Punch rivet

Abstract

Punch rivet (100), which comprises: a headboard (10); a shaft part (30) which is integrally connected to the head part (10); a plurality of ribs (50) formed in a spiral shape on an outer peripheral surface of the shaft part (30) along a longitudinal direction of the shaft part (30) and integrally connected to the head part (10); and a straight part (70) formed integrally on an upper part of the rib (50) at a connecting part at which the head part (10) and the rib (50) are connected, wherein the shaft part (30) is a circular cylinder, the ribs (50) are arranged on the outer peripheral surface of the shaft part (30) with a uniform distance therebetween, the shaft part (30) has a connecting end (32) connected to the head part (10) and a free end (34) which is an end opposite to the connecting end (32), and the ribs (50) are formed in a spiral shape from the connecting end (32) of the shaft part (30) to the free end (34) of the shaft part (30), and the straight part (70) is integrally connected to the connecting part to which the ribs (50) and the head part (10) are connected, and a straight portion (71) formed in the straight portion (70) extends in the upper portion of the rib (50) from an inner surface of the rib (50) to a lower surface of the head portion (10) along an axial direction of the shaft portion (30), wherein the inner surface is a surface facing the lower surface of the head part (10).

Description

BACKGROUND OF THE INVENTION(a) Field of the Invention

[0001] The present invention relates to a self-piercing rivet. In particular, the present invention relates to a self-piercing rivet that can join two or more objects together. (b) Description of the prior art

[0002] Environmental problems are of great importance to the automotive industry, and the use of aluminum alloys and plastic materials in a vehicle body to reduce the weight of the vehicle body and reduce fuel consumption is one of the solutions to the environmental problems.

[0003] For these purposes, alternative joining methods instead of conventional spot welding have been investigated and developed during the assembly of a vehicle body.

[0004] For some time now, a self-piercing riveting system using a self-piercing rivet has been increasingly used. Self-piercing rivets are described, for example, in DE 10 2013 105 343 A1 and DE 600 14 413 T2.

[0005] According to conventional riveting techniques, objects to be joined, such as steel sheets, are joined by forming a head portion after drilling a rivet hole and inserting a rivet into the rivet hole. However, the rivet is forced into the objects to be joined by hydraulic or pneumatic pressure, without forming the rivet hole as in self-pierce riveting techniques. At this time, the rivet undergoes plastic deformation, joining the objects to be joined together.

[0006] A self-piercing rivet is used to join metal sheets according to the self-piercing riveting technique, and the self-piercing rivet has a head and a partially hollow cylindrical shank.

[0007] For example, the shank of a self-piercing rivet penetrates an upper sheet using a punch of a setting tool. At this time, the shank is held by a die and deformed outward. Furthermore, since the shank is pressed into a lower sheet in a state where the head portion is held by the upper sheet, the upper and lower sheets are joined.

[0008] Conventionally, the punch is provided at an upper part of a C-frame, and an anvil is provided at a lower part thereof.

[0009] In a conventional technique, two objects to be joined are placed between the punch and the anvil, and then the rivet is pressed by the punch, pierces the upper object to be joined, is encapsulated at the lower object to be joined, and is deformed outward through a forming cavity of the anvil, and thus the objects to be joined are integrally joined.

[0010] The joining technique using the self-piercing rivet can be used to assemble aluminum sheets in a vehicle body, which is not easy to do by spot welding.

[0011] Likewise, the self-piercing riveting system can provide excellent strength and fatigue resistance properties and avoid deformation on a sheet near the rivet, so that the self-piercing riveting system can be acceptable from an aesthetic point of view.

[0012] However, in a conventional technique, a shank of the self-piercing rivet (hereinafter referred to as a "rivet") pierces the upper object to be joined, is encapsulated by the lower object to be joined, and is deformed outward by the anvil, and thus the rivet cannot be easily removed from the objects to be joined.

[0013] This means that in conventional technology, if it is necessary to separate the objects to be joined, the rivet must be disassembled or the rivet part must be pulled out, thus damaging and deforming the objects to be joined. Therefore, the objects to be joined must be replaced without reuse.

[0014] Likewise, in the conventional technique, since the punch and anvil are used to press the rivet to connect the objects to be joined, an applicable degree of freedom of riveting may be reduced due to interactions with other equipment.

[0015] Since the shank of the conventional self-piercing rivet is designed as an annular punching edge, a penetrated part of the upper sheet is completely punched out by the annular edge when the shank penetrates the upper sheet and is pressed into the lower sheet.

