Spot welding method
A spot welding method including: a main energization step of energizing a pair of opposing electrodes in pressure contact with both outer surfaces of a set of sheets where multiple sheet materials are stacked, thereby to cause melting between facing surfaces of the sheet materials; and a pressing variation step of, prior to the main energization step, causing a pulsation of pressing force applied to the set of sheets from the electrodes. A resin material such as an adhesive or a sealant may be interposed between the facing surfaces of at least a pair of the sheet materials. The period of the pulsation is 0.01 to 0.7 seconds. The amplitude of the pulsation is 10% to 90% with respect to a reference value of the pressing force. The set of sheets may include a first and a second steel sheet, and an aluminum alloy sheet that are stacked in order.
1 . A spot welding method comprising:
energizing a pair of opposing electrodes in pressure contact with both outer surfaces of a set of sheets comprising two or more sheet materials which are stacked, thereby to cause melting between facing surfaces of the two or more sheet materials; and
pulsating a pressing force applied to the set of sheets from the pair of opposing electrodes only prior to energizing the pair of opposing electrodes,
wherein each electrode in the pair of electrodes is in contact with a different outer surface of the set of sheets simultaneously.
2 . The spot welding method according to claim 1 , wherein the pulsation has a period of 0.01 to 0.7 seconds.
3 . The spot welding method according to claim 1 , wherein the pulsation has an amplitude that is 10% to 90% with respect to a reference value of the pressing force.
4 . The spot welding method according to claim 1 , wherein a resin material is interposed between the facing surfaces of the two or more sheet materials.
5 . The spot welding method according to claim 4 , wherein the resin material is an adhesive or a sealant.
6 . The spot welding method according to claim 1 , wherein each of the electrodes has a radius of curvature of 10 to 100 mm at a tip portion to be in contact with one of the sheet materials.
7 . The spot welding method according to claim 1 , wherein the set of sheets comprises at least a first steel sheet, a second steel sheet, and an aluminum alloy sheet that are stacked in order.
8 . The spot welding method according to claim 7 , wherein
the main energization step comprises:
generating a molten pool between the facing surfaces of the first steel sheet and the second steel sheet without melting the aluminum alloy sheet; and
causing a melting reaction between the facing surfaces of the second steel sheet and the aluminum alloy sheet after generating the molten pool between the facing surfaces,
the first steel sheet and the second steel sheet are joined via a first nugget, and
the second steel sheet and the aluminum alloy sheet are joined via a second nugget that contains an intermetallic compound generated by the melting reaction,
wherein the first and the second nugget are formed from the molten pool.
9 . The spot welding method according to claim 8 , further comprising
cooling after the generating of the molten pool and prior to the causing of the melting reaction, lowering a temperature of the set of sheets in contact with the electrodes through no energization or energization with a current value smaller than that during the generating of the molten pool.
10 . The spot welding method according to claim 1 , wherein the main energization step includes an upslope portion in which an amount of energization is gradually increased.