WO2008136643A2

WO2008136643A2 - Manufacturing method for assembling nut

Info

Publication number: WO2008136643A2
Application number: PCT/KR2008/002570
Authority: WO
Inventors: Heung Kyu Kim
Original assignee: Doha Industry Co., Ltd.
Priority date: 2007-05-08
Filing date: 2008-05-07
Publication date: 2008-11-13
Also published as: WO2008136643A3; TW200920513A; JP2008279458A; TWI328477B; CN101743075B; CN101743075A; JP3998216B1

Abstract

Disclosed is a method of fabricating a clamping nut, which can be performed with low costs because no loss occurs. A hollow-cylindrical half-finished work with a closed end is formed by drawing a metallic sheet, an inner hollow-cylindrical part 4 projecting inward from the closed end 4a by reverse-drawing the hollow-cylindrical half-finished work, performing a process for increasing the thickness of the inner hollow-cylindrical part 4 so as to form a clamping part, si¬ multaneously piercing the closed end 4a of the inner hollow-cylindrical part 4. The process for increasing the thickness is preferably performed by multi-stage press-drawing which reduces the surface area of the outer surface of the inner hollow-cylindrical part 4 by a press-drawing punch, so that a volume of the material of the inner hollow-cylindrical part 4 corresponding to the reduced surface area is converted into the thickness of the inner hollow-cylindrical part 4 by plastic flow. In addition, the process for increasing the thickness may be preferably performed by swaging.

Description

MANUFACTURING METHOD FOR ASSEMBLING NUT

Technical Field

[1] The present invention relates to a method of fabricating a clamping nut through drawing of a metallic sheet. Background Art

[2] A conventional clamping nut 50 used for assembling an electronic product, such as a

PDP (Plasma Display Panel) or an LCD (Liquid Crystal Display), has a cross-sectional shape as shown in FIG. 11. The clamping nut 50 is used for mounting an electronic component or an electronic substrate on a metallic substrate or in a housing.

[3] The clamping nut 50 includes a cylindrical nut body 51, and a flange part 51 at the base of the nut body 51, and threads 53 are formed through the clamping nut 50. A groove 54 is formed between the nut body 51 and the flange part 52. The clamping nut 50 is inserted in a mounting hole formed in the metallic substrate or the housing, and then the groove 54 is engaged with the circumferential edge of the mounting hole. In this manner, the clamping cut 50 is mounted on the substrate or in the housing. Such a clamping nut 50 is fabricated through cutting or hot forging as disclosed in Patent Document 1 or Patent Document 2.

[4] If the clamping nut 50 is fabricated through cutting, there is a problem in that a long processing time and large labor force are needed. In addition, phosphor bronze with good machinability has been employed as a material of such a clamping nut in consideration of smooth cutting. However, there is a problem in that the phosphor bronze is an expensive material and that the material is lost because the groove 54 is formed through cutting. If such a clamping nut 50 is fabricated through hot forging, the clamping nut 50 will have a poor surface characteristic and state. In addition, because the forging is conducted in a high temperature environment, there is a problem in that the working environment is very poor.

[5] For the above-mentioned reasons, a clinching nut and a method of fabricating the same have been proposed as disclosed in Patent Document 3. The clinching nut is fabricated by forming a flange part and a hollow-cylindrical part initiating from the flange part through drawing of a metallic sheet, piercing the bottom of the hollow- cylindrical part, and forming threads through the inner surface of the hollow- cylindrical part.

[6] However, if the clinching nut is used for mounting an electronic component or an electronic substrate on a metallic substrate or in a housing, the following problems occur: [7] i) Because the portion for forming the threads does not have a sufficient thickness, in practice, it is difficult to form the threads. In addition, because the portion is inferior in strength, the portion may be deformed when the clinching nut is used for mounting an electronic component or an electronic substrate.

[8] ii) Because the contact area between the clinching nut and the electronic component or the electronic substrate (see FIGs. 2-4 of Patent Document 3) is not sufficient when the electronic component or the electronic substrate is mounted, the electronic component or the electronic substrate is unstable after mounting, and the surface pressure is increased to such an extent that the electronic component or the electronic substrate may be fractured due to concentrated stress.

[9] As a result, what is desired is to provide a method of fabricating a clamping nut, which can be performed with low costs without inducing loss of material, wherein the clamping nut allows an electronic component or an electronic substrate to be stably mounted.

[10] [Patent Document 1] Japanese Un-examined Patent Publication No. 2002-227817

[11] [Patent Document 2] Japanese Un-examined Patent Publication No. 2000-326047

[12] [Patent Document 3] Japanese Un-examined Patent Publication No. 2006-297455

Disclosure of Invention Technical Problem

[13] The present invention is to provide a method of fabricating a clamping nut, which can be performed with low costs without inducing loss of material.

