Expecting the unexpected, a must for accurate brakeforming

The paper describes the problems related to an oversimplification of the air bending process. It is explained that the bending process can consist of several stages, in particular the final stage can be different from case to case. Not recognising this often results in bending errors that are not understood. The behaviour of the sheet curvature during the bending process and for different tool parameters is described. The understanding of this behaviour is crucial for the correct calculation of the punch penetration and the bend allowance. The paper describes how these can be calculated in a correct manner, and also explains the consequences of applying models, standards or thumb rules that are valid for one phase to another phase. The problems emanating from this are discussed, and solutions are suggested. The main conclusion is that expecting the unexpected is the first step towards predicting the unexpected. This is a requirement for the successful use of air bending.