JPH10263720A - Pierced earring punch and piercing method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To induce a compression residual stress in the peripheral direction at the peripheral edge part of a hole to be pierced and to reduce lowering of fatigue strength due to the notch effect of the hole having an opening part by making the tip part of a pierced earring punch smaller than the opening part and providing a hole enlarging part having the size roughly equal to the opening part at a back end side. SOLUTION: This pierced earring punch 20 is provided with a small tip part 22 having the diameter smaller than the diameter of an opening part of the hole 12b to be pierced in a steel plate 12 and a large hole enlarging part 24 of a back end side having roughly the same diameter as the diameter of the opening part. When descending the punch 20, a hole having the opening part of a diameter (d) is pierced in the steel plate 12. When further descending the punch 20, the hole enlarging part 24 of the punch 20 is inserted into the hole of the diameter (d), the hole of the diameter (d) is enlarged to a hole 12b of the diameter D. At this time, the peripheral edge part of the hole 12b is stretched in the peripheral direction and compressed in the radial direction. After the punch 20 is pulled out, the diameter of the hole 12b becomes slightly smaller than a diameter D of the hole enlarged part 24.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a piercing punch used for drilling a hole in a workpiece, and a method of drilling a hole in a workpiece.

[0002]

2. Description of the Related Art Drilling for drilling holes in a workpiece such as a steel plate using a piercing punch is widely performed. A conventional drilling method using a piercing punch will be described with reference to FIG.

FIGS. 3A and 3B are schematic views showing a conventional piercing punch and a method for drilling a hole. FIG. 3A shows a state immediately before the hole is drilled, and FIG. ,
(C) shows a state immediately after the hole is drilled.

In making a hole in the steel sheet 12 with the piercing punch 10, the steel sheet 12 is placed on a die 14 and the steel sheet 12 is punched out with the piercing punch 10. While the piercing punch 10 is punching the steel plate 12, the steel plate 12 is pulled toward the center of the hole (in the direction of arrow A) as shown in FIG. Therefore, in the portion of the steel plate 12 corresponding to the peripheral edge portion 12a of the hole, a compressive stress is induced in the circumferential direction of the hole, and a tensile stress is induced in the radial direction of the hole. As a result, as shown in (c), after the hole is drilled and the hole debris 13 is generated, a tensile residual stress in the circumferential direction is induced in the peripheral portion 12a of the hole, and the fatigue strength may be reduced.

By the way, when a tensile or bending load is applied to a perforated workpiece, stress concentration occurs at the peripheral portion of the perforated hole, and the fatigue strength (durable strength) is reduced.
, Durability is remarkably reduced. The reduction in fatigue strength due to the stress concentration is called a notch effect. Normal,
When the shape of the workpiece is the same, the stress concentration coefficient is also the same, but when the material of the workpiece is different, the notch effect is different. Generally, the higher the strength of the material, the higher the notch sensitivity and the higher the notch effect. For this reason, if a smooth material has a fatigue strength proportional to its tensile strength, drilling a hole in the smooth material will cause the fatigue strength of both the high-strength material and the low-strength material to approach, and in some cases, reverse. Sometimes.

[0006]

As described above, when a hole is formed in a workpiece, a tensile residual stress is induced at the peripheral portion of the hole, and a load is applied to the workpiece having the hole. And the notch effect occurs. In the workpiece having the holes formed in this way, the residual stress of the tensile force and the notch effect of the holes generally affect each other, and the fatigue strength is reduced.

[0007] In view of the above circumstances, an object of the present invention is to provide a piercing punch and a drilling method capable of reducing a notch effect caused by a drilled hole.

[0008]

A piercing punch according to the present invention for achieving the above object is a piercing punch for drilling a hole having an opening of a predetermined size in a workpiece. (2) having a thickness substantially equal to that of the opening having the predetermined width;
It is characterized by including a hole expanding portion formed on the rear end side with respect to the front end portion.

Here, the tip may be longer than (3) the depth of a hole formed in the workpiece.

[0010] The tip may have a cross section similar to the shape of the opening having the predetermined size.

Further, the tip portion may have a thickness in the range of (5) 85% or more and 95% or less of the thickness of the hole expanding portion.

According to a second aspect of the present invention, there is provided a drilling method for drilling a hole having an opening having a predetermined width in a workpiece. Drill a hole smaller than the hole in the workpiece, and then
This small hole is enlarged to form a hole having an opening having the predetermined width.

Here, the small hole may have an opening having a size in the range of 85% to 95% of the opening having the predetermined size.

When the piercing punches described in the above (1) to (5) are used in order to drill the small hole in the above (6) and to enlarge this hole, continuous piercing can be easily performed. However, a well-known drill or laser may be used for drilling a small hole, and a conventional piercing punch may be used for expanding the small hole.

