Punching method and device

Abstract

Provided is a punching method with which it is possible to easily improve the roundness of a circular punched part punched out of a plate material. Second pilot holes 19b for an intended part 27 intended to serve as the outer circumference 9 of a circular core piece 5 are formed, in a belt-like plate material 3, on the radially outer side of the intended part 27, the plate material 3 is positioned by engaging first pilot pins 25a with the second pilot holes 19b so as not to restrain the plate material 3 in a direction of rotation about the intended part 27, and the outer circumference 9 of the core piece 5 is punched out in the state in which the plate material 3 is positioned.

Description

Punching Method and Device 【0001】 The present invention relates to a punching method and device for punching circular punched parts such as core pieces used in the cores of rotating electrical machines. 【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 punched part while feeding a strip-shaped electromagnetic steel plate forward. In this punching device, during punching, a pilot pin is inserted into a pilot hole formed in the electromagnetic steel plate to position the electromagnetic steel plate. 【0003】 The pilot holes are formed at multiple locations on both sides in the width direction of the electromagnetic steel plate 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 where the electromagnetic steel plate bends in the width direction, there may be a difference in the pitch between adjacent pilot holes in the feeding direction between one side and the other side in the width direction. For this reason, 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 plate, the pilot pins are moved according to the difference in the pitch of the pilot holes caused thereby. Then, the electromagnetic steel plate 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 punched part from a plate material. 【0006】 Japanese Unexamined Patent Application Publication No. 2021 - 74761 【0007】 The problem to be solved is that it has not been possible to easily improve the roundness of the circular punched part punched from the plate material. 【0008】The present invention provides a punching method comprising forming an unrestrained pilot hole in a strip-shaped sheet material on the radially outer side of a portion to be punched out in a circular area, engaging an unrestrained pilot pin with the unrestrained pilot hole to position the sheet material so that it is unrestrained in a rotational direction around the portion to be punched out in a circular area, and then punching out the circular area while the sheet material is positioned. 【0009】 Furthermore, the present invention provides a punching device comprising: an unrestrained pilot punch that forms an unrestrained pilot hole in a strip-shaped sheet material on the radially outer side of a portion to be formed into a circular punched-out section; an unrestrained pilot pin that engages with the unrestrained pilot hole to position the sheet material, thereby unrestraining the sheet material in a rotational direction centered on the portion to be formed into a circular punched-out section; and a punch that punches out the circular punched-out section while the sheet material is positioned. 【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 Embodiment 1 of the present invention. Figure 2 is a plan view showing a part of the sheet metal in Figure 1. Figure 3 is a cross-sectional side view showing a part of the punching device in Figure 1. Figure 4 is a cross-sectional side view showing a part of the punching device in Figure 3 during punching. Figure 5 is a plan view showing the positioning of the sheet metal by the first pilot pin and the first pilot hole in the first processing stage of Figure 1. Figure 6 is a plan view showing the positioning of the sheet metal by the second pilot pin and the second pilot hole in the second processing stage of Figure 1. Figure 7 is a plan view showing the positioning of the sheet metal by the first pilot pin and the first pilot hole when the sheet metal has a lateral curvature, relating to a comparative example. Figure 8 is a graph comparing the roundness of the outer circumference of the core pieces of Embodiment 1 and the comparative example. Figure 9 is a plan view showing the positioning of the sheet metal by the second pilot pin and the second pilot hole in the second processing stage according to a modified example of Embodiment 1 of the present invention. Figure 10 is a plan view showing the positioning of a plate material by a second pilot pin and a pilot hole in a second processing stage according to Embodiment 2 of the present invention. 【0012】In one embodiment of the punching method, an unrestrained pilot hole 19b is formed in a strip-shaped sheet material 3 on the radially outer side of the planned portion 27 that will become a circular punched portion 9. An unrestrained pilot pin 25b is engaged with the formed unrestrained pilot hole 19b in a rotational direction around the planned portion 27 to position the sheet material 3. With the sheet material 3 in this positioned state, the circular punched portion 9 is punched out. 【0013】 Multiple unrestrained pilot holes 19b are provided at multiple locations on the radially outer side of the planned portion 27, and the unrestrained pilot pin 25b may be smaller in the rotational direction than the unrestrained pilot holes 19b. 