FR2878175A1 - METHOD AND DEVICE FOR ELECTRICAL WELDING BY POINTS - Google Patents

Abstract

The present invention relates to a method and an electric spot welding device, improving the dissipation capacities of the vibratory energy of the structures assembled by weld points. According to the invention, a permanent contact zone is created (35, 50). elements to be welded together, in the immediate vicinity of the weld point, and a field of contact pressures in said zone.The invention applies particularly to the automotive industry.

Description

Method and device for electric spot welding

  The present invention relates to a method and an electrical spot welding device, improving the dissipation capabilities of the vibratory energy of welded spot welded structures.

  Many objects include sheets joined by electric soldering spots. This is particularly the case of motor vehicles whose bodies are composed of sheets assembled to each other. Vehicle manufacturers are constantly looking for solutions to increase the comfort of drivers and passengers. This is particularly the case of acoustic comfort and vibratory comfort. The engine and other mechanical devices, such as running gear, generate vibrations that propagate in the body and are likely to vibrate sheets, especially at the places of their assembly. The noises thus caused are audible in the passenger compartment, which deteriorates the quality of the acoustic comfort. It is indeed irritating to hear noises, often referred to as "body noises", whose source is difficult to identify and therefore to remedy. The vibrations can also spread in the steering wheel which is annoying for the driver.

  The solution generally adopted by car manufacturers to eliminate vibrations is to stiffen the crates. However, this solution is accompanied by an inevitable increase in the weight of the vehicles, which increases the fuel consumption, the emission of particles and gaseous pollutants and the cost of manufacturing the vehicles.

  Surface treatments of the cockpit panels can also be carried out in order to limit the bending vibrations of these panels. For this, we use soundproofing plates, called "IFF plates" (for "soundproofing foil fuse"). These plates generally consist of a layer of damping material, this layer possibly being surmounted by a stress plate.

  This solution also has the disadvantage of increasing the weight of the vehicles.

  Another solution consists in integrating vibratory energy dissipation devices at judiciously selected locations of the mechanical members and the bodywork so as to obtain an effective damping of the vibrations. These devices, called acoustic drummers, consist of a mass surrounded by a viscoelastic material with high dissipative power. The mass is set in motion by the vibrations to be absorbed and the movement of the mass is dampened by the viscoelastic material. Drummers absorb vibrations in relatively narrow frequency and temperature ranges that depend on their characteristics. Outside these frequency and temperature ranges, the vibrations are not or are not absorbed very much. In addition, drummers can not always be placed in the desired places, for lack of space. Finally, the addition of drummers increases the weight of vehicles, causing the disadvantages already mentioned when increasing the stiffness of the body.

  The present invention proposes a method and a device for electrical welding by points of elements between them, for example sheets, promoting the contact and the friction of the elements welded together, which has the effect of increasing the natural dissipation capacities. vibratory energy of structures assembled by electric welding spots. In the particular case of a motor vehicle body, according to the invention is promoted contacts and friction of the assembled sheets by electric welding which increases the natural capacity for dissipation of vibration of the body.

  More specifically, the invention relates to a method of electrically welding elements between them in which at least one weld point is produced by passing an electric current between two electrodes flanking said elements to be welded and coming into contact with said elements. said method being characterized by creating a zone of permanent contact of said elements with each other in the immediate vicinity of said welding point. The contact zone preferably, but not necessarily, surrounds the weld spot.

  According to one embodiment, a pressure is applied on said zone thus creating a contact pressure field in said zone. This pressure can be applied during or after the cooling of the weld.

  The value of the pressure is preferably chosen, for a given contact zone surface, so as to make the dissipation of vibratory energy by the contact zone substantially maximal.

  According to one embodiment, the pressure is chosen between 0.01 MPa and 1 MPa and is applied for a period of time of between 10 to 300 ms. In general, the contact zone has substantially the shape of a ring with an inside diameter greater than 4 mm and an outside diameter of less than 25 mm. The invention also relates to a device for electric welding by means of a point between them, for the implementation of the method defined above. The device conventionally comprises two welding electrodes facing each other and between which can be positioned the elements to be welded, means for moving the electrodes to bring them into contact with the elements to be welded at the point where the welding point must be realized then to separate them from said elements, and a source of electric current to supply the electrodes. The device is characterized in that it comprises means for applying a pressure in the vicinity of the weld point so as to create a permanent contact zone.

