JP5747448B2 - Punching hole punching and punching hole machining method with improved fatigue characteristics and hydrogen cracking resistance - Google Patents

Description

  The present invention relates to a method for punching a workpiece such as iron, aluminum, titanium, magnesium and alloys thereof used in automobiles, home appliances, building structures, ships, bridges, construction machines, various plants, penstocks, and the like, and The present invention relates to a punch for punching, and particularly relates to an improvement in fatigue characteristics and an improvement in hydrogen cracking resistance of a punched end face caused by punching holes.

  Work materials such as automobiles, home appliances, and building structures are often punched with a punch 2 and a die 3 as shown in FIG. As shown in FIG. 2, the punched surface is formed by the workpiece 1 being entirely pushed by the punch 2 within the clearance between the punch 2 and the die 3 (hereinafter referred to as “clearance” unless otherwise specified). In this case, the workpiece 1 is drawn into the punch and die clearance) and the workpiece 1 drawn into the clearance between the punched surface 2 and the die 3 is formed. It consists of a fracture surface 6 formed by breaking the material 1 and a flash 7 generated on the back surface of the workpiece 1.

  Punching has the advantage of low cost, but has the disadvantage that the fatigue strength and hydrogen cracking resistance of the cut end face are inferior compared to laser processing and machining.

  The following describes conventional technologies aimed at improving the fatigue strength of the punched end face and improving the resistance to hydrogen cracking.

  Patent Document 1 aims to reduce the residual stress at the time of cutting in order to prevent cracks at the end of the punched and cut ends, specifically, delayed fracture due to cracks due to the entry of hydrogen. As described above, there is described an invention in which a cutting blade having a divergent shape (tapered shape) is formed from a blade tip portion to the edge of a blade, and a hole is expanded or pressed on the entire front surface of the entire cross section.

  Also, it is not a technique aimed at improving the hydrogen cracking resistance characteristics of the punched end face, but as a technique aimed at improving the fatigue characteristics of the punched end face, the cutting blade (punch) As an invention relating to the shape, a piercing punch having a tip portion having a diameter smaller than the inner diameter of the punched hole, a hole expanding portion having a diameter substantially the same as the inner diameter of the punched hole, and a hole smaller than a hole having an opening having a predetermined width A drilling method for forming a hole having an opening of the predetermined width by expanding the small hole in a workpiece and then forming a hole having the opening of the predetermined width is disclosed in Patent Document 2 with a punch having an enlarged diameter portion. A punching method with an improvement that delays crack generation by rounding the surface is disclosed in Patent Document 3 as a cutting blade having a side surface parallel to the punching direction at the tip and an upward diameter formed on the upper portion of the cutting blade. Punch and punching method using the punch having a tapered portion is disclosed respectively in Patent Document 4 that.

  The technologies disclosed in Patent Documents 1 to 4 have several problems when considering the effects of improving fatigue strength and hydrogen cracking resistance and mass production. The inventions disclosed in Patent Literatures 1 to 4 are all methods of smoothing by rubbing the very surface layer of the punched end surface called so-called burnishing by the taper portion of the punched punch. Because the part is rubbed greatly, the wear amount of the punch is larger than the normal punch, and when the diameter is expanded, the force that pushes the material near the punch to the die side also causes the material near the die shoulder to flow, and the pilot hole (the first drilled Holes) The flash generated during processing becomes even larger, which may adversely affect fatigue strength and hydrogen cracking resistance. Furthermore, when punching and hole expansion are performed with an integral punch, the punch stroke amount required for drilling is particularly large in the method described in Patent Document 4, and there is usually a limitation on the punch stroke amount in a press device. Therefore, the method cannot be used depending on its ability.

JP 2006-289491 A JP-A-10-263720 Japanese Patent Laid-Open No. 11-254055 JP-A-11-333530

  The present invention has been invented in view of the above-described problems, and can stably improve the fatigue strength and hydrogen cracking resistance of the punched end face regardless of the type of material and target member, and can be used in mass production sites. An object of the present invention is to provide a punching hole processing method and a punch for punching hole processing that can be easily applied and that have excellent fatigue strength and hydrogen cracking resistance.

  In order to solve the above problems, the gist of the present invention is as follows.

