EP3986655A1

EP3986655A1 - Hollow welding pin for assembling two different materials

Info

Publication number: EP3986655A1
Application number: EP20746242.5A
Authority: EP
Inventors: David Mercs; Maxime SALLERIN
Original assignee: LISI Automotive SAS
Current assignee: LISI Automotive SAS
Priority date: 2019-06-20
Filing date: 2020-06-19
Publication date: 2022-04-27
Also published as: CA3143390A1; FR3097456B1; FR3097716B1; FR3097456A1; MX2021015891A; MA56530A; FR3097716A1; US20220355409A1; WO2020254735A1

Abstract

Method for assembling a metal sheet (40) and an iron-based metal part (80), comprising a step of fitting a tubular pin (10) which is open at both ends by punching through the metal sheet (40) with a shank of the pin with the pin being retained (10) by the metal sheet, wherein a pad is detached from the first metal sheet (40) and a flange of the pin abuts against the surface of the metal sheet (40) once the through-punching has been carried out, and the elastic returns of the shank of the pin (10) and the metal sheet (40) compress the outer surface of the shank, or by overmoulding the pin in the metal sheet, and subsequently a step of welding a metal tube of the pin (10) to the iron-based metal (80) by bringing a free end (24) of the metal tube into contact with the surface of the iron-based metal part (80) by means of electric resistance welding (90).

Description

Title of the invention: Hollow weld pin for assembly of two different materials

[0001] The invention relates to the assembly of materials of a different nature, which cannot be welded directly by resistance. The structures targeted are in particular those of motor vehicles, such as the body, to contribute to their weight reduction and to the reduction of greenhouse gas emissions. The invention relates, for example, to the mechanical assembly of a steel sheet with a sheet of an aluminum alloy such as Al-Si-Mg or Al-Si-Mg-Mn, or of a composite material, or of a thermoplastic polymer. with or without fiber reinforcement. It is known to use rivets and electric welding, but the rivet shanks are not retained by the punched sheet, which makes it difficult to use before welding. What is more, and this is a major problem, the heads of the rivets make the assembly heavier.

[0002] The invention thus relates to a hollow weld pin to allow the mechanical assembly of sheets of a different nature with a mass gain induced by the weld pin reduced as much as possible to achieve the objective of lightening motor vehicles . Thus, the connecting element is a pin which is, by virtue of its form factor, retained by the punched sheet, which facilitates use before welding. In addition, the hollow character of the pin significantly lightens the assembly, which constitutes a significant advance.

[0003] To achieve this objective, a method is proposed for assembling a sheet and an iron-based metal part comprising a step of fitting with retention by the sheet of a hollow pin, by through punching of the sheet with a barrel of said hollow pin, a pellet detaching from the sheet, a collar of the pin abutting against the surface of the sheet once the through-punching has been carried out, or by overmolding of said barrel in the sheet, then a step welding of a metal cylinder of the pin to the iron-based metal part by bringing a free end of the metal cylinder into contact with the surface of the iron-based metal part and electric resistance welding. According to another definition, the assembly is done with a punching step passing through the sheet with a hollow cylinder - or tube - of electrically conductive metal, one end of which has a flaring which abuts against the surface of the sheet. once through punching or overmolding carried out, then a step of welding the hollow metal cylinder to the iron-based metal part by bringing a free end of the metal cylinder into contact hollow opposite to the flare with the surface of the iron-based metal part and application of an electric resistance welding electrode to the mouth of the flare. And according to yet another definition of the invention, a hollow part, generally flat, of circular section parallel to its plane, having an axis of symmetry of revolution, rigid, and open at both ends, is used. Thus, the method is a method of assembling a sheet and an iron-based metal part comprising a step of placing a through tubular stud open at both ends by punching the sheet with a barrel. of said pin with retention of said was by the sheet, a collar of the pin abutting against the surface of the sheet once the through punching has been carried out, and the elastic returns of the barrel of the pin and of the sheet compressing the outer surface of the barrel a pellet detaching from the first sheet, or by overmolding said barrel in the sheet, then a step of welding a metal tube of the pin on the metal part based on iron by contacting a free end of the metal tube with the surface of the metal part based on iron and electric resistance welding.

[0004] The hollow weld pin according to the invention makes it possible to:

[0005] pass through a metal, composite or thermoplastic sheet, with thicknesses less than or equal to 4mm, then to allow a rigid integral maintenance of the sheet with the pin after punching or overmolding, while offering at least an accessible or even protruding part in the form of a ring surrounding a hollow, or of a ring portion, weldable by electrical resistance,

[0006] making a metal, composite or thermoplastic sheet equipped with one or more hollow weld studs according to the invention, ready to be welded locally by electrical resistance on a second sheet mainly made of iron-steel, stainless steel or even possibly in different applications, cast iron -, so as to achieve a robust mechanical assembly between two materials which cannot be directly welded together by electrical resistance.

