Patent Publication Number: US-11038408-B2

Title: Method for manufacturing magnet embedded core

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application is the U.S. National Stage entry of International Application Number PCT/JP2017/012034 filed under the Patent Cooperation Treaty having a filing date of Mar. 24, 2017, which claims priority to international Application Number PCT/JP2016/002009 having a filing date of Apr. 13, 2016, international Application Number PCT/JP2016/004123 having a filing date of Sep. 9, 2016, and international Application Number PCT/JP2016/082291 having a filing date of Oct. 31, 2016, which are incorporated herein by reference. 
     TECHNICAL FIELD 
     The present invention relates to a method and a device for manufacturing a magnet embedded core having magnets embedded therein. 
     BACKGROUND ART 
     Conventionally, it is known to manufacture a magnet embedded core by inserting a magnet into each of a plurality of magnet insertion holes extending axially in a rotor core, charging resin material in liquid form into the magnet insertion holes, and curing the charged resin material to fix the magnets in the rotor core. By fixing the magnets in the respective magnet insertion holes with the resin, the magnetic property of the rotor core can be stabilized, and the rotor core is enabled to follow the rotating magnetic field created by the stator in a stable manner. 
     In conjunction with such a method for manufacturing a magnet embedded core, it is known, for example, to place a rotor core, along with an intermediate die, in a mold die assembly having an upper die and a lower die, the lower die being provided with a tubular pot and a plunger vertically movable in the pot, and pressure-feed mold resin melted in the pot by moving the plunger upward such that the mold resin is charged into the magnet insertion holes of the rotor core via runners and gates formed between the intermediate die and the lower die, and is thereafter thermally cured. See Patent Document 1, for instance. 
     PRIOR ART DOCUMENT(S) 
     Patent Document(s) 
     Patent Document 1: JP2014-79056A 
     SUMMARY OF THE INVENTION 
     Task to be Accomplished by the Invention 
     According to the prior art such as that disclosed in Patent Document 1, when the mold die assembly is opened and the molded rotor core is removed after the resin molding, cured resin inevitably remains in the runners or the likes, and this remaining resin (unnecessary resin) is eventually separated from the rotor core and discarded. Therefore, in view of minimizing the material cost of the resin material or from other points of view, it is desirable to prevent such unnecessary resin from being created. 
     The present invention was made in view of such a problem of the prior art, and has a primary object to prevent creation of such unnecessary resin from the resin material used for fixing magnets. 
     Means to Accomplish the Task 
     One embodiment of the present invention provides a device for manufacturing a magnet embedded core including a magnet embedded in resin filling a magnet insertion hole extending axially in a motor core, the device comprising: a resin charging device configured to charge the resin in solid form into the magnet insertion hole; a magnet insertion device configured to insert the magnet into the magnet insertion hole; and a heating device configured to heat the motor core to melt the resin in solid form in the magnet insertion hole. 
     Owing to this arrangement, since the solid resin is charged into the magnet insertion hole, and melts in the magnet insertion hole, as opposed to the case of injection molding in which the molten resin is filled into the magnet insertion hole under pressure via runners and gates provided in the die assembly, the resin material is prevented from remaining in places such as runners and gates. Thereby, the creation of unnecessary resin in the step of fixing the magnet in the magnet insertion hole can be avoided. 
     Preferably, the device for manufacturing a magnet embedded core further comprises a pressurization device configured to pressurize the molten resin in the magnet insertion hole. 
     Owing to this arrangement, the voids that may remain in the molten resin are expelled or contracted so that the magnet can be fixed by the resin relatively free of voids in a reliable manner. 
     Preferably, the manufacturing device further comprises an upper die and a lower die configured to clamp the motor core between the upper die and the lower die. 
     Thus, the motor core can be clamped between the upper die and the lower die. 
     Preferably, the manufacturing device further comprises a pressurization device configured to pressurize the molten resin in the magnet insertion hole via the upper die and die lower die. 
     Thus, the molten resin in the magnet insertion hole is pressurized while the motor core is clamped between the upper die and the lower die, the pressurization step can be performed in a reliable manner, and the magnet can be fixed by the resin relatively free of voids in an even more reliable manner. 
     In this manufacturing device, preferably, the resin charging device is configured to charge the resin into the magnet insertion hole in the motor core placed on the lower die. 
     Thus, no extra position is required to be set aside for charging the resin. 
     In this manufacturing device, preferably, the resin charging device is configured to charge the resin into the magnet insertion hole in the motor core outside the upper die and the lower die. 
     Thereby, the use efficiency of the upper die and the lower die can be improved, and the manufacturing cost may be reduced. 
     In this manufacturing device, preferably, the magnet insertion device is configured to insert the magnet into the magnet insertion hole in the motor core placed on the lower die. 
     Thus, no extra position is required to be set aside for inserting the magnet. 
