Punching method and apparatus

Abstract

Provided is a punching method capable of easily improving the roundness of a circular punched section punched out from a plate material. An inside pilot pin 25b is fitted into an inside pilot hole 19b which serves as an opening section formed radially inside of a planned section 27 acting as the outer periphery 9 of a core piece 5 that is a circular punched section in a belt-shaped plate material 3. If the plate material 3 has a lateral bend, the plate material 3 is positioned inside of the planned section 27 in a state in which the lateral bend remains, and the outer periphery 9 of the core piece 5 is punched out from the plate material 3 which has been positioned inside of the planned section 27.

Description

Punching Method and Device 【0001】 The present invention relates to a punching method and device for punching a circular punching part such as a core piece used for the core of a rotating electrical machine. 【0002】 As a conventional punching device, for example, as disclosed in Patent Document 1, there is known a device that punches the inner or outer circumference of a ring-shaped metal plate as a circular punching part while feeding a strip-shaped electromagnetic steel sheet forward. In this punching device, during punching, a pilot pin is inserted into a pilot hole formed in the electromagnetic steel sheet for positioning. 【0003】 The pilot holes are formed at a plurality of positions on both sides in the width direction of the electromagnetic steel sheet, outside the planned part that is expected to be punched as the outer circumference of the metal plate. Due to the influence of lateral bending in which the electromagnetic steel sheet bends in the width direction, there may be a difference in the pitch between adjacent pilot holes in the feed direction between one side and the other side in the width direction. Therefore, the pilot pins are provided corresponding to the pilot holes and are configured to be movable. 【0004】 When lateral bending occurs in the electromagnetic steel sheet, the pilot pins are moved according to the difference in the pitch of the pilot holes caused thereby. Then, the electromagnetic steel sheet is positioned with the lateral bending remaining, and punching is performed in this state to improve the roundness of the metal plate. 【0005】 However, in such a conventional punching device, the structure and control for the movement of the pilot pins become complicated, so it has not been possible to easily improve the roundness of the outer or inner circumference of the metal plate. The same problem commonly occurs when punching a circular punching part from a plate material. 【0006】 Japanese Patent Application Laid-Open No. 2021-74761 【0007】 The problem to be solved is that it has not been possible to easily improve the roundness of the circular punching part punched from the plate material. 【0008】The present invention provides a punching method in which an inner pilot pin is fitted into an opening formed radially inward of a planned circular punched portion on a strip-shaped sheet material, the sheet material is positioned inside the planned portion while the lateral curvature remains if the sheet material has a lateral curvature, and the circular punched portion is punched out from the sheet material that has been positioned inside the planned portion. 【0009】 Furthermore, the present invention provides a punching device comprising: an inner pilot pin that fits into an opening formed radially inward of a planned circular punched portion on a strip-shaped sheet material, and positions the sheet material inside the planned portion while the lateral curvature remains if the sheet material has a lateral curvature; and a punch that punches out the circular punched portion from the sheet material that has been positioned inside the planned portion. 【0010】 This invention makes it possible to easily improve the roundness of a circular punched-out portion made from a sheet material. 【0011】 Figure 1 is a plan view showing a sheet metal in relation to a punching device according to an embodiment of the present invention. Figure 2 is a cross-sectional side view of a part of the punching device of Figure 1. Figure 3 is a cross-sectional side view of a part of the punching device of Figure 2 during punching. Figure 4 is a plan view showing the positioning of the sheet metal by the outer pilot pin and outer pilot hole of the first processing stage of Figure 1. Figure 5 is a plan view showing the positioning of the sheet metal by the inner pilot pin and inner pilot hole of the second processing stage of Figure 1. Figure 6 is a plan view showing the positioning of the sheet metal by the inner pilot pin and inner pilot hole of Figure 5 when the sheet metal has a lateral curvature. Figure 7 is a plan view relating to a comparative example, showing the positioning of the sheet metal by the outer pilot pin and outer pilot hole when the sheet metal has a lateral curvature. Figure 8 is a graph comparing the roundness of the outer circumference of the core pieces of the embodiment and the comparative example. 【0012】In one embodiment of the punching method, an inner pilot pin 25b is fitted into an opening 19 formed radially inward of a planned circular punched-out portion 27 on a strip-shaped sheet material 3. If the sheet material 3 has a lateral curve, the sheet material 3 is positioned inside the planned portion 27 while the lateral curve remains. The circular punched-out portion 9 is then punched out from the sheet material 3 that has been positioned inside the planned portion 27. 