METHOD AND DEVICE FOR RESISTANCE WELDING STEEL SANDWICH SHEETS

Abstract

A method of resistance welding a component to a sandwich sheet, which includes a thermoplastic layer disposed between two metallic outer layers, may involve heating a region of the sandwich sheet to be welded such that the thermoplastic layer softens, displacing the thermoplastic layer from the region by pressing the outer layers together, and welding the outer layers to the component by an electrical current flow for welding in a first circuit. The first circuit may include a first power source via a first welding electrode arranged at a side of the sandwich sheet and a second welding electrode arranged at a side of the component. This method is easy to run and achieves short cycle times due at least in part to the region being heated by a current flow for preheating in a second circuit that comprises a second power source and an electrical conductor that is arranged between the first welding electrode and the sandwich sheet.”

Claims

1.-15. (canceled)

16. A method of resistance welding a component to a sandwich sheet that comprises a thermoplastic layer disposed between two metallic outer layers, the method comprising: heating a region of the sandwich sheet to be welded such that the thermoplastic layer softens; displacing the thermoplastic layer in the region to be welded by pressing the two metallic outer layers together; and welding the two metallic outer layers to the component by an electrical current flowing for welding in a first circuit via a first welding electrode disposed at a side of the sandwich sheet and a second welding electrode disposed at a side of the component, wherein the first circuit comprises a first power source, wherein the region of the sandwich sheet to be welded is heated by an electrical current flowing for preheating in a second circuit, wherein the second circuit comprises a second power source and an electrical conductor that is disposed between the first welding electrode and the sandwich sheet.

17. The method of resistance welding of claim 16 further comprising: activating the second power source so that the electrical current is flowing for preheating in the second circuit; and activating the first power source after the second power source has been activated so that the electrical current is flowing for welding in the first circuit.

18. The method of resistance welding of claim 16 further comprising at least one of activating the first power source or deactivating the second power source based on a measurement representative of displacement of the thermoplastic layer from the region to be welded.

19. The method of resistance welding of claim 18 wherein the measurement representative of displacement of the thermoplastic layer from the region to be welded is based on an electrical property of the sandwich sheet.

20. The method of resistance welding of claim 18 wherein the measurement representative of displacement of the thermoplastic layer from the region to be welded is based on a position of the first or second welding electrodes.

21. The method of resistance welding of claim 16 wherein the electrical conductor disposed between the first welding electrode and the sandwich sheet is a conductor tape.

22. The method of resistance welding of claim 21 wherein the conductor tape is disposed between the first welding electrode and the sandwich sheet with a tape holder.

23. The method of resistance welding of claim 16 wherein the electrical conductor disposed between the first welding electrode and the sandwich sheet is in direct contact with at least one of the first welding electrode or the sandwich sheet.

24. The method of resistance welding of claim 16 wherein the electrical conductor includes a first region having a first electrical resistance and a second region having a second electrical resistance, wherein the second electrical resistance is greater than the first electrical resistance.

25. The method of resistance welding of claim 24 wherein the second region of the electrical conductor is disposed in a contact region of the first welding electrode with the sandwich sheet.

26. The method of resistance welding of claim 24 further comprising insulating the first region from the first welding electrode with a region for insulation of the electrical conductor.

27. An apparatus for resistance welding a component to a sandwich sheet comprising a thermoplastic layer disposed between metallic outer layers, the apparatus comprising: a first welding electrode that is positionable on a side of the sandwich sheet; a second welding electrode that is positionable on a side of the component; a first circuit through which an electrical current for welding can flow, at least through the first and second welding electrodes, wherein the first circuit comprises a first power source; means for displacing the thermoplastic layer from a region of the sandwich sheet to be welded; and a second circuit comprising a second power source and an electrical conductor that is positionable between the first welding electrode and the sandwich sheet.

28. The apparatus for resistance welding of claim 27 further comprising control means coupled to the first and second power sources, wherein the control means is configured to activate the second power source first so that there is an electrical current for preheating flowing in the second circuit, wherein the control means is configured to activate the first power source after the second power source has been activated so that the electrical current for welding can flow in the first circuit.

29. The apparatus for resistance welding of claim 28 wherein the control means is configured to receive a measurement representative of displacement of the thermoplastic layer from the region to be welded for purposes of at least one of activating the first power source or deactivating the second power source.

30. The apparatus for resistance welding of claim 29 wherein the measurement is based on an electrical property of the sandwich sheet.

