanism actualized by the insertion pin  47  is used. Therefore, compared to the third variation example, the cylinder rod  31 B and the shaft portion  252   a  can be connected with more certainty by a simple and easy operation. 
     Fifth Variation Example 
     A fifth variation example is an example of still another connection method for connecting the holding pin  25  and the driving unit  31 . In the fifth variation example, as shown in  FIGS. 19A to 19C , instead of the lock mechanism actualized by rotation used in the above-described third variation example, a lock mechanism actualized by a magnet is used. 
     In this instance, a cylinder rod  31 C of the driving unit  31  and a shaft portion  253   a  of the holding pin  25  are composed of a magnetic material, such as an iron-based metal. A permanent magnet  48  is embedded and fixed in a magnet housing hole in the one axial end portion (the right end portion in  FIGS. 19A to 19C ) of the cylinder rod  31 C. The magnet housing hole is open on the axial end. Meanwhile, an insertion hole  49  is provided in the end portion on the opposite side of the blocking portion  25   b  (the left end portion in  FIGS. 19A to 19C ) of the shaft portion  253   a  of the holding pin  25 . The one axial end portion of the cylinder rod  31 C is inserted into the insertion hole  49 . 
     The connection operation in the fifth variation example is performed as follows. First, as shown in  FIG. 19A , the shaft portion  253   a  of the holding pin  25  and the cylinder rod  31 C are disposed in a state in which the respective axial end surfaces oppose each other in the axial direction D1. From this state, as shown in  FIG. 19B , the tip portion of the cylinder rod  31 C is relatively moved in the axial direction D1 and inserted into the insertion hole  49  of the shaft portion  253   a.    
     As a result, as shown in  FIG. 19C , the cylinder rod  31 C and the shaft portion  253   a  are firmly connected by the attraction force of the permanent magnet  48  embedded in the tip portion of the cylinder rod  31 C. The connection operation is thereby completed. 
     In the connection method of the fifth variation example, the lock mechanism actualized by a magnet is used. Therefore, the cylinder rod  31 C and the shaft portion  253   a  can be connected with certainty by a very simple and easy operation. 
     Sixth Variation Example 
     A sixth variation example is a manufacturing method for manufacturing the rotor  10  using a casting apparatus shown in  FIG. 20 . In a manner similar to that according to the first embodiment, the manufacturing method is performed based on the flowchart in  FIG. 1 . The casting apparatus used in the sixth variation example includes the mold  21 , an energizing member  32 , and a pressing member  33 . The mold  21  includes the fixed mold  22  and the movable mold  23 . 
     In the sixth variation example as well, at the setting step S 10 , in a manner similar to that according to the first embodiment, the plurality of steel plates  11   a  that are set in the mold  21  are held by the holding pin  25 . The holding pin  25  includes the shaft portion  25   a  and the blocking portion  25   b . The pressing member  33  presses and moves the holding pin  25  in the axial direction D1. However, the sixth variation example differs from the first embodiment in that the pressing member  33  is not directly connected and fixed to the holding pin  25 . This difference will be described in detail hereafter. 
     In the sixth variation example, at the setting step S 10 , the holding pin  25  is set in a predetermined position in the fixed mold  22  in a state in which the plurality of steel plates  11   a  are held. After the mold  21  is closed, the holding pin  25  is capable of being pressed from both axial sides by the energizing member  32  disposed on the one axial end side (the right side in  FIG. 20 ) and the pressing member  33  disposed on the other axial end side (the left side in  FIG. 20 ). 
     The energizing member  32  is disposed on the molten metal introduction passage  24  in the movable mold  23 . The energizing member  32  includes a movable body  32   a  and a coil spring  32   b . The movable body  32   a  is disposed so as to be in contact with the blocking portion  25   b  of the holding pin  25 . The movable body  32   a  can be moved in the axial direction D1. The coil spring  32   b  energizes the movable body  32   a  towards the other axial end side. The movable body  32   a  is energized towards the other axial end side (the direction of arrow A1 shown in  FIG. 20 ) at all times by the energizing force of the coil spring  32   b . The energizing member  32  presses the blocking portion  25   b  towards the other axial end side at all times using the movable body  32   a.    
