SHEET METAL PERFORATING DEVICE.

Abstract

A sheet metal punching device 11 according to the present invention includes: a die 13 designed to support a sheet metal 1; and a punch 15 configured to form a circular punched hole 3 in the sheet metal 1 supported by the die 13, wherein the punch 15 includes: a main body piece 17; a cylindrical punched piece 19; a rotating piece 21 rotatably arranged about a central axis of the punched piece 19 as an axis of rotation; and a coated abrasive 23 provided on an outer circumferential surface of the rotating piece 21.a spring 25 disposed between the main body piece 17 and the die-cut piece 19 so that it is capable of contracting and extending in a die-cutting direction, contracting and accumulating elastic energy until the die-cut piece 19 comes into contact with and punches the metal sheet 1, and releasing the elastic energy and extending after the die-cut piece punches the metal sheet 1; and a rotary motion conversion device 27 configured to convert a linear motion of the die-cut piece 19 due to the extension of the spring 25 into a rotary motion of the rotary piece 21.

Description

SHEET METAL SIDE DIE CUTTING DEVICE FIELD OF INVENTION The present invention relates to a sheet metal punching device, and more particularly to a sheet metal punching device that forms a punched hole with improved fatigue resistance of a sheared edge. BACKGROUND OF THE INVENTION It is known that the sheared edge of a punched hole in a sheet metal subjected to punching has lower fatigue strength than the end surface of a hole machined by a drill or similar means. This is because residual tensile stress in the circumferential direction of the punched hole is generated by the punching process, the end surface is roughened, and so on (see Non-Patent Bibliography 1), leading to fatigue fracture in automotive parts and similar applications. Therefore, it is desired to improve the properties of the sheared edge of the punched hole in the sheet metal subjected to punching to enhance fatigue strength. To form a punched hole with improved sheared edge properties, for example, the following technique has been proposed. Patent Bibliography 1 and Patent Bibliography 2 propose a method of subjecting a sheet of metal to plastic deformation to form a groove beforehand and then punching the sheet of metal. Meanwhile, Patent Bibliography 3 proposes a method of rubbing a sheared edge of a punched hole in a sheet of metal by providing, on a punch positioned on one side of the base end farther away than a cutting piece located on one side of the distal end of the punch, a larger piece having a larger diameter than the cutting piece, and moving the punch further in a punched direction from a state where the cutting piece penetrates the punched hole to allow the larger piece to pass through the hole.Meanwhile, patent bibliography 4 proposes a method that uses a combination of a punch, a die, and a workpiece holder to subject a metal sheet to die-cutting while pressing the metal sheet with the workpiece holder along with the movement of the punch. List of references Patent bibliography Patent Bibliography 1: JP 2009-12018 A Patent Bibliography 2: JP 2008-137073 A Patent Bibliography 3: WO 2009-125786 A Patent Bibliography 4: JP 2004-283875 A Non-patent bibliography Non-patent bibliography 1: Yoshitake et al., Proceedings of the Japan Society of Automotive Engineers, vol. 33, no. 4, pages 203-208 (2002). BRIEF DESCRIPTION OF THE INVENTION Technical problem However, in the methods described in Patent Bibliography 1 and Patent Bibliography 2, because another mold is needed in addition to a tool to form a punched hole in a sheet of metal, there is the problem of increasing the number of steps and low productivity. Furthermore, the method described in Patent Bibliography 3 has the problem of LRRznn / rznz / e / YiAi that the sheet metal around the punched hole deforms when the larger piece passes through the punched hole. Furthermore, the method described in patent bibliography 4 is described as a method in which fatigue resistance can be improved by increasing the ratio of a cutting surface at the shear edge. However, even when employing the above method, a fracture surface remains at the shear edge, and therefore, the occurrence of cracks at the fracture surface cannot be sufficiently suppressed. Moreover, since a specially shaped support is required for the parts, the scope of application is limited. The present invention has been made in view of the above problems, and aims to provide a sheet metal punching device capable of forming a punched hole that has improved shear edge properties in a single step