Drilling method

Abstract

To provide a drilling method which can easily form a hole whose diameter is a board thickness of a work-piece or less.SOLUTION: A drilling method comprises the steps of: forming a prepared hole 20 in a tabular work-piece W; forming a rear side counterbore part 23 at a formation part of the prepared hole 20 from the lower side of the work-piece W; and forming, after forming the rear side counterbore part 23, a punch hole 24 in the formation part of the prepared hole 20 from an upper side of the work-piece W.SELECTED DRAWING: Figure 3

Description

[Technical Field]

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

[0002] Conventionally, there are processing methods for drilling holes in plate-shaped workpieces such as metal plates. Patent Document 1 discloses a processing method in which a pilot hole is drilled in the plate material as the workpiece, and then the portion of the plate material where the pilot hole is to be formed is punched from above using a punching process, thereby forming a small hole with a diameter equal to or smaller than the thickness of the plate material. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Publication No. 9-216021 Summary of the Invention [Problem to be solved by the invention]

[0004] In the processing method disclosed in Patent Document 1, the plate material in which the small holes are formed is SPHC (hot-rolled mild steel plate) with a thickness of 4.5 mm. However, when attempting to form holes having a diameter equal to or less than the plate thickness using the processing method disclosed in Patent Document 1 in, for example, a thick stainless steel plate, which has higher shear strength than SPHC, it is difficult to form the holes in the desired shape. Therefore, when forming holes having a diameter equal to or less than the plate thickness in a thick stainless steel plate, it is expected that the work will be done manually by an operator using, for example, a drill press, which raises concerns about an increase in labor hours. [Means for solving the problem]

[0005] A drilling method according to one aspect of the present invention includes the steps of: forming a pilot hole in a plate-shaped workpiece; forming a cylindrical backside counterbore portion from below the workpiece at a portion where the pilot hole is to be formed; and, after forming the backside counterbore portion, forming a punch hole from above the workpiece at the portion where the pilot hole is to be formed. a processing length of the punch hole is equal to or smaller than a punch diameter of the punch hole, the punch hole is formed by a first punch assembly and a first die assembly sandwiching the workpiece vertically, and a first punch tip included in the first punch assembly punching out a portion where the pilot hole is to be formed downward, and the opening diameter of a first die hole included in the first die assembly and opening toward the first punch assembly is larger than the counterbore diameter of the backside counterbore portion. .

[0006] In the above-described drilling method, a backside counterbore is formed in the portion where the pilot hole is to be formed before the punch hole is formed, so the portion where the punch hole is to be formed is already thinner than the plate thickness of the workpiece. For example, even if the workpiece is a thick plate made of stainless steel, punch holes with a punch diameter equal to or smaller than the plate thickness can be automatically formed by using a die such as a punching die. Furthermore, because the backside counterbore is formed from below the workpiece in the portion where the pilot hole is to be formed, there is no need to turn the workpiece over for each processing step, for example, taking into account the surface on which the attachment object will later be fixed to the workpiece. [Effects of the Invention]

[0007] According to one aspect of the present invention, it is possible to provide a drilling method that can easily form a hole having a diameter equal to or smaller than the plate thickness of a workpiece. [Brief explanation of the drawings]

[0008] [Figure 1] FIG. 1 is a diagram illustrating a process of forming a pilot hole 20 in a workpiece W. As shown in FIG. [Figure 2] FIG. 2 is a diagram for explaining a process of forming a backside counterbore 23 from below the workpiece W at the portion where the pilot hole 20 is to be formed. [Figure 3] FIG. 3 is a diagram for explaining the process of forming punch holes 24 from above the workpiece W in the portions where pilot holes 20 are to be formed. [Figure 4] FIG. 4 is a diagram for explaining the process of forming the tapped hole 25 from above the workpiece W in the portion where the punched hole 24 is to be formed. [Figure 5] FIG. 5 is a diagram for explaining a process of forming the front counterbore portion 26 from above the workpiece W in the portion where the pilot hole 20 is to be formed. [Figure 6] FIG. 6 is a diagram for explaining a process of forming a backside counterbore portion 27 from below the workpiece W in the portion where the pilot hole 20 is to be formed. [Figure 7] FIG. 7 is a diagram for explaining the process of forming punch holes 28 in the portions where the pilot holes 20 are to be formed. [Figure 8]FIG. 8 is a diagram for explaining the process of forming tapped holes 29 from above the workpiece W in the portions where punched holes 28 are to be formed. [Figure 9] FIG. 9 is a diagram for explaining a process of forming a front-side counterbore portion 26 from above the workpiece W and simultaneously forming a back-side counterbore portion 27 from below the workpiece W in the portion where the pilot hole 20 is to be formed. DETAILED DESCRIPTION OF THE INVENTION

[0009] Hereinafter, a drilling method according to an embodiment of the present invention will be described in detail with reference to the drawings. In the description of the drawings, the same parts are given the same reference numerals and the description will be omitted. In addition, in the following description, the expressions "upward" or "downward" or "vertical direction" will be used. Here, the vertical direction corresponds to the vertical direction, but there may be cases where a slight inclination from the vertical direction is acceptable.

[0010] First Embodiment 1 to 4 are schematic cross-sectional views showing steps of a drilling method according to a first embodiment. The drilling method according to this embodiment is a method for forming punched holes or tapped holes in a plate-shaped workpiece W. The workpiece W assumed in this embodiment is a thick metal plate. The material of the workpiece W may be, for example, a stainless steel plate such as SUS304 specified in the Japanese Industrial Standards (JIS G 4304, etc.). Furthermore, the "thick plate" in this embodiment is assumed to be a plate having a thickness t in the range of approximately 3 mm to 6 mm. However, the thickness of the workpiece W may be smaller or larger than the range presented above.

