KR20240003214A - piercing method - Google Patents

Abstract

The present invention is a piercing method, comprising: (a) seating a molded material on a first lower die in which a first molding hole portion is formed; (b) moving a first piercing punch including a first punch head having a first diameter up and down to a position corresponding to the first forming hole part, thereby forming a first through hole part in the object to be formed; (c) Forming a second through-hole portion in the molded material by moving a second piercing punch including a second punch head having a second diameter larger than the first diameter up and down to a position corresponding to the first through-hole portion. steps; and (d) expanding and forming the second through-hole portion by moving an expansion punch including a conical expansion head up and down to a position corresponding to the second through-hole portion. may include.

Description

Piercing method {piercing method}

The present invention relates to a piercing method, and more specifically, to a piercing method that can improve burring properties by forming a through hole in a molded material to reduce cracks that may occur during burring processing.

Recently, in the automobile industry, the number of cases of applying ultra-high-strength steel to automobile bodies or various parts has been steadily increasing in accordance with the strengthening of regulations and safety standards related to the environment and fuel efficiency.

A method of machining screw holes in a steel plate includes burring, which involves forming a base hole and pressing it with a punch larger than the base hole. If the thickness of the steel plate is thick enough to form a thread, a screw hole can be machined through a tapping drill without a burring process. However, in the case of a thin steel plate, it is difficult to machine a screw hole, and a cylindrical wall is formed in the basic hole through burring. . Burring is also called hole flanging because it has the characteristic of forming a cylindrical wall through burring.

If burring processing is not performed, the initial steel plate thickness may be increased unnecessarily to bolt the steel plate, or the process of welding nuts may be added. However, this method not only increases the unit cost of the part, but also makes the final product heavy and clunky. Therefore, using the burring process when manufacturing plates into machine parts has the advantage of reducing work time and costs and improving the aesthetics of the final product.

However, in the process of producing automobile parts by performing the above-described burring process, fine cracks occur on the shear surface of the material during the hole piercing process due to the characteristics of low elongation and low molding processability of high-strength materials, which occur in the subsequent burring process. There were problems that resulted in multiple cracks.

The present invention is intended to solve several problems, including the problems described above. By piercing the material in two stages, the shear stress generated at the fracture surface is changed from tensile stress to compressive stress, thereby alleviating shear sensitivity and reducing the shear stress generated by shear. The purpose is to provide a piercing method that can improve the burring performance of materials by reducing damage. However, these tasks are illustrative and do not limit the scope of the present invention.

According to one embodiment of the present invention, a piercing method is provided. The piercing method includes the steps of: (a) seating a molded material on a first lower die in which a first molding hole portion is formed; (b) moving a first piercing punch including a first punch head having a first diameter up and down to a position corresponding to the first forming hole part, thereby forming a first through hole part in the object to be formed; (c) Forming a second through-hole portion in the molded material by moving a second piercing punch including a second punch head having a second diameter larger than the first diameter up and down to a position corresponding to the first through-hole portion. steps; and (d) expanding and forming the second through-hole portion by moving an expansion punch including a conical expansion head up and down to a position corresponding to the second through-hole portion. may include.

According to one embodiment of the present invention, in step (b), the step between the first molding hole portion and the first punch head is applied to the molded material within a range of 5% to 30% of the thickness of the molded material. This may be a step of forming the first through hole portion.

According to one embodiment of the present invention, in step (c), the step between the first molding hole portion and the second punch head is formed on the molded material within a range of 5% to 30% of the thickness of the molded material. This may be a step of forming the second through-hole portion.

According to one embodiment of the present invention, step (c) includes: (c1) seating the molded material on a second lower die in which a second molding hole portion is formed; and (c2) forming the second through-hole portion in the molded material within a range where the step between the second molded hole portion and the second punch head is 5% to 30% of the thickness of the molded material; may include.

According to one embodiment of the present invention, in step (d), the expansion head may have a bottom surface having a fourth diameter that is at least larger than the second diameter.

According to one embodiment of the present invention, step (d) may be a step of moving the expansion punch up and down in a direction opposite to the direction in which the second piercing punch forms the second through-hole portion in the molded object. .

According to one embodiment of the present invention, after step (d), (e) forming a burring hole portion by moving a burring punch including a burring head having a third diameter larger than the second diameter up and down; may further include.

According to one embodiment of the present invention, in step (b), the first diameter may have a length of 50% to 90% of the third diameter.

According to one embodiment of the present invention, after step (e), (f) moving a tap drill up and down to form a tap hole in the burring hole portion; may further include.

According to one embodiment of the present invention, before the step (b), (g) the needle punch including the tip is moved up and down to the position where the first through hole portion is to be formed to give the molded material a diameter greater than the first diameter. Forming a preliminary through hole portion having a small diameter; may further include.