without requiring any other mold besides a die to form a punched hole, inhibiting the generation of cracks on the shear edge and improving fatigue resistance. Solution to the problem A sheet metal punching device according to the present invention includes: a die including a circular opening and configured to support a sheet metal; and a punch configured to form a circular punched hole in the sheet metal supported by the die, wherein the punch includes: a main body piece; a punched cylindrical portion provided with a distal end; a rotating piece provided between the main body piece and the punched portion to be rotatable about a central axis of the punched portion as an axis of rotation; a coated abrasive disposed on an outer circumferential surface of the rotating piece and configured to polish a sheared edge of the punched hole;a spring disposed between the main body piece and the stamped piece so that it is capable of contracting and extending in a stamped direction, the spring being configured to contract and accumulate a portion of a stamped load as elastic energy until the stamped piece makes contact and stamps the sheet metal, releasing the elastic energy, and extending after the stamped piece stamps the sheet metal; and a rotational motion conversion device configured to convert a linear motion in the stamped direction of the stamped piece due to the extension of the spring into a rotary motion of the rotating piece. The rotary motion conversion device may include: a plate-shaped grid provided to extend in the die-cutting direction from a distal end of the main body part; a first gear arranged to be rotated about an axis orthogonal to the die-cutting direction and including a first spur gear meshing with the plate-shaped grid, and a first bevel gear provided coaxially with the first spur gear; a second gear arranged to be rotated about an axis parallel to the die-cutting direction and including a second bevel gear meshing with the first bevel gear, and a second spur gear provided coaxially with the second bevel gear; a gear support provided in the die-cut part to rotatably support each of the first and second gears;and a cylindrical grid provided on one side of the inner circumferential surface of the rotating part and configured to mesh with the second spur gear.; Positive effects of the invention LRRznn / rznz / e / γΐΛΐ In the present invention, by forming the die and polishing the sheared edge of the die-cut hole, it is possible to reduce the irregularity of the sheared edge and prevent the direction of a polishing mark on the sheared edge from coinciding with the direction of a crack generated on the sheared edge when a load is repeatedly applied to the sheet metal in which the die-cut hole is formed. It is also possible to form the die-cut hole of the sheared edge that has excellent fatigue resistance in a single step without requiring a power source other than the power source for die-cutting the sheet metal.Furthermore, according to the present invention, an improvement in formability can be expected by preventing ductile fracture of the sheared edge during pressure molding after stamping, and an improvement in delayed fracture characteristics, where a brittle-like fracture occurs after a predetermined time in a state where a sheet of metal with a stamped hole is subjected to a static load. Additionally, by reducing the irregularity of the sheared edge to decrease the surface area, an improvement in coating properties and corrosion resistance of the coating material can also be expected. BRIEF DESCRIPTION OF THE FIGURES FIGS. 1A, 1B and 1C are a cross-sectional view illustrating a sheet metal stamping device according to an embodiment of the present invention and an operation thereof (FIG. 1A before stamping, FIG. 1B spring contraction, FIG. 1C immediately after stamping and polishing). FIG. 2 is a perspective view illustrating an example of a specific configuration of a rotational motion conversion device of the sheet metal stamping device according to the embodiment of the present invention. FIGS. 3A and 3B are a cross-sectional view illustrating a punch and operation of the sheet metal punching device according to the embodiment of the present invention (part 1) (FIG. 3A before punching, FIG. 3B spring retraction). FIGS. 4A and 4B are a cross-sectional view illustrating the punch and operation of the sheet metal stamping device according to the embodiment of the present invention (part 2) (FIG. 4A immediately after stamping and polishing, FIG. 4B punch removal). FIG. 5 is a diagram illustrating a fatigue sample used in a fatigue test in an example. FIGS. 6A and 6B are a