JOINTING ELEMENT WITH A SEMI-SPHERICAL PROTUBER ENSURING MULTI-MATERIAL ASSEMBLY

Abstract

JOINTING ELEMENT WITH A SEMI-SPHERICAL PROTUBER ENSURING MULTI-MATERIAL ASSEMBLY The present invention relates to a joining element (2), intended to irreversibly join a first part (5) to a second part by electric resistance welding, comprising: - a head (4) intended to bear on the first part; and - an axial portion (6) comprising, at a distal end (8), a connecting face (10) intended to be electrically resistance welded to the second part; remarkable in that the distal end forms a protuberance (9) comprising said connecting face and projecting from an inferior face (6.1) of the axial portion, said protuberance having a diameter (d) equal to at most 80% of a total diameter (D) of said axial portion, so as to form a hollow space (12) around said protuberance between the connecting face and the inferior face. (Figure to be published with the abbreviation: Figure 1)

Description

Title of the invention: JOINTING ELEMENT WITH A SEMI-SPHERICAL PROTUBER ENSURING MULTI-MATERIAL ASSEMBLY technical field

[0001] The present invention relates to the field of motor vehicles, more particularly to the field of multi-material part assemblies of motor vehicles. Previous technique

[0002] In the context of a multi-material assembly, i.e. aluminium / steel, steel / composite, steel / plastic, etc. assembly, the use of joining elements to ensure a rigid bond by gluing and / or welding of the different parts is conventionally widespread, in particular to ensure welding by electric welding, in which the joining element is directly welded to a second part, while being linked to the first part, thus obtaining an assembly of the two parts by means of an electrically welded joint.

[0003] An example of multi-material welding is notably known from published patent document EP 2 127 797 Al which discloses a spot welding process, by means of a pin having a flared portion which is engaged with a light part, and forming a weld bead presented at an interface between the pin and a steel part.

[0004] However, the problem raised in the context of multi-material joining by electric welding is the presence of a gap between the two welded parts and / or at the weld. This gap is generally linked to a problem with the contact of the joining pin with the second part to be welded, which is caused either by an excess of material at the interface of the two parts, or by a lack of material at said interface. This can result in a degradation of the overall strength and physical resistance of the welded joint.

[0005] To ensure a sound and void-free electrically welded joint, providing a robust bond with multi-material parts, it is necessary to address the plating problem during electrical welding. Description of the invention

[0006] The present invention aims to overcome at least one of the drawbacks of the aforementioned prior art. More particularly, the invention aims to provide a simple, efficient, and economical solution for joining two parts made of different materials by electric welding, while ensuring a sound and robust connection.

[0007] To this end, the invention relates to a joining element, intended to irreversibly join a first part to a second part by electric resistance welding, comprising: - a head designed to rest on the first piece; and - an axial portion extending from the head and intended to pass through an orifice in the first piece, said axial portion comprising, at a distal end, a connecting face intended to be electrically resistance welded to the second piece; remarkable in that the distal end forms a protrusion comprising said connecting face and projecting from an inferior face of the axial portion, said protrusion having a diameter equal to at most 80% of a total diameter of said axial portion, so as to form a hollow space around said protrusion between the connecting face and the inferior face.

[0008] Preferably, the axial portion comprises a cylinder of essentially constant diameter along its entire axial extent, i.e., from the head to the lower face. The lower face is preferably flat and perpendicular to the axial extent of the axial portion. Advantageously, the diameter of the protrusion is measured at a junction between the connecting face and the lower face of the axial portion.

[0009] Advantageously, the joining element and the second part are obtained from a metallic material, and are preferably formed from steel, while the first part can, for example, be formed from aluminum. Preferably, the head is continuously circular and comprises an external upper face that is smooth and free of radial notches or grooves.

[0010] According to one embodiment, the protuberance has a hemispherical shape, and the connecting face includes a generally convex envelope between the lower face and a center of said connecting face.

[0011] Preferably, the connecting face comprises a fully convex transverse profile.

[0012] According to one embodiment, the diameter of the protuberance is equal to at least 30% of the total diameter of the axial portion and at most 60% of said total diameter.

[0013] According to one embodiment, the axial portion extends from the head to the connecting face over a total axial length corresponding to at least 1 and at most 5 mm in addition to a total axial extent of the orifice.

[0014] Advantageously, the total axial extent of the orifice is presented between an upper surface and a lower surface of the first piece, said lower surface being intended to come into contact with the second piece during electrical resistance welding.

[0015] According to one embodiment, the protrusion extends axially by at least 2 mm and at most 10 mm from the underside.

