Mating electrodes for resistance spot welding of aluminum workpieces to steel workpieces

Patent metadata

Field	Value
Publication number	US-10766095-B2
Application number	US-201715442155-A
Country	US
Kind code	B2
Filing date	Feb 24, 2017
Priority date	Mar 1, 2016
Publication date	Sep 8, 2020
Grant date	Sep 8, 2020

Abstract

A spot weld may be formed between an aluminum workpiece and an adjacent overlapping steel workpiece with the use of opposed spot welding electrodes that have mating weld faces designed for engagement with the outer surfaces of the workpiece stack-up assembly. The electrode that engages the stack-up assembly proximate the aluminum workpiece includes a central ascending convex surface and the electrode that engages the stack-up assembly proximate the steel workpiece has an annular surface. The mating weld faces of the first and second spot welding electrodes distribute the passing electrical current along a radially outwardly expanding flow path to provide a more uniform temperature distribution over the intended spot weld interface and may also produce a deformed bonding interface within the formed weld joint. Each of these events can beneficially affect the strength of the weld joint.

First claim

The invention claimed is:

1. A method comprising:
providing a workpiece stack-up assembly that comprises a steel workpiece and adjacent aluminum workpiece that overlaps with the steel workpiece to establish a faying interface therebetween, the workpiece stack-up assembly having a first outer surface proximate the aluminum workpiece and an opposed second outer surface proximate the steel workpiece;
pressing a first spot welding electrode against the first outer surface of the workpiece stack-up assembly, the first spot welding electrode comprising a weld face that includes a central ascending convex surface that rises above an annular surface that surrounds the central ascending convex surface, wherein, at least initially, the central ascending convex surface makes contact with the first outer surface of the workpiece stack-up assembly and the surrounding annular surface of the weld face of the first welding electrode does not;
pressing a second spot welding electrode against the second outer surface of the workpiece stack-up assembly, the second spot welding electrode comprising a weld face that includes a central descending concave surface that drops below an annular surface that surrounds the descending concave surface, wherein, at least initially, the annular surface of the weld face of the second welding electrode makes contact with the second outer surface of the workpiece stack-up assembly and the descending concave surface does not;
passing an electrical current between the weld faces of the first and second spot welding electrodes across the faying interface of the steel and aluminum workpieces to cause melting of the aluminum workpiece and the formation of a molten weld pool within the aluminum workpiece that wets an adjacent surface of the steel workpiece, the electrical current being distributed along a radially outwardly expanding flow path that extends from the ascending convex surface of the weld face of the first spot welding electrode to the annular surface of the weld face of the second spot welding electrode such that a density of the electrical current is higher in the aluminum workpiece at an interface with the central ascending convex surface of the weld face of the first spot welding electrode than in the steel workpiece at an interface with the annular surface of the weld face of the second spot welding electrode; and, thereafter,
terminating passage of the electrical current between the weld faces of the first and second spot welding electrodes so that the molten weld pool solidifies into a weld joint that bonds the steel and aluminum workpieces together, and wherein the weld joint includes a bonding interface with the adjacent surface of the steel workpiece that is deformed toward the central descending concave surface of the weld face of the second spot welding electrode.

2. The method set forth in claim 1 , wherein an outer workpiece surface of the aluminum workpiece provides the first outer surface of the workpiece stack-up assembly and an outer workpiece surface of the steel workpiece provides the second outer surface of the workpiece stack-up assembly, and wherein the first spot welding electrode is pressed against the outer workpiece surface of the aluminum workpiece and the second spot welding electrode is pressed against the outer workpiece surface of the steel workpiece.

3. The method set forth in claim 1 , wherein the aluminum workpiece comprises an aluminum alloy substrate having a surface oxide layer thereon.

4. The method set forth in claim 1 , wherein the central ascending convex surface of the weld face of the first welding electrode is a sectional portion of a sphere having a radius of curvature between 50 mm and 5 mm.

5. The method set forth in claim 1 , wherein the central descending concave surface of the weld face of the second welding electrode is an intruding depression of a sectional portion of a sphere having a radius of curvature between 50 mm and 5 mm.

6. The method set forth in claim 1 , wherein a constant gap equal to an overall thickness of the workpiece stack-up assembly is maintained between the central ascending convex surface and the central descending concave surface during passage of the electrical current between the first and second spot welding electrodes.

7. The method set forth in claim 1 , wherein the annular surface of the weld face of the first welding electrode comes into contact with the first outer surface of the workpiece stack-up assembly during passage of the electrical current between the weld faces of the first and second spot welding electrodes, thereby causing the radially outwardly expanding flow path of the electrical current to cease to exist.

8. A method comprising:
pressing a central ascending convex surface of a weld face of a first spot welding electrode against a first outer surface of a workpiece stack-up assembly that includes a steel workpiece and an adjacent aluminum workpiece that overlaps with the steel workpiece, the first outer surface of the workpiece stack-up assembly being proximate the aluminum workpiece;
pressing an annular surface of a weld face of a second spot welding electrode against a second outer surface of the workpiece stack-up assembly that is opposed to the first outer surface, the annular surface of the weld face of the second spot welding electrode surrounding a central descending concave surface that extends below the annular surface of the weld face of the second spot welding electrode and is complimentary in shape to the central ascending convex surface of the weld face of the first spot welding electrode, the second outer surface of the workpiece stack-up assembly being proximate the steel workpiece, and wherein the weld face of the first spot welding electrode and the weld face of the second spot welding electrode are aligned with and centered on a common axis;
forming a resistance spot weld that bonds together the steel and aluminum workpieces, wherein forming the resistance spot weld comprises passing an electrical current between the central ascending convex surface of the weld face of the first spot welding electrode and the annular surface of the weld face of the second spot welding electrode so that the electrical current passed between the weld face of the first spot welding electrode and the weld face of the second spot welding electrode is distributed along a radially outwardly expanding flow path that extends from the first spot welding electrode to the second spot welding electrode such that a density of the electrical current is higher in the aluminum workpiece at an interface with the central ascending convex surface of the weld face of the first spot welding electrode than in the steel workpiece at an interface with the annular surface of the weld face of the second spot welding electrode.

9. The method set forth in claim 8 , wherein the spot weld is comprised of a weld joint contained entirely within the aluminum workpiece that includes a bonding interface with an adjacent surface of the steel workpiece that is deformed toward the second spot welding electrode.

10. The method set forth in claim 8 , wherein the weld face of the first spot welding electrode further includes an annular surface that surrounds the central ascending convex surface.

11. The method set forth in claim 10 , wherein the central ascending convex surface of the weld face of the first welding electrode is a sectional portion of a sphere having a radius of curvature between 50 mm and 5 mm.

12. The method set forth in claim 8 , wherein the central descending concave surface of the weld face of the second welding electrode is an intruding depression of a sectional portion of a sphere having a ra

Assignees

• Gm Global Tech Operations Llc

Inventors

• Wang hui-ping
• Carlson Blair E
• Sigler David R
• Karagoulis Michael J

Classifications

• B23K2101/34

  Coated articles {; Surface treated articles} · CPC title

• B23K11/30 Primary

  Features relating to electrodes · CPC title

• B23K11/11

  Spot welding · CPC title

• B23K11/163

  Welding of coated materials · CPC title

• B23K11/115

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