Countersinking method

Abstract

To provide a countersinking method capable of stably providing a desired countersinking shape without damaging the surface of a workpiece irrespective of the hardness of the workpiece.SOLUTION: This countersinking method for forming a countersinking shape having a countersinking surface of a prescribed angle on a sheet metal workpiece (W) comprises: a first step of forming a lower hole (W1); a second step of plastically deforming one opening edge of the lower hole (W1) by a first punch (62) having an inclined part (621) of a first countersinking angle (θ1) larger than a prescribed angle (α) to form a primary countersinking surface (W21) of the first countersinking angle (θ1); and a third step of plastically deforming the primary countersinking surface (W21) by a second punch (63) having an inclined part (631) of a prescribed angle (α) to form a secondary countersinking surface (W31) of a prescribed angle (α) having an aperture equal to that (φW21) of the primary countersinking surface (W21).SELECTED DRAWING: Figure 3A

Description

[Technical Field]

[0001] The present invention relates to a countersinking method. [Background technology]

[0002] A method of performing countersinking using a two-step punching process, consisting of a first step in which a pilot hole is formed and a second step in which the countersink is performed, is known, and is described as prior art in Patent Document 1. In this method, the pilot hole is formed in the first step to be larger than the final diameter, and when one side of the opening of the pilot hole is plastically deformed into a cone shape in the second step, part of the material is plastically flowed to reduce the inner diameter on the other side of the opening to the desired inner diameter.

[0003] However, in reality, most of the material that plastically flows in the second step escapes radially outward from the pilot hole, and only a small amount flows to reduce the inner diameter of the pilot hole. As a result, there are cases where the workpiece warps significantly due to distortion caused by the material escaping outward, while the pilot hole does not shrink, making it impossible to form the intended shape.

[0004] A technology that solves this problem is described in Patent Document 2. The technology described in Patent Document 2 involves providing an annular protrusion on the upper surface of the die used in the punching process in the second step, and causing the protrusion to dig into the underside of the workpiece in an annular shape during punching. This digging of the protrusion suppresses the amount of plastically flowing material that flows outward, while also increasing the amount that flows inward, which reduces the size of the pilot hole. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Unexamined Patent Publication No. 137529 / 1983 [Patent Document 2] Japanese Patent Application Laid-Open No. 2010-264474 Summary of the Invention [Problem to be solved by the invention]

[0006] However, the conventional technology described in Patent Document 2 leaves room for improvement in that when the workpiece is made of a hard material, the protrusions do not easily bite into the workpiece, making it difficult to obtain the desired effect, and annular marks are left on the lower surface of the workpiece. In other words, there is a need for a countersinking method that does not leave marks on the surface of the workpiece and that can stably obtain the desired countersink shape regardless of the hardness of the workpiece. [Means for solving the problem]

[0007] A first aspect of one or more embodiments is a countersinking method for forming a countersink shape having a countersink surface at a predetermined angle in a sheet metal workpiece, the method comprising: a first step of drilling a pilot hole in the workpiece; a second step of plastically deforming one opening edge of the pilot hole with a first punch having an inclined portion with a first countersink angle greater than the predetermined angle to form a primary countersink surface at the first countersink angle; and a third step of plastically deforming the primary countersink surface with a second punch having an inclined portion with the predetermined angle to form a secondary countersink surface at the predetermined angle and with an opening diameter the same as that of the primary countersink surface. The countersinking method includes the steps of:

[0008] A second aspect of one or more embodiments is a countersinking method for forming a countersink shape with a countersink surface angle of α in a sheet metal workpiece, the method comprising: a first step of forming a pilot hole in the workpiece using n punches (n is a desired integer greater than or equal to 2) such that the kth countersink angle of the kth punch (k is an integer between 1 and k and n) decreases as k increases; a second step of plastically deforming one opening edge of the pilot hole with the first punch to form a primary countersink surface with the first countersink angle; and a kth step of machining in ascending order from k=2 to k=n to form a countersink shape with an nth countersink surface with a countersink angle of α and an opening diameter the same as the opening diameter of the primary countersink surface. [Effects of the Invention]

[0009] According to the countersinking method of one or more embodiments of the present invention, the surface of the workpiece is not marked, and the desired countersink shape can be stably obtained regardless of the hardness of the workpiece. [Brief explanation of the drawings]