【0014】 In this case, the unrestrained pilot hole 19b may be an elongated hole aligned with the direction of rotation. 【0015】 Alternatively, the punching method may involve forming a restraining pilot hole 19a in the plate material 3 to restrain the plate material 3 in the rotational direction. In this case, the plate material 3 is positioned by fitting a restraining pilot pin 25a into the restraining pilot hole 19a. Then, with the plate material 3 in a restrained position, the inner circumference 7 is punched out radially inward of the planned portion 27. 【0016】 The punching device 1 may include an unrestrained pilot punch 15, an unrestrained pilot pin 25b, and a punch 21b. The unrestrained pilot punch 15 forms an unrestrained pilot hole 19b in the strip-shaped sheet material 3 on the radially outer side of the planned portion 27 which will become a circular punched portion 9. The unrestrained pilot pin 25b engages with the unrestrained pilot hole 19b to position the sheet material 3, leaving it unrestrained in the rotational direction around the planned portion 27. The punch 21b punches out the circular punched portion 9 while the sheet material 3 is positioned. 【0017】 The unrestrained pilot punch 15 may have multiple unrestrained pilot holes 19b formed at radially outer locations of the planned portion 27. 【0018】The punching device 1 may also include a restraining pilot punch 18, a restraining pilot pin 25a, and an inner circumference punch 21a. The restraining pilot punch 18 forms a restraining pilot hole 19a in the sheet metal 3 for restraining the sheet metal 3 in the rotational direction. The restraining pilot pin 25a fits into the restraining pilot hole 19a to position the sheet metal 3. The inner circumference punch 21a punches out the inner circumference 7 radially inward of the target portion 27 while the sheet metal 3 is in a restrained position. 【0019】 Alternatively, the punching method and apparatus 1 may sequentially feed the sheet material 3 while engaging the restraining pilot pin 25a with the restraining pilot hole 19a upstream in the feeding direction of the sheet material 3, and engaging the unrestrained pilot pin 25b with the unrestrained pilot hole 19b downstream in the feeding direction. 【0020】 Alternatively, the punched portion 9 may be the outer circumference of a circular core piece 5 used in the core of a rotating electric machine. 【0021】 [Punching device] Figure 1 is a plan view showing a sheet material in relation to the punching device according to Embodiment 1 of the present invention. Figure 2 is a plan view showing a part of the sheet material in Figure 1. Figure 3 is a cross-sectional side view of a part of the punching device in Figure 1, and Figure 4 is a side view of the same device during punching. 【0022】 As shown in Figures 1 to 4, 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 be limited to punching out circular punching sections, 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 configuration of Embodiment 1 may be applied to each row, or second pilot holes 19b, which are unconstrained pilot holes similar to those in Embodiment 1, may be provided at both ends in the width direction of the sheet material 3, as described later. 【0023】The punched core pieces 5, though 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 its inner circumference 7 and outer circumference 9 are annular plate shapes that form the inner circumference and punched portion of this embodiment, respectively. In the case of a stator core piece, the inner circumference has a shape that includes multiple toothed portions. 【0024】 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. In Figures 3 and 4, the pilot punching stage 11 and the second processing stage 13b show different cross-sections of the sheet material 3, and the first processing stage 13a and the second processing stage 13b show different cross-sections of the sheet material 3. 【0025】 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. 【0026】 The pilot punching stage 11 is located upstream in the feeding direction of the sheet material 3 and includes a first pilot punch 18 and a first pilot die 20, as well as a second pilot punch 15 and a second pilot die 17. In Figure 3, the second pilot punch 15 and the second pilot die 17 are shown, while the first pilot punch 18 and the first pilot die 20, which are located in a different cross-section from the second pilot punch 15 and the second pilot die 17, are indicated by their reference numerals in parentheses only. 【0027】 The first pilot punch 18 and the first pilot die 20 are the constrained pilot punch and constrained pilot die of this embodiment. The first pilot punch 18 is supported by the upper die 8, and the first pilot die 20 is supported by the lower die 10. 【0028】These first pilot punches 18 and first pilot dies 20 are located on both sides of the width direction of the sheet material 3, and form first pilot holes 19a, which are restraining pilot holes, on both sides of the width direction of the sheet material 3. The width direction refers to the direction along the width of the sheet material 3, perpendicular to the feed direction of the sheet material 3. The feed direction is the left-right direction in Figures 1 to 4. 