Mechanical properties of steels joined with spot welding process

In this thesis, it is aimed to produce steel beams with high bending strength by joining steel sheets and pipes by spot welding method. In the first stage, the effects of sheet thickness, welding current and number of spot welds on the tensile strength were investigated on the samples welded from the steel sheets in the form of small plates. It has been determined that the spot welds thrown close to the edge of the plate do not hold. It has been observed that the welding current, which gives the highest spot-welding strength, varies depending on the wall thickness of the joined sheets. The tensile strength of the junction area of the sheet metals joined by spot welding increased as the wall thickness increased. Increasing the number of spot welds from 1 to 2 significantly increased the tensile strength of the joint area, while increasing the number of spot welds to 3 or 5 did not significantly change the tensile strength. In the second stage, flanged pipes were produced by bending the pipe ends at an outward 90° angle of 0.6 mm, using prepared molds and a 200-ton press, in order to spot-weld the pipes to the sheets. By arranging the flanged pipes in such a way as to leave a pipe thickness gap between them, 64x370 mm beams were obtained by joining the sheet metal plates with 4 spot welding from the top and bottom per pipe. In the beams, the pipe diameter is 32 mm, the wall thickness is 0.7 mm, and the sheet thickness is 1,2 mm or 2 mm. The bending loads of the beams produced using sheet metal with 1,2 mm and 2 mm wall thickness were determined as 232.19 kg and 339.26 kg. In the bending test, the pipes transferred the load without bending. It was observed that while the deformation was limited in the lower and upper sheets of the beam with a sheet thickness of 2 mm, the spot welds in the junction areas were thrown and the beam deformation was shaped depending on this situation. It has been observed that with the reduction of the sheet thickness to 1.2 mm, the deformations of the lower and upper sheets of the beam have increased, and the spot welds in the joint area have preserved their strength. It has been observed that the number of spot welds should be increased in order to have higher bending strength. It was concluded that reducing the wall thickness of the pipes used can improve the energy dissipation behavior of the beam.