The punch for punching holes according to the present invention is a punch for punching holes for punching holes to be processed on a workpiece to be punched by a punch and a die. , And the target hole punch portion is formed of a pillar body, and n is a positive integer of 2 or more, and the pilot hole punch portion is n The n number of columns are arranged coaxially so that the center axis is on the center axis of the target hole punch column, and the cross-sectional shape perpendicular to the side surface of the column is It is a similar figure which reduced the cross-sectional shape perpendicular | vertical to the side surface of the punch part column body for target holes toward the central axis, and the n column bodies with respect to the cross-sectional shape perpendicular to the side surface of the punch part column body for target holes The similarity ratio of the cross-sectional shape perpendicular to the side is smaller than 1 and different from each other The n pillars are arranged in descending order of the similarity ratio from the target hole punch part side, and the tapered part is formed of a part of a cone, and the target hole punch part pillar and the bottom hole part are arranged. The cross-sectional shape perpendicular to the central axis is sandwiched between the pillar body having the largest similarity ratio of the hole punch portion, and the cross-sectional shape perpendicular to the side surface of the target hole punch portion pillar body is The similarity ratio gradually changes to a cross-sectional shape perpendicular to the side surface of the columnar body, the difference in diameter of the cross-sectional shape perpendicular to the side surface of the adjacent punch hole columnar body, and the pilot hole The difference between the diameter of the cross-sectional shape perpendicular to the side surface of the columnar body having the maximum similarity in the punch portion columnar body and the diameter of the cross-sectional shape perpendicular to the side surface of the target hole punching column body is 0. It is 5 mm or more and 1 mm or less.

  In the punch for punching holes according to the present invention, the column may be a cylinder.

  In the punch for punching holes according to the present invention, the column may be a prism.

Furthermore, the punching hole processing method of the present invention is a punching hole processing method for a workpiece using the punching hole processing punch described above, wherein the height of each of the n pillars of the pilot hole punching portion is A punch for punching holes larger than the plate thickness of the workpiece is used, and a pilot hole is formed in the workpiece using a pilot hole punch portion in order from a column having a cross-sectional shape perpendicular to the side surface of the column. After punching out once, the hole is pushed and widened by a taper portion, and the diameter of the hole is made the diameter of the target hole.

Furthermore, the punched hole machining method of the present invention is characterized in that the material of the workpiece is iron or an Al—Zn—Mg alloy.

  According to the present invention, a tool having high fatigue strength and high resistance to hydrogen cracking can be processed without causing seizure or wear of the tool.

It is a longitudinal cross-sectional view which shows a punching process typically. It is a longitudinal cross-sectional view which shows typically the characteristic of a punching fracture surface. It is a longitudinal cross-sectional view which shows typically the punching process by the conventional punch with a taper. It is a longitudinal cross-sectional view which shows typically the punching process by the conventional different punch with a taper. It is a longitudinal cross-sectional view which shows typically the punching process by the conventional different punch with a taper. It is a front view which shows the punch for punching holes in this invention used in Example 1. FIG. 2 is a plan view showing a hole fatigue test piece used in Example 1. FIG. It is a perspective view which shows the hole fatigue test piece used in Example 2, 3. FIG.

  Exemplary embodiments of the present invention will be described below in detail with reference to the accompanying drawings. In addition, in this specification and drawing, about the component which has the substantially same function structure, duplication description is abbreviate | omitted by attaching | subjecting the same code | symbol.

  In an attempt to improve the fatigue strength and hydrogen cracking resistance characteristics of the punched hole, the present inventors expand the diameter of the prepared hole after performing the prepared hole processing as shown in FIGS. By using such a punch 8 with a taper, the fracture surface of the punched end face of the workpiece 1 can be smoothed, and it has been confirmed that there is an effect on fatigue strength and hydrogen cracking resistance. However, if a tapered punch 8 having a diameter-enlarged punch shape with a large diameter expansion amount and a large taper angle is used, a machining phenomenon as shown in FIG. 5 occurs, and the fracture surface due to the diameter expansion can only be smoothed. Therefore, it has been found that the effects of improving fatigue strength and hydrogen cracking resistance are reduced. In order to prevent such processing modes from appearing, when the taper angle is reduced by reducing the diameter expansion amount, the fracture surface can be partially smoothed by diameter expansion, but the amount is reduced. The effects of increasing fatigue strength and hydrogen cracking resistance were small.

  Therefore, the present inventors reduced the punching amount of the pilot hole to be opened at one time, and if the residual stress of the processed cross section can be further reduced by opening the pilot hole twice or more, the punching is performed with a small diameter expansion amount. It was thought that the fatigue strength of the end face could be improved. Hereinafter, a case where the pilot hole is opened twice will be described as an example.

