One of the most significant manufacturability-criterions of a tubular component in bending and/or hydroforming operation is the formability limit of the selected tube material. Currently the most common tool used to determine the material formability is the North American "standard" forming limit diagram (FLD) developed for low carbon sheet steels. It was shown, that applying the experimental FLDs developed for high strength steel materials or standard FLC on rotary draw bending process would, however, lead to under-utilization of the tube material. Therefore, on the basis of the elementary theory of bending and introducing the bendforming-related "Displacement of Neutral Axis" as a bend parameter, new relationships were developed for accurate prediction of principal bending strains. Subsequently, the residual strains from tubing process were taken in consideration to determine the exact bendability limit for tubular components in rotary draw bending. The position of so-called Bending Limit Curve "BLC" becomes, beside the wall thickness and the n-value of the tube material, also a function of outside diameter of considered tube.
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