Punching device and method

Abstract

Provided is a punching device capable of punching in which the roundness of an iron core piece is taken into account. In the present invention, punches 9, 11, and 13 are provided corresponding to a plurality of stages 3, 5, and 7 across which a common steel plate 2 is arranged and which sequentially perform punching of the steel plate 2 to form iron core pieces 27, the punches 9, 11, and 13 of the plurality of stages 3, 5, and 7 are lowered together to punch the steel plate 2, and the tip position of the punch 13 in the punching direction is set so that the punching timing thereof is later than that of the punches 9 and 11.

Description

Punching device and method

[0001] The present invention relates to a punching device and method for punching core pieces used in laminated cores for rotating electrical machines.

[0002] A conventional punching device includes a device having multiple stages, as described in Patent Document 1. Steel plates are arranged across the multiple stages, and punches are sequentially punched into the steel plates to form core pieces in the final stage.

[0003] This punching device is configured so that the punch with the largest punching load presses the steel plate at the earliest timing, since quality would be reduced if punching were performed simultaneously on all stages.

[0004] However, in such conventional punching devices, a high load acts locally on the die due to the punch with the largest punching load that presses the steel plate first. This causes deformation of the die, etc., causing the punch to tilt relative to the steel plate, which reduces the punching accuracy of punches in other stages that press the steel plate thereafter. As a result, there is a problem of reduced processing accuracy of the core pieces.

[0005] Japanese Patent Application Laid-Open No. 2023-179359

[0006] The problem to be solved is the reduction in machining accuracy of the core pieces.

[0007] The present invention provides a punching device comprising punches provided corresponding to a plurality of stages across which a common steel plate is arranged and which sequentially punch the steel plate to form iron core pieces, the punches of the plurality of stages descending together to punch the steel plate, and the punches having tip positions in the punching direction such that the punching timing at the stage with the greatest punching load is delayed relative to the punching timing at at least one other stage.

[0008] The present invention provides a punching method in which a common steel plate is arranged across a plurality of stages in which punching is performed sequentially to form iron core pieces, and punches of the plurality of stages are lowered together to punch the steel plate in the plurality of stages, and the punch timing of the stage with the largest punching load is delayed relative to at least one other stage.

[0009] The present invention can improve the machining accuracy of the core pieces.

[0010] Fig. 1 is a schematic diagram of a punching device according to a first embodiment of the present invention. Fig. 2 is a plan view of a steel plate punched by the punching device of Fig. 1. Fig. 3 is a schematic diagram of an upper die of a punching device according to a first modified example of the first embodiment. Fig. 4 is a schematic diagram of an upper die of a punching device according to a second modified example of the first embodiment, viewed from the feed direction of the steel plate. Fig. 5 is a schematic diagram of a punching device according to a second modified example. Fig. 6 is a plan view of a steel plate punched by the punching device of Fig. 5. Fig. 7 is a schematic diagram showing a cross section of a part of a punching device according to a second modified example of the second embodiment.

[0011] A punching device 1 in one embodiment is arranged across a common steel plate 2 and includes punches 9, 11, 13, 41, 43, and 45 on multiple stages 3, 5, 7, 35, 37, and 39, respectively, that sequentially punch the steel plate 2 to form iron core pieces 27 and 53. The punches 9, 11, 13, 41, 43, and 45 on the multiple stages 3, 5, 7, 35, 37, and 39 all descend to punch the steel plate 2. The punches 9, 11, 13, 41, 43, and 45 have tip positions in the punching direction such that the punching timing on stage 7, where the punching load is greatest, is delayed relative to the punching timing on at least one of the other stages 3, 5, 35, 37, and 39.

[0012] It is preferable that punches 9, 11, 13, 41, 43, and 45 have a punching timing that is slower at stage 7 where the punching load is the largest than at all other stages 3, 5, 35, 37, and 39.

[0013] The stages may include a first stage 3, a second stage 5, and a third stage 7. The first stage 3 punches out the inner circumferential circle 21 of the core piece 27. The second stage 5 punches out the outer circumferential circle 23 of the core piece 27. The third stage 7 punches out the punched portion 25 of the core piece 27. The punching load of the third stage 7 is relatively large compared to the first and second stages 3 and 5. In this case, the tip position of the third stage 7 in the punching direction is set so that the punching timing is later than the punches 9 and 11 of the first and second stages 3 and 5.

[0014] The punching device 1 may include at least one other stage 3, 5, 35, 37, 39 upstream and downstream of the stage 7 where the punching load is maximum.

