Bending in a V-die has been used to indicate the outcome of bending in cold roll forming, although little direct correlation has been performed. In this work direct comparison of the springback in both processes was performed using six samples of automotive steels in a conventional roll forming line where the transverse springback is measured. A bend of similar radius was formed in a V-die and the springback determined. In general, the springback in V-die forming was greater than in roll forming, in some cases by a factor of 2. The theoretical springback angle was determined for all steels using a simple and approximate analytical equation and compared to the experimental roll forming and bending results. While for the roll forming process good agreement was achieved the theoretical values significantly underestimated springback in the V-bending process.

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The common grades of steel used in roll forming are: hot rolled, high strength low alloy and recovery annealed cold rolled sheet. These steels are prone to ageing and are often skin passed and/or roller leveled to eliminate ageing as this can lead to problems in forming. Shape defects such as bow, twist and camber can be increased due to a change of the elastic-plastic transition point of the material. In consideration of this effect the knowledge of the material properties in the elastic plastic transition range is necessary if the processes are to be modelled accurately. Previous studies have indicated that residual stresses are not well identified in the standard tensile test, but were shown clearly in a bending test. The elastic plastic transition in bending and the moment curvature characteristic were changed significantly by a light cold rolling reduction. In this work the FEA package Abaqus is used to investigate the effect of residual stresses introduced through skin passing and/or roller leveling on the bending/yielding behaviour of mild steel. Therefore, a skin passing/ roller leveling process is simulated, followed by a subsequent bending test. Residual stress free sheet is compared in bending to just "skin passed", "roller leveled" and a combined "skin passed and roller leveled" strip. Skin passing significantly reduces the bending yield stress due to residual stresses. This has a softening effect on subsequent bending operations. A roller level process prior to roll forming can restore the bending yield stress by reducing the residual stress across the thickness. This has implications for forming aged material.