DESC:TECHNICAL FIELD
Present disclosure generally relates to a mechanical fastening structure for joining workpieces. Particularly but not exclusively, the present disclosure relates to a rivet for joining the workpieces. Further, embodiments of the disclosure disclose a self-piercing rivet for butt-joining the workpieces.

BACKGROUND OF THE DISCLOSURE
Advent of industrial revolution led to infancy of metal working processes. The industrial revolution demands strong and durable parts for various industrial needs. However, parts which are produced by conventional processes may not be accurate and could not be mass produced. The industrial revolution is able to pave way for manufacturing individual parts, assemblies or any other large scale structures. Based on application usage, the metal working process may be categorized into a number of machining processes. Few of the key machining processes are broadly categorized to a forming process, a cutting process, a joining process etc.

The joining process involves connecting or linking two or more workpieces into a single structure. Typically, the joining process involves connecting two or more workpieces either by a lap-joining technique and/or by a butt-joining technique. In the lap-joining technique, the workpieces overlap for joining the workpieces and thickness of resultant joint would be a combination of the thickness of the workpieces. In the butt-joining technique, ends of the workpieces are placed together for joining the workpieces. For either of the lap joining technique and the butt joining technique, joining processes such as welding, riveting, soldering, brazing and the like are used. Predominantly, welding is the preferred process for joining workpieces, due to their inherent characteristic of producing stronger joints, faster fabrication process and smoother finish.

However, the welding process may entirely be dependent on the skill of an operator or a welder. Moreover, particularly for butt-joint technique, the welding process may induce stress concentration or develop uneven stress distribution at the vicinity of the weld joint, due to uneven heating and cooling of the workpieces during the welding process. This effect inherently affects the microstructure of the workpieces, which may deteriorate strength characteristics of the workpieces.

The present disclosure is directed to overcome one or more limitations stated above.

The information disclosed in this background of the disclosure section is only for enhancement of understanding of the general background of the invention and should not be taken as an acknowledgement or any form of suggestion that this information forms the prior art already known to a person skilled in the art.

SUMMARY OF THE DISCLOSURE
One or more shortcomings of conventional process is overcome, and additional advantages are provided through the provision of the rivet as described in the present disclosure. Additional features and advantages are realized through the techniques of the present disclosure. Other embodiments and aspects of the disclosure are described in detail herein and are considered a part of the disclosure.

In one non-limiting embodiment of the present disclosure, a rivet for joining workpieces is disclosed. The rivet is configured for mechanically joining the workpieces together. The rivet comprises a head defining a top surface and a bottom surface. A shank extends from the bottom surface of the head. The rivet includes a plurality of legs extending from the shank, each of the plurality of legs comprising an inner leg portion and an outer leg portion. The outer leg portion of each of the plurality of legs is defined with a curved surface extending from a root end to a tip end, projecting inwardly towards a rivet axis.

In an embodiment, the inner leg portion of each of the plurality of legs is defined with at least one of a straight profile and a curved profile from the root end to the tip end. Profile of the inner leg portion and the outer leg portion of each of the plurality of legs provides uniform load distribution during joining.

In an embodiment, the tip end of each of the plurality of legs is chamfered.

In an embodiment, the shank is defined with an inner shank portion and an outer shank portion. The outer shank portion is configured with a curved profile, projecting inwardly towards the rivet axis for uniform load distribution during joining. The inner shank portion of the shank is defined with curved surface with a predetermined radius of curvature, and the inner shank portion is configured to receive portions of each of the plurality of workpieces during joining, geometrically locking each of the plurality of workpieces.

In an embodiment, the joining of the plurality of workpieces is done by a punch and die assembly. The method comprises, positioning the plurality of workpieces on the die, such that at least a portion of each of the plurality of workpieces is placed over a plurality of cavities provided in a die. Ends of each of the plurality of workpieces put against one another, and on dome of the die between the plurality of cavities. The method further includes piercing the rivet onto the plurality of the workpieces by a punch, wherein the plurality of legs of the rivet plastically deforms the plurality of workpieces and a portion of each of the plurality of workpieces is received by an inner shank portion of the rivet during joining, geometrically locking each of the plurality of workpieces. Also, profile of the die for joining the plurality of workpieces is configured to match profile of the rivet.

It is to be understood that the aspects and embodiments of the disclosure described above may be used in any combination with each other. Several of the aspects and embodiments may be combined together to form a further embodiment of the disclosure.