[0015] In the punching method, the steel plate 2 is placed across a plurality of stages 3, 5, 7, 35, 37, and 39 that sequentially punch a common steel plate 2 to form the iron core pieces 27 and 53, and punches 9, 11, 13, 41, 43, and 45 of the plurality of stages 3, 5, 7, 35, 37, and 39 all descend to punch the steel plate 2 in the plurality of stages 3, 5, 7, 35, 37, and 39. In stage 7, where the punching load is greatest, the punching timing of punch 13 is delayed relative to at least one of the other stages 3, 5, 35, 37, and 39.

[0016] [Punching Apparatus] Fig. 1 is a schematic diagram of a punching apparatus according to Example 1 of the present invention. Fig. 2 is a plan view of a steel plate punched by the punching apparatus of Fig. 1.

[0017] 1 punches out core pieces 27 to be used in a motor core, which is a laminated core for a rotating electrical machine. The motor core in this embodiment is a stator core, but may also be a rotor core.

[0018] This punching device 1 includes an upper die 15 and a lower die 17. These upper die 15 and lower die 17 include first, second, and third stages 3, 5, and 7 as multiple stages arranged along the feed direction of the steel plate 2. The stages represent individual steps when the iron core piece 27 is formed through multiple steps.

[0019] The first to third stages 3, 5, and 7 are arranged so that a common steel plate 2 is straddled therebetween, and punching of the steel plate 2 is performed sequentially in the feed direction to form the iron core pieces 27. These first to third stages 3, 5, and 7 are equipped with punches 9, 11, and 13, respectively.

[0020] The punches 9, 11, and 13 are attached to an upper die 15. The punches 9, 11, and 13 are configured to descend together with the upper die 15. Due to this descent, a stripper (not shown) presses the steel sheet 2 against the lower die 17 in advance, and the upper die 15 further descends relative to the lower die 17. As a result, the punches 9, 11, and 13 of the first to third stages 3, 5, and 7 further descend to punch the steel sheet 2.

[0021] The lower mold 17 has a die 17a corresponding to the second stage 5. The die 17a is provided with a squeeze ring 17c connected to a die body 17b. The die body 17b punches out the core pieces 27 in cooperation with the punch 11, and the squeeze ring 17c applies lateral pressure to the punched core pieces 27 to hold them in place. Therefore, in the second stage 5, the core pieces 27 punched out by the punch 11 and die 17a are sequentially held and stacked in the die 17a. Although not shown, the lower mold 17 is provided with dies corresponding to the first and third stages 3 and 7.

[0022] In the punching device 1 of this embodiment, as shown in Figures 1 and 2, the first stage 3 punches the inner periphery of the core piece 27, the second stage 5 punches the outer periphery of the core piece 27, and the third stage 7 punches the shape of the core piece 27.

[0023] However, the stage setting is arbitrary, and other stages such as forming a caulking portion by recesses and projections or applying adhesive can be added.

[0024] Inner peripheral punching in the first stage 3 punches out the inner peripheral circle 21 of the core piece 27. Outer peripheral punching in the second stage 5 punches out the outer peripheral circle 23 of the core piece 27. Shape punching in the third stage 7 punches out the slot portion 25 of the core piece 27. Note that in Figure 2, the portion that will become the outer peripheral circle 23 of the core piece 27 is indicated by a dashed line D. Also, the hole after outer peripheral punching of the core piece 27 is indicated as the outer peripheral circle 23.

[0025] The inner circumferential circle 21 and the outer circumferential circle 23 are punched concentrically to form the iron core pieces 27, and the slots 25 are arranged at equal intervals in the circumferential direction of the inner circumferential circle 21 and the outer circumferential circle 23. The slots 25 are arranged on circles concentric with the inner circumferential circle 21 and the outer circumferential circle 23.

[0026] [Tip Position] The punches 9, 11, and 13 of the first to third stages 3, 5, and 7 have their tip positions in the punching direction set according to the difference in punching load.

[0027] In this embodiment, the punching load of the third stage 7 is relatively large compared to the first and second stages 3 and 5. For this reason, the tip positions of the punches 9, 11, and 13 are set so that the punching timing of the third stage 7, which has the largest punching load, is delayed compared to all the other stages 3 and 5.