【0013】 Alternatively, the punching method may involve forming an outer pilot hole 19a on the radially outer side of the target portion 27 of the strip-shaped plate material 3. In this case, an outer pilot pin 25a is fitted into the outer pilot hole 19a to position the plate material 3 on the outside of the target portion 27. Then, in this positioned state, the opening 19 may be punched out radially inward of the punching portion 9. 【0014】 The punching device 1 comprises an inner pilot punch 21a, an inner pilot pin 25b, and a punch 21b. The inner pilot punch 21a fits into an opening 19 formed radially inward of the planned portion 27 that will become a circular punched portion 9 on a strip-shaped sheet material 3, and positions the sheet material 3 inside the planned portion 27 while retaining the lateral curvature if the sheet material 3 has a lateral curvature. The punch 21b punches out the circular punched portion 9 from the sheet material 3 that has been positioned inside the planned portion 27. 【0015】 The punching device 1 may also include an inner pilot punch 21a, an outer pilot punch 15, and an outer pilot pin 25a. The outer pilot punch 15 forms an outer pilot hole 19a radially outward of the target portion 27 in the strip-shaped sheet material. The outer pilot pin 25a fits into the outer pilot hole 19a to position the sheet material 3 outside the target portion 27. The inner pilot punch 21a may punch an opening 19 radially inward of the target portion 27 of the sheet material 3 that has been positioned outside the target portion 27. 【0016】 In the punching method and apparatus 1, while the sheet material 3 is being fed forward, the outer pilot pin 25a may be fitted into the outer pilot hole 19a upstream in the feeding direction of the sheet material 3, and the inner pilot pin 25b may be fitted into the opening 19 downstream in the feeding direction. 【0017】The opening 19 is preferably positioned to coincide with the lateral curvature neutral axis NA. 【0018】 For positioning the plate material 3, it is preferable to leave the plate material 3 unrestrained in the rotational direction around the opening 19. 【0019】 The punched portion can be of various types, but it may be the outer circumference 9 of a circular core piece 5 used in the core of a rotating electric machine. 【0020】 [Punching device] Figure 1 is a plan view showing a sheet material in relation to a punching device according to an embodiment of the present invention. Figure 2 is a cross-sectional side view of a part of the punching device shown in Figure 1, and Figure 3 is a side view of the same device during punching. 【0021】 As shown in Figures 1 to 3, the punching device 1 punches out multiple core pieces 5, which are metal plates, from a sheet material 3, which is a strip-shaped electromagnetic steel sheet, using a progressive press. The punching device 1 does not need to punch out circular punched-out sections from the sheet material 3, and is not limited to punching out core pieces 5. In this embodiment, the punching to punch out one core piece 5 is performed in a single row on the sheet material 3 using multiple processing stages 13, which will be described later, but the punching to punch out multiple core pieces 5 may be performed in multiple rows. In this case, for example, the inner pilot pins 25b, which will be described later, may be fitted in all or some of the rows. 【0022】 The punched core pieces 5, although not shown, are stacked to form a laminate such as the core of a rotating electric machine. The core may be either a stator core or a rotor core. In this embodiment, each core piece 5 is a core piece of a rotor core and is an annular plate shape with an inner circumference 7 and an outer circumference 9 being punched portions. The core pieces of the rotor core may have openings such as magnet insertion holes, but these are not shown or described. 【0023】 The punching device 1 of this embodiment includes an upper die 8 and a lower die 10, a pilot punching stage 11, and a plurality of processing stages 13. 【0024】The upper die 8 moves up and down relative to the lower die 10, enabling punching of the sheet material 3 at the pilot punching stage 11 and the processing stage 13. The up and down movement of the upper die 8 relative to the lower die 10 can be performed by an appropriate drive mechanism, as is well known. 【0025】 The pilot punching stage 11 includes an outer pilot punch 15 and an outer pilot die 17. These outer pilot punch 15 and outer pilot die 17 form an outer pilot hole 19a on the radially outer side of the planned portion 27 of the sheet metal 3. The planned portion 27 is the part of the sheet metal 3 that is to be punched out as the outer circumference 9 of the core piece 5. 【0026】 The pilot punching stage 11 is located upstream in the feed direction of the sheet metal 3. The outer pilot punch 15 is supported by the upper die 8, and the outer pilot die 17 is supported by the lower die 10. These outer pilot punch 15 and outer pilot die 17 are located on both sides of the sheet metal 3 in the width direction. As a result, the outer pilot holes 19a are formed on both sides of the sheet metal 3 in the width direction. The width direction of the sheet metal 3 refers to the direction along the width of the sheet metal 3 that is perpendicular to the feed direction. The feed direction is the left-right direction in Figures 1 to 3. 