【0029】 The first pilot holes 19a are formed in the plate material 3 through the feeding of the plate material 3 in relation to the planned portion 27 that is to be punched out as the outer circumference 9 of the core piece 5. In this embodiment, the first pilot holes 19a are formed at four locations on the radially outer side of the planned portion 27, on both sides in the feeding direction and on both sides in the width direction of the planned portion 27. In a plan view, each first pilot hole 19a is positioned to face the V-shaped valley portion (opening) of the second pilot hole 19b, which will be described later, in the width direction. 【0030】 Each first pilot hole 19a is for positioning the plate material 3 while constraining it in the rotational direction. Each first pilot hole 19a has a circular planar shape. However, the shape of the first pilot hole 19a is not limited to a circle, as long as the first pilot pin 25a can be fitted into it to restrain the plate material 3 in the rotational direction. 【0031】 The second pilot punch 15 and the second pilot die 17 are the unrestrained pilot punch and unrestrained pilot die of this embodiment. The second pilot punch 15 is supported by the upper die 8, and the second pilot die 17 is supported by the lower die 10. 【0032】 These second pilot punches 15 and second pilot dies 17 are located on both sides in the width direction of the sheet material 3, and form unrestrained pilot holes, which are second pilot holes 19b, on both sides in the width direction of the sheet material 3. 【0033】 The second pilot hole 19b is formed radially outward from the planned portion 27 that is to be punched out as the outer circumference 9 of the core piece 5 in the plate material 3 as the plate material 3 is fed. In this embodiment, it is formed at four locations radially outward from the planned portion 27, on both sides in the feed direction and on both sides in the width direction. 【0034】These second pilot holes 19b are for positioning the plate material 3 while keeping it unrestrained in the rotational direction around the planned portion 27 of the plate material 3. Each second pilot hole 19b is an elongated hole that is long in the rotational direction. The rotational direction coincides with the circumferential direction around the planned portion 27, but it may also be a straight line approximating the arc of the planned portion 27. The rotational direction is one in which stress due to lateral bending, etc., is reduced by keeping the plate material 3 unrestrained. Furthermore, the rotational direction is at least the positive direction of rotation in which the plate material 3 attempts to rotate around the planned portion 27. Therefore, unrestraint is performed at least in the positive direction of rotation, and may be performed in both the positive and negative directions of rotation. 【0035】 In this embodiment, the second pilot hole 19b is formed in a linear shape inclined with respect to the feed direction and width direction along the rotation direction. This linear second pilot hole 19b consists of a second pilot hole 19b1 that functions on one side of the target portion 27 and a second pilot hole 19b2 that functions on the other side of the target portion 27, which are arranged adjacent to each other in the feed direction (Figure 2). In a plan view, the adjacent second pilot holes 19b1 and 19b2 have opposite inclinations and form a V-shape connected to each other. 【0036】 The multiple processing stages 13 consist of a first processing stage 13a and a second processing stage 13b, which remove 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. 【0037】 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. 【0038】 In the first processing stage 13a, the first punch 21a punches out the inner circumference 7 of the core piece 5. 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. 【0039】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 3 and 4, 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, as shown in Figures 3 and 4, the first processing stage 13a and the second processing stage 13b may be separated 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. 【0040】 In the second processing stage 13b, the second punch 21b punches out the outer circumference 9 of the core piece 5, which is a circular punched-out section. 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. 【0041】 In the 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. 【0042】 In each processing stage 13, the sheet metal 3 is positioned using the pilot hole 19 and the pilot pin 25 during punching. In this embodiment, as the sheet metal 3 is fed forward, the first pilot pin 25a is fitted into the first pilot hole 19a upstream in the feeding direction of the sheet metal 3, and the second pilot pin 25b is engaged with the second pilot hole 19b downstream in the feeding direction. 【0043】 Figure 5 is a plan view showing the positioning of the plate material 3 by the first pilot pin 25a and the first pilot hole 19a of the first processing stage 13a. 【0044】 In the first processing stage 13a, the first pilot pin 25a is fitted into the first pilot hole 19a of the plate material 3. As described above, the first 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 planned section 27, and the first pilot pin 25a is supported in four places on the upper die 8 corresponding to these first pilot holes 19a. 