Fastener Insertion Device

Abstract

A rivet die (13) for a riveting tool (2) is disclosed. The rivet die (13) includes a body (20) defining an upper surface (39). The rivet die (13) further includes a die cavity (21) formed in the upper surface (39). The die cavity (21) is at least partially defined by a base surface (42). The base surface (42) includes a groove (50) extending at least partially around a central axis C, and a first portion (46) and a second portion (48) through which the central axis C passes. The groove (50) is disposed radially outward of the first portion (46). The second portion (48) is disposed radially outward of the groove (50). The groove (50) and the second portion (48) abut each other at an interface (56). The first portion (46) defines a first portion depth d1 in a direction along the central axis C. The interface (56) defines an interface depth d5 ​​in a direction along the central axis C. The depth d1 of the first portion is less than the interface depth d5.

Description

[Technical Field]

[0001] (Technical field) The present invention relates to rivet dies, riveting tools incorporating such dies, and related methods, which have particular, but not exclusive, application to forming self-piercing riveted joints in which a rivet is inserted into a workpiece comprising sheet material. [Background technology]

[0002] (Background technology) Rivets can be used in a variety of applications and are commonly used to fasten multiple layers (or sheets) of workpieces together. In some applications, the rivet may be inserted into a workpiece containing only a single layer (or sheet). Self-piercing rivets do not require the workpiece to contain a pre-formed hole; the rivet punches a hole in the workpiece to accept the rivet during the riveting operation.

[0003] The use of self-piercing rivets in the joining process reduces the number of manufacturing steps compared to traditional riveting, which requires first creating a hole in the workpiece, inserting a rivet into the hole, and then upsetting (deforming the protruding end of the rivet, which is inserted through the hole) (expanding and connecting with the workpiece). In a self-piercing riveting operation, no hole is first created in the workpiece; instead, the self-piercing rivet is driven directly into the workpiece, creating its own hole that extends partway through the workpiece. The rivet shank is upset as it is driven into the workpiece. Self-piercing riveting operations typically use a die to support the workpiece while the rivet is inserted (driven) into it. The die can have a flat surface or can have a cavity to accommodate and / or direct the plastic flow of the workpiece material during the riveting operation to assist in the deformation of the rivet shank to create the required connection.

[0004] Low-ductility materials, such as cast aluminum, generally have a higher likelihood of crack formation during riveting operations. Cracks are undesirable because they can lead to, for example, fluid ingress which can lead to corrosion and ultimately joint failure. It is an object of the present invention to provide a rivet die, riveting tool, and related method that obviates or mitigates disadvantages of existing apparatus and methods, whether mentioned above or otherwise, and / or to provide an improved or alternative rivet die, riveting tool, or method. Summary of the Invention

[0005] (Summary of the Invention) In a first aspect of the present invention, a rivet die for a riveting tool is provided. The rivet die includes a body defining a top surface. The rivet die further includes a die cavity formed in the top surface. The die cavity is at least partially defined by a base surface. The base surface includes a groove extending at least partially around a central axis, a first portion through which the central axis passes, and a second portion. The groove is disposed radially outward of the first portion. The second portion is disposed radially outward of the groove. The groove and the second portion abut each other at an interface. The first portion defines a depth of the first portion in a direction along the central axis. The interface defines a depth of the interface in a direction along the central axis. The depth of the first portion is shallower than the depth of the interface.

[0006] The depth of the first portion may be understood to refer to the minimum depth of the first portion. The depth of the interface may be understood to refer to the minimum depth of the interface.

[0007] The groove may be an annular groove.

[0008] When a die according to this aspect of the invention is used to perform a riveting operation on a workpiece, the material of the workpiece flexes so as to be supported by the first portion of the base surface (and the upper surface of the body, particularly a portion of the upper surface radially outward of the die cavity). Because the depth of the first portion is shallower than the depth of the interface and the groove is located radially outward of the first portion, the workpiece is supported centrally throughout the riveting operation. Because the workpiece is supported centrally throughout the riveting operation, the workpiece is subjected to compressive stress throughout the riveting operation. Exposure of the workpiece to compressive stress throughout the riveting operation advantageously reduces the possibility of cracking of the workpiece occurring during the riveting operation.

[0009] As the riveting operation continues, the workpiece material deforms into the groove, compressing the material received in the groove. Compressing the material received in the groove further reduces the likelihood of cracking the workpiece during the riveting operation. Additionally, any cracks that may form are at least partially closed by this compression.

[0010] The second portion can define a depth of the second portion extending in a direction along the central axis, and the overall depth of the first portion can be less than the overall depth of the second portion.

[0011] When the total depth of the first portion is less than the total depth of the second portion, the amount of compression experienced by the workpiece during the riveting operation can be increased relative to a situation where the depth of a portion of the second portion is less than the depth of a portion of the first portion. Increasing the amount of compression further reduces the likelihood of cracks forming during the riveting operation.

[0012] The first portion may be a flat surface. The entire first portion may be a flat surface.

[0013] The first portion being planar may be understood to mean that all points of the first portion lie in a common plane.

[0014] The plane of the first portion may be substantially perpendicular to the central axis.

[0015] When the first portion is planar, stress distribution in the workpiece during the riveting operation is preferably more uniform than when the first portion is non-planar. The more uniform stress distribution preferably further reduces the likelihood of cracks forming during the riveting operation.

[0016] The first portion can define a diameter relative to the central axis, and the second portion can define a radial width.

[0017] The ratio of the diameter of the first portion to the radial width of the second portion may be less than four.

[0018] In other words, the radial width of the second portion multiplied by two may be greater than the radius of the first portion.

[0019] The ratio of the diameter of the first portion to the radial width of the second portion can be calculated by dividing the diameter of the first portion by the radial width of the second portion.

[0020] When the ratio of the diameter of the first portion to the radial width of the second portion is less than 4, or in any other embodiment disclosed herein, the interface between the groove and the second portion may be located at an inflection point defined by the base surface. The inflection point may be located at a location where the base surface changes from concave to convex as one moves radially outward along the base surface from the radial midpoint of the groove.

[0021] When the ratio of the diameter of the first portion to the radial width of the second portion is less than 4, or in any other embodiment disclosed herein, the interface between the groove and the first portion may be located at an inflection point defined by the base surface. The inflection point may be located at a location where the base surface changes from concave to convex as one moves radially inward along the base surface from the radial midpoint of the groove.

[0022] In cases where the ratio of the diameter of the first portion to the radial width of the second portion is less than 4, or in any other embodiment disclosed herein, the radially outer end of the second portion may be located at an inflection point defined by the base surface. The radially outer end of the second portion may join a sidewall of the base surface. The inflection point may be located at a location where the base surface changes from concave to convex when moving radially outward along the second portion of the base surface.

[0023] The diameter of the first portion may extend to the interface between the first portion and the groove. The radial width of the second portion may extend, in a direction perpendicular to the central axis, from the interface between the groove and the second portion of the base surface to a radially outer end of the second portion, as defined above.

[0024] When the ratio of the diameter of the first portion to the radial width of the second portion is less than 4, the workpiece material is better supported during rivet insertion because the likelihood of the workpiece flowing into the groove without contacting the second portion is reduced. If the workpiece flows into the groove without contacting the second portion, the workpiece is more likely to crack during rivet insertion. Therefore, the above ratio preferably reduces the likelihood of the workpiece cracking during the rivet insertion operation using the die.