Technical Solution

[14] In order to solve the above-mentioned problem, there is provided a method of fabricating a clamping nut including the steps of: drawing a metallic sheet, thereby forming a hollow-cylindrical half- finished work having a flange part, an outer hollow- cylindrical part, and a closed end; reverse-drawing the closed end of the hollow- cylindrical half- finished work, thereby forming an inner hollow-cylindrical part with a closed end, the hollow-cylindrical part projecting inward from the closed end; and performing a process for increasing the thickness of the inner hollow-cylindrical part, thereby forming a clamping part, simultaneously piercing the closed end of the inner hollow-cylindrical part.

[15] In addition, through slitting, one or more projections projecting outward from the outer periphery of the outer hollow-cylindrical part are formed at an area adjacent to the open end of the outer hollow-cylindrical part opposite to the closed end, and one or more fastening holes are formed between the projections and the flange part, so that the inner and outer sides of the outer hollow-cylindrical part communicate with each other. [16] Furthermore, threads may be formed through the clamping part through tapping.

[17] The reverse-drawing is preferably performed as free-drawing for forming the inner hollow-cylindrical part in a state in which the inside of the outer hollow-cylindrical part is not restrained.

[18] The process for increasing the thickness of the inner hollow-cylindrical part may be preferably performed through multi-stage press-drawing, the multi-stage press-drawing including the steps of: setting the half- finished work on a die in a state in which the flange part is positioned upward, the die including a setting bore receiving the outer hollow-cylindrical part, and a guide protrusion projecting from the bottom of the setting bore and having an outer diameter smaller than the inner diameter of the inner hollow-cylindrical part; and lowering a press-drawing punch so that the tip end of the press-drawing punch penetrates between the outer hollow-cylindrical part and the inner hollow-cylindrical part, thereby reducing the surface area of the outer surface of the inner hollow-cylindrical part, wherein a volume of the material of the inner hollow- cylindrical part corresponding to the reduced surface area is converted into the thickness of the inner hollow-cylindrical part, thereby increasing the thickness of the inner hollow-cylindrical part.

[19] In addition, the process for increasing the thickness of the inner hollow-cylindrical part may performed through swaging, the swaging step including the steps of: setting the half-finished work on a die in a state in which the flange part is positioned upward, the die including a setting bore receiving the outer hollow-cylindrical part, and a guide protrusion projecting from the bottom of the setting bore and having an outer diameter smaller than the inner diameter of the inner hollow-cylindrical part; lowering a swaging punch, the swaging punch being received in a hollow-cylindrical sleeve, so that the sleeve is freely slidable in relation to the swaging punch, and the sleeve having an inner diameter larger than the outer diameter of the inner hollow-cylindrical part; rendering the tip end of the swaging punch to come into contact with the closed end of the inner hollow-cylindrical part in a state in which the sleeve is inserted between the outer hollow-cylindrical part and the inner hollow-cylindrical part; and further lowering the swaging punch so as to press the inner hollow-cylindrical part, so that the material of the inner hollow-cylindrical part fills, by plastic flow, a space formed by the inside of the sleeve and the outer side of the swaging punch, thereby increasing the thickness of the inner hollow-cylindrical part.

[20] The slitting may include the steps of: setting the half-finished work on a slitting die in a state in which the flange part is positioned upward, the slitting die having a setting bore receiving the outer hollow-cylindrical part, and one or more slitting edges formed at the inlet area of the setting bore, the slitting edges being formed with radial recesses at a predetermined angle; and lowering a slitting punch having a shape corresponding to the slitting die.

Advantageous Effects

[21] According to the present invention, a clamping nut is fabricated through the steps of: drawing a metallic sheet, thereby forming a hollow-cylindrical half- finished work having a flange part, an outer hollow-cylindrical part, and a closed end; reverse- drawing the closed end of the hollow-cylindrical half- finished work, thereby forming an inner hollow-cylindrical part with a closed end, the hollow-cylindrical part projecting inward from the closed end; and performing a process for increasing the thickness of the inner hollow-cylindrical part, thereby forming a clamping part, simultaneously piercing the closed end of the inner hollow-cylindrical part. As a result, the material of the clamping nut is not lost, and no step for cutting is added, whereby it is possible to substantially reduce the manufacturing costs. In addition, according to the present invention, because the clamping nut can be fabricated from an inexpensive rolled steel sheet, it is possible to save material costs. If such a clamping nut is fabricated according to the present invention, it is possible to reduce the manufacturing costs by 30 to 40% as compared to the case in which such a clamping nut is fabricated through cutting or the like, as in the prior art.

[22] In addition, according to the present invention, it is possible to automatically and continuously fabricate clamping nuts with a transfer press or the like. As a result, clamping nuts can be efficiently mass-produced. Further more, if the clamping nuts are fabricated according to the present invention, the surface characteristics and conditions of the clamping nuts are very good as compared to those fabricated through forging as in the prior art, and it is not necessary to fabricate the clamping nuts in a poor environment.

[23] If a clamping nut is fabricated through drawing according to the present invention, an unnecessary portion in the clamping nut is reduced in volume as compared to that fabricated through cutting or the like as in the prior art. Consequently, it is possible to reduce the weight of the clamping nut by about 60 to 80% as compared to a conventional clamping nut.