     As a result, the bottom surface of the blocking portion  25   b  is in contact with the end surface on the one axial end side of the plurality of steel plates  11   a  that are set in the mold  21 . The opening on molten metal feeding side of the center shaft hole  12  is blocked by the blocking portion  25   b . This blocked state is maintained at the casting step S 20 . 
     The pressing member  33  includes a driving unit  33   a  and an air cylinder  33   b . The driving unit  33   a  is disposed on the other axial end side of the fixed mold  22 . The air cylinder  33   b  is driven by the driving unit  33   a . The air cylinder  33   b  is disposed in a state in which the shaft portion  25   a  of the holding pin  25  and a cylinder rod  33   c  oppose each other in the axial direction D1. The holding pin  25  holds the plurality of steel plates  11   a  and is set in the mold  21 . In this instance, the tip of the cylinder rod  33   c  that advances and retracts in the axial direction D1 is not connected and fixed to the shaft portion  25   a  of the holding pin  25  by a fixing piece or the like. 
     At the cutoff step S 30 , the pressing member  33  advances the cylinder rod  33   c  using the driving unit  33   a  with a pressing force that is greater than the energizing force of the energizing member  32 . The tip of the cylinder rod  33   c  thereby presses the axial end surface of the shaft portion  25   a , and moves the holding pin  25  towards the one axial end side (the direction of arrow A2 shown in  FIG. 20 ). As a result, the blocking portion  25   b  is placed in contact with the outer peripheral wall surface of the sloped passage  24   b . The molten metal is thereby cut off. 
     When the cylinder rod  33   c  is subsequently retracted, the holding pin  25  is pressed towards the other axial end side by the energizing force of the energizing member  32 . The blocking portion  25   b  returns to the initial position that is in contact with the end surface on the one axial end side of the steel plates  11   a.    
     In the sixth example, the holding pin  25  is pressed at all times towards the other axial end side (the retracting side of the cylinder rod  33   c ; the direction of arrow A1 shown in  FIG. 20 ) by the energizing member  32 . Therefore, the cylinder rod  33   a  is not required to be connected and fixed to the shaft portion  25   a.    
     As described above, in the sixth variation example, the holding pin  25  can be pressed from both axial sides by the energizing member  32  disposed on the one axial end side and the pressing member  33  disposed on the other axial end side. The energizing member  32  presses the blocking portion  25   b  of the holding pin  25  towards the other axial end side at all times. 
     Therefore, the cylinder rod  33   c  of the pressing member  33  that operates at the cutoff step S 30  and the shaft portion  25   a  of the holding pin  25  are not required to be connected and fixed together. Therefore, a fixing piece can be eliminated. 
     Seventh Variation Example 
     In a seventh variation example, instead of the holding pin  25  used in the above-described first embodiment, a blocking pin  35  is used to block the opening on the molten metal feeding side of the center shaft hole  12  of the plurality of steel plates  11   a  set in the mold  21 , as shown in  FIG. 21 . The blocking pin  35  includes a passage partition surface  35   c  that partitions the inner peripheral surface of the sloped passage  24   b.    
     The blocking pin  35  is composed of a shaft portion  35   a  and a circular truncated cone-shaped blocking portion  35   b . The blocking portion  35   b  is provided integrally with one axial end portion (the left end portion in  FIG. 21 ) of the shaft portion  35   a . The blocking pin  35  is disposed on the molten metal introduction passage  24  in the movable mold  23 . The blocking portion  25   b  is connected to the end surface on the one axial end side of the shaft portion  35   a  so that the end portion on the small diameter side is coaxial with the end surface. 
     At the setting step S 10 , the blocking pin  35  is disposed in a state in which the end surface on the one axial end side of the plurality of steel plates  11   a  set in the mold  21  oppose the bottom surface on the large diameter side of the blocking portion  35   b . The blocking pin  35  is disposed so as to be coaxial with the plurality of steel plates  11   a.    
     A driving unit  36  is disposed on the other axial end side (the right side in  FIG. 21 ) of the blocking pin  35 . The driving unit  36  includes an air cylinder  36   a  that moves the blocking pin  35  in the axial direction D1. The tip of a cylinder rod  36   b  of the air cylinder  36   a  is connected and fixed to the other axial end portion of the shaft portion  35   a  by a fixing piece (not shown). 