[0025] The diameter of the first portion may be greater than or equal to the radial width of the second portion.

[0026] The groove may define a radial width of the groove. The radial width of the groove may be at least 5% of the diameter of the first portion.

[0027] The radial width of the groove may be up to 300% (ie up to four times larger) than the diameter of the first portion.

[0028] The die cavity can define a die cavity depth in a direction along the central axis. The groove can define a groove depth in a direction along the central axis.

[0029] The depth of the die cavity can be understood to refer to the maximum depth of the die cavity. The depth of the die cavity can extend from the top surface of the body (particularly, from a portion of the top surface radially outward of the die cavity) to the base surface of the groove (which is a portion of the base surface that defines the base of the groove). The depth of the groove can also extend from the interface to the base surface of the groove.

[0030] The depth of the groove may be 75% or less of the depth of the die cavity.

[0031] The depth of the groove may be 40% or less of the depth of the die cavity.

[0032] When the groove depth defines 75% or less of the die cavity depth, compression of the workpiece material entering the groove during the riveting operation is increased compared to when the groove depth defines more than 75% of the die cavity depth. Increasing the compression experienced by the workpiece material entering the groove further reduces the likelihood of cracks forming during the riveting operation. Additionally, the closing force applied to cracks formed during the riveting operation is increased compared to when the groove depth defines more than 75% of the die cavity depth.

[0033] The depth of the interface may be at least 3% greater than the depth of the first portion.

[0034] The depth of the interface may be at least 5% greater than the depth of the first portion. The depth of the interface may be at most 0.05 mm greater than the depth of the first portion. The depth of the interface may be at most 0.1 mm greater than the depth of the first portion.

[0035] The depth of the interface may be up to 300% greater than the depth of the first portion.The depth of the interface may be up to 200% greater than the depth of the first portion.

[0036] When the interface depth is at least 3% greater than the first portion depth, the likelihood of the workpiece being subjected to tensile forces is reduced compared to when the interface depth is less than 3% greater than the first portion depth, which further advantageously reduces the likelihood of cracks forming in the workpiece during the riveting operation.

[0037] At least a portion of the first portion may be perpendicular to the central axis. At least a portion of the second portion may be perpendicular to the central axis.

[0038] The entire first portion may be perpendicular to the central axis, and the entire second portion may be perpendicular to the central axis.

[0039] The rivet die may further include a stem. The stem may extend from a lower surface of the body. The lower surface may be opposite the upper surface.

[0040] The upper surface can define an outer rim, which can be disposed radially outward of the die cavity.

[0041] The outer rim may be disposed radially outward of the base surface.

[0042] The groove may define a radial midpoint. The radial midpoint may define a radial midpoint diameter. The groove may be configured such that the radial midpoint diameter is equal to or greater than the inner diameter of the rivet bore provided in the riveting tool prior to insertion of the rivet.

[0043] The radial midpoint of a groove may be understood to refer to the radial midpoint between the radially innermost edge and the radially outermost edge of the groove. The radial midpoint of a groove may be the locus of points located at the midpoint radius relative to the central axis.

[0044] Following a riveting operation on a workpiece comprising multiple sheets of material to be joined, the bottom sheet of the workpiece (the sheet located farthest from the top surface of the workpiece, which is the surface of the workpiece first contacted by the rivet during the riveting operation) defines a minimum thickness (which may be the shortest distance between a portion of the top surface of the bottom sheet and a portion of the bottom surface of the bottom sheet). If the minimum thickness is too small, the joint produced by the riveting operation will be prone to failure. For example, the joint will be susceptible to moisture ingress, which may cause corrosion. The minimum thickness for any riveting operation is generally located in the area of ​​the rivet tip. If the radial midpoint diameter is equal to or greater than the inner diameter of the rivet bore provided in the riveting tool, the minimum thickness of the workpiece will be greater than if the radial midpoint diameter is smaller than the inner diameter of the rivet bore. This advantageously reduces the likelihood of joint failure resulting from the riveting operation.

[0045] The first portion of the base surface may be continuous.

[0046] A first portion of the base surface being continuous may be understood to mean that the first portion does not include holes, recesses, etc. In some embodiments, a first portion of the base surface being continuous may be understood to mean that the first portion does not include discontinuities or irregularities.

[0047] In a second aspect of the present invention, there is provided a riveting tool configured to insert a rivet into a workpiece, the riveting tool comprising a die according to the first aspect of the present invention arranged below a punch that is reciprocable by an actuator.

[0048] The advantages discussed above in relation to the first aspect of the invention apply mutatis mutandis to this aspect.

[0049] According to a third aspect of the present invention, there is provided a method of forming a joint. The method of forming a joint includes providing a riveting tool according to the second aspect of the present invention. The method further includes providing a rivet to the riveting tool. The method further includes providing a workpiece. The method further includes positioning the workpiece between a die and a punch. The method further includes forcing the rivet into the workpiece by advancing the punch using an actuator.

[0050] The workpiece may comprise two or more sheets (which may also be called layers).

[0051] The rivet may be a self-piercing rivet.

[0052] The groove can define a radial midpoint. The radial midpoint can define a radial midpoint diameter. The rivet can define a shank outer diameter. The radial midpoint diameter can be equal to or greater than the bore inner diameter.

[0053] The shank major diameter can refer to the diameter of the outside circumference of the shank before the rivet is driven into the workpiece. The shank major diameter may also be the maximum diameter (relative to the central axis of the rivet) of the tip of the rivet shank before the rivet is driven into the workpiece. The tip may be the portion of the rivet that is located the greatest axial distance from the rivet head.

[0054] The advantages discussed above in relation to the first aspect of the invention apply mutatis mutandis to this aspect.

[0055] At least one of the layers (or sheets) of the workpiece may be made from a material having a ductility of 12% or less.

[0056] All of the layers of the workpiece may be made from one or more materials having a ductility of 12% or less. At least one or all of the layers of the workpiece may be made from one or more materials having a ductility of 8% or less.

[0057] The material may be a cast material. The material may be cast aluminum.

[0058] The workpiece may include an upper sheet defining an upper surface of the workpiece. The workpiece may include a lower sheet defining a lower surface of the workpiece.

[0059] After being driven into the workpiece, the rivet does not have to penetrate the underside of the workpiece.

[0060] The bottom sheet may be formed from a material that is less ductile than the top sheet.

[0061] The lower sheet may be formed from a cast material. The lower sheet may have a ductility of less than 12% elongation to break. The lower sheet may have a ductility of less than 10% elongation to break. The lower sheet may be at least 2 mm thick. The lower sheet may be up to 5 mm thick.

[0062] The rivet may have a hardness of at least 380 HV10 and / or up to 580 HV10.

[0063] According to a fourth aspect of the present invention there is provided a product or component of a product produced using a method according to the third aspect of the present invention.

[0064] The product may be a vehicle.

