JOINTING ELEMENT ENSURING A MULTI-MATERIAL ASSEMBLY OF THREE THICKNESSES

Abstract

JOINTING ELEMENT FOR MULTI-MATERIAL ASSEMBLY OF THREE THICKNESSES The present invention relates to a joining element (2) for irreversibly joining a first part (3) and a second part (5) to a third part (7) by electric resistance welding, comprising: - a head (4) for bearing against the first part; and - an axial portion extending from the head and for passing through the first and second parts, respectively, to be electrically resistance welded to the third part; notable in that the axial portion has a stepped cross-section comprising a first stage (6.1) having a first diameter and for being crimped into a first orifice (3.1) of the first part, and a second stage (6.2) having a second diameter smaller than said first diameter and for being crimped into a second orifice (5.1) of the second part. (Figure to be published with the abbreviation: Figure 2)

Description

Title of the invention: JOINTING ELEMENT ENSURING A MULTI-MATERIAL ASSEMBLY OF THREE THICKNESSES 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 friction welding, in which the joining element is brought into contact and pressed in rotation against the two parts to be assembled, in order to force the bond between said two parts by plastic deformation.

[0003] There is also another type of joining element that allows for multi-material assembly by electric welding. Indeed, these joining elements are conventionally welded directly to a part, which generally corresponds to a sheet thickness, while being connected to another part, thus obtaining an assembly of several superimposed parts, for example two or three thicknesses, by means of one or more electrically welded joints.

[0004] The published patent document US 2018 / 0354231 Al discloses an assembly of three sheets together by a rivet having a distal end welded to one of the three sheets, the two other remaining sheets being pre-welded together before assembly by said rivet.

[0005] However, the solution proposed in the document requires that all the sheet metal parts be weldable and conductive in order to allow for both electrical welding between at least two of said sheets and welding from the distal end of the rivet to the third of said sheets. Thus, said solution does not allow for the assembly of three parts, two of which are neither weldable nor conductive, for example, being made of insulating material, composite material, or any other material that does not allow for their welding by electrical connection.

[0006] For this purpose, there is a need to assemble three different materials, without necessarily having two weldable sheets, in order to obtain, for example, a multi-material assembly of three parts having at most one steel part suitable for welding. Description of the invention

[0007] 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 and effective solution for joining three parts made of different materials by electric welding, two of which are non-weldable and / or non-conductive.

[0008] To this end, the invention relates to a joining element, intended to irreversibly join a first part and a second part to a third part by electric resistance welding, comprising: - a head designed to rest on the first piece; and - an axial portion extending from the head (4) and intended to pass through, respectively, a first orifice in the first piece and a second orifice in the second piece, said axial portion comprising, at a distal end, a connecting face intended to be electrically resistance welded to the third piece; remarkable in that the axial portion has a stepped section comprising a first stage having a first diameter intended to be crimped into the first orifice of the first piece, and a second stage having a second diameter smaller than said first diameter intended to be crimped into the second orifice of the second piece.

[0009] Advantageously, the joining element and the third piece are obtained from a metallic material, and are preferably formed from steel.

[0010] Preferably, the head is continuously circular, and includes an external upper face that is smooth and free of radial notches or grooves.

[0011] According to one embodiment, the second diameter corresponds to at most 90% of the first diameter.

[0012] According to one embodiment, the first stage comprises a first circular rib forming a circular shoulder with the head.

[0013] According to one embodiment, the second stage comprises a second circular rib coaxial with the first circular rib.

[0014] According to one embodiment, each of the first and second circular ribs is continuous over 360° around a principal axis of the axial portion.

[0015] Preferably, the main axis extends substantially perpendicularly to the head.

[0016] According to one embodiment, each of the first and second circular ribs has an inclination of at most 45° with respect to a principal axis of the axial portion.

[0017] According to one embodiment, the distal end of the axial portion has a third diameter smaller than each of the first and second diameters.

[0018] According to one embodiment, the third diameter corresponds to at most 90% of the second diameter.

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

[0020] Advantageously, the axial portion is set in each of the two respective orifices of the first piece and the second piece, by means of the stepped section and circular ribs.

[0021] The invention also relates to a motor vehicle comprising an assembly of at least three parts by means of a joining element, notable in that said joining element is according to the invention.