cross-sectional view illustrating a sheared edge of a punched hole formed in a sheet of metal by cutting. DETAILED DESCRIPTION OF THE INVENTION To solve the above problems, the inventors of the present invention first carried out intensive studies on the properties and fatigue resistance of a sheared edge of a punched hole obtained by punching. Figure 6A illustrates a cross-sectional (side surface) view of a punched hole 3 formed by punching a metal sheet 1. A sheared edge 5 of the punched hole 3 divides into a cut surface 5a and a fracture surface 5b. When a load is repeatedly applied to this metal sheet 1 in which the punched hole 3 is formed, as illustrated in the top view of Figure 6B, a crack 7 is likely to develop on the fracture surface 5b. LRRznn / rznz / e / γΐΛΐ of the sheared edge 5, resulting in a fatigue fracture from crack 7. Furthermore, on an uneven fracture surface 5b, with a section where the holes are continuous in a direction stamped by the punch serving as the starting point, crack 7 develops due to tensile stress in the circumferential direction of the stamped hole, applied due to shear or stress such as bending of the sheet metal. It has also become clear that the generation of crack 7 is accelerated even if the direction of the polishing mark left on the sheared edge 5 is in the direction of the stamping. Therefore, the inventor has obtained the finding that, by using a punch having a die-cut cylindrical portion, a rotating piece rotating about a central axis of the die-cut portion as the axis of rotation, and a coated abrasive disposed on an outer circumferential surface of the rotating piece, subjecting a sheet of metal to die-cutting to form a die-cut hole, rotating the rotating piece in a state where the rotating piece is located inside the die-cut hole, and polishing a sheared edge of the die-cut hole with the coated abrasive, it is possible to form the die-cut hole and polish the sheared edge in a single step such that the direction of a polish mark and the direction of a crack do not coincide with each other, and thus solve the above problem. Furthermore, the inventor has conceived an idea that, by providing a spring between a main body part and the die-cut piece at a distal end of the punch and providing a device for accumulating a portion of a die-cut load as spring elastic energy and releasing the elastic energy accumulated in the spring after die-cutting to rotate the rotating piece, allows the sheared edge to be polished without requiring a power source to rotate the rotating piece other than a power source for cutting. The following describes a sheet metal stamping device according to an embodiment of the present invention. Note that in this specification and in the figures, elements having substantially the same function and configuration are indicated with the same reference symbols, and redundant descriptions are omitted. Furthermore, in the figures used in the following description, to facilitate understanding of the features, the characteristics may be illustrated in an enlarged manner for convenience, but the dimensions, ratios, and the like of each component are not necessarily the same as the actual dimensions, proportions, and the like. As illustrated in FIGS. 1A to 1C as an example, a sheet metal punching device 11 (hereinafter referred to as “punching device 11”) according to the embodiment of the present invention forms the punched hole 3 in the sheet metal 1 using a die 13 and a punch 15. The die 13 has a circular opening 13a and is designed to support the metal sheet 1. The punch 15 includes a main body piece 17, a die-cut cylindrical piece 19 provided at its distal end in the die-cutting direction, a rotating piece 21, a coated abrasive 23, a spring 25, and a rotary motion conversion device 27. The rotating part 21 is provided between the main body part 17 and the stamped part 19 so that it can rotate around the central axis of the stamped part 19 as the axis of rotation. The coated abrasive 23 is provided on the outer circumferential surface of the rotating part 21 and is designed to polish the sheared edge 5 of the punched hole 3 by rotating the rotating part 21. LRRznn / rznz / e / YiAi Spring 25 is positioned between the main body part 17 and the die-cutting piece 19 so that it can compress and extend in the direction of the die-cutting. Then, during the die-cutting process of the sheet metal 1, by moving the punch 15 in the die-cutting direction, spring 25 compresses and stores part of the die-cutting load as elastic energy until the die-cutting piece 19 makes contact and punches the sheet metal 1. After the die-cutting piece 19 punches the