[0016] According to one embodiment, the protrusion is configured so that a capacity of the hollow space, delimited by the orifice when the axial portion passes through said orifice, is substantially equal to a total volume of the protrusion.

[0017] According to one embodiment, the protuberance is disposed in the center of the axial portion.

[0018] According to one embodiment, the total diameter of the axial portion is substantially constant over an entire axial extent of said axial portion, between the head and the lower face.

[0019] The invention also relates to a method for assembling a first part to a second part by means of a joining element, comprising the steps: - making an opening in the first piece; - superposition of the first piece and the second piece; - insertion of a connecting element through the orifice; - application of an electric current through the joining element and the second piece in such a way as to achieve a weld of the joining element with said second piece; remarkable in that the joining element is according to the invention.

[0020] The invention also relates to a motor vehicle comprising an assembly of at least two parts by means of a joining element, notable in that said joining element is according to the invention.

[0021] The features of the invention are advantageous in that the hollow space around the protrusion between the mating face and the lower face allows for the incorporation of a material filler during resistance welding. This ensures good contact between the two parts, resulting in a welded joint free of recesses, which helps maintain the quality of multi-material assemblies and thus improves the overall robustness of motor vehicles. Furthermore, the manufacturing of the welding element is simple. Brief description of the drawings

[0022] [Fig-1] represents a cross-sectional view of a joining element according to the invention, comprising an axial portion engaged with a corresponding orifice of a first part, and comprising a distal end forming a protuberance provided with a connecting face;

[0023] [Fig.2] illustrates a cross-sectional view during an electric resistance welding step of the first and second parts, using the joining element according to the invention;

[0024] [Fig.3] schematically represents a cross-sectional view of the two parts assembled by electric resistance welding using the joining element according to the invention. Detailed description

[0025] Fig. 1 represents a perspective view of a joining element 2 according to the invention, which is intended to irreversibly join two parts having different materials by electric resistance welding.

[0026] The joining element 2 preferably comprises a substantially cylindrical shape and in revolution about a principal axis 2.1 visible in [Fig.2], thus forming a joining pin 2, and will be designated as such in the remainder of this description.

[0027] As illustrated, the pin 2 includes a head 4 intended to bear against an upper surface 5.2 of a first piece 5 of the two pieces to be assembled, when said pin 2 passes through a corresponding orifice 5.1 on the first piece 5.

[0028] Preferably, the pin 2 comprises an axial portion 6 extending along the main axis 2.1 from the head 4, and ending at a distal end 8 of said pin 2, with a connecting face 10 intended to be electrically resistance welded to a second piece of the two pieces to be assembled.

[0029] Advantageously, the distal end 8 forms a protrusion 9 extending from an inferior face 6.1 of the axial portion 6 and having the connecting face 10, said protrusion 9 preferably comprising a hemispherical shape, is positioned at the center of the inferior face 6.1, that is to say, it is centered with respect to the principal axis 2.1

[0030] Preferably, the connecting face 10 forms a general convex envelope 10.2 extending in revolution at 360° around a center 10.1 of said connecting face 10, said center 10.1 being coincident with the main axis 2.1 of the joining pin 2.

[0031] The protuberance 9 has a diameter "d" equal to at most 80% of a total diameter "D" of the axial portion 6. The total diameter D being essentially constant over an entire axial extent "a" of the axial portion 6.

[0032] Preferably, the diameter d of the protuberance 9 being equal to at least 30% and at most 60% of the total diameter D of the axial portion 6. More preferably, the total diameter D corresponds to about twice (±10%) the diameter d of the protuberance 9.

[0033] In this configuration, the protrusion 9 has with the lower face 6.1 a hollow space 12 around the connecting face 10. Said hollow space 12 being axially delimited by a lower face 5.3 of the first piece 5 to be welded, and advantageously allows to accommodate the finishing of the material during the electrical resistance welding in order to guarantee a correct plating of the pin 2 to the second piece.

[0034] In this respect, the protrusion 9 is configured so that a capacity of the hollow space 12, delimited by the orifice 5.1, is substantially equal (or with a variation of ±20%) to a total volume of said protuberance 9. Thus, the finishing of the material coming essentially from the protuberance 9, can cover the entire hollow space 12, thus ensuring a suitable filling avoiding the creation of hollows or excess material.

[0035] It can be seen that when the head 4 of the pin 2 bears against an upper face 5.2 of the first part 5, the protrusion 9 extends axially (along the principal axis 2.1) beyond the lower surface 5.3 by an overhang "p" between 1 mm and 5 mm. For this purpose, the axial portion 6 comprises a total axial length "L" equal to the sum of a total axial extent "e" of the first part 5 and the overhang P-

[0036] The protrusion 9 extends axially, from the lower face 6.1 to the center 10.1 of the connecting face 10, by at least 2 mm and at most 10 mm.

