JPH0350649B2 - - Google Patents

Description

Detailed Description of the Invention A. Object of the Invention (1) Industrial Application Field The present invention relates to a workpiece having a hole, in which a hole is bored in the wall of the workpiece in a direction perpendicular to the axis of the hole. This invention relates to a method for drilling into a wall.

(2) Conventional technology Conventionally, when drilling a hole in the wall of a workpiece, it is common to use a drill from the outside of the workpiece, but chips may remain in the hole.
In order to avoid creating edges at the inner end of the drilled hole, insert an insert into the workpiece and drive the piercing punch held by the insert radially outward of the hole so that the wall of the workpiece is There is also a technique in which a hole is drilled in the section and the inner peripheral edge thereof is curved.

(3) Problems to be solved by the invention By the way, when the master cylinder of a brake device is a workpiece and the return port to the reservoir is bored in the wall of the master cylinder, the return port is smaller than the inner diameter of the master cylinder. The hole diameter is very small, and the rigidity of the piercing punch becomes a problem.
In particular, it is necessary to improve the positional precision of the perpendicularity and backlash of the piercing punch relative to the master cylinder wall during punching. However, in the above-mentioned conventional drilling process, the piercing punch is relatively large and has sufficient strength relative to the wall thickness and inner diameter of the workpiece, so the accuracy is not that big of a problem, and therefore special No consideration was given.

For this reason, if the conventional method is applied as is to drilling the return port of the master cylinder, there will be a gap between the insert and the inner surface of the hole for attaching and removing the insert, and the fitting accuracy of the guide pin and positioning hole will be lower. Due to the roughness of the punch, the insert can wobble or pivot radially within the hole during the punching operation. In addition, the insert itself has become elongated and has a free end, making it easy to bend, so the piercing punch may not operate at right angles to the workpiece, or may become bent during punching or punching. Furthermore, the piercing punch may be damaged due to bending force when returning after punching.

In order to solve such problems, it is possible to increase the hole diameter, that is, the outer diameter of the piercing punch, or to set the length of the piercing punch as short as possible. However, if the outer diameter of the piercing punch is increased, the hole after punching cannot fully perform its function. In addition, when polishing and regenerating a piercing punch, if the length of the piercing punch is short, the curved part under the neck of the piercing punch must be precisely corrected to form a curve around the inner edge of the small diameter hole. figure,
It becomes expensive.

Therefore, the present applicant has proposed a method in which the workpiece and the insert are fixed together and then punched using a piercing punch.This method solves the above problems, but the master cylinder Since the wall thickness is relatively large, it is difficult to form a return port only by punching with a piercing punch, so a pilot hole is drilled from the outside of the wall before punching with a piercing punch. There is a need.

However, if the position of the pilot hole is misaligned, there is a possibility that the piercing punch will be damaged due to misalignment of its conical bottom. In addition, the inner end of the return port facing the inner surface of the master cylinder hole is required to prevent the piston cup attached to the piston from being eaten away, and to this end, a predetermined length of sheared surface with a piercing punch must be secured. Therefore, it is necessary to improve the rigidity of the cylinder body with the pilot hole formed. However, in order to reduce uneven thickness caused by misalignment of the conical bottom of the prepared hole and prevent damage to the piercing punch, it is better to have a large drill tip angle. In order to ensure rigidity, it is better to have a small drill tip angle, and there are mutually contradictory requirements regarding the drill tip angle.

The present invention has been made in view of the above circumstances, and is designed to balance two contradictory requirements regarding the tip angle of a drill for preparing a pilot hole, thereby preventing breakage of the piercing punch, and improving the length of the sheared surface by the piercing punch. It is an object of the present invention to provide a method for drilling into a wall of a workpiece having a hole, which makes it possible to ensure the following.

B. Structure of the Invention (1) Means for Solving Problems According to the method of the present invention, a drill whose tip angle is set at 90 to 120 degrees is attached to the wall of the workpiece using a guide tube that moves according to the movement of the drill. After guiding the hole to the outer surface and drilling the wall from the outside, the piercing punch is driven radially outward from the inside of the hole to form a small diameter hole in the wall that is coaxial with the large diameter hole formed by drilling. At the same time as punching, the inner peripheral edge of the small diameter hole was formed into a curve.