[0007] According to advantageous and optional characteristics

[0008] - the electrical resistance welding electrode is sized and applied such that all angular sectors of the mouth of the flare are used simultaneously to transmit energy for the weld;

[0009] - the hollow metal cylinder (tube) is formed beforehand by stamping and cutting a sheet of low-alloy steel of 0.5, 1 or 2 mm thickness;

- The metal part to be assembled is connected to the electrical ground. P is also presented, in the context of the invention, a sheet for mechanical assembly pre-equipped with a hollow pin comprising a hollow cylinder (tube) passing through electrically conductive metal, which on one side of the sheet has a flare which abuts against the surface of the sheet and which on the other face of the sheet has a free end. The sheet retains the hollow pin. It is also defined as a sheet for mechanical assembly retaining a tube open at its two ends and passing through, made of electrically conductive metal, which on one face of the sheet has a flare which abuts against the surface of the sheet and which on the other face of the sheet has a free end.

[0012] According to advantageous and optional characteristics

[0013] - It may be a sheet of aluminum alloy, or a sheet of thermoplastic polymer with or without fibrous reinforcement, in particular a fibrous reinforcement with long fibers, or a sheet of composite material with an organic or ceramic matrix with or without a fibrous reinforcement, in particular a fibrous reinforcement with long fibers;

- The hollow metal cylinder (tube) may be of low-alloy stamped steel;

- the material of the hollow metal cylinder can be kept away from the sheet material by an additional cylinder of the pin, or additional tube, the free end of the hollow metal cylinder protruding from a free end of the additional cylinder ;

[0016] the additional cylinder can be made of stainless steel, of hardened steel, or of a non-metallic material which is refractory to heat;

- the hollow metal cylinder and the additional cylinder can be assembled by welding, glue, clamping or plastic deformation between respective end flanges of the cylinders on the flare side, or even blocked relative to each other by inserting a shim between an internal surface of the additional cylinder and an opposite external surface of the hollow metal cylinder, or by the presence on the internal diameter of the additional cylinder of radially projecting parts favoring an embedding of the additional cylinder around the hollow metal cylinder;

[0018] The assembly can include electrical insulation between the material of the hollow metal cylinder and the material of the additional cylinder;

It can include a spacing, according to a cylindrical development and over the height of the electrically conductive metal cylinder, between the material of the hollow metal cylinder and the material of the additional cylinder - The free end of the hollow metal cylinder may be smooth, or have an interior or exterior chamfer, or have a corrugation on its perimeter, or have slots on its perimeter.

The invention also consists of an assembly of a sheet and an iron-based metal part comprising a hollow pin (tube) comprising an electrically conductive metal cylinder passing through the sheet and one end of which has a flaring in abutment against the surface of the sheet, the hollow metal cylinder being welded to the iron-based metal part. It extends to a motor vehicle whose structure includes at least one assembly according to the invention.

There is also proposed a method of repairing an assembly or a motor vehicle according to the invention, the rod of a conductive metal pin composed of a head and a rod of length chosen for the the repair being placed in the recess of said electrically conductive metal cylinder, the head resting against the flare of the cylinder and an electric welding electrode being applied to the head to weld the rod to the sheet.

[0023] The invention will now be described in relation to the figures.

[0024] Figure 1 is a sectional view of a pin according to a first embodiment of the invention.

[0025] Figures 2 to 4 are sectional views of successive stages of implementation of a pin according to Figure 1.

[0026] Figure 5 is an explanation of phenomena involved in the steps of the figures mentioned above.

[0027] Figures 6 and 7 are sectional views of subsequent successive steps in implementing a pin according to Figure 1.

[0028] Figure 8 shows the manufacture of a pin according to Figure 1.

[0029] Figure 9 shows an example of implementation at the stage of Figure 4 as well as the force curves applied during the steps of Figures 2 to 4 in four separate implementations with a sheet of the same type.

[0030] Figure 10 shows the change in the force required for the punching of Figures 2 to 4 depending on the strength of the punched sheet, for three separate implementations.

Figure 11 shows the steps of Figures 2 to 4 and 6 and 7 in the form of micrographic sections. Figure 12 shows an assembly between an aluminum alloy sheet and a steel sheet, resulting from the process at the end of the implementation of the step of Figure 7, after rupture of the alloy sheet aluminum due to a mechanical shear test to which the weld according to the invention has withstood.

[0033] Figure 13 is a sectional view of a pin according to a second embodiment of the invention.

Figures 14 to 17 show sectional views of variants of the pin of Figure 13.

[0035] Figure 18 shows in section the final step of implementation of the pin according to Figure 13.

[0036] Figure 19 shows a sectional view of another variant of the pin of Figure 13.

[0037] Figure 20 shows the composition of a pawn according to Figure 13.

[0038] Figure 21 shows results after placing the pin of Figure 13 on three sheets of different materials.

[0039] FIG. 22 shows three variants of a pin according to the first embodiment.

[0040] Figure 23 shows a repair method according to one aspect of the invention of an assembly using the invention.

[0041] Figures 24 to 29 show a further embodiment of the invention.

[0042] Figure 30 shows an embodiment of the manufacture of a solder pin according to the invention alternative to the embodiment of Figure 8.