The foregoing summary is illustrative only and is not intended to be in any way limiting. In addition to the illustrative aspects, embodiments, and features described above, further aspects, embodiments, and features will become apparent by reference to the drawings and the following detailed description.

BRIEF DESCRIPTION OF ACCOMPANYING DRAWINGS
The novel features and characteristic of the disclosure are set forth in the appended specification. The disclosure itself, however, as well as a preferred mode of use, further objectives and advantages thereof, will be best understood by reference to the following description of an illustrative embodiment when read in conjunction with the accompanying drawings. One or more embodiments are now described, by way of example only, with reference to the accompanying drawings wherein like reference numerals represent like elements and in which:

Figure 1 illustrates a front view of a rivet for joining workpieces, in accordance with an embodiment of the present disclosure.

Figure 2 illustrates a front view of a die for supporting the rivet of Figure 1, in accordance with an embodiment of the present disclosure.

Figure 3 illustrates a perspective view of the rivet and the die during the joining process, in accordance with an embodiment of the present disclosure.

Figure 4 illustrates a front view of the rivet and the die during the joining process, in accordance with an embodiment of the present disclosure.

Figure 5 illustrates the workpieces being deformed by the rivet during the joining process, in accordance with an embodiment of the present disclosure.

Figure 6 illustrates a front view of the joining process depicting the rivet geometrically locked with the workpieces, in accordance with an embodiment of the present disclosure.

Figure 7a illustrates a joint formed along entire width of the workpieces, in accordance with an embodiment of the present disclosure.

Figure 7b illustrates a joint formed along partial width of the workpieces, in accordance with an embodiment of the present disclosure.

Figure 8 illustrates a front view of the rivet joined to the workpieces depicting design parameters considered for an optimum joint, in accordance with an embodiment of the present disclosure.

Figure 9 illustrates a graphical representation of the effect of rivet thickness on joint strength, in accordance with an embodiment of the present disclosure.

Figure 10 illustrates a front view of the rivet joined to the workpieces, depicting thickness of the workpieces after deformation, in accordance with an embodiment of the present disclosure.

Figure 11 illustrates a graphical representation of variation of joint strength vs leg thickness of the workpieces, in accordance with an embodiment of the present disclosure.

Figure 12 illustrates a graphical comparison of variation of joint strength with stroke, between experimental and simulated results, in accordance with an embodiment of the present disclosure.

Figure 13 illustrates a graphical comparison of variation of joint strength with stroke between various workpieces, in accordance with an embodiment of the present disclosure.

The figures depict embodiments of the disclosure for purposes of illustration only. One skilled in the art will readily recognize from the following description that alternative embodiments of the structures and methods illustrated herein may be employed without departing from the principles of the disclosure described herein.

DETAILED DESCRIPTION
While the embodiments of the disclosure are subject to various modifications and alternative forms, specific embodiment thereof has been shown by way of example in the figures and will be described below. It should be understood, however, that it is not intended to limit the disclosure to the particular forms disclosed, but on the contrary, the disclosure is to cover all modifications, equivalents, and alternative falling within the scope of the disclosure.

It is to be noted that a person skilled in the art would be motivated from the present disclosure that discloses a rivet, which may vary based on the configuration of the workpieces. However, such modifications should be construed within the scope of the disclosure. Accordingly, the drawings show only those specific details that are pertinent to understand the embodiments of the present disclosure, so as not to obscure the disclosure with details that will be readily apparent to those of ordinary skill in the art having the benefit of the description herein.

The terms “comprises”, “comprising”, “includes” or any other variations thereof used in the disclosure, are intended to cover a non-exclusive inclusion, such that an assembly that comprises a list of components does not include only those components but may include other components not expressly listed or inherent to such system, or assembly, or device. In other words, one or more elements in an assembly proceeded by “comprises… a” does not, without more constraints, preclude the existence of other elements or additional elements in the system or device.

The following paragraphs describe the present disclosure with reference to Figures 1 to 10. In the figures, the same element or elements which have similar functions are indicated by the same reference signs.

Figure 1 in one exemplary embodiment of the present disclosure which illustrates a rivet (100) for joining a plurality of workpieces (7) together. The rivet (100) is configured for mechanically joining the plurality of workpieces (7) [shown in Figure 3], without altering material characteristics of the workpieces (7).