  According to one embodiment, the means for applying a contact pressure comprise at least one movable piston between an open position and a clamping position for which the elements to be welded are pressed against each other between said piston and a support fixed, thus creating the contact zone. Preferably, the piston surrounds one of said electrodes.

  According to another embodiment, the means for applying a contact pressure comprise two pistons facing each other, each of them being in the immediate vicinity of one of the electrodes and movable between an open position and a clamping position for which the pistons press the elements against each other so as to create the contact zone. Preferably, the pistons each have a substantially annular shape, each of them surrounding one of the electrodes.

  Other advantages and features of the invention will become apparent from the following description of several embodiments of the invention, given by way of non-limiting example, with reference to the accompanying drawings and in which: FIG. 1 shows an example of structure to be welded; FIG. 2 illustrates the spot welding method according to the prior art; - Figure 3 is a section of an electric welding point on which is indicated the area of application of the contact pressures; - Figure 4 is a top view of an electric welding point with a contact zone according to the invention; FIG. 5 is a diagrammatic section of an electric spot welding device 20 enabling the creation of a contact zone; - Figures 6 and 7 respectively illustrate a first and a second embodiment of the method of creating a contact area and application of a contact pressure.

  FIG. 1 shows an exemplary application of the invention where it is a matter of spot welding two elements, which are sheets 10 and 12. Each sheet is folded to form an edge 14, called a "tornbed edge". welding points 16 being made between the fallen edges. This structure is typical of sheet metal assembly in the automotive industry. However, there are assemblies by electrical welding by points of more than two elements between them (three or four for example). The invention is therefore not limited to an assembly of two elements only.

  Conventionally, illustrated in Figure 2, the welding process according to the prior art, uses two electrodes 20 and 22 facing each other and located on either side of the two sheets 24 and 26 that are to be welded. The welding process can be broken down into four phases. The two electrodes are first moved towards each other so as to firmly press the plates 24 and 26 (Figure 2a). This is the docking stage. An electric current then flows through the electrodes (FIG. 2b), thus making it possible to reach the melting temperature of the metal at the level of the contact zone of the elements to be assembled. This is the actual welding step. After stopping the flow of electric current, the melted zone cools causing the assembly of the two elements (Figure 2c) by the creation of a weld point 28. This is the forging step. The last step (Figure 2d) is to move the electrodes away from each other, thus stopping the pressure of the electrodes on the elements.

  FIG. 3 shows in section an electric welding point assembling two elements 30 and 31. This soldering point consists of a zone 32 formed by the molten metal and of a zone 33, located around the zone 32, constituted by the part of the elements 30 and 31 affected by the temperature rise during the welding operation. Residual contact pressure remains in the zone 34 situated at the junction of the welded elements and 31 and around the molten metal zone 32. The value of this residual contact pressure depends on the welding process and in particular on the docking phase illustrated in Figure 2a.

  According to the present invention, a new permanent contact zone 35 is created between the elements to be welded, by applying a pressure on a contact surface S (in this new zone created, the elements 30 and 31 come into contact). This pressure gives rise to a field of contact pressures in the contact zone, between the elements 30 and 31.

  Thus the dissipation of vibratory energy by friction of the welded elements increases, and can even fully absorb vibrations propagating in the welded elements. Preferably, this contact zone 35 surrounds the residual pressure zone 34.

  As illustrated in FIG. 4, which represents a view from above of the weld point of FIG. 3, the zone of molten metal 32 generally has a substantially circular shape. The residual pressure zone 34 then takes the form of a ring surrounding the zone 32 and the permanent contact zone 35 is preferably created around the zone 34 and of annular shape. In general, the permanent contact zone is created in the immediate vicinity of the weld point and does not necessarily surround the residual pressure zone 34 and does not necessarily have the shape of a ring. This form is however advantageous.

