US 12,186,828 B2
Double-sided friction stir welding method, methods for producing cold-rolled steel strip and coated steel strip, double-sided friction stir welding apparatus, and facilities for producing cold-rolled steel strip and coated steel strip
Muneo Matsushita, Tokyo (JP); Shohei Iwata, Tokyo (JP); and Yasushi Kitani, Tokyo (JP)
Assigned to JFE STEEL CORPORATION, Tokyo (JP)
Appl. No. 17/764,090
Filed by JFE STEEL CORPORATION, Tokyo (JP)
PCT Filed Sep. 18, 2020, PCT No. PCT/JP2020/035410
§ 371(c)(1), (2) Date Mar. 25, 2022,
PCT Pub. No. WO2021/060176, PCT Pub. Date Apr. 1, 2021.
Claims priority of application No. 2019-173666 (JP), filed on Sep. 25, 2019.
Prior Publication US 2022/0371119 A1, Nov. 24, 2022
Int. Cl. B23K 20/00 (2006.01); B23K 20/12 (2006.01); B23K 101/18 (2006.01); B23K 103/04 (2006.01)
CPC B23K 20/1255 (2013.01) [B23K 20/1225 (2013.01); B23K 20/123 (2013.01); B23K 2101/18 (2018.08); B23K 2103/04 (2018.08)] 5 Claims
OG exemplary drawing
 
1. A double-sided friction stir welding method comprising, in butt welding or lap welding between a tailing end of a preceding steel strip and a leading end of a following steel strip:
pressing two rotating tools, which are disposed on a first surface and a second surface of a butt portion or overlap portion of the steel strips, against the butt portion or overlap portion of the steel strips; and
moving the rotating tools in a welding direction while rotating the rotating tools in opposite directions to each other, so that an unwelded portion of the steel strips is softened by frictional heat generated between the rotating tools and the unwelded portion of the steel strips, and the softened portion is stirred with the rotating tools to generate plastic flow so as to weld the steel strips together,
wherein the two rotating tools each have an end portion formed to have a shape of one of a circular planar surface, a circular convex curved surface, and a circular concave curved surface,
the end portions are each made of a material harder than the steel strips,
wherein, when a height of the convex curved surface of each end portion is denoted by dv (mm), a diameter D (mm) of each end portion and the height dy of the convex curved surface satisfy formula (4):
dv/D≤0.06  (4),
wherein, when a depth of the concave curved surface of each end portion is denoted by dc (mm), the diameter D (mm) of each end portion and the depth dc of the concave curved surface satisfy formula (5):
dc/D≤0.03  (5),
wherein an inclination angle α(°) at which rotation axes of the two rotating tools are inclined backward in the welding direction with respect to a normal to a surface of the unwelded portion of the steel strips, the diameter D (mm) of each end portion, and a distance G (mm) between the end portions of the two rotating tools satisfy formula (1) and formula (2):
0≤α≤3  (1)
0.25×t−0.2×D×sin α≤G≤0.8×t−0.2×D×sin α  (2)
where t represents a thickness (mm) of each steel strip for butt welding of the steel strips, or a total thickness (mm) of the overlapped steel strips for lap welding of the steel strips, and
wherein the diameter D (mm) of each end portion satisfies formula (3):
4×t≤D≤20×t  (3).