The rivet (100) comprises a head (1) having a top surface (1a) and a bottom surface (1b). A shank (2) extends from the bottom surface (1b) of the head (1) and acts as a primary load bearing member for the rivet (100). A plurality of legs (3) extends from the shank (2), wherein each of the plurality of legs (3) are configured to deform and geometrically lock each of the plurality of workpieces (7) together, thereby joining the plurality of workpieces (7). Each of the plurality of legs (3) is defined with a tip end (3c), configured to indent or deform each of the plurality of workpieces (7), and a root end (3d). In an embodiment, the tip end (3c) may be chamfered for improving indentation performance of the tip end (3c).

Further, a die (4) [shown in Figure. 2] is provided beneath the rivet (100) and is adapted to support the plurality of workpieces (7) during the joining process. The die (4) may be configured with a plurality of cavities (4a) for receiving the plurality of legs (3). At least one dome (4b) may be provided in-between each of the plurality of cavities (4a). In an embodiment, the profile combination of the at least one dome (4b) and the plurality of cavities (4a), may complement the profile combination of the inner shank portion (2a) of the shank (2) and the plurality of legs (3). In other words, the profile of the die (4) is configured to match the profile of the rivet (100), to facilitate the joining process. Further, the die (4) includes a base (5) connectable to a bed of a punch and die assembly [not shown in Figures].

In an embodiment, the joining process may be a butt-joining process capable of joining the plurality of workpieces (7) together. In another embodiment, the joining process may be any of the butt-joining process, lap-joining process and the like.

In an embodiment, the top surface (1a) of the head (1) has a flat profile configured to support a punch (6), wherein the punch (6) is adapted to apply load on the head (1) during the butt-joining operation. The head (1) of the rivet (100) may be configured with a predetermined thickness (Lh) corresponding to the load and design requirements of the rivet (100). The head (1) of the rivet (100) may be configured with a cross-section selected from at least one of geometric shapes such as but not limiting to a cylindrical cross-section, a rectangular cross-section, a square cross-section and the like, which serves feasibility and design requirement.

In an embodiment, the shank (2) of the rivet (100) may extend from the bottom surface (1b) of the head (1) by a predetermined thickness (Ls), corresponding to the load and design requirements of the rivet (100). The diameter of the shank (2) of the rivet (100) is selected corresponding to the diameter of the head (1), as per design feasibility and requirement. In an embodiment, the shank (2) may be configured with a diameter lesser than that of the head (1), to form a T-shaped structure. In another embodiment the shank (2) may be configured with a diameter equal to that of the head (1). The shank (2) of the rivet (100) may include an inner shank portion (2a) and an outer shank portion (2b). The outer shank portion (2b) of the shank (2) may be configured with a curved profile, projecting inwardly towards the rivet axis (A-A’) for uniform load distribution during deformation. The inner shank portion (2a) of the shank (2) may be configured with a radius of curvature (R) for housing ends of the plurality of workpieces (7) so deformed, during the butt-joining process. The radius of curvature (R) of the inner shank portion (2a) may be selected such that ends of the plurality of workpieces (7) contact the inner shank portion (2a) to form a flush configuration. In another embodiment, radius of curvature (R) of the inner shank portion (2a) may be selected based on design feasibility and requirement.