(2) Effect In the method of the present invention, since the drill is guided to the outer surface of the wall of the workpiece by the guide tube, eccentricity of the large diameter hole caused by the drill can be suppressed, and moreover, the tip angle of the drill can be adjusted to 90~
Experimental results confirmed that setting the angle to 120 degrees satisfies the lifespan of the pierced bunch and the length of the sheared surface.

(3) Embodiment Hereinafter, an embodiment of the present invention will be described with reference to the drawings.
In the figure, first and second pistons 3 and 4 are slidably engaged with a bottomed cylindrical cylinder portion 2 of a cylinder body 1, and these pistons 3 and 4 move forward and backward in conjunction with each other.

A bottomed hole 5 is bored in the cylinder portion 2, and a first piston 3 with a first return spring 6 interposed between the closed end surface 5a of the bottomed hole 5 and the closed end surface 5a is located at the front and rear ends of the first piston 3. Piston cups 7 and 8 are respectively attached and slid into the bottomed hole 5. Also, the second piston 4
A second return spring 9 and a piston spacing regulating means 10 are interposed between the piston 3 and the first piston 3, and a piston cup 11 is attached to the front end of the piston cup 11 to be slid into the bottomed hole 5. The closed end surface 5a of the bottomed hole 5 and the first
A first hydraulic chamber 12 is defined between the piston 3 and the piston 3;
A second hydraulic chamber 13 is defined between the first and second pistons 3 and 4. Further, the intermediate portions of each piston 3, 4 are formed to have a small diameter so as to define first and second auxiliary oil chambers 14, 15 between the intermediate portions and the inner surface of the bottomed hole 5.
Moreover, hydraulic brake circuits (not shown) are connected to output ports 16 and 17 that are connected to the respective hydraulic chambers 12 and 13, respectively.

An auxiliary oil reservoir 18 is integrally protruded from the upper side of the cylinder body 1, and a synthetic resin oil tank 19, which cooperates with the reservoir R, is connected to the upper end of the auxiliary oil reservoir 18. The auxiliary oil reservoir 18 is connected to the first and second oil reservoirs by a partition wall 20 that is integrated with the cylinder body 1.
The first oil reservoir chamber 21 is divided into oil reservoir chambers 21 and 22, and when each piston 3, 4 is located at a predetermined retraction limit, the first oil reservoir chamber 21 communicates with the first hydraulic chamber 12 via a first return port 23. At the same time, it communicates with the first auxiliary oil chamber 14 via the first supply port 24, and the second
The oil reservoir chamber 22 communicates with the second hydraulic chamber 13 through an oil passage 25 parallel to the bottomed hole 5 and a second return port 26, and also communicates with the second hydraulic chamber 13 through a second supply port 27 connected to the oil passage 25. It communicates with the oil chamber 15.

The first return port 23 has a small diameter hole 28 which is orthogonal to the axis of the bottomed hole 5 and opens into the inner surface of the bottomed hole 5.
and a first oil reservoir chamber 2 coaxially connected to the small diameter hole 28.
The second return port 27 consists of a large diameter hole 29 opening at the bottom hole 5 and a small diameter hole 30 opening at the inner surface of the bottomed hole 5 perpendicular to the axis of the bottomed hole 5; The large diameter hole 31 is connected to the oil passage 25 and opens into the oil passage 25.

When machining the first and second return ports 23, 26, the large diameter holes 29, 31 are drilled from the outside of the cylinder body 1 as pilot holes, and after drilling these pilot holes, the small diameter holes 28 are drilled from the outside of the cylinder body 1. , 30 are punched out to be coaxially continuous from the inner side of the bottomed hole 5.

The cylinder body 1 is treated as a workpiece when machining the first and second return ports 23 and 26, but there is a part near the opening end surface 1a of the cylinder body 1 for joining to a negative pressure booster (not shown). A flange portion 32 is integrally provided, and a plurality of insertion holes 33 as positioning holes parallel to the bottomed hole 5 are bored in this flange portion 32 . The insertion hole 33 has a large diameter part 34 and a small diameter part 35 coaxially connected in order from the open end side of the cylinder body 1, and the stepped part between the large diameter part 34 and the small diameter part 35 has the cylinder body 1. A tapered receiving surface 36 is provided which becomes larger in diameter toward the open end side. This insertion hole 33 is for inserting a bolt (not shown) during connection with the negative pressure booster, but as will be described later, the insert 37 is inserted during processing of the first and second return ports 23 and 26. It is also used for positioning (see Figures 2 and 3).