sheet metal 1, spring 25 releases the stored elastic energy and extends. Note that the die-cutting direction is the direction in which the punch 15 moves relative to the die 13 to form the punched hole 3 in the sheet metal 1. The rotary motion conversion device 27 is configured to convert a linear motion in the die-cutting direction of the die-cut part 19 due to the extension of the spring 25 into a rotary motion of the rotary part 21. An example of a specific configuration of the rotary motion conversion device 27 is illustrated in FIGS. 2 to 4B As illustrated in FIGS. 2 to 4B, the rotary motion conversion device 27 includes a plate-shaped grid 29, a first gear 31, a second gear 33, and a gear holder 35. The plate-shaped grid 29 is provided to extend in the die-cutting direction from a distal end of the main body piece 17, and moves together with the main body piece 17 when the punch 15 moves in the die-cutting direction. As illustrated in FIG. 2, the first gear 31 includes a first spur gear piece 31a meshing with the plate-shaped grid 29 and a first bevel gear piece 31b provided coaxially with the axis of rotation of the first spur gear piece 31a, and is rotatably arranged about an axis orthogonal to the direction of punching (about an axis C1 in FIG. 2). Here, the first spur gear piece 31a and the first bevel gear piece 31b are connected by a first gear shaft piece 31c so that they can rotate coaxially. As illustrated in FIG. 2, the second gear 33 includes a second bevel gear 33a meshing with the first bevel gear 31b and a second spur gear 33b provided coaxially with the axis of rotation of the second bevel gear 33a, and rotatably arranged about an axis parallel to the direction of punching (about axis C2 in FIG. 2). Here, the second bevel gear 33a and the second spur gear 33b are connected by a second gear shaft 33c so that they can rotate coaxially. As illustrated in FIGS. 3A to 3B and 4A to 4B, the gear support 35 is provided in the die-cut piece 19 to rotatably support each of the first gear 31 and the second gear 33. A cylindrical grid 37 is provided on the inner circumferential surface side of the rotating part 21 and meshes with the second spur gear 33b. As illustrated in FIG. 2, the cylindrical grid 37 is the same as the rotating part 21, and the coated abrasive 23 is directly bonded to the outer circumferential surface of the cylindrical grid 37. However, the cylindrical grid 37 is not limited to one that is the same as the rotating part 21, and may be provided separately on the inner circumferential surface side of the rotating part 21, for example. LRRznn / rznz / e / γΐΛΐ The operation of the die-cutting device 11 in the process of forming the die-cut hole 3 in the metal sheet 1 using the die-cutting device 11 is described below with reference to FIGS. 1A to 4B. First, the metal sheet 1 is positioned so that it extends irregularly over the opening 13a of the die 13, the metal sheet 1 is held at both ends and the punch 15 is installed on the metal sheet 1 (FIG. 1 and FIG. 3A). Next, the punch 15 moves in the direction of the punching, and the spring 25 contracts until the punch 15 comes into contact with the metal sheet 1 and punches the metal sheet 1. As a result, a part of a punched load accumulates in the spring 25 as elastic energy (FIG. 1B and FIG. 3B). Subsequently, punch 15 is further applied with a stamping load to cause the stamped part 19 to punch the metal sheet 1, so that the elastic energy stored in spring 25 is released and spring 25 extends. As a result, the stamped part 19 moves linearly in the stamping direction towards the opening 13a of die 13, and the rotating part 21 is positioned inside punch 3 (FIG. 1C and FIG. 4A). Along with the linear motion of the die-cut piece 19, as illustrated in FIG. 2, the plate-shaped grid 29 moves relatively in the opposite direction to the die-cutting direction, and the first gear 31 rotates through the first spur gear piece 31a meshing with the plate-shaped grid 29. The rotation of the first gear 31 is then transmitted to the second bevel gear piece 33a meshing with the first bevel gear piece 31b, and the second gear 33 rotates. Thus, the rotation of the second gear 33 is transmitted to the rotating part 21 (the cylindrical grid 37 in FIG. 2) which meshes with the second part of the spur gear 33b, and the rotating part 21 rotates. As a result, the sheared edge 5 of the punched hole 3 is polished by the coated abrasive 23 arranged on the outer circumferential surface of the rotating part 21 (FIG. 1C and FIG. 4A). After the spring 25 has fully extended and the rotation of the rotating part 21 has stopped, the punch 15 moves in the