Determining material properties of sheet metal on a press brake

During the last decade, several attempts have been made to develop bending models for air bending. All models, whether they are sophisticated or very simple, need adequate input. Principally, the results of a bending model can never surpass the quality of the input. Whereas, e.g. the thickness of a sheet can be ascertained from straightforward measurements, the material properties are difficult to determine, and—in most cases—are not provided by the sheet metal manufacturer with adequate accuracy. In several studies it is shown that the influence of material properties on the output of bending models is substantial. For example Young’s modulus and the Ludwik–Nadai parameters are important in this respect. Based on the concepts derived from in-process control techniques, this paper describes a material test procedure that can ameliorate the input of bending models. The procedure is to be implemented on a standard press brake, without the aid of laboratory testing equipment. In order to determine the different material properties, the punch force–displacement diagram is recorded. Based on this diagram, and on fundamental knowledge of the air bending process, values for the material properties are deduced.