Figure 31 shows a variant of the establishment of the pin, for certain materials of the sheet.

[0044] [Fig. 1] In Figure 1, there is shown a hollow weld pin 10 according to a first embodiment of the invention which may consist of a metal part 20 obtained by plastic deformation of a sheet or a piece - or , according to one definition, a metal cylinder intended for hot forming by rolling, extruding or forging. The part is remarkable because it has a collar 21 in a plane and is extended on its lower face by a barrel having the shape of a hollow cylinder of revolution 22 of length L22, perpendicular to the plane of the collar, taken from the lower surface of the flange 21, and the axis of symmetry 60 of which is perpendicular to the plane of the flange 21, in particular to its upper surface 23 (furthest from the shaft) which is flat. Thus, the metal part 20 constitutes a tube. [0045] [Fig. 2] In Figure 2, the annular surface 24 of the end of the hollow cylindrical barrel 22 opposite the flange 21 is flat and can be brought into contact with the upper surface 41, flat, of a sheet 40 while the lower surface 42 of the sheet 40, also flat, is pressed onto a punching die 50 admitting a symmetry of revolution whose axis of symmetry coincides with the axis of symmetry of the barrel 22, and whose internal diameter is greater than the external diameter De22 of the barrel 22 according to the rules defined by a person skilled in the art. To allow the punching of the sheet 40, the mechanical resistance of the part 20 must be greater than the mechanical resistance of the sheet 40 and the length L22 of the barrel 22 must be greater than the thickness of the sheet 40.

[0046] [Fig. 3] In Figure 3, there is shown the application of a force F increasing over time and perpendicular to the surface 23 which allows the annular surface 24 of the end of the cylindrical barrel to conform with the upper surface of the sheet 40 which deforms elastically until the applied force F reaches a critical value Fe which causes the elastic limit of the sheet 40 to be exceeded, and the start of its plastic deformation and its punching until a pellet 70 forms in the deformed sheet 40, detaches therefrom and is discharged through the bore of the punching die. The tubular character was 22 facilitates the radial elastic deformation of the pin 10 during punching. The elastic return of the sheet 40 after punching causes a contraction of the sheet around the external diameter De22 of the barrel 22 and therefore a compressive stress on the external surface 25 of the barrel 22. Once the sheet 40 has been punched by the weld pin hollow 10 the outer surface 25 of the barrel 22 slides on the cut inner surface, or slice, of the sheet 40 until the lower surface 26 of the flange comes to rest on the surface 41 of the sheet. The combined elastic returns of the sheet 40 and the tubular barrel 22 after punching result in radial compressive stresses on the outer surface 25 of the barrel 22 due to the contraction of the sheet 40 and the extension of the barrel 22.

[0047] [Fig. 4] In FIG. 4, at this stage, the hollow weld pin 10 is mechanically retained by the sheet 40 and has a projecting annular surface 24 on the surface thereof. The assembly forms a sheet ready to be resistance welded to another sheet predominantly made of iron, via the annular surface 24, at the end of the shank of the hollow weld pin 10.

[0048] [Fig. 5] Without this constituting a limit of the invention and of the scope of the description, the various stages of the operation of punching the sheet 40 by the pin to weld hollow 10 can also be illustrated, in Figure 5, following the evolution of the punching force F as a function of time:

[0049] Reference 1: conformation of the contact between the annular surface of the end of the barrel and the upper surface of the sheet,

Reference 2: elastic deformation of the sheet up to the critical punching force Fe,

[0051] Reference 3: plastic deformation of the sheet up to the critical punching force Fp,

[0052] Reference 4: punching of the sheet,

[0053] Reference 5: sliding of the external surface of the barrel on the internal surface of the punching

[0054] Reference 6: contact of the lower surface of the flange on the upper surface of the sheet and sudden increase in the punching force.

[0055] [Fig. 6] In Figure 6, the sheet 40 equipped with the hollow weld pin 10, or several similar pins, is placed above the sheet 80 in steel, stainless steel (in some applications in cast iron), that is - ie mainly made of iron, on an overlap area in accordance with the technical specifications of the assembly. The annular and projecting contact surface 24 is brought into contact with the upper surface 81 of the sheet 80 with a force Fl perpendicular to the planes of the two sheets and applied to the surface 23 via a resistance welding electrode 90.

[0056] [Fig. 7] In FIG. 7, the passage of current between the electrode 90 and the sheet 80, electrically connected to ground, causes the current to flow into the part 20, mainly in the barrel 22, and causes the local melting of the end of the latter near the annular contact surface 24 as well as its plastic deformation constituting a melted and collapsed mass 27 under the effect of the force Fl. The plastic deformation and the forces applied cause a plastic deformation of the sheet 40 less mechanically resistant than the hollow weld pin, and makes it possible on the one hand to compensate for any variations in thickness of the sheet 40 and on the other hand to generate a robust mechanical assembly which is not very sensitive to relaxation in service.