31. The apparatus for resistance welding of claim 29 wherein the measurement is based on a position of the first or second welding electrodes.

32. The apparatus for resistance welding of claim 27 wherein the electrical conductor is a conductor tape.

33. The apparatus for resistance welding of claim 32 wherein the conductor tape is disposed between the first welding electrode and the sandwich sheet with a tape holder.

34. The apparatus for resistance welding of claim 27 wherein the electrical conductor includes a first region having a first electrical resistance and a second region having a second electrical resistance, wherein the second electrical resistance is greater than the first electrical resistance.

35. The apparatus for resistance welding of claim 34 wherein the electrical conductor includes a region for insulation of the first region from the first welding electrode.

Description

[0036] The invention is to be elucidated in detail hereinafter with reference to working examples in conjunction with the drawing. The drawing shows, in

[0037] FIGS. 1a,b a schematic diagram of a first working example of an apparatus of the invention for performance of a first working example of a method of the invention during preheating;

[0038] FIG. 2 a schematic diagram of the working example from FIG. 1 during welding;

[0039] FIG. 3 a schematic diagram of the working example from FIG. 1 during multipoint resistance welding;

[0040] FIGS. 4a,b a schematic diagram of a further working example of an apparatus of the invention for performance of a further working example of a method of the invention during preheating;

[0041] FIG. 5 a schematic diagram of the working example from FIG. 4 during welding and

[0042] FIG. 6 a schematic diagram of a further apparatus for performance of a further method.

[0043] FIG. 1a shows a schematic diagram of a first working example of an inventive apparatus 1 for performance of a first working example of a method of the invention during preheating. The apparatus 1 serves for resistance welding of a sandwich sheet 2 to at least one further component 4, for example a metallic component. The sandwich sheet 2 has a thermoplastic layer 2c arranged between metallic outer layers 2a, 2b. The apparatus has a first welding electrode 6 arranged on the side of the sandwich sheet 2, and a second welding electrode 8 arranged on the side of the further metallic component 3. Additionally provided, by the first power source 10 and the first electrical wires 12, are means of providing a first circuit. As a result, it is possible to conduct a current flow for welding Is through the first and second welding electrodes 6, 8 (shown in FIG. 2).

[0044] In addition, the first welding electrode 6 serves as a means of displacing the thermoplastic layer 2c of the sandwich sheet 2 from the region of the sandwich sheet 2 to be welded. It is likewise possible to provide means of applying forces, for instance welding tongs (not shown).

[0045] Additionally provided is a second circuit comprising an electrical conductor 14 arranged between the first welding electrode 6 and the sandwich sheet 2, a second power source 16 and second electrical wires 18. The electrical conductor 14 arranged between the first welding electrode 6 and the sandwich sheet 2 takes the form of a conductor tape and is arranged by means of a tape holder 22 between the first welding electrode 6 and the sandwich sheet 2. In this case, the electrical conductor tape 14 forms a direct contact with the first welding electrode 6 and the sandwich sheet 2. The electrical conductor tape 14 has a first region 14a having a first specific electrical resistance and a second region 14b having a second specific electrical resistance for heating of the region of the sandwich sheet 2 to be welded. The first region 14a is made, for example, from copper, and the second region 14b from tungsten. As a result, the second specific electrical resistance is greater than the first specific electrical resistance. Finally, the electrical conductor tape 14 has a region 14c for insulation of the first region 14a with respect to the welding electrode 6.

[0046] FIG. 1b shows a modification of the conductor tape 14 in the region of contact formation with the first welding electrode 6.

[0047] Since the second region 14b is arranged in the contact region of the first welding electrode 6 with the sandwich sheet 2, the region of the sandwich sheet 2 to be welded can be heated particularly efficiently, so that the thermoplastic layer 2c softens quickly and is displaced from the welding region by pressing the outer layers 2a, 2b together. This is effected by a current flow for preheating I.sub.V in the second circuit, which is shown in FIG. 1a by the arrows. The electrical energy is transformed here to heat by the electrical resistance of the second region 14b and the passage resistance between the first region 14a and the second region 14b.

[0048] Additionally provided is a control means 20 which comprises a trigger switch and is coupled to the first and second power sources 10, 16. The control means is set up such that the second power source 16 is activated first, so that there is current flow for preheating I.sub.V in the second circuit.

[0049] The softening and displacement of the thermoplastic layer 2c, so that the outer layers 2a, 2b are in metallic contact, is determined by the consideration of a measurement representative of this. This may, for example, be a drop in the electrical resistance between the welding electrodes 6, 8 or a distance traveled by the first welding electrode 6 that corresponds to the thickness of the thermoplastic layer 2c.