[0011] The drilling method according to this embodiment includes the steps of forming pilot holes 20 in a plate-shaped workpiece W, and forming backside counterbore portions 23 from below the workpiece W in the portions where the pilot holes 20 are to be formed. The drilling method also includes the step of, after forming the backside counterbore portions 23, forming punch holes 24 from above the workpiece W in the portions where the pilot holes 20 are to be formed. The drilling method may further include the step of, after forming the punch holes 24, forming tapped holes 25 from above the workpiece W in the portions where the punched holes 24 are to be formed. Hereinafter, this embodiment will be described by way of example, with reference to a case where tapped holes for M4 screws are finally formed in a stainless steel plate having a plate thickness t of 6 mm.

[0012] 1 is a diagram for explaining a process of forming a pilot hole 20 in a workpiece W. Hereinafter, the process of forming the pilot hole 20 will be referred to as a "pilot hole processing process." In the pilot hole processing process, the pilot hole 20 is formed using, for example, a laser processing machine 1.

[0013] The laser processing machine 1 irradiates a processing portion with a laser beam Ls generated by a laser oscillator (not shown) via a laser processing head. In Fig. 1, part of the laser processing head of the laser processing machine 1 is depicted.

[0014] The workpiece W is placed on, for example, a work table 2 on which a dust collection duct 2a is formed. The workpiece W is placed on a placement surface 2b of the work table 2, which is a horizontal surface. That is, in the pilot hole drilling process, the plate-shaped workpiece W is placed flat along a generally horizontal surface. Here, of the main planes of the workpiece W, the main plane facing upward is the front surface 21, and the main plane facing downward is the back surface 22. In this case, the back surface 22 of the workpiece W comes into contact with the placement surface 2b of the work table 2. The dust collection duct 2a is arranged so as to be located below the portion of the workpiece W where the pilot hole 20 is formed.

[0015] The laser processing machine 1 can form a pilot hole 20 that penetrates the workpiece W from the front surface 21 to the back surface 22 by irradiating the workpiece W with a laser beam Ls from above toward the front surface 21. Molten material and fumes generated by the irradiation of the laser beam Ls are collected by the dust collection duct 2a, but residual material (dross) may remain near the pilot hole on the underside of the workpiece W. Note that in the following figures, the pilot hole diameter d1 of the pilot hole 20 is assumed to be constant throughout the entire pilot hole 20. However, depending on the structure of the laser processing machine 1, the pilot hole diameter d1 may gradually decrease from the front surface 21 toward the back surface 22. The pilot hole diameter d1 can be calculated backward from the punch diameter of the punch hole 24 for tapping an M4 screw. For example, if the punch diameter is set to 3.4 mm, the pilot hole diameter d1 may be set to 3.0 mm, which is the punch diameter minus 0.4 mm.

[0016] 2 to 9 are performed by a punch press machine equipped with a burring die, a punching die, a tapping die, or a plurality of other dies, or a punch laser combined machine equipped with a laser processing machine and a punch processing machine in one. Since the configuration of a punch press machine or the like is well known, a description thereof will be omitted below.

[0017] FIG. 2 is a diagram illustrating a process of forming a backside counterbore portion 23 from below the workpiece W in the portion where the pilot hole 20 is to be formed. Hereinafter, the process of forming the backside counterbore portion 23 will be referred to as the "counterbore processing process." FIG. 2(a) is a diagram illustrating the state in the vicinity of the portion where the pilot hole 20 is to be formed during the counterbore processing process. FIG. 2(b) is a cross-sectional view of the workpiece W in which the backside counterbore portion 23 has been formed. The counterbore processing process is performed after the pilot hole processing process. In the counterbore processing process, the backside counterbore portion 23 is formed using, for example, a burring die 3.

[0018] The burring die 3 includes a die assembly 4 (third die assembly) and a punch assembly 5 (third punch assembly). The die assembly 4 and the punch assembly 5 face each other in the vertical direction, sandwiching the workpiece W therebetween. The die assembly 4 is disposed on the back surface 22 side of the workpiece W. The punch assembly 5 is disposed on the front surface 21 side of the workpiece W. The die assembly 4 includes, for example, an ejector plate 4a and a die tip 4c. The ejector plate 4a is an annular member that receives upward elastic force from a spring (not shown) and moves within a certain range in the vertical direction. However, the ejector plate 4a may be configured to be fixed in a predetermined position and support the workpiece W without moving in the vertical direction. The ejector plate 4a has a die hole 4b as a through hole through which the die tip 4c passes in the vertical direction without contacting it, and a die-side pressing surface 4d that contacts the back surface 22 of the workpiece W. During the countersinking process, the ejector plate 4a presses and supports the workpiece W from below. The die tip 4c is a columnar member that moves within a certain range in the vertical direction upon receiving an upward elastic force from a spring (not shown), and is a forming part that forms the backside counterbore portion 23. On the other hand, the punch assembly 5 includes, for example, a punch body 5a having a punch-side pressing surface 5b that contacts the surface 21 of the workpiece W. The punch body 5a presses the workpiece W from above downward. In this embodiment, the entire punch-side pressing surface 5b is flat. In other words, the punch body 5a, including the portion facing the die tip 4c, contacts the workpiece W on a flat surface. Note that an assembly that forms a hole or burring in the workpiece W from below upward, such as the die assembly 4, is sometimes called an upward burring die.

