The invention provides a method for manufacturing a finned square rectangular
steel tube. The method comprises the following steps: (1) carrying out trimming on the inner angle of the end face of a
welding edge, wherein the trimming angle phi is 45+ / -2 degrees, and the trimming left root h meets the equation: h=1 / 2 thickness of a plate+ / -0.5mm; (2) carrying out pre-profiling of cold bending on
strip steel through a die, and forming the shape and corresponding size of a product preliminarily; (3) carrying out extruding
welding through four rollers: using an upper
extrusion roller, a lower
extrusion roller, a left
extrusion roller and a right extrusion roller for extrusion, and bending a side extrusion roller of a finned edge by 3-6 degrees for carrying out high-frequency
welding on the end face of the welding edge and the surface of the inner side of the finned edge; (4) planning welding burrs: planning outer burrs through an arc blade and avoiding the finned edge, and regulating the angle of a planer tool until the included
angle alpha 1 between the planer tool and the vertical direction of the finned edge is 6 degrees, wherein the
angle alpha 2 of the bottom of a planer tool is 18 degrees; (5) carrying out
sizing shaping: when the four rollers are sized and shaped in an extrusion mode, bending the side extrusion roller of the finned edge by 2-3 degrees, and enabling the angle of the finned edge to meet the standard requests. The product produced through the method is good in shape of the cross section, good in surface quality, free of scratch, good in planeness, and stable and qualified in welding.