[24] In addition, according to the present invention, it is possible to increase the thickness of the inner hollow-cylindrical part through a process for increasing the thickness. Therefore, threads can be formed through the inner hollow-cylindrical part with an increased thickness, and the strength of the clamping part can be enhanced. Furthermore, when mounting an electronic component or substrate, the electronic component or substrate comes into contact with the bottom (open end) of the outer hollow-cylindrical part, a sufficient contact area can be secured, and the electronic component or substrate can be stably mounted. In addition, because surface pressure is increased, it is possible to prevent the fracture of the electronic component or substrate.

[25] Furthermore, according to the present invention, through slitting, one or more projections projecting outward from the outer periphery of the outer hollow-cylindrical part are formed at an area adjacent to the open end of the outer hollow-cylindrical part opposite to the closed end, and one or more fastening holes are formed between the projections and the flange part, so that the inner and outer sides of the outer hollow- cylindrical part communicate with each other. As such, if the clamping nut is engaged in the mounting hole formed in an object to be joined, the projections are inserted into the mounting hole, thereby applying high compressive force to the circumferential surface of the mounting hole, and the material of the object to be joined fills the fastening holes, it is possible to rigidly and fixedly join the object and the clamping nut.

[26] In addition, if the threads are formed in the inner hollow-cylindrical part through tapping, a conventional screw can be engaged with the clamping nut, even if the screw is not a tapping screw.

[27] In addition, if the reverse-drawing is performed as free-drawing for forming the inner hollow-cylindrical part in a state in which the inside of the outer hollow-cylindrical part is not restrained, it is possible to form the inner hollow-cylindrical part without reducing the thickness thereof.

[28] According to an embodiment of the present invention, the process for increasing the thickness of the inner hollow-cylindrical part may be performed by multi-stage press- drawing, the multi-stage press-drawing including the steps of: setting the half-finished work on a die in a state in which the flange part is positioned upward, the die including a setting bore receiving the outer hollow-cylindrical part, and a guide protrusion projecting from the bottom of the setting bore and having an outer diameter smaller than the inner diameter of the inner hollow-cylindrical part; and lowering a press- drawing punch so that the tip end of the press-drawing punch penetrates between the outer hollow-cylindrical part and the inner hollow-cylindrical part, thereby reducing the surface area of the outer surface of the inner hollow-cylindrical part, wherein a volume of the material of the inner hollow-cylindrical part corresponding to the reduced surface area is converted into the thickness of the inner hollow-cylindrical part, thereby increasing the thickness of the inner hollow-cylindrical part. As such, because the thickness of the clamping part is increased, it is possible to form threads with a tapping screw, and the strength of the clamping part can be increased.

[29] In addition, according to another embodiment of the present invention, the process for increasing the thickness of the inner hollow-cylindrical part may be performed by swaging, the swaging including the steps of: setting the half- finished work on a die in a state in which the flange part is positioned upward, the die including a setting bore receiving the outer hollow-cylindrical part, and a guide protrusion projecting from the bottom of the setting bore and having an outer diameter smaller than the inner diameter of the inner hollow-cylindrical part; lowering a swaging punch, the swaging punch being received in a hollow-cylindrical sleeve, so that the sleeve is freely slidable in relation to the swaging punch, and the sleeve having an inner diameter larger than the outer diameter of the inner hollow-cylindrical part; rendering the tip end of the swaging punch to come into contact with the closed end of the inner hollow-cylindrical part in a state in which the sleeve is inserted between the outer hollow-cylindrical part and the inner hollow-cylindrical part; and further lowering the swaging punch so as to press the inner hollow-cylindrical part, so that the material of the inner hollow- cylindrical part fills, by plastic flow, a space formed by the inside of the sleeve and the outer side of the swaging punch, thereby increasing the thickness of the inner hollow- cylindrical part. As such, because the thickness of the clamping part is increased, it is possible to clamp an object or to form threads with a tapping screw, and the strength of the clamping part can be increased.

[30] Finally, according to another embodiment of the present invention, the slitting may include the steps of: setting the half-finished work on a slitting die in a state in which the flange part is positioned upward, the slitting die having a setting bore receiving the outer hollow-cylindrical part, and one or more slitting edges formed at the inlet area of the setting bore, the slitting edges being formed with radial recesses at a predetermined angle; and lowering a slitting punch having a shape corresponding to the slitting die. As such, because the projections and the fastening holes are both can be simultaneously formed only by lowering the slitting punch, the manufacturing efficiency is high- Brief Description of the Drawings

[31] The foregoing and other objects, features and advantages of the present invention will become more apparent from the following detailed description when taken in conjunction with the accompanying drawings in which:

[32] FIG. 1 shows a perspective view of a clamping nut which is fabricated according the inventive method of fabricating a clamping nut;

[33] FIG. 2 shows a vertical cross-sectional view of FIG. 1;

[34] FIG. 3 shows a horizontal cross-sectional view of FIG. 1;

[35] FIG. 4 shows a bottom view of FIG. 1;

[36] FIG. 5 shows steps of the inventive method of fabricating a clamping nut;

[37] FIGs. 6A and 6B show views for describing the sub-steps of a reverse-drawing step;

[38] FIG. 7 is a view for describing a multi-stage press forming step;

[39] FIG. 8 shows a view for describing the sub-steps of the swaging step; [40] FIG. 9 shows a view for describing a slitting step;

[41] FIG. 10 shows a view for describing a method of coupling a clamping nut to an object to be mounted; and

[42] FIG. 11 shows a cross-sectional view of a conventional clamping nut.

