A welding method and a welding apparatus using the same control heat emission amounts of interfaces of a welding subject to be similar by adjusting cross-sectional areas of two welding tips arranged on both outer facing surfaces of a panel type welding subject, superimposed in multi-layers, to simultaneously form a nugget diameter.

A spot welded joint of at least two steel sheets is provided. At least one of the steel sheets presents yield strength above or equal to 600 MPa, an ultimate tensile strength above or equal to 1000 MPa, uniform elongation above or equal to 15%. The base metal chemical composition includes 0.05≤C≤0.21%, 4.0≤Mn≤7.0%, 0.5≤Al≤3.5%, Si≤2.0%, Ti≤0.2%, V≤0.2%, Nb≤0.2%, P≤0.025%, B≤0.0035%, and the spot welded joint contains a molten zone microstructure containing more than 0.5% of Al and containing a surface fraction of segregated areas lower than 1%, said segregated areas being zones larger than 20 μm.sup.2 and containing more than the steel nominal phosphorus content.

A spot welded joint of at least two steel sheets is provided. At least one of the steel sheets presents yield strength above or equal to 600 MPa, an ultimate tensile strength above or equal to 1000 MPa, uniform elongation above or equal to 15%. The base metal chemical composition includes 0.05≤C≤0.21%, 4.0≤Mn≤7.0%, 0.5≤Al≤3.5%, Si≤2.0%, Ti≤0.2%, V≤0.2%, Nb≤0.2%, P≤0.025%, B≤0.0035%, and the spot welded joint contains a molten zone microstructure containing more than 0.5% of Al and containing a surface fraction of segregated areas lower than 1%, said segregated areas being zones larger than 20 μm.sup.2 and containing more than the steel nominal phosphorus content.

Method for the manufacture of a galvannealed steel sheet includes the following steps: A) the provision of a pre-coated steel sheet coated with a first coating comprising iron and nickel, such steel sheet having the following chemical composition in weight percent 0.10<C<0.40%, 1.5<Mn<3.0%, 0.7<Si<2.0%, 0.05<Al<1.0%, 0.75<(Si+Al)<3.0% and on a purely optional basis, one or more elements such as Nb≤0.5%, B≤0.005%, Cr≤1.0%, Mo≤0.50%, Ni≤1.0%, Ti≤0.5%, the remainder of the composition making up of iron and inevitable impurities resulting from the elaboration, B) the thermal treatment of such pre-coated steel sheet at a temperature between 600 to 1000° C., C) the hot-dip coating of the steel sheet obtained in step B) with a second coating based on zinc and D) an alloying treatment to form a galvannealed steel sheet.

Method for the manufacture of a galvannealed steel sheet includes the following steps: A) the provision of a pre-coated steel sheet coated with a first coating comprising iron and nickel, such steel sheet having the following chemical composition in weight percent 0.10<C<0.40%, 1.5<Mn<3.0%, 0.7<Si<2.0%, 0.05<Al<1.0%, 0.75<(Si+Al)<3.0% and on a purely optional basis, one or more elements such as Nb≤0.5%, B≤0.005%, Cr≤1.0%, Mo≤0.50%, Ni≤1.0%, Ti≤0.5%, the remainder of the composition making up of iron and inevitable impurities resulting from the elaboration, B) the thermal treatment of such pre-coated steel sheet at a temperature between 600 to 1000° C., C) the hot-dip coating of the steel sheet obtained in step B) with a second coating based on zinc and D) an alloying treatment to form a galvannealed steel sheet.

The first database 38 outputs the welding current 44, the energization time 46, and the pressing force 48, etc. corresponding to the basic elements 32 including the kind of material, the thickness of material and the type of electrode. The second database 40 outputs the trend formula 52 used for correcting the output from the first database 38 depending on the property of the additional element 34. The element selecting device 36 selects an element and performs searching in the databases 38 and 40. The operating device 42 executes a correction operation process for applying the search result in the second database 40 to the search result in the first database 38, and outputs the welding condition 50 including the welding current 44, the energization time 46, and the pressing force 48.

The first database 38 outputs the welding current 44, the energization time 46, and the pressing force 48, etc. corresponding to the basic elements 32 including the kind of material, the thickness of material and the type of electrode. The second database 40 outputs the trend formula 52 used for correcting the output from the first database 38 depending on the property of the additional element 34. The element selecting device 36 selects an element and performs searching in the databases 38 and 40. The operating device 42 executes a correction operation process for applying the search result in the second database 40 to the search result in the first database 38, and outputs the welding condition 50 including the welding current 44, the energization time 46, and the pressing force 48.

A method for checking quality when resistance-welding workpiece includes pressing welding electrodes with an electrode force against a weld spot of the workpieces using an electrode drive and energizing the welding electrodes with a welding current for a duration of a welding time in order to liquefy a surface of the workpieces. The method further includes determining, at a first time before a beginning of the liquefaction, a first value of a welding electrode parameter identifying a position of one or both electrodes, and determining, at a second time after the beginning of the liquefaction, a second value of the welding electrode parameter identifying a position of one or both electrodes. The method further includes comparing the first value and the second value and, evaluating a quality of the welding process based on the comparison.

An apparatus for supplying a welding tip of a welder and an apparatus for replacing the same include a fixed bracket secured to a support. The apparatus includes an actuator coupled to the fixed bracket and a first moving member moved by the actuator. A second moving member is coupled to the first moving member and hingedly coupled to the fixed bracket. A third moving member is hingedly coupled to the second moving member. A first welding tip removal member is coupled to the third moving member to separate a welding to tip coupled to a shank. A fourth moving member is disposed opposite to the first moving member. A fifth moving member is coupled to the fourth moving member and hingedly coupled to the fixed bracket. A sixth moving member is coupled to the fifth moving member. A second welding tip removal member is coupled to the sixth moving member.

An apparatus for supplying a welding tip of a welder and an apparatus for replacing the same include a fixed bracket secured to a support. The apparatus includes an actuator coupled to the fixed bracket and a first moving member moved by the actuator. A second moving member is coupled to the first moving member and hingedly coupled to the fixed bracket. A third moving member is hingedly coupled to the second moving member. A first welding tip removal member is coupled to the third moving member to separate a welding to tip coupled to a shank. A fourth moving member is disposed opposite to the first moving member. A fifth moving member is coupled to the fourth moving member and hingedly coupled to the fixed bracket. A sixth moving member is coupled to the fifth moving member. A second welding tip removal member is coupled to the sixth moving member.