Bending behaviour and oil canning in roll forming a steel channel

Abstract

In roll forming a wide flat channel, problems were experienced with wrinkling, or 'oil canning' in the web. This is a common shape problem in roll forming wide panels that have flat regions in the profile. Coils from four different suppliers were used in production; with three of these, wrinkling could be controlled, but one coil had to be discarded. Tensile tests performed on all materials did not identify major differences in the coils although one material showed a slight indication of ageing. Free bending tests were performed with a new standalone bend tester specifically developed for material characterisation on the shop floor. The bending tests performed on strips cut in the longitudinal direction showed a greater difference between coils; the material giving unacceptable wrinkling had a significantly higher moment curvature characteristic indicating substantial ageing. All materials showed some coil set and the bending properties depended on the direction in which the specimen was bent, i.e. in the same or opposite direction to the coil set. A finite element analysis was performed on the process which indicated significant plastic deformation in the flange, but very little in the web. Possible links between the unusual bending behaviour and oil canning in the web are suggested and the work indicates the desirability of performing free bending tests in addition to the customary tensile testing in roll forming applications.

Flange wrinkling in incremental shape rolling

“…Four elements through the blank thickness were used with an element size of 1 mm and 2.5 mm in the X and the Z directions, respectively. A "frictionless contact" was assumed between the forming roll and the blank surfaces to avoid convergence issues [22]. To minimize the penetration of the rigid bodies into the blank surfaces at the constraint locations, the "hard contact condition" was applied [23].…”

Prototyping of straight section components using incremental shape rolling

“…Symmetry was applied to the blank with an X-lock boundary on all nodes along the symmetric line of the sheet to restrict material movement in the X-direction. A "frictionless contact" surface to surface contact interaction algorithm was applied between the forming roll and the sheet surfaces to avoid convergence issues [24]. The "hard contact condition" was used to minimize the penetration of the rigid surfaces into the sheet surfaces at the constraint locations [9].…”

A novel incremental sheet metal forming process for long and open section profiles

“…Only the transversal half of the profile was modelled due to the symmetry of the shape about the Y-Z plane. A "frictionless contact" was assumed between the forming roll and the blank surfaces to avoid convergence issues [12]. To minimize the penetration of the rigid bodies into the blank surfaces at the constraint locations, the "hard contact condition" was applied [13].…”