Method and device for producing lamination core

Abstract

Provided are a method and a device for producing a lamination core, which make it possible to predict occurrence of weld cracks and further facilitate prevention of the weld cracks. The method is for producing a lamination core 1 in which a plurality of core pieces 7 are laminated, and involves welding by applying pressure to the lamination core 1 in the lamination direction, and setting the cumulation of the compression amount of the lamination core 1 by application of the pressure, the contraction amount of the lamination core 1 in the lamination direction at a welded portion, and the spring back amount of the lamination core 1 by release of the pressure, to be within the compression limitation of the lamination core 1.

Description

Manufacturing method and device for laminated core

[0001] The present invention relates to a method and an apparatus for manufacturing a laminated core in which a plurality of core pieces are stacked.

[0002] A conventional method for manufacturing a laminated core is described in Patent Document 1. In this manufacturing method, for example, a laminated core obtained by applying a first load is welded while being pressed with a second load that is equal to or less than the first load.

[0003] Such welding reduces springback in the lamination direction of the laminated core, thereby suppressing cracks in the weld beads.

[0004] However, this manufacturing method does not take into consideration the relationship between compression due to pressure applied to the laminated core during welding, contraction due to cooling after welding, and springback due to pressure release, which limits the ability to suppress weld cracks, which are cracks in the weld bead.

[0005] Patent No. 7078424

[0006] The problem to be solved is that there is a limit to how much weld cracking can be prevented in laminated cores.

[0007] The present invention provides a method for manufacturing a laminated core in which multiple core pieces are stacked, in which the laminated core is pressurized in the stacking direction and welded, so that the cumulative amount of compression of the laminated core due to the pressurization, the amount of contraction of the laminated core in the stacking direction at the welded location, and the amount of springback of the laminated core due to the release of the pressurization are within the compression limit of the laminated core.

[0008] The present invention also provides a laminated core manufacturing device that includes a pressure mechanism that applies pressure to a laminated core in the stacking direction, the laminated core being formed by stacking multiple core pieces; a welding mechanism that welds the pressurized laminated core in the stacking direction; and a control unit that controls the pressure mechanism so that the cumulative amount of compression of the laminated core due to the pressure, the amount of contraction of the laminated core in the stacking direction at the welded location, and the amount of springback of the laminated core due to the release of the pressure is within the compression limit of the laminated core.

[0009] The present invention can improve the suppression of weld cracks in laminated cores.

[0010] FIG. 1 is a perspective view of a laminated core according to Example 1 of the present invention. FIG. 2 is a plan view of the laminated core of FIG. 1. FIG. 3 is an enlarged photograph showing weld cracks in a laminated core when the manufacturing method of Example 1 is not applied. FIG. 4 is an enlarged photograph showing shrinkage due to welding of the laminated core of FIG. 1. FIG. 5 is an enlarged photograph showing pressure applied to unwelded portions of the laminated core of FIG. 1. FIG. 6 is a graph showing the height state of a laminated core including welded and unwelded portions. FIG. 7 is a plan view showing the surface pressure of pressure applied to welded and unwelded portions. FIG. 8 is a graph showing the relationship between the compression limit of a laminated core, the amount of compression when pressurized, the amount of shrinkage due to welding, and the amount of springback due to release of pressure. FIG. 9 is a schematic diagram showing a manufacturing apparatus for the laminated core of Example 1. FIG. 10 is a schematic diagram showing the manufacturing apparatus of FIG. 9 during welding. FIG. 11 is an enlarged side view of a portion of the manufacturing apparatus according to Example 2. FIG. 12 is an enlarged cross-sectional view of a portion of the manufacturing apparatus of FIG. 11.

[0011] The present invention achieves the objective of improving the suppression of weld cracks in laminated cores by using a manufacturing method and apparatus that ensures that the cumulative amount of compression of the laminated core due to pressure, the amount of contraction of the laminated core in the lamination direction at the welded points, and the amount of springback of the laminated core due to the release of pressure is within the compression limit of the laminated core.