  If we consider the fallen edges (Figure 1), usually used in the automotive industry, they have a width of about 15 mm and solder points have a diameter of about 6 mm. Under these conditions, the surface S of the permanent contact zone 35 that can be created to cause friction between the sheets is formed by a ring having a minimum inside diameter of about 6 mm and a maximum outside diameter of about 10 mm. mm. However, on the one hand there are electrical welding points with a diameter of around 4 mm and in this case the minimum inner diameter of the ring is 4 mm and, on the other hand, dropped edges of width greater than 15 mm. are sometimes used, the maximum outer diameter of the crown can then extend up to 25 mm.

  For a determined contact surface S, the dissipation of the vibratory energy by friction is maximum for a determined value of contact pressure between sheets. This maximum value, and therefore optimal, can be determined, for example, experimentally for a given welding structure. With the surface of the ring of internal diameter of about 6 mm and outer diameter of about 10 mm, the pressure of the permanent contact area varies from 0.01 MPa to 1 MPa depending on the characteristics of the sheets to be welded.

  FIG. 5 schematically represents a device making it possible to create, by applying a pressure, a permanent contact zone 50, of annular shape, between two sheets 51 and 52 to be electrically welded to one another by one or more points. Welding. Two welding electrodes 53 and 54 are fixed facing each other in frames or enclosures respectively 55 and 56. Unrepresented means are used to move the electrodes to bring them into contact with the elements to be welded, to the where the soldering point is to be made, and then to separate them from those elements. An electric power source (not shown) feeds the electrodes to perform the solder. Located around the electrodes and partly inside the frames 55 and 56, two movable pistons 57 and 58, of annular shape, face each other. Chassis and pistons are electrically isolated from welding electrodes. The pistons 57 and 58 can slide in the frames respectively 55 and 56, around the electrodes 53 and 54, between an open position illustrated in FIG. 5, the pistons not being in contact with the sheets to be welded, and a position of clamping in which the pistons exert a contact pressure on the sheets, thereby creating the permanent contact area 50 around the weld spot. The movement of the pistons can for example be controlled by a system with hydraulic cylinders or by a pneumatic system. The hydraulic or pneumatic system is advantageously controlled by the pressure applied to the mobile pistons when they are in the clamping position. This slaving is used to obtain precisely the desired contact pressure field in the permanent contact zone 50. The resulting contact pressures depend on the force applied to the moving pistons and the rigidity of the plates to be welded.

  According to another embodiment not shown, one of the movable pistons 57 or 58 is replaced by a fixed support on which rests one of the plates 51 or 52 placed opposite this fixed part. The pressure creating the permanent contact zone is then exerted by the remaining piston 57 or 58, the sheets being held pressed between the piston and the fixed support.

  FIG. 6 illustrates an embodiment of the method according to the present invention, according to which a zone of permanent contact is created by application of a contact pressure: during the forging phase (cooling of the molten metal resulting in welding of the sheets) . The method is illustrated using the device of FIG. 5. The docking (FIG. 6a) and welding (FIG. 6b) phases are identical to those of the method of the prior art illustrated in FIGS. 2a and 2b. The application of the contact pressure is carried out during the forging phase illustrated in FIG. 6c. The movable pistons 57 and 58 are approached from the welding plates 50 and 51 to the contact. The hydraulic or pneumatic system then applies a pressure P on the surface S of the sheets surrounding the weld point. The sheets are then brought into contact, creating a permanent contact zone 50 and generating a field of contact pressures at the interface between the two sheets. The pressure application time is about 10 ms to 300 ms. The welding cycle ends with the raising of the electrodes 53 and 54 and the moving pistons 57 and 58 (FIG. 6d), then these latter are raised to their initial position (FIG. 6e) for a following cycle of creating a weld spot electric.

  FIG. 7 illustrates another embodiment of the method according to the present invention, according to which a permanent contact zone is created by applying a contact pressure after the forging phase.

  The docking (FIG. 7a), welding (FIG. 7b) and forging (FIG. 7c) phases are identical to those of the prior art welding process illustrated in FIGS. 2a, 2b and 2c. After the forging cycle (FIG. 7c), the electrodes 53 and 54 are raised as illustrated in FIGS. 7d to 7f.