Best Mode for Carrying Out the Invention

[43] (Regarding a clamping nut fabricated according to the present invention)

[44] Hereinafter, exemplary embodiments of the present invention will be described with reference to the accompanying drawings.

[45] FIG. 1 shows a perspective view of a clamping nut which is fabricated according the inventive method of fabricating a clamping nut. FIG. 2 shows a vertical cross-sectional view of FIG. 1, FIG. 3 shows a horizontal cross-sectional view of FIG. 1, and FIG. 4 shows a bottom view of FIG. 1. The clamping nut 1 includes an outer hollow- cylindrical part 2, a flange part 3, an inner hollow-cylindrical part 4 (clamping part), a plurality of fastening holes 5, and a plurality of projections 6.

[46] The outer hollow-cylindrical part 2 is formed in a shape of a hollow cylinder with one closed end. The horizontal cross-sectional shape of the outer hollow-cylindrical part 2 is circular. The flange part 3 extends from the open end of the outer hollow- cylindrical part 2 perpendicular to the axial direction of the outer hollow-cylindrical part 2. As shown in FIGs. 3 and 4, the flange part 3 takes a hexagonal shape in the present embodiment.

[47] The inner hollow-cylindrical part 4 is formed in a hollow-cylindrical shape, and extends from the closed end 2a of the outer hollow-cylindrical part 2 into the inside of the outer hollow-cylindrical part 2 coaxial to the outer hollow-cylindrical part 2. The inner hollow-cylindrical part 4 serves as a clamping part. The inner circumferential surface of the inner hollow-cylindrical part 4 is formed with threads 7.

[48] The projections 6 are formed around an area adjacent to the open end of the outer hollow-cylindrical part 2, wherein each of the projections 6 projects outward from the outer circumferential surface of the outer hollow-cylindrical part 2 at a predetermined angle. In addition, the projections 6 project inward from the outer hollow-cylindrical part 2 as well. The fastening holes 5 are formed between the flange part 6 and the projections 6 of the outer hollow-cylindrical part 2, so that the inside and outside of the outer hollow-cylindrical part 2 communicate with each other.

[49] (Regarding the inventive method of fabricating a clamping nut)

[50] Now, the inventive method of fabricating the clamping nut 1 will be described. FIG.

5 shows steps of the inventive method of fabricating a clamping nut.

[51] Through a blanking step, a blank of a rolled steel sheet is extracted in such a manner that a circular opening is formed in the steel sheet, thereby forming a circular blank. The circular blank is transferred to a first drawing step. In the first drawing step, the circular blank is set on a drawing die with a drawing opening, a circular recess being formed around the top of the drawing opening, and a substantially cylindrical punch is lowered from the upper side so as to plastically deform the circular blank, thereby forming a cylinder shape with a closed end.

[52] If the first drawing step is terminated, the firstly drawn hollow-cylindrical half- finished work with a closed end is transferred to second and third drawing steps in sequence, so that the firstly drawn hollow-cylindrical half-finished work is gradually drawn more deeply, thereby forming a thirdly drawn hollow-cylindrical half- finished work with a closed end. The principal parameters of each of the first to third drawing steps are the radius of a punch and an opening of a die, a distance between the punch and the die, drawing rate, punch force, die cushion pressure, lubrication, etc. If the third drawing step is terminated, the thirdly drawn hollow-cylindrical half-finished work with a closed end is transferred to a reverse-drawing step.

[53] FIGs. 6A and 6B show views for describing the sub-steps of a reverse-drawing step.

The reverse-drawing step consists of a free-drawing step (FIG. 6A) and a net-shape forming step (FIG. 6B). The die 19 used in the free-drawing step has a substantially cylindrical setting protrusion 19a as shown in FIG. 6 A. The diameter of the setting protrusion 19a is somewhat smaller than the inner diameter of the external hollow- cylindrical part 2. The punch 20 used in the free-drawing step has a cylindrical shape as shown in FIG. 6A.

[54] The hollow-cylindrical half-finished work with a closed end is set on the die 19 in such a manner that the flange part 3 is positioned downward, and then the punch 20 is lowered so that the punch 20 comes into contact with and plastically deforms the closed end 2a of the hollow-cylindrical half- finished work, thereby forming an inner hollow-cylindrical part 4. Like this, the free-drawing step is performed in a state in which the inner and outer sides of the outer hollow-cylindrical part 2 are not restrained.