[0019] The burring die 3 can form the backside counterbore portion 23 by having the die tip 4c included in the die assembly 4 strike the portion where the pilot hole 20 is to be formed upward while the die assembly 4 and the punch assembly 5 sandwich the workpiece W vertically. While a typical burring die is used to form burring in a pilot hole, the burring die 3 used in this embodiment does not form burring. The counterbore diameter d2 of the backside counterbore portion 23 is set to be larger than the punch diameter of the punch hole 24 (see FIG. 3 ) that is adapted to tapping for an M4 screw. For example, when the punch diameter is set to 3.4 mm, the counterbore diameter d2 is larger than 3.4 mm. The counterbore depth dp1 of the backside counterbore portion 23 may be, for example, 2.0 to 3.0 mm, which corresponds to approximately three pitches of the M4 screw.

[0020] FIG. 3 is a diagram illustrating the process of forming punch holes 24 in the areas where pilot holes 20 are to be formed. Hereinafter, the process of forming punch holes 24 will be referred to as the "punch hole processing process." FIG. 3(a) is a diagram illustrating the state near the areas where punch holes 24 are to be formed during the punch hole processing process. FIG. 3(b) is a cross-sectional view of the workpiece W in which punch holes 24 have been formed. The punch hole processing process is performed after the countersink processing process. In the punch hole processing process, punch holes 24 are formed using, for example, a punching die 6.

[0021] The punching die 6 includes a punch assembly 7 (first punch assembly) and a die assembly 8 (first die assembly). The punch assembly 7 and the die assembly 8 face each other in the vertical direction, sandwiching the workpiece W therebetween. The punch assembly 7 is disposed on the front surface 21 side of the workpiece W. The die assembly 8 is disposed on the back surface 22 side of the workpiece W. The punch assembly 7 includes, for example, a punch body 7a and a punch tip 7c. The punch body 7a is a cylindrical member that moves within a certain range in the vertical direction upon receiving downward elastic force from an elastic member (not shown). The punch body 7a has a body hole 7b as a through hole that allows the punch tip 7c to pass through in the vertical direction without contacting it, and a punch-side pressing surface 7d that comes into contact with the front surface 21 of the workpiece W. During the punch hole processing process, the punch body 7a presses the workpiece W from above downward. The punch tip 7c is a columnar member that moves within a certain range in the vertical direction when subjected to downward resilience from a resilient device (not shown) and serves as a forming section for forming the punch holes 24. Meanwhile, the die assembly 8 includes, for example, an ejector plate 8a. The ejector plate 8a is an annular member that moves within a certain range in the vertical direction when subjected to upward resilience from a resilient device (not shown). However, the ejector plate 8a may be configured to support the workpiece W by being fixed in a predetermined position without moving vertically. The ejector plate 8a has a die hole 8b (first die hole) as a through hole through which the punch tip 7c, which has penetrated the workpiece W from the punch assembly 7, passes vertically without contacting the workpiece W, and a die-side pressing surface 8c that contacts the back surface 22 of the workpiece W. During the punch hole processing process, the ejector plate 8a presses and supports the workpiece W from below. A die that forms through holes in a thick plate workpiece W, such as the punching die 6, is sometimes called a thick plate punch-piercing die.

[0022] The punching die 6 can form the punch hole 24 by punching the portion where the pilot hole 20 is to be formed downward with the punch assembly 7 and the die assembly 8 sandwiching the workpiece W vertically. The punch diameter d3 of the punch hole 24 is set to a dimension suited to tapping for an M4 screw, e.g., 3.4 mm, as described above. The processing length L1 of the punch hole 24, which is the axial length of the punch hole 24, corresponds to the thickness t of the workpiece W minus the counterbore depth dp1. When the workpiece W is a thick stainless steel plate, as in this embodiment, the processing length L1 of the punch hole 24 is preferably smaller than or equal to the punch diameter d3. That is, in this embodiment, the processing length L1 of the punch hole 24 is approximately 3 mm. The die hole 8b of the die assembly 8 is a cylindrical space whose axial direction is the vertical direction and is continuous with the die-side pressing surface 8c and opens toward the punch assembly 7. As shown in FIG. 3(a), the opening diameter d4 of the die hole 8b is larger than the counterbore diameter d2 of the backside counterbore portion .

[0023] FIG. 4 is a diagram illustrating a process of forming a tapped hole 25 from above the workpiece W in the portion where the punched hole 24 is to be formed. Hereinafter, the process of forming the tapped hole 25 will be referred to as the "tapping process." FIG. 4(a) is a diagram illustrating the state of the vicinity of the portion where the tapped hole 25 is to be formed during the tapping process. FIG. 4(b) is a cross-sectional view of the workpiece W in which the tapped hole 25 has been formed. The tapping process is performed after the punched hole processing process. In the tapping process, the tapped hole 25 is formed using, for example, a tapping die 9.

[0024] The tapping die 9 includes a punch assembly 10 and a die assembly 11. The punch assembly 10 and the die assembly 11 face each other in the vertical direction, sandwiching the workpiece W therebetween. The punch assembly 10 is disposed on the front surface 21 side of the workpiece W. The die assembly 11 is disposed on the back surface 22 side of the workpiece W. The punch assembly 10 includes, for example, an end ring 10a and a tap 10c. The end ring 10a is a cylindrical member that covers the outer peripheral region of the tap 10c. The end ring 10a has an inner flange 10b as a through-hole that allows the tap 10c to pass through in the vertical direction without contact. The tap 10c is a columnar member that moves within a certain range in the vertical direction when subjected to downward elastic force from a spring (not shown) and rotates around its axis when subjected to rotational force from a rotation mechanism (not shown). This tap 10c is a forming portion that forms the tapped hole 25. A threaded portion matching the shape of the tapped hole 25 is pre-formed in the tap 10c. On the other hand, the die assembly 11 includes a die body 11a, which is, for example, an annular member. The die body 11a has a die hole 11b as a through hole through which the tap 10c, which has been passed through the workpiece W from the punch assembly 10, passes in the vertical direction without contacting the workpiece W, and a contact surface 11c that comes into contact with the back surface 22 of the workpiece W. Note that FIG. 4 shows a state in which the end ring 10a is not in contact with the surface of the workpiece W. However, the end ring 10a may press and support the surface of the workpiece W while the tapped hole is being machined with the tap 10c. By pressing and supporting the surface of the workpiece W with the end ring 10a, it is possible to prevent the workpiece W from moving up and down during tapping.