[0028] The punching timing may be set so that the third stage 7, which has the largest punching load, is delayed relative to at least one of the other stages 3 or 5. For example, the punching timing may be delayed in the third stage 7 relative to the first stage 3 and in the second stage 5 relative to the third stage 7, or delayed in the third stage 7 relative to the second stage 5 and in the first stage 3 relative to the third stage 7.

[0029] The punching load is the load required for punching by the press, and depends on the processing perimeter of the punches 9, 11, and 13. The processing perimeter is the outer perimeter dimension of the cross section of each punch. As the processing perimeter becomes longer, the punching load becomes larger.

[0030] In this embodiment, the processing circumferential length of the punch 13 in the third stage 7 is the sum of the punches that punch out each slot portion 25, and is longer than that of the first and second stages 3 and 5. Therefore, the punching load in the third stage 7 is the largest among the first to third stages 3, 5, and 7.

[0031] However, depending on the number of slots 25, the machining circumferential length of the punch 13 in the third stage 7 may become shorter relative to the punches 9 and 11 in the first and second stages 3 and 5. For this reason, the punching load of the punch 13 is not necessarily the greatest in the third stage 7. The same applies when other stages are added.

[0032] 1 shows the height of the tip positions of punches 9, 11, and 13 when punch 9 is in contact with the surface of steel sheet 1. This surface of steel sheet 1 is when steel sheet 1 is fed onto lower die 17 and pressed onto lower die 17 by a stripper.

[0033] Using the surface of this steel plate 1 as a reference, the heights of the tip positions of the punches 9, 11, and 13 from the upper die 15 have the relationship: height H0 of the tip position of the punch 9 > height H1 of the tip position of the punch 11 > height H2 of the tip position of the punch 13. In other words, the protruding length of the punch 13 in the third stage 7 from the upper die 15 is shorter than the protruding lengths of the punches 9 and 11 in the first and second stages 3 and 5, and the protruding length of the punch 11 in the second stage 5 is shorter than the protruding length of the punch 9 in the first stage 3.

[0034] By setting the tip position in this way, the timing at which the upper die 15 descends to punch out the steel plate 1 is the order of the punches 9, 11 and 13 of the first, second and third stages 3, 5 and 7.

[0035] The timing of punching by the punch 13 in the third stage 7 may be intermediate among the first to third stages 3, 5, and 7.

[0036] The first and third stages 3 and 7 are arranged upstream of the second stage 5 in the feeding direction of the steel sheet 1. The feeding direction is also the extending direction of the steel sheet 1 and the arrangement direction of the stages 3, 5, and 7. Between the first and third stages 3 and 7, the first stage 3 may be arranged upstream of the third stage 7. In this case, at least one other stage 3 and at least one other stage 5 are located upstream and downstream of the third stage 7, respectively.

[0037] [Punching Method] In the punching method of this embodiment, first, the steel sheet 2 is fed and placed between the upper die 15 and the lower die 17. At this time, the steel sheet 2 is placed across multiple stages 3, 5, and 7. In the first punching, the leading end of the steel sheet 2 in the feed direction is placed on the third stage 7, and in the second punching, the steel sheet 2 is placed across the first stage 3 and the third stage 7. Then, in the third punching and thereafter, the steel sheet 2 is placed across the first to third stages 3, 5, and 7.

[0038] In punching, when the upper die 15 descends, the punches 9, 11, and 13 of the first, second, and third stages 3, 5, and 7 also descend. This descent causes a stripper (not shown) on the upper die 15 side to press down on the steel sheet 2. Next, the punches 9, 11, and 13 protrude from the stripper, and in the third and subsequent punchings, the inner circumferential circle 21, the outer circumferential circle 23, and the slot portion 25 are punched out.

[0039] The timing of this punching is such that, according to the setting of the tip positions, the punches 9, 11, and 13 of the first, second, and third stages 3, 5, and 7 are punched in this order. In the second punching, the punches 9 and 13 of the first and third stages 3 and 7 are punched in this order.

[0040] That is, in the third and subsequent punching operations, punch 9 with the smallest punching load performs the first punching of steel plate 2, followed by punch 11, and punch 13 with the largest punching load performs the last punching. In the second punching operation, punch 9 with the smallest punching load performs the first punching, followed by punch 13 with the largest punching load. The timing of punching by punch 13 in third stage 7 may be set to be intermediate among the first to third stages 3, 5, and 7 as described above.

[0041] Therefore, for punches 9, 11, and 13, the third stage 7, which has the largest punching load, has a slower punching timing than the other first and second stages 3 and 5.