【0027】 The multiple processing stages 13 consist of a first processing stage 13a and a second processing stage 13b, which punch out the inner circumference 7 and outer circumference 9 of the core piece 5, respectively. Each processing stage 13 is equipped with a punch 21, a die 23, and a pilot pin 25. 【0028】 The punch 21 is supported by the upper die 8, and the die 23 is supported by the lower die 10. In each processing stage 13, the punch 21 descends relative to the die 23 to punch out the core piece 5. 【0029】In the first processing stage 13a, the inner circumference 7 of the core piece 5 is punched out by the first punch 21a, which is an inner pilot punch. The first punch 21a has a circular outer circumference whose roundness is adjusted together with the inner circumference of the first die 23a, and this outer circumference punches out the inner circumference 7 of the core piece 5. The punched-out inner circumference 7 defines the inner pilot hole 19b, which is the opening in this embodiment. Note that the opening is not limited to the dedicated inner pilot hole 19b, but can be any opening formed in a product such as the core piece 5 that can be reused as an inner pilot hole. 【0030】 The second processing stage 13b is positioned adjacent to the first processing stage 13a, downstream in the feeding direction of the sheet metal 3. In Figures 2 and 3, the first processing stage 13a and the second processing stage 13b are shown separated in the feeding direction for convenience, because the cross-section of the sheet metal 3 is different for the first processing stage 13a and the second processing stage 13b. Alternatively, the first processing stage 13a and the second processing stage 13b may be separated, as shown in Figures 2 and 3, and an idle stage may be placed between the two processing stages 13a and 13b. The idle stage is a waiting stage where punching of the sheet metal 3 is not being performed. 【0031】 In this second processing stage 13b, the second punch 21b punches out the outer circumference 9 of the core piece 5, which is the circular punched portion in this embodiment. The second punch 21b has a circular outer circumference whose roundness is adjusted together with the inner circumference of the second die 23b, and this outer circumference punches out the outer circumference 9 of the core piece 5. 【0032】 In this second processing stage 13b, core pieces 5 are punched out from the sheet material 3, and the punched core pieces 5 are held in the second die 23b. Subsequent punched core pieces 5 are then stacked on top of these held core pieces 5. 【0033】 In each processing stage 13, the sheet metal 3 is positioned by fitting a pilot pin 25 into a pilot hole 19 during punching. In this embodiment, while the sheet metal 3 is fed forward, the outer pilot pin 25a is fitted into the outer pilot hole 19a upstream in the feeding direction of the sheet metal 3, and the inner pilot pin 25b is fitted into the inner pilot hole 19b downstream in the feeding direction. 【0034】 Figure 4 is a plan view showing the positioning of the plate material 3 by the outer pilot pin 25a and outer pilot hole 19a of the first processing stage 13a. 【0035】 In the first processing stage 13a, the outer pilot pin 25a is fitted into the outer pilot hole 19a of the plate material 3. The outer pilot holes 19a are located in four places on both sides in the feed direction and on both sides in the width direction relative to the target portion 27. 【0036】 The outer pilot pins 25a are supported at four locations on the upper die 8, corresponding to the outer pilot holes 19a. Each outer pilot pin 25a is a rod-shaped body with a circular cross-section. The tip of each outer pilot pin 25a protrudes toward the sheet metal 3 in the punching direction, more than the tip of the first punch 21a. 【0037】 The outer pilot pin 25a engages with the outer pilot hole 19a as the upper die 8 descends, prior to punching by the first punch 21a. Therefore, the outer pilot pin 25a enables the inner pilot hole 19b to be punched radially inward of the planned portion 27 while the plate material 3 is positioned outside the planned portion 27. 【0038】 Furthermore, if the plate material 3 has a lateral curve as shown by the dashed line in Figure 4, the position of the outer pilot hole 19a will be shifted relative to the position of the outer pilot pin 25a. Lateral curve of the plate material 3 means that, in a plan view, the plate material 3 curves in the feeding direction with one side in the width direction being inward and the other side being outward. The shift between the position of the outer pilot hole 19a and the position of the outer pilot pin 25a is such that the outer pilot hole 19a and the outer pilot pin 25a can be fitted together. 【0039】Therefore, by fitting the outer pilot pin 25a into the outer pilot hole 19a, the deviation is corrected along with the lateral bending of the plate material 3. In this case, since the downstream outer pilot hole 19a is shared with the second processing stage 13b, it is preferable not to use it by not fitting the outer pilot pin 25a. Further, when there is another stage between the first processing stage 13a and the second processing stage 13b, it is preferable not to use the outer pilot hole 19a on the downstream side of the stage closest to the second processing stage 13b. 