[0025] With the workpiece W placed on the die assembly 11, the tapping die 9 can form the tapped hole 25 by gradually threading the portion where the punch hole 24 is to be formed downward with the tap 10c included in the punch assembly 10. In this embodiment, the tap 10c compatible with tapping for M4 screws is used, so that the tapped hole 25 compatible with fastening the M4 screw is formed in the portion where the punch hole 24 was formed. Furthermore, the processing length L2, which is the axial length of the tapped hole 25, corresponds to the length obtained by subtracting the counterbore depth dp1 from the plate thickness t of the workpiece W. That is, in this embodiment, the processing length L2 of the tapped hole 25 is the same as the processing length L1 of the punch hole 24.

[0026] In this way, by completing the series of drilling processes from the pilot hole drilling process to the tapping process, a tapped hole 25 is formed in the workpiece W with a countersunk portion (back side countersunk portion 23) remaining, as shown in Figure 4(b).

[0027] Next, the effects of the drilling method according to the first embodiment will be described.

[0028] The drilling method according to this embodiment includes a step of forming pilot holes 20 in a plate-shaped workpiece W (pilot hole processing step), and a step of forming backside counterbore portions 23 from below the workpiece W in the portions where the pilot holes 20 are to be formed (counterbore processing step). The drilling method also includes a step of forming punch holes 24 from above the workpiece W in the portions where the pilot holes 20 are to be formed after the backside counterbore portions 23 have been formed (punch hole processing step).

[0029] In the drilling method according to this embodiment, punch holes 24 are formed in a plate-shaped workpiece W, for example, as a pre-process for forming tapped holes. First, before forming the punch holes 24, a backside counterbore 23 is formed in the portion where the pilot holes 20 are to be formed. Therefore, the punch holes 24 are not formed in the entire pilot holes 20 that were originally formed in the pilot hole drilling process, but are formed in the pilot holes 20 that remain after the backside counterbore 23 is formed. Therefore, the portion where the punch holes 24 are to be formed can be made thinner than the plate thickness t in advance. As a result, even if the workpiece W is a thick plate made of stainless steel, for example, punch holes 24 having a punch diameter d3 equal to or less than the plate thickness t can be automatically formed using a die such as a punching die.

[0030] Furthermore, when a workpiece W with tapped punch holes 24 is used as a component of a product, another component (hereinafter referred to as the "attachment target") is often attached to the surface 21 of the workpiece W using a screw. As a comparative example, consider a case in which a counterbore is formed from above the workpiece W in the area where the pilot holes 20 are formed, in the same direction as the punch hole machining direction. In this case, the counterbore is formed on the surface 21 of the workpiece W. When a screw is inserted through the attachment target and fastened to the tapped hole formed in the punch hole to secure the attachment target to the surface 21 of the workpiece W, a gap corresponding to the counterbore is generated between the attachment target and the tapped hole. Such a gap in the fastening area can cause the screw to loosen. Furthermore, the distance from the surface 21 to the tapped hole is increased by the presence of the gap, which may require the use of a screw longer than a standard screw. Furthermore, depending on the counterbore diameter and depth, significant warping of the workpiece W may occur. On the other hand, in order to deal with such a predicted event, it is conceivable to turn the workpiece W over as necessary for each machining process, for example. However, in this case, a machining design that takes this into consideration in advance is required, and there is a risk that the series of drilling processes will become complicated.

[0031] In contrast, in the countersinking process of this embodiment, the backside countersink portion 23 is formed from below the workpiece W in the portion where the pilot hole 20 is formed. In other words, the backside countersink portion 23 is formed on the back surface 22 side of the workpiece W. Therefore, even if an object to be attached is fixed to the workpiece W using a screw as in the above comparative example, no gap due to the countersink portion is created between the object to be attached and the tapped hole, which reduces the cause of loosening of the screw. Furthermore, standard screws can be used for fastening. Furthermore, according to this embodiment, warping of the workpiece W is less likely to occur, and there is no need to turn the workpiece W over for each processing step.

[0032] Therefore, according to this embodiment, a drilling method for easily forming a hole having a diameter equal to or smaller than the plate thickness t of the workpiece W can be provided.

[0033] In the punching method according to this embodiment, the processing length L1 of the punch hole 24 may be smaller than or equal to the punch diameter d3 of the punch hole 24.

[0034] According to this drilling method, even if the workpiece W is a thick plate made of stainless steel, the punched holes 24 can be formed using a so-called punch-pierce die for thick plates.

[0035] Furthermore, in the punching method according to this embodiment, punch hole 24 may be formed by a first punch tip included in the first punch assembly downwardly punching out the portion where pilot hole 20 will be formed, with the first punch assembly and the first die assembly sandwiching workpiece W in the vertical direction. Furthermore, opening diameter d4 of the first die hole included in the first die assembly and opening toward the first punch assembly side may be larger than counterbore diameter d2 of back-side counterbore portion 23.