2 and 3, a bottomed hole 5 of the cylinder body 1 as a workpiece is mounted on the base 39.
a punch unit 40 for punching and forming a pair of small-diameter holes 28 and 30 in the cylinder body 1; and a clamp for clamping the cylinder body 1 between the punch unit 40. unit 41 and the large diameter holes 29, 31 prior to drilling the small diameter holes 28, 30.
A drill unit 42 for drilling holes is provided.

The insert 37 of the punch unit 40 is fixed and arranged horizontally by a support frame 38 fixed on a base 39, and the clamp unit 41 has a center provided on the outer surface of the closed end of the cylinder body 1. A tapered pressing member 44 that fits into the hole 43 (see FIG. 1) is provided. Moreover, the pressing member 44 is provided at the tip of the piston rod of a pressing cylinder 45 having a horizontal axis.
5 is driven up and down by a cylinder 46 and a link mechanism 47. Therefore, the insert body 37 is inserted into the bottomed hole 5 of the cylinder body 1 while the press member 44 is lowered, and then the press member 44 is raised and then the press member 44 is pressed and moved toward the insert body 37 side. This makes it possible to clamp the cylinder body 1.

In FIGS. 4 and 5, the insert 37 is
First, second, third, and fourth covers 51, 52, 53, and 54 are removably connected to an insert body 50, which is basically a half-cylindrical shape, in order from the base end side, to form a cylindrical shape. be done. The proximal end of the insert main body 50 and the first cover 51 are each integrally provided with a protruding portion that constitutes a flange portion 55 when coupled to each other, and the flange portion 55 is connected to the support frame 38 of the punch unit 40. is combined with Furthermore, a ring-shaped contact member 49 for positioning by contacting the open end surface 1a of the cylinder body 1 is fitted and fixed to the base ends of the insert body 50 and the first cover 51. The outer diameter of the insert 37 is set to such an extent that it can be inserted into the bottomed hole 5 of the cylinder body 1, and the insert 37 has small diameter holes 28, 30 when inserted into the bottomed hole 5. A pair of pierce punches 56 and 57 are held movably along the radial direction of the insert 37 in correspondence with the positions to be pierced.

In FIGS. 6 and 7, the insert body 50
are provided with radially extending grooves at axially spaced positions that are closed by second and fourth covers 52 and 54, respectively, to form rectangular guide holes 58 and 59. In the guide holes 58 and 59,
The prismatic support pieces 60 and 61 are slid together, respectively. Each support piece 60, 61 has a piercing punch 5.
6 and 57 are respectively fixed.

That is, each support piece 60, 61 has a guide hole 5.
Attachment holes 62, 63 and screw holes 64, 65 extending along lines 8, 59 are coaxially drilled, and piercing punches 56, 57 are inserted into the attachment holes 62, 63. In addition, the screw holes 64 and 65 are provided with a piercing punch 5.
Pierce punch 56,5 in contact with the rear end of 6,57
Screw members 66 and 67 for adjusting the amount of protrusion of the tip of the insert body 37 from the outer surface of the insert body 37 are screwed together so that they can move forward and backward. In addition, fixing screw members 68 and 69 that are screwed into a part of the outer surface of each of the piercing punches 56 and 57 are screwed into the support pieces 60 and 61. 5
The positions of 6 and 57 are fixed.

A small-diameter cylindrical perforation part 70 having an outer diameter corresponding to the inner diameter of the small-diameter holes 28 and 30 is coaxially provided at the tip of each of the piercing punches 56 and 57 via a curved step part 71, respectively. The curved stepped portion 71 is formed by curvedly forming the inner end edges of the small diameter holes 28 and 30, and is formed so that it is concave inward and becomes larger in diameter toward the rear end side.