[0022] The features of the invention are advantageous in that the stepped cross-section of the axial portion ensures effective retention of the first and second parts prior to welding the joining element to the third part. The circular ribs further facilitate crimping the joining element into the corresponding hole, thus securing a multi-material assembly with two non-weldable parts without requiring a second weld.

[0023] The joining element is specifically designed for electric welding, ensuring a bond without air confinement to preserve the quality of multi-material assemblies, with robustness that meets the quality standards and requirements of electric welding. Furthermore, its manufacture is simple. Brief description of the drawings

[0024] [Fig-1] represents a perspective view of a joining element according to the invention, comprising an axial portion having a stepped section comprising circular ribs intended to be crimped into corresponding holes of parts to be assembled.

[0025] [Fig. 2] schematically represents a cross-sectional view of three parts assembled by electric resistance welding using the joining element of [Fig. 1]. Detailed description

[0026] Figure 1 shows a perspective view of a joining element 2 according to the invention, which is intended to irreversibly join three parts 3, 5 and 7 having different materials, by electric resistance welding.

[0027] The joining element 2 preferably comprises a substantially cylindrical shape and in revolution about a principal axis 2.1, thus forming a joining pin 2, and will be designated as such in the remainder of this description.

[0028] The pin 2 includes a head 4 intended to bear against a first piece of the three pieces to be assembled. This will be detailed in [Fig. 2] in this description.

[0029] 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 third piece of the three pieces to be assembled.

[0030] The connecting face 10 may comprise a generally flat profile as illustrated in [Fig. 1], or a convex profile. Said face 10 may alternatively comprise at least one groove acting as a vent allowing the evacuation of any gases that may be produced during electric welding with the third part.

[0031] Advantageously, the axial portion 6 has a stepped section comprising a first stage 6.1 having a first diameter Dl, and a second stage 6.2 having a second diameter D2 lower than said first diameter DL Each of the first and second stages 6.1 and 6.2 being intended to engage, preferably by crimping, in an orifice of the corresponding part to be assembled.

[0032] Preferably, the second diameter D2 corresponds to at most 90% of the first diameter DL. More preferably, Dl is approximately 20% (±10%) greater than D2. The difference between diameters Dl and D2 advantageously creates a clearance that further facilitates the engagement of the pin 2 in the corresponding holes of the parts to be assembled.

[0033] Preferably, the first stage 6.1 comprises a first circular rib 6.1 forming a circular shoulder 12 with the head 4. The second stage 6.2 in turn comprises a second circular rib 6.2 which is coaxial with the first circular rib 6.1, along the main axis 2.1.

[0034] It can be seen that the ribs 6.1, 6.2 are slightly inclined laterally outwards with respect to the main axis 2.1. Preferably, each of the first and second circular ribs 6.1, 6.2 has an inclination of at most 45° with respect to the main axis 2.1. Advantageously, such an inclination makes it possible to guarantee a tight hold of the rib in the corresponding orifice, thus ensuring an effective fixing (by crimping) allowing the parts to be assembled more securely.

[0035] The distal end 8 of the axial portion 6 has a third diameter D3 which is smaller than each of the first and second diameters D1 and D2.

[0036] Preferably, the third diameter D3 corresponds to at most 90% of the second diameter D2. More preferably, D2 is greater than D3 by about 20% (±10%).

[0037] [Fig.2] schematically represents a cross-sectional view of an assembly 9 of three parts 3, 5, 7 joined by electric resistance welding using the joining pin 2 of [Fig.1].

[0038] Assembly 9 can, for example, correspond to a body part of a motor vehicle 1.

[0039] The joining pin 2 according to the invention comprises an upper face 4.1 of the head 4 which is completely smooth and free of radial notches or grooves. Indeed, since the pin 2 enables electric welding, such irregularities in the head do not require them to transmit a rotational movement, for example, to ensure friction welding.

[0040] The invention proposes a method for assembling the first part 3 and a second part 5 to the third part 7, comprising a first step of making a first orifice 3.1 in the first part 3, this being less wide than a diameter of the head 4 of the pin 2. Then, a second orifice 5.1 is made at the level of the second part 5, and which is less wide than the first orifice 3.1.