In an embodiment, the plurality of legs (3) may extend up to a predetermined length (Ll) over the shank (2). The predetermined length (Ll) of the plurality of legs (3) may be selected such that, rigidity of the plurality of legs (3) is sufficient to enable deformation of the plurality of workpieces (7) during the joining process. Each of the plurality of legs (3) may be defined by an outer leg portion (3a) and an inner leg portion (3b). The outer leg portion (3a) may be configured with a curved profile of a predefined radius. The curved profile facilitates uniform distribution of load from the tip end (3c) of the plurality of legs (3) to the shank (2). This configuration therefore ensures rigidity of the plurality of legs (3) during deformation of the plurality of workpieces (7). The inner leg portion (3b) of each of the plurality of legs (3) may be configured with a straight or a curved profile, as per design feasibility and requirement. The profile of the inner leg portion (3b) may also supplement the rigidity provided by the profile of the outer leg portion (3a). The profile combination of the outer leg portion (3a) and the inner leg portion (3b) of each of the plurality of legs (3) may provide uniform load distribution, thereby ensuring the rigidity of the plurality of legs (3) during deformation. The curvature of the inner leg portion (3b) of each of the plurality of legs (3) adjoins the shank (2) of the rivet (100). Further, ends of each of the plurality of legs (3) may incline towards the rivet axis (A-A’) of the rivet (100) for improving the rigidity of the plurality of legs (3). The inclination may be selected such that, an optimum rigidity may be obtained without affecting the angle of the tip end (3c) of the plurality of legs (3). This configuration thus ensures an equilibrium between the deformation characteristics and the rigidity of the plurality of legs (3). Also, the plurality of legs (3) may be configured with a predetermined thickness (tL) [shown in Figure 8] for deforming the plurality of workpieces (7) for joining each of the plurality of workpieces (7). The predetermined thickness (tL) may be selected such that, the plurality of legs (3) only deforms the plurality of workpieces (7), without affecting material characteristics of the plurality of workpieces (7). In other words, the predetermined thickness (tL) may be selected such that, the plurality of workpieces (7) does not undergo deterioration in material characteristics upon deformation. Each of the plurality of legs (3) may be eccentrically positioned from the rivet axis (A-A’) of the rivet (100). Further, each of the plurality of legs (3) may be spaced apart by a predetermined inner width (IW) [as shown in Figure 1]. The predetermined width (IW) is selected based on the design feasibility and requirement. Each of the plurality of legs (3) may be located on the shank (2) based on dimensions of an outer width (OW) relative to the dimensions of the head (1). The outer width (OW) is selected based on the design feasibility and requirement.

In an embodiment, the combination of dimensions of the head (1), the shank (2) and the plurality of legs (3) provides length (L) of the rivet (100). In an embodiment, the length (L) of the rivet (100) may be varied based on design feasibility and requirement.

In an embodiment, the head (1), the shank (2) and the plurality of legs (3) are co-axial. In another embodiment, the plurality of legs (3) may be eccentrically aligned with the central axis (A-A’) of the rivet (100). In another embodiment, the plurality of legs (3) and the shank (2) may be eccentrically aligned with the rivet axis (A-A’) of the rivet (100).

In an embodiment, the rivet (100) is made of metallic materials such as but not limiting to aluminium alloy, steel, copper, monel and like which suits design feasibility and requirement. In another embodiment, the rivet (100) may be made of non-metallic materials or composite materials.

In an embodiment, the die (4) may be made of metallic materials such as but not limiting to iron, steel and the like which suits design feasibility and requirement. In another embodiment, the die (4) may be made of non-metallic materials or composite materials.

Figure 3 in one exemplary embodiment of the present disclosure illustrates a perspective view of positions of the rivet (100) and the die (4) over the plurality of workpieces (7). As illustrated, the plurality of workpieces (7) are placed on the die (4), which may be fixed on bed of a punching machine. The plurality of workpieces (7) may be placed such that, ends of each of the workpieces (7) are placed over the plurality of cavities (4a) and each of the ends meet at the at least one dome (4b) to facilitate the joining process. The rivet (100) may be then aligned on the plurality of workpieces (7), such that, each of the plurality of legs (7) is located on each of the plurality of workpieces (7) and the each of the plurality of legs (3) point towards the plurality of cavities (4a) provided on the die (4). In this configuration, the punch (6) may be operated to apply load on the rivet (100). Upon application of load, the plurality of legs (3) deforms each of the plurality of workpieces (7) [as shown in Figure 4]. At the same time, the plurality of legs (3) enable bending of ends of the plurality of workpieces (7) towards the inner leg portion (3b) of the shank (2) [as shown in Figure 5], thereby geometrically locking the plurality of workpieces (7) rigidly. This, geometrical locking of the plurality of workpieces (7) may facilitate mechanical joining the plurality of workpieces (7) together [as shown in Figure 6]. The rivet (100) may be configured with a width equal to that of the width of the plurality of workpieces (7), thereby forming a joint along the entire width of the plurality of workpieces (7) [as shown in Figure 7a]. The rivet (100) may be configured with a width lesser than that of the width of the plurality of workpieces (7), thereby forming a joint smaller than the width of the plurality of workpieces (7) [as shown in Figure 7b].

Exemplary Experimental data:
Design of experiments (DOE)
The following five parameters and four levels for each parameter are considered in simulation.

