The aim is to examine carefully the start of a press-braking process in which thin flat strips begin to be deformed in order to plastically form V-shaped items. To this end the large elastic deformation of strips in V-die bending is analysed to obtain the relationship between the punch force and the punch displacement. The process consists of two stages: air bending and partial straightening at the strip ends along the die. The range of applicability of the elastica-like solutions is discussed and provides criteria for the onset of plastic forming. Numerical results and magnitudes for load versus punch displacement, suitably non-dimensionalized, for 90° V-die bending, are presented.
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