[0065] According to a fifth aspect of the present invention, a method for forming a self-piercing rivet joint between separate portions of workpieces is disclosed. The method includes: i) providing a die defining a central axis and a die cavity defining a base surface; ii) the workpiece; iii) a punch; and iv) a self-piercing rivet. The method further includes positioning the workpiece between the die and the punch. The method further includes using the punch to drive the rivet into the workpiece such that: i) at least a portion of the workpiece flows into contact with the base surface of the die; ii) at least a portion of the workpiece flows radially outward; iii) at least a portion of the workpiece flows downward into a groove in the base surface of the die; iv) at least a portion of the workpiece substantially fills the groove; and v) at least a portion of the workpiece flows radially outward beyond the groove. As the rivet is driven into the workpiece, the rivet expands such that the rivet interlocks with at least a portion of the workpiece, thereby creating a joint between the separate portions of the workpiece.

[0066] Throughout this specification, the term "flow" when used in reference to a workpiece may be understood to refer to deformation of the associated portion of the workpiece.

[0067] At least a portion of the workpiece may flow upward and at least a portion of the workpiece may flow downward to substantially fill the groove.

[0068] Flow below or above the workpiece may be understood to mean that the direction of flow has a vertical component, i.e. the flow is not purely horizontal.

[0069] At least a portion of the workpiece flowing upward may also flow radially outward. At least a portion of the workpiece flowing downward may also flow radially outward.

[0070] With at least a portion of the flow flowing upward and at least a portion of the workpiece flowing downward to substantially fill the groove, the workpiece material is compressed by different portions of the workpiece flowing in different directions, which reduces the likelihood of cracks forming in the workpiece during joint formation and also helps close any cracks that may form during joint formation.

[0071] At least a portion of the workpiece may flow downward to substantially fill the groove.At least a portion of the workpiece may flow upward to substantially fill the groove.

[0072] (i) to (v) may be started sequentially.

[0073] One or more of (i) to (v) may occur simultaneously with one or more other of i) to v).

[0074] Sequentially means in the specified order (i.e., (i), (ii), (iii), (iv), then (v)).

[0075] The radial outward flow of the workpiece can bring the workpiece into contact with the sidewall of the die.

[0076] The groove may be disposed radially outward of the first portion of the base surface. The second portion of the base surface may be disposed radially outward of the groove. The groove and the second portion may abut each other at an interface.

[0077] The first portion defines a depth of the first portion in a direction along the central axis, and the interface defines a depth of the interface in a direction along the central axis, the depth of the first portion being shallower than the depth of the interface.

[0078] The workpiece may flow radially outward along a first portion of the base surface in step (ii).

[0079] The workpiece may flow radially outward along the second portion of the base surface in step (v). [Brief explanation of the drawings]

[0080] BRIEF DESCRIPTION OF THE DRAWINGS [Figure 1] 1 shows a rivet insertion device according to an embodiment of the present invention, including a rivet die according to an embodiment of the present invention. [Figure 2] 2 shows a cross-sectional side view of the rivet insertion device of FIG. 1. [Figure 3] 2 shows a cross-sectional side view of the rivet die of FIG. 1. [Figure 4] 4 shows an enlarged view of section "A" in FIG. 3. [Figure 5] 1 shows a computed simulator cross-sectional side view of a rivet insertion device according to one embodiment of the present invention during a first stage of the fastener insertion process. [Figure 6] 1 shows a computer-simulated cross-sectional side view of a rivet insertion device according to one embodiment of the present invention during a second stage of the fastener insertion process. [Figure 7] FIG. 10 shows a computer-simulated cross-sectional side view of a rivet insertion device according to one embodiment of the present invention during a third stage of the fastener insertion process. [Figure 8] FIG. 10 shows a computer-simulated cross-sectional side view of a rivet insertion device according to one embodiment of the present invention during a fourth stage of the fastener insertion process. [Figure 9] FIG. 10 shows a computer-simulated cross-sectional side view of a rivet insertion device according to one embodiment of the present invention during a fifth stage of the fastener insertion process. [Figure 10] FIG. 10 shows a computer-simulated cross-sectional side view of a rivet insertion device according to one embodiment of the present invention at a sixth stage of the fastener insertion process. DETAILED DESCRIPTION OF THE INVENTION

[0081] Next, an embodiment of the present invention will be described with reference to the accompanying drawings.

[0082] (Mode for Carrying Out the Invention) 1 shows a rivet insertion device (riveting tool) 2 and an associated carrier. The carrier comprises a C-frame 4 having an upper jaw 6 and a lower jaw 8. A die assembly 10 is mounted on the lower jaw 8 of the C-frame 4. The rivet insertion device 2 inserts rivets into a workpiece (not shown) positioned above the die assembly 10, as described further below.

[0083] The rivet insertion device 2 includes an electric drive 12 that operates to drive an inertia-driven reciprocating punch (not visible in FIG. 1 ) that moves axially within a cylindrical housing 14 and a nose assembly 16. While an inertia-driven drive is shown, other forms of drive may be used. For example, the electric drive may include an electric motor that directly drives the punch (and may be controlled based on real-time feedback regarding the position of the punch). In another example, a hydraulic drive may be used. However, an electric drive may be preferred because it does not require the delivery of hydraulic fluid (which can be difficult to deliver and may pose a health and safety risk if leaked). The reciprocating punch is used to insert the rivet from the nose assembly 16 through a workpiece (not shown). The reciprocating punch can contact the head of the rivet and apply a force to the rivet that drives the rivet into the workpiece. The rivet insertion device 2 may further include an additional drive (not visible) that may be used to clamp the nose assembly 16 onto the workpiece during rivet insertion and rivet upsetting (as described further below). The electric drive 12 and the additional drive may be independently controllable (e.g., using a controller). The additional drive may be, for example, an electric drive or a hydraulic drive. One example of a drive that may be used to clamp the nose assembly 16 onto a workpiece is described in U.S. Pat. No. 5,752,305.

[0084] The rivets are fed under air (or other gas) pressure through a delivery tube (not shown) to nose assembly 16. The rivets are then inserted into the workpiece. In an alternative arrangement, the rivets may be fed by being carried to nose assembly 16 on a carrier tape.

[0085] A control system 23 is configured to control the delivery of rivets to the nose assembly 16 and to control the operation of the reciprocating punch. The control system 23 may also control other parts of the rivet insertion apparatus 2, such as the drive that moves the punch and the drive that moves the nose. The control system 23 may include a processor and memory that stores instructions for the operation of the rivet insertion apparatus 2. The processor may process the instructions and provide an output that controls the operation of the rivet insertion apparatus 2.

[0086] The die assembly 10 is shown in more detail in FIG. 2. The die assembly 10 includes a die 13 supported on the lower jaw 8 of the C-frame 4 by a die holder adapter 18 received in a bore 19 through the jaw 8. The die 13 is sometimes referred to as a rivet die because it is intended for use with a rivet insertion device. In some embodiments, the die holder adapter 18 is not provided. In embodiments without a die holder adapter, the die 13 is secured directly to the C-frame 4. The die 13 is generally cylindrical about a central axis (not shown in FIG. 2). The die 13 includes a head (or body) 20 extending along the central axis and having a stem 22 depending therefrom. The stem 22 has a reduced diameter compared to the head 20. A lower surface 23 extends radially relative to the central axis and is defined below the head 20. The lower surface 23 is annular. The adapter 18 has a generally cylindrical body having a first end 25 that is received in a bore 19 in the jaw 8 of the C-frame 4 with a close fit, and a second hollow end 26 that receives the die stem 22 such that the annular lower surface 23 of the die rests on an upper surface 27 of the second end 26. A sealing member, such as an O-ring, may be provided between the adapter 18 and an upper surface 28 of the jaw 8 surface in which the bore 19 is defined. The adapter body has a radially outwardly extending flange 29 defined partway along its outer surface, one of the radially extending surfaces resting on the upper surface 28 of the jaw 8 immediately surrounding the bore 19. The second hollow end 26 tapers inwardly and terminates in an annular upper surface 27 against which the lower surface 23 of the head 20 rests. The tapered second end 26 allows the die 13 to rest flush with the upper surface 27 of the second end 26. A cylindrical bore 30 extends within the adapter body from the second end 26 to a position substantially midway along the length of the adapter body and receives the die stem 22 by a snug or friction fit.