Insert body 50 and first to fourth covers 51 to 5
4, a rectangular sliding hole 72 extending along the axial direction is formed, and this sliding hole 72 is connected to a drive source (not shown) disposed within the support frame 38 of the punch unit 40. The cam slider 73 is slidably moved back and forth. The cam slider 73
, cam holes 74 and 75 are provided at positions corresponding to the support pieces 60 and 61, respectively.
0 and 61 are engaged with cam holes 74 and 75 to move in accordance with the movement of the cam slider 73. In other words, the cam holes 74 and 75 form the piercing punches 56 and 57 as they move toward the distal end of the cam slider 73.
The pins 76 and 77 are formed so as to be inclined toward the rear end side and project from the support pieces 60 and 61, and are engaged with the cam holes 74 and 75. Therefore, as the cam slider 73 moves, each support piece 60, 6
1, that is, each piercing punch 56, 57 is inserted into the insert body 3.
7, and in particular as the cam slider 73 moves toward its distal end, each piercing punch 56, 57 moves in a direction in which the piercing portion 70 at its distal end protrudes from the outer surface of the insert body 37. do.

Referring also to FIG. 8, a cylindrical cover 78 made of synthetic resin is provided on the outer periphery of the tip end of the insert body 50.
are fitted. Further, at the tip of the insert body 50, an end plate portion 79 that closes the tip of the sliding hole 72;
A closing member 81 consisting of a cylindrical portion 80 whose side surface is partially cut flat to allow movement of the cam slider 73 is removably fixed by a screw member.

This closing member 81 has a screw hole 82 coaxial with the insert body 37 , and a screw member 83 having a conical tip is screwed into the screw hole 82 . A screw member 84 for fixing the position is screwed together. One side screw member 8
3 is screwed into the screw hole 82 with its tip as a protrusion 85 protruding from the tip of the closing member 81, that is, the insert body 37.

In FIG. 9, the flange portion 55 of the insert 37
A plurality of guide pins 90 are floatingly supported in correspondence with the insertion holes 33 in the cylinder body 1.
A support member 91 is fixed to the flange portion 55 by bolts 92 on the side opposite to the flange portion 32 of the cylinder body 1, and the support member 91 has a support hole 93 that opens toward the insertion hole 33 side. 3
The hole extends parallel to the axis of 7. The guide pin 90 is formed by integrally providing a tapered tip 95 that becomes smaller in diameter toward the front at the tip of a shaft portion 94 that is slidably fitted into a support hole 93.
The angle is set smaller than the angle of the receiving surface 36 in the insertion hole 33.

An engaging member 96 screwed onto the support member 91 engages with the outer surface of the intermediate portion of the shaft portion 94 in order to limit the axial movement of the guide pin 90 . In addition, the guide pin 90
A coiled spring 98 surrounding the support member 91 is interposed between the engagement plate 97 that engages with the tip 95 of the guide pin 90 and the flange 55, and the spring force of this spring 98 causes the guide pin 90 to Forced to fire toward the side.

Referring again to FIGS. 2 and 3, the drill unit 42 has a pair of large diameter holes 2 in the cylinder body 1.
a pair of drills 101 for drilling holes 9, 31;
102, and these drills 10
1 and 102 are rotationally driven while moving in a horizontal direction orthogonal to the cylinder body 1 which is clamped horizontally between the punch unit 40 and the clamp unit 41.

A pair of horizontal guide rails 103 and 104 are laid on the base 39 and perpendicular to the insert 37, and a movable table 105 is movably fitted into these guide rails 103 and 104. A support plate 106 is erected at the front end of the moving table 105, that is, the end on the insert body 37 side, and a pair of guide tubes 107 and 108 extending horizontally toward the insert body 37 are provided on the upper part of the support plate 106. Fixed. These guide tubes 107 and 108 correspond to the large diameter holes 29 and 31 of the cylinder body 1, and correspond to the large diameter holes 29 and 31 of the cylinder body 1.
It is fixed to the support plate 106 with an interval corresponding to 9 and 31. Further, a column 109 is erected at the rear end of the movable table 105. Further, a piston rod 111 of a cylinder 110 having an axis parallel to the guide rails 103 and 104 is connected to the rear end of the moving table. As a result, the movable table 105 moves to the cylinder 1.
It moves horizontally in response to the expansion and contraction operations of 10.

A frame 112 is supported on the upper part of the column 109 so as to be movable relative to the movable table 105, and this frame 112 is driven by a drive means (not shown). A head 113 provided at the front end of the frame 112 has a pair of spindles 114,
115 are arranged, and these spindles 1
Drills 101 and 102 are attached to 14 and 115. Further, a motor 11 for rotationally driving spindles 114 and 115 is provided at the rear end of the frame 112.
8 is fixed and supported.

The guide tubes 107, 108 are the drill 101,
102, and their lengths are set so that they simultaneously abut against the outer surface of the cylinder body 1 at portions corresponding to the large diameter holes 29, 31.

