Investigations into the resistance spot welding of newly developed sheets made of higher-strength and ultrahigh-strength steels

At SLV Duisburg, higher-strength steel materials of the DP, RA, CP and MS types were investigated in various strength stages and coating variants.

Welding ranges were established for the characterisation of the weldability of the various materials - similar and in combinations. For the different variants, this was carried out on the basis of individual welding ranges with at least three force stages and a constant welding time. Where this appeared to be sensible, the welding times were also varied.

In order to guarantee the comparability of the values, the 2,500 N, 3,400 N and 5,000 N force stages as well as a welding time of 14 per were stipulated after preliminary tests for sheet thicknesses around 1.5 mm. For sheet thicknesses around 0.7 mm, the 1,700 N, 2,500 N and 3,400 N power stages were utilised with a welding time of 10 per.

The welding technology processing of newly developed, high-strength polyphase steels by means of resistance spot welding sets more stringent requirements on the electrode force to be applied. In the investigations, an adjustment of the welding parameters towards higher electrode forces led to a generally wider current range and to the formation of macroscopically flawless weld nuggets.