[55] The principal process parameters of the free-drawing step are the shape of the punch

20, the drawing rate and punching force at the time of roughly forming the inner hollow-cylindrical part 4, etc.

[56] When the free-drawing step is terminated, the semi-finished work is shaped in the form of the inner hollow-cylindrical part 4. As shown in FIG. 6B, the net-shape forming die 21 used in the net-shape forming step takes a cylindrical shape, and a groove serving as a net-shaping recess 21a is coaxially formed on the top of the net- shape forming die 21. The outer diameter of the net-shape forming die 21 is somewhat smaller than the inner diameter of the outer hollow-cylindrical part 2. As shown in FIG. 6B, the net-shape forming die 22 used in the net-shape forming step has a net- shape forming protrusion 22a in a cylindrical shape. [57] The half-finished work roughly formed with the inner hollow-cylindrical part 4 is set on the net-shape forming die 21 in such a manner that the flange part 3 is positioned downward, and the net-shape forming punch 22 is lowered and plastically deforms the roughly formed inner hollow-cylindrical part 4 so that the space between the net-shape forming recess 21a and the net-shape forming protrusion 22a is filled with the material of the half -finished work, thereby forming the net- shape of the inner cylinder- shape part 4.

[58] As described above, the reverse-drawing step for forming the inner hollow- cylindrical part 4 is divided into the free-drawing step and the net-shape forming step, and the inner hollow-cylindrical part 4 is roughly formed through free-drawing without restraining the inner and outer sides of the outer hollow-cylindrical part 2. As such, it is possible to prevent the hindrance of plastic flow, and hence to prevent the thickness of the inner hollow-cylindrical part from being thinned, wherein the hindrance of plastic flow is caused when the outer hollow-cylindrical part 2 is restrained.

[59] Although the free-drawing step in the present embodiment is performed without restraining both the inner and outer sides of the outer hollow-cylindrical part 2, it is possible to prevent the thickness of the inner hollow-cylindrical part 4 from being thinned, even if the inner hollow-cylindrical part 4 is roughly formed in the state in which only the inner side of the outer hollow-cylindrical part 4 is not restrained.

[60] When the reverse-drawing step is terminated, the half-finished work with the inner hollow-cylindrical part 4 is transferred to a multi-stage press-drawing step.

[61] FIG. 7 is a view for describing a multi-stage press-drawing step. The die 23 used in the multi-stage press-drawing step is formed with a cylindrical setting bore 23a as shown in FIG. 7. The outer hollow-cylindrical part 2 is received in the setting bore 23a. A guide punch 23b is installed within the setting bore 23a. The guide punch 23b has a guide protrusion 23d projecting from a substantially cylindrical base member 23c. The cross-section of the guide protrusion 23d is circular and coaxial to the setting bore 23a. Because the outer diameter 23d is smaller than the inner hollow-cylindrical part 4, a gap between the inner hollow-cylindrical part 4 and the guide protrusion 23d is remained empty when the half-finished work formed with the inner hollow-cylindrical part 4 is set on the die 23.

[62] The press-drawing punch 24 used in the multi-stage press-drawing step has a cylindrical shape, and a drawing recess 24a is formed on the tip end 24b of the press- drawing punch 24. The cross-sectional shape of the drawing recess 24a is circular and coaxial to the periphery of the press-drawing punch 24. The inner diameter of the drawing recess 24a is smaller than the outer diameter of the inner hollow-cylindrical part 4.

[63] In the multi-stage press-drawing step, the outer hollow-cylindrical part 2 is inserted to the drawing recess 24a in the state in which the flange part 3 is positioned upward, whereby the half- finished work is set on the die 23. From this state, if the press- drawing punch 24 is lowered, the tip end 24b is inserted between the outer hollow- cylindrical part 2 and the inner hollow-cylindrical part 4. As described above, because the inner diameter of the drawing recess 24a is smaller than the outer diameter of the inner hollow-cylindrical part 24, the inner hollow-cylindrical part 4 is narrowed by the drawing recess 24a. Consequently, the outer surface of the inner hollow-cylindrical part 4 is reduced, and the volume corresponding to the reduced amount of the outer surface plastically flows and is converted to the thickness of the inner hollow- cylindrical part 4, thereby increasing the thickness of the inner hollow-cylindrical part 4. Meanwhile, because the inner side of the inner hollow-cylindrical part 4 is restrained in shape by the guide protrusion 23d, the shape of the inner side of the inner hollow- cylindrical part 4 is maintained as it is. In addition, because the inner hollow- cylindrical part 4 is subjected to the axial compressive force of the press-drawing punch 24, the height of the hollow-cylindrical part 4 is compressed to the height of the guide protrusion.