Rivet parameters:
Rivet vertical height: P1 (3.0, 4.0, 4.5, 5.0)
Rivet breadth (opening): P2 (3.5, 5.0, 6.5, 8.5)

Die parameters:
Die breadth (opening): P3 (6.0, 8.0, 9.5, 11.0)
Die depth: P4 (0.8, 1.5, 1.8, 2.0)
Die corner radius: P5 (0.2, 0.6, 0.8, 1.0)

The parameters and their level are shown in Table 1 and combinations of parameters are considered are shown in
Table 2
Table 1: Parameter and its level values
Level/Parameter P1 P2 P3 P4 P5
1 3.0 3.5 6.0 0.5 0.6
2 4.0 5.0 8.0 1.5 0.6
3 4.5 6.5 9.5 1.8 0.8
4 5.0 8.5 11.0 2.0 1.0

Table 2: Orthogonal array for optimization

S.NO/TOOL Rivet Die
Result
(N)
Vh Outer Br Die Br Depth Corner R
P1 P2 P3 P4 P5
L1 1 1 1 1 1 1227.54
L2 1 2 2 2 2 1574.4
L3 1 3 3 3 3 1414.5
L4 1 4 4 4 4 1389.9
L5 2 1 2 3 4 1057.8
L6 2 2 1 4 3 738
L7 2 3 4 1 2 1242.3
L8 2 4 3 2 1 1033.2
L9 3 1 3 4 2 799.5
L10 3 2 4 3 1 0
L11 3 3 1 2 4 0
L12 3 4 2 1 3 787.2
L13 4 1 4 2 3 0
L14 4 2 3 1 4 0
L15 4 3 2 4 1 0
L16 4 4 1 3 2 0

Further, figure 8 in one exemplary embodiment, illustrates various parameters which influence the strength of the joint formed between the rivet (100) and the plurality of workpieces (7).

As illustrated, the joint strength between the rivet (100) and the plurality of workpieces (7), may be dependent on parameters such as but not limiting to rivet thickness (tc), rivet leg thickness (tL) and lowest thickness (ts) of each of the plurality of workpieces (7). In an embodiment, the parameters affecting the joint strength varies based on design feasibility and requirement.

In an embodiment, analytical formulas are proposed to assess dependency of joint strength of the plurality of workpieces (7), after joining, or samples [as shown in Figures 7a and 7b]. The simulations are carried out to determine the joint strength, by applying tensile load perpendicularly to the rivet axis (A-A’).

Rivet central thickness:

The load P on rivet leg is eccentric; the rivet strength is given by

Tensile strength: s_max=P_c/A+Mc/I
Compression strength: ?-s?_max=P_c/A-Mc/I
I=(bd^3)/12
M=?2P?_c·e
On solving for P_c we get the joint strength of the rivet (100).
Where s_max is the yield strength of rivet (100),
b is out of plane length of rivet (100),
d is thickness of rivet (100) at its axis,
c is the surface distance from the neutral axis,
e distance of resultant force from the neutral axis.

A graph indicating, effect of rivet thickness (tc) on joint strength is illustrated in Figure 9. In view of Figure 9 and calculations by aforementioned equations, it may be evident that strength of the joint is proportional to the rivet (100) thickness (tc).

Rivet leg thickness:

s_max=Mc/I
I=(bd^3)/12
M=P_l·l

On solving for P_l we get the joint strength of the rivet (100).

b Is out of plane rivet length,

d Rivet leg thickness.

A graph indicating, effect of leg thickness (tl) on joint strength is illustrated in Figure 10. In view of Figure 10 and calculations by aforementioned equations, it may be evident that joint strength is proportional to the leg thickness (tl).

Further, a graph indicating variation of joint strength vs leg thickness of workpieces is represented in Figure 11.

Sheet thickness:
The effect of thickness of each of the plurality of workpieces (7) on joint strength is illustrated in Figures 10 and 11. As illustrated in Figure 10, the thickness of each of the plurality of workpieces (7) refers to a thickness between the tip end (3c) of the plurality of legs (3) and each of the plurality of workpieces (7) after deformation.

Now, If t_n is lowest sheet thickness,

Strength of the joint P_n=s_12·area,

s_12 is the state of stress based on yield strength,

For example, in Error! Reference source not found.,

s_12=s_y and area =(t_n·b),

Where t_n is lowest sheet thickness and b out of plane sheet length.

Then, P_n=s_y·(t_n·b)

In view of Figure 10 and calculations by aforementioned equations, it is evident that joint strength is proportional to the sheet thickness (tn).