     Before the subsequent casting step S 20  is started, the blocking pin  35  is pressed towards the one axial end side (the left side in  FIG. 21 ; the direction of arrow A2) by the operation of the driving unit  36 . The blocking pin  35  is placed in a state in which the bottom surface on the large diameter side of the blocking portion  35   b  is in contact with the end surface on the one axial end side of the plurality of steel plates  11   a  set in the mold  21  (see  FIG. 21 ). 
     As a result, the opening on the molten metal feeding side of the center shaft hole  12  of the plurality of steel plates  11   a  is blocked. The outer peripheral surface of the blocking portion  35   b  serves as the passage partition surface  35   c  that partitions the inner peripheral surface of the sloped passage  24   b.    
     Then, at the cutoff step S 30  performed after completion of the casting step S 20 , the blocking pin  35  is pulled towards the other axial end side (the right side in  FIG. 21 ) by the operation of the driving unit  36 . The passage partition surface  35   c  of the blocking portion  35   b  comes into contact with the outer peripheral wall surface of the sloped passage  24   b . The molten metal is thereby cut off. 
     As described above, in the seventh variation example, at the setting step S 10 , the plurality of steel plates  11   a  are set in the mold  21 . The opening on the molten metal feeding side of the center shaft hole  12  of the steel plates  11   a  is blocked by the blocking pin  35 . The blocking pin  35  has the passage partition surface  35   c  that partitions the inner peripheral surface of the sloped passage  24   b . The blocking pin  35  is disposed so as to be in contact with the one axial end surface of the steel plates  11   a.    
     As a result, inflow of molten metal into the center shaft hole  12  of the plurality of steel plates  11   a  set in the mold  21  can be reliably prevented using the blocking portion  35   b  of the blocking pin  35  that partitions the inner peripheral wall of the sloped passage  24   b.    
     In addition, at the cutoff step S 30 , the driving unit  36  moves the blocking pin  35  in the axial direction D1. The passage partition surface  35   c  of the blocking portion  35   b  comes into contact with the outer peripheral wall surface of the sloped passage  24   b . The molten metal is thereby cut off. As a result, the cutoff step S 30  can be simply and easily performed using the blocking pin  35 . 
     Eighth Variation Example 
     In an eighth variation example, instead of the blocking pin  35  used in the above-described seventh example, a blocking pin  51  is used to block the opening on the molten metal feeding side of the center shaft hole  12  of the plurality of steel plates  11   a  set in the mold  21 , as shown in  FIG. 22 . The blocking pin  51  includes a passage partition surface  51   c  that partitions the inner peripheral surface of a cylindrical passage  24   c.    
     Instead of the sloped passage  24   b  provided in the first embodiment and the like, the molten metal introduction passage  24  in the mold  21  in the eighth variation example is provided with a cylindrical passage  24   c . The cylindrical passage  24   c  extends in the axial direction D1 with a substantially fixed diameter and communicates with the gate  24   a.    
     The blocking pin  51  that is used in the eighth variation example is formed into a columnar shape. A tapered portion is formed in the one axial end portion (the left end portion in  FIG. 22 ) of the blocking pin  51 . The tapered portion decreases in diameter towards the one axial end side. At the setting step S 10 , the blocking pin  51  is disposed in a state in which the end surface on the one axial end side of the plurality of steel plates  11   a  set in the mold  21  oppose the end surface on the one axial end side (the tip surface of the tapered portion) of the blocking pin  51 . The blocking pin  51  is disposed so as to be coaxial with the plurality of steel plates  11   a.    
     A coil spring  52  is disposed on the other axial end side (the right side in  FIG. 22 ) of the blocking pin  51 . The coil spring  52  energizes the blocking pin towards the other axial end side (the direction of arrow A1 shown in  FIG. 22 ) at all times. As a result, the end surface on the one axial end side (the tip surface of the tapered portion) of the blocking pin  51  is in contact with the end surface on the other axial end side of the plurality of steel plates  11   a  set in the mold  21 . The opening on the molten metal feeding side of the center shaft hole  12  is blocked by the blocking pin  51 . 
