METHOD AND APPARATUS FOR RESISTANCE WELDING OF STEEL SANDWICH SHEETS

Abstract

A method for resistance welding a metallic component to a sandwich metal sheet with a thermoplastic layer disposed between two metallic cover layers may involve heating a region of the sandwich metal sheet to be welded such that the thermoplastic layer softens, displacing the thermoplastic layer from the region by compressing the cover layers, and welding the cover layers with the metallic component by means of a flow of electrical current in a first circuit via a first welding electrode disposed on a side of the sandwich metal sheet and a second welding electrode disposed on a side of the metallic component. The method for resistance welding has short cycle times, and a compact design and a process-reliable welded connection can be achieved. The method may further involve heating the region to be welded by a flow of current in a second circuit comprising the first welding electrode and an electrical conductor disposed between the first welding electrode and the sandwich metal sheet.”

Claims

1.-15. (canceled)

16. A method for resistance welding a sandwich metal sheet to a metallic component, wherein the sandwich metal sheet comprises a thermoplastic layer disposed between two metallic cover layers, the method comprising: heating a region of the sandwich metal sheet to be welded in such a way that the thermoplastic layer softens; displacing the softened thermoplastic layer from the region by compressing the two metallic cover layers; and welding the metallic component to one or both of the two metallic cover layers by way of a flow of electrical current in a first circuit via a first welding electrode disposed on a side of the sandwich metal sheet and a second welding electrode disposed on a side of the metallic component, wherein the region of the sandwich metal sheet to be welded is heated by a flow of electrical current in a second circuit that comprises the first welding electrode and an electrical conductor disposed between the first welding electrode and the sandwich metal sheet.

17. The method of claim 16 wherein a conductor ribbon is used as the electrical conductor disposed between the first welding electrode and the sandwich metal sheet.

18. The method of claim 17 further comprising disposing the conductor ribbon with a ribbon-guiding system between the first welding electrode and the sandwich metal sheet.

19. The method of claim 17 wherein the electrical conductor makes contact directly with at least one of the first welding electrode or the sandwich metal sheet.

20. The method of claim 16 wherein the flow of electrical current for welding in the first circuit passes via the first welding electrode, the electrical conductor disposed between the first welding electrode and the sandwich metal sheet, the sandwich metal sheet, the metallic component, and the second welding electrode that is in contact with the metallic component.

21. The method of claim 16 wherein the flow of electrical current for heating in the second circuit passes via the first welding electrode, the electrical conductor disposed between the first welding electrode and the sandwich metal sheet, and a shunt conductor.

22. The method of claim 16 further comprising at least temporarily disconnecting the first circuit as the region of the sandwich metal sheet to be welded is heated by the flow of electrical current in the second circuit.

23. The method of claim 22 wherein disconnecting the first circuit occurs by way of spacing apart the second welding electrode from the metallic component or a separate switch.

24. The method of claim 16 wherein the two metallic cover layers are compressed by the first welding electrode and a spacer element disposed on the side of the metallic component.

25. The method of claim 16 further comprising adapting the electrical conductor disposed between the first welding electrode and the sandwich metal sheet to the welding to be performed.

26. The method of claim 16 further comprising measuring electrical properties of the sandwich metal sheet.

27. A device for resistance welding a metallic component to a sandwich metal sheet having a thermoplastic layer disposed between metallic cover layers, the device comprising: a first welding electrode configured to be disposed on a side of the sandwich metal sheet; a second welding electrode configured to be disposed on a side of the metallic component; means for making available a first circuit, wherein the means conduct a welding current at least via the first and second welding electrodes; means for displacing the thermoplastic layer of the sandwich metal sheet from a region of the sandwich metal sheet to be welded; a second circuit comprising the first welding electrode and an electrical conductor configured to be disposed between the first welding electrode and the sandwich metal sheet, wherein a flow of current in the second circuit is configured to heat the region of the sandwich metal sheet to be welded.

28. The device of claim 27 wherein the electrical conductor is a conductor ribbon.

29. The device of claim 28 further comprising a ribbon-guiding system with which the conductor ribbon can be disposed between the first welding electrode and the sandwich metal sheet.

30. The device of claim 27 wherein the electrical conductor is configured to be disposed between the first welding electrode and the sandwich metal sheet such that the electrical conductor is configured to make contact directly with at least one of the first welding electrode or the sandwich metal sheet.

Description

[0030] In the text which follows, the invention will be explained in more detail on the basis of exemplary embodiments in conjunction with the drawing, in which:

[0031] FIG. 1 shows a schematic illustration of an exemplary embodiment of a device and of a method during the flow of current for heating;

[0032] FIG. 2 shows a schematic illustration of the exemplary embodiment from FIG. 1 during the flow of current for welding;

[0033] FIG. 3 shows a schematic illustration of a further exemplary embodiment of a device and of a method during the flow of current for heating;

[0034] FIG. 4 shows a schematic illustration of a further exemplary embodiment of a device and of a method during the flow of current for heating;

[0035] FIG. 5 shows a schematic illustration of the exemplary embodiment from FIG. 4 during the flow of current for welding,

[0036] FIG. 6 shows a schematic illustration of the time profile of the force applied by the welding electrodes; and

[0037] FIG. 7 shows a further schematic illustration of an exemplary embodiment of a device.

