Abstract
Bending is one of the processes, which are most commonly performed in sheet metal forming. It is quite difficult to determine the moment of formation of defects in the form of cracks on the surface of the sheet metal. This is very often the criterion for the rejection of the product. For this reason, it is important to evaluate the state of the surface of the sheet metal along with the line of bending, because there are the largest deformations, leading to the formation of defects such as localized necking or cracks. Application of 3D digital microscope is presented to evaluate the surface condition of the V-bent specimens. The parameter Wmax obtained from the analysis of the geometry of the sheet metal surface with the usage of the 3D visualization is introduced. In contrast to the surface roughness parameters, it does not average the highest and the lowest points in the given area. Its value depends directly on the deepest localized necking currently occurring in the study area, which may be followed by a crack initiation. Due to this, it makes possible to define better the moment of cracking. Images of surfaces of V-bent specimens made of aluminum sheets EN AW-2017A (PA6) commonly used in the automotive and aerospace industries were subjected to detailed analysis. Using computer modeling of the bending process, the values of strain have been determined at the surface of the sheet in the bending line. On this basis, the analysis of dependence of the parameter Wmax on thickness of sheet metal as well as geometry of the tools has been conducted. The presented possibility of determining the moment of crack initiation allows to safely perform the bending process by avoiding formation of defects on the surface of the aluminum sheet.