[0012] That is, the manufacturing method of the laminated core 1 is a manufacturing method of a laminated core 1 in which a plurality of core pieces 7 are stacked. In this manufacturing method, the laminated core 1 is pressed in the stacking direction, welded, and then the pressure is released. At this time, the cumulative amount of compression of the laminated core 1 due to the pressure, the amount of contraction of the laminated core 1 in the stacking direction at the welded parts, and the amount of springback of the laminated core 1 due to the release of the pressure is set within the compression limit of the laminated core 1.

[0013] The welding is performed sequentially at a plurality of locations in the circumferential direction of the laminated core 1. At the end of the sequential welding at a plurality of locations, the cumulative amount of compression, shrinkage, and springback of the laminated core 1 may be set to be within the compression limit of the laminated core 1.

[0014] In one embodiment, the pressure load may be reduced so that the cumulative amount of compression, shrinkage, and springback of the laminated core 1 falls within the compression limit of the laminated core 1 .

[0015] In another embodiment, the pressure may be applied by a pressure plate 27. In this case, the pressure position of the pressure plate 27 is fixed so that the cumulative amount of compression, shrinkage, and springback of the laminated core 1 is within the compression limit of the laminated core 1.

[0016] In yet another embodiment, the pressure may be applied by the pressure plate 27 and the pusher 33. In this case, the pusher 33 is moved to fill the gap S between the laminated core 1 and the pressure plate 27 due to shrinkage of the laminated core 1 in the lamination direction at the welded points, and presses the laminated core 1 in the gap S together with the pressure applied by the pressure plate 27.

[0017] The manufacturing apparatus 15 includes a pressurizing mechanism 17, a welding mechanism 19, and a control unit 21. The pressurizing mechanism 17 pressurizes the laminated core 1 in the stacking direction. The welding mechanism 19 welds the pressed laminated core 1 in the stacking direction. The control unit 21 controls the load of pressurization by the pressurizing mechanism 17 so that the cumulative amount of compression, shrinkage, and springback of the laminated core 1 is within the compression limit of the laminated core 1.

[0018] The welding mechanism 19 may sequentially perform welding at a plurality of locations in the circumferential direction of the laminated core 1. In this case, the control unit 21 may control the load so that the cumulative amount of compression, shrinkage, and springback of the laminated core 1 is within the compression limit of the laminated core 1 at the end of the welding at a plurality of locations sequentially performed on the laminated core 1.

[0019] In one embodiment, the control unit 21 may reduce the load when applying pressure so that the cumulative amount of compression, contraction, and springback of the laminated core 1 falls within the compression limit of the laminated core 1 .

[0020] In another embodiment, the pressure mechanism 17 may include a pressure plate 27. In this case, the control unit 21 may fix the pressure position of the pressure plate so that the cumulative amount of compression, contraction, and springback of the laminated core 1 is within the compression limit of the laminated core 1.

[0021] In another embodiment, the manufacturing apparatus 15 may include a pressure plate 27, a welding mechanism 19, and a pusher 33. The pusher 33 is movably supported by the pressure plate 27 in the stacking direction, and follows the gap S between the pressure plate 27 and the laminated core 1 to pressurize the laminated core 1 within the gap S in addition to the pressure applied by the pressure plate 27.

[0022] [Laminated Core] Fig. 1 is a perspective view of a laminated core according to Example 1 of the present invention. Fig. 2 is a plan view of the laminated core of Fig. 1. In the following description, the lamination direction, circumferential direction, radial direction, and axial direction refer to the lamination direction, circumferential direction, radial direction, and axial direction of the laminated core, respectively.

[0023] The laminated core 1 in FIGS. 1 and 2 is a stator core for a rotating electrical machine. This laminated core 1 is formed by axially stacking core pieces 7 made of multiple annular plate materials and integrating them with multiple welds 5 on the outer periphery. The state in which the core pieces 7 are stacked before the welds 5 are formed may include a state in which the core pieces 7 are joined by crimping or a state in which the core pieces 7 are not joined by crimping, as long as the core pieces 7 are in a stacked state. The core pieces 7 are formed, for example, by punching from electromagnetic steel sheets. Instead of punching, the core pieces 7 may also be formed by laser cutting or wire cutting. The laminated core 1 can also be used as a rotor core. In this case, welds can be formed on the inner periphery, outer periphery, magnet mounting holes, etc. of the rotor core.

