Resistance spot welding process capable of eliminating welding nugget hole shrinkage defect of cold-rolling dual-phase steel plate

Abstract

The invention relates to a resistance spot welding process capable of eliminating a welding nugget hole shrinkage defect of a cold-rolling dual-phase steel plate. The process comprises the following steps that (a) at least one cold-rolling dual-phase steel plate is provided, and the cold-rolling dual-phase steel plate has the thickness of (t); (b) a preheating step is carried out, the cold-rolling dual-phase steel plate is preheated by PC (preheating current), and a calculation formula of the PC that PC is greater than or equal to 5t+4 (unit: kiloamperes) is obtained; (c), a welding step is carried out, the cold-rolling dual-phase steel plate is subjected to resistance spot welding by WC (welding current), and a calculation formula of the WC that WC is equal to blast current-0.2 (unit: kiloamperes) is obtained, wherein the blast current is the current when welding sparks start to occur. Therefore, the welding nugget hole shrinkage defect of the cold-rolling dual-phase steel plate can be completely eliminated, and the welding nugget bonding intensity is improved.

Description

technical field [0001] The invention relates to a resistance spot welding process, in particular to a resistance spot welding process capable of eliminating weld nugget shrinkage defects of cold-rolled dual-phase steel plates. Background technique [0002] Resistance spot welding is a main welding method used to join steel plates in the automobile manufacturing process. On average, each small car contains about 3600 welding points. In recent years, due to the increasing demand for lightweight car bodies, the proportion of high-tensile automotive steel plates used in car bodies has gradually increased. However, the tolerance of such steel plates to weld nugget defects has relatively decreased, especially those that lead to brittle fracture of weld nuggets. The main reason - shrinkage cavity defects. [0003] It is known that when the cold-rolled dual-phase steel plates are joined by resistance spot welding, under the welding current that has not yet produced flying explosion...

AI Technical Summary

Problems solved by technology

In recent years, due to the increasing demand for lightweight car bodies, the proportion of high-tensile automotive steel plates used in car bodies has gradually increased. However, the tolerance of such steel plates to weld nugget defects has relatively decreased, especially those that cause brittle fracture of weld nuggets. Main cause - shrinkage cavity defects

[0003] It is known that when cold-rolled dual-phase steel plates are joined by resistance spot welding, under the welding current that has not yet caused flying explosions (welding sparks), shrinkage defects are likely to occur between the steel plates due to incomplete welding, especially when the thickness of the steel plates exceeds 2mm , this kind of defect is more obvious, and the shrinkage cavity defect will lead to a decrease in the strength of the weld nugget and cause brittle fracture

It is known that the arc-shaped flat-top electrode tip is used to provide uniformly distributed compressive stress to reduce the occurrence of weld nugget defects, but this improvement method can only reduce the crack defects around the weld nugget, because of its influence on the central area of ​​the weld nugget. The pressure exerting ability is poor, so the unfavorable phenomenon that the shrinkage cavity defects are concentrated in the center of the weld nugget cannot be avoided after resistance spot welding

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