[0087] It should be understood that in other embodiments, the bore 19 in the lower jaw 8 of the C-frame has a reduced diameter so that the die holder adapter 18 can be eliminated, in which case the lower jaw 8 of the C-frame in the area around the bore 19 functions to hold the die directly via the die stem.

[0088] FIG. 3 shows a cross-sectional side view of the die 13. The die head 20 includes a die top surface 39. The die surface 39 includes an outer rim 40. The die surface 39 includes a base surface 42. The outer rim 40 is disposed radially outward of the base surface 42. The die surface 39 includes a sidewall 44. The sidewall 44 extends between the outer rim 40 and the base surface 42. The outer rim 40 includes a generally flat (radially extending) portion. During a riveting operation, the outer rim 40 supports a workpiece (not shown in FIG. 3 ) into which a rivet (not shown in FIG. 3 ) is inserted, as described in more detail below. A die cavity 21 is formed in the die top surface (or upper surface) 39. The die cavity 21 defines a die cavity volume. The die cavity volume may be larger than the volume of a rivet to be inserted into a workpiece using a fastener insertion device having the die 13. This reduces the likelihood of cracks forming in the workpiece as a result of the fastener insertion action.

[0089] The stem 22 of the die 13 includes a flat land 31. To secure the die 13 to the adapter 18, a fastener, such as a grub screw, passes through the adapter and through an opening that engages the flat land 31. If no adapter is provided, the fastener would pass through the C-frame and through an opening that engages the flat land 31.

[0090] FIG. 4 shows an enlarged view of region "A" in FIG. 3. The die cavity 21 is partially defined by a base surface 42. The base surface 42 may also be referred to as a base portion (of the die surface 39). The die cavity 21 is partially defined by a sidewall 44. The sidewall 44 extends circumferentially around the base surface 42. Thus, the sidewall 44 may be referred to as a circumferential sidewall. The sidewall 44 is shaped so that the die cavity 21 is generally frustoconical. However, in other, not shown, embodiments, the sidewall 44 may extend parallel to the central axis C so that the die cavity is generally cylindrical. The base surface 42 includes a first portion 46, a second portion 48, and a groove 50. The groove 50 is disposed radially outward of the first portion 46. The second portion 48 is disposed radially outward of the groove 50. Thus, the groove 50 is radially disposed between the first portion 46 and the second portion 48 .

[0091] The central axis C of the die 13 passes through the first portion 46. The first portion 46 is generally perpendicular to the central axis C. In some embodiments, part or all of the first portion may not be perpendicular to the central axis C. The first portion 46 is generally planar. In some embodiments, the first portion 46 may be dome-shaped. If the first portion 46 is dome-shaped, the first portion 46 may be convex or concave. The first portion 46 is continuous. The first portion 46 being continuous may be understood to mean that the first portion 46 does not include any holes, recesses, or other discontinuities. In some embodiments, the first portion 46 may not be continuous. The first portion 46 defines a diameter D1 extending between diametrically opposed points, each point being located where the first portion 46 is adjacent to (or in contact with) a groove 50. The first portion 46 defines a first portion depth d1. The first portion depth d1 extends in a direction along the central axis C. The first portion depth d1 extends from the outer rim 40 of the die 13 to the first portion 46 of the base surface 42. The depth d1 may extend from a portion of the outer rim 40 that may be referred to as the top of the outer rim, which is the portion of the outer rim that is located furthest from the stem 22 along the central axis C.

[0092] The second portion 48 is generally planar (i.e., the second portion 48 may include a planar portion or may be completely planar). The second portion 48 is continuous. The second portion 48 being continuous may be understood to mean that the second portion 48 does not include any holes, recesses, or other discontinuities. In some embodiments, the second portion 48 may not be continuous. The second portion 48 is generally annular. The second portion 48 defines a radial width r2. The radial width r2 of the second portion 48 is the radial distance between i) where the second portion 48 is adjacent to the sidewall 44 and ii) where the second portion 48 is adjacent to the groove 50. The diameter D1 of the first portion 46 is equal to or greater than the radial width r2 of the second portion 48. However, in other embodiments, the diameter D1 of the first portion 46 may be less than the radial width r2 of the second portion 48. The size of the radius of the first portion 46 and the radial width of the second portion 48 relative to each other may be determined based on, for example, the materials from which the workpieces to be joined in a riveting operation using the die 13 are made. The second portion 48 is generally perpendicular to the central axis C. The second portion 48 is generally parallel to the first portion 46. In some embodiments, at least a portion of the second portion 48 may be inclined (i.e., not parallel) relative to the first portion 46. In some embodiments, at least a portion of the second portion 48 may be curved. The second portion 48 defines a second portion depth d2. The second portion depth d2 extends in a direction along the central axis C. The second portion depth d2 extends from the outer rim 40 of the die 13 to the second portion 48 of the base surface 42. The depth d2 may extend from a portion of the outer rim, which may be considered the top of the outer rim 40, which is the portion of the outer rim that is located farthest from the stem 22 along the central axis C. The depth d2 of the second portion is greater than the depth d1 of the first portion. In the illustrated embodiment, the overall depth d2 of the second portion 48 is greater than the overall depth d1 of the first portion 46. In some embodiments, the depth of at least a portion of the second portion 48 may be less than the depth of the first portion 46.

[0093] Groove 50 extends around (or surrounds) central axis C. Groove 50 extends circumferentially around central axis C. Groove 50 is generally annular. In some embodiments, groove 50 may be arc-shaped and thus may extend only partially around central axis C. In some embodiments, groove 50 may be formed from multiple sections, which may also be arc-shaped. In radial cross section, groove 50 is generally U-shaped or parabolic. In other embodiments, groove 50 need not be U-shaped in cross section, but may be any other suitable shape. For example, in cross section, groove 50 may be V-shaped or hyperbolic. Groove 50 is defined by a groove base surface 52.

[0094] The die cavity 21 defines a die cavity depth d3. The depth d3 may also be referred to as the cavity groove depth. The die cavity depth d3 extends in a direction along the central axis C. The die cavity depth d3 extends from the outer rim 40 of the die 13 to a portion of the base surface 52 of the groove 50 having a maximum depth (i.e., a portion of the base surface that is furthest along the central axis C toward the stem 22 of the die). The depth d3 may extend from a portion of the outer rim that may be considered the top of the outer rim 40, which is the portion of the outer rim that is located furthest from the stem 22 along the central axis C.