     In this manufacturing device, preferably, the magnet insertion device is configured to insert the magnet into the magnet insertion hole in the motor core outside the upper die and the lower die. 
     Thereby, the use efficiency of the upper die and the lower die can be improved, and the manufacturing cost may be reduced. 
     Preferably, this manufacturing device further comprises a heating oven configured to heat the motor core outside the upper die and the lower die. 
     Thereby, the use efficiency of the upper die and the lower die can be improved, and the manufacturing cost may be reduced. 
     Another aspect of the present invention provides a method for manufacturing a magnet embedded core including a magnet embedded in resin filling a magnet insertion hole extending axially in a motor core, the method comprising: a resin charging step of charging the resin in solid form into the magnet insertion hole; a magnet insertion step of inserting the magnet before or after the resin charging step; a melting step of melting the resin in the magnet insertion hole; and a curing step of curing the molten resin. 
     Owing to this arrangement, since the solid resin is charged into the magnet insertion hole, and melts in the magnet insertion hole, as opposed to the case of injection molding in which the molten resin is filled into the magnet insertion hole under pressure via runners and gates provided in the die assembly, the resin material is prevented from remaining in places such as runners and gates. Thereby, the creation of unnecessary resin in the step of fixing the magnet in the magnet insertion hole can be avoided. 
     Preferably, the manufacturing method further comprises a resin pressurization step of pressurizing the molten resin. 
     According to this method, the voids that may remain in the molten resin are expelled or contracted so that the magnet can be fixed by the resin relatively free of voids in a reliable manner. 
     In this manufacturing method, preferably, the melting step comprises at least partly melting the solid resin by the motor core which is preheated prior to the resin charging step. 
     Thereby, the time period required for the motor core to reach a temperature required for melting the solid thermosetting resin in the melting step can be reduced so that the manufacturing efficiency can be improved. 
     In this manufacturing method, preferably, the solid resin is formed by molding uncured raw material resin in powder or granular form into a prescribed shape. The solid resin molded into the prescribed shape may include the solid resin molded to conform to the shape of the magnet insertion hole. 
     Thereby, the amount of the solid resin that is to be charged into the magnet insertion hole can be set to a correct amount beforehand. Also, the handling of the solid resin can be improved, and the work efficiency in the resin charging step can be improved. 
     In this manufacturing method, preferably, at least one of outer surfaces of the solid resin is in contact with an inner surface of the motor core defining the magnet insertion hole. 
     Thereby, the heat transfer from the motor core to the solid resin is performed in an efficient manner so that the time period required for melting the solid resin in the magnet insertion hole can be reduced, and the manufacturing efficiency can be improved. 
     In this manufacturing method, preferably, the solid resin is in uncured, granular form. The solid resin in uncured, granular form may include tablets. 
     Thereby, without regard to the shape of the magnet insertion hole and the necessary amount of the resin, the solid resin can be charged into the magnet insertion hole both correctly and easily. 
     In this manufacturing method, the magnet may be preheated before being inserted into the magnet insertion hole. In this case, the heat of the magnet inserted into the magnet insertion hole effectively contributes to the melting of the solid resin so that the time period required for melting the solid resin in the melting step can be reduced, and the manufacturing efficiency can be improved. 
     Effects of the Invention 
     The device and the method for manufacturing a magnet embedded core according to the present invention can prevent the creation of unnecessary resin from the resin used for fixing the magnet. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWING(S) 
         FIG. 1  is a perspective view of an example of a magnet embedded core manufactured b a manufacturing method according to the present invention; 
         FIG. 2  is a vertical sectional view of the magnet embedded core shown in  FIG. 1 ; 
         FIG. 3  is a front view of a manufacturing device for the magnet embedded core according to an embodiment of the present invention, partly in section; 
         FIG. 4  is a front view of the manufacturing device partly in section in a resin charging step; 
         FIG. 5  is a front view of the manufacturing device partly in section in a magnet insertion step; 
         FIG. 6  is a front view of the manufacturing device partly in section when magnets are already inserted; 
         FIG. 7  is a front view of the manufacturing device partly in section in a resin melting step; 
         FIG. 8  is a front view of the manufacturing device partly in section immediately before fully closing a die assembly; 
         FIG. 9  is a front view of the manufacturing device partly in section in a pressurization step; 
         FIG. 10  is a front view of a manufacturing device for the magnet embedded core according to another embodiment of the present invention, partly in section; 
         FIG. 11  is a vertical sectional view of a manufacturing device for the magnet embedded core according to yet another embodiment of the present invention; 
         FIG. 12  is a vertical sectional view of a manufacturing device for the magnet embedded core according to yet another embodiment of the present invention; and 
         FIG. 13  is a vertical sectional view of a manufacturing device for the magnet embedded core according to yet another embodiment of the present invention. 
     