opposite direction to the die-cutting direction to remove the punch 15 from the die-cut hole 3 (FIG. 4B). As described above, according to the sheet metal punching device 11 in the embodiment of the present invention, a portion of the punched load of the sheet metal 1 by the punch 15 is stored in the spring 25 as elastic energy. After punching the sheet metal 1 to form the punched hole 3, the elastic energy stored in the spring 25 is released, causing the rotating part 21 to rotate. Then, the coated abrasive 23 provided on the outer circumferential surface of the rotating part 21 polishes the sheared edge 5 of the punched hole 3, so that the rotating part 21 rotates without requiring a power source other than the power source for punching the sheet metal 1. The sheared edge 5 is polished in a single step to form the punched hole 3 with reduced irregularities. Furthermore, it is possible to prevent the direction of a polishing mark on the sheared edge 5, polished by the coated abrasive 23, from coinciding with the direction of a crack generated on the sheared edge 5 when a load is repeatedly applied to the metal sheet 1 in which the punched hole 3 is formed. As a result, it is possible to prevent a crack from forming on the sheared edge 5 when a repeated load is applied, and to form the punched hole 3 with fatigue resistance. LRRznn / rznz / e / YiAi improved. Furthermore, according to the sheet metal die-cutting device 11, in accordance with this modality, there is an improvement in formability by avoiding ductile fracture of the sheared edge 5 when pressure molding is performed after die-cutting, an improvement in the delayed fracture characteristics of the die-cut hole 3, and an improvement in the coating properties and corrosion resistance of a coating material can also be expected by reducing the irregularity of the sheared edge 5 to reduce the surface area. Note that the spring force 25 can be any force as long as the force is sufficient to punch the metal sheet 1 into a state where the spring contracts when the punched piece 19 comes into contact with the metal sheet 1. Meanwhile, the rotating part 21 is preferably cylindrical in shape. The coated abrasive 23 is not limited to one provided to cover the entire outer circumferential surface of the rotating part 21, and may be one provided on a portion of the outer circumferential surface of the rotating part 21. Meanwhile, to sufficiently polish the sheared edge 5 of the punched hole 3 by rotating the rotating part 21, the coated abrasive 23 is preferably adjusted so that the coated abrasive 23 provided on the outer circumferential surface of the rotating part 21 extends outward from the outer circumferential surface of the punched part 19, i.e., the outer diameter of the coated abrasive 23 disposed on the outer circumferential surface of the rotating part 21 is equal to or greater than the outer diameter of the punched part 19. However, when the outer diameter of the coated abrasive 23 arranged on the outer circumferential surface of the rotating part 21 is greater than the outer diameter of the die 19, after the rotating part 21, provided with the coated abrasive 23 on its outer circumferential surface, is inserted into the die hole 3, the coated abrasive 23 extends outward from the sheared edge 5 of the die hole 3. As a result, even if the rotating part 21 can be inserted into the die hole 3, when the rotating part 21 rotates, the coated abrasive 23 polishes not only the sheared edge 5 but also the opening 13a of the die 13, so the service life of the coated abrasive 23 may be reduced.Accordingly, the outer diameter of the coated abrasive 23 provided on the outer circumferential surface of the rotating part 21 is preferably approximately the same as the inner diameter of the opening 13a of the die 13. Meanwhile, the punch 15 used in the above description is one in which the surface of the coated abrasive 23 is parallel to the direction of the punching, i.e., an angle Θ (see FIG. 3A) formed by the surface of the coated abrasive 23 and a cross section orthogonal to the central axis 19a of the punched piece 19 is 90°. However, the angle Θ formed by the surface of the coated abrasive 23 and the cross-section orthogonal to the central axis 19a of the punched piece 19 is not limited to 90°. For example, as a preliminary test, the punched hole 3 can be formed in the sheet metal 1 without providing the coated abrasive 23 to the punch 15, and an angle θ' (see FIGS. 6A to 6B) formed by the fracture surface 5b on the sheared edge 5 and the surface 1a of the sheet metal 1 can be measured. Subsequently, the angle Θ can be adjusted within a predetermined