[0024] The welds 5 are formed along the stacking direction, and in this embodiment, they are formed at eight locations in the circumferential direction as shown in Figure 3. The number of welds 5 is not limited to eight and can be increased or decreased relative to eight. Each weld 5 is formed within a radial recess 9 (see Figure 4) on the outer periphery of the laminated core 1. A weld protrusion 9a (see Figure 5) is located within the recess 9 before welding. Each weld 5 has a weld bead 13 formed by linear welding in the stacking direction to the weld protrusion 9a. Note that welding may be performed at locations on the laminated core 1 where welding is planned, and is not limited to using the recess 9 or weld protrusion 9a.

[0025] The laminated core 1 is welded by the manufacturing method of this embodiment, thereby suppressing weld cracks in the welded portion 5 (weld bead 13). Fig. 3 is an enlarged photograph showing weld cracks C in the laminated core 1 when the manufacturing method of this embodiment is not applied. The mechanism by which such weld cracks C occur will be described.

[0026] [Mechanism of Weld Cracking] Fig. 4 is an enlarged photograph showing shrinkage due to welding of the laminated core of Fig. 1. Fig. 5 is an enlarged photograph showing pressure being applied to an unwelded portion of the laminated core of Fig. 1.

[0027] When welding the laminated core 1, the laminated core 1 is supported in an unwelded state on a support jig, which will be described later, and is pressed in the stacking direction by a pressure ring 27, which is a pressure plate in this embodiment, as shown in Figures 4 and 5. This pressure causes the laminated core 1 to compress and shrink in the stacking direction. In this state, welding such as TIG welding or laser welding is performed in the stacking direction at the weld projections 9a in the recesses 9, and a weld bead 13 is formed at the weld portion 5.

[0028] This welding is performed sequentially at multiple locations, for example, eight locations, in the circumferential direction. The welding at multiple locations is performed sequentially for each pair of welding projections 9a located on both sides in the radial direction with respect to the center of the laminated core 1. However, welding may be performed sequentially at one location at a time.

[0029] As the welded portions 5 cool, they shrink in the lamination direction, causing the laminated core 1 to shrink in the lamination direction at the contracted portions, as shown in Figure 4. This causes the upper surface of the laminated core 1 to separate from the pressure ring 27 at these portions, leaving a gap S. Meanwhile, unwelded portions remain pressed in the lamination direction by the pressure ring 27, as shown in Figure 5. As a result, the surface pressure of the pressure ring 27 increases at the unwelded portions of the laminated core 1.

[0030] Fig. 6 is a graph showing the height state of the laminated core 1 including welded and unwelded portions, and Fig. 7 is a plan view showing the surface pressure state of pressurization at the welded and unwelded portions.

[0031] The height, or the dimensional state in the stacking direction, of the laminated core 1 including the welded and unwelded portions of Figures 4 and 5 is as shown in Figure 6. Figure 6 shows the state in which welding has been performed up to the third pair of eight pairs of welding positions. In this state, the height is low at each welded position, and the height is high at the last unwelded fourth pair. The symbols in Figure 6 indicate the welding order, with the first pair being numbered 1, the second pair being numbered 2, the third pair being numbered 3, and the fourth pair being numbered 4.

[0032] The change in surface pressure due to the change in height of the laminated core 1 is shown in Figure 7. In Figure 7, the white areas A are welded areas where the surface pressure is low. The dark areas are unwelded areas where the surface pressure is high. The cross-hatched areas are areas other than welded and unwelded areas. Welded area A has contracted due to welding, and the surface pressure is lower than that of unwelded area B.

[0033] As described above, as the surface pressure increases, the amount of shrinkage (compression amount) due to compression of the laminated core 1 increases. Therefore, the cumulative amount of compression of the laminated core 1 and the amount of shrinkage (contraction amount) due to contraction of the weld bead 13 at that location gradually increases as welding progresses (the number of unwelded areas decreases). It was found that weld cracks occur when the cumulative amount of compression and contraction of the laminated core 1 minus the amount of springback when the laminated core 1 is released from the cumulative amount of compression and contraction of the laminated core 1 exceeds the compression limit of the laminated core 1. The amount of springback is the magnitude of springback, which is the phenomenon in which the laminated core 1 tends to expand in the lamination direction when pressure is released. The compression limit refers to the state in which the laminated core 1 is compressed in the lamination direction to tightly contact the core pieces 7, i.e., the limit at which the laminated core 1 can be compressed.