    
    
     EMBODIMENT(S) FOR CARRYING OUT THE INVENTION 
     Preferred embodiments of the present invention are described in the following with reference to the appended drawings. 
     An example of a magnet embedded core manufactured by a manufacturing method according to the present invention is described in the following, with reference to  FIGS. 1 and 2 . 
     The magnet embedded core  100  has a motor core  101  including a plurality of magnet insertion holes  104 , and magnets  110  positioned in the respective magnet insertion holes  104 . The motor core  101  is formed by stacking a plurality of iron core laminates  106  each formed by punching and consisting of a disk formed with openings for defining a center hole  102  and the magnet insertion holes  104 . 
     The magnet insertion holes  104  are arranged around the center hole  102 , and are each provided with a substantially rectangular shape in plan view (shape of cross section). Each magnet insertion hole  104  extends axially through the motor core  101  in the stacking direction (axial direction), and defines a substantially rectangular space having an upper opening  105  on an upper end surface  108  of the motor core  101 . Each magnet insertion hole  104  is passed axially through the motor core  101  in the illustrated embodiment, but may also be provided with a closed bottom by omitting the opening for defining the magnet insertion hole  104  in the lowermost iron core laminate  106 . 
     Each magnet  110  has a substantially rectangular parallelepiped shape, and is fixed in position relative to the motor core  101  by resin  112  filled in the magnet insertion hole  104 . The resin  112  may consist of a thermosetting resin such as epoxy resin that can be cured by being heated to a temperature higher than a prescribed curing temperature. 
     Each magnet  110  may consist of, for example, a ferrite-based sintered magnet or a permanent magnet (with or without magnetization) such as a neodymium magnet. The axial length of each magnet  110  is smaller than the axial length of the magnet insertion hole  104 , and the end surface (in this case, the upper surface) of the magnet  110  is covered with the resin  112 . 
     The width (the dimensions in the tangential direction of the motor core  101  and the radial direction of the motor core  101 ) of each magnet  110  is smaller than the width (the dimensions in the tangential direction of the motor core  101  and the radial direction of the motor core  101 ) of the magnet insertion hole  104 . The magnet  110  is inwardly offset (or offset toward the center of the motor core  101 ) in the magnet insertion hole  104  so that the inwardly facing surface  110 A of the magnet  110  makes a surface contact with (abuts against) the inner surface  104 A of the magnet insertion hole  104 . In the drawings, for the convenience of description, the clearance between each surface defining the magnet insertion hole  104  (excluding the inner surface  104 A) and the corresponding side surface of the magnet  110  (excluding the inwardly facing surface  110 A) is shown greater than the practical size, it is to be noted that the magnet  110  may be placed in the magnet insertion hole  104  so as to be offset outwardly. 
     A manufacturing device for the magnet embedded core of the illustrated embodiment is described in the following with reference to  FIGS. 3 to 9 . 
     The manufacturing device of the illustrated embodiment includes a device main body  1 . The device main body  1  includes a plurality of tie bars  14 , a flat lower fixed platen  10  fixed to the lower ends of the tie bars  14 , a flat upper fixed platen  12  fixed to the upper ends of the tie bars  14 , and a movable platen  16  engaged by the tie bars  14  slidably in an axial direction (vertical direction) so as to be movable in the vertical direction between the lower fixed platen  10  and the upper fixed platen  12 . The lower fixed platen  10 , the upper fixed platen  12 , and the movable platen  16  squarely oppose one another. 
     A lower die  18  forming a fixed die is attached to the upper surface  11  of the lower fixed platen  10 . An upper die  20  forming a movable die is attached to the lower surface  17  of the movable platen  16 . 
     The lower die  18  consists of a flat plate that has an upper surface  19  supporting a conveying tray  21 , the conveying tray  21  being conveyed into and out of this position by a conveying device (not shown in the drawings) such as a robot arm. The conveying tray  21  consists of a flat plate, and a number of such conveying trays  21  are provided for the single device main body  1  so that a motor core  101  is placed (preset) on each conveying tray  21  outside the device main body  1  (another place outside the lower die  18  and the upper die  20 ). By feeding the conveying trays  21  each carrying a motor core  101  onto a prescribed position on the lower die  18  one after another, the operating efficiency of the device main body  1  including the upper die  20  and the lower die  18  for interposing one motor core  101  at a time can be improved. Each motor core  101  is correctly positioned on the corresponding conveying tray  21  with the aid of a positioning member (not shown in the drawings) provided on the conveying tray  21 . 
     A cylindrical heating device  70  is detachably arranged on the outer periphery of the motor core  101 . The heating device  70  may consist of a high-frequency induction heating device or the like. By heating the motor core  101 , the resin  114  (see  FIG. 5 ) in a solid state charged into the magnet insertion hole  104  is melted. 
     The upper die  20  is provided with a substantially flat lower surface  22  which opposes a substantially flat upper end surface  108  of the motor core  101  placed on the lower die  18  so that the motor core  101  can be pressurized in the lamination direction (in the downward direction) by lowering the movable platen  16 . The lower surface  22  is provided with pressurization projections  24  in parts thereof aligning with the respective magnet insertion holes  104 . Each pressurization projection  24  is provided with a rectangular shape in plan view which is conformal to the shape of the magnet insertion hole  104  in plan view. As shown in  FIG. 9 , when the movable platen  16  is lowered, the pressurization projections  24  close the upper openings  105  of the magnet insertion holes  104 , and pressurize the molten resin  116  in each magnet insertion hole  104 . The pressurization projections  24  may also consist of members separate from the upper die  20  and be resiliently supported by springs or the like so as to be vertically movable relative to the upper die  20 . 
     A clamping device (pressurization device)  30  including a toggle link mechanism  42  is provided between the upper fixed platen  12  and the movable platen  16 . The toggle link mechanism  42  is configured to drive the movable platen  16  toward and away from the lower fixed platen  10  (in the vertical direction), and includes an upper link  34  having one end pivotally connected to a lower part of the upper fixed platen  12  via a pivot shaft  32 , and a lower link  38  having one end pivotally connected to an upper part of the movable platen  16  via a pivot shaft  36 . The other ends of the upper link  34  and the lower link  38  are pivotally connected to each other via a pivot shaft  40 . 