[0015]

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is a schematic view showing an embodiment of a piercing punch and a method for drilling a hole according to the present invention, wherein (a) shows a state immediately before the hole is drilled, and (b) shows a state immediately before the hole is drilled. This shows a state in the middle, and (c) shows a state immediately after the hole is formed. 1, the same components as those in FIG. 3 are denoted by the same reference numerals.

First, the piercing punch 20 will be described.

The piercing punch 20 has a thin tip portion 22 having a diameter d shorter than the diameter D 'of the opening of the hole 12b formed in the steel plate 12, and a thick hole expanding portion having a diameter D substantially equal to the diameter D'. 24. The diameter d of the distal end portion 22 is in the range of 85% or more and 95% or less of the diameter D of the hole expanding portion 24, and is 90% here. If the diameter d of the distal end portion 22 is less than 85% of the diameter of the hole expanding portion 24, burring (standing of the hole edge) may occur at the peripheral portion of the hole 12b. On the other hand, when the diameter d of the distal end portion 22 exceeds 95% of the diameter D of the hole expanding portion 24, the compressive residual stress described later decreases. The hole expanding portion 24 is formed on the rear end side of the piercing punch 20 with respect to the distal end portion 22, and a smoothly curved portion 26 is formed between the hole expanding portion 24 and the distal end portion 22. The length L of the tip 22 is longer than the thickness t of the steel plate 12 (the depth of the hole 12b). Furthermore, the tip 2
2 has a cross-sectional shape similar to the shape of the hole 12b formed in the steel plate 12, and is circular here.

A drilling method using the above-described piercing punch 20 will be described.

The piercing punch 20 is used by being set in a well-known drilling device. When the piercing punch 20 is lowered from the state shown in FIG. 1A, a hole having an opening having a diameter d is formed in the steel plate 12 as shown in FIG. 1B. When the piercing punch 20 is further lowered, the hole expanding portion 24 of the piercing punch 20 is inserted into the hole having the diameter d, and the hole having the diameter d is enlarged to the hole 12b having the diameter D. At the time of this enlargement, the periphery of the hole 12b is pulled in the circumferential direction and is compressed in the radial direction. For this reason, after the hole 12b has been drilled and the piercing punch 20 has been pulled out from the hole 12b, the diameter D 'of the hole 12b becomes slightly smaller than the diameter D of the hole enlarged portion 24, and the peripheral edge 12c of the hole 12b has a circumferential direction. , A compressive residual stress is induced. As a result, the increase in the fatigue strength due to the compressive residual stress reduces the decrease in the fatigue strength due to the notch effect of the hole 12b, so that the fatigue strength of the steel sheet 12 is higher than that of the steel sheet drilled by the conventional method. The strength will be improved.

Using a high-tensile steel as a workpiece, a hole 12b (diameter 12 mm) is drilled using a conventional piercing punch 10 (see FIG. 3) and a piercing punch 20 of the present invention (see FIG. 1), and a high-tensile steel is formed. The durability of the steel was compared. The high-tensile steel plate was 20 cm in length, 3 cm in width, and 6 mm in thickness, and repeatedly applied tensile stress (250 MPa). The high-strength steel sheet perforated with the piercing punch 20 is
Was about 4 times more durable than a high-tensile steel sheet with holes formed using

In the above-described example, a circular hole is formed in the steel plate 12, but the present invention is not limited to this, and the present invention can be applied to an oval or rectangular hole. When the hole is elliptical or rectangular, the cross-sectional shapes of the tip portion 22 of the piercing punch 20 and the hole expanding portion 24 are also elliptical or rectangular.

Referring now to FIG. 2, an example of a method for determining whether residual stress has been induced at the peripheral portion of the hole 12b of the steel plate 12 shown in FIG. 1 will be described.

FIG. 2A is an explanatory view showing a procedure for cutting a steel plate to determine the presence or absence of residual stress, and FIG.
FIG. 3 is a plan view showing a test piece for determining the presence or absence of residual stress.

As shown in FIG. 2A, a steel plate 12 having a length equal to the thickness (here, 6 mm) of the steel plate 12 in a radial direction (direction of arrow B) from an edge 12e of a hole 12b formed in the steel plate 12.
Is cut in a predetermined width, and then cut in the direction of arrow C concentrically with the hole 12b. The cutting is performed by laser or water jet along the broken line. The reason is that if a laser or a water jet is used, a predetermined width can be cut easily and with high accuracy, and the influence of processing distortion such as thermal distortion accompanying the cutting is small.