According to an embodiment of the present invention made as described above, after performing the first piercing, the shear stress mode that occurs on the fracture surface as the second piercing is performed, which can form a through hole larger than the first piercing. By changing from tensile stress mode to compressive stress mode, shear sensitivity can be alleviated and shear damage can be reduced to improve the burring performance of the material.

In addition, the upper surface where the punch first contacts the material is cut into a relatively clean cross-section, but the lower surface, where the material falls off, has an uneven cross-section due to the complex stress state inside the material, so the expansion punch is lifted and lowered to the lower surface. Through expansion molding, Shiki can expand the hole and cleanly reprocess the uneven cross section. Of course, the scope of the present invention is not limited by this effect.

1 is a flowchart showing a piercing method according to an embodiment of the present invention.
Figure 2 is a flowchart specifically showing step (c) of the piercing method according to an embodiment of the present invention.
Figure 3 is a flow chart including step (g) of the piercing method according to an embodiment of the present invention.
4 to 8 are cross-sectional views showing the cross-section of material processing holes according to each step of the piercing method according to an embodiment of the present invention.
Figure 9 is a cross-sectional view showing a cross-section of a material processing hole according to step (g) of the piercing method according to another embodiment of the present invention.
Figures 10 and 11 are tables summarizing the results of experiments using a piercing method according to an embodiment of the present invention by diameter of the punch head.

Hereinafter, various preferred embodiments of the present invention will be described in detail with reference to the attached drawings.

The embodiments of the present invention are provided to more completely explain the present invention to those skilled in the art, and the following examples may be modified into various other forms, and the scope of the present invention is as follows. It is not limited to examples. Rather, these embodiments are provided to make the present disclosure more faithful and complete and to fully convey the spirit of the present invention to those skilled in the art. Additionally, the thickness and size of each layer in the drawings are exaggerated for convenience and clarity of explanation.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the present invention will now be described with reference to drawings that schematically show ideal embodiments of the present invention. In the drawings, variations of the depicted shape may be expected, for example, depending on manufacturing technology and/or tolerances. Accordingly, embodiments of the present invention should not be construed as being limited to the specific shape of the area shown in this specification, but should include, for example, changes in shape resulting from manufacturing.

As shown in Figure 1, the piercing method according to an embodiment of the present invention includes (a) seating the molded material (P) on the first lower die 10 in which the first molded hole portion (H1) is formed. Step, (b) moving the first piercing punch 30 including the first punch head 31 having the first diameter D1 up and down to a position corresponding to the first forming hole portion H1, and forming the molded material. Forming a first through-hole portion (P1) in (P), (c) a second piercing punch including a second punch head 41 having a second diameter (D2) larger than the first diameter (D1) 40) moving up and down to a position corresponding to the first through hole portion (P1) to form a second through hole portion (P2) in the molded material (P), (d) comprising a conical expansion head (51). Expanding and forming the second through-hole portion (P2) by moving the expansion punch 50 up and down to a position corresponding to the second through-hole portion (P2), (e) a third diameter (D3) larger than the second diameter (D2) ) forming the burring hole portion (P3) by moving the burring punch 60 including the burring head 61 up and down, and (f) moving the tap drill 70 up and down to tap the burring hole portion (P3). It may include forming the hole (P4).

In addition, as shown in FIG. 2, step (c) of the piercing method according to an embodiment of the present invention includes seating the molded material on the second lower die in which the second molding hole portion H2 is formed, and , forming the second through-hole portion (H2) in the molded material (P) within the range where the step between the second molded hole portion (H2) and the second punch head 41 is 5% to 30% of the thickness of the molded material. May include steps.

In addition, as shown in FIG. 3, the piercing method according to an embodiment of the present invention includes (b) a first piercing punch 30 including a first punch head 31 having a first diameter D1; Before the step of forming the first through-hole portion (P1) in the molded material (P) by moving it up and down to a position corresponding to the first forming hole portion (H1), (g) a needle punch including a tip portion (g) 80) may be moved up and down to the position where the first through hole portion (P1) is to be formed, thereby forming a preliminary through hole portion (P0) having a diameter smaller than the first diameter (D1) in the molded material (P). there is.

Hereinafter, a piercing method according to an embodiment of the present invention will be described in detail with reference to FIGS. 4 to 9.

As shown in FIG. 4, according to the piercing method according to an embodiment of the present invention, the molded material P is seated on the first lower die 10 where the first molded hole portion H1 is formed, and the molded material P is formed. 1 After fixing with the upper die 20, the first piercing punch 30 including the first punch head 31 having a first diameter D1 is moved to a position corresponding to the first forming hole H1. By moving it up and down, the first through-hole portion (P1) can be formed in the molded material (P). The first punch head 31 can move up and down on the central axis L of the first forming hole H1.