[0036] In the above example using the drawings, the first punch assembly corresponds to the punch assembly 7 provided in the punching die 6, and the first die assembly corresponds to the die assembly 8 provided in the punching die 6. Also, the first punch tip corresponds to the punch tip 7c included in the punch assembly 7.

[0037] According to this punching method, in the punch hole processing step of this embodiment, the opening diameter d4 of the first die hole included in the first die assembly is set larger than the counterbore diameter d2 of the backside counterbore portion 23. As a result, burrs are less likely to occur on the fracture surface compared to when the opening diameter d4 is set smaller than the counterbore diameter d2, and the shear surface is formed well, making it easier to perform the subsequent tapping process. In this regard, this is particularly effective when the workpiece W has a relatively thick plate thickness t and a relatively high material strength (shear strength), such as when the workpiece W is a thick plate made of stainless steel.

[0038] The drilling method according to this embodiment may also include a step of forming tapped holes 25 from above the workpiece W in the areas where the punched holes 24 are to be formed (tapping step) after the punched holes 24 are formed.

[0039] According to this drilling method, the processes from the pilot hole drilling process to the tapping process can be performed as a series of drilling processes in a punch press machine or a punch laser combined machine. Here, in the tapping process, the tapped hole 25 is formed from above the workpiece W. Therefore, in addition to the machining direction of the backside counterbore portion 23 in the counterbore machining process and the machining direction of the punch hole 24 in the punch hole machining process, it is not necessary to turn the workpiece W over between machining processes, and this makes it possible to avoid the series of drilling processes becoming complicated.

[0040] Second Embodiment 5 to 8 are schematic cross-sectional views showing the flow of a drilling method according to a second embodiment. The drilling method according to this embodiment is a method for forming punched holes or tapped holes in a plate-shaped workpiece W, similar to the first embodiment. In each of FIGS. 5 to 8, the same components as those used to carry out the drilling process according to the first embodiment are given the same reference numerals, and detailed description thereof will be omitted below. In the first embodiment, a counterbore portion (rear-side counterbore portion 23) was formed only on the rear surface 22 side of the workpiece W before the punch hole processing process. In contrast, in the second embodiment, counterbore portions are formed on both the front surface 21 side and the rear surface 22 side of the workpiece W before the punch hole processing process.

[0041] The drilling method according to this embodiment includes the steps of forming pilot holes 20 in a plate-shaped workpiece W, forming a front-side counterbore portion 26 from above the workpiece W in the portion where the pilot holes 20 are to be formed, and forming a back-side counterbore portion 27 from below the workpiece W in the portion where the pilot holes 20 are to be formed. The drilling method also includes the step of forming punch holes 28 from above the workpiece W in the portion where the pilot holes 20 are to be formed, after forming the front-side counterbore portion 26 and the back-side counterbore portion 27. The drilling method may further include the step of forming tapped holes 29 from above the workpiece W in at least the portion where the punched holes 28 are to be formed, after forming the punched holes 28. Hereinafter, this embodiment will be described, as in the first embodiment, with reference to a case where tapped holes for M4 screws are finally formed in a stainless steel plate having a plate thickness t of 6 mm.

[0042] First, the process of forming the pilot holes 20 in the workpiece W is the same as the pilot hole processing process in the first embodiment described with reference to FIG. 1, and therefore a detailed description thereof will be omitted.

[0043] FIG. 5 is a diagram illustrating a process of forming a front-side counterbore portion 26 from above the workpiece W in the portion where the pilot hole 20 is to be formed. Hereinafter, the process of forming the front-side counterbore portion 26 will be referred to as the "first counterbore processing process." FIG. 5(a) is a diagram illustrating the state near the portion where the pilot hole 20 is to be formed during the first counterbore processing process. FIG. 5(b) is a cross-sectional view of the workpiece W in which the front-side counterbore portion 26 has been formed. The first counterbore processing process is performed after the pilot hole processing process. In the first counterbore processing process, the front-side counterbore portion 26 is formed using, for example, a burring die 12. Note that in this embodiment, the back-side counterbore portion 27 formed in the second counterbore processing process described below is positioned as the main counterbore portion. In contrast, the front-side counterbore portion 26 formed in the first counterbore processing process is positioned as an additional counterbore portion.

[0044] The burring die 12 includes a punch assembly 13 (second punch assembly) and a die assembly 14 (second die assembly). The punch assembly 13 and the die assembly 14 face each other in the vertical direction, sandwiching the workpiece W therebetween. The punch assembly 13 is disposed on the front surface 21 side of the workpiece W. The die assembly 14 is disposed on the back surface 22 side of the workpiece W. The punch assembly 13 includes, for example, a punch body 13a and a punch tip 13c. The punch body 13a is a cylindrical member that moves within a certain range in the vertical direction upon receiving downward elastic force from an elastic member (not shown). The punch body 13a has a body hole 13b as a through hole through which the punch tip 7c passes in the vertical direction without contacting it, and a punch-side pressing surface 13d that contacts the front surface 21 of the workpiece W. During the first countersinking process, the punch body 13a presses the workpiece W from above downward. The punch tip 13c is a columnar member that moves within a certain range in the vertical direction when subjected to a downward resilient force from a resilient device (not shown) and is a forming part that forms the front-side counterbore portion 26. Meanwhile, the die assembly 14 includes, for example, an ejector plate 14a. The ejector plate 14a is an annular member that moves within a certain range in the vertical direction when subjected to an upward resilient force from a resilient device (not shown). The ejector plate 14a may be fixed at a predetermined position without moving vertically. The ejector plate 14a has a die hole 14b (second die hole) and a die-side pressing surface 14c that contacts the back surface 22 of the workpiece W, coaxially with the punch tip 13c included in the punch assembly 13. During the first counterbore processing step, the ejector plate 14a presses the workpiece W from below upward.