     The clamping device  30  includes a hydraulic cylinder device  46 . The hydraulic cylinder device  46  is configured to drive the toggle link mechanism  42 , and includes a cylinder tube  47  having a base end pivotally connected to a fixed frame  3  of the device main body  1  via a pivot shaft  44  and a piston rod  48  projecting outwardly from a free end of the cylinder tube  47 . A tip end of the piston rod  48  is pivotally connected to the other ends of the upper link  34  and the lower link  38  via the pivot shaft  40 . 
     The die clamping device  30  causes the movable platen  16  to be positioned at the uppermost position (die open position) when the piston rod  48  has retreated and the toggle link mechanism  42  is in the maximally folded state as shown in  FIG. 3 , and causes the movable platen  16  to be positioned at the lowermost position (die close position) when the piston rod  48  has advanced and the toggle link mechanism  42  is in the maximally extended state as shown in  FIG. 9 . In the maximally folded state shown in  FIG. 3 , the angle formed between the upper link  34  and the lower link  38  is minimized. In the maximally extended state shown in  FIG. 9 , the upper link  34  and the lower link  38  extend along a vertical straight line (angle formed between the upper link  34  and the lower link  38 =180 degrees). The maximally extended state can be detected by measuring the vertical position of the movable platen  16  with a linear sensor (not shown) or any other per se known method. 
     In the maximally extended state shown in  FIG. 9 , the upper die  20  is located at the lowermost position together with the movable platen  16 , and the lower surface  22  of the upper die  20  is in surface contact with the upper end surface  108  of the motor core  101  placed on the lower die  18  so that the motor core  101  is pressurized in the stacking direction, and the pressurization projections  24  engage the respective magnet insertion holes  104  to close the upper openings  105  thereof and pressurize the molten resin  116  in the respective magnet insertion holes  104 . This state is referred to as a clamped state (pressurized state). 
     Upper ends of a plurality of tubular members  60  extending axially toward the lower die  18  and having closed bottom ends are fixed to the upper die  20 . The tubular members  60  are arranged around the center of the motor core  101  positioned on the prescribed position of the lower die  18  via the conveying tray  21 , and each receive a piston  62  in a vertically slidable manner. Each piston  62  has a tip end portion  66  that projects out of the corresponding tubular member  60  via a through hole  64  formed in the bottom wall (lower end) of the tubular member  60 . A tip end surface  67  of each tip end portion  66  squarely opposes the upper surface  19  of the lower die  18 . 
     In each tubular member  60 , a compression coil spring  68  is provided between the upper die  20  and the piston  62 . Each compression coil spring  68  urges the corresponding piston  62  toward the bottom end of the tubular member  60  or, in other words, toward the side of the lower die  18 . The urging threes applied to the pistons  62  by the compression coil springs  68  in the respective tubular members  60  may be equal to one another. 
     The tip end surfaces  67  of the pistons  62  are positioned (by appropriately dimensioning the associated component parts) so as to simultaneously come into contact with the upper surface  19  of the lower die  18  as the upper die  20  approaches the lower die  18  or, more specifically, when the upper die  20  descends to a point slightly short of a position where the lower surface  22  of the upper die  20  comes into surface contact with the upper end surface  108  of the motor core  101 , as shown in  FIG. 8 . 
     The manufacturing device of this embodiment includes a resin charging device  80  (see  FIG. 4 ) and a magnet insertion device  90  (see  FIG. 5 ). 
     As shown in  FIG. 4 , the resin charging device  80  includes a substrate  82 , a plurality of resin holding members  86  provided on the substrate  82  and defining resin holding holes  84 , respectively, corresponding to the respective magnet insertion holes  104 , and a shutter plate  88  that is rotatably attached to the lower bottom surface of the substrate  82  to selectively shield the lower end openings of the resin holding holes  84 . By a conveying device (not shown in the drawings) such as a robot arm or the like, the resin charging device  80  is placed on the upper end surface  108  of the motor core  101  on the lower die  18 . 
     The resin holding holes  84  are each configured to hold the resin  114  in solid form (hereinafter, solid resin  114 ). The solid resin (resin block)  114  is obtained by molding uncured material resin in powder or granular form into a substantially rectangular parallelepiped shape that matches the shape of the magnet insertion hole  104  by using a tabletting machine or the like (not shown in the drawings) in a preliminary molding process. 
     As shown in  FIG. 5 , the magnet insertion device  90  includes a substrate  92 , a plurality of magnet holding members  96  provided on the substrate  92  and defining magnet holding holes  94 , respectively, corresponding to the respective magnet insertion holes  104 , and a shutter plate  98  that is rotatably attached to the lower bottom surface of the substrate  92  to selectively shield the lower end openings of the magnet holding holes  94 . By a conveying device (not shown in the drawings) such as a robot arm or the like, the magnet insertion device  90  is placed on the upper end surface  108  of the motor core  101  on the lower die  18 . 
     Next, the process of fixing the magnets  110  inserted in the respective magnet insertion holes  104  with the resin  112  is described in the following with reference to  FIGS. 3 to 9 . 
     First of all, as shown in  FIG. 3 , as a motor core loading step, when the movable platen  16  is at the uppermost position, and the upper die  20  is separated from the lower die  18  to a maximum extent (a die open state), the conveying tray  21  carrying a motor core  101  is placed (loaded) on a prescribed position on the lower die  18  by using a conveying device (not shown in the drawings). 
     Next, as shown in  FIG. 4 , as a resin charging step, in the die open state, the resin charging device  80 , in which solid resin  114  is placed in each resin holding hole  84 , is moved onto the upper end surface  108  of the motor core  101  by using a conveying device (not shown in the drawings). Thereafter, the lower end openings of the resin holding holes  84  are opened by the rotation of the shutter plate  88  with the result that the solid resin  114  in each resin holding hole  84  falls and is thereby charged into the corresponding magnet insertion hole  104 . 