By cutting as described above,
The test piece 30 shown in (b) is obtained. In order to determine the presence or absence of residual stress, the cutting width W in the radial direction is measured. When the cutting width W is the same as the above-mentioned predetermined width, it can be determined that no residual stress has been induced at the peripheral portion of the hole 12b, or that almost no residual stress has been induced. When the cutting width W is smaller than the predetermined width, it can be determined that the tensile residual stress has been induced. The reason for this is that the residual tensile stress is released by cutting with a laser or a water jet, and the diameter D ′ of the hole 12b becomes smaller. On the other hand, when the cutting width W is larger than the predetermined width, it can be determined that the compressive residual stress has been induced. This is because the residual stress of compression is released by cutting with a laser or a water jet, and the diameter D ′ of the hole 12b increases.

[0027]

As described above, when drilling a hole using the piercing punch of the present invention, a hole having a predetermined width is formed by expanding the hole drilled at the front end portion. Is formed on the workpiece. When the hole expanding portion expands the hole drilled at the tip, a compressive residual stress is induced in the circumferential direction at the peripheral edge of the hole having the opening having a predetermined width. As a result, due to the increase in the fatigue strength caused by the compressive residual stress, the notch effect of the hole having the opening having the predetermined width is reduced, and the fatigue strength of the workpiece is improved.

Here, when the tip of the piercing punch is longer than the depth of the hole formed in the workpiece,
Since the circumferential residual compressive stress induced in the peripheral portion of the drilled hole is large, the fatigue strength of the workpiece is further improved.

In the case where the tip of the piercing punch has a cross-sectional shape similar to the shape of the opening having a predetermined width, a relatively large circumferential residual compressive residue is formed at the peripheral edge of the drilled hole. Since stress can be induced, the fatigue strength of the workpiece is more reliably improved.

Further, when the tip of the piercing punch has a thickness in the range of 85% or more and 95% or less of the thickness of the hole enlarged portion, a larger peripheral portion is formed on the periphery of the opened hole. Since the compressive residual stress in the direction can be induced, the fatigue strength of the workpiece is more reliably improved.

According to the drilling method of the present invention, a small hole is enlarged to form a hole having an opening of a predetermined width. , A compressive residual stress is induced. As a result, the increase in the fatigue strength due to the residual compressive stress reduces the decrease in the fatigue strength due to the notch effect of the hole having the opening having a predetermined width. The fatigue strength of the workpiece drilled by the method of the present invention is higher than the fatigue strength of the workpiece.

Here, when the small hole has an opening having a width in the range of 85% to 95% of the opening having a predetermined width, the small hole is provided at the periphery of the opened hole. Since a larger circumferential residual compressive stress is more reliably induced, the fatigue strength of the workpiece is more reliably improved.

[Brief description of the drawings]

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematic view showing an embodiment of a piercing punch and a drilling method according to the present invention, wherein (a) shows a state immediately before drilling, and (b) shows a state in the middle of drilling. (C) shows the state immediately after the hole is drilled.

FIG. 2A is an explanatory view showing a procedure for cutting a steel sheet to determine the presence or absence of residual stress, and FIG. 2B is a plan view showing a test piece for determining whether or not residual stress exists. FIG.

FIGS. 3A and 3B are schematic diagrams showing a conventional piercing punch and a drilling method, wherein FIG. 3A shows a state immediately before drilling a hole, and FIG.
Shows a state in the middle of drilling a hole, and (c) shows a state just after the hole is drilled.

[Explanation of symbols]

 Reference Signs List 12 steel plate 12b hole 12c perimeter of hole 20 piercing punch 22 tip end 24 hole expansion

Claims (6)

[Claims] 1. A piercing punch for drilling a hole having an opening of a predetermined width in a workpiece, wherein a tip portion narrower than the opening of the predetermined width and substantially the same as the opening of the predetermined width. A pierced punch, having a diameter that is larger than that of the front end and a hole expanding portion formed on a rear end side of the front end. 2. The piercing punch according to claim 1, wherein the tip portion is longer than a depth of a hole formed in the workpiece. 3. The piercing punch according to claim 1, wherein the tip has a cross-sectional shape similar to the shape of the opening having the predetermined width. 4. The device according to claim 1, wherein the tip has a thickness in the range of 85% to 95% of the thickness of the hole expanding portion.
Or the piercing punch according to 3. 5. A method for drilling a hole having an opening having a predetermined width in a workpiece, wherein a hole smaller than the hole having an opening having a predetermined width is drilled in the workpiece. Forming a hole having an opening of the predetermined size by enlarging the hole. 6. The drilling method according to claim 5, wherein the small hole has an opening having a size in a range of 85% to 95% of the opening having the predetermined size. .