[0016] Since the penetrated part of the upper sheet punched out by the shaft cannot form a mechanical interlock of the upper and lower sheets and remains as dead metal, the joining strength of the upper and lower sheets may be impaired.

[0017] Furthermore, since the dead metal cannot connect the upper and lower sheets with sufficient strength, the upper sheet twists relative to the lower sheet.

[0018] Accordingly, various techniques are used to prevent twisting of the upper sheet according to known methods. For example, multiple rivets are used to prevent twisting of the upper sheet.

[0019] If multiple rivets are used, processes can become complicated, productivity can be affected, and product costs can increase due to an increase in processes and components.

[0020] Since the shank of the rivet is designed as an annular punching edge, the shank penetrates into the upper sheet with an annular shape and increases a joining stress according to conventional techniques.

[0021] The above information disclosed in this Background section is provided only to enhance understanding of the background of the invention and may therefore contain information that does not constitute prior art already known to a person skilled in the art in this country. SUMMARY OF THE INVENTION

[0022] The present invention has been made with respect to a self-piercing rivet having the advantage of easy removal of the rivet by improving a shape of a shank part.

[0023] The present invention has been made with respect to a self-piercing rivet having further advantages in that the joining load and the insertion power can be reduced but the shear strength can be increased, and interference with other equipment can be reduced by allowing one-sided riveting using a punch, thus improving a degree of freedom of riveting.

[0024] The present invention has been made with respect to a self-piercing rivet having advantages in that a penetrated portion enhances the joining strength of objects to be joined by improving a shape of a shank portion so as not to completely punch out the penetrated portion.

[0025] The present invention has been made with respect to a self-piercing rivet having advantages in preventing relative rotation of objects to be joined using the penetrated part which is not completely punched out even though only one rivet is used.

[0026] The present invention has been made with respect to a self-piercing rivet with advantages of preventing damage to a forging die in a forging process of a rivet, increasing the life of the forging die, promoting mass production of the rivet, and improving the joining strength of objects to be joined.

[0027] A self-piercing rivet according to the present invention comprises: a head portion; a shank portion integrally connected to the head portion; a plurality of ribs formed on an outer peripheral surface of the shank portion along a longitudinal direction of the shank portion in a spiral shape and integrally connected to the head portion; and a straight portion integrally formed at a connecting portion at which the head portion and the rib are connected.

[0028] The shaft part is a circular cylinder, the ribs are arranged on the outer peripheral surface of the shaft part with a constant distance therebetween, the shaft part has a connecting end connected to the head part and a free end which is an end opposite to the connecting end, and the ribs are formed in a spiral shape from the connecting end of the shaft part to the free end of the shaft part.

[0029] The straight part is integrally connected to the connecting part at which the ribs and the head part are connected, and a straight portion formed in the straight part extends in the upper part of the rib from an inner surface of the rib to a lower surface of the head part along an axial direction of the shaft part, the inner surface being a surface facing the lower surface of the head part.

[0030] The straight part has a circumferential surface that corresponds to the outer circumferential surface of the shaft part.

[0031] The straight part can guide the rivet so that it can be removed from a forging die without difficulty when the rivet is ejected from the forging die.

[0032] The rib may have a rib surface having a predetermined width and rib side surfaces having a predetermined thickness between an outer peripheral surface of the shaft part and the rib surface.

[0033] The thickness of the rib can be greater than the width of the rib.

[0034] The ribs may pierce an upper plate member and a lower plate member that overlap each other, be plastically deformed within the lower plate member, and be fixed to the lower plate member.

[0035] In one or more exemplary embodiments, since the ribs are formed with a shank portion in a spiral shape, the rivet can twist during press-fitting for joining the objects to be joined, and the self-piercing rivet can be removed from the target portion for riveting the objects to be joined by a torque in the opposite spiral direction of the ribs.

[0036] Thus, in one or more exemplary embodiments, if it is necessary to separate the objects to be joined again, the rivet can be easily removed without being disassembled or pulling out the riveting part, and thus the objects to be joined can be reused.

[0037] In one or more exemplary embodiments, since the spiral ribs are formed on the shank part, the total surface area of the rivet can be increased, the shear strength with respect to the upper and lower plate members can be improved, and a joining load and press-in performance of objects to be joined can be reduced, thus the operational stability of the self-pierce riveting system can be improved.