     When the charging of the solid resin  114  into the resin holding holes  84  is completed, the resin charging device  80  is removed from the lower die  18  (carried out to the outside of the device main body  1 ) by a conveying device (not shown in the drawings). 
     Next, as a melting step, the solid resin  114  disposed in each magnet insertion hole  104  is heated within each magnet insertion hole  104  by the heat transferred from the motor core  101  which is heated by the heating device  70 . As a result, each solid resin  114  starts melting in the magnet insertion hole  104 . 
     As shown in  FIG. 5 , each piece of the solid resin  114  has at least one outer surface, or outer surfaces  114 A and  114 B in the illustrated embodiment which are in surface contact with the inner surfaces  104 A and  104 B of the corresponding magnet insertion hole  104 . As a result, the heat transfer from the motor core  101  to each piece of solid resin  114  is efficiently performed as compared with the case where there is a gap between the two so that the heating of the solid resin  114  in each magnet insertion hole  104  can be performed rapidly and in a thermally efficient manner. 
     In a magnet insertion step which is performed prior to or concurrently with the melting step, as shown in  FIG. 5 , while still in the die open state, the magnet insertion device  90  having the magnets  110  received in the respective magnet holding holes  94  is conveyed onto the upper end surface  108  of the motor core on the lower die  18  by using a conveying device (not shown in the drawings). Thereafter, the lower end openings of the magnet holding holes  94  are opened by the rotation of the shutter plate  98 , and the magnets  110  in the respective magnet holding holes  94  fall and are thereby inserted into the corresponding magnet insertion holes  104 . As shown in  FIG. 6 , the insertion of each magnet  110  is performed, with one of the outer surfaces  110 A of the magnet  110  being brought into contact with the inner surface  104 A of the corresponding magnet insertion hole  104  on the side of the center hole  102 , until the lower end surface of the magnet  110  abuts against the upper surface of the solid resin  114  received in the magnet insertion hole  104 . 
     When the insertion of the magnets  110  into the respective magnet holding holes  94  is completed, the magnet insertion device  90  is removed from the lower die  18  (conveyed out to the outside of the device main body  1 ) by a conveying device (not shown in the drawings). 
     The magnets  110  to be inserted into the magnet insertion holes  104  may be heated in advance (preheated) to a predetermined temperature by using a heating oven (not shown in the drawings) or the like. In this case, the solid resin  114  in each magnet insertion hole  104  is directly heated by the heat of the corresponding magnet  110  in addition to being heated by the heat from the motor core  101  which is heated by the heating device  70 . Thereby, the time required for melting, the solid resin  114  in the melting step is shortened, and the manufacturing efficiency of the magnet embedded core  100  is improved. Melting of the solid resin  114  means that the raw material resin constituting the solid resin  114  is brought to a liquid state or softened to have a certain fluidity. 
     Next, once the solid resin  114  has melted, each magnet  110  is pushed toward the bottom of the magnet insertion hole  104 . At this time, the liquid level of the molten resin  116  (see  FIG. 7 ) gradually rises in the magnet insertion hole  104  as the magnet  110  is pushed down further. 
     As shown in  FIG. 7 , when the magnet  110  is pushed fully into the prescribed placement position or to the bottom of the magnet insertion hole  104 , the molten resin  116  fills the gap between the inner surface of the magnet insertion hole  104  remote from the center hole  102  and the corresponding outer side surface of the magnet  110 , and the liquid level of the resin  112  rises above the upper surface of the magnet  110 . 
     Next, the piston rod  48  is caused to move forward by supplying a hydraulic pressure to the hydraulic cylinder device  46 . As the piston rod  48  advances, the angle formed by the upper link  34  and the lower link  38  increases, and the toggle link mechanism  42  becomes progressively extended so that the upper die  20  moves downward along with the movable platen  16 . 
     As shown in  FIG. 8 , when the upper die  20  has descended to a position where the lower surface  22  thereof is slightly short of the upper end surface  108  of the motor core  101 , the tip end surfaces  67  of the pistons  62  abut on the upper surface  19  of the lower die  18 . 
     As the toggle link mechanism  42  further extends, and the upper link  34  and the lower link  38  extend in a straight line as shown in  FIG. 9  (or, in other words, the toggle link mechanism  42  has fully extended), the lower surface  22  of the upper die  20  comes into surface contact with the upper end surface  108  of the motor core  101  to pressurize the motor core  101  in the stacking direction, and the pressurization projections  24  engage the corresponding magnet insertion holes  104  to close the upper openings  105  and to pressurize the molten resin  116  in the magnet insertion holes  104  as a resin pressurization step (clamped and pressurized state). 
     By this clamping action, the gaps between adjacent iron core laminates  106  are reduced or eliminated so that leakage of the molten resin  116  into the gaps between the adjacent iron core laminates  106  is decreased or avoided. Also, by pressurizing the molten resin  116  in the magnet insertion holes  104 , voids that may be remaining in the molten resin  116  are expelled or contracted in a favorable manner. 
     While in this clamped state, as a curing step, the motor core  101  is heated to a higher temperature than the temperature in the melting step by the heating device  70 . As a result, the molten resin  116  is further heated by the heat from the motor core  101  so that the molten resin  116  chemically reacts, and cures irreversibly. The magnets  110  in the magnet insertion holes  104  are thereby fixed to the motor core  101  by the cured resin  112  (see  FIG. 2 ), and the magnet embedded core  100  is completed. The completed magnet embedded core  100  is conveyed out of the device main body  1  together with the conveying tray  21  by a conveying device (not shown in the drawings). 
     Since the curing process of the molten resin  116  is performed in the clamped state in which the motor core  101  is pressurized by the upper die  20  and the upper opening  105  is closed, the resin  112  fixes the magnets  110  with a slight or no leakage of the resin  112  into the gaps between the adjacent iron core laminates  106 . Thereby, the magnet embedded core  100  having a stable quality with excellent magnetic property can be obtained. 
