JOINING ELEMENT WITH A HALF-SPHERICAL PROTUBERANCE ENSURING MULTI-MATERIAL ASSEMBLY

Abstract

JUNCTION ELEMENT WITH A HALF-SPHERICAL PROTUBERANCE ENSURING MULTI-MATERIAL ASSEMBLY The present invention relates to a joining element (2), intended to irreversibly connect a first part (5) to a second part by electrical 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 forming a protuberance (9) comprising said connecting face and projecting from a lower 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 lower face. (Figure to be published with the abstract: Figure 1)

Description

Title of the invention: JOINING ELEMENT WITH A HALF-SPHERICAL PROTUBERANCE ENSURING MULTI-MATERIAL ASSEMBLY Technical field

[0001] The present invention relates to the field of motor vehicles, more particularly the field of assemblies of multi-material parts of motor vehicles. Prior art

[0002] In the context of a multi-material assembly, i.e. aluminum / steel, steel / composite, steel / plastic, etc. assembly, the use of joining elements to ensure a rigid connection 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 junction.

[0003] An example of multi-material welding is notably known from published patent document EP 2 127 797 A1 which discloses a spot welding process, using a pin provided with 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 assembly by electric welding is the presence of a recess between the two welded parts and / or at the weld, said recess generally being linked to a problem of plating of the junction pin with the second part to be welded, which is caused either by a surplus 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 health and overall physical strength of the welded joint.

[0005] To ensure a healthy, void-free electrically welded joint, ensuring a robust bond with multi-material parts, it is necessary to address the plating problem during electric welding. Statement of the invention

[0006] The present invention aims to overcome at least one of the drawbacks of the aforementioned state of the art. More particularly, the invention aims to propose a simple, efficient and economical solution allowing assembly of two parts of different materials by electric welding while guaranteeing a healthy and robust junction.

[0007] To this end, the invention relates to a joining element, intended to irreversibly connect a first part to a second part by electrical resistance welding, comprising: - a head intended to rest on the first part; and - an axial portion extending from the head and intended to pass through an orifice in the first part, said axial portion comprising, at a distal end, a connecting face intended to be welded by electrical resistance to the second part; remarkable in that the distal end forming a protuberance comprising said connecting face and projecting from a lower face of the axial portion, said protuberance 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 protuberance between the connecting face and the lower face.

[0008] Preferably, the axial portion comprises a cylinder of essentially constant diameter along an entire axial extent of said axial portion, 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 protuberance is measured at a junction between the connecting face and the lower face of the axial portion.

[0009] Advantageously, the joining element as well as 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 which is smooth and devoid of radial notches or grooves.

[0010] According to one embodiment, the protuberance has a semi-spherical shape, and the connecting face comprises a general domed envelope between the lower face and a center of said connecting face.

[0011] Preferably, the connecting face comprises a fully curved 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 to 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 part, said lower surface being intended to come into contact with the second part during electrical resistance welding.

[0015] According to one embodiment, the protuberance extends axially by at least 2 mm. and not more than 10 mm from the underside.

[0016] According to one embodiment, the protuberance 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 protuberance.

[0017] According to one embodiment, the protuberance is arranged 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 of assembling a first part to a second part by means of a joining element, comprising the steps: - making an orifice in the first part; - superposition of the first piece and the second piece; - insertion of a joining element through the orifice; - applying an electric current through the joining element and the second part so as to weld the joining element with said second part; 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, remarkable in that said joining element is according to the invention.

[0021] The measures of the invention are advantageous in that the hollow space presented around the protuberance between the connecting face and the lower face makes it possible to accommodate a finishing of the material during electrical resistance welding. This thus makes it possible to ensure good plating of the two parts, thus obtaining a welded joint free of recesses and which makes it possible to preserve the quality of multi-material assemblies, thus improving the overall robustness of motor vehicles. In addition, the manufacture of the welding element is simple. Brief description of the drawings

[0022] [Fig-1] represents a 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 sectional view during a step of electrical resistance welding of the first and second parts, by means of the joining element according to the invention;

[0024] [Fig.3] schematically represents a 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 electrical resistance welding.