[0050] If it is detected by the control means 20 that the thermoplastic layer 2c has been displaced from the welding region (as shown in FIG. 2), the second power source 16 is deactivated and the first power source 10 is activated, such that there is current flow for welding I.sub.S in the first circuit.

[0051] FIG. 2 shows a schematic diagram of the working example from FIG. 1 during welding. The control means 20 deactivates the second power source 16 and activates the second power source 10. The welding current I.sub.S, as shown by the arrows in FIG. 2, flows in the first circuit through the electrical wires 12, the first and second welding electrodes 6, 8, the further component 4 and the sandwich sheet 2. As a result of this, the outer layers 2a, 2b are welded to the further component 4 by the electrical current flow for welding I.sub.S.

[0052] FIG. 3 shows a schematic diagram of the working example from FIG. 1 during multipoint resistance welding. By contrast with the case shown in FIGS. 1 and 2, there is already a weld bond 24 in FIG. 3. By virtue of a second circuit having been provided with a second power source 16, the electrical connection between the first and second welding electrodes 6, 8 that results from the weld bond 24 does not result in any undesirable branch currents during the preheating. Instead, there is current flow for preheating I.sub.V as already shown in FIG. 1.

[0053] FIG. 4a shows a schematic diagram of a second working example of an inventive apparatus 1′ for performance of a working example of a method of the invention during preheating. The apparatus 1′ and the method conducted therewith are similar to the apparatus 1 and the method conducted therewith. In this respect, reference is made at first to the description for FIGS. 1 to 3.

[0054] The apparatus 1′ again has an electrical conductor 14′ which takes the form of conductor tape and is arranged by means of the tape holder 22′ between the first welding electrode 6 and the sandwich sheet 2 in direct contact therewith. The electrical conductor tape 14′ again has a first region 14a′, a second region 14b′ having a higher specific electrical resistance for heating of the region to be welded, and a region 14c′ for insulation of the first region 14a′ with respect to the welding electrode 6.

[0055] FIG. 4b shows an enlargement of the conductor tape 14′ in the region of contact formation with the first welding electrode 6.

[0056] By contrast with the apparatus 1, however, the regions of the electrical conductor tape 14′ of the apparatus 1′ are arranged differently. In the contact region of the electrical conductor 14′ with the sandwich sheet 2 is arranged exclusively the second region 14b′ having the higher specific electrical resistance, which is in contact with the first welding electrode 6 and the sandwich sheet 2. This is adjoined on all sides by the first region 14a′. The insulating region 14c′ prevents direct electrical contact between the first region 14a′ and the first welding electrode 6 in the region of the electrode cap of the first welding electrode 6. By contrast with the conductor tape 14, however, the conductor tape 14′ does not have any insulating region 14c′ in the region of the tape holder 22′, since the tape holder 22′ already has a region 26 for insulation of the welding electrode 6 with respect to the electrical conductor tape 14′.

[0057] As already described, by virtue of the arrangement of the second region 14b′ in the contact region of the first welding electrode 6 with the sandwich sheet 2, the region of the sandwich sheet 2 to be welded can be heated particularly efficiently, such that the thermoplastic layer 2c softens quickly and is displaced from the weld region by pressing the outer layers 2a, 2b together. This is effected by current flow I.sub.V in the second circuit, which is indicated by the arrows in FIG. 4a.

[0058] Subsequently, as shown in FIG. 5 by means of the arrows and as already described in connection with FIG. 2, the sandwich sheet 2 can be welded to the further component 4 by means of the current for welding I.sub.S.

[0059] FIG. 6 shows a schematic diagram of a further apparatus 1″ for performance of a further method. The apparatus 1″ is of similar construction to the apparatus 1′, and the same electrical conductor tape 14′ is used. By contrast with the apparatus 1′ described in FIG. 4, however, the apparatus 1″ does not have a second power source. Instead, the preheating current I.sub.V is also provided by the first power source 10. For this purpose, an electrical bridge 28 is provided, which connects the first power source 10 to the conductor tape 14′ via the tape holder 22″, bridging over the second welding electrode 8, the further component 4 and the sandwich sheet 2. Thus, the second circuit for preheating comprises the first power source 10, some of the first electrical wires 12, the first welding electrode 6, the electrical conductor tape 14′ and the electrical bridge 28. The preheating current can then flow as shown by the arrows in FIG. 6.