     In addition, the outer peripheral surface of the tapered portion of the blocking pin  51  serves as a passage partition surface  51   c  that partitions the inner peripheral surface of the cylindrical passage  24   c . The blocked state is maintained at the casting step S 20 . The ring-shaped gate  24   a  that is formed in the periphery of the tapered portion of the blocking pin  51  increases in width in the radial direction D2 towards the one axial end side, because the one axial end side of the blocking pin  51  is tapered. Therefore, fluidity of the molten metal is improved. 
     A cutoff member  53  is disposed on the entrance side of the cylindrical passage  24   c . The cutoff member  53  is formed into an elongated columnar shape. At the cutoff step S 30 , the cutoff member  53  cuts off the molten metal in the cylindrical passage  24   c . The cutoff member  53  is disposed so as to be aligned in parallel with the blocking pin  51 . The tip of the cutoff member  53  is positioned at the entrance of the cylindrical passage  24   c . The driving unit  36  is disposed on the other axial end side of the cutoff member  53 . The driving unit  36  includes the air cylinder  36   a  that moves the cutoff member  53  in the axial direction D1. The tip of a cylinder rod  36   b  of the air cylinder  36   a  is connected and fixed to the other axial end portion of the cutoff member  53  by a fixing piece (not shown). As a result, at the cutoff step S 30 , the cutoff member  53  is moved towards the one axial end side (the direction of arrow A1 shown in  FIG. 22 ) by the operation of the driving unit  36 . The molten metal in the cylindrical passage  24   c  is thereby cut off. 
     As described above, in the eighth example, the molten metal introduction passage  24  is provided with the cylindrical passage  24   c . The cylindrical passage  24   c  communicates with the gate  24   a . Therefore, the molten metal that is fed into the molten metal introduction passage  24  can be smoothly sent from the cylindrical passage  24   c  towards the gate  24   a  so as to be even in the circumferential direction D3. 
     In addition, at the setting step S 10 , the plurality of steel plates  11   a  are set in the mold  21 . The opening on the molten metal feeding side of the center shaft hole  12  of the steel plates  11   a  is blocked by the blocking pin  51 . The blocking pin  51  has the passage partition surface  51   c  that partitions the inner peripheral surface of the cylindrical passage  24   c . The blocking pin  51  is disposed so as to be in contact with the one axial end surface of the steel plates  11   a.    
     As a result, inflow of molten metal into the center shaft hole  12  of the plurality of steel plates  11   a  set in the mold  21  can be prevented with certainty using the blocking pin  51  that partitions the inner peripheral wall of the cylindrical passage  24   c.    
     In addition, at the cutoff step S 30 , the driving unit  36  moves the cutoff member  53  in the axial direction D1. The molten metal in the cylindrical passage  24   c  is thereby cut off. As a result, the cutoff step S 30  can be simply and easily performed using the cutoff member  53 . 
     Ninth Variation Example 
     A ninth variation example differs from the above-described eighth variation example in that a cutoff member  55  is used instead of the cutoff member  53  used in the eighth variation example. As shown in  FIG. 23 , the cutoff member  55  has a cylindrical shape of which one end is open. The cutoff member  55  in the ninth variation example houses the rear end side (the right end side in  FIG. 23 ) of the blocking pin  51  therein. The cutoff member  55  is disposed coaxially with the blocking pin  51  and is capable of relative movement in the axial direction D1. The end portion on the opening side (the left side in  FIG. 23 ) of the cutoff member  55  is positioned at the entrance of the cylindrical passage  24   b.    
     The driving unit  36  is disposed on the bottom portion side (the right side in  FIG. 23 ) of the cutoff member  55 . The driving unit  36  includes the air cylinder  36   a  that moves the cutoff member  55  in the axial direction D1. The tip of a cylinder rod  36   b  of the air cylinder  36   a  is connected and fixed to the other axial end portion of the cutoff member  55  by a fixing piece (not shown). 
     As a result, in the ninth variation example as well, the cutoff member  55  is moved towards the one axial end side (the direction of arrow A1 shown in  FIG. 23 ) by the operation of the driving unit  36 . The molten metal in the cylindrical passage  24   b  is thereby cut off. Other configurations in the ninth variation example are the same as those in the eighth variation example. These configurations are given the same reference numbers. Detailed description thereof is omitted. 
     The ninth variation example that is configured as described above achieves operations and effects similar to those of the eighth variation example.