[0026] The joining element 2 preferably comprises a substantially cylindrical shape and in revolution around a main 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 comprises a head 4 intended to bear on an upper surface 5.2 of a first part 5 of the two parts to be assembled, when said pin 2 passes through a corresponding orifice 5.1 on the first part 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, by a connecting face 10 intended to be welded by electrical resistance to a second part of the two parts to be assembled.

[0029] Advantageously, the distal end 8 forms a protuberance 9 extending from a lower face 6.1 of the axial portion 6 and having the connecting face 10, said protuberance 9 preferably comprising a half-spherical shape, is positioned in the center of the lower face 6.1, that is to say that it is centered relative to the main axis 2.1

[0030] Preferably, the connecting face 10 forms a general curved envelope 10.2 extending in revolution at 360° around a center 10.1 of said connecting face 10, said center 10.1 being merged 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 approximately twice (±10%) of the diameter d of the protuberance 9.

[0033] In this configuration, the protuberance 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 part 5 to be welded, and advantageously allows the material to be housed at the end during electrical resistance welding in order to guarantee correct plating of the pin 2 to the second part.

[0034] In this respect, the protuberance 9 is configured in such a way 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 filling of the material coming essentially from the protuberance 9, can cover the entirety of the hollow space 12, thus guaranteeing suitable filling avoiding the creation of recesses 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 protuberance 9 protrudes axially (along the main axis 2.1) the lower surface 5.3, by an overhang “p” of 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 protuberance 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 sectional view during a step of electrical resistance welding of the first 5 and second 7 parts, by means of 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 producing 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 the parts 5 and 7, welding to be carried out by passing an electric current through the junction pin 2.

[0040] Here, the protrusion p of the axial extent of the protuberance 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 connecting face 10 to the second part 7, thus promoting an efficient passage of current through the pin 2, resulting locally in a progressive increase in temperature, with a view to obtaining a welded junction free of voids.

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

[0042] The assembly 3 may, for example, correspond to a body part of a motor vehicle 1.

[0043] Advantageously, the head 4 securely holds the first part 5 with the second part 7, and the welded junction 16 visible in [Fig. 3] is sound and free from any recess that could compromise its rigidity, the assembly 3 is therefore rigid. This is notably thanks to the shape and position of the protuberance which made it possible during electric welding to eliminate the risk of the presence of a defect in the contact of the two parts 5, 7 and the creation of voids at the weld. Indeed, the flow of material having perfectly filled the dedicated hollow space, made it possible to ensure good plating of the pin 2 against the second part 7, and therefore preserving the mechanical properties of the junction 16 as well as the robustness of the assembly 3.

Claims

Claims

1. A joining element (2) intended to irreversibly connect a first part (5) to a second part (7) by electrical resistance welding, comprising: - a head (4) intended to bear on 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 protuberance (9) comprising said connecting face (10) and projecting from a lower face (6.1) of the axial portion (6), said protuberance (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 protuberance (9) between the connecting face (10) and the lower face (6.1).

2. A joining element (2) according to claim 1, wherein the protuberance (9) has a semi-spherical shape, and the connecting face (10) comprises a generally curved 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 one of claims 1 and 2, in which the diameter (d) of the protuberance (9) is equal to at least 30% of the total diameter (D) of the axial portion (6) and to at most 60% of said total diameter (D).

4. Joining element (2) according to one of claims 1 to 3, in which 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 one of claims 1 to 4, in which the protuberance (9) extends axially by at least 2 mm and at most 10 mm from the lower face (6.1).

6. Junction element (2) according to one of claims 1 to 5, wherein the protuberance (9) is configured so that a capacity 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 protuberance (9).

7. Junction element (2) according to one of claims 1 to 6, in which the protuberance (9) is arranged in the center (2.1) of the axial portion (6).

8. Joining element (2) according to one of claims 1 to 7, in which 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. 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 with said second part (7); characterized in that the joining element (2) is according to 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 one of claims 1 to 8.

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