ORIGINAL ARTICLE Local deformation in roll forming Buddhika Abeyrathna 1 & Bernard Rolfe 2 & Peter Hodgson 1 & Matthias Weiss 1 Received: 29 January 2016 /Accepted: 23 May 2016 # Springer-Verlag London 2016 Abstract In a previous paper, a simple model was devel- oped to extend the application of the traditional flower pattern diagram as a design tool for roll forming. The position of a point on the strip as it passes through each set of rolls can be identified as a series of points in the two-dimensional flower pattern diagram. In three dimen- sions, these points will lie on a non-circular cylindrical surface having its axis parallel to the machine axis. Assuming that these points are joined by a smooth curve, the forming path of a point on the strip as it passes through the roll forming process can be obtained as a plane curve on the plane development of this surface. It was shown in previous work that the longitudinal mem- brane strain and, in certain cases, local curvature of the sheet are functions of the slope of this plane curve. In this work, the strains on both surfaces at the edge of a strip in the forming of a simple V-channel are measured using strain gauges. It is shown that near the point of contact with the rolls, the strains differ by nearly an order of magnitude from those determined from the simple model which assumes that the trajectory is a smooth curve. A modification of the forming path is obtained from the measured bending strains. Although the changes in dis- placement are small, the peak values of strain near the point of roll contact are large and a consequence of highly localised changes in the forming path as the strip passes over each roll. Measurement of this perturbation in the forming path is difficult as the region is obscured by the forming rolls. The technique described here permits the reconstruction of this path and identifies a new area of investigation of longitudinal strains in roll forming. These are often associated with shape defects such as bow, warping and end flare. Keywords Roll forming . Longitudinal edge strain . Local deformation 1 Introduction Roll forming is a well-established manufacturing process for making long products of constant cross section from sheet and strip; a coil is fed through a number of roll stands that incre- mentally bend the sheet to the desired profile. Historically, the flower pattern diagram has been used in the design of the pro- cess; in this diagram, cross-section profiles at each set of rolls are superimposed and a point on the strip as it passes through the rolls can be identified by a series of points on the diagram. Assuming these points can be joined by a smooth curve, the forming path can be constructed as a space curve [1]; they showed that this can be transformed to a plane curve and that the axial strain at the mid-surface, ε m , and longitudinal curva- ture of the flange, 1 ρ , at the point are functions of the local slope, β, of this plane curve, and are given approximately by ε m ¼ 1 2 β 2 and 1 ρ ¼ - β h ð1Þ where h is the distance from the longitudinal axis of bending to the point. * Buddhika Abeyrathna buddhika.a@research.deakin.edu.au 1 Institute for Frontier Materials, Deakin University, Waurn Ponds, Pigdons Rd., VIC 3216 Geelong, Australia 2 School of Engineering, Deakin University, Waurn Ponds, Pigdons Rd., VIC 3216 Geelong, Australia Int J Adv Manuf Technol DOI 10.1007/s00170-016-8962-0