[0010] [Figure 1] FIG. 1 is a cross-sectional view illustrating a first step of a countersinking method according to one embodiment of the present invention. [Figure 2A] FIG. 2A is a cross-sectional view illustrating a second step of the countersinking method according to one embodiment. [Figure 2B] FIG. 2B is a cross-sectional view illustrating the plastic flow in the second step. [Figure 3A] FIG. 3A is a cross-sectional view illustrating a third step of the countersinking method according to one embodiment. [Figure 3B] FIG. 3B is a cross-sectional view illustrating the plastic flow in the third step. [Figure 4A] FIG. 4A is a cross-sectional view showing a first embodiment of a die set that can be used in one embodiment of the countersinking method. [Figure 4B] FIG. 4B is a cross-sectional view showing a second embodiment of a die set that can be used in one embodiment of the countersinking method. [Figure 5] FIG. 5 is a flow chart showing the steps of one embodiment of a countersinking method. [Figure 6] FIG. 6 is a flow diagram illustrating a generalized procedure for one embodiment of a countersinking method. DETAILED DESCRIPTION OF THE INVENTION

[0011] A countersinking method according to one embodiment of the present invention will be described with reference to FIGS. 1 to 5. FIG. 1 is a cross-sectional view illustrating a first step of the countersinking method according to one embodiment of the present invention. FIG. 2A is a cross-sectional view illustrating a second step of the countersinking method according to one embodiment of the present invention. FIG. 2B is a cross-sectional view illustrating plastic flow in the second step. FIG. 3A is a cross-sectional view illustrating a third step of the countersinking method according to one embodiment of the present invention. FIG. 3B is a cross-sectional view illustrating plastic flow in the third step. FIG. 4A is a cross-sectional view illustrating a first embodiment of a die set that can be used in the countersinking method according to one embodiment of the present invention. FIG. 4B is a cross-sectional view illustrating a first embodiment of a die set that can be used in the countersinking method according to one embodiment of the present invention. FIG. 5 is a flow chart illustrating the steps of the countersinking method according to one embodiment of the present invention.

[0012] In one embodiment of the countersinking method of the present invention, a sheet metal workpiece W is countersunk in three steps, steps 1 to 3. The workpiece W is, for example, a cold-rolled steel plate (SPC) sheet metal with a thickness Wt of 1.0 mm. As a prerequisite, the angle of the slope of the conical countersink shape (countersink angle θ2 in FIG. 3A) is defined as angle α. Here, angle α is set to 90°, corresponding to the cross recess countersunk head connector machine screw specified in JIS B1111 (2017). As an example of a machine screw applicable to the countersunk shape, a machine screw with a nominal diameter of M3 will be described.

[0013] As shown in Figures 1 and 5, the first step (S1) is a pilot hole forming step in which a pilot hole W1 with an inner diameter φW1 is formed in the workpiece W. A well-known punching process can be used to form the pilot hole W1. Of course, the method is not limited to punching, and laser processing may also be used. The inner diameter φW1 is, for example, φ4.4 mm.

[0014] After the pilot hole W1 is formed, the second step is carried out. The mold used in the second step is, for example, a set of a die KD and a punch KP shown in Fig. 4A. The die KD and the punch KP are mounted, for example, on a punch press (not shown) and used for punching.

[0015] The punch die KP includes a punch guide 61 and a punch 62. The punch 62 is hereinafter also referred to as the first punch 62. The punch 62 has a cylindrical base 620 centered on an axis CL62, and the lower end of the base 620 is tapered into a truncated cone shape by an inclined portion 621. In the punch 62, a countersink angle θ1, which is the inclination angle of the inclined portion 621 about the axis CL62, is larger than a predetermined angle α. Hereinafter, the countersink angle θ1 is also referred to as the first countersink angle θ1. The outer diameter of the base 620 is larger than the opening diameter φW21 of the first countersink surface W21 formed by the countersinking process. The countersink angle θ1 is, for example, 120° larger than the angle α, and the opening diameter φW21 is φ6.0 mm, corresponding to a machine screw with a nominal diameter of M3.

[0016] The punch guide 61 has a lower surface 61a that comes into contact with the upper surface of the workpiece W. A through hole 61b is formed in the lower surface 61a and is centered on an axis CL62 that extends vertically, and supports the punch 62 so that it can move up and down with almost no play.