【0040】 In addition, FIGS. 2 and 3 show the case where the downstream outer pilot hole 19a is used. The number of the outer pilot holes 19a and the outer pilot pins 25a to be used can be arbitrarily set. 【0041】 FIG. 5 is a plan view showing the positioning of the plate material 3 by the inner pilot pin 25b and the inner pilot hole 19b in the second processing stage 13b. 【0042】 In the second processing stage 13b, as shown in FIG. 5, the inner pilot pin 25b fits into the inner pilot hole 19b. The inner pilot hole 19b of the present embodiment consists of the center hole of the core piece 5. The inner pilot pin 25b consists of a single rod-shaped body with a circular cross-section that fits into the inner pilot hole 19b. 【0043】 However, the inner pilot pin 25b may be constituted by a plurality of rod-shaped bodies. In this case, the plurality of inner pilot pins 25b are arranged so as to contact a plurality of locations on the inner circumference of the inner pilot hole 19b and fit into the inner pilot hole 19b as a whole. 【0044】 The inner pilot pin 25b is supported at the center of the second punch 21b corresponding to the inner pilot hole 19b. The tip of the inner pilot pin 25b in the punching direction protrudes toward the plate material 3 side with respect to the tip of the second punch 21b in the punching direction. 【0045】This inner pilot pin 25b fits into the inner pilot hole 19b prior to the second punch 21b as the upper die 8 descends. Therefore, the inner pilot pin 25b enables the punching of the outer periphery 9 of the core piece 5 with the plate material 3 positioned inside the planned part 27. 【0046】 This inner pilot pin 25b does not restrain the plate material 3 in the rotational direction centered on the inner pilot hole 19b. That is, the inner pilot pin 25b and the inner pilot hole 19b are relatively rotatable in a state of being fitted to each other. Non-restraint means that the restraining force in the rotational direction is weak compared to the case of completely restraining (restraining so as not to move) the plate material 3 in the rotational direction. Therefore, non-restraint includes not only the case where the plate material 3 is not completely restrained in the rotational direction but also the case where the plate material 3 is slightly restrained in the rotational direction. Note that the non-restrained rotational direction is at least the positive direction of the rotational direction in which the plate material 3 tends to rotate around the planned part 27 due to lateral bending or the like. Therefore, non-restraint may be performed at least in the positive direction of the rotational direction, and may be performed in both the positive and negative directions of the rotational direction. 【0047】 In the inner pilot hole 19b of the present embodiment, keys 29 facing each other in the feeding direction project from the circular inner periphery 7. For this reason, the inner pilot pin 25b has recesses 31 on its circular outer peripheral surface to avoid these keys 29. The recesses 31 have a gap with respect to the keys 29 in the circumferential direction, and allow relative rotation of the inner pilot pin 25b and the inner pilot hole 19b within the range of the gap. 【0048】 Considering the magnitude of the lateral bending of the plate material 3, it is sufficient to allow relative rotation of the inner pilot pin 25b and the inner pilot hole 19b within the range of the gap as in the present embodiment. When the inner pilot hole 19b does not have the keys 29, relative rotation of the inner pilot pin 25b and the inner pilot hole 19b may be allowed by making the inner pilot pin 25b a simple circle. 【0049】 FIG. 6 is an enlarged plan view showing the positioning of the plate material 3 by the inner pilot pin 25b and the inner pilot hole 19b when the plate material 3 has lateral bending. 【0050】In the second processing stage 13b, if the plate material 3 has a lateral curvature, the plate material 3 is positioned by fitting the inner pilot pin 25b and the inner pilot hole 19b inside the planned portion 27 while the lateral curvature remains. This suppresses the stress generated in the plate material 3 in the positioned state. 【0051】 In this case, the inner pilot hole 19b is positioned differently from the state in which the plate material 3 is not curved laterally, and as a result, a portion of the lateral curvature of the plate material 3 is corrected by the amount of this displacement. Furthermore, since the inner pilot hole 19b in this embodiment is positioned to coincide with the neutral axis NA of the lateral curvature, the positional displacement due to the lateral curvature is small. The neutral axis NA refers to the portion of the plate material 3 in which no stress is generated due to the lateral curvature. 【0052】 [Punching Method] In the punching method of this embodiment, as shown in Figures 1 to 3, when punching out core pieces 5 from the sheet material 3 while sequentially feeding the sheet material 3 using the punching device 1, the roundness of the outer circumference 9 of the core piece 5 is improved. The roundness of the outer circumference of the core piece 5 means 1 / 2 of the difference between the maximum outer diameter and the minimum outer diameter. Similarly, the roundness of the inner circumference of the core piece 5 means 1 / 2 of the difference between the maximum inner diameter and the minimum inner diameter. 