[0095] The groove 50 and the first portion 46 of the base surface 42 of the die cavity 21 meet or abut each other at a first interface 54. The first interface 54 is located at a radially innermost position where, when moving radially outward from the first portion 46, the angle between the central axis C and a normal extending from the base surface 42 is greater than 15 degrees. In some embodiments, the first interface 54 may be located at a radially innermost position where, when moving radially outward from the first portion 46, the angle between the central axis C and a normal extending from the base surface is greater than 45 degrees. The angle between the central axis C and a normal extending from the base surface that defines the location of the first interface 54 may be determined by the geometry of the first portion 46. Note that throughout this specification, the angle between the central axis C and a normal extending from the base surface 42 refers to an acute angle, rather than an obtuse angle, between the central axis C and a normal extending from the base surface 42. In some embodiments, the first interface 54 may be located elsewhere. For example, in some embodiments, first interface 54 may be located at an inflection point defined by base surface 42. The inflection point may be located at a location where base surface 42 changes from concave to convex when moving radially inward along base surface 42 from radial midpoint 57 of groove 50.

[0096] The first interface 54 defines a first interface depth d4. The first interface depth d4 extends in a direction along the central axis C. The first interface depth d4 extends from the outer rim 40 of the die 13 to the first interface 54. The first interface depth d4 may extend from a portion of the outer rim that can be said to be the top of the outer rim 40, which is the portion of the outer rim that is located furthest from the stem 22 along the central axis C.

[0097] The depth d4 of the first interface is shallower than the depth d2 of the second portion. In some embodiments, the depth of at least a portion of the second portion d2 may be shallower than the depth d4 of the first interface. The base surface 42 of the die 13 is rounded in the region of the first interface 54. In other, not shown, embodiments, the base surface 42 may have any suitable geometric shape in the region of the first interface 54. For example, the base surface 42 may be chamfered in the region of the first interface 54, or an apex may separate the groove 50 and the first portion 46.

[0098] The groove 50 and the second portion 48 of the base surface 42 of the die cavity 21 meet at a second interface 56. Moving radially inward from the second portion 48, the second interface 56 is located at a radially innermost position where the angle between the central axis C and a normal extending from the base surface 42 is greater than 15 degrees. In some embodiments, the second interface 56 may be located at a radially innermost position where the angle between the central axis C and a normal extending from the base surface is greater than 45 degrees when moving radially inward from the second portion 48. The angle between the central axis C and the normal extending from the base surface that defines the location of the second interface 56 may be determined by the geometry of the second portion 48. In some embodiments, the second interface 56 may be located at another location. For example, in some embodiments, the second interface 56 may be located at an inflection point defined by the base surface 42. The inflection point defining the position of the second interface 56 may be located at a position where the base surface 42 changes from concave to convex when moving radially outward along the base surface 42 from the radial midpoint 57 of the groove 50.

[0099] The second interface 56 defines a second interface depth d5. The second interface depth d5 ​​extends in a direction along the central axis C. The second interface depth d5 ​​extends from the outer rim 40 of the die 13 to the second interface 56. The second interface depth d5 ​​may extend from a portion of the outer rim that can be said to be the top of the outer rim 40, which is the portion of the outer rim that is located furthest from the stem 22 along the central axis C.

[0100] The depth d1 of the first portion 46 is shallower than the depth d5 ​​of the second interface. In some embodiments, the depth of at least a portion of the first portion 46 is shallower than the depth d5 ​​of the second interface. In some embodiments, the entire depth of the first portion 46 is shallower than the depth d5 ​​of the second interface. As explained in more detail below, this, in combination with the groove 50 being located radially outward of the first portion 46, results in the workpiece into which the rivet is inserted being centered throughout the majority of the riveting operation using the die 13. The base surface 42 of the die 13 is rounded in the region of the second interface 56. In other, not shown, embodiments, the base surface 42 may have any suitable geometric shape in the region of the second interface 56. For example, the base surface 42 may be chamfered in the region of the second interface 56, or an apex may separate the groove 50 and the second portion 48. In the illustrated embodiment, the depth d5 ​​of the second interface is at least 3% deeper than the depth d1 of the first portion. The depth d5 ​​of the second interface may be up to 300% deeper than the depth d1 of the first portion, thereby reducing the likelihood of cracks forming in the workpieces during a riveting operation using the die 13. The difference between the depth d1 of the first portion and the depth d5 ​​of the second interface may be selected based, for example, on the materials from which the workpieces to be joined during a riveting operation using the die 13 are made. The depth d1 of the first portion is shallower than the depth d5 ​​of the second interface regardless of the location of the second interface 56.

[0101] The radial midpoint 57 of the groove 50 is equidistant from the first interface 54 and the second interface 56. The radial midpoint 57 defines a radial midpoint diameter. The radial midpoint of the groove may be the locus of points located at the midpoint radius (half the midpoint diameter) relative to the central axis. In this embodiment, the radial midpoint 57 is located substantially at the portion of the groove 50 having the greatest depth (i.e., the portion of the base surface furthest along the central axis C toward the stem 22 of the die). This need not be the case for other geometries of the die 13. The radial midpoint 57 (i.e., the radial midpoint diameter) is configured to be equal to or greater than the bore inner diameter of the rivet provided in the rivet insertion device (not shown in FIG. 4 ). The bore inner diameter may refer to the diameter (relative to the central axis) of the inner circumference of the shank before the rivet is driven into the workpiece. The bore inner diameter may be the diameter (relative to the central axis of the rivet) of the cylindrical section of the rivet bore before the rivet is driven into the workpiece. If the bore does not include a cylindrical section, the bore inner diameter may be the diameter of the apex or tangent point between the leading inner bore portion and the adjacent portion of the bore. The leading inner bore geometry is the portion of the bore adjacent the rivet tip. The tip may be the portion of the rivet located at the greatest axial distance from the rivet head. The rivet tip is shown in more detail in Figures 5-10.

[0102] Having the radial midpoint diameter equal to or greater than the rivet shank inner diameter provided in the rivet insertion device reduces the likelihood of the rivet penetrating completely through the workpiece into which it is inserted during a riveting operation using die 13. Complete penetration of the rivet through the workpiece is undesirable because it can lead to fluid ingress, which can lead to corrosion, for example. Complete penetration of the workpiece can be considered when the rivet passes through all of one or more sheets of the workpiece, with the tip of the rivet exposed through the underside of the workpiece opposite the top surface of the workpiece into which the rivet was originally driven.

[0103] The groove 50 defines a radial width. The radial width of the groove 50 is defined by the radial distance between the first interface 54 and the second interface 56. The radial width of the groove 50 is at least 5% of the diameter D1 of the first portion 46 of the base surface 42 of the die cavity 21. The radial width of the groove 50 is at least 20% of the diameter D1 of the first portion 46 of the base surface 42 of the die cavity 21. The radial width of the groove 50 may be up to 300% of the diameter D1 of the first portion 46. The radial width of the groove 50 may be up to 250% of the diameter D1 of the first portion 46. Having a radial width of the groove 50 in this range advantageously optimizes compression of the workpiece 62 within the groove, reducing the likelihood of cracks forming in the workpiece during the rivet insertion operation and closing any cracks that may have formed.