[0038] FIG. 1 shows, in the first instance, a schematic illustration of an exemplary embodiment of a device 1a and a method during the flow of current for heating. With the device 1a, it is possible to perform resistance welding of a sandwich metal sheet 2 which has two metallic cover layers 2a, 2b and a thermoplastic layer 2c arranged between the metallic cover layers 2a, 2b, having a further metallic component 3, for example a solid metal sheet, for example a steel sheet. The device has a first welding electrode 4 and a second welding electrode 5. In this context, the first welding electrode 4 is arranged on the side of the sandwich metal sheet 2, and the second welding electrode 5 is arranged opposite on the side of the component 3. The device 1a makes available, with the power source 6 and the electrical wired 7, means for making available a first circuit. In addition, a force can be applied to the sandwich metal sheet 2 via the first welding electrode 4, with the result that the plastic layer 2c can be displaced. Means for applying force to the first and second welding electrodes 4, 5 are not illustrated in FIG. 1. This can be implemented, for example, by means of welding tongs.

[0039] In the device 1a, a second circuit is also provided which comprises the first welding electrode 4 and an electrical conductor 8 which can be arranged and is arranged between the first welding electrode 4 and the sandwich metal sheet 2. The electrical conductor 8 is embodied here as a conductor ribbon 8 which is arranged via a ribbon-guiding system 9 between the first welding electrode 4 and the sandwich metal sheet 2. In this context, the conductor ribbon 8 is in direct contact with the first welding electrode 4, on the one hand, and with the metallic cover layer 2a, on the other. The conductor ribbon 8 is additionally connected via a shunt conductor 10 to the power source 6. In this exemplary embodiment, the electrical wires 7 are insulated with respect to the conductor ribbon 8. A flow of current in the second circuit therefore passes via the electrical wires 7, the first welding electrode 4, the conductor ribbon 8 and the shunt conductor 10, with the result that the pre-heating current I.sub.V flows in the second circuit. In particular, current can pass to the conductor ribbon 8 only via the first welding electrode 4. Heat for softening the plastic layer 2c is generated by means of the contact resistance between the first welding electrode 4 and the conductor ribbon 8 and the material resistance of the conductor ribbon 8.

[0040] At the same time, the cover layers 2a, 2b of the sandwich metal sheet 2 are compressed by the first and the second welding electrodes 4, 5, with the result that the first welding electrode 4 displaces the plastic layer 2c in the welding region. The result of the displacement of the plastic layer 2c is illustrated here in FIG. 2.

[0041] FIG. 2 then shows a schematic illustration of the exemplary embodiment from FIG. 1 during the flow of current for welding. The fact that the plastic layer 2c is now displaced from the welding region and the metallic cover layers 2a, 2b are in contact can be detected, for example, by virtue of the fact that the resistance between the cover layers 2a, 2b drops abruptly. In this case, the electrical resistance between the first and the second welding electrodes 4, 5 was measured by means of a weld controller (not illustrated). The welding current I.sub.S can then be made available by means of the power source 6. In any case, the current in the first circuit flows via the electrical wires 7, the first welding electrode 4, the conductor ribbon 8, the metallic cover layers 2a, 2b, the further component 3, the second welding electrode 5 and in turn via the electrical wires 7. Further elements can also be provided in the circuit. In this context, a welding nugget 11 is formed which connects the metallic cover layers 2a, 2b of the sandwich metal sheet to the further metallic component 3. Since the conductor ribbon 8 is also arranged between the first welding electrode 4 and the cover layer 2a, it can also influence the actual welding process. An asymmetrical electrode design is effectively present for the first and second welding electrodes 4, 5, since the first welding electrode is, in contrast with the second welding electrode 5, in contact with the welded elements via the conductor ribbon 8. The production of the welding nugget 11 can be influenced by this. For example, the conductor ribbon 8 can be selected in such a way that in contrast to a symmetrical electrode design the welding nugget is shifted in the direction of the sandwich metal sheet. This can ensure that the metallic cover layer 2a is also connected. A flow of current via the shunt conductor 10 can be negligible given a correspondingly high resistance of the conductor ribbon 8. Alternatively, a switch, for example a shunt conductor 10, can also be provided for disconnecting the second circuit.

[0042] FIG. 3 shows a schematic illustration of a further exemplary embodiment of a device 1b and of a method during the flow of current for heating. The device 1b and the method which is carried out therewith correspond essentially to the device 1a and to the method carried out therewith. In this respect, reference is made initially to the description relating to FIGS. 1 and 2. In contrast to the device 1a, the device 1b has a switch 12 for disconnecting the electrical wire 7 between the second welding electrode 5 and the power source 6, with the result that the first circuit can be disconnected without disconnecting the second circuit. The switch 12 can be embodied for example in a mechanical or electrical fashion, for example as a thyristor circuit. The disconnection occurs during the heating of the welding point to the pre-heating current I.sub.V by means of previous opening of the switch 12. This has the advantage that the method can be applied even in the case of multipoint resistance welding. If a spot weld connection 13 has already been produced, the pre-heating current IV would in any case not flow exclusively via the conductor ribbon 8 and the shunt conductor 10 but rather in any case also via the spot weld connection 13 which has already been formed, and via the second welding electrode 5. This is prevented by opening the switch 12, with the result that effective heating of the welding point is not adversely affected.