[0041] In this configuration, the three parts 3, 5 and 7 can be superimposed, and the pin 2 can be inserted into the holes 3.1 and 5.1 in a single pass, until the connecting face comes into contact with the third part 7. This advantageously ensures a considerable saving of time.

[0042] Thus, electric welding can be carried out by applying an electric current through the junction pin 2 and the third part 7, so as to produce a weld enabling the whole of the three parts to be fixed.

[0043] Advantageously, the circular shoulder 12 allows the first part 3 to be effectively held to the second part 5 after the electric welding operation. The head 4 thus allows the first part 3 to be securely held to the third part 7 via the second part 5; the assembly 9 is therefore rigid, thanks in particular to the stepped cross-section of the axial portion 6 and the circular ribs 6.1 and 6.2 which first made it possible to rigidly link the first part 3 and the second part 5 together, without requiring welding or any special secondary fastening between said two parts 3 and 5, before being definitively linked to the third part 7.

[0044] Advantageously, the first part 3 and the second part 5 are made of non-weldable materials, while the third part 7 is the only one that can be welded with the joining pin 2.

[0045] The circular ribs 6.1 and 6.2 advantageously act as two stop points (terminal contact point) following material consumption during welding of the bonding face with the third part 7, indicating the end of the welding.

[0046] The junction 14 visible in [Fig.2] is advantageously sound and free from any hollowness which could compromise its rigidity, and allowing, in combination with the crimping of the circular ribs 6.1, 6.2 in the corresponding orifices 3.1, 5.1 to ensure the robustness of the assembly 9.

[0047] Alternatively, the invention can also make it possible to ensure the assembly of more than three pieces of different materials, for example, with a stepped section carrying a plurality of steps, with in particular as many steps (of circular ribs) as there are pieces to be assembled.

Claims

Demands

1. Joining element (2), intended to irreversibly join a first part (3) and a second part (5) to a third part (7) by electric resistance welding, comprising: - a head (4) intended to bear against the first part (3); and - an axial portion (6) extending from the head (4) and intended to pass, respectively, through a first orifice (3.1) in the first part (3) and a second orifice (5.1) in the second part, said axial portion (6) comprising, at a distal end (8), a connecting face (10) intended to be electrically resistance welded to the third part (7); characterized in that the axial portion (6) has a stepped section comprising a first stage (6.1) having a first diameter (Dl) and intended to be crimped into the first orifice (3.1) of the first part (3), and a second stage (6.2) having a second diameter (D2) smaller than said first diameter (Dl) and intended to be crimped into the second orifice (5.1) of the second piece (5).

2. Joining element (2) according to claim 1, wherein the second diameter (D2) corresponds to at most 90% of the first diameter (Dl).

3. Joining element (2) according to any one of claims 1 and 2, wherein the first stage (6.1) comprises a first circular rib (6.1) forming a circular shoulder (12) with the head (4).

4. Junction element (2) according to claim 3, wherein the second stage (6.2) comprises a second circular rib (6.2) coaxial with the first circular rib (6.1).

5. Joining element (2) according to any one of claims 3 and 4, wherein each of the first and second circular ribs (6.1, 6.2) is continuous over 360° around a principal axis (2.1) of the axial portion (6).

6. Joining element (2) according to any one of claims 3 to 5, wherein each of the first and second circular ribs (6.1, 6.2) has an inclination of at most 45° with respect to a principal axis (2.1) of the axial portion (6).

7. A connecting element (2) according to any one of claims 1 to 6, wherein the distal end (8) of the axial portion (6) has a third diameter (D3) smaller than each of the first and second diameters (Dl, D2).

8. Joining element (2) according to claim 7, wherein the third diameter (D3) corresponds to at most 90% of the second diameter (D2).

9. A method for assembling a first part (3) and a second part (5) to a third part (7) by means of a joining element (2), comprising the steps: - making a first hole (3.1) in the first part (3); - making a second hole (5.1) in the second part (5); - superimposing the first part (3), the second part (5) and the third part (7); - inserting a joining element (2) through the first and second holes (3.1, 5.1); - applying an electric current through the joining element (2) and the third part (7) so as to weld the joining element (2) to said third 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 (9) of at least three parts (3, 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 9.

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