[0104] The second portion 48 of the base surface 42 of the die cavity 21 and the sidewall 44 of the die cavity meet at a third interface 58. The third interface 58 is located at a radially outermost position where, when moving radially outward from the second portion 48, the angle between the central axis C and a normal extending from the base surface 42 is greater than 15 degrees. In some embodiments, the third interface 58 may be located at a radially outermost position where, when moving radially outward from the second portion 48, the angle between the central axis C and a normal extending from the base surface is greater than 45 degrees. The angle between the central axis C and the normal extending from the base surface that defines the location of the third interface 58 may be determined by the geometry of the second portion 48 and / or the sidewall 44. The radial width of the second portion 48 is the radial distance between the second interface 56 and the third interface 58. In some embodiments, the radial width of the second portion 48 may be the radial distance from the second interface 56 to the radially outer end of the second portion 48. The radially outer end of the second portion 48 may be located at an inflection point defined by the base surface 42. The inflection point may be located where the base surface changes from concave to convex when moving radially outward from the second portion 48 along the base surface 42. The sidewall 44 meets the second portion 48 at the radially outer end of the second portion 48. In some embodiments, the radially outer end of the second portion 48 may coincide with the third interface 58.

[0105] The third interface 58 defines a third interface depth d6. The third interface depth d6 extends in a direction along the central axis C. The third interface depth d6 extends from the outer rim 40 of the die 13 to the third interface 58. The depth d6 may extend from a portion of the outer rim that may be considered the top of the outer rim 40, which is the portion of the outer rim that is located furthest from the stem 22 along the central axis C.

[0106] The depth d6 of the third interface is greater than the depth d1 of the first portion. However, in some embodiments, the depth d6 of the third interface may be shallower than the depth of at least a portion of the first portion 46. The base surface 42 of the die 13 is rounded in the region of the third interface 58. In other, not shown, embodiments, the base surface 42 may have any suitable geometric shape in the region of the third interface 58. For example, the base surface 42 may be chamfered in the region of the third interface 58, or an apex may separate the second portion 48 and the sidewall 44. During the riveting operation, the workpiece does not contact the third interface 58 (see, e.g., FIG. 10 ). This is because the workpiece is supported by both the outer rim 40 and the second interface 56 during later stages of the riveting operation (see, e.g., FIGS. 9 and 10 ). However, in some embodiments, the workpiece may contact the third interface 58. Whether the workpiece contacts the third interface depends, for example, on the material from which the workpiece is made, the total thickness of the workpiece 62, and the geometric shape of the base surface 42 in the region of the third interface 58. The depth d6 of the third interface is greater than the depth d1 of the first portion, regardless of the location of the third interface 58.

[0107] The sidewall 44 of the die cavity 21 and the top surface 40 of the die 13 meet at a fourth interface 60. The fourth interface 60 is located at the radially innermost position where, when moving radially inward from the top surface 40, the angle between the central axis C and a normal extending from the die surface 39 is greater than 15 degrees. In some embodiments, the fourth interface 60 may be located at the radially innermost position where, when moving radially inward from the top surface 40, the angle between the central axis C and a normal extending from the base surface is greater than 45 degrees. The angle between the central axis C and the normal extending from the base surface that defines the location of the fourth interface 60 may be determined by the geometry of the top surface 40 and / or the sidewall 44. The die surface 39 is rounded in the region of the fourth interface 60. In other, not shown, embodiments, the die surface 39 may comprise any suitable geometric shape in the region of the fourth interface 60. For example, die surface 39 may be chamfered in the area of ​​fourth interface 60 or an apex may separate sidewall 44 and top surface 40 .

[0108] Note that for all of the aforementioned distances (d1-d6), the distances are measured (along the central axis) from the same portion of the outer rim 40. This portion of the outer rim can be said to be the top of the outer rim, which is the portion of the outer rim that is located furthest from the stem 22 along the central axis C.

[0109] The groove 50 defines a groove depth d7. The groove depth d7 extends in a direction along the central axis C. The groove depth d7 extends from the second interface 56 to a portion of the base surface 52 of the groove 50 having the greatest depth (i.e., a portion of the base surface farthest along the central axis C toward the stem 22 of the die). The groove depth d7 refers to the maximum depth of the groove 50. The groove depth d7 is equal to the second interface depth d5 ​​subtracted from the cavity groove depth d3. The groove depth d7 constitutes 75% or less of the cavity groove depth d3. In some embodiments, the groove depth d7 may be 50% or less of the cavity groove depth d3. The size of the groove depth d7 relative to the size of the cavity groove depth d3 may be selected based, for example, on the materials from which the workpieces to be joined in a riveting operation using the die 13 are made.

[0110] A riveting operation performed using the die 13 will now be described with reference to Figures 5-10. Figure 5 illustrates a first stage of the riveting operation. A workpiece 62 is shown received between the opposing nose assembly 16 and die 13. The workpiece 62 includes an upper sheet (or layer) 62a and a lower sheet (or layer) 62b. One or both of the upper sheet 62a and the lower sheet 62b may be made from aluminum. The lower sheet 62b may be formed from a material that is less ductile and / or less deformable than the upper sheet 62a. The lower sheet 62b may be made from a material having a ductility of 12% or less, preferably 10% or less, elongation to break. The lower sheet 64b may be at least 2.5 mm, preferably 3 mm, thick.

[0111] The upper sheet 62a has an upper surface 64 and a lower surface 66. The upper surface 64 of the upper sheet 62a faces the lower surface 66. The upper surface 64 of the upper sheet 62a is the upper surface of the workpiece 62. The lower sheet 62b has an upper surface 68 and a lower surface 70. The upper surface 68 faces the lower surface 70. The lower surface 70 is the lower surface of the workpiece 62. In the illustrated embodiment, the workpiece 62 includes two sheets (or layers), the upper sheet 62a and the lower sheet 62b. However, in some non-illustrated embodiments, the workpiece may include three or more sheets, or may include only a single sheet. At least one or all of the sheets may have a ductility of 12% or less. In some embodiments, at least one or all of the sheets may have a ductility of 8% or less. Materials with ductility within these ranges are prone to cracking during the rivet insertion operation. Using the die 13 with these materials is particularly preferred because the geometry of the die 13 reduces the likelihood of cracks forming during the rivet insertion operation. At least one of the sheets may be made of a non-heat-treated cast material. At least one of the sheets may be a cast material, aluminum, possibly cast aluminum, or magnesium. Workpiece 62 may include at least two sheets.

[0112] In this specification, when describing a workpiece, it means the top part which is closest to the rivet punch (and therefore furthest from the die) when in use, and the bottom part which is furthest from the rivet punch (and therefore closest to the die) when in use.

[0113] The rivet 71 is received within the nose assembly 16 of the rivet insertion device 2. The rivet 71 includes a head 72 and a shank 74 depending from the head. The shank 74 defines a rivet cavity 76. The shank 74 defines a shank outer diameter. The shank 74 defines a shank inner diameter. The rivet 71 includes a tip 78. The tip 78 faces the head 72. The tip 78 is the portion of the rivet 71 furthest from the head 72. The tip 78 defines a tip diameter. The tip 78 may define a flat land or a ring cutting edge. If the tip 78 defines a flat land, the tip diameter may be the average diameter of the flat land (i.e., the midpoint diameter). If the tip 78 defines a ring cutting edge, the tip diameter is the diameter of the ring cutting edge. The rivet 71 preferably has a hardness of at least 380 HV10 and / or at most 580 HV10.