[0037] Fig. 2 illustrates a cross-sectional view during an electric resistance welding step of the first 5 and second 7 pieces, using the joining pin 2 according to the invention.

[0038] The invention proposes a method of assembling the first part 5 to the second part 7, comprising a first step of making an orifice 5.1 in the first part 5, this being at least equal to the diameter D of the axial portion and less wide than the head 4 of the pin 2.

[0039] Electrodes “E” allow, on either side of parts 5 and 7, to ensure welding by the passage of an electric current through the junction pin 2.

[0040] Here, the exceeding p of the axial extent of the protrusion 9, beyond the lower surface 5.3 of the first part 5, makes it possible to guarantee an optimized contact point 10.1 of the bonding face 10 to the second part 7, thus promoting an efficient current passage through the pin 2, resulting locally in a progressive increase in temperature, in order to obtain a welded junction free of voids.

[0041] Fig. 3 schematically represents a cross-sectional view of an assembly 3 of two parts 5 and 7, assembled by electric resistance welding using the joining pin 2 according to the invention.

[0042] Assembly 3 can, for example, correspond to a body part of a motor vehicle 1.

[0043] Advantageously, the head 4 securely holds the first part 5 to the second part 7, and the welded joint 16 visible in [Fig. 3] is sound and free of any hollows that could compromise its rigidity; the assembly 3 is therefore rigid. This is due in particular to the shape and position of the protrusion, which, during electric welding, eliminated the risk of a contact defect between the two parts 5 and 7 and the creation of voids at the weld. Indeed, the material flow, having perfectly filled the dedicated hollow space, ensured a good the slamming of the pawn 2 against the second piece 7, and thus preserving the mechanical properties of the junction 16 as well as the robustness of the assembly 3.

Claims

Demands

1. Joining element (2), intended to irreversibly join a first part (5) to a second part (7) by electric resistance welding, comprising: - a head (4) intended to bear against the first part (5); and - an axial portion (6) extending from the head (4) and intended to pass through an orifice (5.1) in the first part (5), said axial portion (6) comprising, at a distal end (8), a connecting face (10) intended to be electrically resistance welded to the second part (7); characterized in that the distal end (8) forming a protrusion (9) comprising said connecting face (10) and projecting from a lower face (6.1) of the axial portion (6), said protrusion (9) having a diameter equal to at most 80% of a total diameter of said axial portion (6), so as to form a hollow space around said protrusion (9) between the connecting face (10) and the lower face (6.1).

2. Joining element (2) according to claim 1, wherein the protrusion (9) has a hemispherical shape, and the connecting face (10) comprises a generally domed envelope (10.2) between the lower face (6.1) and a center (10.1) of said connecting face (10.1).

3. Joining element (2) according to any one of claims 1 and 2, wherein the diameter (d) of the protrusion (9) is equal to at least 30% of the total diameter (D) of the axial portion (6) and at most 60% of said total diameter (D).

4. Joining element (2) according to any one of claims 1 to 3, wherein the axial portion (6) extends from the head (4) to the connecting face (10) over a total axial length (L) corresponding to at least 1 and at most 5 mm in addition to a total axial extent (e) of the orifice (5.1).

5. Joining element (2) according to any one of claims 1 to 4, wherein the protrusion (9) extends axially by at least 2 mm and at most 10 mm from the lower face (6.1).

6. A connecting element (2) according to any one of claims 1 to 5, wherein the protrusion (9) is configured so that a content of the hollow space (12), delimited by the orifice (5.1) when the axial portion (6) passes through said orifice (5.1), is substantially equal to a total volume of the protrusion (9).

7. Connecting element (2) according to any one of claims 1 to 6, wherein the protuberance (9) is located at the center (2.1) of the axial portion (6).

8. Joining element (2) according to any one of claims 1 to 7, wherein the total diameter (D) of the axial portion (6) is substantially constant over an entire axial extent (a) of said axial portion (6), between the head (4) and the lower face (6.1).

9. A method for assembling a first part (5) to a second part (7) by means of a joining element (2), comprising the steps: - making an orifice (5.1) in the first part (5); - superimposing the first part (5) and the second part (7); - inserting a joining element (2) through the orifice (5.1); - applying an electric current through the joining element (2) and the second part (7) so as to weld the joining element to said second part (7); characterized in that the joining element (2) is according to any one of claims 1 to 8.

10. Motor vehicle (1) comprising an assembly (3) of at least two parts (5, 7) by means of a joining element (2), characterized in that said joining element (2) is according to any one of claims 1 to 8.

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