Figure 12, in one exemplary embodiment of the present disclosure illustrates a graph illustrating comparison of the experimental data with the simulated data, based on optimum parameters obtained from aforementioned calculations.

In an embodiment, the optimum parameters of the rivet (100) are mentioned below:

Central thickness (tc): 1.5 mm
Rivet leg thickness (tl): 0.85 mm
Sheet thickness (tn): 0.76 mm

Further, as illustrated in Figure 12, the simulation results match with the experimental results and thus, it is evident that the mechanical joint obtained by the rivet (100) may be capable of withstanding the load similar to the joints obtained by other conventional joining techniques.

In an embodiment, for determining the strength of joint when the width of the rivet (100) is lesser than that of the width of each of the plurality of workpieces (7) [as shown in Figure 7b], additional parameters are considered, which are iterated below.
Rivet thickness (tc),
Leg thickness (tl),
Sheet failure outside rivet (100)
Sheet failure inside rivet (100)

The first two parameters are same as explained earlier. In the previous type of joint, failure is considered at yield stress and in the present joint, the failure occurs at fracture stress. In this joint, deformations are restricted by side of workpieces projected on either side of the rivet (100).

Sheet failure outside rivet
The tensile strength of 2 mm thickness of each of the plurality of workpieces (7) is calculated by:
Ft =s · (b·ts+2·2·a)
Where b is the length of the rivet (100).

Sheet failure inside rivet
Shear strength of each of the plurality of workpieces (7) inside the rivet (100) is computed by:

Two vertical faces of each area: Area (A) = b · TS

Shear strength Fs=? · (2·A+b · TS)

Where T is the shear strength of each of the plurality of workpieces (7)

This shear strength is constant irrespective of change in leg thickness (tl) and rivet thickness (tc).

For the plurality of workpieces (7) under study, maximum strength observed is 3.8 {SD 0.158} kN as shown in Figure 13. In an embodiment, the illustration shown in Figure 13, pertains computation of strength of the rivet (100) with 10mm dimension and interface length of each of the plurality of workpieces (7) being 25mm. In this case, the area adjacent to rivet (100) is required to be sheared, which provides additional rigidity to the joint. It is observed that the failure happened in this joint is due to the failure of the plurality of legs (3) of the rivet (100).

Equivalents:
With respect to the use of substantially any plural and/or singular terms herein, those having skill in the art can translate from the plural to the singular and/or from the singular to the plural as is appropriate to the context and/or application. The various singular/plural permutations may be expressly set forth herein for sake of clarity.

It will be understood by those within the art that, in general, terms used herein, and especially in the appended claims (e.g., bodies of the appended claims) are generally intended as “open” terms (e.g., the term “including” should be interpreted as “including but not limited to,” the term “having” should be interpreted as “having at least,” the term “includes” should be interpreted as “includes but is not limited to,” etc.). It will be further understood by those within the art that if a specific number of an introduced claim recitation is intended, such an intent will be explicitly recited in the claim, and in the absence of such recitation no such intent is present. For example, as an aid to understanding, the following appended claims may contain usage of the introductory phrases “at least one” and “one or more” to introduce claim recitations. However, the use of such phrases should not be construed to imply that the introduction of a claim recitation by the indefinite articles “a” or “an” limits any particular claim containing such introduced claim recitation to inventions containing only one such recitation, even when the same claim includes the introductory phrases “one or more” or “at least one” and indefinite articles such as “a” or “an” (e.g., “a” and/or “an” should typically be interpreted to mean “at least one” or “one or more”); the same holds true for the use of definite articles used to introduce claim recitations. In addition, even if a specific number of an introduced claim recitation is explicitly recited, those skilled in the art will recognize that such recitation should typically be interpreted to mean at least the recited number (e.g., the bare recitation of “two recitations,” without other modifiers, typically means at least two recitations, or two or more recitations). Furthermore, in those instances where a convention analogous to “at least one of A, B, and C, etc.” is used, in general such a construction is intended in the sense one having skill in the art would understand the convention (e.g., “a system having at least one of A, B, and C” would include but not be limited to systems that have A alone, B alone, C alone, A and B together, A and C together, B and C together, and/or A, B, and C together, etc.). In those instances where a convention analogous to “at least one of A, B, or C, etc.” is used, in general such a construction is intended in the sense one having skill in the art would understand the convention (e.g., “a system having at least one of A, B, or C” would include but not be limited to systems that have A alone, B alone, C alone, A and B together, A and C together, B and C together, and/or A, B, and C together, etc.). It will be further understood by those within the art that virtually any disjunctive word and/or phrase presenting two or more alternative terms, whether in the description, claims, or drawings, should be understood to contemplate the possibilities of including one of the terms, either of the terms, or both terms. For example, the phrase “A or B” will be understood to include the possibilities of “A” or “B” or “A and B.”

