The continuous die is not easy to use, the cost is high, the production cycle is long, and it is not easy to maintain, and a large tonnage punch is needed. You can bend Step 2 directly into a U-shape. Step 3, use two semicircular concave dies (a circle) to invert the U-shaped workpiece on the lower die, and then bend it into a cylindrical shape. You can also bend step 2 into a W-shape [wave shape] and directly bend it into a cylinder with the mold of step 4, but the positioning needs to be changed.