[64] After the multi-stage press-drawing step is terminated, the inner diameter of the hollow-cylindrical part 4 becomes substantially equal to the inner diameter of the drawing recess 24a, and the inner diameter of the inner hollow-cylindrical part 4 becomes substantially equal to the outer diameter of the guide protrusion 24a. Like this, it is possible to increase the thickness of the inner hollow-cylindrical part 4 by properly setting the inner diameter of the drawing recess 24a and the outer diameter of the guide protrusion 23d. In addition, according to the present embodiment, the thickness of the inner hollow-cylindrical part 4 is increased by about 3% by performing multi-stage press-drawing one time. According to the present embodiment, if the multi-stage press-drawing is performed three to four times by using a press- drawing punch 24a having a drawing recess 24a with a smaller inner diameter, and a guide punch 23b having a guide protrusion 23d with a smaller outer diameter, it is possible to increase the thickness of the inner hollow-cylindrical part 4 by about 10%. If the multi-stage drawing step is terminated, the half-finished work is transferred to a piercing step.

[65] In the piercing step, the half-finished work is set on a piercing die (not shown), and the punch is lowered to pierce the closed end 4a of the inner hollow-cylindrical part 4 (FIG. 5). When the piercing step is terminated, the half-finished work is transferred to a swaging step.

[66] FIG. 8 shows a view for describing the sub-steps of the swaging step. As shown in

FIG. 8, the die 26 used in the swaging step is formed with a cylindrical setting bore 26a. The outer hollow-cylindrical part 2 is received in the setting bore 26a. A guide punch 27 is installed within the setting bore 26a. The guide punch 27a has a guide protrusion 27b protruding from the top of a substantially cylindrical base member 27a. The cross-sectional shape of the guide protrusion 27b is circular and coaxial to the setting bore 26a. The outer diameter of the guide protrusion 27b is somewhat smaller than the outer diameter of the inner hollow-cylindrical part 4.

[67] The punch used in the swaging step includes a hollow-cylindrical sleeve 28, and a cylindrical swaging punch 29 received in the sleeve 28. The sleeve 28 is freely slidable in relation to the swaging punch 29. The outer diameter of the swaging punch 29 is somewhat smaller than the inner diameter of the sleeve 28. At least one spring 30 is mounted on the top of the sleeve. The inner diameter of the sleeve 28 is larger than the inner hollow-cylindrical part 4, and thus a clearance c is formed between them as shown in FIG. 8.

[68] In the swaging step, the half-finished work is set on the die 26 by inserting the outer hollow-cylindrical part 2 into the setting bore 26a in the state in which the flange part 3 is positioned upward. The sleeve 28 and the swaging punch 29 are lowered. If the sleeve 28 is inserted between the outer hollow-cylindrical part 2 and the inner hollow- cylindrical part 4, and the tip end of the sleeve 28 comes into contact with the closed end 2a of the outer hollow-cylindrical part 2, the spring 30 is compressed, and the lowering of the sleeve 28 is stopped. In addition, if the swaging punch 29 is lowered, the inner hollow-cylindrical part 4 is compressed. However, because the inner side of the inner hollow-cylindrical part 4 is restrained by the guide protrusion 27b of the guide punch 27, the material of the inner hollow-cylindrical part 2 cannot plastically flow inward. As the swaging punch 29 is lowered, the material of the inner hollow- cylindrical part 2 outwardly plastically flows. Consequently, the material fills the space between the inside of the sleeve 28 and the outside of the swaging punch 29, thereby increasing the thickness of the inner hollow-cylindrical part 4. Assuming that the thickness of the inner hollow-cylindrical part 4 prior to performing the swaging is t, the thickness of the inner hollow-cylindrical part 4 is increased to t+c through the swaging, wherein c indicates the increased thickness. According to the present embodiment, the thickness of the inner hollow-cylindrical part 4 is increased by about 10 to 30%.

[69] The principal process parameters of the swaging step are the punching force of the swaging punch 29, the ratio of the thickness to the length of the inner hollow- cylindrical part 4, lubrication, etc. If the swaging step is terminated, the half- finished work is transferred to a slitting step.

[70] As described above, through the multi-stage press-drawing or swaging, the thickness of the inner hollow-cylindrical part is increased, thereby forming a clamping part.

[71] FIG. 9 shows a view for describing a slitting step. The slitting die used in the slitting step is formed with a cylindrical setting bore 32a, as shown in FIG. 9. The setting bore 32a is somewhat larger than the outer periphery of the outer hollow-cylindrical part 2. The outer hollow-cylindrical part 2 is received within the setting bore 32a. A plurality of slitting edges 32b are formed at the inlet area of the setting bore 32a by a plurality of radial recesses.

[72] The slitting punch 33 used in the slitting step is cylindrical. The outer diameter of the slitting punch 33 is somewhat smaller than the inner diameter of the outer hollow- cylindrical part 2. The slitting punch 33 has a plurality of slitting projections 33a projecting from the periphery of the slitting punch 33 at the positions corresponding to the positions of the slitting edges 32b, wherein the shape of the slitting projections 33a corresponds to that of the slitting edges 33b in shape. In other words, the slitting projections 33a project from the periphery of the slitting punch 33 at a predetermined angle. If the slitting punch 33 is lowered, the slitting punches 33a are engaged with the slitting edges 33b.

