Optimization Process of Double Spots Welding of High Strength Steel Using in the Automotive Industry

Abstract

 Double spot welding for high-strength low alloy steel which is a new steel grade.  The results showed that optimum welding parameters are welding current of 8800 Amp, welding time of 20 cycles, and electrode force of 1900 N.  Pull out failure mode because of high plastic deformation.  The shunt effect phenomenon influences the mechanical properties of double spot welding.Resistance Spot Welding (RSW) is one of the most important welding techniques used in the automotive industry because it is an economic process and is suitable for many materials. Many parameters affect the mechanical and microstructural properties of nugget formation and its strength, like welding current, electrode force, and welding time. Therefore, optimizing the RSW process to get the optimum welding parameters is necessary for automobile manufacturing companies. High-strength steel is widely used in the automotive industry because of its superior characteristics such as high strength-weight ratio, ductility, fatigue, and corrosion resistance. This paper presents an optimization process for RSW using the Taguchi method for high strength low alloy steel (HSLA) DOCOL 500 LA, considered a new steel grade. Two spots were used in this work.The mechanical and microstructural tests are achieved to get the maximum nugget strength, nugget diameter, different welding zones microstructures, microhardness values, and failure modes. The results showed that optimum welding parameters were welding current of 8800 Amp, welding time of 20 cycles, and electrode force of 1900 N. The failure mode for optimum conditions was a full pullout with tearing of the welded sheets because of high plastic deformation and absorbed energy. The maximum microhardness value is in the fusion zone, the heat-affected region, and finally, in the base material due to the nugget zone's rapid melting and solidification process.

Mechanical behavior and failure mechanism of resistance spot welded Aluminum and Copper joint used in the lightweight structures

“…Increasing the concentration of heat makes the resulting joint much weaker. In dissimilar welds, two different metals are welded together that have different chemical compositions and mechanical properties (12).…”

“…It's the most widely used test due to the simple specimen form and type of loading. It shows if the weld meets the required levels of strength and ductility (12). A universal testing apparatus with a deformation rate of 1 mm/min was used to perform tensile-shear testing.…”

“…Generally, the quality of welded joints determines their structural integrity. Thus, in every manufacturing process, altering the welding procedure and ensuring the quality of the welded joints are crucial (9)(10)(11)(12).…”

The Electrical and Mechanical Aspects of Aluminum and Copper Resistance Spot Weld Joints

“…RSW is one of the greatest techniques for sheet metal manufacturing because of its simplicity, flexibility, and ability to offer features in the form of a workpiece [1][2][3][4][5][6][7][8]. RSW is a technique for joining two pieces of metal using an electric current to weld the lap joints in the interface surfaces [1,2,[6][7][8][9][10][11]. The structural strength and integrity mainly depend on the condition of the welded area [1,8,[12][13][14][15][16].…”

“…In previous studies, researchers have focused on microstructural changes, mechanical behavior, hardness, failure modes, mechanical properties, and the HAZ of RSW joints [1,10,11,22]. The electrical resistance in copper and aluminum alloys is wellknown.…”