     Furthermore, since the curing process is performed while the resin  112  in the magnet insertion holes  104  is pressurized by the pressurization projections  24  as a resin pressurization step, voids that may be remaining in the molten resin  116  are expelled or contracted in a favorable manner before the molten resin  116  is fully cured so that the magnets  110  can be fixed in a reliable manner by the resin  112  having few voids therein. 
     As the resin  112  used for fixing the magnets  110 , the solid resin  114  is charged into the magnet insertion holes  104 , and the solid resin  114  is melted in the magnet insertion holes  104 . Therefore, as opposed to the injection molding process in which the molten resin is filled into the magnet insertion holes  104  under pressure via runners and gates formed in the die assembly, wastage of the resin remaining in the runners and the gates can be avoided, and the material cost is reduced. Also, by using the solid resin  114 , the amount of the solid resin  114  to be charged into the magnet insertion holes  104  can be correctly set without any excess or shortage, and the handling of the material resin can be improved so that the work efficiency of the resin charging step can be improved. 
     In the course of the upper die  20  descending from the state in which the tip end surfaces  67  of the pistons  62  are in contact with the upper surface  19  of the lower die  18  to the clamped state, the compression coil springs  68  are compressed by the downward movement of the upper die  20 , along with the tubular member  60 , relative to the pistons  62 , and provide a spring three that urges the lower die  18  and the upper die  20  away from each other. 
     As a result, in the maximum extended state of the toggle link mechanism  42 , the pressurizing force acting on the motor core  101  is reduced by the sum of the spring forces provided by the compressive deformation of the compression coil springs  68 . Namely, the clamping force provided by the toggle link mechanism  42  is partially canceled, and the pressurizing force acting upon the motor core  101  in the stacking direction is reduced from the rated clamping force provided by the toggle link mechanism  42  in the most extended state. 
     As a result, even if an inexpensive general-purpose toggle type clamping device  30  capable of obtaining a repeated stable clamping force (resin pressurizing force) of up to several tens of tons is used, an appropriate pressurizing force can be obtained in a stable manner without applying an excessive pressuring force to the motor core  101  when the die assembly is closed so that the motor core  101  is prevented from being excessively deformed in the stacking direction and the molten resin  116  is not excessively pressurized. As a result, even though the molten resin  116  is cured in the clamped state, the planarity of the motor core  101  following the opening of the die assembly is not impaired, and the molten resin  116  is prevented from leaking from the magnet insertion holes  104  to the outside. 
     In addition, since the motor core  101  is not deformed excessively in the lamination direction at the time of clamping, no excessive stress is produced in the resin  112  which is cured in the magnet insertion holes  104  of the motor core  101  when the die assembly is opened so that peeling and cracking of the resin  112  in the magnet insertion holes  104  can be avoided. 
     Thus, the leakage of the molten resin  116  to the outside of the magnet insertion holes  104  can be avoided, and the shape precision and the dimensional precision of the motor core  101  can be ensured at the same time. Therefore, the magnet embedded core  100  having a stable quality can be efficiently manufactured. 
     The pressurizing force that actually acts on the motor core  101  at the time of clamping the die assembly or when the toggle link mechanism  42  is maximally extended depends on the rated clamping force of the clamping device  30  and the spring properties such as the spring constant, the compressive deformation and the preload of the compression coil springs  68 . Therefore, the actual pressurizing force acting upon the motor core  101  when the die assembly is closed can be freely adjusted by changing the spring properties. Therefore, even though the rated clamping force of the clamping device  30  is a fixed value, the pressurizing force actually applied to the motor core  101  when the die assembly is closed can be freely selected. 
     The proper pressurizing force when filling the magnet embedded core  100  with the resin varies depending on specifications such as the size of the motor core  101  and the number of the iron core laminates. In the present embodiment, filling of the resin for a wide range of magnet embedded cores  100  with varying specifications can be performed with an optimum pressurizing force for each of the wide range of magnet embedded cores  100  simply by changing the spring properties of the compression coil springs  68  even though the same device main body  1 , lower die  18  and upper die  20  are used. Therefore, the investment for the manufacturing device for filling resin for a wide range of magnet embedded cores  100  can be reduced. In other words, with a minimum investment in the manufacturing device, the manufacturing device can be easily adapted to the process of filling resin for a wide range of magnet embedded cores  100 . 
     Since the compression coil springs  68  are arranged around the center of the center hole  102  of the motor core  101  positioned on the lower die  18  via the conveying tray  21 , the partial canceling of the clamping force of the toggle link mechanism  42  by the spring force of the compression coil springs  68  is prevented from becoming uneven around the center of the motor core  101 . 
     As a result, the pressurizing force acting on the motor core  101  in the stacking direction in the fully clamped state is prevented from becoming uneven around the center of the motor core  101  owing to the compression coil springs  68  so that undesired distortion of the motor core  101  can be avoided. 
     Furthermore, the compressive deformation of each compression cod spring  68  is guided by the corresponding tubular member  60  without undergoing a bending deformation. In addition, because the piston  62  engages the lower die  18  during the movement of the upper die  20  toward the lower die  18 , the compression cod spring  68  may be provided with a relatively short length without regard to the opening stroke of the die assembly. 
     The lower die  18  is fixed to the lower fixed platen  10  while the upper die  20  is fixed to the movable platen  16 , and the compression cod springs  68  are arranged in parallel to one another between the lower die  18  and the upper die  20  so that the spring force of the compression coil springs  68  acts directly upon the lower die  18  and the upper die  20 . In particular, the lower die  18  and the upper die  20  are not supported by or suspended from the lower fixed platen  10  or the movable platen  16  via the compression coil springs  68  in a floating manner. Therefore, the lower die  18  and the upper die  20  are prevented from tilting or otherwise becoming unstable. Owing to such arrangements, a proper clamping action can be ensured at all times. 