[0114] In the first stage of the riveting operation, the tip 78 of the rivet 71 engages the upper surface 64 of the upper sheet 62a of the workpiece 62. A punch 80 of the rivet insertion device 2 engages the head 72 of the rivet 71, and the lower surface 70 of the workpiece 62 engages the upper surface (particularly the outer rim 40) of the die 13. The punch 80 then drives the rivet 71. In this example riveting operation, the punch 80 drives the rivet 71 into the die 13 at a speed of up to 400 mm / s and with a maximum driving force of up to 85 kN. However, in other examples, any suitable speed and driving force can be used.

[0115] 6 illustrates the second stage of the riveting operation. At this stage, the rivet 71 has been driven into the workpiece 62 such that the tip 78 of the rivet 71 has been driven through the upper sheet 62a of the workpiece 62. At this stage of the riveting operation, the tip 78 of the rivet 71 contacts the upper surface 68 of the lower sheet 62b of the workpiece 62. As the rivet 71 has been driven through the upper sheet 62a, a slug 82 has been severed from the upper sheet 62a and received within the rivet cavity 76. As a result of the punch driving force, the workpiece 62 (specifically, the lower surface 70 of the workpiece where the rivet is located) has deflected toward the base surface 42 of the die cavity 21.

[0116] 7 illustrates the third stage of the riveting operation. During this stage, the workpiece 62 continues to deflect so that the workpiece 62 (specifically, the underside 70 of the workpiece where the rivet is located) contacts the first portion 46 of the base surface 42 of the die face 39. After initial contact with the first portion 46, the workpiece 62 flows radially outward. This radial outward flow of the workpiece 62 continues until the first portion 46 is covered by the workpiece 62. The workpiece 62 remains in contact with the first portion 46 of the base surface 42 throughout the remainder of the riveting operation. Thus, the workpiece 62 is centrally supported relative to the punch 80 and die 13 throughout the majority of the riveting operation. Because the workpiece 62 is centrally supported throughout the majority of the riveting operation, the workpiece 62 is under compressive stress throughout this portion of the riveting operation. At this stage of the riveting operation, the workpiece 62 is supported on its underside by the outer rim 40 of the die 13 and by the first portion 46 of the base surface 42 of the die cavity 21 .

[0117] FIG. 8 illustrates the fourth stage of the riveting operation. During this stage, the continued advancement of the punch 80 deforms material from the lower sheet 62b of the workpiece 62 into the groove 50 in the base surface 42 of the die face 39. To enter the groove 50, at least a portion of the workpiece 62 flows downward. As the punch 80 advances, material from the lower sheet 62b of the workpiece 62 advances radially outward along the surface of the groove 50. Typically, during this stage of the rivet insertion operation, the shank 74 of the rivet 71 begins to flare. That is, the shank 74 of the rivet 71 begins to deform radially outward. The flaring of the shank 74 of the rivet 71 connects the material of the rivet 71 and the workpiece 62, thereby securing the rivet 71 to the workpiece 62. The stage of the rivet insertion process at which the rivet begins to flare may vary and may occur before or after the stage illustrated in FIG. 8. The stage at which flaring begins is a function of the characteristics of the rivet, such as the hardness of the material from which the rivet is made and the geometry of the rivet.

[0118] FIG. 9 illustrates a fifth stage of the riveting operation. In this stage, continued advancement of the punch 80 deforms the lower sheet 62b of the workpiece 62 so that the lower sheet 62b fills the groove 50 in the base surface 42 of the die face 39. To fill the groove 50, at least a portion of the workpiece 62 flows downward, and at least a portion of the workpiece 62 flows upward. FIG. 11 illustrates the direction of flow of the workpiece 62 during a stage of the riveting operation between the fourth and fifth stages. As can be seen, part A flows downward and radially outward. At least a portion of part A flows along the surface of the groove 50. Part B flows radially outward. At least a portion of part B flows along the surface of the groove 50. Part C flows radially outward and upward. At least a portion of part C flows along the surface of the groove 50. Part D flows downward and radially outward. Part E flows upward and radially outward. At least a portion of portion E flows along the surface of groove 50 .

[0119] Referring back to FIG. 9 , during the fifth stage of the riveting operation, the workpiece 62 is supported on its underside by the first portion 46 of the base surface 42 of the die surface 39, by the groove 50, by the outer rim 40 of the die surface 39, and by the second interface 56. Also, during this stage of the riveting operation, material from the workpiece 62 fills the groove 50. The material from the workpiece 62 filling the groove 50 reduces the amount of radial outward flow of the workpiece compared to when the groove 50 is not present. Reducing the amount of radial outward flow is desirable because it reduces the likelihood of cracks forming in the workpiece 62 during the riveting operation. Because the depth d1 of the first portion is shallower than the depth d5 ​​of the second interface, the workpiece 62 remains centrally supported during this stage of the riveting operation. A centrally supported workpiece 62 applies compressive stress to the workpiece 62, thereby reducing the likelihood of cracks forming during the riveting operation. During this stage of the riveting operation, the rivet 71 continues to expand, enhancing the connection between the rivet 71 and the workpiece 62 .

[0120] FIG. 10 illustrates the sixth and final stage of the riveting operation. During this stage of the riveting operation, the material of the workpiece 62, particularly the material of the lower sheet 62b of the workpiece 62, is deformed radially outward. The radially outward deformation of the workpiece 62 brings the workpiece 62 into contact with the second portion 48 of the base surface 42 of the die surface 39. Thus, during this stage of the riveting operation, the lower surface of the workpiece 62 is supported by the first portion 46 of the base surface 42, by the groove 50 in the base surface 42, by the second portion 48 of the base surface 42, and by the outer rim 40 of the die surface 39. Even if cracks form in the workpiece 62 during the previous stage of the riveting operation, the compression experienced by the workpiece during this stage at least partially closes such cracks. Closing any cracks that may form is desirable because it reduces the likelihood of contaminant ingress through the cracks in the formed joint and therefore reduces the likelihood of the created joint failing, for example, through corrosion, fatigue cracking, or moisture ingress-related failure. During this stage of the riveting operation, the rivet 71 continues to expand, further enhancing the connection between the rivet 71 and the workpiece 62 .

[0121] Following the sixth stage of the riveting operation, which ends when the punch 80 retracts, the riveting operation is complete. After inserting the rivet 71 into the workpiece 62, the rivet 71 does not penetrate the underside 70 of the workpiece 62. This advantageously reduces the possibility of workpiece corrosion, which could lead to joint failure. This differs from other types of workpiece fastening operations, such as inserting a self-piercing rivet stud, in which the inserted fastener (e.g., stud) penetrates the entire thickness of the workpiece. In this example, to secure the inserted fastener to the workpiece, the inserted fastener must expand so that the tip of the fastener contacts the underside of the workpiece. This means that the fastener shank must be able to undergo significant deformation without breaking. For this reason, such fasteners must be made of a much softer, more deformable material than the self-piercing rivets used in combination with the riveting die of the present invention. The use of a much softer, more deformable material to form the self-piercing rivet stud, as compared to the self-piercing rivet, means that the geometry used for dies for such fasteners, as in the present invention, is significantly different from that used for self-piercing riveting operations.