In FIG. 10, each drill 101, 102
is a small-diameter spiral blade portion 11 at the tip of the guide shaft portion 116.
7 is provided, and the spiral blade part 117
The tip angle α is set in the range of 90 to 120 degrees. Moreover, the lengths of both the large diameter holes 29 and 31 are different, and the length L of the spiral blade portion 117 in both the drills 101 and 102 is the same as that of the corresponding large diameter hole 2.
9 and 31, respectively.

Next, to explain the operation of this embodiment, when drilling the first and second return ports 23 and 26 in the cylinder body 1, the bottomed hole 5 and the first and second oil reservoir chambers 21 and 26 are The cylinder body 1, which has a concave portion corresponding to the cylinder body 1, is horizontally clamped between a punch unit 40 and a clamp unit 41. At this time, the insert 37 of the punch unit 40 is inserted into the bottomed hole 5, and the cylinder body 1 is substantially integrated with the insert 37. That is, the clamp unit 41 is a pressing member 44 fitted into the center hole 43 of the cylinder body 1;
The cylinder body 1 is pressed against the support frame 38 side of the punch unit 40, and the opening end surface 1 of the cylinder body 1 is pressed.
a comes into contact with the abutting member 49, and the protrusion 85 bites into the closed end surface 5a of the bottomed hole 5, thereby achieving axial positioning. On the other hand, the tip portion 95 of the guide pin 90 floatingly supported by the flange portion 55 of the insert body 37 tapers into the receiving surface 36 of the insertion hole 33 provided in the flange portion 32 of the cylinder body 1 .
Therefore, the circumferential relative position of the cylinder body 1 with respect to the insert 37 is determined. Moreover, since the guide pin 90 is resiliently biased by the spring 98, the flange portion 32 which has not been finished is
Even if there is a large variation in the dimensions, the tip portion 95 reliably contacts the receiving surface 36, and the circumferential position is reliably determined.

In this state, the cylinder body 1 is supported horizontally between the punch unit 40 and the clamp unit 41 with the wall portions where the first and second return ports 23 and 26 are to be formed located on the drill unit 42 side. Mobile platform 10 of unit 42
A pair of large diameter holes 29 and 31 are bored in the wall of the cylinder body 1 as shown in FIG.
At this time, the guide tubes 107 and 108 are also moving so as to come into contact with the outer surface of the wall of the cylinder body 1, and each drill 101 and 102 rotates while being guided by the guide tubes 107 and 108. Large diameter holes 29 and 31 are bored in the wall.

By the way, if the large diameter holes 29, 31 are deviated from their normal positions, the tip angle α of each drill 101, 102 will be
The resulting deviation of the conical bottom acts as uneven thickness during the subsequent punching process, acts as a bending force on the piercing punches 56, 57, and may cause breakage of the piercing punches 56, 57.
However, when the eccentricity accuracy is constant, the bending force due to the uneven thickness increases as the tip angle α becomes smaller.
From the viewpoint of preventing damage to the tip 57, the larger the tip angle α is, the more advantageous it is. On the other hand, the small diameter holes 28 and 30 in the first and second return ports 23 and 26 are required to prevent the piston cups 7 and 11 from being eaten away.
It is necessary to secure a predetermined amount of shear surface side length l of 8 and 30. However, the small diameter holes 28, 30 are punched only with the pierce punches 56, 57 without using a die;
Curved shaping of the inner edge of 0 is also performed at the same time, so
Hole diameter accuracy and shear surface length l of small diameter holes 56, 57
In order to ensure this, it is necessary to improve the rigidity of the cylinder body 1 as a workpiece, and from this point of view, it is better to reduce the tip angle α of each drill 101, 102.

As described above, there are mutually contradictory requirements regarding the tip angle α, and these requirements cannot be satisfied under conventional machining accuracy. However, under conditions in which the drills 101 and 102 are guided by guide tubes 107 and 108 to improve the precision of the machining position using the relatively long drills 101 and 102, the tip angle α
By setting the angle between 90 and 120 degrees, it becomes possible to balance and satisfy the above two contradictory requirements.