【0045】 Each first pilot pin 25a is a rod-shaped body with a circular cross-section. The tip of the first pilot pin 25a protrudes toward the plate material 3 side in the punching direction from the tip of the first punch 21a. Therefore, the first pilot pin 25a fits into the first pilot hole 19a prior to punching by the first punch 21a due to the downward movement of the upper die 8. 【0046】 By fitting the first pilot pin 25a and the first pilot hole 19a, the plate material 3 is constrained in the feeding direction, width direction, and rotational direction. As a result, the first pilot pin 25a can punch the inner circumference 7 inside the radial direction of the planned portion 27 in the positioned state of the plate material 3. 【0047】 In the case where the plate material 3 has a lateral bend as shown by the two-dot chain line in Fig. 5, the position of the first pilot hole 19a will be displaced with respect to the position of the first pilot pin 25a. The lateral bend of the plate material 3 means that in a plan view, the plate material 3 curves with respect to the feeding direction with one side in the width direction as the inner side and the other side as the outer side. The displacement between the position of the first pilot hole 19a and the position of the first pilot pin 25a is such that the first pilot hole 19a and the first pilot pin 25a can fit with each other. 【0048】 Therefore, when the first pilot pin 25a fits into the first pilot hole 19a, the displacement along with the lateral bend of the plate material 3 is corrected. In this case, since the downstream first pilot hole 19a is located on the side of the second processing stage 13b, it is preferable to make it unused without fitting the first pilot pin 25a. Also, when there is another stage between the first processing stage 13a and the second processing stage 13b, it is preferable to make the downstream first pilot hole 19a of the stage closest to the second processing stage 13b unused. In Figs. 3 and 4, the case where the downstream first pilot hole 19a is used is shown. The number of the first pilot holes 19a and the first pilot pins 25a to be used can be arbitrarily set. 【0049】 Fig. 6 is a plan view showing the positioning of the plate material 3 by the second pilot pin 25b and the second pilot hole 19b in the second processing stage 13b. 【0050】In the second processing stage 13b, as shown in Figure 6, the second pilot pins 25b engage with the second pilot holes 19b. The second pilot holes 19b are located in four places on both sides in the feed direction and on both sides in the width direction relative to the planned section 27, as described above, and the second pilot pins 25b are supported in four places on the upper die 8 corresponding to these second pilot holes 19b. 【0051】 Each second pilot pin 25b is formed to be smaller in the rotational direction than the second pilot hole 19b. In this embodiment, it is made of a rod-shaped body with a circular cross-section. The tip of the second pilot pin 25b in the punching direction protrudes toward the plate material 3 side relative to the tip of the second punch 21b in the punching direction. Therefore, the second pilot pin 25b is inserted into and engages with the second pilot hole 19b ahead of the second punch 21b as the upper die 8 descends. 【0052】 When the second pilot pin 25b is inserted into the second pilot hole 19b, it engages with the inclined surface 26 of the second pilot hole 19b (see Figure 2), thereby constraining the plate material 3 in the feed direction and width direction. In this engaged state, the second pilot pin 25b is not constrained along the second pilot hole 19b, thus leaving the plate material 3 unconstrained in the rotational direction. As a result, the second pilot pin 25b is positioned in an unconstrained rotational direction around the target portion 27 of the plate material 3, enabling punching of the outer circumference 9 of the core piece 5, which is a circular punching portion. 【0053】 The unrestrained rotation of the plate material 3 means that the restraining force is weaker compared to the case where the plate material 3 is completely restrained in the rotational direction (restrained so that it does not move in the rotational direction). This includes not only cases where the plate material 3 is not completely restrained in the rotational direction, but also cases where the plate material 3 is slightly restrained in the rotational direction. The rotational direction of the unrestrained rotation is at least the positive direction of rotation in which the plate material 3 attempts to rotate around the planned part 27 due to lateral bending, etc. Therefore, the unrestrained rotation only needs to be performed at least in the positive direction of rotation as described above, and may be performed in both the positive and negative directions of rotation. 【0054】Furthermore, if the plate material 3 has a lateral curve as shown by the dashed line in Figure 6, the position of the second pilot hole 19b will be shifted relative to the position of the second pilot pin 25b. The shift between the positions of the second pilot hole 19b and the second pilot pin 25b is such that the second pilot hole 19b and the second pilot pin 25b can engage (insert) with each other. In this embodiment, since the second pilot hole 19b is an elongated hole, it is possible to easily accommodate the shift in the positions of the second pilot hole 19b and the second pilot pin 25b. 