[0038] In one or more exemplary embodiments, since a die provided with a receiving part can be used to appropriately hold the objects to be joined, no separate anvil of a conventional technique is required, thus interactions can be minimized, and a degree of freedom of riveting can be improved.

[0039] In one or more exemplary embodiments, an upper and a lower plate member provided with holes as a target part for riveting may be connected by riveting, and thus the die does not need to be provided with a receiving part such as a hole or a groove, and a lower surface of the lower plate member may be flat.

[0040] Therefore, in one or more exemplary embodiments, the flat lower surface of the lower plate member may meet the needs of the automotive industry, which prefers objects to be joined without protrusions.

[0041] In one or more exemplary embodiments, since the penetrated part is not completely punched out, the relative rotation of objects to be joined can be prevented even though only one rivet is used, and the joining strength of the objects to be joined can be improved.

[0042] In one or more exemplary embodiments, since one or very few rivets can join the objects to be joined, productivity can be improved and manufacturing costs can be reduced by reducing the number of riveting operations and elements.

[0043] Furthermore, since a straight part is formed at a connecting part of a head part and a rib, it is possible to prevent damage to a forging die in a forging process and increase the life of the forging die, and improve the mass production of the rivet.

[0044] Furthermore, since the straight part is integrally formed at a connecting part of the rib and the head part, a clearance formed between the upper plate member and the ribs is reduced by the straight part, and the joining strength of the upper plate member and the lower plate member is improved when an upper plate member and a lower plate member are joined.

[0045] Furthermore, the self-piercing rivet according to an exemplary embodiment of the present invention can be used for joining a high-strength sheet and an aluminum sheet. BRIEF DESCRIPTION OF THE DRAWINGS

[0046] The drawings illustrate exemplary embodiments of the present invention and are not intended to limit any aspect of the invention in any way. Fig. 1 is a drawing showing a self-piercing rivet according to an exemplary embodiment of the present invention. Fig. 2 is a perspective view of a self-piercing rivet according to an exemplary embodiment of the present invention. Fig. 3 and Fig. 4 are drawings for explaining an operation of a self-piercing rivet according to an exemplary embodiment of the present invention. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0047] The present invention will now be described in more detail with reference to the accompanying drawings, in which exemplary embodiments of the invention are shown. As those skilled in the art will appreciate, the described embodiments may be modified in various different ways, all without departing from the spirit or scope of the present invention.

[0048] The description of components not required for explaining the present invention will be omitted, and the same components are designated by the same reference numerals in this description.

[0049] Furthermore, the size and thickness of the components shown in the drawings may differ from the actual size and thickness of the components for better understanding and ease of description. Therefore, the present invention is not limited to the drawings.

[0050] In the detailed description, the enumeration numbers are used to distinguish components with the same names and have no other special meanings.

[0051] In the description, unless expressly stated otherwise, the word "comprise" and variations such as "comprises" or "comprising" are understood to include the listed elements but not to exclude any other elements.

[0052] In the description, terms such as “part” and “means” mean a unit of a comprehensive element with at least one function or movement.

[0053] Fig. 1 is a drawing showing a self-piercing rivet according to an exemplary embodiment of the present invention.

[0054] In the description, objects to be joined can be defined as base materials for joining with a rivet, and a joined article can be defined as a machined article from which the objects to be joined are joined by rivets.

[0055] In Fig. 1, a self-piercing rivet 100 (hereinafter referred to as a “rivet”) according to an exemplary embodiment of the present invention connects at least two metal sheets.

[0056] As examples in this description, two metal sheets are used, and the two metal sheets are referred to as upper plate member 1 and lower plate member 2, respectively.

[0057] In the specification, an upper surface or a top surface is defined as a surface facing upward in the drawings, and a lower surface or a bottom surface is defined as a surface facing downward in the drawings.

[0058] One of the sheets 1 and 2, respectively, arranged in an upper position in the drawings is referred to as the upper plate member 1, and the other sheet is referred to as the lower plate member 2 for ease of understanding. Although other plate members may be arranged between the upper plate member 1 and the lower plate member 2, for ease of understanding, the self-piercing rivet 100 for connecting the upper plate member 1 and the lower plate member 2 will be described.

[0059] The terms described above are defined for convenience of understanding, and thus the terms cannot limit the spirit or scope of the present invention, and further definitions may be used in the description as appropriate for convenience of understanding.

[0060] The self-piercing rivet 100 can connect objects to be joined, such as the upper and lower plate elements 1 and 2, which overlap each other, by a self-piercing rivet system.