[0034] FIG. 8 is a graph showing the relationship between the compression limit of a laminated core, the amount of compression when pressurized, the amount of shrinkage due to welding, and springback.

[0035] In FIG. 8, the vertical axis represents the load when the pressure ring 27 presses the laminated core 1, and the horizontal axis represents the height displacement at the welded portion.

[0036] In the laminated core 1, as shown in Fig. 8, when the cumulative sum of the compression amount of the laminated core 1 (core compression amount in Fig. 8), the shrinkage amount of the weld bead 13 at that location (bead shrinkage amount in Fig. 8), and the springback amount exceeds the compression limit of the laminated core 1, a cleavage force acts on the weld bead 13 to separate the core pieces 7 by that amount. As a result, cracks occur in the weld bead 13, leading to weld cracking.

[0037] In the manufacturing method of this embodiment, the occurrence of such weld cracks can be predicted, and the weld cracks are more effectively suppressed.

[0038] [Laminated Core Manufacturing Method and Apparatus] Fig. 9 is a schematic diagram showing a laminated core manufacturing apparatus 15. Fig. 10 is a schematic diagram showing the manufacturing apparatus 15 during welding.

[0039] The manufacturing method of this embodiment is realized using a manufacturing apparatus 15. However, the manufacturing method can also be performed without using the manufacturing apparatus 15. The manufacturing apparatus 15 includes a pressure mechanism 17, a welding mechanism 19, and a control unit 21, as shown in FIGS.

[0040] The pressure mechanism 17 applies pressure to the laminated core 1 in the stacking direction. This pressure mechanism 17 includes a support jig 23, a pressure ring 25, and a pressure ring 27 as a pressure plate. The support jig 23 has a core metal 23b on a base 23a that supports the laminated core 1. The pressure ring 25 is provided on the base 23a around the core metal 23b.

[0041] The pressure ring 25 abuts against and supports the lower surface of the laminated core 1 supported by the support jig 23. The pressure ring 27 is provided in a press machine (not shown) or the like, and applies pressure to the upper surface of the laminated core 1 in the stacking direction together with the pressure ring 25 on the lower surface. The pressure ring 27 does not release the pressure load until welding is completed, and follows the rotation direction of the laminated core 1. Note that the pressure plate is not limited to the ring-shaped pressure ring 27, and may have a plate-shaped portion that can apply pressure to the laminated core 1.

[0042] The pressure-receiving ring 25 and the pressure ring 27 can be driven to rotate, and this rotation positions the laminated core 1 in a pressurized state relative to the welding mechanism 19 in the circumferential direction.

[0043] The welding mechanism 19 welds the pressed laminated core 1 in the lamination direction. This welding mechanism 19 has laser irradiation units 29 arranged on both sides of the laminated core 1 supported by the pressure mechanism 17. This allows the laser irradiation units 29 to weld to each pair of welding protrusions 9a of the laminated core 1 on the pressure mechanism 17. Note that the welding mechanism 19 is not limited to laser welding and may perform other types of welding. For example, if the welding mechanism 19 performs TIG welding or the like, a welding torch may be provided instead of the laser irradiation units 29.

[0044] The control unit 21 is a computer equipped with a CPU, ROM, RAM, etc., and has installed therein a welding program for the laminated core 1. The welding program for the laminated core 1 may be stored in a portable recording medium as the welding program for the laminated core 1.

[0045] The welding program for the laminated core 1 causes the computer to realize a welding control function and a pressure control function.

[0046] The welding control function presses the laminated core 1 in the lamination direction with a set load, and operates the welding mechanism 19 to weld the laminated core 1 in the lamination direction.

[0047] The pressure control function controls the pressure load applied by the pressure mechanism 17 so that the cumulative amount of compression, shrinkage, and springback of the laminated core 1 falls within the compression limit of the laminated core 1. In this embodiment, the pressure load applied by the pressure mechanism 17 is controlled so that the cumulative amount of compression, shrinkage, and springback of the laminated core 1 falls within the compression limit of the laminated core 1 at the last welding step performed sequentially at multiple locations around the circumferential direction of the laminated core 1, for example, at the fourth pair of eight locations out of four pairs.