[0045] The burring die 12 can form the front-side counterbore portion 26 by having the punch tip 13c of the punch assembly 13 strike the portion where the pilot hole 20 is to be formed downward while the punch assembly 13 and the die assembly 14 sandwich the workpiece W vertically. The burring die 12 used in this embodiment does not form burring. The counterbore diameter d6 of the front-side counterbore portion 26 is set to be larger than the punch diameter of the punch hole 28 for tapping an M4 screw and smaller than the counterbore diameter d2 of the back-side counterbore portion 27. The counterbore depth dp2 of the front-side counterbore portion 26 is set to, for example, 1.0 to 1.5 mm, taking into account re-deformation that occurs when the back-side counterbore portion 27 is formed upward in the next process. Furthermore, the die hole 14b of the die assembly 14 is a cylindrical space with its axis extending vertically. It is continuous with the die-side pressing surface 14c and opens toward the punch assembly 13. As shown in FIG. 5(a), the opening diameter d5 of the die hole 14b is the same as the counterbore diameter d6 of the front-side counterbore portion .

[0046] FIG. 6 is a diagram illustrating a process of forming a backside counterbore portion 27 from below the workpiece W in the portion where the pilot hole 20 is to be formed. Hereinafter, the process of forming the backside counterbore portion 27 will be referred to as the "second counterbore processing process." FIG. 6(a) is a diagram illustrating the state in the vicinity of the portion where the pilot hole 20 is to be formed during the second counterbore processing process. FIG. 6(b) is a cross-sectional view of the workpiece W in which the backside counterbore portion 27 has been formed. The second counterbore processing process is performed after the first counterbore processing process. In the second counterbore processing process, for example, the backside counterbore portion 27 is formed using a burring die 3, similar to the counterbore processing process in the first embodiment.

[0047] The burring die 3 can form the back-side counterbore portion 27 by having the die assembly 4 and the punch assembly 5 sandwich the workpiece W in the vertical direction and the die tip 4c included in the die assembly 4 strike the portion where the pilot hole 20 is to be formed upward. The counterbore diameter of the back-side counterbore portion 27 may be the same as the counterbore diameter d2 of the back-side counterbore portion 23 in the first embodiment. On the other hand, the counterbore depth dp3, which is the depth of the back-side counterbore portion 27, is shallower than the counterbore depth dp1 in the first embodiment by the amount that the front-side counterbore portion 26 has already been formed above it, and is, for example, 1.5 to 2.0 mm.

[0048] FIG. 7 is a diagram illustrating the step of forming punch holes 28 in the areas where pilot holes 20 are to be formed. The step of forming punch holes 28 in this embodiment is basically the same as the punch hole processing step in the first embodiment, and punch holes 28 may be formed using a punching die 6, for example. FIG. 7(a) is a diagram showing the state near the areas where punch holes 28 are to be formed during the punch hole processing step. FIG. 7(b) is a cross-sectional view of workpiece W in which punch holes 28 have been formed. The punch hole processing step is performed after the second countersinking step.

[0049] The punching die 6 can form the punch hole 28 by punching the portion where the pilot hole 20 is to be formed downward with the punch assembly 7 and the die assembly 8 sandwiching the workpiece W between them. The punch diameter of the punch hole 28 is the same as the punch diameter d3 of the punch hole 24 in the first embodiment. The processing length L3, which is the axial length of the punch hole 28, corresponds to the thickness t of the workpiece W minus the counterbore depths dp2 and dp3. As described above, the counterbore diameter d6 of the front-side counterbore portion 26 is larger than the punch diameter d3 of the punch hole 28 and smaller than the counterbore diameter d2 of the back-side counterbore portion 27. Therefore, even when the punch hole 28 is formed in the punch hole processing step, both the front-side counterbore portion 26 and the back-side counterbore portion 27 remain. Furthermore, in this embodiment as well, the opening diameter d4 of the die hole 8b is larger than the counterbore diameter d2 of the backside counterbore portion 27, as shown in FIG. 7(a).

[0050] FIG. 8 is a diagram illustrating the step of forming a tapped hole 29 from above the workpiece W in the portion where the punched hole 28 is to be formed. The step of forming the tapped hole 29 in this embodiment is basically the same as the tapping step in the first embodiment, and the tapped hole 29 may be formed using a tapping die 9, for example. FIG. 8(a) is a diagram showing the state near the portion where the tapped hole 29 is to be formed during the tapping step. FIG. 8(b) is a cross-sectional view of the workpiece W in which the tapped hole 29 has been formed. The tapping step is performed after the punched hole processing step.

[0051] With the workpiece W placed on the die assembly 11, the tapping die 9 can form the tapped hole 29 by gradually threading the portion where the punch hole 28 is to be formed downward using the tap 10c included in the punch assembly 10. In this embodiment, a tap 10c compatible with M4 screw tapping is used, and a tapped hole 29 compatible with fastening an M4 screw is formed in the portion where the punch hole 28 was formed. Here, depending on the setting of the counterbore diameter d6 of the front-side counterbore portion 26, as shown in FIG. 8 , the tapped hole 29 will be formed not only in the portion where the punch hole 28 was formed but also in the portion where the front-side counterbore portion 26 was formed. In this case, the processing length L4, which is the axial length of the tapped hole 29, corresponds to the thickness t of the workpiece W minus only the counterbore depth dp3 of the back-side counterbore portion 27. That is, in this embodiment, the processing length L4 of the tapped hole 29 is longer than the processing length L3 of the punch hole 28.