[0061] That is, the self-piercing riveting system presses the rivet 100 into the upper plate member 1 and the lower plate member 2, which overlap each other, with a predetermined pressure, and is configured to connect the upper plate member 1 and the lower plate member 2 by plastic deformation of the upper plate member 1, the lower plate member 2 and the rivet 100.

[0062] In an exemplary embodiment of the present invention, the upper plate member 1 and the lower plate member 2 are made of a plastic material, a rubber material, an aluminum sheet, or a steel sheet (including a high-strength steel sheet).

[0063] The upper plate element 1 and the lower plate element 2 can be made of the same material or of different materials.

[0064] The self-piercing riveting system to which the self-piercing rivet 100 according to an exemplary embodiment of the present invention is applicable may be provided for a robot and may include a punch unit 4 for pressing the rivet 100 and a die 6 for holding the upper and lower plate members 1 and 2 overlapping each other.

[0065] The punch unit 4 feeding the rivet 100 comprises a punch cylinder driven by hydraulic pressure or pneumatic pressure and a punch actuated by the punch cylinder.

[0066] The punch unit 4 may use an impact device for quickly and continuously impacting the rivet 100.

[0067] It is well known that the punch unit 4 of the self-piercing riveting system can be used in a so-called SPR system (self-piercing riveting system), and thus a detailed description thereof is omitted in this description.

[0068] In an exemplary embodiment of the present invention, the supporting die 6 which absorbs impact force during the rivet driving operation may be mounted in a conventional C-frame such as an anvil die, or the die 6 may be a separate plate-like structure for holding the overlapping upper and lower plate members 1 and 2.

[0069] In the die 6, a receiving part 8 is formed as a hole or dome for receiving a plastically deformed part of a predetermined target portion for riveting the upper and lower plate members 1 and 2. In an exemplary embodiment of the present invention, the receiving part 8 of the die 6 is a hole, as shown in the drawings for clarity.

[0070] The receiving part 8 receives a plastically deformed part of the predetermined target part for riveting the upper and lower plate elements 1 and 2.

[0071] In an exemplary embodiment of the present invention, the target part for riveting the upper and lower plate members 1 and 2 may be flat without a hole.

[0072] The rivet 100 applicable to the self-piercing riveting system according to an exemplary embodiment of the present invention penetrates the upper plate member 1 by pressing by the punch unit 4, is pressed into the lower plate member 2, and plastically deforms the upper and lower plate members 1 and 2 through the receiving hole 8 of the die 6, so as to integrally connect the upper plate member 1 and the lower plate member 2.

[0073] The self-piercing rivet 100 according to an exemplary embodiment of the present invention prevents damage to a forging die 9 (see Fig. 4) during a forging process of a base material of the rivet, prolongs the service life of the forging mold 9, improves the mass production of the rivet and improves the joining strength of objects to be joined.

[0074] In the following, the self-piercing rivet 100 according to an exemplary embodiment of the present invention will be described in detail with reference to Fig. 1 and the attached drawings.

[0075] Fig. 2 is a perspective view of a self-piercing rivet according to an exemplary embodiment of the present invention.

[0076] In Fig. 1 and Fig. 2, the self-piercing rivet 100 according to an exemplary embodiment of the present invention essentially comprises a head portion 10, a shank portion 30, ribs 50, and a straight portion 70, and each component will be described in detail.

[0077] The self-piercing rivet 100 is formed by a forging process by pressing a base material of the rivet (called 'strand') in the forging die 9, and a forming projection, a forming groove, and a forming hole are formed corresponding to the head part 10, the shank part 30, the ribs 50, and the straight part 70 in the forging die 9.

[0078] The head portion 10 receives a load from the punch unit 4 and has a disc shape with a predetermined thickness.

[0079] The head part 10 can support the target part for riveting the upper plate member 1 when the rivet 100 plastically deforms the upper and lower plate members 1 and 2 that overlap each other.

[0080] In an exemplary embodiment of the present invention, the shaft part 30 plastically deforms the riveting target part of the upper and lower plate members 1 and 2 that overlap each other and is integrally connected to a lower part of the head part 10.

[0081] The shaft part 30 may be a solid circular cylinder, and thus no bending can occur during pressing by the punch unit 4.

[0082] Hereinafter, a part of the shaft part 30 connected to the head part 10 is referred to as a connecting end 32, and an opposite part of the shaft part 30 is referred to as a free end 34.