[0048] In this embodiment, the load control is a reduction in the load. This load reduction only needs to be performed so that the cumulative amount of compression, shrinkage, and springback of the laminated core 1 at the final welding is within the compression limit of the laminated core 1, and may be performed one or more times while the welding is being performed sequentially at multiple locations. By reducing the load when applying pressure while the welding is being performed sequentially at multiple locations, it is possible to suppress an increase in the compression amount of the laminated core 1 as the welding progresses. The load reduction may be performed each time the welding is performed at multiple locations.

[0049] In the manufacturing method using such manufacturing apparatus 15, when the laminated core 1 is pressurized in the stacking direction and welded, the pressure is adjusted so that the cumulative amount of compression in the stacking direction of the laminated core 1 due to pressure, the amount of contraction in the stacking direction due to welding, and the amount of springback when the pressure is released is within the compression limit of the laminated core 1.

[0050] When pressurizing the laminated core 1, the laminated core 1 is first supported on the support jig 23 shown in Fig. 9 and then placed on the pressure ring 25. The laminated core 1 is then pressed from above with a set load by the pressure ring 27 as shown in Fig. 10.

[0051] The set load is determined so that at least initially, in this embodiment, in the first welding of the first pair, the cumulative amount of compression, shrinkage, and springback of the laminated core 1 is within the compression limit of the laminated core 1. The amount of compression, shrinkage, and springback can be determined in advance by experiment or the like.

[0052] The first pair of welding projections 9 a of the laminated core 1 on the pressure mechanism 17 is positioned in the circumferential direction by the laser irradiation unit 29. Then, the laser irradiation unit 29 irradiates the first pair of welding projections 9 a with a laser over the entire lamination direction. This completes welding of the first pair of welding projections 9 a to the laminated core 1.

[0053] This welding causes shrinkage in the lamination direction of the weld bead 13. A gap S is formed between the pressure ring 27 and the laminated core 1 at this shrinkage portion.

[0054] In this way, when the welding of the first pair is completed, the surface pressure due to the application of pressure increases at the other unwelded portions. As a result, the amount of compression at the unwelded portions of the laminated core 1 increases compared to before the welding of the first pair. The cumulative amount of this increased compression of the laminated core 1, the amount of contraction due to the welding of the first pair, and the amount of springback of the laminated core 1 due to the release of pressure falls within the compression limit due to the setting of the pressure load as described above.

[0055] Then, welding of the next second pair of welding projections 9a is also performed so that the cumulative amount of increasing compression, shrinkage and springback of the laminated core 1 falls within the compression limit.

[0056] For example, if it is predicted that the cumulative amount of compression, shrinkage, and springback of the laminated core 1, which will increase due to welding, will exceed the compression limit before welding the second pair of weld projections 9a, the pressure load is reduced before welding the second pair. The predicted amounts of compression, shrinkage, and springback at this time may be obtained in advance by experiment or the like, as in determining the set load.

[0057] Alternatively, the applied pressure load may be reduced by comparing the cumulative amount of compression, shrinkage, and springback at the completion of the first welding pair with a threshold value. Alternatively, the load may be automatically reduced as each welding is completed, as long as the surface pressure required for welding can be maintained.

[0058] The automatic load reduction can be performed, for example, by reducing the surface pressure of the laminated core 1, which is expected to increase as welding is completed. That is, when welding is performed while applying pressure to the laminated core 1 with a constant load, the surface pressure of the applied pressure at the welded portions decreases due to the contraction of the weld beads 13, and the surface pressure at the unwelded portions becomes relatively high. When the surface pressure increases, the amount of compression of the laminated core 1 increases at the unwelded portions, so this expected increase in surface pressure can be reduced.

[0059] The reduction rate of the load is preferably about 99% to 45% of the initial pressure load applied to the laminated core 1. This reduction in load makes it possible to maintain, for example, the initial surface pressure at the unwelded portions.

[0060] The pressure position of the pressure ring 27 can also be fixed to a specified value. The pressure position is the position of the pressure ring 27 in the lamination direction of the laminated core 1. By fixing it in this way, it is possible to suppress an increase in surface pressure at unwelded portions.