[0052] In this way, by completing the series of drilling processes from the pilot hole drilling process to the tapping process, a tapped hole 29 is formed in the workpiece W with a countersunk portion (back side countersunk portion 27) remaining, as shown in Figure 8(b).

[0053] The drilling method according to the second embodiment includes processing steps similar to those of the drilling method according to the first embodiment, and is therefore advantageous in that it prevents the processing steps from becoming too complicated, even if the workpiece W is a thick plate with high strength, as in the first embodiment.

[0054] Furthermore, the drilling method according to this embodiment includes a step (first countersinking step) of forming front side countersink portion 26 from above workpiece W at the formation portion of pilot hole 20 before forming back side countersink portion 27 (before the second countersinking step). In this case, countersink diameter d6 of front side countersink portion 26 may be larger than punch diameter d3 and smaller than countersink diameter d2 of back side countersink portion 27.

[0055] According to this drilling method, a back-side counterbore portion 27 is formed on the back surface 22 of the workpiece W, while a front-side counterbore portion 26 is also formed on the front surface 21 of the workpiece W. This offsets the warpage of the workpiece W from above, thereby reducing the overall warpage. Furthermore, when forming the pilot holes 20 using, for example, a laser processing machine 1 in the pilot hole drilling process, even if residue remains in the pilot holes 20, the residue can be removed from above the workpiece W simultaneously with forming the front-side counterbore portion 26. Furthermore, if the workpiece W is a thick stainless steel plate, the workpiece W has high rigidity. Therefore, even if the workpiece W is placed on the dust collection duct 2a in the pilot hole drilling process, deformation of the workpiece W is unlikely to occur. Furthermore, the counterbore diameter d6 of the front-side counterbore portion 26 is set to be larger than the punch diameter d3 but smaller than the counterbore diameter d2 of the back-side counterbore portion 27. Therefore, a tapped hole 29 can be formed in the portion where the front-side counterbore portion 26 is formed. Therefore, the machining length L4 of the tapped hole 29 can be made longer than the machining length L2 of the tapped hole 25 in the first embodiment.

[0056] Furthermore, in the drilling method of this embodiment, front-side counterbore portion 26 is formed by, with the second punch assembly and the second die assembly sandwiching workpiece W in the vertical direction, causing a second punch tip included in the second punch assembly to strike downwardly against the portion where pilot hole 20 is to be formed. In this case, opening diameter d5 of the second die hole included in the second die assembly and opening toward the second punch assembly side may be the same as counterbore diameter d6 of front-side counterbore portion 26.

[0057] In the above example using the drawings, the second punch assembly corresponds to the punch assembly 13 provided in the burring die 12, and the second die assembly corresponds to the die assembly 14 provided in the burring die 12. The second punch tip corresponds to the punch tip 13c included in the punch assembly 13, and the second die hole corresponds to the die hole 14b included in the die assembly 14.

[0058] According to this drilling method, the opening diameter d5 of the second die hole and the countersink diameter d6 of the front countersink portion 26 are the same, making it easier to balance the biasing forces of the second punch assembly and the second die assembly, which are biased by their respective elastic devices to face each other.

[0059] In the second embodiment, the first countersinking process for forming the front-side countersink portion 26 is performed before the second countersinking process for forming the back-side countersink portion 27. However, the present embodiment is not limited to this, and the front-side countersink portion 26 and the back-side countersink portion 27 may be formed simultaneously in one countersinking process.

[0060] 9 is a diagram illustrating a process of forming a front-side counterbore portion 26 from above the workpiece W and simultaneously forming a back-side counterbore portion 27 from below the workpiece W in the portion where pilot hole 20 is to be formed. In FIG. 9, the same components as those used to carry out the drilling process according to the second embodiment are given the same reference numerals, and detailed description thereof will be omitted below. In this counterbore process, for example, a burring die 16 is used to form front-side counterbore portion 26 and back-side counterbore portion 27.

[0061] The burring die 16 includes a punch assembly 17 and a die assembly 18. The punch assembly 17 corresponds to the punch assembly 13 included in the burring die 12. The die assembly 18 corresponds to the die assembly 4 included in the burring die 3. The punch assembly 17 includes, for example, a punch body 17a and a punch tip 17c. The punch body 17a is a cylindrical member that receives a downward elastic force from a spring (not shown) and moves within a certain range in the vertical direction. The punch body 17a has a body hole 17b as a through-hole through which the punch tip 17c passes in the vertical direction without contacting the body hole 17b, and a punch-side pressing surface 17d that contacts the surface 21 of the workpiece W. During the countersinking process, the punch body 17a presses the workpiece W from above downward. The punch tip 17c is a columnar member that moves within a certain range in the vertical direction upon receiving a downward resilient force from a resilient device (not shown) and serves as a forming part for forming the front-side counterbore portion 26. Meanwhile, the die assembly 18 includes, for example, an ejector plate 18a and a die tip 18c. The ejector plate 18a is an annular member that moves within a certain range in the vertical direction upon receiving an upward resilient force from a resilient device (not shown). The ejector plate 18a may be fixed in a predetermined position without moving vertically. The ejector plate 18a has a die hole 18b as a through-hole through which the die tip 18c passes vertically without contacting the workpiece W, and a die-side pressing surface 18d that contacts the back surface 22 of the workpiece W. During the counterbore processing process, the ejector plate 18a presses the workpiece W upward from below. The die tip 18c is a columnar member that receives an upward resilient force from a resilient device (not shown) and moves within a certain range in the vertical direction, and is a forming part that forms the backside counterbore portion 27.