[0017] The die tool KD includes a die 51 having a flat upper surface 51a that faces the underside of the workpiece W. A relief hole 51b is formed in the upper surface 51a as a through-hole whose axis is an axis CL51 that extends in the vertical direction. The relief hole 51b is formed so as not to interfere with the tip of the punch 62 that descends during countersinking.

[0018] For the punching processes in the second and third steps, a die mold KDA may be used instead of the die mold KD, as shown in FIG. 4B. The die mold KDA has a die 52 instead of the die 51. The die 52 has a flat upper surface 52a that faces the underside of the workpiece W. A mortar-shaped recess 52b is formed on the upper surface 52a, with an axis Cl52 extending in the vertical direction as its axis. The inner surface of the recess 52b has an inclined surface 52c that faces and abuts against the inclined portion 621 of the punch 62 at the lowest position of the punch 62 as it descends at a predetermined stroke.

[0019] Due to the above-described configuration, the die 52 does not have the relief hole 51b, which is a through hole that the die 51 has. Therefore, the die 52 is strong and has sufficient resistance to the high pressing force received from the punch 62. In order to obtain high strength, the die 52 is formed with a recess 52b instead of the relief hole 51b of a through hole. The recess 52b has an inclined surface 52c shaped to come into face-to-face contact with the inclined portion 621 of the punch 62. Therefore, local stress is unlikely to occur in the recess 52b, and defects such as chipping of the opening edge of the recess 52b are unlikely to occur.

[0020] The punch tool KP and die tool KD are configured to perform punching with their axes CL51 and CL61 aligned. In the second step, the axis CL1 of the pilot hole W1 in the workpiece W is aligned with the axis CL51 and the axis CL61, and the punch 62 is lowered by a predetermined stroke by the operation of a drive unit (not shown) of the punch press. This performs countersinking, which causes a predetermined plastic deformation in the pilot hole W1. Figure 2B shows the state when the punch 62 has risen slightly after countersinking.

[0021] The countersinking process in the second step forms the primary countersink shape shown in Figures 2A and 2B. The primary countersink shape has a conical primary countersink surface W21 and a secondary pilot hole W22. Specifically, the upper portion of the pilot hole W1 forms the primary countersink surface W21, which is a cone-shaped inclined surface at a countersinking angle θ1, and the lower portion of the pilot hole W1 forms the secondary pilot hole W22, which has an inner diameter φW22 reduced from the inner diameter φW1. As mentioned above, the inner diameter φW1 is φ4.4 mm, and the inner diameter φW22 is, for example, φ4.17 mm. Details of this transformation are described below with reference to Figure 2B.

[0022] Figure 2B is a cross-sectional view, but the hatching of the cross-sectional area has been hidden to simplify the drawing. The dotted areas represent areas where thickness has increased or decreased due to plastic flow. Specifically, these are the annular plastically deformed area M1 where thickness has decreased, and the annular plastically deformed area M2 where thickness has increased.

[0023] In FIG. 2B, the outline of the pilot hole W1 after the first step before countersinking is shown by a dashed line.

[0024] 5, the punch 62 descends by a predetermined stroke. The lower end position of the predetermined stroke is the position where the inclined portion 621 of the punch 62 interferes with the edge of the pilot hole W1, and the maximum diameter thereof becomes the opening diameter φW21.

[0025] As a result, as shown in Figure 2B, the plastically deformed portion M1, which is a ring-shaped portion with a triangular cross section between the pilot hole W1 (dash-dotted line) and the first countersink surface W21, interferes with the punch 62 and is plastically deformed and reduced in thickness. Part of the plastically deformed portion M1 escapes radially outward from the workpiece W as shown by arrow DR1 in Figure 2B, while the remainder plastically flows downward as shown by arrow DR2. The material that moves downward becomes the plastically deformed portion M2, which is thickened by reducing the diameter of the pilot hole W1 to a range below the pilot hole W1 that does not interfere with the punch 62.

[0026] Here, because the countersink angle θ1 of the inclined portion 621 of the punch 62 is larger than the normal countersink angle α, the downward component of the force applied from the punch 62 to the plastically deformed portion M1 is greater than the horizontal component directed radially outward. In other words, the direction of plastic flow is primarily downward rather than radially outward. Therefore, warping of the workpiece W due to the plastic flow directed radially outward during the second process is unlikely to occur, while the thickness of the pilot hole W1 in the narrowing direction is stably increased.

