JOINING ELEMENT ENSURING MULTI-MATERIAL ASSEMBLY

Abstract

JOINING ELEMENT PROVIDING MULTI-MATERIAL ASSEMBLY The present invention relates to a joining element (2), intended to irreversibly connect a first part to a second part by electrical resistance welding, comprising: - a head (4) intended to bear on the first part; and - an axial portion (6) extending from the head and intended to pass through an orifice in the first part, said axial portion comprising, at a distal end (8), a connecting face (10) intended to be welded by electrical resistance to the second part; remarkable in that the connecting face comprises one or more radial grooves (12) extending radially from a central part (10.1) of said connecting face, and intended to allow evacuation of gases produced during welding. (Figure to be published with the abstract: Figure 1)

Description

Title of the invention: JOINING ELEMENT PROVIDING 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 in order to ensure a rigid connection by gluing and / or by 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 connection between said two parts by plastic deformation.

[0003] There is also another type of joining elements allowing a multi-material assembly by electric welding, and which are 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.

[0004] However, the problem raised in the context of multi-material joining by electric welding is the existence of contaminants and voids within the junction, resulting from poor air evacuation and / or the presence of pollution at the junction during welding, which can result in a degradation of the tensile and shear strength of the welded junction. Indeed, during electric welding, the pollutants are burned, but the gases cannot escape and will rise in the weld to create empty areas, which causes a material health problem (presence of contaminants) inducing fragility and a lack of robustness.

[0005] Published patent document EP 3 717 172 A1 discloses a connecting element used for joining two components by friction welding, comprising a shaft having a distal end face provided with depressions and elevations, designed to prevent material waste during the welding process.

[0006] However, the solution proposed by the document concerns friction welding, and does not meet the specific requirements of electric welding.

[0007] To guarantee an electrically welded joint that preserves material health and ensures a robust connection with multi-material parts, it is imperative to develop a joining element specifically designed for electric welding. Statement of the invention

[0008] 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 and efficient solution allowing assembly of two parts of different materials by electric welding while guaranteeing a healthy and robust junction.

[0009] 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 connecting face comprises one or more radial grooves extending radially from a central part of said connecting face, and intended to allow evacuation of gases produced during welding.

[0010] Advantageously, the joining element as well as the second part are obtained from a metallic material, and are preferably formed from steel.

[0011] Preferably, the head is continuously circular, and comprises an external upper face which is smooth and devoid of radial notches or grooves.

[0012] According to one embodiment, the or each of the radial grooves comprises a bottom comprising an outer portion and an inclined inner portion connecting, at the central part of the connecting face, with a general curved envelope of said connecting face.

[0013] Preferably, the connecting face comprises a fully curved transverse profile, including the central part.

[0014] Advantageously, the general envelope of the connecting face completely covers said connecting face as well as the radial groove(s).

[0015] According to one embodiment, the outer portion is perpendicular to the axial portion or forms an angle with said perpendicular which is less than or equal to 15°, and the inclined inner portion forms an angle with said perpendicular of between 30° and 80°.

[0016] According to one embodiment, the outer portion extends over at least 70% of a total radial extent of the corresponding radial groove.

[0017] According to one embodiment, the central part of the connecting face is included in a circle having a diameter corresponding to at most 10% of a total diameter of the axial portion at its distal end.

[0018] According to one embodiment, the several radial grooves are three or four in number and are distributed angularly in a uniform manner.

[0019] According to one embodiment, the central part of the connecting face forms an equilateral triangle, the inclined inner portion of the or each of the radial grooves extends directly from a corresponding side of said equilateral triangle.

[0020] According to one embodiment, the or each of the radial grooves has a cross-section of substantially rectangular shape extending radially from the central portion, said radial groove comprising a substantially constant transverse width over an entire corresponding radial extent, said transverse width corresponding to at most 15% of a total diameter of the axial portion at its distal end.

[0021] 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.

[0022] 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.

