A metallic plate is curved and folded by means of a press such that a curved portion is formed along an edge thereof, and two opposing straight portions are parallel, which are on two sides of the curved portion; the press includes first and second lower dies, and first and second hydraulic actuated upper dies; the first lower die has notches along it; the second lower die has a trench along it, whose cross-section is like an U; the second upper die has a pressing portion fitting the trench; the plate is first formed with two parallel folded portions, which each defines an obtuse angle, and together define an intermediate portion, with the notches and the first upper die; the width of the intermediate portion equals the arc length of the trench; next, the intermediate portion is sandwiched between and pressed with both the second dies to have the same curvature as the trench.