Damage and fracture prediction during L-bending processes

Sheet metal bending processes is one of the most frequently used manufacturing operations in industry. The development and optimization of bending processes is connected with time consuming and costly experiments. Therefore, the finite clement simulation of the process could be a helpful tool for the designer and quality assurance of the products. The mechanical quality of a part produced by bending is determined by the material properties variation in the domain of the bending arc such as the hardening and damage states as a result of the increase in strain toward the inner and outer surfaces in the bending arc. The accuracy of the damage contour into the sheet is directly related to accuracy of the damage law modeling. After bending, springback occurs upon the removal of the tool. The amount of the elastic recovery depends on the stress level and the modulus of elasticity E of the material. The variations in mechanical sheet properties and sheet thickness after bending present problems as regards the calculation of the required punch displacement and the springback prediction of the bent part. As a result, bend angles arc often not accurate enough to meet today's high tolerance requirements. In order to improve the accuracy of the air bending process, the material properties variation during and after bending must be predicted especially the damage contour within the sheet. The paper describes a finite element model for L-bending process allowing for the prediction of the elastic springback.