[0023] The measures of the invention are advantageous in that the radial grooves on the connecting face act as vents and allow to act as vents, thus allowing the evacuation of gases at the weld and preventing their imprisonment at the right of the junction. In summary, this joining element is specifically designed for electric welding, ensuring a connection without air confinement to preserve the quality of multi-material assemblies, with robustness in accordance with the quality standards and requirements of electric welding. In addition, 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 with a distal end provided with a connecting face provided with several radial grooves;

[0025] [Fig.2] illustrates a sectional view of the joining element of [Fig. 1], along the axis AA crossing the axial portion in line with one of the radial grooves of the connecting face;

[0026] [Fig.3] schematically represents a sectional view of two parts assembled by electrical resistance welding using the joining element according to the invention. Detailed description

[0027] [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.

[0028] 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.

[0029] In this [Fig. 1], the pin 2 is shown vertically upside down so as to better show its connecting face 10.

[0030] The pin 2 comprises a head 4 intended to bear on a first part of the two parts to be assembled. This will be detailed according to [Fig.3], later in this description.

[0031] Preferably, the pin 2 comprises an axial portion 6 extending along the main axis 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.

[0032] Advantageously, the connecting face 10 is provided with at least one radial groove 12 extending radially from a central portion 10.1 of the connecting face 10, and allowing evacuation of gases produced during the electric welding with the second part. Indeed, electric welding results in a local increase in temperature and the generation of gas requiring evacuation, in order to free the junction from any vacuum zones which could weaken the weld.

[0033] In this respect, the connecting face 10 preferably comprises several radial grooves 12 which are three or four in number, distributed angularly in a uniform manner around the main axis of the pin 2. More preferably, the connecting face 10 comprises three radial grooves 12 distributed homogeneously at 120° from one another, so as to cover an entire general envelope 10.2 of the connecting face 10.

[0034] Preferably, the central part 10.1 is included in a (fictitious) circle whose center is crossed by the main axis of the axial portion 6, and having a diameter corresponding to at most 10% of a total diameter D of the axial portion 6 at its distal end 8. Thus, the central part 10.1 is as small as possible, and advantageously corresponds to a point of contact of the connecting face 10 with the second part prior to electric welding, thus guaranteeing a minimal point of contact allowing the passage of electric current to ensure welding.

[0035] The diameter D is preferably between 5 and 10 mm, and is more preferably equal to approximately 8 mm (±2 mm).

[0036] Each radial groove 12 has a cross-section of substantially rectangular shape (seen along a plane perpendicular to the main axis of the pin 2), and extending radially from the central part 10.1 with a transverse width W which is preferably radially constant, or has a variation of less than 20% depending on the radial extent of the corresponding groove 12.

[0037] Preferably, the transverse width W corresponds to approximately 10% of the diameter D of the axial portion 6, and to at most 15% of said total diameter D.

[0038] It can be seen that the central part 10.1 of the connecting face 10 forms an equilateral triangle comprising three equal sides 10.3, and from which extends, respectively, a radial groove 12, and extends, more particularly, and directly, an inclined inner portion 12.1 of the groove 12 which joins an outer portion 12.2 opening onto a laterally external face 6.1 of the outer portion 6.

[0039] Preferably, the three radial grooves 12 are identical, their shapes and in particular the arrangement of their two portions 12.1, 12.2, will be detailed according to [Fig.2],

[0040] [Fig. 2] illustrates a sectional view of the joining pin 2 of [Fig. 1], along the axis AA passing through the axial portion 6 in line with one of the radial grooves 12 of the connecting face 10.

[0041] It can be seen that the general envelope 10.2 of the connecting face 10 comprises a fully curved profile and this, from and, at 360° around the main axis 2.1. It can also be observed that the set of the inclined inner 12.1 and outer 12.2 portions correspond to a bottom of the corresponding radial groove 12, in which said inclined inner portion 12.1 connects directly to the central part 10.1 of the curved general envelope 10.2.

[0042] In this configuration, the groove 12 acts advantageously as a vent during electric welding and allows, firstly thanks to the inclined inner portion 12.1, to recover any gases generated locally, and this, from their creation at the level of the central portion 10.1 and to evacuate them progressively towards the outer portion 12.2, then outside the axial portion 6.