[0042] For this reason, in this embodiment, even if the upper die 15 and the lower die 17 are temporarily deformed due to punching in the third stage 7, the punching in the first and second stages 3 and 5 is completed before that. Therefore, the processing accuracy of the punching in the first and second stages 3 and 5 can be improved, and the processing accuracy of the core pieces 27 can be improved.

[0043] Furthermore, in this embodiment, punching can be performed by the punch 13 of the third stage 7, which has the largest punching load, while positioning the steel plate 2 with the punches 9 and 11 of the first and second stages 3 and 5, which have previously performed punching. This makes it possible to improve the processing accuracy of punching in the third stage 7 and suppress distortion of the steel plate 2 during punching in the third stage 7, thereby more reliably improving the processing accuracy of the core pieces 27.

[0044] Furthermore, since punching in the first and second stages 3 and 5, which are subsequent processes in the feed direction, can be performed on steel plate 2 with reduced distortion, the processing accuracy of the core piece 27 can be more reliably improved.

[0045] Between the punches 9 and 11 of the first and second stages 3 and 5, the punching timing of the punch 11 of the second stage 5, which has a relatively high punching load, is delayed relative to the punching timing of the punch 9 of the first stage 3, which has a relatively low punching load.

[0046] Therefore, in this embodiment, the processing accuracy of the punching performed first in the first stage 3 can be improved. Also, while the steel plate 2 is positioned by the punch 9 of the first stage 3 that performed the punching first, punching by the punch 11 of the second stage 5, which has a relatively large punching load, can be performed. This makes it possible to more reliably improve the processing accuracy of the core pieces 27 and suppress distortion of the steel plate 2 during punching in the first stage 3. Therefore, it is possible to more reliably improve the processing accuracy of the core pieces 27. Also, even if the punching timings of the first and third stages 3 and 7 or the punching timings of the second and third stages 5 and 7 are simultaneous, the processing accuracy of the core pieces 27 can be improved.

[0047] [Modification 1] FIG. 3 is a schematic diagram of an upper die of a punching device according to Modification 1 of the first embodiment.

[0048] In the first modification, the height of the tip position is made different within the punch 13 of the third stage 7 .

[0049] Specifically, the punch 13 is configured as a punch that punches out the slot portion 25, and has a plurality of punch portions 13a that correspond to the slot portion 25. The punch portions 13a have tip positions at different heights. The punch portions 13a are arranged along the circumferential direction, and accordingly, the punch 13 has different punching timings in the circumferential direction.

[0050] By setting the punching timing in this way, the punching load of the punch 13 can be alleviated, and punching accuracy can be more reliably improved. As a result, in this modified example, the accuracy of the slot portion 25 can be more reliably improved, and distortion of the steel plate 2 when punching the slot portion 25 can be suppressed.

[0051] [Modification 2] Fig. 4 is a schematic view of an upper die of a punching device according to Modification 2 of Example 1, viewed from the feeding direction of the steel plate.

[0052] In the above-described first embodiment, the inner circumference circle 21, the outer circumference circle 23, and the slot portion 25 are punched out by punches 9, 11, and 13 of the first to third stages 3, 5, and 7 in one row, but in the second modification, punching is performed simultaneously in multiple rows.

[0053] In the second modification, first, second and third stages 3, 5 and 7, each having the same processing order, are provided in a plurality of rows, for example, two rows, in the width direction of the steel plate 2.

[0054] Among the multiple rows of the first, second, and third stages 3, 5, and 7, the tip positions of the punches 9, 11, or 13 of the same stage 3, 5, or 7 may be set to be not only the same but also different. When the tip positions of the punches 9, 11, or 13 of the same stage 3, 5, or 7 are different, the relationship between the tip positions of the punches 9, 11, and 13 of the different stages 3, 5, and 7 may be set by the average length of the punches 9, 11, or 13 of the same stage 3, 5, or 7, the length of the longest punch, or the length of the shortest punch.

[0055] 4, for example, the punches 9 of the first stage 3 are arranged in two rows in the width direction of the steel sheet 2, and the tip positions of the punches 9 of the same stage 3 differ depending on their lengths. In this case, the tip positions of the punches 9 of the first stage 3 can be set using any of the average value, the longest length, or the shortest length of the tip positions of the punches 9 of the same stage 3 in the two rows. However, in each row, the tip positions of the punches 9, 11, and 13 can be set arbitrarily as long as the relationship between them is maintained.