     Next, a manufacturing device for a magnet embedded core according to another embodiment of the present invention is described in the following with reference to  FIG. 10 . In  FIG. 10 , parts corresponding to those in  FIG. 4  are denoted with like reference numerals, and description of such parts may be omitted. 
     In this embodiment, the resin charging device  80  is placed on the motor core  101  mounted on the conveying tray  21  at a location outside of the device main body  1  including the lower die  18  and the upper die  20 , and charges the solid resin  114  into the magnet insertion holes  104  of the motor core  101 . 
     In this embodiment, the time period during which the device main body  1  is occupied by the resin charging step is eliminated so that the operation efficiency of the device main body  1  is improved. Also, the time period required for manufacturing each magnet embedded core  100  is reduced, and the efficiency of manufacturing the magnet embedded core  100  can be improved. 
     Next, a manufacturing device for a magnet embedded core according to yet another embodiment of the present invention is described in the following with reference to  FIG. 11 . In  FIG. 11 , parts corresponding to those in  FIG. 5  are denoted with like reference numerals, and description of such parts may be omitted. 
     In this embodiment, the magnet insertion device  90  is placed on the motor core  101  mounted on the conveying tray  21  at a location outside of the device main body  1  including the lower die  18  and the upper die  20 , and inserts the magnets  110  into the respective magnet insertion holes  104  of the motor core  101 . 
     In this embodiment, the time period during which the device main body  1  is occupied by the magnet insertion step is eliminated so that the operation efficiency of the device main body  1  is improved. Also, the time period required for manufacturing each magnet embedded core  100  is reduced, and the efficiency of manufacturing the magnet embedded core  100  can be improved. 
     Next, a device for manufacturing a magnet embedded core according to yet another embodiment is described in the following with reference to  FIG. 12 . 
     In this embodiment, a heating oven  120  for heating the motor core  101  is provided separately from the device main body  1  including the lower die  18  and the upper die  20 . The heating oven  120  has a heater  124  for raising the temperature of the oven interior  122 . 
     In this embodiment, the motor core  101  is heated in the heating oven  120  located outside of the device main body  1 . As a result, the motor core  101  is preheated and the time period required to heat the motor core  101  to the temperature necessary for melting the solid resin  114  on the lower die  18  of the device main body  1  is reduced. 
     As a result, the time period during which the device main body  1  is occupied by the resin melting step is reduced so that the operation efficiency of the device main body  1  is improved. Also, the time period required for manufacturing each magnet embedded core  100  is reduced, and the efficiency of manufacturing the magnet embedded core  100  can be improved. 
     Next, a device for manufacturing a magnet embedded core according to yet another embodiment is described in the following with reference to  FIG. 13 . 
     In this embodiment, uncured granular raw material resin  118  is used as the solid resin. 
     The resin holding member  86  of the resin charging device  80  of this embodiment has a funnel shape so that the granular raw material resin  118  can be easily poured therein, and each resin holding member  86  may also serve as a measuring cup for the granular raw material resin  118 . 
     Although the present invention has been described in terms of preferred embodiments thereof, as can be appreciated easily by a person skilled in the art, the present invention is not limited by these embodiments, but can be modified as appropriate without departing from the spirit of the present invention. 
     For instance, the magnet insertion step may be performed before the resin charging step. In this case, since the solid resin is charged into the magnet insertion holes  104  which already contain the magnets  110 , from the viewpoint of ease of feeding the resin into the magnet insertion holes  104 , the resin preferably consists of uncured granular raw material resin  118 . The shapes of the magnet insertion holes  104  and the magnets  110  are not limited to a substantially rectangular parallelepiped shape, but may be any other appropriate shape depending on the required magnetic characteristics and other factors. 
     The resin  112  is not limited to a thermosetting resin, but may consist of a thermoplastic resin. When a thermoplastic resin is used as the resin  112 , a curing step by cooling is performed, instead of the thermal curing step for the thermosetting resin. 
     The magnet insertion holes  104  are not necessarily required to be through holes each having two open ends, but may also be bottomed holes each opening out at only one end surface of the motor core  101 . The filling of the resin into the magnet insertion holes  104  may be performed by using solid resin in sheet form or the like, instead of the solid resin  114  in block form or the granular raw material resin  118 . When solid resin is used, since the load in the die opening direction due to the injection pressure of the resin does not act on the die assembly during the resin charging step, the clamping force may be small. Pressurization of the motor core  101  at the time of the die clamping step is not necessarily required, and may only be required to the extent necessary for removing voids from the molten resin  116  in the magnet insertion holes  104 . Further, the pressurization of the molten resin  116  in the magnet insertion holes  104  may be performed by a separate pressurization device or a pressurizing member, instead of relying on the pressurization projections  24  of the upper die  20 . 
     The toggle link mechanism  42  may be driven by an electric drive unit using a ball screw and a servomotor, instead of the hydraulic cylinder device  46 . In such a case, detection of the maximally extended state of the toggle link mechanism  42  may be detected by any per se known device such as a rotary encoder for detecting the rotational angle of the servomotor. Further, the die clamping device  30  may be driven by a plurality of toggle link mechanisms arranged in parallel to one another. 
     The clamping device  30  is not limited to the one using a toggle link mechanism, but may also consist of those directly actuated by hydraulic pressure or an electric motor. 
     The constituent elements of the foregoing embodiments are not entirely essential for the present invention, but may be suitably omitted or substituted without departing from the scope of the present invention. 
     
