Influence of Welding Current and Electric Butt-Welding of Strip Conditions on the U-Channel Section Strength After Roll-Forming

At research of influence of connection conditions for strip blank with thickness from 1.0 mm to 1.35 mm by electric butt-welding on the tensile strength (Y
b
), the strength index (P) and percentage elongation (δ%) of the formed U-channel section in its flanges and in the web after multi-pass cold roll-forming experimentally varied of voltage in a secondary circuit of a weld coil from 2.7 V to 3.6 V were conducted. After tensile tests, data were obtained characterizing the dependence of the strength characteristics of the section on the thickness of the blank material at stable welding current modes of the butt-welding machine. It was found that the strength properties are distributed unevenly along the cross-section (length of the cross-weld seam), which is associated with unsatisfactory clamping of the strip ends during butt-welding in the mode of switching off (reducing) the welding current. The identified cases of decreased strength characteristics of the open section in one of the flanges and in the web should be unambiguously attributed to the influence of the initial non-parallelism of the ends of the strips to be welded. The welding current mode U = 2.7 V for a strip thickness of 1.0 mm showed the best results.