  The application of the contact pressure is carried out after the forging phase. The moving pistons 57 and 58 are approached from the sheets to be welded to the contact (FIG. 7d). The hydraulic or pneumatic system then applies a pressure P on the area of the sheets surrounding the electrodes.

  The application time of the pressures is as before about 10 ms to 300 ms. The sheets are then brought into contact, creating a permanent contact zone 50 and thus generating a field of contact pressures at the interface between the two sheets. The welding cycle ends with the raising of the electrodes 53 and 54 and the moving pistons 57 and 58 (FIG. 7e), then these latter are returned to their initial position (FIG. 7f) for a following cycle of creation of a point of electric weld.

  The invention is not limited to the embodiments described and alternative embodiments can be made without departing from the scope of the invention. Thus, the permanent contact zone may be of any shape, as long as it absorbs the vibrations effectively. The device for creating a permanent contact zone can comprise mechanisms different from one or two annular form pistons. Any appropriate mechanism, within the reach of the skilled person, which allows to create a permanent contact area with a contact pressure field, can be envisaged. Similarly, the embodiments described relate to sheets to be welded together: the invention applies, of course, to all the elements to be welded together by electric welding spots and for which the total or partial absorption of vibratory energy is sought. As indicated above, the number of elements to be welded together is not limited to two, but can be three, four or more.

Claims (14)

  1. A method of electrically welding elements (30, 31, 51, 52) between them, in which at least one welding point (32) is produced by passing an electric current between two electrodes (53, 54) surrounding said elements soldering and coming into contact with said elements, said method being characterized by the creation of a permanent contact zone (35, 50) of said elements between them in the immediate vicinity of said welding point.   2. Method according to claim 1 characterized in that said contact zone (35, 50) surrounds said weld point.   3. Method according to one of the preceding claims characterized in that a pressure is applied on said zone (35, 50) thereby creating a contact pressure field in said zone.   4. The method of claim 3 wherein the passage of the electric current creating the weld is followed by a step of cooling the welded zone, characterized in that said pressure is applied during said cooling step.   5. The method of claim 3 wherein the passage of the electric current creating the weld is followed by a step of cooling the welded zone, characterized in that said pressure is applied after said cooling step.   6. Method according to one of claims 3 to 5 characterized in that the value of said pressure is chosen for a given contact area of the surface, so as to make substantially substantially the dissipation of vibration energy by said contact zone. .   7. The method of claim 6 characterized in that the value of said pressure is chosen between 0.01 MPa and 1 MPa.   8. Method according to one of claims 2 to 7 characterized in that said contact zone (35, 50) has substantially the shape of a ring of internal diameter greater than 4 mm and outer diameter less than 25 mm.   9. Method according to one of claims 3 to 8 characterized in that said pressure is applied for a period of time between 10 to 300 ms.   10. Device for electrically welding elements (51, 52) with each other, for carrying out the method defined in one of the preceding claims, said device comprising two welding electrodes (53, 54) facing each other. and between which can be positioned said elements to be welded, means for moving said electrodes to bring them into contact with said elements to be welded where the welding point must be made and then to separate them from said elements, and a current source electrical device for supplying said electrodes, said device being characterized in that it further comprises means (57, 58) for applying a contact pressure in the vicinity of said welding point so as to create a permanent contact zone (50).   11. Device according to claim 10 characterized in that said means for applying a contact pressure comprise at least one movable piston (57 or 58) between an open position and a clamping position for which said elements to be welded are pressed one against the other between said piston and a fixed support, thereby creating said contact zone.   12. Device according to claim 11 characterized in that said piston surrounds one of said electrodes.   13. Device according to claim 10 characterized in that said means for applying a contact pressure comprise two pistons (57, 58) facing each other, each of them being in immediate proximity to one of said electrodes (53, 54). and movable between an open position and a clamping position for which said pistons press said elements against each other so as to create said contact zone (50).   14. Device according to claim 13 characterized in that said pistons (57, 58) each have a substantially annular shape, each of them surrounding one of said electrodes (53, 54).