[0083] The length of the shaft part 30 may vary according to the thickness of the upper and lower plate members 1 and 2 and so on, and thus, in an exemplary embodiment of the present invention, the length of the shaft part 30 is not limited to specific ranges.

[0084] According to the present invention, the ribs 50 are configured to plastically deform the target part for riveting the upper and lower plate members 1 and 2 to the shaft part 30 by pressing by the punch unit 4, penetrate into the upper plate member 1, pierce the upper and lower plate members 1 and 2, and be plastically deformed.

[0085] Furthermore, the ribs 50 are configured to twist the rivet 100 during the plastic deformation of the target part for riveting the upper and lower plate members 1, penetrate into the upper plate member 1, and pierce the upper and lower plate members 1 and 2 by changing the pressure of the punch unit 4 to torque.

[0086] That is, the ribs 50 cause the rivet 100 to twist during penetration into the upper plate member 1 and piercing the lower plate member 2, and they are plastically deformed and encapsulated within the lower plate member 2, thereby connecting the upper and lower plate members 1 and 2. That is, the upper plate member and the lower plate members 1 and 2 can be connected by a frictional force of the ribs 50 and a plastic deformation of the ribs 50.

[0087] According to the present invention, the ribs 50 integrally protrude from an outer peripheral surface of the shaft part 30 and are arranged in a spiral shape along the longitudinal direction of the shaft part 30. There are a plurality of ribs 50, and they are arranged on the outer peripheral surface of the shaft part 30 at constant intervals.

[0088] Specifically, the ribs 50 of the present invention are integrally connected to the head portion 10, are formed in a spiral shape from the connecting end 32 to the free end 34 of the shaft portion 30, and are arranged at constant intervals along a circular arc of the shaft portion 30.

[0089] The ribs 50 are formed from the connecting end 32 to the free end 34 of the shaft portion 30 to form a spiral 51 (shown as a dot-dash line in the drawing). For example, the ribs 50 twist clockwise along the longitudinal direction of the shaft portion 30 to form the spiral 51.

[0090] The ribs 50 can also twist counterclockwise along the longitudinal direction of the shaft part 30 to form the spiral 51.

[0091] In an exemplary embodiment of the present invention, a pitch angle α of the spiral 51 can be 30 to 60°. That is, the helix of the ribs 50 and an axial line X of the shaft part 30 form an angle between 10 and 45°. The pitch angle α of the ribs 50 can vary according to the strength of the objects to be joined.

[0092] In this case, the pitch angle α means an angle between the spiral 51 along the connecting end 32 and the free end 34 of the shaft part 30 and the axial line X of the shaft part 30, and is also called helix angle.

[0093] For example, in an exemplary embodiment of the present invention, the ribs 50 form four spirals 51 along the connecting end 32 and the free end 34 of the shaft portion 30.

[0094] The pitch angle and the number of spirals of the ribs 50 are set within a range such that the ribs 50 can plastically deform the riveting target portion of the upper and lower plate members 1 and 2, penetrate the upper plate member 1, pierce the upper and lower plate members 1 and 2, and be plastically deformed. In one or more exemplary embodiments of the present invention, the pitch angle and the number of spirals of the ribs 50 can also be determined through various simulation tests.

[0095] If the pitch angle of the rib 50 is less than 30°, the length of the ribs 50 is insufficient, so that the relative proportion of the ribs 50 penetrating the upper plate member 1 and encapsulated within the lower plate member 2 is insufficient. Therefore, the joining force (connecting force) of the ribs 50 with respect to the upper and lower plate members 1 and 2 may be insufficient.

[0096] Furthermore, if the lead angle of the rib 50 is less than 30°, the number of the ribs 50 formed in the outer circumferential direction of the shaft part 30 can be increased, and thus the encapsulated part of the upper and lower plate members 1 and 2, which is arranged between the ribs 50, can be reduced, so that the joining force (connecting force) of the ribs 50 with respect to the upper and lower plate members 1 and 2 can be reduced.

[0097] On the other hand, if the pitch angle of the ribs 50 is over 60°, the manufacturing of the ribs 50 may be difficult. Also, at the time when the ribs 50 plastically deform the riveting target portion of the upper and lower plate members 1 and 2 with the shaft portion 30, the ends of the ribs 50 may be plastically deformed without piercing the upper plate member 1, and the objects to be joined may not be sufficiently joined.

