Resistance spot welding steel and aluminum workpieces with hot welding electrode at aluminum workpiece

Patent metadata

Field	Value
Publication number	US-9839971-B2
Application number	US-201414488799-A
Country	US
Kind code	B2
Filing date	Sep 17, 2014
Priority date	Sep 20, 2013
Publication date	Dec 12, 2017
Grant date	Dec 12, 2017

Abstract

A method of resistance spot welding a steel workpiece to an aluminum or aluminum alloy workpiece involves providing a workpiece stack-up that includes a steel workpiece and an aluminum workpiece and preheating the welding electrode that is meant to contact the aluminum or aluminum alloy workpiece. The method further involves pressing the preheated welding electrode and another welding electrode against opposite sides of the workpiece stack-up, with the preheated welding electrode abutting the aluminum or aluminum alloy workpiece, and passing an electrical current between the two welding electrodes at a weld site to initiate and grow a molten weld pool within the aluminum or aluminum alloy workpiece.

First claim

The invention claimed is:

1. A method comprising:
providing a workpiece stack-up that includes a steel workpiece and an aluminum or aluminum alloy workpiece;
providing a first welding electrode for contacting the steel workpiece and a second welding electrode for contacting the aluminum or aluminum alloy workpiece;
preheating the second welding electrode by passing electrical current between the first and second welding electrodes to generate heat in the second welding electrode while cooling of the second welding electrode is restricted or halted, the preheating of the second welding electrode being performed before the second welding electrode is pressed against the workpiece stack-up;
pressing the first and second welding electrodes against opposite sides of the workpiece stack-up at a weld site after preheating, the first welding electrode abutting the steel workpiece and the second welding electrode abutting the aluminum or aluminum alloy workpiece; and
passing electrical current between the first and second welding electrodes and through the workpiece stack-up at the weld site to initiate and grow a molten weld pool within the aluminum or aluminum alloy workpiece.

2. The method as set forth in claim 1 , wherein the second welding electrode is constructed from a material that has an electrical conductivity of 3.48×10 7 S/m or less.

3. The method as set forth in claim 1 , wherein the second welding electrode includes an insert made of a metal material with an electrical resistivity that is greater than an electrical resistivity of a material of the second welding electrode.

4. The method as set forth in claim 3 , wherein the insert is made of a stainless steel, a copper-tungsten alloy, or molybdenum.

5. The method as set forth in claim 1 , wherein the preheating of the second welding electrode comprises restricting a cooling operation of the second welding electrode to 50% or less of the cooling operation at full capacity during passage of the electrical current.

6. The method as set forth in claim 1 , wherein the preheating of the second welding electrode comprises halting entirely a cooling operation of the second welding electrode during passage of the electrical current.

7. The method as set forth in claim 1 , wherein preheating brings the second welding electrode to a temperature between 200° C. and 900° C.

8. The method as set forth in claim 7 , wherein the second welding electrode is maintained at the temperature of between 200° C. and 900° C. during preheating and through initiation and growth of the weld pool within the aluminum or aluminum alloy workpiece.

9. The method as set forth in claim 1 , further comprising:
ceasing the passing of electrical current between the first and second welding electrodes and through the workpiece stack-up after the molten weld pool has been initiated and grown; and
keeping the first and second welding electrodes pressed against the workpiece stack-up until the molten weld pool initiated and grown within the aluminum or aluminum alloy workpiece has solidified into a weld nugget.

10. The method as set forth in claim 1 , wherein a thermocouple device or an optical infrared temperature measuring device measures a temperature of the second welding electrode at least during the preheating of the second welding electrode.

11. The method as set forth in claim 1 , wherein the second welding electrode has a larger body than the first welding electrode.

12. The method as set forth in claim 1 , wherein the preheating of the second welding electrode comprises:
bringing the first and second welding electrodes together such that a first weld face of the first welding electrode comes into direct contact with a second weld face of the second welding electrode;
passing electrical current between the first and second welding electrodes while the first and second weld faces are in contact.

13. The method as set forth in claim 1 , wherein the preheating of the second welding electrode comprises:
pressing the first and second welding electrodes in alignment against opposite sides of a plate, the plate being made of a metal material with an electrical resistivity that is greater than that of the second welding electrode;
passing electrical current between the first and second welding electrodes and through the plate.

14. The method set forth in claim 13 , wherein the plate is an exposed area of the steel workpiece that is not part of the workpiece stack-up.

15. A method comprising:
providing a workpiece stack-up that includes a steel workpiece and an aluminum or aluminum alloy workpiece;
bringing a first welding electrode and a second welding electrode together such that a first weld face of the first welding electrode comes into direct contact with a second weld face of the second welding electrode;
passing electrical current between the first and second welding electrodes at a current level of 20 kA to 40 kA while the weld faces of first and second welding electrodes are in direct contact and while cooling of the second welding electrode is restricted or halted to preheat the second welding electrode to a temperature between 200° C. and 900° C.;
separating the first welding electrode and the second welding electrode from each other;
pressing the first and second welding electrodes against opposite sides of the workpiece stack-up with the first welding electrode abutting the steel workpiece and the second welding electrode abutting the aluminum or aluminum alloy workpiece;
passing electrical current between the first and second welding electrodes and through the workpiece stack-up at the weld site to initiate and grow a molten weld pool within the aluminum or aluminum alloy workpiece; and
ceasing the passing of electrical current between the first and second welding electrodes and through the workpiece stack-up and allowing the molten weld pool to solidify into a weld nugget before retracting the first and second welding electrodes from the workpiece stack-up.

16. The method as set forth in claim 15 , wherein cooling of the second welding electrode is restricted when the weld faces of the first and second welding electrodes are in direct contact by restricting a cooling operation of the second welding electrode to 50% or less of the cooling operation at full capacity.

17. The method as set forth in claim 15 , wherein cooling of the second welding electrode is halted when the weld faces of the first and second welding electrodes are in direct contact.

18. The method as set forth in claim 15 , wherein the electrical current is passed between the first and second welding electrodes for 100 ms to 5,000 ms.

19. The method as set forth in claim 15 , wherein the second welding electrode is maintained at the temperature of between 200° C. and 900° C. during solidification of the molten weld pool.

20. A method comprising:
providing a workpiece stack-up that includes a steel workpiece and an aluminum or aluminum alloy workpiece;
providing a first welding electrode for contacting the steel workpiece and a second welding electrode for contacting the aluminum or aluminum alloy workpiece;
bringing a first weld face of the first welding electrode and a second weld face of a second welding electrode into direct contact with one another or into contact with opposite sides of a plate having an electrical resistivity that is greater than an electrical resistivity of the second welding electrode;
passing electrical current between the first and second welding electrodes while cooling of the s

Assignees

• Gm Global Tech Operations Llc

Inventors

• Schroth James G
• Sigler David R
• Perry Thomas A

Classifications

• B23K2103/20

  Ferrous alloys and aluminium or alloys thereof · CPC title

• B23K11/115

  by means of two electrodes placed opposite one another on both sides of the welded parts · CPC title

• B23K11/34

  Preliminary treatment · CPC title

• B23K11/20 Primary

  of different metals · CPC title

• B23K2203/20

  Operations & Transport · mapped topic