At this time, the first through hole portion is formed in the molded material (P) within a range where the step between the first molded hole portion (H1) and the first punch head (31) is 5% to 30% of the thickness of the molded material (P). (P1) can be molded. If the step difference between the first forming hole portion (H1) and the first punch head 31, that is, the punching clearance of the primary piercing process, is 5% or less, the first punch head 31 and the first lower die Galling due to friction at (10) increases, and when the clearance is more than 30%, the gap between the first punch head (31) and the first lower die (10) is large, causing deformation of the molded material (P), so the clearance is increased. It is preferable to form the first through hole portion (P1) in the molded material (P) within the range of 5% to 30%.

In addition, the first diameter D1 of the first punch head 31 is formed to have a length of 50% to 90% of the third diameter D3 of the burring hole portion P3, which is the final hole size on which the burring process was performed. , It can be formed to have a length that can form the first through-hole portion (P1) while leaving 50% to 200% of the thickness (t) of the molded material (P).

As shown in FIG. 5, a second piercing punch 40 including a second punch head 41 having a second diameter D2 larger than the first diameter D1 of the first punch head 31. The second through-hole portion (P2) can be formed on the molded material (P) by moving it up and down to a position corresponding to the first through-hole portion (P1). The second punch head 41 can move up and down on the central axis L of the first forming hole H1.

Therefore, as the hole size for burring is divided into two and piercing is performed, the shear stress mode generated at the fracture surface is changed from the tensile stress mode to the compressive stress mode, thereby alleviating the shear sensitivity and reducing the shear damage to the molded material. The burring performance of (P) can be improved.

At this time, a second through hole portion ( P2) can be formed. If the punching clearance of the secondary piercing process is 5% or less, a secondary shear surface occurs and formability deteriorates, and if the clearance is 30% or more, the second punch head 41 and the first lower die 10 are damaged. Since the gap is large and causes deformation and burrs in the material, which deteriorates formability, it is preferable to form the second through-hole portion (P2) in the material to be molded (P) within a clearance range of 5% to 30%. .

Here, if the level difference between the first lower die 10 and the second punch head 41 does not satisfy the punching clearance within the predetermined range described above, although not shown in the drawing, the level difference of the second punch head 41 The molded material (P) can be seated on the second lower die in which the second molded hole portion that can satisfy the range of 5% to 30% is formed, and the second through-hole portion (P2) can be molded. The first lower die 10 and the second lower die are installed in the same mold or

As shown in FIG. 6, the expansion punch 50 including the conical expansion head 51 is moved up and down to a position corresponding to the second through hole portion P2 to expand and mold the second through hole portion P2. You can. The conical expansion head 51 has a bottom surface having a fourth diameter D4 that is at least larger than the second diameter D2, so that the second through-hole portion P2 can be expanded and molded.

At this time, the expansion punch 50 may be moved up and down in a direction opposite to the direction in which the second piercing punch 40 forms the second through-hole portion H2 in the object P. In the process of the second piercing punch 40 forming the second through-hole portion H2 on the object P, the upper surface where the second punch head 41 first contacts the object P has a relatively clean cross section. Although it is cut, the lower surface from which the material is later removed appears to have an uneven cross section depending on the complex stress state inside the material.

Therefore, for example, when the second piercing punch 40 is lowered to form the second through-hole portion H2 in the object P, the expansion punch 50 is raised and lowered to expand and form the second through-hole portion P2. Non-uniform cross sections can be neatly reprocessed.

As shown in FIG. 7, the burring hole portion (P3) can be formed by moving the burring punch 60 including the burring head 61 having a third diameter (D3) larger than the second diameter (D2) up and down. there is. The burring hole portion (P3) may form a cylindrical pillar while pressing the outer peripheral surface of the burring hole portion (P3) based on the central axis (L) of the second through hole portion (H2) along the moving direction of the burring head 61. Thereafter, as shown in FIG. 8, the tap drill 70 can be moved up and down to form a tap hole (P4) in the burring hole portion (P3) where the cylindrical pillar is formed.

As shown in FIG. 8, the first piercing punch 30 including the first punch head 31 having a first diameter D1 is moved up and down to a position corresponding to the first forming hole portion H1. , Before the step (b) of forming the first through-hole portion (P1) on the molded material (P), the needle punch 80 including the tip is moved up and down to the position where the first through-hole portion (P1) is to be formed. A preliminary through-hole portion (P0) having a diameter smaller than the first diameter (D1) can be formed on the molded material (P).

In the process of forming the first through-hole part (P1) in the molded material (P) through this preliminary through-hole part (P0), the shear stress mode generated on the fracture surface is changed from the tensile stress mode to the compressive stress mode, thereby increasing the shear sensitivity. can alleviate and reduce shear damage.