  As shown in FIG. 6, the punch for punching holes of the present invention is a punch 11 for punching holes in which a target hole punch portion D, a taper portion C, and pilot hole punch portions B and A are continuously integrated. It is. The target hole punch portion D is composed of a pillar 11d, and the pilot hole punch portions B and A are composed of two pillars 11b and 11a. The two pillars 11b and 11a are arranged so that the central axis is coaxial with the central axis of the pillar 11d of the target hole punch portion D, and the cross-sectional shape perpendicular to the side surfaces of the pillars 11b and 11a is the target hole. This is a similar shape obtained by reducing the cross-sectional shape perpendicular to the side surface of the pillar 11d of the punch part D for use toward the central axis. The similarity ratios A / D and B / D of the cross-sectional shapes perpendicular to the side surfaces of the two columnar bodies 11b and 11a with respect to the cross-sectional shape of the columnar body 11d of the target hole punch portion D are smaller than 1 and different from each other. The columns 11b and 11a are arranged in descending order of similarity from the column 11d side of the target hole punch portion D. The tapered portion C is formed of a part of a cone, such as a truncated cone or a truncated pyramid, and the similarity ratio between the column 11d of the target hole punch D and the columns 11b and 11a of the pilot hole punches B and A. Is sandwiched between the largest pillar body 11b, and the cross-sectional shape perpendicular to the central axis is similar to the above-described similarities among the pilot hole punch parts B and A from the cross-sectional shape perpendicular to the side surface of the pillar body 11d of the target hole punch part D It gradually changes to a cross-sectional shape perpendicular to the side surface of the pillar 11b having the largest ratio. The “similarity ratio” in the present invention means an area ratio of a cross-sectional shape perpendicular to the central axis of the column. The difference between the diameters of the cross-sectional shapes perpendicular to the side surfaces of the pillars 11b, 11a of the two adjacent pilot hole punches B, A is 1 mm or less, and the pillars 11b of the pilot hole punches B, A 11a, the difference between the diameter of the cross-sectional shape perpendicular to the side surface of the columnar body 11b having the maximum similarity ratio and the diameter of the cross-sectional shape perpendicular to the side surface of the columnar body 11d of the target hole punch portion D is also 1 mm or less. . The reason for “1 mm or less” is based on the fatigue test results shown in the examples described later. The column bodies 11d, 11b, and 11a are cylinders or prisms. Here, the “diameter” in the present invention means the maximum length of diagonal lines in a cross-sectional shape perpendicular to the side surface when the column bodies 11d, 11b, and 11a are prisms.

  Using such a punch 11 for punching holes, a pilot hole that is smaller than the diameter of the target hole, which is the final shape, is punched twice in a single processing step, and then the pilot hole is turned into the target hole. Drill holes to expand to a diameter of. When the column is a cylinder, the difference (rb−ra) between the radius ra of the pilot hole punch portion A and the radius rb of the pilot hole punch portion B and the radius rb of the pilot hole punch portion B and the target hole punch portion D The difference (rd−rb) in the radius rd of each is within 0.5 mm, and the height (length in the central axis direction) of the pilot hole punch portion A and the pilot hole punch portion B are both processed. A taper-shaped diameter-expanded portion that is equal to or greater than the plate thickness of the material 1, is punched with a pilot hole punch portion A, and further punched with a pilot hole punch portion B, and then increases to the diameter of the target hole. By using the tapered portion C to contact the workpiece 1 and perform hole processing to push the prepared hole to the diameter of the target hole, the fatigue strength and hydrogen cracking resistance of the punched end face can be reduced with a small amount of diameter expansion. Can be improved.

