Research On Laser Gap-butt Joint Welding Of Automotive High-strength Steel With Hot Wire Filler

Laser welding has many advantages over traditional welding techniques in aspectsof precision, efficiency, reliability and automaticity. Recent years, as the requirementof energy saving and emission reduction, many automotive companies have carried outresearches on the reduction of car body weight. Laser welding, as one of the advancedmanufacturing techniques that promoting the reduction of car body weight, has beenused widely in the automotive industry. However, laser welding demands a hi ghprecision fit up of the workpiece, especially when a butt joint is used, which restrictsthe application of it on the automobile to a certain extent. In order to reduce the strictrequirement of fit up of the workpiece during laser welding, in this paper, experimenthas been conducted to weld the automotive high-strength steel with various butt jointgaps using laser welding with hot wire filler.Firstly, the feasibility of laser welding of automobile body-in-white has beenanalyzed, and some solutions to the feasibility issues, including the interference of thecomponents, the selection of the joint configuration and the clamping of theworkpieces, were proposed. The integrated fixture for laser cutting and laser weldingof the tube-like component were proposed, and a new structure was also designed for it.Secondly, the appropriate wire feeding parameters were selected for the laser weldingwith hot wire filler, the formula for calculating the wire temperature was obtained.Thirdly, the orthogonal test was conducted to the1.2mm automobile high-strengthsteel DP800with a small butt joint gap, and a set of optimized welding parameterswere obtained; and the wire temperature was measured with the thermal infraredimager under the optimized welding parameters, and the wire heating current for laserwelding of the workpiece with hot wire filler under various butt joint gap wascalculated. Lastly, laser welding of the steel plates with hot wire filler under variousbutt joint gaps was conducted, and fine welds were obtained with the optimizedwelding parameters.The welding result under various wire heating current was analyzed, and it could beconcluded that the wire heating current has an effect on the stability of the weldingprocess, when the wire heating current was appropriate, the welding process was stable;by comparing the result of the laser welding with the hot wire and cold wire, it was found that the required input power were reduced by12%when the hot wire was used.The properties of the welds with different butt joint gaps were inspected, including thedetection of the weld bead surface, the weld cross section, the tensile strength, theenergy spectrum analysis and the metallographical analysis. The distribution of wireelement among the weld was uniform, and the metallographic phase in the welds ofvarious butt joint gap was alike. The fine weld can be obtained when the butt joint gapis less than1.2mm; the tensile strength of the weld reaches the base metal when thebutt joint gap is less than1.0mm.By applying the laser welding with hot wire filler, the required butt joint gap canbe increased to a large extent, reducing the demanded fit up precision; and the requiredinput power is reduced using the laser welding with the hot wire filler compared to thecold wire filler, thus improved the power utilization efficiency.