[0027] After the second process is performed to form the first countersink shape, the third process, countersinking, is performed as shown in (S3) of FIG. 5. The third process, countersinking, forms the second countersink shape shown in FIGS. 3A and 3B. The second countersink shape has only a conical second countersink surface W31. A punch 63, shown in FIG. 3A, is used for the third process. Hereinafter, the punch 63 will also be referred to as the second punch 63. The punch 63 has a cylindrical base 630, the lower end of which is formed into a truncated cone shape with a tapered diameter at the bottom by a sloped portion 631. The sloped portion 631 has a countersink angle θ2, which is the inclination angle range of the sloped portion 631 about the axis CL63, equal to a predetermined angle α. The outer diameter of the base 630 is larger than the opening diameter φ311 of the second countersink surface W31 formed in the third countersink process. The lower limit position of the downward stroke of the punch 63 is set so that the opening diameter φ311 is the same as the opening diameter φW21. That is, for example, the countersinking angle θ2 is set to 90°, and the opening diameter φ311 is set to φ6.0 mm, the same as the opening diameter φW21.

[0028] When the thickness Wt of the workpiece W is 1.0 mm, the punch 63 interferes with the punch 63 from the upper surface Wa of the secondary pilot hole W22 down to 0.92 mm below the lower limit of its downward stroke, while the remaining 0.08 mm is non-interfering. Therefore, as shown in Figure 3B, the thinned portion is the annular plastically deformed portion M3 with a narrow triangular cross section between the primary countersink surface W21 and the secondary countersink surface W31. That is, part of the plastically deformed portion M3 plastically flows radially outward in a ring-like shape as indicated by arrow DR3, while the remaining portion flows downward as indicated by arrow DR4. The portion that no longer interferes with the punch 63 increases in thickness in the radial direction, forming the plastically deformed portion M4. The plastically deformed portion M4 is a portion that freely reduces in diameter and increases in thickness without interfering with the punch 63. The axial length of the plastically deformed portion M4 is in the short range of about 0.08 mm as described above, and the inner diameter φ312 is reduced from φ4.17 mm to, for example, about φ4.0 mm due to the increased thickness.

[0029] The plastically deformed portion M3 that is thinned by the second countersinking process has a countersinking angle θ2 of angle α, but its volume is sufficiently smaller than that of the plastically deformed portion M1 that is thinned by the first countersinking process, so the effect of the radially outward plastic flow of the plastically deformed portion M3 on the warping of the workpiece W is so small that it can be practically ignored.

[0030] As described above, according to the countersinking method of one embodiment of the present invention, the surface of the workpiece W is not scratched, and the plastic flow generated by the countersinking is divided into a primary countersinking and a secondary countersinking, gradually plastically deforming the workpiece W into a desired shape. This makes it difficult for the workpiece W to warp, and no protrusions are required to dig into the underside of the workpiece W to induce plastic flow. Therefore, the desired countersink shape can be stably formed on the workpiece W regardless of the hardness of the workpiece W.

[0031] One aspect of one or more embodiments of the present invention is not limited to the configurations described above, and may be modified without departing from the spirit of the present invention.

[0032] The number of times countersinking is performed after drilling the pilot holes is not limited to two times (second and third steps) as described above, but may be three or more times as shown in Fig. 6. In this case, the punch used in each step is designed so that the countersinking angle gradually decreases with each step.

[0033] In other words, if the number of times the countersinking process is performed is n (n is an integer greater than or equal to 3) and k is an integer between 1 and 1, then the countersinking angle θk of the kth punch Pk used in the kth process is set so that k is greater than or equal to 2 and the countersinking angle θk is less than the countersinking angle θ(k-1).

[0034] In this case, as shown in Figure 6, the countersinking procedure is as follows: first, a pilot hole W1 is formed (S21). Next, k is set to 1 (S22), and countersinking is performed with the kth punch Pk (S23). Next, k is set to k + 1 (S24), and it is determined whether k is equal to n (S25). If not (No), the process returns to (S23). If yes (Yes), countersinking is performed with the nth punch Pn (S26), and the countersinking ends.

[0035] In this way, the countersinking process of one embodiment of the present invention may be performed multiple times by changing the punch so that the countersinking angle θk gradually decreases toward the predetermined angle α with each iteration. This suppresses the amount of plastic flow each time and allows the workpiece W to be plastically deformed little by little into the desired shape, thereby further reducing warping of the workpiece W and enabling the desired countersink shape to be obtained stably and accurately without leaving any marks on the workpiece W.