[73] In the slitting step, the half-finished work is set on the slitting die 32 by inserting the outer hollow-cylindrical part 2 into the setting bore 32a in the state in which the flange part is positioned upward. From this state, if the slitting punch 33 is lowered, the slitting projections 33a are engaged with the slitting edges 32b, thereby shearing the area adjacent to the open end of the outer hollow-cylindrical part 4, thereby forming fasting openings 5 in the area as shown in FIGs. 1 and 2. At the same time, the sheared area is coined by the slitting projections 33a, thereby forming the projections 6. The principal process parameters of the slitting step are the distance between the slitting die 32 and the slitting punch 33, the angle of cutting edge of the slitting projections 33a, and the slitting force. If the slitting step is terminated, the half-finished work is transferred to a trimming step.

[74] In the trimming step, the unnecessary portion of the flange part 3 of the half-finished work is trimmed into a non-circular shape, such as a rectangular, hexagonal, octagonal, or saw tooth shape. In the present embodiment, the flange part 3 is formed in a hexagonal shape as shown in FIGs. 1 to 4.

[75] In the present embodiment, the steps of blanking to trimming are performed by a transfer press (A press apparatus performing each of the above-mentioned steps by transferring a half-finished work to individual dies with a transfer unit). Like this, the steps of blanking to trimming can be automatically and continuously performed by a transfer press, thereby efficiently producing clamping nuts. In addition, a half-finished work may be sequentially transferred from the blanking step to the trimming step (This may be performed by a press apparatus which has a plurality of molds arranged at a predetermined interval and sequentially transferred within a die, so that individual steps are sequentially performed while transferring a half- finished work by the above- mentioned interval for each step, wherein the press apparatus is also called as progressive press).

[76] After the trimming step is terminated, the half-finished work is formed with threads within the inner hollow-cylindrical part 4, which is a clamping part, in a tapping step. The tapping step is formed by a rolling tap or a machine tap.

[77] When the tapping step is terminated, grease, cut chips and foreign matter attached to the half-finished work are removed through a cleaning step including pretreatment cleansing, degreasing cleansing, and water cleansing. If the cleaning step is terminated, the half-finished work is plated in a plating step including electroless plating, molten zinc plating, or the like, whereby a clamping nut 1 is completed. By plating the surface of the clamping nut 1 in this manner, it is possible to improve corrosion resistance, whereby it is possible to prevent deterioration of the clamping nut, which is caused as time goes by. If the clamping nut 1 is fabricated from a non-ferrous metal, it is possible to omit the plating step.

[78] (Method of joining a clamping nut to an object 40 to be joined)

[79] Next, a description will be made regarding a method of joining a clamping nut 1 fabricated by the inventive method to an object 40. FIG. 10 shows a view for describing a method of joining a clamping nut to an object to be mounted. The clamping nut 1 is joined to an object 40 in a press riveting step. The object 40 is formed with a mounting hole 40a which is somewhat larger than the outer periphery of the outer hollow-cylindrical part 2. The insertion die 35 used in the press riveting step is formed with a setting bore 35a which is somewhat larger than the outer periphery of the outer hollow-cylindrical part 2, so that the setting bore 35a receives the outer hollow-cylindrical part 2. A substantially cylindrical forming punch 36 is arranged above the setting bore 35 a.

[80] The object 40 is set on the insertion die 35 in such a manner that the mounting hole

40a and the setting bore 35a are coaxial to each other, and the outer hollow-cylindrical part 2 is inserted into the mounting hole 40a and the setting bore 35a, thereby setting the clamping nut 1. In this state, if the press forming punch 36 is lowered, the projections 6 are plastically deformed and penetrate into the mounting hole 40a, and the flange part 3 is also inserted into the object 40. When the flange part 3 is inserted into the object 40, the material of the object 40 plastically flows into the fastening holes 5 by the volume of the flange part 3 press-fitted in the object 40, thereby filling the fastening holes 5. The projections 6 are inserted into the mounting hole 40a in this manner, and strong compressive force is applied to the surface of the mounting hole 40a, whereby the clamping nut is fixedly joined to the object 40. In addition, because the material of the object 40 fills the fastening holes 5, the object 40 and the clamping nut 1 are more rigidly and fixedly joined to each other.

[81] As described above, because the flange part 3 is formed in a non-circular shape, such as a rectangular, hexagonal, octagonal, or saw tooth shape, and inserted into the object 40, the clamping the rotation of the clamping nut 1 is suppressed when a screw is engaged the clamping nut 1, thereby preventing the fracture of joint between the clamping nut 1 and the object 40.

[82] The principal process parameters of the press-riveting step are the distance between the mounting hole 40a of the object 40 and the clamping nut 1, the thickness of the projections 6, and the width and height of the fastening holes 5.