[0061] Thereafter, in the same manner as described above, the laminated core 1 is pressurized and welded from the third pair onwards, until the final fourth pair is completely welded, so that the cumulative amounts of compression, shrinkage and springback of the laminated core 1 are within the compression limit of the laminated core 1.

[0062] Therefore, it is possible to suppress the cleavage force acting between the core pieces 7 due to spring back of the laminated core 1 or the like, and to suppress weld cracks in the weld bead 13.

[0063] In this embodiment, the load applied during pressurization is reduced so that the cumulative amount of compression, shrinkage, and springback of the laminated core 1 is within the compression limit, thereby suppressing an increase in the amount of compression of the laminated core 1 as the welding progresses, and more reliably suppressing weld cracks in the weld bead 13.

[0064] Fig. 11 is an enlarged side view of a portion of a manufacturing apparatus according to Example 2. Fig. 12 is an enlarged cross-sectional view of a portion of the manufacturing apparatus shown in Fig. 11. Since Example 2 has a basic configuration in common with Example 1, components that are the same as or correspond to those in Example 1 are designated by the same reference numerals, and redundant explanations will be omitted.

[0065] In Example 2, the pusher 33 is caused to follow the gap S between the laminated core 1 and the pressure ring 27 due to shrinkage of the laminated core 1 in the stacking direction, which occurs at the welding point. As a result, the laminated core 1 is pressed by the pusher 33 within the gap S in addition to the pressure applied by the pressure ring 27. For this reason, the manufacturing apparatus 15 of this example includes a surface pressure maintaining mechanism 31 in addition to the pressure mechanism 17, welding mechanism 19, and control unit 21. Note that following the gap S refers to following the gap S in the stacking direction, and it does not matter whether it follows the gap S in the circumferential direction.

[0066] 11 and 12, the surface pressure maintaining mechanism 31 includes a pusher 33 and a compression spring 35. Instead of the compression spring 35, a hydraulic cylinder, a pneumatic cylinder, a solenoid, or the like may be used.

[0067] The pusher 33 is supported by the pressure ring 27 so as to be movable in the stacking direction. The pusher 33 in this embodiment is a shaft-shaped member integrally provided with a spring seat 33a. The shape of the pusher 33 is not particularly limited as long as it can fit into the gap S.

[0068] The pusher 33 is capable of passing through a through-hole 27a of the pressure ring 27 and protruding toward the laminated core 1. The through-hole 27a is connected to a spring accommodating hole 27b. A spring seat 33a is disposed in the spring accommodating hole 27b. A compression spring 35 is disposed in the spring accommodating hole 27b. The compression spring 35 is disposed between a nut 37 threaded onto the upper side of the accommodating hole 27a and the spring seat 33a.

[0069] The surface pressure maintaining mechanism 31 is disposed corresponding to one, more than one, or all of the plurality of welding locations to be sequentially performed. The surface pressure maintaining mechanism 31 in this embodiment corresponds to all of the welding locations.

[0070] When a gap S occurs in the weld bead 13 due to shrinkage at the welding location, the compression spring 35 of the surface pressure holding mechanism 31 pushes the pusher 33 toward the laminated core 1 in accordance with the gap S. As a result, the pusher 33 follows the gap S and presses the laminated core 1 within the gap S.

[0071] Therefore, in this embodiment, the surface pressure due to pressurization at the welded portions can be maintained by the surface pressure maintaining mechanism 31 in accordance with the amount of shrinkage of the laminated core 1 in the lamination direction, thereby suppressing an increase in surface pressure throughout the laminated core 1. Note that the surface pressure maintained by the surface pressure maintaining mechanism 31 only needs to be maintained so that the cumulative amount of compression, shrinkage, and springback of the laminated core 1 at the welded portions is within the compression limit, and to that extent, an increase in surface pressure at unwelded portions may be acceptable.

[0072] In this way, in the second embodiment, the surface pressure of the laminated core 1 is maintained, so that the increase in the amount of compression as the welding progresses can be suppressed, and the suppression of weld cracks in the weld bead 13 can be reliably improved.

[0073] In addition, the second embodiment can also achieve the same effects as the first embodiment. Furthermore, the second embodiment can be combined with the first embodiment.