【0055】 The second pilot pin 25b engages with the second pilot hole 19b, correcting the lateral curvature of the plate material 3. The stress generated in the plate material 3 by this correction is due to the constraints on the feed direction and width direction of the plate material 3, since the plate material 3 is not constrained in the rotational direction. 【0056】 [Punching Method] In the punching method of this embodiment, as shown in Figures 1, 3, and 4, 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 9 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 7 of the core piece 5 means 1 / 2 of the difference between the maximum inner diameter and the minimum inner diameter. Since a smaller roundness is better, improving the roundness means reducing the roundness. 【0057】 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 first and second pilot holes 19b and 19b are punched out in the pilot punching stage 11, and the inner circumference 7 and outer circumference 9 of the core piece 5 are punched out in the processing stage 13. 【0058】 In the pilot punching stage 11, as shown in Figure 4, the first pilot punch 18 and the second pilot punch 15 descend together with the upper die 8 to punch out the first pilot hole 19a and the second pilot hole 19b in the sheet metal 3. 【0059】In the first processing stage 13a, the first pilot pin 25a and the first punch 21a descend together with the upper die 8. At this time, the first pilot pin 25a is inserted into and fitted into the first pilot hole 19a prior to punching by the first punch 21a. As a result, the plate material 3 is positioned outside the planned portion 27 (see Figure 5). 【0060】 If the plate material 3 is curved laterally, the curve of the plate material 3 is corrected (the plate material 3 is corrected to be aligned with the feeding direction) while the plate material 3 is positioned. In this case, as described above, it is preferable to leave the first pilot hole 19a downstream of the first processing stage 13a unused by not fitting the first pilot pin 25a into it. 【0061】 In this positioning state, the descending first punch 21a punches out the inner circumference 7 as the inner circumference of the core piece 5. When the plate material 3 has a lateral curvature, the punching of the inner circumference 7 is performed while the plate material 3 is under stress due to the constraint. Therefore, when the positioning of the plate material 3 is released, the inner circumference 7, which is released from stress, may deform, but this deformation has little effect on the roundness because the diameter of the inner circumference 7 is relatively small. 【0062】 In the second processing stage 13b, the second pilot pin 25b and the second punch 21b descend together with the upper die 8. At this time, the second pilot pin 25b engages with the second pilot hole 19b prior to punching by the second punch 21b (see Figures 2 and 6). 【0063】 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 feed direction), similar to the first processing stage 13a. However, in the second processing stage 13b, the plate material 3 is not constrained in the rotational direction. Therefore, rotational stress is not generated in the plate material 3 or is suppressed, and the stress generated in the plate material 3 can be reduced. In this embodiment, because the second pilot hole 19b is straight, the plate material 3 is slightly constrained in the rotational direction, so some stress is generated. However, since the rotational stress generated in the plate material 3 is suppressed, the stress generated in the plate material 3 can be reduced. 【0064】Furthermore, since the plate material 3 is straightened to a state aligned with the feed direction in the first processing stage 13a, the lateral curvature of the plate material 3 occurs after the first processing stage 13a. Therefore, compared to the lateral curvature of the plate material 3 due to the accumulation of processing in the first processing stage 13a and the second processing stage 13b, the lateral curvature that needs to be corrected during positioning in the second processing stage 13b is smaller. As a result, the stress generated in the plate material 3 due to 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 plate material 3 by the first pilot pin 25a and the first pilot hole 19a when the plate material 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, the first pilot pin 25a is fitted into the first pilot hole 19a in the second processing stage 13b. This straightens the plate material 3, which has a lateral curvature, to a state aligned with the feed direction, while positioning it while constraining it in the feed direction, width direction, and rotation direction. 【0068】 If the outer circumference 9 of the core piece 5 is punched out in this positioning state, the outer circumference 9 of the core piece 5 will deform significantly, as shown by the dashed line in Figure 7, for example, because it is released from the stress imposed by the punching. As a result, the roundness of the outer circumference 9 of the core piece 5 deteriorates. 【0069】 Figure 8 is a graph comparing the roundness of the outer circumference 9 of the core piece 5 of Example 1 and the Comparative Example. 