Given the absence of thermal decoupling between the part 20 and the sheet 40 after punching - there is contact between the external surface of the barrel and the internal surface, or edge, of the sheet in its punched area - , this assembly method is more suitable for the assembly of two metal sheets than a composite or thermoplastic sheet 40 on a sheet 80 mainly based on iron.

[0058] [Fig. 8] Figure 8 shows an example of the range of deformation of a hollow weld pin according to the invention using a 10-step stamping / cutting process of a low alloy steel sheet. thickness 1 mm. The hollow weld pin has a mechanical strength close to 500 MPa after shaping (the mechanical strength of the part is deduced from a Vickers hardness measurement). Alternatively, a thickness of 0.5mm or 2mm can be used, as examples.

[0059] [Fig. 30] Figure 30 shows another embodiment of the manufacture of a pin as shown in Figures 1 to 7. It consists of the plastic deformation of a piece of steel cut from a coil of steel wire (grade 17B2, for example) with a diameter possibly calibrated by spinning, for example 8 mm, with a few millimeters in length. The figure shows the different cold forging stations with the application of a die and a punch. A depastillage is carried out at the end of the process so as to form the through hole, crossing right through.

[0060] [Fig. 9] FIG. 9 shows images of an example of the result of the punching / retaining operation of a hollow weld pin according to an embodiment of the invention on a sheet, seen from one side, then from the other. The images show the protruding and annular surface of the shank of the hollow weld pin after punching, as well as the surface of the flange on which the electrode is then applied. The hollow pin remains stuck in the aluminum (or other material if the sheet used is different, as mentioned) after punching due to the mechanical forces of retraction of the aluminum sheet after punching, possibly supplemented by a slight swelling of the barrel of the hollow pin . Thus, the tubular character of the barrel 22 facilitates the radial elastic deformation of the pin 10 during punching.

FIG. 9 also shows the force curves for four punching tests of the same 2 mm thick aluminum alloy sheet characterized by a mechanical strength of 250 MPa. The four tests demonstrate the good reproducibility of punching with a critical force Fp close to 9,000 N, whether the operation is carried out slowly or rapidly. Once the punching has been carried out, the pin can hardly be unbuttoned from the sheet, because its form factor allows it to be retained by the punched sheet: given its thickness, the pin is wide enough to be retained. [0062] [Fig. 10] Various tests were carried out with punching sheets with the 2 mm thick aluminum alloy pin with different levels of mechanical strength between 250 and 430 MPa. FIG. 10 shows a linear behavior of the punching force Fp as a function of the mechanical resistance of the sheet for a constant thickness of 2mm.

The different parts of Figure 11 show the different stages of the assembly of an aluminum alloy sheet 2 mm thick on a steel sheet using the hollow weld pin according to the invention , in the form of micrographic sections after coating in a resin and polishing.

[0064] [Fig. 11 A] Part a of FIG. 11 shows a hollow weld pin in section.

[0065] [Fig. 11B] Part b of Figure 11 shows a hollow weld pin and aluminum alloy sheet after the punching / holding operation.

[0066] [Fig. 11C] Part c of Figure 11 shows a hollow weld pin and the aluminum alloy sheet after resistance welding to a steel sheet.

[0067] [Fig. 11D] Part d of FIG. 11 is an enlarged image of one half of the hollow weld pin in section showing the welded area and the phenomenon of plastic deformation of the end of the barrel and of the alloy sheet. aluminum. The image also highlights a modification of the micro structure of the hollow weld pin at the level of the barrel revealing the privileged passage of current during resistance welding.

[0068] [Fig. 12] Finally, FIG. 12 shows the photograph of an assembly between an aluminum alloy sheet and a steel sheet using the hollow weld pin according to the invention after a mechanical shear test, which highlights evidence of a rupture of the aluminum sheet and not of the weld, attesting to a certain level of mechanical strength of the assembly according to the invention.

In the case of a break in the aluminum alloy sheet, the force applied causing the failure depends directly on the mechanical strength of the aluminum sheet and on the shear resistant section. Thus, in the case of an aluminum alloy sheet of thickness 2 mm with a mechanical strength of 250 MPa and a shear-resistant section of 30 mm ² , for example, the force causing the rupture is equal to 7 500 N. In a real application, at the level of the body of a vehicle for example, neither the rupture of the hollow stud to be welded, nor the rupture of one of the plates of the assembly is desired. The result of the test shown in figure 12 makes it possible to guarantee that the hollow weld pin withstands a force maximum of 7,500N, meeting the requirements for an automotive hybrid assembly application.

[0070] [Fig. 13] According to a second embodiment, shown in Figure 13, and having certain advantages, the hollow weld pin 10 according to the invention may consist of a first metal part 20 as described above, but whose barrel is positioned internally vis-à-vis the axis, and a second metal part 30, whose barrel is positioned externally vis-à-vis the axis.

The internal 20 and external 30 hollow parts respectively have flanges 21 and 31, and hollow cylindrical barrels 22 and 32, the axes of symmetry 60 and 61 of which are perpendicular to the upper 33 and lower 26 surfaces of the flanges 31 and 21, respectively, these two surfaces being plane rings.