[0098] Thus, in one or more exemplary embodiments, the pitch angle of the ribs 50 is set in a range such that the ribs 50 can plastically deform the riveting target portion of the upper and lower plate members 1 and 2, penetrate the upper plate member 1, pierce the upper and lower plate members 1 and 2, and be plastically deformed. In one or more exemplary embodiments of the present invention, the pitch angle can be set to 30°~60°.

[0099] The pitch angle and the number of spirals of the ribs 50 can be determined by various simulation tests.

[0100] The spiral length of the ribs 50 may vary according to the length of the shaft part 30, the thickness of the upper and lower plate members 1 and 2, the pitch angle, and so on, and thus, in an exemplary embodiment of the present invention, the spiral length of the ribs 50 is not limited to specific ranges.

[0101] Each rib 50 has a rib surface 53 with a width B and rib side surfaces 55 with a thickness T between the outer peripheral surface of the shaft part 30 and the rib surface 53. The rib side surfaces 55 have an inner surface 55a and an outer surface 55b based on the rib surface 53 along a moving direction of the rib 50. In the description, the inner surface 55a is defined as a surface facing a lower surface of the head part 10, and the outer surface is defined as a surface opposite the inner surface 55b.

[0102] In one or more exemplary embodiments, the thickness T of the rib 50 is greater than the width B of the rib 50.

[0103] The relationship between the thickness T of the rib side surface 55 and the width B of the rib surface 53 can cause the ribs 50 to be encapsulated with a sufficient encapsulation area (area) within the lower plate member 2.

[0104] The straight part 70 minimizes damage to the forging die 9 and the impact force applied to the forging die 9 when the rivet 100 is ejected from the forging die 9 after the rivet 100 is formed in the forging die 9.

[0105] Furthermore, the straight part 70 guides the rivet 100 so that it can be removed from the forging die 9 without difficulty when the rivet 100 is ejected from the forging die 9 (in other words, when the rivet 100 is removed from the forging die 9 by an ejector pin).

[0106] Furthermore, since the straight part 70 reduces the clearance between the ribs 50 and the objects to be connected, the connectability of the objects to be connected is improved.

[0107] The straight part 70 may be integrally formed at a connected part when the head part 10 and the rib 50 are connected.

[0108] Specifically, a straight portion 71 formed in the straight portion 70 extends from the inner surface 55a to the lower surface of the head portion 10 along an axial direction of the shaft portion 30.

[0109] In Fig. 2, the straight part 70 may be integrally formed on an upper part of the rib 50, have a same area as the rib surface 53, and be integrally connected to the connecting end 32 and the lower surface of the head part 10.

[0110] That is, the straight portion 70 has a peripheral surface 71b corresponding to the outer peripheral surface of the shaft portion 30, and the straight portion 71 extends from the inner surface 55a to the lower surface of the head portion 10 in the upper part of the rib 50.

[0111] In the following, an operation of the self-piercing rivet 100 according to an exemplary embodiment of the present invention will be described in detail with reference to the accompanying drawings.

[0112] Fig. 3 and Fig. 4 are drawings for explaining an operation of a self-piercing rivet according to an exemplary embodiment of the present invention.

[0113] First, the functionality of a Fig. 3A shown comparative example.

[0114] The self-piercing rivet 100 according to an exemplary embodiment of the present invention has the straight part 70, but a self-piercing rivet 200 according to the comparative example does not have a straight part.

[0115] The self-piercing rivet 200 according to the comparative example can be formed by pressing a base material of the rivet in a forging die 109 having a forming projection, a forming groove, and a forming hole corresponding to a head portion 101, a shank portion (not shown), and a rib 103.

[0116] When the self-piercing rivet 200 according to the comparative example is formed by pressing the base material of the rivet in the forging die 109, the rib forming part may break because a tensile load is applied to a rib forming part to be sharply formed (see “a” in Fig. 3A) is applied.

[0117] Generally, since the forging die 109 is made of a material with high hardness and brittleness, the forging die 109 resists compression force but is sensitive to tensile stress. Since tensile stress is applied to the rib forming part of the forging die 109 when the base material of the rivet is stamped, the rib forming part is easily broken.

[0118] Meanwhile, when the self-piercing rivet 200 according to the comparative example is ejected from the forging die 109 after forming the self-piercing rivet 200, the rib 103 presses the rib forming part by means of the ejector.

[0119] Therefore, a tensile load is applied to the rib forming part by the rib 103, thus the rib forming part can easily break.

[0120] Accordingly, damage occurs in the forging die 109 during the forging process of the self-piercing rivet 200, so that the service life of the forging die 109 is shortened and mass production of the rivet is affected.