Figures 10 and 11 are tables illustrating the results of a material processing experiment conducted using a piercing method according to an embodiment of the present invention. As shown in Figure 10, the present applicant conducted an experiment to form a final hole with a diameter of 72 mm by performing a burring process after piercing with a diameter of 54.84 mm. It was confirmed that microcracks occurred after burring during conventional 1-step single piercing processing. Even when using the piercing method according to an embodiment of the present invention, fine cracks were observed even when piercing with a diameter of 10 mm and 20 mm in the first piercing was performed, followed by a second piercing and a burring process.

However, when piercing with a diameter of 30 mm or more in the first piercing was performed and then the second piercing was performed and the burring process was performed, a good cutting surface with no microcracks could be obtained.

Afterwards, as shown in FIG. 11, the hole expansion ratio was measured through hole expansion molding after piercing. The HER when hole expansion molding was performed after a conventional 1-step single piercing process was 33.9%, but when the second piercing was performed after the first piercing with a diameter of 30 mm and hole expansion molding was performed, the HER was 38.3%. The HER increased by 4.4% compared to the conventional single piercing, and when the second piercing was performed after the first piercing with a diameter of 40 mm and hole expansion molding was performed, the HER was 49.9%, an increase of 16% compared to the conventional single piercing, and the HER was 49.9%, and the HER increased by 16% compared to the conventional single piercing, with a diameter of 45 mm. The HER when performing the second piercing and hole expansion molding after the first piercing was 54.6%, an increase of 20.7% compared to the conventional single piercing.

Therefore, using the piercing method according to an embodiment of the present invention, secondary piercing is performed after the first piercing and hole expansion molding is performed to change the shear stress mode occurring on the fracture surface from the tensile stress mode to the compressive stress mode. Shear sensitivity can be alleviated, shear damage can be reduced, the burring performance of the material can be improved, and a good hole expansion ratio can be obtained.

The present invention has been described with reference to the embodiments shown in the drawings, but these are merely exemplary, and those skilled in the art will understand that various modifications and equivalent other embodiments are possible therefrom. Therefore, the true scope of technical protection of the present invention should be determined by the technical spirit of the attached patent claims.

10: first lower die
20: upper die
30: 1st piercing punch
40: Second piercing punch
50: extended punch
60: Burring punch
70: Tap Dring
P: Molded material
H1: First molded hole part
H2: Second molded hole part
D1: first diameter
D2: second diameter
P1: Spare through hole part
P1: 1st through hole part
P2: Second through-hole portion
P3: Burring hole part
R: transfer roll
L: optical path
a: first angle

Claims (10)

(a) seating a molded material on the first lower die in which the first molding hole portion is formed;
(b) moving a first piercing punch including a first punch head having a first diameter up and down to a position corresponding to the first forming hole part, thereby forming a first through hole part in the object to be formed;
(c) Forming a second through-hole portion in the molded material by moving a second piercing punch including a second punch head having a second diameter larger than the first diameter up and down to a position corresponding to the first through-hole portion. steps; and
(d) expanding and forming the second through-hole portion by moving an expansion punch including a conical expansion head up and down to a position corresponding to the second through-hole portion;
Including, piercing method. According to claim 1,
In step (b),
A piercing method, wherein the first through-hole portion is formed in the molded material within a range where the step between the first molded hole portion and the first punch head is 5% to 30% of the thickness of the molded material. According to claim 1,
In step (c),
A piercing method, wherein the second through-hole portion is formed in the molded material within a range where the step between the first molded hole portion and the second punch head is 5% to 30% of the thickness of the molded material. According to claim 1,
In step (c),
(c1) seating the molded material on a second lower die in which a second molding hole portion is formed; and
(c2) forming the second through-hole portion in the molded material within a range where the step between the second molded hole portion and the second punch head is 5% to 30% of the thickness of the molded material;
Including, piercing method. According to claim 1,
In step (d) above,
The expansion head is,
A piercing method, wherein a bottom surface having a fourth diameter is formed to be at least larger than the second diameter. According to claim 1,
In step (d),
A piercing method wherein the expansion punch is moved up and down in a direction opposite to the direction in which the second piercing punch forms the second through-hole portion in the molded material. According to claim 1,
After step (d) above,
(e) forming a burring hole portion by moving a burring punch including a burring head having a third diameter larger than the second diameter up and down;
Further comprising a piercing method. According to claim 7,
In step (b),
The first diameter has a length of 50% to 90% of the third diameter. According to claim 7,
After step (e) above,
(f) forming a tap hole in the burring hole portion by moving the tap drill up and down;
Further comprising a piercing method. According to claim 1,
Before step (b) above,
(g) moving the needle punch including the tip up and down to the position where the first through hole portion is to be formed, thereby forming a preliminary through hole portion having a smaller diameter than the first diameter in the molded material;
Further comprising a piercing method.