【0070】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. 【0071】 As described above, the punching method and punching apparatus 1 of this embodiment form a second pilot hole 19b in the strip-shaped sheet material 3 for the intended portion 27 that will become the outer circumference 9 of the core piece 5, which is a circular punched-out portion. The second pilot pin 25b is engaged with the formed second pilot hole 19b to position the sheet material 3 without restraining it in the rotational direction. In this positioned state of the sheet material 3, the outer circumference 9 of the core piece 5 is punched out. 【0072】 Therefore, when the plate material 3 has a lateral curvature, the outer circumference 9 of the core piece 5 can be punched out while suppressing the stress on the plate material 3, and the 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. 【0073】 Furthermore, in the punching method and punching apparatus 1 of this embodiment, a first pilot hole 19a is formed in the sheet metal 3 to restrain the sheet metal 3 in the rotational direction. The sheet metal 3 is positioned by fitting a first pilot pin 25a into the formed first pilot hole 19a. Then, with the sheet metal 3 positioned in this rotationally restrained state, the inner circumference 7 of the core piece 5, which is the inner circumference, is punched out. 【0074】 Therefore, the relatively small diameter inner circumference 7, which is easier to ensure roundness, can be formed with high precision by positioning using the first pilot hole 19a and the first pilot pin 25a, prioritizing positioning accuracy. 【0075】 Furthermore, in the punching method and punching apparatus 1 of this embodiment, while the sheet material 3 is fed forward, the first pilot pin 25a is fitted into the first pilot hole 19a upstream in the feeding direction of the sheet material 3, and the second pilot pin 25b is engaged with the second pilot hole 19b downstream in the feeding direction. 【0076】 Therefore, the lateral bending of the plate material 3 when engaging the second pilot pin 25b with the second 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. 【0077】Figure 9 is a plan view showing a part of the plate material 3 according to a modified example of Embodiment 1 of the present invention. 【0078】 In the modified example shown in Figure 9, the second pilot hole 19b is circular. The second pilot pin 25b has a smaller cross-sectional shape than the second pilot hole 19b and engages with the outside of the second pilot hole 19b in a direction intersecting the rotational direction, which in this modified example is the radial direction of the planned portion 27. 【0079】 Therefore, the plate material 3 is positioned by engagement with the second pilot pin 25b and the second pilot hole 19b, and is unrestrained in the rotational direction around the planned portion 27. 【0080】 Even with this modified example, the same effects and advantages as in Example 1 can be achieved. 【0081】 Figure 10 is a plan view showing the positioning of a plate material by a second pilot pin and a pilot hole in a second processing stage according to Embodiment 2 of the present invention. Since Embodiment 2 has the same basic configuration as Embodiment 1, components corresponding to Embodiment 1 are indicated by the same reference numerals, and redundant explanations are omitted. 【0082】 In this embodiment, the pilot hole 19 is used as both a restraining pilot hole and a pilot hole. That is, the pilot hole 19 corresponds to the one in Embodiment 1 where the second pilot hole 19b is omitted and only the first pilot hole 19a is formed in the plate material 3. 【0083】 The second pilot pin 25b is formed to be smaller than the pilot hole 19 in the rotational direction, and when engaged with the pilot hole 19, it leaves the plate material 3 unrestrained in the rotational direction. Specifically, the cross-sectional shape of the second pilot pin 25b is elliptical, and the minor axis of the cross-sectional shape is aligned with the rotational direction. 【0084】 When the second pilot pin 25b is engaged with the pilot hole 19, there is a clearance between the second pilot pin 25b and the pilot hole 19. Therefore, the plate material 3 is unrestrained in the rotational direction within the range of the clearance between the second pilot pin 25b and the pilot hole 19. 【0085】Therefore, the same effects and advantages as in Example 1 can be achieved in Example 2. Furthermore, there is no need to provide a dedicated pilot hole for unrestraining the plate material 3 in the rotational direction, which simplifies the structure of the punching device 1. 【0086】 Even with this modified example, the same effects and advantages as in Example 2 can be achieved. 【0087】 1 Punching device 3 Sheet material 5 Core piece 7 Inner circumference (inner part) 9 Outer circumference (punching part) 15 Second pilot punch (unrestrained pilot punch) 17 Second pilot die (unrestrained pilot die) 19a First pilot hole (restrained pilot hole) 19b Second pilot hole (unrestrained pilot hole) 18 First pilot punch (restrained pilot punch) 20 First pilot die (restrained pilot die) 21a First punch (inner circumference punch) 21b Second punch 25a First pilot pin (restrained pilot pin) 25b Second pilot pin (unrestrained pilot pin) 27 Planned part