The upper surface 33 of the flange 31 has an annular surface 38 in contact with the lower surface 26 of the flange 21, so that the flanges 21 and 31 can be assembled mechanically by affixing. The internal diameter Di32 of the external barrel 32 is strictly greater than the external diameter De22 of the internal barrel 22 so that the internal surface 39 of the external barrel 32 is never in contact with the external surface 25 of the internal barrel 22. This has the effect. consequence of generating an empty volume 100 between the drums of the outer 30 and inner 20 parts. The length L22 of the shank 22 is necessarily greater than the total height - measured from the upper surface of the collar to the end of the shank - of the part 30 , sum of the length L32 of the shank 32 and the thickness e30 of the flange of the external part 30, so that the hollow weld pin 10 has a projecting annular surface 24, end of the internal shank 22 projecting from the external shank 32.

[0073] [Fig. 14] The outer 30 and inner 20 parts must be assembled together on the annular contact area 38 by resistance welding, gluing, clamping or plastic deformation, so as to avoid any relative movement between the outer 30 and inner parts. 20 during an external request.

[0074] [Fig. 15] The external part 30 can also have a shape adapted to the level of its collar 31 to receive the internal part 20 which can be fitted with a tight fit, as shown in FIG. 15.

[0075] [Fig. 16] Conversely, the internal part 20 can also have a shape adapted to the level of its collar 21 to receive the external part 30 which can be fitted with a tight fit, as shown in FIG. 16. [0076] [Fig. 17] Finally, an additional piece 110 can be inserted by force between the internal surface 39 of the external barrel 32 and the external surface 25 of the barrel 22, to mechanically hold the external 30 and internal 20 pieces together by force. , as shown in figure 17.

Ideally, during the assembly of the outer 30 and inner 20 parts, the barrels 32 and 22 have the same axis of symmetry 63, so that the distance separating the surfaces 39 and 25 is constant to create a volume void 100 having a symmetry of revolution about the axis 63. The separation can be 0.5mm at least, for example 1 mm, to be adapted according to the exact implementation.

[0078] [Fig. 18] The different steps of the punching operation described above with the first embodiment of the hollow weld pin can be repeated with the second embodiment of the hollow weld pin consisting of the outer 30 and inner 20 parts. A difference consists of in the presence of the annular protruding surface 24 of the inner barrel which comes into contact with the upper surface 41 of the sheet 40 before the annular protruding surface 34 of the outer barrel. This difference acts favorably on the punching operation because it allows the sheet 40 to be placed under tension locally, before the annular projecting surface 34 begins the punching operation.

The punching / retention operation can be reproduced on different areas of the sheet 40 depending on the technical specification of the future assembly with the sheet 80.

The resistance welding operation for the assembly of the sheets 40 and 80 is similar to that described for the first embodiment of the hollow weld pin, using the annular surface 24 of the internal part 20 to make the welding. Preferably, a low alloy steel with good weldability is used for this internal part 20, such as CIO steel, DC01 steel, or 17B2 steel. Conversely, the steel used for the external part 30 is preferably a stainless steel to prevent corrosion in contact with a sheet made of carbon fiber composite material, in particular.

[0081] However, a difference is observed. During resistance welding, the empty volume 100, naturally filled with air, acts as thermal resistance and makes it possible to protect the sheet 40 against too great a rise in temperature which could adversely affect its mechanical properties, in particular when the sheet 40 is made of a composite or thermoplastic material. The empty volume 100 also allows the flow under the force Fl of the material of the barrel 22 of the internal part 20 made softer, softer, during resistance welding. The possibility of plastically deforming the barrel 22 during the resistive welding operation makes it possible to compensate for any variations in thickness of the sheet 40 and to generate a robust mechanical assembly which is not very sensitive to relaxation in service.

The use of two external 30 and internal 20 parts for the realization of the second embodiment of the hollow weld pin makes it possible to combine different materials for the two parts and to avoid the development of galvanic corrosion of the 'assembly, in case of association of a carbon fiber composite with a steel sheet in the presence of humidity during the use phase. With the second embodiment of the hollow weld pin according to the invention, the outer part 30, in contact with the part made of carbon fiber composite material, can be made with a stainless steel while the inner part 20 in contact with the part. steel part is made with low alloy steel to ensure the quality of resistance welding. Under these conditions, the durability and mechanical strength of an assembly between a sheet of carbon fiber composite material and a second sheet of steel is guaranteed.

In another example, the outer part 30 can be made from a deformable steel and having undergone, after shaping, a quenching heat treatment optionally followed by tempering so as to greatly increase its mechanical properties. Under these conditions, the external part 30 allows easier punching of the sheet 40, while the internal part 20, made of mild steel, allows quality welding with a sheet 80 mainly made of iron.

In another example, the outer part 30 can be made with a refractory material with high mechanical strength so as to facilitate punching and to minimize the heat exchange between the outer part 30 and the sheet 40 during the welding of the internal part 20 on a sheet 80 mainly made of iron.