【0053】 In punching out the core piece 5, the sheet metal 3 is repeatedly fed and stopped in a progressive manner using an appropriate feeding device such as a roller, and when the feeding of the sheet metal 3 stops, the upper die 8 descends relative to the lower die 10. As a result, the outer pilot hole 19a of the sheet metal 3 is punched out at the pilot punching stage 11, and the inner circumference 7 and outer circumference 9 of the core piece 5 are punched out at the processing stage 13. 【0054】 In the pilot punching stage 11, as shown in Figure 3, the outer pilot punch 15 descends together with the upper die 8 to punch an outer pilot hole 19a into the sheet metal 3. The outer pilot hole 19a is formed radially outward from the planned portion 27. 【0055】In the first processing stage 13a, the outer pilot pin 25a and the first punch 21a descend together with the upper die 8. At this time, the outer pilot pin 25a is inserted into and fitted into the outer pilot hole 19a prior to punching by the first punch 21a (see Figure 4). As a result, the positioning of the plate material 3 is performed outside the planned section 27. 【0056】 If the plate material 3 is curved laterally, the plate material 3 is positioned while the curve is corrected (the plate material 3 is corrected to be aligned with the feeding direction). In this case, as described above, it is preferable to leave the outer pilot hole 19a downstream of the first processing stage 13a unused by not fitting the outer pilot pin 25a into it. 【0057】 In this positioning state, the descending first punch 21a punches out the inner circumference 7 of the core piece 5, and the punched-out inner circumference 7 demarcates the inner pilot hole 19b. 【0058】 If the plate material 3 has a lateral curvature, the inner circumference 7 is punched out while stress is present in the plate material 3. Therefore, when the positioning of the plate material 3 is released, the inner circumference 7, which is released from stress, may deform. However, this deformation has little effect on the roundness of the inner circumference 7 because the diameter of the inner circumference 7 is relatively small. 【0059】 However, it is also possible to drill a pilot hole with a smaller diameter than the inner circumference 7 radially inward, fit a pilot pin into it, and then punch out the inner circumference 7. 【0060】 In the second processing stage 13b, the inner pilot pin 25b and the second punch 21b descend together with the upper die 8. At this time, the inner pilot pin 25b is inserted into and fitted into the inner pilot hole 19b prior to punching by the second punch 21b (Figures 5 and 6). This positions the plate material 3 inside the planned section 27. 【0061】If the plate material 3 has a lateral curvature, the plate material 3 is positioned inside the planned section 27 with the lateral curvature of the plate material 3 remaining. In this embodiment, the lateral curvature is slightly corrected by the amount of the displacement of the inner pilot hole 19b compared to the state in which the plate material 3 is not curved, and stress is generated in the plate material 3. However, this stress is significantly reduced compared to the case in which the lateral curvature of the plate material 3 is completely corrected using the outer pilot pin 25a. 【0062】 Furthermore, since the inner pilot hole 19b in this embodiment is positioned to coincide with the neutral axis NA of the lateral curvature, the positional displacement due to lateral curvature is small. Therefore, the stress generated in the plate material 3 can be reduced. 【0063】 Furthermore, in this embodiment, the inner pilot hole 19b and the inner pilot pin 25b are fitted together so as to be rotatable relative to each other, and the plate material 3 is not constrained in the rotational direction around the inner pilot hole 19b. As a result, stress on the plate material 3 in the rotational direction is not generated or is suppressed, and the stress generated on the plate material 3 can be reduced even further. 【0064】 Furthermore, since the plate material 3 is straightened in the feeding direction during the first processing stage 13a, the lateral curvature of the plate material 3 occurs after the first processing stage 13a. Therefore, the lateral curvature of the plate material 3 in the second processing stage 13b is smaller compared to the cumulative lateral curvature of the plate material 3 during the first processing stage 13a and the second processing stage 13b. As a result, the stress generated in the plate material 3 due to its positioning in the second processing stage 13b can be reduced. 【0065】 In this positioning state, the descending second punch 21b punches out the outer circumference 9 of the core piece 5 at the target portion 27 of the plate material 3. This improves the roundness of the outer circumference 9 of the core piece 5. If the plate material 3 has a lateral curvature, the stress generated in the plate material 3 during positioning is reduced as described above, so deformation of the outer circumference 9 of the core piece 5, which is released from stress by punching, can be suppressed. This suppression of deformation improves the roundness of the outer circumference 9 of the core piece 5. 