RESISTANCE SPOT WELDING OF ALUMINUM-TO-ALUMINUM, ALUMINUM-TO-STEEL, AND STEEL-TO- STEEL IN A SPECIFIED SEQUENCE AND USING A COVER

• US 20170297138A1
• Filed: 04/19/2017
• Published: 10/19/2017
• Est. Priority Date: 04/19/2016
• Status: Active Grant

• Current Assignee: GM Global Technology Operations LLC (General Motors Company)
• Original Assignee: GM Global Technology Operations LLC (General Motors Company)
• Inventors: Sigler, David R., Carlson, Blair E., Karagoulis, Michael J.
• Granted Patent: US 10,682,724 B2
• Time in Patent Office: Days
• CPC Class Codes: B23K 11/115 by means of two electrodes placed opposite one another on both sides of the welded parts
• CPC Class Codes: B23K 11/166 of galvanized or tinned materials
• CPC Class Codes: B23K 11/185 of aluminium or aluminium alloys
• CPC Class Codes: B23K 11/20 of different metals
• CPC Class Codes: B23K 11/24 Electric supply or control circuits therefor
• CPC Class Codes: B23K 11/3009 Pressure electrodes
• CPC Class Codes: B23K 11/3063 Electrode maintenance, e.g. cleaning, grinding
• CPC Class Codes: B23K 11/315 with one electrode moving on a linear path
• CPC Class Codes: B23K 2101/006 Vehicles
• CPC Class Codes: B23K 2101/185 Tailored blanks
• CPC Class Codes: B23K 2103/04 Steel or steel alloys
• CPC Class Codes: B23K 2103/10 Aluminium or alloys thereof
• CPC Class Codes: B23K 2103/20 Ferrous alloys and aluminium or alloys thereof

Abstract

A series of many electrical resistance spot welds is to be formed in members of an assembled, but un-joined, body that presents workpiece stack-ups of various combinations of metal workpieces including all aluminum workpieces, all steel workpieces, and a combination of aluminum and steel workpieces. A pair of spot welding electrodes, each with a specified weld face that includes oxide-disrupting features, is used to form the required numbers of aluminum-to-aluminum spot welds, aluminum-to-steel spot welds, and steel-to-steel spot welds. A predetermined sequence of forming the various spot welds may be specified for extending the number of spot welds that can be made before the weld faces must be restored. And, during at least one of the aluminum-to-steel spot welds, a cover is inserted between the weld face of one of the welding electrodes and a side of a workpiece stack-up that includes the adjacent aluminum and steel workpieces.

Claims

1. A method of resistance spot welding workpiece stack-ups of different combinations of metal workpieces with a single weld gun using the same set of welding electrodes, the method comprising:

providing a weld gun that carries a set of opposed welding electrodes, each of the opposed welding electrodes having a weld face that comprises oxide-disrupting structural features;

forming a set of aluminum-to-aluminum spot welds, each of the aluminum-to-aluminum spot welds comprising an aluminum nugget that fusion welds two or more aluminum workpieces together;

forming a set of aluminum-to-steel spot welds, each of the aluminum-to-steel spot welds comprising a weld joint contained within an aluminum workpiece that weld bonds the aluminum workpiece to an adjacent steel workpiece, and wherein forming at least one of the set of aluminum-to-steel spot welds comprises inserting a cover between a weld face of one of the opposed welding electrodes and a side of a workpiece stack-up that includes the aluminum workpiece and the adjacent steel workpiece to isolate the weld face from the side of the workpiece stack-up during current flow through the workpiece stack-up; and

forming a set of steel-to-steel spot welds, each of the steel-to-steel spot welds comprising a steel nugget that fusion welds two or more steel workpieces together.

2. The method set forth in claim 1, wherein the oxide-disrupting structural features on one or both of the weld faces of the opposed welding electrodes comprises a series of upstanding circular ridges that are centered about and surround a central axis of the weld face and which project outwardly from a base weld face surface of the weld face, the series of upstanding circular ridges including anywhere from two circular ridges to ten circular ridges starting from an innermost ridge that immediately surrounds the central axis of the weld face and ending with an outermost ridge that is farthest from the central axis of the weld face.

3. The method set forth in claim 1, wherein the oxide-disrupting structural features on one or both of the weld faces of the opposed welding electrodes comprises a series of recessed circular grooves that are centered about and surround a central axis of the weld face and which intrude inwardly into a base weld face surface of the weld face, the series in recessed grooves including anywhere from two circular grooves to ten circular grooves starting from an innermost groove that immediately surrounds the central axis of the weld face and ending with an outermost groove that is farthest from the central axis of the weld face.