[0086] [Fig. 19] Finally, an electrically insulating part 120 can be placed between the flanges 21 and 31 of the internal 20 and external 30 parts so that the external part 30 is not passed through by the electric current during the welding of the part 20. and the possible contact of the surface 34 with the sheet 80 connected to the ground. Under these conditions, additional thermal protection is provided to the sheet 40, the part 30 being heated by the passage of an electric current during welding.

The part 120 of the previous example can be replaced by an insulating surface treatment, resistant to temperature, and localized at the level of the upper surface 33 of the collar 31. Such a surface treatment can be produced by way of dry - PVD, projection thermal, for example - and may consist of a refractory oxide for example, such as A1203.

The presence of an intermediate part 120 or of a localized surface treatment should not prevent the mechanical assembly of parts 20 and 30. Under these conditions, assemblies as shown in Figures 15, 16 and 17 can be considered.

[0089] [Fig. 20] Figure 20 shows the combination of the inner 20 and outer 30 parts to form the second embodiment of the hollow weld pin according to the invention

[0090] [Fig. 21] Figure 21 shows three cases of punching in three sheets 2 mm thick of different types: aluminum alloy with a mechanical strength of 430 MPa for sheet 200, composite with 80% carbon fibers and 20% of epoxy resin for sheet 210, unsaturated polyester loaded with 29% glass fibers for sheet 220. For these three materials, the punching forces are respectively 18,600, 9,300, and 4,500 N. The figure 21 thus highlights the good quality of the punching for different types of materials. The principles of the invention are applicable even with the high mechanical strength of the sheet 200 namely 430MPa as has been mentioned.

For the two embodiments of the hollow weld pin, the free end of the barrel 22 or 32 being welded to the steel sheet may have an internal chamfer, or a corrugation (a wave) , or crenellations on its perimeter, or any other shape which does not interfere with the punching operation, but which makes it possible to reduce the contact area with the steel sheet 80 during resistance welding. Under these conditions, the intensity of the welding current can be reduced as well as the heating of the various parts through which the current passes.

[0092] [Fig. 22] Figure 22 shows three examples of a hollow weld pin according to the first embodiment, with three different geometries of the annular projecting surface of the free end of the barrel: with an internal chamfer (oriented towards the inside of the cylinder) for annular surface 240, with corrugation along the perimeter (of amplitude parallel to the axis) for annular surface 241, and with crenellations along the perimeter (the sides of the crenellations being parallel to the axis) for the annular surface 242.

Experience shows that bevelled drums or drums with corrugations behave well during punching, even with sheets whose mechanical strength is greater than 300 MPa, whereas the slots at the end of the drum tend to crush during punching. punching.

[0094] [Fig. 23] In FIG. 23, there is shown the possibility of adding, in the event of failure of the weld, the hollow pin formed for the illustration, according to the second mode of realization, of the hollow parts 20 and 30, to be able to take advantage of the hollow character of the pin, remained in the hypothesis in place despite its failure, to carry out a simple repair. In this case, the hole in the hollow pin is used to introduce the rod of a standard pin 250, which is then welded by electric welding using an electrode applied to its head, accessible above the hollow pin, opposite the free end of its rod which is in contact with the sheet 80. The same principle is applicable with the hollow pin of the first embodiment of the invention. The head of the standard pin is further supported on the outer face of the collar of the hollow pin to clamp the two sheets 40 and 80, respectively of steel and either of aluminum or of a composite material or the like, one against the other.

[0095] [Fig. 24] Referring to Figures 24 to 29, another approach, to provide effective thermal protection of the sheet 40 during its assembly with a steel sheet 80, consists of making a washer 130 which has on its internal diameter three radially projecting parts 131, the ends of which are distributed over a diameter D around the axis of the washer very slightly less than the external diameter of the barrel 22 of the internal hollow part 20.

[0096] [Fig. 25] This washer also has a thickness el30 less than the height L22 of the barrel 22 of the internal hollow part 20.

[0097] [Fig. 26] In figure 26, we see the assembly of the washer 130 on the inner hollow part 20, and more precisely on its shaft 22. The washer 130 is pushed until it meets the surface of the collar 21 facing the shaft 22 , to form the hollow weld pin 10.

[0098] [Fig. 27] Thus the washer 130 can be force-mounted on the barrel 22 with three points of contact only, at 120 ° to each other for example, generating a stable support for the washer 130 on the barrel 22, as well as three successive air volumes 132 over three angular sectors of the toric space between the barrel 22 and the washer 130. These air volumes 132 are delimited from one another by the radially projecting parts 131. L The difference between the diameter D and the outside diameter of the barrel 22 is controlled to ensure a press fit which prevents the washer 130 from separating from the part 20 without the application of a significant external force.