[0062] In the burring die 16, with the punch assembly 17 and the die assembly 18 sandwiching the workpiece W in the vertical direction, the die tip 18c included in the die assembly 18 first strikes upward the portion where the pilot hole 20 is to be formed, thereby forming the back side counterbore portion 27. At the same time, the burring die 16 can form the front side counterbore portion 26 by having the punch tip 17c included in the punch assembly 17 strike downward the portion where the pilot hole 20 is to be formed.

[0063] According to such a drilling method, the process of forming the front side countersunk portion 26 and the process of forming the back side countersunk portion 27 are unified, which can be advantageous in simplifying the series of drilling processes.

[0064] In the above-described embodiments, a case where a tapped hole for an M4 screw is finally formed in a workpiece W made of a stainless steel plate having a thickness t of 6 mm has been described as an example. However, according to the drilling method of each of the above-described embodiments, a tapped hole for a screw of a size other than the above-described example can be finally formed in a workpiece W having a thickness or material other than the above-described example. For example, according to the drilling method of each of the above-described embodiments, a tapped hole for an M3 screw can also be finally formed in a workpiece W made of a stainless steel plate having a thickness t of 4 mm.

[0065] In each of the above embodiments, an upward burring die 3 or the like is exemplified as a die for forming the backside counterbore portion 23 or the like in each counterbore processing step. However, it is not essential to use a burring die in each counterbore processing step, and for example, when strict processing accuracy is not required for molding, a general punching die may be used.

[0066] The present invention is not limited to the above-described embodiment, and various modifications are possible without departing from the spirit of the present invention. [Explanation of symbols]

[0067] 3 Burring mold 4 Die Assembly 4c Die Chip 5 Punch assembly 5a Punch Body 7 Punch assembly 7c punch tip 8 Die Assembly 8b Die hole 13 Punch assembly 13c punch tip 14 Die assembly 14b Die hole 20 pilot holes 23 Backside counterbore 24 punch holes 25 tapped holes 26 Front counterbore 27 Backside counterbore 28 punch holes 29 tapped holes d2 Counterbore diameter of the backside counterbore d3 Punch diameter of punch hole d4 Die hole opening diameter d5 Die hole opening diameter d6 Counterbore diameter of front counterbore L1 Punch hole processing length L3 Punch hole processing length double work

Claims

1. A step of forming a pilot hole in a plate-shaped workpiece; forming a cylindrical backside counterbore portion from below the workpiece at a portion where the pilot hole is to be formed; and forming a punch hole from above the workpiece in the portion where the pilot hole is to be formed after forming the back side counterbore portion, The processing length of the punch hole is equal to or smaller than the punch diameter of the punch hole, the punch hole is formed by punching a portion where the pilot hole is to be formed downward with a first punch tip included in the first punch assembly while the workpiece is sandwiched between a first punch assembly and a first die assembly in the vertical direction, A drilling method, wherein the opening diameter of a first die hole included in the first die assembly and opening toward the first punch assembly side is larger than the counterbore diameter of the backside counterbore portion.

2. a step of forming a front side counterbore portion from above the workpiece at a portion where the pilot hole is formed, before or at the same time as forming the back side counterbore portion; The hole-making method according to claim 1 , wherein a counterbore diameter of the front-side counterbore portion is larger than a punch diameter of the punch hole and smaller than a counterbore diameter of the rear-side counterbore portion.

3. the front-side counterbore portion is formed by a second punch tip included in the second punch assembly striking downward a portion where the pilot hole is to be formed, with the workpiece sandwiched between a second punch assembly and a second die assembly in the vertical direction, 3. The drilling method according to claim 2, wherein the opening diameter of the second die hole included in the second die assembly and opening toward the second punch assembly is the same as the counterbore diameter of the front counterbore portion.

4. The drilling method according to any one of claims 1 to 3, further comprising the step of forming a tapped hole from above the workpiece at least in the portion where the punched hole is formed, after the punched hole is formed.

5. A step of forming a pilot hole in a plate-shaped workpiece; forming a backside counterbore portion from below the workpiece at a portion where the pilot hole is to be formed; forming a punch hole from above the workpiece in a portion where the pilot hole is to be formed after forming the back side counterbore portion; and forming a front side counterbore portion from above the workpiece at a portion where the pilot hole is formed before or simultaneously with forming the back side counterbore portion, a counterbore diameter of the front-side counterbore portion is larger than a punch diameter of the punch hole and smaller than a counterbore diameter of the rear-side counterbore portion; the front-side counterbore portion is formed by, with the workpiece sandwiched between a second punch assembly and a second die assembly in the vertical direction, striking downward with a second punch tip included in the second punch assembly a portion where the pilot hole is to be formed, an opening diameter of a second die hole included in the second die assembly and opening toward the second punch assembly side is set to be the same as the counterbore diameter of the front-side counterbore portion; Drilling method.

6. The punching method according to claim 5 , wherein the length of the punched hole is set to be smaller than or equal to the punch diameter of the punched hole.

7. The punch hole is formed by vertically sandwiching the workpiece between a first punch assembly and a first die assembly, and punching a portion where the pilot hole is to be formed downward with a first punch tip included in the first punch assembly; The drilling method according to claim 6, wherein the opening diameter of a first die hole included in the first die assembly and opening toward the first punch assembly is made larger than the countersink diameter of the backside countersink portion.

8. The drilling method according to any one of claims 5 to 7, further comprising the step of forming a tapped hole from above the workpiece at least in the portion where the punched hole is to be formed, after the punched hole is formed.

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