  The same applies when the pilot hole is opened three times or more. In general, the punch for punching holes of the present invention in the case of forming n pilot holes is a punch for punching holes in which a target hole punch portion, a tapered portion, and a pilot hole punch portion are continuously integrated. . The target hole punch portion is composed of a column body, and n is a positive integer of 2 or more, and the pilot hole punch portion is composed of n column bodies. The n columns are arranged so that the central axis is coaxial with the central axis of the target hole punch column, and the cross-sectional shape perpendicular to the side surface of the column is perpendicular to the side surface of the target hole punch column. This is a similar shape obtained by reducing a simple cross-sectional shape toward the central axis. The similarity ratio of the cross-sectional shapes perpendicular to the side surfaces of the n column bodies is smaller than 1 and different from each other, and the n column bodies are arranged in descending order of the similarity ratio from the column body side of the target hole punch portion. The taper part consists of a part of a cone, such as a truncated cone and a truncated pyramid, and is sandwiched between the target hole punch part and the pilot hole punch part with the largest similarity ratio, and is perpendicular to the central axis. The sectional shape gradually changes from a sectional shape perpendicular to the side surface of the column of the target hole punch portion to a sectional shape perpendicular to the side surface of the column having the maximum similarity ratio of the pilot hole punch portion. The difference in diameter of the cross-sectional shape perpendicular to the side surface of the adjacent pilot hole punch column is 1 mm or less, and the column of the pilot hole punch unit is perpendicular to the side of the column having the largest similarity ratio. The difference between the diameter of the cross-sectional shape and the diameter of the cross-sectional shape perpendicular to the side surface of the target hole punch column is also 1 mm or less. The reason for “1 mm or less” is based on the fatigue test results shown in the examples described later. The column body is a cylinder or a prism. Using such punches for punching holes, the pilot holes are expanded one after another, and finally, if the taper part C is used to push the target holes, the fatigue strength and hydrogen cracking resistance of the punched end face can be reduced with a small diameter. Characteristics can be improved.

  An axial force fatigue test of the hole fatigue test piece 9 shown in FIG. 7 was performed using a punch 11 for punching holes to which the present invention shown in FIG. The punching hole 10 of the test piece 9 in FIG. 7 is a conventional example in which a punch having a radius of curvature of the cutting edge of 0 mm and a diameter of 10 mm is used as a comparative example in addition to the method to which the present invention is applied (Invention Examples 1 and 2). Processing using a one-step punching method (Comparative Example 1), and processing using the punch hole processing punch 11 shown in FIG. 4) was also performed. A 540 MPa class steel plate having a thickness of 1.6 mm was used as a workpiece. The punch 11 for punching holes to which the present invention is applied, for example, in the case of the present invention example 1, as shown in FIG. 6, the target hole punch part D, the taper part C, and the pilot hole punch part B , A is a punch for punching holes in which A is continuously integrated. The target hole punch portion D comprises a cylinder 11d (φ10.0 mm), and the pilot hole punch portions B and A have two columns 11b (φ9.5 mm × 1.8 mm), 11a (φ9.0 mm × 1. 8 mm). The two cylinders 11b and 11a are coaxially arranged on the center axis of the cylinder 11d of the target hole punch part D, and the tapered part C is formed of a cone 11c (height 1.2 mm). A cross-sectional shape sandwiched between the cylinder 11d of the hole punch portion D and the cylinder 11b of the pilot hole punch portion B is perpendicular to the side surface of the cylinder 11d of the target hole punch portion D (φ10 .0 mm) gradually changes to a cross-sectional shape (φ9.5 mm) perpendicular to the side surface of the cylinder 11b of the pilot hole punch portion B. After punching the pilot hole with the pilot hole punch part A and further punching the pilot hole with the pilot hole punch part B, the taper part C having a taper-shaped enlarged portion that becomes thicker to the diameter of the target hole is used. Hole processing was performed in contact with the workpiece and expanding the prepared hole to the target hole. The fatigue test condition was a load control fatigue test in which the stress ratio (= minimum load / maximum load) was 0, and was performed at room temperature and in the atmosphere. The life in which the control of the load becomes difficult was regarded as the rupture life, and the evaluation was performed in the stress range where the rupture life was 2 million times.

  Note that a common die was used for drilling holes in the example and the comparative example, and the die diameter was 10.3 (mm) where the clearance was 9.4% (0.15 mm) of the plate thickness in normal punching. Moreover, the stroke amount after a punch contacted the workpiece at the time of drilling was 6.6 mm. The difference in diameter between the pilot hole punch portion A and the pilot hole punch portion B and the difference in diameter between the pilot hole punch portion B and the target hole punch portion D are as shown in Table 1 below.

  The results of the fatigue test are shown in Table 1. The fatigue strength of the test piece drilled by applying the present invention is about 130 MPa, usually about 90 MPa by punching, and there is no seizure of the diameter expansion punch, and the effectiveness of the hole drilling method according to the present invention is confirmed. I was able to.