[0056] [Punching device] Fig. 5 is a schematic diagram of a punching device according to Example 2. Fig. 6 is a plan view of a steel plate punched by the punching device of Fig. 5. Note that Example 2 has a basic configuration in common with Example 1, and corresponding components are denoted by the same reference numerals, and redundant explanations will be omitted.

[0057] As shown in FIGS. 5 and 6, the punching device 1 of Example 2 includes rotor core stages 35, 37, and 39 arranged in series upstream of stator core stages 3, 5, and 7 in the feeding direction of the steel plate 2.

[0058] As a result, at least one other stage 3, 5, 35, 37, and 39 is provided upstream and downstream of the third stage 7 of the stator core, where the punching load is greatest. Specifically, the rotor core stages 35, 37, and 39 are located upstream of the third stage 7 of the stator core, and the stator core stages 3 and 5 are located downstream of the third stage 7 of the stator core.

[0059] The punching device 1 of this embodiment has an upper mold 15A equipped with punches 9, 11, 13 configured in the same manner as in the first embodiment and a lower mold 17A equipped with a die 17a for the stages 3, 5, and 7 of the stator core.

[0060] The rotor core stages 35, 37, and 39 have an upper mold 15B equipped with punches 41, 43, and 45, and a lower mold 17B equipped with a die 17a. The upper mold 15B is separated from the upper mold 15A so as to operate separately. The lower mold 17B is also separated from the lower mold 17A and provided separately.

[0061] In punching the core pieces 53 of the rotor core of the second embodiment, the first stage 35 punches the inner periphery, the second stage 37 punches the outer periphery, and the third stage 39 punches the shape.

[0062] The inner peripheral punching of the first stage 35 of the rotor core punches out the inner peripheral circle 47 of the core piece 53. The outer peripheral punching of the second stage 37 punches out the outer peripheral circle 49 of the core piece 53. The shape punching of the third stage 39 punches out the magnet insertion holes 51 of the core piece 53.

[0063] The inner circumferential circle 47 and the outer circumferential circle 49 are punched concentrically to form the iron core pieces 53, and the magnet insertion holes 51 are arranged at equal intervals in the circumferential direction. The magnet insertion holes 51 are arranged concentrically with the inner circumferential circle 47 and the outer circumferential circle 49.

[0064] 6, the portion that will become the outer circumferential circle 23 of the core piece 27 of the stator core is indicated by a dashed line D1, and the portion that will become the outer circumferential circle 49 of the core piece 53 of the rotor core is indicated by a dashed line D2. Also, the holes formed after punching out the outer peripheries of the core pieces 27 and 53 are indicated as the outer circumferential circles 23 and 49.

[0065] [Tip Position] As shown in FIG. 5 , in Example 2, the tip positions in the punching direction of punches 9, 11, and 13 of the first to third stages 3, 5, and 7 of the stator core and punches 41, 43, and 45 of the first to third stages 35, 37, and 39 of the rotor core are set so that the punching timing differs between at least two stages.

[0066] Specifically, the punch 13 of the third stage 7 of the stator core has the highest punching load. For this reason, of all the punches for the iron core pieces 27 and 53 of the stator core and rotor core, the punch 13 is set to the lowest tip height H2.

[0067] As in the first embodiment, the punches 9 and 11 of the first and second stages 3 and 5 of the stator core have their tip positions set at heights H0 and H1.

[0068] The punches 41, 43, and 45 of the first to third stages 35, 37, and 39 of the rotor core have tip heights set to H0, H1, and H0, respectively.

[0069] Among the punches 41, 43, and 45, the punch 43 in the second stage 37 has the largest punching load, and the tip position in the punching direction is set so that the punching timing differs from the punches 41 and 45 in the first and third stages 35 and 39.

[0070] [Punching Method] In the punching method of this embodiment, first, the steel sheet 2 is fed and placed between the upper die 15B and the lower die 17B. In the first punching, the leading end of the steel sheet 2 in the feed direction is placed in the third stage 39 of the rotor core, and in the second punching, the steel sheet 2 is placed across the first stage 35 to the third stage 39 of the rotor core. Then, in the third and subsequent punchings, the steel sheet 2 is placed across the first to third stages 35, 37, and 39 of the rotor core. During the fourth to sixth punchings, the steel sheet 2 sequentially straddles the first to third stages 3, 5, and 7 of the stator core. Thereafter, the steel sheet 2 is placed across all stages of the rotor core and the stator core.