While various aspects and embodiments have been disclosed herein, other aspects and embodiments will be apparent to those skilled in the art. The various aspects and embodiments disclosed herein are for purposes of illustration and are not intended to be limiting, with the true scope and spirit being indicated by the following claims.
List of reference Numerals
REFERENCE NUMERALS DESCRIPTION
100 Rivet
1 Head of the rivet
1a Top surface of the head
1b Bottom surface of the head
2 Shank of the rivet
2a Outer shank portion
2b Inner shank portion
3 A plurality of legs
3a Outer leg portion
3b Inner leg portion
3c Tip end of the plurality of legs
3d Root end of the plurality of legs
4 Die
4a Plurality of cavities on the Die
4b Dome on the Die
5 Base of the Die
6 Punch
7 Plurality of workpieces
H Length of head of the rivet
IW Inner width between the plurality of legs
OW Outer width between the plurality of legs
Lh Head thickness
Ls Shank thickness
Ll Leg length ,CLAIMS:We claim:
1. A rivet (100) for joining a plurality of workpieces (7), the rivet (100) comprising:
a head (1) defining a top surface (1a) and a bottom surface (1b);
a shank (2) extending from the bottom surface (1b) of the head (1); and
a plurality of legs (3) extending from the shank (2), each of the plurality of legs (3) comprising an inner leg portion (3b) and an outer leg portion (3a), wherein the outer leg portion (3a) of each of the plurality of legs (3) is defined with a curved surface extending from a root end (3d) to a tip end (3c), projecting inwardly towards a rivet axis (A-A’).

2. The rivet (100) as claimed in claim 1, wherein the inner leg portion (3b) of each of the plurality of legs (3) is defined with at least one of a straight profile and a curved profile from the root end (3d) to the tip end (3c).

3. The rivet (100) as claimed in claim 1, wherein the outer leg portion (3a) of each of the plurality of legs (3) facilitates uniform distribution of load from the root end (3d) to the tip end (3c) of the plurality of legs (3) to the shank (2).

4. The rivet (100) as claimed in claim 1, wherein profile of the inner leg portion (3b) and the outer leg portion (3a) of each of the plurality of legs (3) provides uniform load distribution during joining.

5. The rivet (100) as claimed in claim 1, wherein the tip end (3c) of each of the plurality of legs (3) is chamfered.

6. The rivet (100) as claimed in claim 1, wherein, the shank (2) is defined with an inner shank portion (2a) and an outer shank portion (2b).

7. The rivet (100) as claimed in claim 6, wherein the outer shank portion (2b) is configured with a curved profile, projecting inwardly towards the rivet axis (A-A’) for uniform load distribution during joining.

8. The rivet (100) as claimed in claim 6, wherein the inner shank portion (2a) is defined with curved surface with a predetermined radius of curvature (R), the inner shank portion (2a) is configured to receive portions of each of the plurality of workpieces (7) during joining, geometrically locking each of the plurality of workpieces (7).

9. A method for joining a plurality of workpieces (7), by punch and die assembly, the method comprising:
positioning, the plurality of workpieces (7) on a die (4), such that at least a portion of each of the plurality of workpieces (7) is placed over a plurality of cavities (4a) provided in the die (4), wherein, the ends of each of the plurality of workpieces (7) but against one another on a dome (4b) of the die between the plurality of cavities (4a); and
piercing a rivet (100) as claimed in any of the preceding claims, onto the plurality of workpieces (7) by a punch (6) , wherein a plurality of legs (3) of the rivet (100) plastically deforms the plurality of workpieces (7) and a portion of each of the plurality of workpieces (7) is received by an inner shank portion (2a) of the rivet (100) during joining, geometrically locking each of the plurality of workpieces (7).
10. The method as claimed in claim 8, wherein:
profile of the die (4) for joining the plurality of workpieces (7), is configured to match profile of the rivet (100).