[0121] However, in Fig. 3B, the self-piercing rivet 100 according to an exemplary embodiment of the present invention has the straight part 70 formed at the connecting part where the head part 10 and the rib 50 are connected.

[0122] The self-piercing rivet 100 according to an exemplary embodiment of the present invention can be formed by stamping the base material of the rivet in the forging die 9 with the forming projection, the forming groove and the forming hole corresponding to the head part 10, the shank part (not shown), the ribs 50 and the straight part 70.

[0123] Here, a straight area corresponding to the straight part 70 of the rivet 10 in a rib forming part (see “b” in Fig. 3B) of the forging mold 9.

[0124] When the base material of the rivet is stamped in the forging die 9 during the forging process, the rib forming part does not break because no tensile load is applied to the rib forming part of the forging die 9.

[0125] Furthermore, since no tensile load is applied to the rib forming part when the rivet 200 is ejected from the forging mold 9, the rib forming part does not break.

[0126] Therefore, it is possible to prevent damage to the forging die 9 during the forging process of the rivet 100, the service life of the forging die 9 is extended, and mass production of the rivet is improved.

[0127] Hereinafter, a joining operation of the objects to be joined using the self-piercing rivet 100 according to an exemplary embodiment of the present invention will be described in detail.

[0128] In Fig. 1, Fig. 2 and Fig. 4, the upper and lower plate elements 1 and 2, which overlap each other, are placed on the plate-like die 6.

[0129] In one or more exemplary embodiments, the die 6 may not be an anvil provided on a conventional C-frame. The die 6 may be a separate plate-like structure for holding the overlapping upper and lower plate elements 1 and 2.

[0130] The target part for riveting the upper and lower plate elements 1 and 2 may have no holes and may be arranged on the receiving part 8 of the die 6.

[0131] In this state, the punch unit 4 of the self-pierce riveting system is moved to the target part for riveting the upper and lower plate members 1 and 2, and the rivet 100 is fed to the punch unit 4.

[0132] Then, the cylinder of the punch unit 4, driven by hydraulic pressure or pneumatic pressure, is actuated so that the punch presses on the head part 10 of the rivet 100.

[0133] Then, the ribs 50 together with the shaft part 30 plastically deform the target part for riveting the upper and lower plate elements 1 and 2.

[0134] When the target part for riveting of the upper and lower plate elements 1 and 2 is plastically deformed, the deformed part of the target part for riveting can protrude from the lower surface of the lower plate element 2 and is received in the receiving part 8 of the die 6.

[0135] At this time, the ends of the ribs 50 pierce the upper plate member 1 by pressing the punch unit 4, and it is plastically deformed within the lower plate member 2.

[0136] In one or more exemplary embodiments, the ribs 50 forming the spirals 51 from the connecting end 32 to the free end 34 cause the rivet 100 to twist upon penetrating the upper plate member 1, pierce the lower plate member 2, and be plastically deformed and encapsulated within the lower plate member 2, thereby connecting the upper and lower plate members 1 and 2 due to the torque.

[0137] That is, the ribs 50 can change the compressive force received from the punch unit 4 into a torque.

[0138] In one or more exemplary embodiments, the ribs 50 plastically deform the target part for riveting the upper and lower plate members 1 and 2 to the shaft part 30, the ends of which twist and penetrate the upper plate member 1, pierce the upper and lower plate members 1 and 2 and are plastically deformed, so as to integrally connect the upper and lower plate members 1 and 2.

[0139] The plastically deformed ends of the ribs 50 are encapsulated within the lower plate element 2 so as to form a mechanical interlock of the upper and lower plate elements 1 and 2.

[0140] In one or more exemplary embodiments, the deformed part of the upper plate member 1 can be connected to each other according to a space between the ribs 50 because the twisting rivet 100 penetrates the upper plate member 1 and pierces the lower plate member 2.

[0141] That is, although the ends of the ribs 50 penetrate into the upper plate member 1, the target part for riveting of the upper plate member 1 is not completely separated, so that the target parts of riveting of the upper plate member 1 except the penetrated part can be connected to each other.

[0142] Since the dead metal that is completely punched out cannot remain, the deformed part of the target part is used for riveting the upper plate member 1 to reinforce the joining strength of the upper plate member 1 and the lower plate member 2.