[0074] REFERENCE SIGNS LIST 1 laminated core 7 core piece 15 laminated core manufacturing device 17 pressure mechanism 19 welding mechanism 21 control unit 31 surface pressure holding mechanism

Claims

1. A method for manufacturing a laminated core in which a plurality of core pieces are stacked, comprising the steps of: pressurizing the laminated core in the stacking direction and welding the laminated core; and ensuring that the cumulative amount of compression of the laminated core due to the pressurization, the amount of contraction of the laminated core in the stacking direction at the welded points, and the amount of springback of the laminated core due to the release of the pressurization are within the compression limit of the laminated core.

2. A method for manufacturing a laminated core as claimed in claim 1, wherein the welding is performed sequentially at a plurality of locations around the circumferential direction of the laminated core, and the cumulative amount of the compression, contraction and springback at the end of the sequential welding at a plurality of locations is within the compression limit of the laminated core.

3. A method for manufacturing a laminated core according to claim 1 or 2, comprising reducing the load applied when applying pressure so that the cumulative amount of compression, contraction and springback falls within the compression limit of the laminated core.

4. A method for manufacturing a laminated core according to claim 1 or 2, wherein the pressurization is performed by a pressurizing plate, and the pressurizing position of the pressurizing plate is fixed so that the cumulative amount of compression, contraction and springback is within the compression limit of the laminated core.

5. A method for manufacturing a laminated core as claimed in claim 1 or 2, wherein the pressure is applied by a pressure plate, and a pusher is moved into a gap between the laminated core and the pressure plate caused by shrinkage of the laminated core in the lamination direction at the welded points, thereby pressing the laminated core within the gap while applying pressure with the pressure plate.

6. A method for manufacturing a laminated core having a plurality of stacked core pieces, the laminated core is pressurized in the stacking direction to weld, the welding is performed sequentially at a plurality of locations around the circumferential direction of the laminated core, and the load applied when applying pressure is reduced while the sequential welding of the plurality of locations is in progress.

7. A method for manufacturing a laminated core in which a plurality of core pieces are stacked, comprising the steps of: pressing the laminated core in the stacking direction with a pressure plate to weld it; the welding being performed sequentially at a plurality of points around the circumferential direction of the laminated core; and moving a pusher into a gap between the laminated core and the pressure plate caused by shrinkage of the laminated core in the stacking direction at the welded points, to pressurize the laminated core within the gap while also applying pressure with the pressure plate.

8. A manufacturing device for a laminated core, comprising: a pressurizing mechanism for pressurizing a laminated core having a plurality of stacked core pieces in a stacking direction; a welding mechanism for welding the pressurized laminated core in the stacking direction; and a control unit for controlling the load of pressurization by the pressurizing mechanism so that the cumulative amount of compression of the laminated core due to the pressurization, the amount of contraction of the laminated core in the stacking direction at the welded points, and the amount of springback of the laminated core due to the release of the pressurization is within the compression limit of the laminated core.

9. An apparatus for manufacturing laminated cores as claimed in claim 8, wherein the welding mechanism sequentially performs the welding at a plurality of locations in the circumferential direction of the laminated core, and the control unit controls the load so that the cumulative amount of the compression amount, the contraction amount and the springback amount at the end of the welding at the plurality of locations sequentially performed is within the compression limit of the laminated core.

10. An apparatus for manufacturing laminated cores according to claim 8 or 9, wherein the control unit reduces the load during pressurization so that the cumulative amount of compression, contraction and springback falls within the compression limit of the laminated core.

11. An apparatus for manufacturing laminated cores as claimed in claim 8 or 9, wherein the pressurizing mechanism includes a pressurizing plate which applies the pressurizing force, and the control unit fixes the pressurizing position of the pressurizing plate so that the cumulative amount of compression, contraction and springback is within the compression limit of the laminated core.

12. A manufacturing device for a laminated core comprising: a pressure plate which pressurizes a laminated core having a plurality of stacked core pieces in a stacking direction; a welding mechanism which welds the pressed laminated core in the stacking direction, performing the welding sequentially at a plurality of locations in the circumferential direction; and a pusher which is movably supported in the stacking direction by the pressure plate and which follows a gap between the laminated core and the pressure plate caused by shrinkage of the laminated core in the stacking direction that occurs at the welded locations, and which pressurizes the laminated core within the gap while being pressed by the pressure plate.

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