[83] Although, in the present embodiment, the threads 7 are formed in the clamping part, i.e. in the inner hollow-cylindrical part 4, in the tapping step described above, the tapping step may be omitted if the clamping nut is clamped by a tapping screw.

[84] Although, in the present embodiment, the thickness of the area forming the clamping part in the inner hollow-cylindrical part is increased through multi-stage press-drawing and swaging, the thickness of the inner hollow-cylindrical part 4 may be increased by using only one of the multi-stage press-drawing and the swaging as desired. In addition, although, in the above-mentioned embodiments, multi-stage press-drawing is performed, then piercing is performed, and then swaging is performed, the present invention is not limited to the order of these steps, and the order of the steps may be optionally determined.

[85] Furthermore, the material used for the inventive method of fabricating a clamping nut is not limited to a rolled steel sheet, and the inventive method is applicable to any type of metallic sheets, including a non-ferrous metal sheet, such as a copper sheet, a stainless steel plate, an aluminum sheet, etc.

Claims

[1] A method of fabricating a clamping nut comprising the steps of: drawing a metallic sheet, thereby forming a hollow-cylindrical half- finished work having a flange part 3, an outer hollow-cylindrical part 2, and a closed end

2a; reverse-drawing the closed end of the hollow-cylindrical half- finished work, thereby forming an inner hollow-cylindrical part 4 with a closed end 4a projecting inward from the closed end; and performing a process for increasing the thickness of the inner hollow-cylindrical part 4 of the half- finished work, simultaneously piercing the closed end 4a of the inner hollow-cylindrical part 4 of the half-finished work, thereby forming a clamping part,.

[2] The method as claimed in claim 1, further comprising the step of slitting for forming one or more projections 6 projecting outward from the outer periphery of the outer hollow-cylindrical part 2 at an area adjacent to the open end opposite to the closed end 2a, and for forming one or more fastening holes 5 between the projections 6 and the flange part 3, so that the inner and outer sides of the outer hollow-cylindrical part 2 communicate with each other.

[3] The method as claimed in claim 1 or 2, further comprising the step of: forming threads 7 through the clamping part.

[4] The method as claimed in any of claims 1 to 3, wherein the reverse-drawing is performed as free-drawing for forming the inner hollow-cylindrical part 4 in a state in which the inside of the outer hollow-cylindrical part 2 is not restrained.

[5] The method as claimed in any of claims 1 to 4, wherein the process for increasing the thickness of the inner hollow-cylindrical part 4 is performed by multi-stage press-drawing, the multi-stage press-drawing comprising the steps of: setting the half- finished work on a die 23 in a state in which the flange part 3 is positioned upward, the die comprising a setting bore 23a receiving the outer hollow-cylindrical part 2, and a guide protrusion projecting from the bottom of the setting bore 23 a and having an outer diameter smaller than the inner diameter of the inner hollow-cylindrical part; and lowering a press-drawing punch 24 so that the tip end of the press-drawing punch penetrates between the outer hollow-cylindrical part 2 and the inner hollow- cylindrical part 4, thereby reducing the surface area of the outer surface of the inner hollow-cylindrical part 4, wherein a volume corresponding to the reduced surface area is converted into the thickness of the inner hollow-cylindrical part, thereby increasing the thickness of the inner hollow-cylindrical part 4.

[6] The method as claimed in any of claims 1 to 5, wherein the process for increasing the thickness of the inner hollow-cylindrical part 4 is performed by swaging, the swaging comprising the steps of: setting the half- finished work on a die 26 in a state in which the flange part 3 is positioned upward, the die 26 comprising a setting bore 26a receiving the outer hollow-cylindrical part, and a guide protrusion 27b projecting from the bottom of the setting bore 26a and having an outer diameter smaller than the inner diameter of the inner hollow-cylindrical part 4; lowering a swaging punch 29, the swaging punch being received in a hollow- cylindrical sleeve 28, so that the sleeve 28 is freely slidable in relation to the swaging punch 29, and the sleeve 28 having an inner diameter larger than the outer diameter of the inner hollow-cylindrical part 4; rendering the tip end of the swaging punch 29 to come into contact with the closed end of the inner hollow-cylindrical part 4 in a state in which the sleeve 28 is inserted between the outer hollow-cylindrical part 2 and the inner hollow- cylindrical part 4; and further lowering the swaging punch 29 so as to press the inner hollow-cylindrical part 4, so that the material of the inner hollow-cylindrical part 4 fills, by plastic flow, a space formed by the inside of the sleeve 28 and the outer side of the swaging punch 29, thereby increasing the thickness of the inner hollow- cylindrical part 4.

[7] The method of as claimed in claim 2, wherein the slitting step comprising the steps of: setting the half-finished work on a slitting die 32 in a state in which the flange part 3 is positioned upward, the slitting die having a setting bore 32a receiving the outer hollow-cylindrical part 4, and one or more slitting edges formed at the inlet area of the setting bore 32a, the slitting edges being formed with radial recesses at a predetermined angle; and lowering a slitting punch 33 having a shape corresponding to the slitting die 32.