[0099] [Fig. 28] Once the washer 130 is integral with the part 20, the outer face 133 of the washer is used for punching the sheet 40 and its retention in the sheet 40. The outside diameter of the washer 130, referenced De 130, is necessarily less than the outside diameter of the flange 21 of the part 20, referenced De21, so as to generate a surface 134 annular contact, on the face of the collar looking towards the barrel, with the sheet 40 after punching. This contact face is formed by the surface of the face of the collar looking from the barrel which projects from the washer 130, due to the smaller diameter of the latter. The surface 134 guarantees the mechanical strength of the assembly of the sheets 40 and 80 after welding, avoiding unbuttoning.

[0100] The end 24 of the barrel 22, opposite the flange 21, can advantageously have a double chamfer so as to increase the contact resistance during welding with the steel sheet 80 and therefore to reduce the welding current intensity.

[0101] [Fig. 29] When welding end 24 of barrel 22, heat diffusion into washer 130 can only take place through the three protrusions 131, and is therefore very limited. Thus, washer 130 heats up much less than was 22 during the resistance welding operation. Taking into account the heat loss in the washer 130, the sheet 40, which receives heat through the washer, heats up less than the washer and than was 22. The washer 130 can advantageously be made of a material which has reduced thermal conductivity to limit heating of the sheet 40 to the maximum. Thus, for example, the washer 130 can be made of stainless steel, or of refractory steel. The washer 130 can advantageously, and from a point of view of the manufacturing cost which one wishes to be reduced, be produced by stamping.

[0102] In the foregoing, we have mentioned the introduction of the one- or two-piece pin into the sheet of non-electrically conductive material by punching with depastillage, and retention of the pin. Alternatively, if the sheet of non-electrically conductive material is manufactured by molding or compression of the rolling, thermocompression, stamping type, which is easily the case if the material is a thermoplastic polymer material, a thermosetting resin or a composite material comprising woven fibers impregnated with a polymeric resin, then the pin or, if the pin is in two pieces, the external part of the pin (the additional cylinder) can be introduced into the sheet as soon as it is hot-shaped, by overmolding. The pawn (or the outer piece of the pawn if the pawn is in two pieces) is then retained by the contraction of the material around the barrel during cooling.

[0103] [Fig. 31] If the molded or laminated material is a thermoplastic reinforced with long fibers, at least some of which are oriented in a single direction in the plane, cutting the long fibers by punching is avoided, since the long fibers can be arranged locally in the material around the pin, the presence of the latter deflecting them locally on either side of the location it occupies on the sheet without calling into question the regular presence of long fibers throughout the part, upstream and downstream of the pin in the direction of the fibers. This makes it possible to ensure the solidity of the part, the fibers of which retain all their integrity, and therefore ensure, if necessary, the transmission of forces from the downstream side of the pin to the upstream side thereof, or vice versa.

[0104] This manufacture by inserting the pin during the manufacture of the part is conceived in particular with the two-part pin, the outer part providing thermal protection to the polymer or composite material for the electric welding step. It is specified that the internal part of the pin can be present during overmolding, or be introduced later.

[0105] The invention applies in particular to the automotive sector, for the assembly of body parts or body parts made of steel and aluminum alloy, or for the assembly of parts made of steel and of polymer material, or of composites. .

Claims

[Claim 1] A method of assembling a sheet (40) and an iron-based metal part (80) comprising a step of placing a tubular pin (10) open at both ends by punching passing through the sheet (40) with a shank of said pin with retention of said barrel (10) by the sheet, a pellet (70) detaching from the first sheet (40), a collar of the pin abutting against the surface of the sheet (40) once the through punching has been carried out, and the elastic returns of the barrel of the pin (10) and of the sheet (40) compressing the outer surface of the barrel, or by overmolding said pin into the sheet, then a welding step a metal tube of the pin (10) on the iron-based metal part (80) by bringing a free end (24) of the metal tube into contact with the surface of the iron-based metal part (80) and electrical resistance welding (90).

[Claim 2]. Sheet for mechanical assembly retaining a tube open at both ends and passing through, made of electrically conductive metal (20), which on one side of the sheet has a flare (21) which abuts against the surface of the sheet (40) ) and which on the other face of the sheet has a free end (24).

[Claim 3]. Sheet for mechanical assembly according to claim 2, characterized in that it is an aluminum alloy sheet (200), or a polymer sheet (220) with or without fiber reinforcement, or a sheet of composite material with an organic matrix (210) or ceramic with or without fibrous reinforcement.

[Claim 4]. Sheet metal for mechanical assembly according to Claim 2 or Claim 3, characterized in that the material of the metal tube open at both ends (20) being kept separate from the material of the sheet (40) by an additional tube ( 30), the free end (24) of the metal tube open at both ends protruding from a free end (34) of the additional tube (30).

[Claim ô]. Sheet metal for mechanical assembly according to Claim 4, characterized in that the additional tube (30) is made of stainless steel, of hardened steel, or of a non-metallic material refractory to heat.