[0071] During punching, when upper dies 15B and 15A descend, first to third stages 35, 37, and 39 of the rotor core and stator core, and punches 41, 43, and 45 of 3, 5, and 7, and punches 9, 11, and 13 also descend. This descent causes strippers (not shown) of upper dies 15B and 15A to press down on steel sheet 2. Next, punches 41, 43, and 45 and 9, 11, and 13 protrude from the strippers (not shown) and punch out inner circumferential circles 47 and 21, outer circumferential circles 49 and 23, magnet insertion holes 51, and slot portions 25.

[0072] The timing of the punching process is such that, depending on the setting of the tip positions, punches 41 and 45 punch the rotor core first at the same timing, followed by punch 43.

[0073] That is, punches 41 and 45 with relatively low punching loads perform punching first, and punch 43 with a relatively high and maximum punching load performs punching later.

[0074] Furthermore, punching of the stator core is performed in the same manner as in Example 1, in the order of punches 9, 11, and 13. In punching the rotor core and the stator core as a whole, punch 9 of the stator core is punched simultaneously with punches 41 and 45 of the rotor core, punch 11 of the stator core is punched simultaneously with punch 43 of the rotor core, and finally punch 13 of the stator core is punched.

[0075] Therefore, even when the core pieces 27 and 53 of the rotor core and the stator core are punched together, the machining accuracy of the core pieces 27 and 53 can be improved.

[0076] Furthermore, the punch 43 punches out the iron core pieces 53 of the rotor core at a timing that is later than that of at least one of the stages 41 and 45 .

[0077] This makes it possible to more reliably improve the machining accuracy of the core pieces 53 of the rotor core. In addition, the second embodiment can also achieve the same effects as the first embodiment.

[0078] [Modification] FIG. 7 is a schematic cross-sectional view of a punching device according to a modification of the second embodiment.

[0079] 7, in the punching device 1 according to the modified example, punches 41, 43, 45, 9, 11, and 13 for the rotor core and the stator core are provided in a common upper die 15. Accordingly, a common lower die 17 is provided with a die 17a corresponding to the second stages 37 and 5 for the rotor core and the stator core.

[0080] In this modified example, the same effects as those of the second embodiment can be achieved.

[0081] 1 Steel plate 3 First stage (for stator core) 5 Second stage (for stator core) 7 Third stage (for stator core) 9, 11, 13 Punch (for stator core) 27 Core piece (for stator core) 35 First stage (for rotor core) 37 Second stage (for rotor core) 39 Third stage (for rotor core) 41, 43, 45 Punch (for rotor core) 53 Core piece (for rotor core)

Claims

1. A punching device comprising punches provided corresponding to a plurality of stages that are arranged across a common steel plate and sequentially punch the steel plate to form core pieces, wherein the punches of the plurality of stages all descend to punch the steel plate, and the punch has a tip position in the punching direction where the punching timing at the stage with the maximum punching load is later than the punching timing of at least one other stage.

2. The punching device according to claim 1, wherein the punch has a punching timing that is later than that of all other stages at the stage with the maximum punching load due to the tip position.

3. The punching device according to claim 1, wherein the stages include a first stage for punching the inner peripheral circle of the core piece, a second stage for punching the outer peripheral circle of the core piece, and a third stage for punching the cut-out portion of the core piece, the punching load of the third stage is relatively large compared to the first and second stages, and the punch of the third stage has a punching timing that is later than that of the punches of the first and second stages due to the tip position.

4. The punching device according to claim 1, further comprising at least one of the other stages upstream and downstream of the stage with the maximum punching load.

5. A punching method in which a steel plate is arranged across a plurality of stages that sequentially punch the common steel plate to form core pieces, the punches of the plurality of stages all descend to perform punching on the steel plate at the plurality of stages, and the punching timing of the punch is later than that of at least one other stage at the stage with the maximum punching load.

6. The punching method according to claim 5, wherein the punching timing of the punch is later than that of all other stages at the stage with the maximum punching load.

7. The punching method according to claim 5, wherein the stage includes a first stage for punching the inner peripheral circle of the iron core piece, a second stage for punching the outer peripheral circle of the iron core piece, and a third stage for punching the shaped cut portion of the iron core piece, the punching load of the third stage is relatively large with respect to the first and second stages, and the punch of the third stage has a different punching timing from the punches of the first and second stages. Punching method.

8. The punching method according to claim 5, wherein at least one of the other stages is positioned upstream and downstream of the stage where the punching load is maximum. Punching method.

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