Spot welding method for high-strength steel sheet excellent in joint strength

Abstract

When two high-strength steel sheets (1A, 1B) having a sheet thickness ratio of 2 to 5, inclusive, and both having a tension strength of 780 MPa to 1850 MPa, inclusive, are overlapped with each other and resistance spot welding is performed, a first energizing process that is a preliminary energization with an applied pressure of P1 kN and a welding current of I1 kA and a second energizing process that is a main energization with an applied pressure of P2 kN and a welding current of I2 kA are performed, wherein the sheet thickness ratio is defined as the ratio of the total steel sheet thickness to the thickness of a steel sheet on the thinner side (the thickness per sheet if the two steel sheets (1A, 1B) have the same thickness). The applied pressures P1 and P2 are set to a constant applied pressure of P = P1 = P2 through the first energizing process and the second energizing process. In addition, when an average sheet thickness of the steel sheets (1A, 1B) is assumed to be t mm, the applied pressure P is set in the range expressed by the formula {0.5 ≤ P ≤ 3.0t(1 / 3)}. The welding current I1 is set in the range of 30% to 90%, inclusive, of the welding current I2. The second energizing process is initiated within 0.1 s after the completion of the first energizing process.

Description

technical field [0001] The present invention relates to a spot welding method of a high-strength steel sheet having excellent joint strength by spot welding to form a welded portion in processes such as manufacturing of automobile parts or assembling a vehicle body. Background technique [0002] In recent years, in the automotive field, in order to reduce fuel consumption and reduce carbon dioxide gas (CO 2 ) for the purpose of reducing the weight of the vehicle body and improving crash safety, the demand for using high-strength steel sheets in the body or components is increasing. On the other hand, spot welding is mainly used in processes such as body assembly and component mounting. [0003] Tensile strength and fatigue strength are listed as important properties of a spot-welded joint (hereinafter referred to as a spot-welded joint), but tensile strength is the most important. The tensile strength of spot-welded joints includes tensile shear strength (TSS) measured by ...

AI Technical Summary

Problems solved by technology

When the above spatter occurs, it is difficult to ensure the nugget diameter of the size required for spot welding, and conversely, it sometimes promotes the occurrence of sinking

In such a case, there will be problems such as joint strength reduction or deviation

In addition, spatter may adhere to the periphery of the welded part, and when it needs to be removed, there is a problem that the workability is reduced.

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