WELD SCHEDULE FOR RESISTANCE SPOT WELDING OF ALUMINUM ALLOY WORKPIECES
First Claim
1. A method of forming resistance spot welds on aluminum-based alloy workpieces, the method comprising:
- forming a stack of two or more sheets of aluminum-based alloy workpieces, the stacked workpieces having faying surfaces at a resistance weld site and opposing outer surfaces at the weld site;
pressing weld faces of opposing resistance weld electrodes against the outer surfaces of the workpieces at the weld site; and
while pressing the weld faces against the workpieces,passing a first stage weld current between the electrodes and through the workpieces at the weld site lasting for a first period of milliseconds, the current being increased to a first stage current value that reduces the electrical resistance between the weld faces to a stable resistance value and heats the workpieces for engagement with the weld faces without melting of the workpieces at their faying surfaces, and then, momentarily reducing current flow to zero with the electrodes still pressed against the surfaces of the workpieces;
passing a second stage weld current between the electrodes and through the workpieces at the weld site lasting for a second period of milliseconds, the peak current being increased to a second stage current value, larger than the first stage current value, for initiating molten weld nugget formation at the faying surfaces of the weld site, and, reducing current flow with the electrodes still pressed against the surfaces of the workpieces;
passing a third stage weld current between the electrodes and through the workpieces at the weld site lasting for a third period of milliseconds, the current being at a third stage rms current value, smaller than the second stage peak current value, for completing molten weld nugget formation at the faying surfaces of the weld site, the third stage being longer than the second stage, and, again, stopping current flow for cooling of the weld site and solidification of the weld nugget; and
thenremoving the weld faces of the opposing weld electrodes from contact with the outer surfaces of the workpieces.
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Accused Products
Abstract
Aluminum-base alloy workpieces have surfaces with films of aluminum oxide which inhibit good contact with weld faces of resistance spot weld electrodes and the faying surfaces of, for example, sheet workpieces stacked for welding. Sometimes, the surfaces of the sheets also are coated with an adhesive or a sealer which further complicates welding. But in accordance with this invention, weld faces of opposing, round, copper welding electrodes are pressed against opposite outside surfaces of the sheets at a spot weld site and weld current is applied to the electrodes in accordance with a three-stage weld schedule to better form each weld. The weld schedule comprises a Conditioning stage (stage 1), a weld nugget Shaping stage (stage 2), and a weld nugget Sizing stage (stage 3).
33 Citations
20 Claims
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1. A method of forming resistance spot welds on aluminum-based alloy workpieces, the method comprising:
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forming a stack of two or more sheets of aluminum-based alloy workpieces, the stacked workpieces having faying surfaces at a resistance weld site and opposing outer surfaces at the weld site; pressing weld faces of opposing resistance weld electrodes against the outer surfaces of the workpieces at the weld site; and
while pressing the weld faces against the workpieces,passing a first stage weld current between the electrodes and through the workpieces at the weld site lasting for a first period of milliseconds, the current being increased to a first stage current value that reduces the electrical resistance between the weld faces to a stable resistance value and heats the workpieces for engagement with the weld faces without melting of the workpieces at their faying surfaces, and then, momentarily reducing current flow to zero with the electrodes still pressed against the surfaces of the workpieces; passing a second stage weld current between the electrodes and through the workpieces at the weld site lasting for a second period of milliseconds, the peak current being increased to a second stage current value, larger than the first stage current value, for initiating molten weld nugget formation at the faying surfaces of the weld site, and, reducing current flow with the electrodes still pressed against the surfaces of the workpieces; passing a third stage weld current between the electrodes and through the workpieces at the weld site lasting for a third period of milliseconds, the current being at a third stage rms current value, smaller than the second stage peak current value, for completing molten weld nugget formation at the faying surfaces of the weld site, the third stage being longer than the second stage, and, again, stopping current flow for cooling of the weld site and solidification of the weld nugget; and
thenremoving the weld faces of the opposing weld electrodes from contact with the outer surfaces of the workpieces. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15)
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16. A method of forming resistance spot welds on aluminum-based alloy workpieces, the method comprising:
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forming a stack of two or more aluminum-based alloy workpieces, the stacked workpieces having faying surfaces at a resistance weld site and opposing outer surfaces at the weld site; pressing weld faces of opposing resistance weld electrodes against the outer surfaces of the workpieces at the weld site; and
while pressing the weld faces against the workpieces,passing a first stage weld current between the electrodes and through the workpieces at the weld site for a first stage time of milliseconds, the momentary current being slowly ramped to a first stage value that reduces the electrical resistance between the weld faces to a stable resistance value and heats the workpieces for engagement with the weld faces without melting of the workpieces at their faying surfaces, and then, momentarily reducing current flow to zero with the electrodes still pressed against the surfaces of the workpieces; passing a second stage weld current between the electrodes and through the workpieces at the weld site for a second stage time of milliseconds, the momentary current being quickly ramped to a second stage peak value, larger than the first stage peak current, for initiating molten weld nugget formation at the faying surfaces of the weld site, and, reducing current flow with the electrodes still pressed against the surfaces of the workpieces; passing a third stage weld current between the electrodes and through the workpieces at the weld site for a third stage time of milliseconds, the rms current being at a third stage value, smaller than the second stage peak current value, for completing molten weld nugget formation at the faying surfaces of the weld site, the third stage time being longer than the second stage time, and, again, stopping current flow for cooling of the weld site and solidification of the weld nugget; and
thenremoving the weld faces of the opposing weld electrodes from contact with the outer surfaces of the workpieces. - View Dependent Claims (17, 18, 19, 20)
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Specification