[0043] FIG. 4 shows a schematic illustration of a further exemplary embodiment of a device 1c and of a method during the flow of current for heating. The device 1c and the method carried out therewith is similar to the devices 1a, 1b and the methods carried out therewith. In this respect, reference is made in the first instance to the description relating to FIGS. 1, 2 and 3. In contrast to this, the ribbon-guiding system is implemented by virtue of the fact that the conductor ribbon 8 is conducted in an electrically conductive fashion to the first welding electrode 4 on the side lying opposite the shunt conductor 10. On the side lying opposite the shunt conductor 10, the conductor ribbon 8 is connected in an electrically insulated fashion to the welding electrode, and connected in an electrically conductive fashion to the shunt conductor 10. Undesired bypassing of the welding region to be heated by the pre-heating current I.sub.V is prevented by the insulated connection.

[0044] As a further difference, the second welding electrode is connected to a spacer element 14 via the elements 14c. The spacer element 14 has an insulating region 14a with which the spacer element makes contact with the component 3. The second welding electrode 5 is arranged spaced apart from the further component 3. The first circuit is disconnected by the insulating region 14a and the spacing apart, with the result that during the heating with the pre-heating current I.sub.V no undesired current flows via the welded connection 13 which has already been formed and via the spacer element 14 itself, such that a further separate switch 12 does not have to be provided.

[0045] Furthermore, the spacer element 14 also comprises spring elements 14b. The spring stiffness of the spring elements 14b of the spacer element 14 is configured here in such a way that during the heating with the pre-heating current I.sub.V the second welding electrode 5 is spaced apart the further metallic component 3 from the component 3 despite the application of a force in the direction of the component 3. The application of force compresses the cover layers 2a, 2b of the sandwich metal sheet, as illustrated in FIG. 5.

[0046] FIG. 5 shows a schematic illustration of the exemplary embodiment from FIG. 4 during the flow of current I.sub.S for welding in the first circuit. A welding force which is increased compared to the force application during the heating is then applied to the welding electrodes 4, 5. As a result, the spring elements 14b yield in such a way that the second welding electrode 5 can make contact with the further component 3. Therefore, the cover layers 2a, 2b can be welded, with the further component 3, to one another by means of the flow of the electrical welding current I.sub.S in the first circuit via the first and second welding electrodes 4, 5 to form a welding nugget 11.

[0047] The conductor ribbon 8 divides the current I.sub.S into the current I.sub.S1 through the first welding electrode and I.sub.S2 through the conductor ribbon 8. The current through the shunt conductor 10 can be ignored here. Therefore, both I.sub.S1 and I.sub.S2 contribute to the welding process. However, a partial current I.sub.S3 flows through the welded connection 13 which has already been formed and which therefore does not contribute to the welding process. I.sub.S3 is, however, very much smaller than I.sub.S1+I.sub.S2, and negligible. In addition, further secondary currents can be diverted through the sandwich metal sheet 2 or the component 3, which secondary currents can, however, also be ignored. The conductor ribbon can advantageously preferably be composed of three sections (not illustrated here) with different materials, which conductor ribbon is, for example, in the external sections/end sections composed of a material which is a good electrical conductor, for example a copper material, and the central region which is arranged, in particular, in the contact-forming region of the welding electrode 4 and the cover layer 2a, from another material, in particular with a high electrical resistance, for example from a steel material or from a tungsten material.

[0048] FIG. 6 shows a schematic illustration of the time profile of the force applied by the welding electrodes 4, 5 to the welded elements 2, 3. Firstly, the force applied to the welded elements 2, 3 is raised to a first value Fi up to the time t.sub.1 and is held constant essentially up to t.sub.2. In this context, the welding region is heated via the second circuit at least temporarily in the time period between t.sub.1 and t.sub.2. If the plastic layer is displaced from the welding region, the force is increased to a second value F.sub.2 up to the time t.sub.3 and is kept essentially constant up to the time t.sub.4. Between t.sub.3 and t.sub.4 the welding is carried out by means of the welding current in the first circuit. Subsequently, the welded components 2, 3 or the welding electrodes 4, 5 can be removed or shifted.

[0049] FIG. 7 shows a schematic illustration of a part of a further exemplary embodiment of a device. The device comprises a first welding electrode 4 and an electrical conductor 8 which can be arranged and is arranged between the first welding electrode 4 and the sandwich metal sheet 2, which conductor 8 is embodied in the form of a welding electrode attachment and is fabricated, for example, from a copper material, wherein a partial region of the attachment 8 is electrically isolated from the welding electrode 4 by means of insulation 15. A material 16 which increases the electrical resistance, and which is fabricated, for example, from a steel material or tungsten material, is inserted underneath the insulation 15, as a junction region between the attachment 8 and the welding electrode 4.