【0066】Figure 7 is a plan view showing the positioning of the sheet metal 3 by the outer pilot pin 25a and outer pilot hole 19a when the sheet metal 3 has a lateral curvature, relating to a comparative example. In Figure 7, the core piece 5 is shown before punching, but for convenience, the core piece 5 after punching is shown by a dashed line. 【0067】 In the comparative example, in the second processing stage 13b, the outer pilot pin 25a is fitted into the outer pilot hole 19a to straighten the plate material 3, which has a lateral curvature, so that it is aligned with the feed direction. When the outer circumference 9 of the core piece 5 is punched out in this straightened position, the outer circumference 9 of the core piece 5, which is released from stress by punching out, deforms significantly, as shown by the dashed line in Figure 7, for example. As a result, the roundness of the outer circumference 9 of the core piece 5 deteriorates. 【0068】 Figure 8 is a graph comparing the roundness of the outer circumference 9 of the core pieces 5 in the example and the comparative example. 【0069】 As shown in Figure 8, the circularity of the outer circumference 9 of the core piece 5 is improved in the embodiment. The vertical axis in Figure 8 represents circularity. 【0070】 As described above, in this embodiment, the punching method and punching apparatus 1 insert an inner pilot pin 25b into an inner pilot hole 19b, which is an opening formed radially inward of the planned portion 27 that will become the outer circumference 9 of the circular punched core piece 5, on a strip-shaped sheet material. If the sheet material 3 has a lateral curve, the sheet material 3 is positioned inside the planned portion 27 while the lateral curve remains. Then, the outer circumference 9 of the core piece 5 is punched out from the sheet material 3 that has been positioned inside the planned portion 27. 【0071】 Therefore, when the plate material 3 has a lateral curvature, the outer circumference 9 of the core piece 5 can be punched out while eliminating or suppressing the stress on the plate material 3, and deformation of the outer circumference 9 of the core piece 5 after punching can be suppressed. For this reason, in this embodiment, the roundness of the outer circumference 9 of the core piece 5 punched out from the plate material 3 can be easily improved. 【0072】 Since the inner pilot hole 19b is positioned to coincide with the laterally curved neutral axis NA, deformation of the outer circumference 9 of the core piece 5 after punching is more reliably suppressed. Therefore, the roundness of the outer circumference 9 of the core piece 5 punched out from the plate material 3 can be improved more reliably. 【0073】 The positioning of the plate material 3 by the inner pilot pin 25b is performed while the plate material 3 is unrestrained in a rotational direction around the inner pilot hole 19b. Therefore, deformation of the outer circumference 9 of the core piece 5 after punching is suppressed more reliably, and the roundness of the outer circumference 9 of the core piece 5 punched out from the plate material 3 can be improved more reliably. 【0074】 Furthermore, in the punching method and punching apparatus 1 of this embodiment, an outer pilot hole 19a is formed on the radially outer side of the target portion 27 of the plate material 3. An outer pilot pin 25a is fitted into the formed outer pilot hole 19a to position the plate material 3 on the outside of the target portion 27. Then, an inner pilot hole 19b (inner circumference 7 of the core piece 5) is punched out from the plate material 3 that has been positioned on the outside of the target portion 27 on the radially inner side of the target portion 27. 【0075】 Therefore, the inner pilot hole 19b, which has a relatively small diameter and is easier to ensure roundness by positioning with the outer pilot hole 19a and outer pilot pin 25a, is formed with priority given to positioning accuracy. The outer circumference 9 of the core piece 5, which requires even greater roundness, is punched out by positioning with this inner pilot hole 19b and inner pilot pin 25b. 【0076】 Therefore, in this embodiment, the roundness of the outer circumference 9 of the core piece 5 punched out from the plate material 3 can be improved more easily and reliably. 【0077】 Furthermore, in the punching method and punching apparatus 1 of this embodiment, while the sheet material 3 is fed forward, the outer pilot pin 25a is fitted into the outer pilot hole 19a upstream in the feeding direction of the sheet material 3, and the inner pilot pin 25b is fitted into the inner pilot hole 19b downstream in the feeding direction. 【0078】 Therefore, the lateral bending of the plate material 3 when fitting the inner pilot pin 25b into the inner pilot hole 19b can be reduced. As a result, the roundness of the outer circumference 9 of the core piece 5 punched out from the plate material 3 can be improved more easily and reliably. 【0079】 The punched-out portion is the outer circumference 9 of the circular core piece 5. Therefore, the inner pilot hole 19b can be formed using the central hole of the core piece 5. 【0080】 1 Punching device 3 Sheet material 5 Core piece 9 Outer circumference (punching area) 15 Outer pilot punch 19a Outer pilot hole 19b Inner pilot hole (opening) 21a First punch (inner pilot punch) 21b Second punch 25a Outer pilot pin 25b Inner pilot pin 27 Planned area