Claims

1. A punching method comprising: forming an unrestrained pilot hole in a strip-shaped sheet material on the radially outer side of a portion to be punched out in a circular area; engaging an unrestrained pilot pin with the unrestrained pilot hole to position the sheet material so that it is unrestrained in a rotational direction around the portion to be punched out in a circular area; and punching out the circular area while the sheet material is positioned.

2. A punching method according to claim 1, wherein the unrestrained pilot holes are provided at a plurality of locations radially outward of the planned portion, and the unrestrained pilot pin is smaller than the unrestrained pilot hole in the rotational direction.

3. A punching method according to claim 2, wherein the unrestrained pilot hole is an elongated hole aligned with the rotational direction.

4. A punching method according to any one of claims 1 to 3, comprising: forming a restraining pilot hole in the plate material for restraining the plate material in the rotational direction; fitting a restraining pilot pin into the restraining pilot hole to position the plate material; and punching out the inner circumference of the plate material radially inward in the positioning state due to the restraint.

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

6. A punching method according to any one of claims 1 to 3, wherein the punching portion is the outer circumference of a circular core piece.

7. A punching device comprising: an unrestrained pilot punch that forms an unrestrained pilot hole in a strip-shaped sheet material on the radially outer side of a planned circular punched-out portion; an unrestrained pilot pin that engages with the unrestrained pilot hole to position the sheet material so as to be unrestrained in a rotational direction around the planned portion; and a punch that punches out the circular punched-out portion while the sheet material is positioned.

8. A punching device according to claim 7, wherein the unrestrained pilot punch has multiple unrestrained pilot holes formed at multiple locations radially outward of the target portion, and the unrestrained pilot pin is smaller in the rotational direction than the unrestrained pilot holes.

9. A punching device according to claim 8, wherein the unrestrained pilot punch forms the unrestrained pilot hole as an elongated hole along the rotational direction.

10. A punching device according to any one of claims 7 to 9, comprising: a restraining pilot punch that forms a restraining pilot hole in the plate material for restraining the plate material in the rotational direction; a restraining pilot pin that fits into the restraining pilot hole to position the plate material; and an inner circumferential punch that punches out the inner circumferential portion radially inward of the target portion while the plate material is positioned by restraint.

11. A punching method according to claim 10, comprising a punching device wherein, while sequentially feeding the sheet material, the restraining pilot pin is fitted into the restraining pilot hole upstream in the feeding direction of the sheet material, and the unrestrained pilot pin is engaged with the unrestrained pilot hole downstream in the feeding direction.

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