error range from the angle θ' measured by the preliminary test. The predetermined error range is, for example, ±300°. LRRznn / rznz / e / γΐΛΐ As a result, the fracture surface 5b, where crack 7 is likely to occur under repeated loading, can be intensively polished. Note that, to install the coated abrasive 23 so that the angle Θ formed by the surface of the coated abrasive 23 and the cross-section orthogonal to the central axis 19a of the die-cut piece 19 becomes a predetermined angle, for example, the shape of the outer circumferential surface of the rotating piece 21 can be appropriately adjusted. Meanwhile, it is preferable to use a general polish for the coated abrasive 23. However, if the coated abrasive 23 does not have stretching properties in the thickness direction, there is a possibility that the coated abrasive cannot be removed from the punched hole 3. Therefore, it is preferable to select the type and material of the coated abrasive 23 appropriately. Furthermore, the number of threads (granulometry size) of the coated abrasive 23 is not particularly limited, but is preferably determined according to the hardness and like of the metal sheet 1, and is preferably around #80 to #240 for a general steel sheet such as metal sheet 1. Note that in the stamping device 11, which has the rotary motion conversion device 27 described above, even when the spring 25 is compressed until the metal sheet 1 is stamped, the first part of the spur gear 31a meshes with the rotating plate-shaped grid 29, causing the rotating part 21 to rotate. At this point, the rotating part 21 rotates in the opposite direction to the rotation of the rotating part 21 after stamping the metal sheet 1. However, the rotation of the rotating part 21 until the metal sheet 1 is stamped does not contribute to the polishing of the sheared edge 5 of the stamped hole 3 and, on the contrary, may shorten the service life of the gear and similar components of the stamping device 11. To deal with this, for example, a ratchet mechanism (not polished) can be provided to prevent reverse rotation of the rotating part 21 in the first spur gear 31a of the first gear 31 in the rotary motion conversion device 27 to suppress reverse rotation of the rotating part 21 until the metal sheet 1 is stamped. Furthermore, the die-cutting device 11 according to this embodiment preferably includes a fall-prevention mechanism 39 as illustrated in Figures 3A to 3B and 4A to 4B, for example. The fall-prevention mechanism 39 includes a die-cut piece 41 formed in a direction opposite to the die-cutting direction from the distal end of the main body piece 17, and a fall-prevention bar 43 provided to extend from the rear end of the die-cut piece 19 into the main body piece 17 and is inserted into the die-cut piece 41. A plug 43a is provided at the rear end of the fall-prevention bar 43 to prevent the fall-prevention bar 43 from dislodging from the die-cut piece 41. As described above, according to the die-cutting device 11 having the fall-prevention mechanism 39, in the process of die-cutting the sheet metal 1, polishing the sheared edge 5, and then extracting the punch 15 from the die-cut hole 3, the plug 43a is caught by the entrance of the die-cut piece 41, so that the die-cut piece 19 can be prevented from falling out of the punch 15. Examples The following describes an experiment performed to confirm the operation and effect of the metal sheet die-cutting device according to the present invention. LRRznn / rznz / e / YiAi In the experiment, firstly, a hot-rolled steel sheet of class 780 MPa (sheet thickness: 2.9 mm) was used as metal sheet 1, and the punched hole 3 was formed in the metal sheet 1 by means of the punching device 11 illustrated in FIGS. 1A to 1C. The outer diameter of die 19 of die-cutting device 11 was set at 10 mm, and the clearance between the outer diameter of die 19 and the inner diameter of opening 13a of die 13 was set at 10%. As coated abrasive 23 provided on the outer circumferential surface of the rotating part 21, coated abrasive with a thread count of #120 was used, the diameter of the coated abrasive 23 provided to the rotating part 21 was fixed at 10 mm, and the angle Θ (see FIG. 3A) formed by the coated abrasive 23 and the cross section 19a orthogonal to the central axis of the stamped part 19 was fixed at 90°. Subsequently, a fatigue specimen 51 having the punched hole 3 as illustrated in FIG. 5 was produced from the metal sheet 1 having the punched hole 3 formed, using the punching device 11. Then, using a Shenck flat bending fatigue testing device, a fatigue test was performed in which a load was repeatedly applied to the