[0043] For this purpose, the inclined inner portion 12.1 has an angle of inclination a with an axis 2.2 perpendicular to the main axis 2.1 of the pin 2, and in which said inner portion 12.1 is inclined towards the envelope 10.2 from the outer portion 2.2. The angle of inclination a is preferably between 30° and 80°, and even more preferably between 50° and 80°. While the outer portion 12.2 is perpendicular to the main axis 2.1 or inclined by at most 15° with respect to the axis perpendicular 2.2.

[0044] Preferably, and along the radial direction of the extent of the groove 12, the outer portion 12.2 is radially wider than the inclined inner portion 12.1, said outer portion 12.2 preferably extends over at least 70% of a total radial extent of said groove 12, and over approximately 80% of said extent, as illustrated in [Fig.2]. Thus, each groove 12 is capable of effectively and progressively evacuating the air that may be present within the junction during electric welding.

[0045] The pin 2 further comprises a circular rib 14 extending completely and in revolution around the main axis 2.1, it makes it possible to act as a stop (terminal contact point) following consumption of material during welding with the second part, indicating the end of the welding.

[0046] The rib 14 makes it possible to form a circular shoulder 16 with the head 4, said shoulder 16 making it possible to hold the first part to the second part after electric welding.

[0047] [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 of figures 1 and 2.

[0048] The assembly 3 may, for example, correspond to a body part of a motor vehicle 1.

[0049] The joining pin 2 according to the invention comprises an upper face 4.1 of the head 4 which is completely smooth and devoid of radial notches or grooves. Indeed, the pin 2 allowing electric welding, does not require such irregularities at the level of the head to transmit a rotational movement, as is necessary by the friction welding elements of the state of the art.

[0050] 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, this being wider than the diameter of the axial portion and less wide than a diameter of the head 4 of the pin 2.

[0051] The junction 18 visible in [Fig.3] is advantageously sound and devoid of any recess which could compromise its rigidity.

[0052] Advantageously, the head 4 securely holds the first part 5 with the second part 7, the assembly 3 is therefore rigid, and this in particular thanks to the radial grooves which made it possible during electric welding to eliminate the risk of contamination of the weld, thus ensuring the preservation of the mechanical properties of the junction and 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 welded by electrical resistance to the second part (6); characterized in that the connecting face (10) comprises one or more radial grooves (12) extending radially from a central portion (10.1) of said connecting face (10), and intended to allow evacuation of gases produced during welding.

2. Joining element (2) according to claim 1, in which the or each of the radial grooves (12) comprises a bottom comprising an outer portion (12.2) and an inclined inner portion (12.1) connecting, at the central part (10.1) of the connecting face (10), with a general curved envelope (10.2) of said connecting face (10).

3. A joining element (2) according to claim 2, wherein the outer portion (12.2) is perpendicular to the axial portion (6) or forms an angle with said perpendicular which is less than or equal to 15°, and the inclined inner portion (12.1) forms an angle (a) with said perpendicular of between 30° and 80°.

4. A joining element (2) according to one of claims 2 or 3, wherein the outer portion (12.2) extends over at least 70% of a total radial extent of the corresponding radial groove (12).

5. Joining element (2) according to one of claims 1 to 4, in which the central part (10.1) of the connecting face (10) is included in a circle having a diameter corresponding to at most 10% of a total diameter (D) of the axial portion (6) at its distal end (8).

6. A connecting element (2) according to one of claims 1 to 5, wherein the plurality of radial grooves (12) are three or four in number and are distributed angularly in a uniform manner.

7. Joining element (2) according to one of claims 2 and 3, in which the central part (10.1) of the connecting face (10) forms an equilateral triangle, the inclined inner portion (12.1) of the or each of the radial grooves (12) extends directly from a corresponding side (10.3) of said equilateral triangle.

8. A joining element (2) according to one of claims 1 to 7, wherein the or each of the radial grooves (12) has a substantially rectangular cross-section extending radially from the central portion (10.1), said radial groove (12) comprising a substantially constant transverse width (W) over a corresponding radial extent, said transverse width (W) corresponding to at most 15% of a total diameter (D) of the axial portion (6) at its distal end (8).

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 9.

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