A square steel pipe is reshaped from a welded round pipe by roll forming. We investigated the effect of the roll diameter on the crosssectional size of the square steel pipe by experimentation and three-dimensional finite element (FE) simulation. When the diameters of the top and bottom roll pairs are larger than those of the pair of side rolls, the cross section width of the formed pipe is less than the height. To equilibrate them, we perform finish forming at the final stage. Furthermore, the width of corner part of the formed pipe is greater than its height. The difference between these two sizes of width and height of the corner part in the final product is greater than those at upstream stands and increases with the ratio of the diameter of top and bottom roll pairs to that of side roll pairs. Offset the smaller roll pairs upstream makes the pipe square. Such offset is effective for producing pipes with equal width and height at the corner.
Square steel pipes are reshaped from welded round pipes by roll-forming. Pipe end deformation after cutting of the square steel pipe was investigated by experimentation and by three-dimensional finite element simulation. Each direction of the residual stresses composed of longitudinal stress and longitudinal-peripheral shear stress becomes reverse with respect to the outer and inner surfaces. A large opening deformation arises at the back end of the product by the release of those residual stresses. The side part receives bending deformation in the surrounding area of the contact zone with a roll. The residual stresses comprising longitudinal stress and longitudinal-peripheral shear stress increase as a result of the reverse bending deformation downstream of the roll center position. The absolute value of residual stress decreases with decreased initial wall thickness.
Square steel pipes are reshaped from welded round pipes by roll-forming. Effects of the roll diameter on the cross-sectional size of the square steel pipe were investigated by experimentation and three-dimensional finite element simulation. When the top roll diameter is greater than that of the side roll, then the width of a corner part of the formed pipe is greater than the height. The square steel pipe was formed by offsetting the small roll to the upstream side to make the width and height of a corner part equal. The offsetting result is affected by the longitudinal contact distance between a roll and a pipe. The geometric contact length and relative offset, the offsetting distance/geometric contact length, were defined. The optimum value of the relative offset was clarified, which increased with the expansion of the contact length of a top roll, the roll gap and the round pipe wall thickness.
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