Effects of Ellipse Preforming on Cross-Sectional Shapes of Square Steel Pipe Formed by Roll Forming

Abstract

A square steel pipe is reshaped from a welded round pipe by roll forming. The effect of ellipse preforming on the cross-sectional size of the square steel pipe was investigated by experiment and three-dimensional finite element simulation. When designing a roll-forming machine for a square steel pipe, the diameter of the paired top and bottom rolls is usually set larger than that of the side roll pair, thereby avoiding interference between the roll axes driven by electric motors. When the diameter of the top roll is larger than that of the side roll, the width of a corner part of the formed pipe is larger than the height. A square pipe was formed from a preformed elliptical pipe to make the width and height of the corner part equal. As a result of ellipse preforming, the peripheral length of a square product increases and the size of the corner part of that product decreases. Therefore, elliptical preforming is effective in forming square pipe with a sharp corner. However, excessive preforming causes a hollow at the flat surface of a square product.