In FIG. 11, curve A shows the life of the piercing punch with respect to the tip angle α, and curve B shows the change in the ratio l/d of the shear surface length l of the small diameter hole to the inner diameter d of the small diameter hole with respect to the tip angle α. Here, as a target level, if the life of the piercing punch is 1000 shots or more and l/d is 1 or more, then in order to satisfy these conditions, the tip angle α must be 90 to 120 degrees as shown in Figure 11. It is good if it is within the range of . When the tip angle α is determined in this way, the piercing punch 56,
Not only will the lifespan of 57 be satisfactory,
The accuracy of the small diameter holes 28, 30 is also satisfactory.

After drilling the large diameter holes 29 and 31 in this manner, by moving the cam slider 73 toward the tip side, the piercing punches 56 and 57 are made to protrude toward the wall of the cylinder body 1, and the small diameter holes 28 and
Punch out 30. As a result, the large diameter holes 29, 31
The small diameter holes 28 and 30 are coaxially connected to form first and second return ports 23 and 26,
Curved shaping of the inner end peripheral edges of the first and second return ports 23 and 26 is also performed at the same time.

At this time, since the cylinder body 1 is substantially integrated with the insert 37 with its circumferential and axial positions determined, the piercing punches 56 and 57 are perpendicular to the wall of the cylinder body 1. Operates in the direction. Therefore, it is possible to avoid bending force acting on the piercing punches 56, 57, and to prevent damage to the piercing punches 56, 57 as much as possible, thereby improving the life of the piercing punches 56, 57. be able to. Moreover, even if the length of the perforation part 70 in each piercing punch 56, 57 is made relatively long, it is possible to prevent breakage as much as possible, and only the tips need to be polished when repolishing the piercing punches 56, 57. , there is no need to modify the curved step portion 71. Therefore, it becomes possible to perform re-polishing at low cost.

After the punching process of the earring punches 56 and 57 is completed, the cam slider 73 moves toward the rear side,
Each piercing punch 56, 57 is returned within the insert 37. Then, the insertion member 37 is pulled out from inside the cylinder body 1 to release the clamped state of the cylinder body 1 by the punch unit 40 and the clamp unit 41, thereby completing the series of drilling operations.

C. Effect of the invention As described above, according to the method of the present invention, the tip angle can be adjusted.
A drill set at 90 to 120 degrees is guided to the outer surface of the wall of the workpiece with a guide tube that moves according to the movement of the drill, and after drilling the wall from the outside, it is drilled radially outward from the inside of the hole. By driving the pierce punch toward the wall, a small diameter hole coaxially connected to the large diameter hole formed by drilling is punched in the wall, and the inner edge of the small diameter hole is curved, so that the angle of the tip of the drill can be adjusted. This makes it possible to balance the contradictory demands of pierce haunches, improve the lifespan of the pierce haunch, and secure the sheared surface length of the pierce punch.

[Brief explanation of drawings]

The drawings show one embodiment of the present invention, and FIG. 1 is a longitudinal cross-sectional side view of a tandem-type master cylinder to which the present invention is applied, FIG. 2 is a plan view of a drilling device, and FIG. 3 is a diagram of FIG. 4 is an enlarged view of FIG. 2 in the direction of the arrow, FIG. 5 is a view of FIG. 4 in the direction of the arrow, FIG. 6 is a sectional view of FIG. Fig. 8 is an enlarged sectional view taken along the - line in Fig. 5, Fig. 9 is an enlarged sectional view taken along the - line in Fig. 4, Fig. 10 is an enlarged view of the tip of the drill, and Fig. 11 is an enlarged sectional view taken along the - line in Fig. 5. A graph showing the experimental results, and FIG. 12 is an enlarged longitudinal sectional view of the return port. 1...Cylinder body as a workpiece, 5...
Bottomed hole as a hole, 28, 30...small diameter hole, 5
6,57...Piercing punch, 101,102...
Drill, 107, 108... Guide tube.

Claims (1)

[Claims] 1. A method for drilling a wall of a workpiece having a hole perpendicular to the axis of the hole, the tip angle being 90 to 120.
A drill set at the same time is guided to the outer surface of the wall of the workpiece by a guide tube that moves according to the movement of the drill, and after drilling the wall from the outside, the drill is guided radially outward from the inside of the hole. A workpiece having a hole, characterized in that a small diameter hole coaxially connected to a large diameter hole formed by drilling is punched in a wall part by driving a piercing punch, and the inner peripheral edge of the small diameter hole is curved. How to drill into the wall.