  Targeting round hole machining with a diameter of 10 mm, the punching hole punch 11 to which the present invention is applied as shown in FIG. For the hole fatigue test piece 12 shown in FIG. 8, the presence or absence of cracks in the processed cross section was measured in order to evaluate hydrogen cracking resistance. The presence / absence of cracks was measured for the entire perimeter of the punched holes after punching and left for 24 hours. The cracked cracks were designated as hydrogen cracking resistance x, and those without cracks were designated as hydrogen cracking resistance ○. The punching hole 13 of the test piece 12 in FIG. 8 is a normal 1 using a punch having a radius of curvature of the cutting edge of 0 mm and a diameter of 10 mm as a comparative example, in addition to the method to which the present invention is applied (Invention Examples 11 and 12). Processing by the step punching method (Comparative Example 11) and processing using the punch hole processing punch 11 shown in FIG. ) Also went. A steel plate having a size of 40 mm × 40 mm and a thickness of 540 MPa class 1.6 mm was used as a workpiece. The punch for punching holes to which the present invention is applied, for example, in the case of Example 11 of the present invention, as shown in FIG. 6, as shown in FIG. 6, the target hole punch portion D, the taper portion C, and the pilot hole punch portion B, This is a punch for punching holes in which A is continuously integrated. The target hole punch portion D comprises a cylinder 11d (φ10.0 mm), and the pilot hole punch portions B and A have two columns 11b (φ9.5 mm × 1.8 mm), 11a (φ9.0 mm × 1. 8 mm). The two cylinders 11b and 11a are coaxially arranged on the center axis of the cylinder 11d of the target hole punch part D, and the tapered part C is formed of a cone 11c (height 1.2 mm). The sectional shape perpendicular to the central axis is sandwiched between the cylinder 11d of the punch part D for punch D and the cylinder 11b of the punch part B for pilot hole, and the sectional shape perpendicular to the side surface of the cylinder 11d of the punch part D for target hole (φ10. 0 mm), and gradually changes to a cross-sectional shape (φ9.5 mm) perpendicular to the side surface of the cylinder 11 b of the pilot hole punch portion B. After punching a pilot hole with the pilot hole punch part A and further punching the pilot hole with the pilot hole punch part B, the taper part C having a taper-shaped diameter-expanded part that becomes thicker to the intended purpose is used for the workpiece. The hole processing which contacted and expanded a pilot hole to the said target hole was performed.

  Note that a common die was used for drilling holes in the example and the comparative example, and the die diameter was 10.3 (mm) where the clearance was 9.4% (0.15 mm) of the plate thickness in normal punching. Moreover, the stroke amount after a punch contacted the workpiece at the time of drilling was 6.6 mm. The difference in diameter between the pilot hole punch portion A and the pilot hole punch portion B and the difference in diameter between the pilot hole punch portion B and the target hole punch portion D are as shown in Table 2 below.

  The results of hydrogen cracking resistance are shown in Table 2. In the test piece subjected to the hole machining by applying the present invention, there was no seizure of the diameter expansion punch, and the effectiveness of the hole machining method according to the present invention could be confirmed.

  Targeting round hole machining with a diameter of 10 mm, the punching hole punch 11 to which the present invention is applied as shown in FIG. For the hole fatigue test piece 12 shown in FIG. 8, the presence or absence of cracks in the processed cross section was measured in order to evaluate hydrogen cracking resistance. The presence / absence of cracks was measured for the entire perimeter of the punched holes after punching and left for 24 hours. The cracked cracks were designated as hydrogen cracking resistance x, and those without cracks were designated as hydrogen cracking resistance ○. The punching hole 13 of the test piece 12 in FIG. 8 is a normal 1 using a punch having a radius of curvature of the cutting edge of 0 mm and a diameter of 10 mm as a comparative example in addition to the method to which the present invention is applied (Invention Examples 21 and 22). Processing by the step punching method (Comparative Example 21), and processing using the one in which the cross-sectional shapes of the pilot hole punch portions A and B for the punch for punching holes shown in FIG. 6 are changed (Comparative Examples 22 to 24) ) Also went. As a workpiece, an Al—Zn—Mg alloy having a size of 40 mm × 40 mm and a thickness of 500 MPa 1.6 mm was used. The punch 11 for punching holes to which the present invention is applied, for example, in the case of Example 21 of the present invention, as shown in FIG. 6, the target hole punch portion D, the taper portion C, and the pilot hole punch portion B. , A is a punch for punching holes in which A is continuously integrated. The target hole punch portion D comprises a cylinder 11d (φ10.0 mm), and the pilot hole punch portions B and A have two columns 11b (φ9.5 mm × 1.8 mm), 11a (φ9.0 mm × 1. 8 mm). The two cylinders 11b and 11a are coaxially arranged on the center axis of the cylinder 11d of the target hole punch part D, and the tapered part C is formed of a cone 11c (height 1.2 mm). The sectional shape perpendicular to the central axis is sandwiched between the cylinder 11d of the punch part D for punch D and the cylinder 11b of the punch part B for pilot hole, and the sectional shape perpendicular to the side surface of the cylinder 11d of the punch part D for target hole (φ10. 0 mm), and gradually changes to a cross-sectional shape (φ9.5 mm) perpendicular to the side surface of the cylinder 11 b of the pilot hole punch portion B. After punching a pilot hole with the pilot hole punch part A and further punching the pilot hole with the pilot hole punch part B, the taper part C having a taper-shaped diameter-expanded part that becomes thicker to the intended purpose is used for the workpiece. The hole processing which contacted and expanded a pilot hole to the said target hole was performed.