[0036] The relationship between the punch KP and the die that form the countersink shape may be reversed. That is, for example, the primary countersink surface W21 may be formed on the lower side of FIG. 2A.

[0037] As described above in detail, a first aspect of one or more embodiments of the present invention is a countersinking method for forming a countersink shape having a countersink surface of a predetermined angle in a sheet metal workpiece W, the countersinking method including: a first step of drilling a pilot hole W1 in the workpiece W; a second step of plastically deforming one opening edge of the pilot hole W1 with a first punch 62 having an inclined portion 621 with a first countersink angle θ1 larger than the predetermined angle α to form a primary countersink surface W21 with the first countersink angle θ1; and a third step of plastically deforming the primary countersink surface W21 with a second punch 63 having an inclined portion 631 with the predetermined angle α to form a secondary countersink surface W31 with the predetermined angle α and an opening diameter φW21 equal to the opening diameter φW21 of the primary countersink surface W21.

[0038] This causes the direction of the plastic flow generated in the first step to be directed downward rather than radially outward, thereby suppressing warping of the workpiece W and stably reducing the diameter and increasing the thickness of the pilot hole W1.

[0039] A second aspect of one or more embodiments of the present invention is a countersinking method for forming a countersink shape with a countersink surface angle α in a sheet metal workpiece W, comprising the following steps: a first step of forming a pilot hole W1 in the workpiece W using n punches (n is a desired integer greater than or equal to 2) such that the kth countersink angle θk of the kth punch Pk (k is an integer between 1 and k and n) decreases as k increases; a second step of plastically deforming one opening edge of the pilot hole W1 with a first punch 62 to form a primary countersink surface W21 with a first countersink angle θ1; and a kth step of machining in ascending order from k=2 to k=n to form a countersink shape with an nth countersink surface with a countersink angle α and an opening diameter φW21 equal to the opening diameter φW21 of the primary countersink surface W21.

[0040] This reduces the amount of plastic deformation that occurs in one countersinking process, thereby further suppressing warping of the workpiece W.

[0041] In addition, the first and second modes may be modified so that the inner diameter φW1 of the prepared hole W1 is reduced by plastic deformation in the second step.

[0042] As a result, when the thickness of the workpiece W is large, the inner diameter φW1 of the pilot hole W1 is stably increased, and a countersink shape having a pilot hole with the desired inner diameter can be obtained. [Explanation of symbols]

[0043] 51,52 Die 51a,52a Top surface 51b Relief hole 52b Recess 52c slope 61 Punch guide 61a Bottom surface 61b Through hole 62,63 Punch 620,630 base 621,631 Slope CL1, CL62, CL51, CL52, CL63 Axis KD, KDA die mold KP punch die M1,M2,M3,M4 Plastic deformation part double work Wa top surface Wt Thickness W1 pilot hole W21 1st countersink surface W22 Secondary pilot hole W31 Second countersink surface θ1,θ2 Countersinking angles φW1, φW22, φ312 Inner diameter φW21, φ311 Opening diameter α angle

Claims

1. In a countersinking method for forming a countersink shape having a countersink surface at a predetermined angle on a sheet metal workpiece, a first step of forming a pilot hole in the workpiece; a second step of plastically deforming one opening edge of the pilot hole with a first punch having an inclined portion with a first countersink angle greater than the predetermined angle to form a first countersink surface with the first countersink angle; a third step of plastically deforming the first countersink surface with a second punch having an inclined portion at the predetermined angle to form a second countersink surface at the predetermined angle and having an opening diameter equal to the opening diameter of the first countersink surface; A countersink processing method including:

2. In a countersinking method for forming a countersink shape with a countersinking surface angle α on a sheet metal workpiece, n punches (n is a desired integer of 2 or more) are arranged such that the kth countersink angle of the kth punch (k is an integer of 1≦k≦n) becomes smaller as k becomes larger, a first step of forming a pilot hole in the workpiece; a second step of plastically deforming one opening edge of the prepared hole with a first punch to form a first countersink surface having a first countersink angle; Then, in the kth process, processing is performed in ascending order from k=2 to k=n, and by the nth process, a countersink shape is formed having an nth countersink surface with an opening diameter equal to the opening diameter of the first countersink surface and a countersink angle of angle α.

3. 3. The countersinking method according to claim 1, wherein the inner diameter of the pilot hole is reduced by plastic deformation in the second step.

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