[0122] 5-10, in some embodiments, the workpiece 62 can contact the sidewall 44 of the die surface 39. The workpiece 62 may deform to the point of contacting the third interface 58. When the workpiece contacts the sidewall 44, the third interface 58, or both, any cracks that may have formed in areas of the workpiece that contact these areas of the die 13 are at least partially closed. Whether the workpiece 62 contacts the sidewall 44, the third interface 58, or both is determined by, for example, the material from which the workpiece 62 is made and the total thickness of the workpiece 62.

[0123] With particular reference to Figures 8, 9 and 10, it can be seen that the geometry of the die is selected so that during the riveting operation, the workpiece (particularly the underside of the workpiece) does not contact the second portion of the base surface of the die before the workpiece (particularly the underside of the workpiece) contacts the second interface 56.

[0124] The embodiments described herein relate to dies having stems depending from the bottom of the body of the die. It will be understood that in other embodiments, the die may not include a stem. In such embodiments, where a distance measured relative to the stem is referenced, the distance is instead measured relative to the bottom of the body of the die.

[0125] The embodiment described herein relates to a rivet 71 having a head 72, a shank 74, and a single-sided open rivet cavity 76. The rivet die geometry can also work for rivets with fully tubular rivet cavities. Fully tubular rivets are preferably used with the rivet die 13 when the workpiece comprises three or more work layers and / or when the total thickness of the workpiece 62 is 8 mm or greater.

[0126] While specific embodiments of the invention have been described above, it will be understood that the invention may be practiced otherwise than as described. The above description is intended to be illustrative and not limiting. Thus, it will be apparent to those skilled in the art that modifications can be made to the invention as described without departing from the scope of the claims set out below.

[0127] When a portion of a die herein is referred to as being planar or substantially planar, the portion may be said to lie on a plane, the plane being perpendicular to the central axis.

Claims

1. A rivet die for a riveting tool, comprising: a body defining a top surface; a die cavity formed in the top surface and at least partially defined by a base surface; the base surface including a groove extending at least partially about a central axis, a first portion through which the central axis passes, and a second portion; the groove is disposed radially outward of the first portion, and the second portion is disposed radially outward of the groove; the groove and the second portion abut each other at an interface; the first portion defines a first portion depth in a direction along the central axis, the interface defines an interface depth in a direction along the central axis, and the first portion depth is less than the interface depth.

2. 2. The rivet die of claim 1, wherein the second portion defines a second portion depth extending in a direction along the central axis, the entire depth of the first portion being less than the entire depth of the second portion.

3. The rivet die of claim 1 or 2, wherein the first portion is flat.

4. A rivet die according to any preceding claim, wherein the first portion defines a diameter relative to the central axis and the second portion defines a radial width.

5. The rivet die of claim 4 , wherein a ratio of the diameter of the first portion to the radial width of the second portion is less than four.

6. 6. A rivet die according to claim 4 or claim 5, wherein the diameter of the first portion is equal to or greater than the radial width of the second portion.

7. A rivet die according to any one of claims 4 to 6, wherein the groove defines a groove radial width, the groove radial width being at least 5% of the diameter of the first portion.

8. 8. The rivet die of claim 1, wherein the die cavity defines a die cavity depth in a direction along the central axis, and the groove defines a groove depth in a direction along the central axis.

9. 9. The rivet die of claim 8, wherein the depth of the groove is no more than 75% of the depth of the die cavity.

10. A rivet die according to any preceding claim, wherein the depth of the interface is at least 3% greater than the depth of the first portion.

11. The rivet die according to any one of claims 1 to 10, wherein at least a part of the first portion and at least a part of the second portion are perpendicular to the central axis.

12. The rivet die of any preceding claim, further comprising a stem extending from a lower surface of the body, the lower surface facing the upper surface.

13. A rivet die according to any preceding claim, wherein the upper surface defines an outer rim disposed radially outward of the die cavity.

14. 14. A rivet die according to any preceding claim, wherein the groove defines a radial midpoint defining a radial midpoint diameter, the groove being configured such that the radial midpoint diameter is equal to or greater than the inner diameter of the rivet bore provided in the riveting tool prior to rivet insertion.

15. A rivet die according to any preceding claim, wherein the first portion of the base surface is continuous.

16. A riveting tool configured to insert a rivet into a workpiece, the riveting tool comprising the die according to any one of claims 1 to 15, arranged below a punch that can be reciprocated by an actuator.

17. 1. A method of forming a joint, comprising: Providing a riveting tool according to claim 16; providing a rivet to the riveting tool; providing a work; positioning the workpiece between the die and the punch; and advancing the punch with an actuator to drive the rivet into the workpiece.

18. 20. The method of claim 17, wherein at least one of the layers of the workpiece is made from a material having a ductility of 12% or less.

19. The workpiece is an upper sheet defining an upper surface of the workpiece; a bottom sheet defining a bottom surface of the workpiece.

20. 20. The method of claim 19, wherein the rivet, after being driven into the workpiece, does not penetrate the underside of the workpiece.

21. 21. A method according to claim 19 or claim 20, wherein the bottom sheet is formed from a material that is less ductile than the top sheet.

22. A method according to any one of claims 17 to 21, wherein the rivet has a hardness of at least 380 HV10 and / or at most 580 HV10.

23. A product or component of a product produced using the method of any one of claims 17 to 22.

24. 24. The product or component part of a product of claim 23, wherein the product is a vehicle.

25. 1. A method of forming a self-piercing riveted joint between separate portions of a workpiece, comprising: providing i) a die defining a central axis and a die cavity defining a base surface, ii) the workpiece, iii) a punch, and iv) a self-piercing rivet; positioning the workpiece between the die and the punch; i) at least a portion of the workpiece flows to contact the base surface of the die; ii) at least a portion of the workpiece flows radially outward; iii) at least a portion of the workpiece flows downward into a groove in the base surface of the die; iv) at least a portion of the workpiece substantially fills the groove; v) using the punch to drive the rivet into the workpiece so that at least a portion of the workpiece flows radially outward beyond the groove; The method wherein the rivet expands while being driven into the workpiece such that the rivet interlocks with at least a portion of the workpiece, thereby creating the joint between the separate portions of the workpiece.

26. 26. The method of claim 25, wherein at least a portion of the workpiece flows upward and at least a portion of the workpiece flows downward to substantially fill the groove.

27. 27. The method of claim 25 or claim 26, wherein (i) to (v) start sequentially.

28. The method of any one of claims 25 to 27, wherein the radially outward flow of the workpiece brings the workpiece into contact with a sidewall of the die.

29. 29. The method of any one of claims 25 to 28, wherein the groove is disposed radially outward of a first portion of the base surface, a second portion of the base surface is disposed radially outward of the groove, and the groove and the second portion meet at an interface.

30. 30. The method of claim 29, wherein the first portion defines a first portion depth in a direction along the central axis, the interface defines an interface depth in a direction along the central axis, and the first portion depth is less than the interface depth.

31. 31. A method according to claim 29 or claim 30, wherein the workpiece flows radially outwardly along the first portion of the base surface in step (ii).

32. A method according to any one of claims 29 to 31, wherein the workpiece flows radially outwardly along the second portion of the base surface in step (v).

Images