fatigue specimen 51 by double twisting. In the fatigue test, fatigue fracture was defined as the moment when the torque decreased by 30% at a normal stress of 300 MPa, and the number of load repetitions until fracture was measured. The load was then set to be applied up to 2 million times, and the fatigue test was completed. In the experiment, an example of the invention was established using fatigue specimen 51 with die-cut hole 3 formed using die-cutting device 11. Additionally, as a comparison object, an example in which fatigue specimen 51 with die-cut hole 3 was prepared using an integrated punch having the same diameter as die-cut part 19 of die-cutting device 11 and subjected to the same fatigue test described above was established as a conventional example. Table 1 illustrates the fatigue test results. LRRznn / rznz / e / γΐΛΐ Table 1 There may be coated abrasive. Number of load repetitions until fracture. Observations: No coated abrasive: 480,000 times (Conventional example). Coated abrasive: 2 million times or more (not fractured). Example of invention. According to Table 1, in the conventional example, fatigue specimen 51 fractured after 480,000 repetitions. In contrast, in the example of the invention, the fatigue specimen did not fracture even after 2 million repetitions, and its fatigue life was improved by a factor of four or more compared to the conventional example. Industrial Applicability According to the present invention, it is possible to provide a sheet metal punching device capable of forming a punched hole having improved shear edge properties in a single step without requiring any other mold besides a die-cutting mold, preventing cracking of the shear edge and improving fatigue resistance. List of reference signs METAL SHEET 1st SURFACE DIE-CUT HOLE SHEARED EDGE 5a CUTTING SURFACE 5b FRACTURE SURFACE FISSURE DIE-CUTTING DEVICE DIE 13a OPENING AWL MAIN BODY PIECE DIE-CUT PIECE with CROSS SECTION ORTHOGONAL TO THE CENTRAL AXIS SWIVEL PIECE COATED ABRASIVE SPRING ROTARY MOTION CONVERSION DEVICE PLATE-SHAPED GRID FIRST GEAR 31a FIRST SPUR GEAR PIECE 31b FIRST PIECE OF THE BEVEL GEAR 31c FIRST PIECE OF THE GEAR SHAFT SECOND GEAR 33a SECOND PIECE OF THE BEVEL GEAR 33b SECOND SPUR GEAR PIECE 33c SECOND PIECE OF THE GEAR SHAFT GEAR SUPPORT CYLINDRICAL GRID FALL PREVENTION MECHANISM DIE-CUT PIECE FALL PREVENTION BAR 43a PLUG SIGN OF FATIGUE

Claims

1. A sheet metal punching device characterized in that it comprises: a die including a circular opening and configured to support a sheet of metal; and a punch configured to form a circular punched hole in the sheet of metal supported by the die, wherein the punch includes: a main body piece; a cylindrical punched piece provided with a distal end; a rotating piece provided between the main body piece and the punched piece to be rotatable about a central axis of the punched piece as an axis of rotation; a coated abrasive disposed on an outer circumferential surface of the rotating piece and configured to polish a sheared edge of the punched hole;a spring disposed between the main body piece and the stamped piece so that it is capable of contracting and extending in a stamped direction, the spring being configured to contract and accumulate a portion of a stamped load as elastic energy until the stamped piece makes contact and stamps the sheet metal, release the elastic energy and extend after the stamped piece stamps the sheet metal; and a rotational motion conversion device configured to convert a linear motion in the stamped direction of the stamped piece due to the extension of the spring into a rotary motion of the rotating piece.

2. The sheet metal punching device according to claim 1, further characterized in that the rotary motion conversion device includes: a plate-shaped grid provided to extend in the punching direction from a distal end of the main body piece; a first gear arranged so as to be rotatable about an axis orthogonal to the punching direction and including a first spur gear meshing with the plate-shaped grid, and a first bevel gear provided coaxially with the first spur gear; a second gear arranged so as to be rotatable about an axis parallel to the punching direction and including a second bevel gear meshing with the first bevel gear, and a second spur gear provided coaxially with the second bevel gear;a gear support provided in the stamped piece to rotatably support each of the first gear and the second gear; and a cylindrical grid provided on one side of the inner circumferential surface of the rotating piece and configured to mesh with the second spur gear.

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