  Note that a common die was used for drilling holes in the example and the comparative example, and the die diameter was 10.3 (mm) where the clearance was 9.4% (0.15 mm) of the plate thickness in normal punching. Moreover, the stroke amount after a punch contacted the workpiece at the time of drilling was 6.6 mm. Further, the difference in diameter between the pilot hole punch portion A and the pilot hole punch portion B and the difference in diameter between the pilot hole punch portion B and the target hole punch portion D are as shown in Table 3 below.

  Table 3 shows the results of the resistance to hydrogen cracking. In the test piece subjected to the hole machining by applying the present invention, there was no seizure of the diameter expansion punch, and the effectiveness of the hole machining method according to the present invention could be confirmed.

  As mentioned above, although preferred embodiment of this invention was described referring an accompanying drawing, it cannot be overemphasized that this invention is not limited to this example. It will be apparent to those skilled in the art that various changes and modifications can be made within the scope of the claims, and these are naturally within the technical scope of the present invention. Understood.

DESCRIPTION OF SYMBOLS 1 Work material 2 Punch 3 Die 4 Droop 5 Shear surface 6 Fracture surface 7 Burr 8 Tapered punch 9 (Hole drilling) Test piece 10 Punching hole 11 Punching holes 11a, 11b, 11d Column 12 (Hole opening) Fatigue) Test piece 13 Punched holes A, B Punch part for pilot hole C Taper part D Punch part for target hole

Claims (5)

In punching holes for punching holes in workpieces that are punched with a punch and die, punching with the target hole punch, taper, and pilot hole punch integrated in one piece A punch for drilling holes,
The target hole punch portion comprises a pillar,
When n is a positive integer of 2 or more, the prepared hole punch portion includes n column bodies, and the n column bodies have a central axis on the central axis of the target hole punch portion column body. The cross-sectional shape perpendicular to the side surface of the columnar body is a similar shape in which the cross-sectional shape perpendicular to the side surface of the target hole punching column body is reduced toward the central axis. The similarity ratio of the cross-sectional shape perpendicular to the side surface of the n number of column bodies to the cross-sectional shape perpendicular to the side surface of the punch portion column body is smaller than 1 and different from each other. Arranged in descending order of the similarity ratio,
The tapered portion is formed of a part of a cone, and is sandwiched between a pillar body having the maximum similarity ratio of the target hole punch section and the pilot hole punch section, and has a cross-sectional shape perpendicular to the central axis. The cross-sectional shape perpendicular to the side surface of the target hole punch portion column body is gradually changing from the cross-sectional shape perpendicular to the side surface of the column body, the similarity ratio of the pilot hole punch portion,
The difference in diameter of the cross-sectional shape perpendicular to the side surface of the adjacent pilot hole punch column, and the diameter of the cross-sectional shape perpendicular to the side surface of the column body having the maximum similarity ratio among the pilot hole punch columns The punch for punching holes, wherein the difference between the diameter of the cross-sectional shape perpendicular to the side surface of the target hole punch column is 0.5 mm or more and 1 mm or less.   The punch for punching holes according to claim 1, wherein the column is a cylinder.   The punch for punching holes according to claim 1, wherein the column is a prism. A punching hole processing method for a workpiece using the punch for punching hole processing according to any one of claims 1 to 3,
With punched hole processing punch larger than the thickness of the n-number of column body each height the workpiece of the pilot hole punch unit,
After punching a pilot hole n times in the workpiece using a pilot hole punch portion in order from a column body having a small cross-sectional shape perpendicular to the side surface of the column body, the hole is expanded by the tapered portion, A punching hole processing method, wherein the diameter is a diameter of a target hole. 5. The punching method according to claim 4, wherein the material of the workpiece is iron or an Al—Zn—Mg-based alloy.

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