[Claim 6]. Sheet metal for mechanical assembly according to one of claims 4 to 5, characterized in that the metal tube open at both ends (20) and the additional tube (30) are assembled by welding, glue, clamping or plastic deformation between respective end flanges (21, 31) of the tubes on the side of the flare, or else blocked relative to each other by inserting a shim (110) between an internal surface of the additional tube and an opposite external surface of the metal tube open to its two ends or else by the presence on the internal diameter of the additional tube of radially projecting parts (131) favoring a fitting of the additional tube around the metal tube open at both ends (20).

[Claim 7]. Sheet metal for mechanical assembly according to one of claims 4 to 6, characterized in that it comprises an electrical insulation (120) between the material of the metal tube open at both ends and the material of the additional tube.

[Claim 8]. Sheet metal for mechanical assembly according to one of claims 4 to 6, characterized in that it comprises a spacing, according to a cylindrical development and over the height of the electrically conductive metal tube, between the material of the metal tube open at its two ends (20) and the material of the additional tube (30).

[Claim 9]. A method of assembling a sheet (40) and an iron-based metal part (80) comprising a step of positioning with retention by the sheet of a hollow pin, by punching through the sheet (40 ) with a shank of said hollow pin (10), a pellet (70) detaching from the sheet (40), a collar of the pin abutting against the surface of the sheet (40) once the through punching has been carried out, or by overmolding of said barrel in the sheet (40), then a step of welding a metal cylinder of the pin (10) on the iron-based metal part (80) by contacting a free end (24) of the cylinder metallic with the surface of the metal part made of iron (80) and electric resistance welding (90).

[Claim 10]. A method of assembling a sheet and a metal part according to claim 9, characterized in that the electrical resistance welding electrode (90) is dimensioned and applied such that all the angular sectors of the metal cylinder are used simultaneously to transmit energy for welding.

[Claim 11]. Sheet for mechanical assembly retaining a hollow pin comprising a through hollow cylinder made of electrically conductive metal (20), which on one side of the sheet has a flare (21) which abuts against the surface of the sheet (40) and which on the other face of the sheet has a free end (24).

[Claim 12]. Sheet for mechanical assembly according to Claim 11, characterized in that it is an aluminum alloy sheet (200), or a polymer sheet (220) with or without fiber reinforcement, in particular a fibrous reinforcement with long fibers, or a sheet of composite material with an organic matrix (210) or ceramic with or without fibrous reinforcement, in particular a fibrous reinforcement with long fibers.

[Claim 13]. Sheet metal for mechanical assembly according to Claim 11 or Claim 12, characterized in that the hollow metal cylinder (20) is made of low-alloy pressed steel.

[Claim 14]. Sheet metal for mechanical assembly according to one of claims 11 to 13, characterized in that the material of the hollow metal cylinder (20) is kept separate from the material of the sheet (40) by an additional cylinder (30) of the pin, the free end (24) of the hollow metal cylinder protruding from a free end (34) of the additional cylinder (30).

[Claim 15]. Sheet metal for mechanical assembly according to Claim 14, characterized in that the additional cylinder (30) is made of stainless steel, of hardened steel, or of a non-metallic material refractory to heat.

[Claim 16]. Sheet metal for mechanical assembly according to Claim 14 or Claim 15, characterized in that the hollow metal cylinder (20) and the additional cylinder (30) are assembled by welding, glue, clamping or plastic deformation between respective end flanges (21, 31) of the cylinders on the flaring side, or even blocked in relation to one another by inserting an internal surface of the additional cylinder and an opposite external surface of the hollow metal cylinder with a shim (110) or again by the presence on the internal diameter of the additional cylinder of radially projecting parts (131) promoting an embedding of the additional cylinder around the hollow metal cylinder (20).

[Claim 17]. Sheet metal for mechanical assembly according to one of claims 14 to 16, characterized in that it comprises an electrical insulation (120) between the material of the hollow metal cylinder and the material of the additional cylinder.

[Claim 18]. Sheet metal for mechanical assembly according to one of claims 14 to 16, characterized in that it comprises a spacing, according to a cylindrical development and over the height of the conductive metal cylinder of electricity, between the material of the hollow metal cylinder (20) and the material of the additional cylinder (30).

[Claim 19]. Sheet metal for mechanical assembly according to one of claims 9 to 18, characterized in that the free end of the hollow metal cylinder (20) is smooth, or has a chamfer (240), or has a corrugation on its perimeter (241), or has slots on its perimeter (242).

[Claim 20]. Assembly of a sheet (40) and an iron-based metal part (80) comprising a hollow pin comprising an electrically conductive metal hollow cylinder (20) passing through the sheet (40) and one end of which has a flaring (21) abutting against the surface of the sheet (40), the hollow metal cylinder (20) being welded to the iron-based metal part (80).

[Claim 21]. Motor vehicle, a structure of which includes at least one assembly according to claim 20.

[Claim 22]. A method of repairing an assembly according to claim 12 or a vehicle according to claim 21, in the event of failure of the weld, characterized in that the rod of a metal conductor (250) composed of a head and d a rod of length chosen for repair is placed in the recess of said electrically conductive metal cylinder (20), the head being pressed against the flare (21) of the cylinder (20) and an electric welding electrode being applied on the head to weld the rod to the sheet.