Claims

1. A punching method comprising: fitting an inner pilot pin into an opening formed radially inward of a planned circular punched-out portion on a strip-shaped sheet material; positioning the sheet material inside the planned portion while the lateral curvature remains if the sheet material has a lateral curvature; and punching out the circular punched-out portion from the sheet material that has been positioned inside the planned portion.

2. A punching method according to claim 1, wherein the opening is positioned to coincide with the neutral axis of the lateral curve.

3. A punching method according to claim 1 or 2, wherein the positioning of the plate material is performed in a rotational direction centered on the opening while leaving the plate material unrestrained.

4. A punching method according to claim 1 or 2, comprising: forming an outer pilot hole radially outward of the planned portion on the plate material; fitting an outer pilot pin into the outer pilot hole to position the plate material outside the planned portion; and punching out the opening radially inward of the planned portion on the plate material that has been positioned outside the planned portion.

5. A punching method according to claim 4, wherein the plate material is fed sequentially, the outer pilot pin is fitted into the outer pilot hole upstream in the feeding direction of the plate material, and the inner pilot pin is fitted into the opening downstream in the feeding direction.

6. A punching method according to claim 1 or 2, wherein the punching portion is the outer circumference of a circular core piece.

7. A punching device comprising: an inner pilot pin that fits into an opening formed radially inward of a planned circular punched portion on a strip-shaped sheet material, and positions the sheet material inside the planned portion while the lateral curvature remains if the sheet material has a lateral curvature; and a punch that punches out the circular punched portion from the sheet material that has been positioned inside the planned portion.

8. A punching device according to claim 7, wherein the opening is positioned to coincide with the neutral axis of the lateral curve.

9. A punching device according to claim 7 or 8, wherein the positioning of the plate material is such that the plate material is unrestrained in the rotational direction around the opening.

10. A punching device according to claim 7 or 8, comprising: an inner pilot punch that punches out the opening radially inward of the planned portion while the plate material is positioned outside the planned portion; an outer pilot punch that forms an outer pilot hole radially outward of the planned portion relative to the plate material; and an outer pilot pin that fits into the outer pilot hole to position the plate material outside the planned portion.

11. A punching method according to claim 10, comprising a punching device comprising: feeding the plate material sequentially while fitting the outer pilot pin into the outer pilot hole upstream in the feeding direction of the plate material, and fitting the inner pilot pin into the opening downstream in the feeding direction.

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