       
         
           
               
             
               
                   
               
               
                 GLOSSARY OF TERMS 
               
               
                   
               
             
            
               
                   
               
            
           
           
               
               
               
               
            
               
                  1 
                 device main body 
                  3 
                 fixed frame 
               
               
                  10 
                 lower fixed platen 
                  11 
                 upper surface 
               
               
                  12 
                 upper fixed platen 
                  14 
                 tie bar 
               
               
                  16 
                 movable platen 
                  17 
                 lower surface 
               
               
                  18 
                 lower die 
                  19 
                 upper surface 
               
               
                  20 
                 upper die 
                  21 
                 conveying tray 
               
               
                  22 
                 lower surface 
                  24 
                 pressurization projection 
               
               
                  30 
                 clamping device 
                  32 
                 pivot shaft 
               
               
                  34 
                 upper link 
                  36 
                 pivot shaft 
               
               
                  38 
                 lower link 
                  40 
                 pivot shaft 
               
               
                  42 
                 toggle link mechanism 
                  44 
                 pivot shaft 
               
               
                  46 
                 hydraulic cylinder device 
                  47 
                 cylinder tube 
               
               
                  48 
                 piston rod 
                  60 
                 tubular member 
               
               
                  62 
                 piston 
                  64 
                 through hole 
               
               
                  66 
                 tip end portion 
                  67 
                 tip end surface 
               
               
                  68 
                 compression coil spring 
                  70 
                 heating device 
               
               
                  80 
                 resin Charging device 
                  82 
                 substrate 
               
               
                  84 
                 resin holding hole 
                  86 
                 resin holding member 
               
               
                  88 
                 shutter plate 
                  90 
                 magnet insertion device 
               
               
                  92 
                 substrate 
                  94 
                 magnet holding hole 
               
               
                  96 
                 magnet holding member 
                  98 
                 shutter plate 
               
               
                 100 
                 magnet embedded core 
                 101 
                 motor core 
               
               
                 102 
                 center hole 
                 104 
                 magnet insertion hole 
               
               
                 104A 
                 inner surface 
                 105 
                 upper opening 
               
               
                 106 
                 iron core laminate 
                 108 
                 upper end surface 
               
               
                 110 
                 magnet 
                 110A 
                 outer surface 
               
               
                 112 
                 resin 
                 114 
                 solid resin 
               
               
                 114A 
                 outwardly facing surface 
                 116 
                 molten resin 
               
               
                 118 
                 material resin 
                 120 
                 heating oven 
               
               
                 122 
                 oven interior 
                 124 
                 heater