4. The method set forth in claim 1, wherein the set of opposed welding electrodes includes a first welding electrode having a first weld face and a second welding electrode having a second weld face, the first weld face being pressed against the cover, which is inserted between the first weld face and an aluminum workpiece surface at a first side of the workpiece stack-up, and the second weld face being pressed against a steel workpiece surface at a second side of the workpiece stack-up during formation of the at least one aluminum-to-steel spot weld.

5. The method set forth in claim 4, wherein the set of aluminum-to-aluminum spot welds is formed first, the set of aluminum-to-steel spot welds is formed after the set of aluminum-to-aluminum spot welds, and the set of steel-to-steel spot welds is formed after the set of aluminum-to-steel spot welds.

6. The method set forth in claim 4, wherein the set of aluminum-to-aluminum spot welds is formed first, the set of steel-to-steel spot welds is formed after the set of aluminum-to-aluminum spot welds, and the set of aluminum-to-steel spot welds is formed after the set of steel-to-steel spot welds, and, wherein, during formation of each of the set of aluminum-to-steel spot welds, the cover is inserted between the first weld face of the first welding electrode and the aluminum workpiece surface at the first side of the workpiece stack-up to isolate the first weld face from the aluminum workpiece surface.

7. The method set forth in claim 4, wherein the cover is a cover plate constructed of material that is more electrically resistive than the first welding electrode and the aluminum workpiece that is bonded to the steel workpiece by the at least one aluminum-to-steel spot weld.

8. The method set forth in claim 7, wherein the cover plate is constructed from a low carbon steel, molybdenum or a molybdenum-based alloy, niobium or a niobium-based alloy, tungsten or a tungsten-based alloy, or a refractory metal composite.

9. The method set forth in claim 4, wherein the cover plate is constructed from a copper alloy that is less electrically resistive than the aluminum workpiece that is bonded to the steel workpiece by the at least one aluminum-to-steel spot weld, yet is more electrically resistive than the first welding electrode.

10. The method set forth in claim 1, wherein the set of opposed welding electrodes includes a first welding electrode having a first weld face and a second welding electrode having a second weld face, the first weld face being pressed against an aluminum workpiece surface at a first side of the workpiece stack-up and the second weld face being pressed against the cover, which is inserted between the second weld face and a steel workpiece surface at a second side of the workpiece stack-up, during formation of the at least one aluminum-to-steel spot weld.

11. The method set forth in claim 10, wherein the set of aluminum-to-aluminum spot welds is formed first, the set of aluminum-to-steel spot welds is formed after the set of aluminum-to-aluminum spot welds, and the set of steel-to-steel spot welds is formed after the set of aluminum-to-steel spot welds.

12. The method set forth in claim 10, wherein the set of aluminum-to-steel spot welds is formed first, the set of aluminum-to-aluminum spot welds is formed after the set of aluminum-to-steel spot welds, and the set of steel-to-steel spot welds is formed after the set of aluminum-to-aluminum spot welds, and, wherein, during formation of each of the set of aluminum-to-steel spot welds, the cover is inserted between the second weld face of the second welding electrode and the steel workpiece surface at the second side of the workpiece stack-up to isolate the second weld face from the steel workpiece surface.

13. The method set forth in claim 10, wherein the cover is a cover plate that includes a planar base and an outwardly extending dome portion, the second weld face of the second welding electrode being pressed against the planar base and the outwardly extending dome portion being pressed against the steel workpiece surface of the second side of the workpiece stack-up.

14. The method set forth in claim 10, wherein the outwardly extending dome portion of the cover plate has a diameter that is less than a diameter of the second weld face of the second welding electrode.

15. The method set forth in claim 14, wherein the outwardly extending dome portion is spherically shaped with a radius of curvature that ranges from 4 mm to 12 mm.

16. The method set forth in claim 10, wherein the cover is constructed from a copper material.

17. The method set forth in claim 1, wherein each of the set of aluminum-to-aluminum spot welds, the set of aluminum-to-steel spot welds, and the set of steel-to-steel spot welds is formed throughout a unitary body-in-white structure of an automotive passenger vehicle.

18. The method set forth in claim 1, further comprising periodically restoring each of the weld faces of the set of opposed welding electrodes.

19. The method set forth in claim 1, wherein inserting the cover comprises rotating an arm that carries the cover about a pivot axis to bring the cover into an inserted position in which the cover is located between the weld face of one of the opposed welding electrodes and the side of the workpiece stack-up.