[0143] The deformed part of the upper plate member 1 is used to create a mechanical lock of the upper plate member 1 and the lower plate members 1 and 2 and to fix the upper plate member 1 and the lower plate member 2 with a predetermined strength.

[0144] Accordingly, although only one rivet is used, the twisting of the upper plate member 1 and the lower plate member 2 is prevented, and the joining strength of the upper plate member 1 and the lower plate member 2 is further improved.

[0145] Furthermore, since the objects to be joined are joined using a rivet, productivity can be improved and manufacturing costs can be reduced by reducing the number of joining operations and components.

[0146] Since the ribs 50 are formed on the shank part 30, the contact area of the entire rivet 100 can be increased, so that the shear strength of the rivet 100 with respect to the upper and lower plate members 1 and 2 is improved, the joining stress and the pressing performance can be reduced, and accordingly the operational stability of the self-piercing riveting system can be improved.

[0147] In one or more exemplary embodiments, an anvil may not be required in a conventional technique for outwardly deforming the rivet, since the plate-like die 6 provided with the receiving part 8 can only be used to hold the upper and lower plate elements 1 and 2. Accordingly, interactions with other devices can be minimized, and the design freedom of the riveting process can be improved.

[0148] Furthermore, the straight part 70 is integrally formed at a connecting part of the rib 50 and the head part 10, a clearance formed between the upper plate member 1 and the ribs 50 is reduced by the straight part 70, and the joining strength of the upper plate member 1 and the lower plate member 2 is improved when an upper plate member 1 and a lower plate member 2 are joined.

[0149] That is, since the clearance formed between the upper plate member 1 and the ribs 50 is filled by the straight part 70, the connecting force is improved by the frictional force of the straight part 70 and the upper plate member 1.

[0150] Meanwhile, since the rivet 100 is twisted along the spiral direction due to the ribs 50 so as to integrally connect the upper and lower plate members 1 and 2, the rivet 100 can be easily removed from the objects to be joined if a torque in the opposite direction to the joining force of the ribs 50 is applied with respect to the objects to be joined.

[0151] Thus, in one or more exemplary embodiments, if it is necessary to separate the objects to be joined again, the rivet can be easily removed without being disassembled or pulling out the rivet part, thus the objects to be joined can be reused.

[0152] While this invention has been described in connection with what is presently considered to be a practical exemplary embodiment, it is to be understood that the invention is not limited to the disclosed embodiments, but on the contrary, various modifications and equivalent arrangements are intended to be included within the spirit and scope of the appended claims.

Claims

[1] Punch rivet (100), which comprises: a headboard (10); a shaft part (30) which is integrally connected to the head part (10); a plurality of ribs (50) formed in a spiral shape on an outer peripheral surface of the shaft part (30) along a longitudinal direction of the shaft part (30) and integrally connected to the head part (10); and a straight part (70) formed integrally on an upper part of the rib (50) at a connecting part at which the head part (10) and the rib (50) are connected, wherein the shaft part (30) is a circular cylinder, the ribs (50) are arranged on the outer peripheral surface of the shaft part (30) with a uniform distance therebetween, the shaft part (30) has a connecting end (32) connected to the head part (10) and a free end (34) which is an end opposite to the connecting end (32), and the ribs (50) are formed in a spiral shape from the connecting end (32) of the shaft part (30) to the free end (34) of the shaft part (30), and the straight part (70) is integrally connected to the connecting part to which the ribs (50) and the head part (10) are connected, and a straight portion (71) formed in the straight portion (70) extends in the upper portion of the rib (50) from an inner surface of the rib (50) to a lower surface of the head portion (10) along an axial direction of the shaft portion (30), wherein the inner surface is a surface facing the lower surface of the head part (10). [2] A self-piercing rivet (100) according to claim 1, wherein the straight part (70) has a peripheral surface corresponding to the outer peripheral surface of the shank part (30). [3] A self-piercing rivet (100) according to claim 1, wherein the rib (50) has a rib surface (53) with a predetermined width and rib side surfaces (55) with a predetermined thickness between an outer peripheral surface of the shank part (30) and the rib surface (53). [4] A punch rivet (100) according to claim 3, wherein the thickness of the rib (50) is greater than the width of the rib (50). [5] A method for producing a self-piercing rivet connection with a self-piercing rivet (100) according to claim 1, wherein the ribs (50) of the self-piercing rivet (100) pierce an upper plate member (1) and a lower plate member (2) which overlap each other, are plastically deformed within the lower plate member (2), and are fixed to the lower plate member (2).

Images