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Resistance spot welding steel and aluminum workpieces with electrode insert

  • US 9,999,939 B2
  • Filed: 12/05/2014
  • Issued: 06/19/2018
  • Est. Priority Date: 12/05/2014
  • Status: Active Grant
First Claim
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1. A method of resistance spot welding, the method comprising:

  • providing a workpiece stack-up that includes a steel workpiece and an aluminum or aluminum alloy workpiece;

    providing a first welding electrode confronting the aluminum or aluminum alloy workpiece and a second welding electrode confronting the steel workpiece, the first welding electrode having an electrode body and an insert, the insert being embedded within the electrode body such that an exposed surface of the insert and a surface of the electrode body that surrounds the insert together constitute a weld face of the first welding electrode, the insert having at least a peripheral portion adjacent to the surrounding electrode body that has an electrical conductivity less than or equal to approximately 20% of the electrical conductivity of commercially pure annealed copper as defined by the IACS as well as a thermal conductivity that is less than or equal to approximately 20% of the thermal conductivity of commercially pure annealed copper, the second welding electrode being composed of a copper alloy;

    bringing the first and second welding electrodes into contact with opposite sides of the workpiece stack-up with the first welding electrode making contact with the aluminum or aluminum alloy workpiece and the second welding electrode making contact with the steel workpiece;

    passing an electrical current between the first welding electrode and the second welding electrode to initiate and grow a molten weld pool within the aluminum or aluminum alloy workpiece, wherein both the exposed surface of the insert and the surface of the electrode body that surrounds the insert on the weld face of the first welding electrode make surface-to-surface contact with the aluminum or aluminum alloy workpiece at the start of current flow, and wherein the electrical current flows between the second welding electrode and the surface of the electrode body that surrounds the insert on the weld face of the first welding electrode such that the electrical current assumes a conical flow pattern within the aluminum or aluminum alloy workpiece and a current density of the electrical current decreases towards the first welding electrode; and

    ceasing the passing of the electrical current between the first welding electrode and the second welding electrode to allow the molten weld pool within the aluminum or aluminum alloy workpiece to solidify into an aluminum weld nugget that forms all or part of a weld joint between the steel and aluminum or aluminum alloy workpieces.

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