Numerical Damage Prediction and Experiments in Deep Drawing of Irregular Square Cup
Deep drawing is an important sheet metal forming process in the industry. The deep drawing of irregular square cup was investigated in this paper. To predict the damage of irregular square cup, different blank hold forces and blank shapes were studied in the numerical model. The experiment was carried out with the optimized blank force holder and blank shapes, the crack and thickness distribution were investigated. The results of the experiment accorded with those of the numerical simulations, which show the validity of the simulation to predict where the damaged zones will appear in the part during the deformation.
Deep drawing of square cups with magnesium alloy AZ31 sheets
The square cup drawing of magnesium alloy AZ31 (aluminum 3%, zinc 1%) sheets was studied by both the experimental approach and the finite element analysis. The mechanical properties of AZ31 sheets at various forming temperatures were first obtained from the tensile tests and the forming limit tests. The test results indicate that AZ31 sheets exhibit poor formability at room temperature, but the formability could be improved significantly at elevated temperatures up to 200 °C. The test results were then employed in the finite element simulations to investigate the effects of process parameters, such as punch and die corner radii, and forming temperature, on the formability of square cup drawing with AZ31 sheets. In order to validate the finite element analysis, the deep drawing of square cups of AZ31 sheets at elevated temperatures was also performed. The experimental data show a good agreement with the simulation results, and the optimal forming temperature, punch radius and die corner radius were then determined for the square cup drawing of AZ31 sheets.
An efficient pseudo-inverse approach for damage modeling in the sheet forming process
Abstract A simplified method called the “inverse approach” (IA) has been developed for sheet forming modeling. The assumptions of proportional loading and simplified tool actions lead to an “one step” algorithm. This IA is less accurate but much faster than classical incremental approaches, so it is largely used in the preliminary design of sheet forming tools. Numerous benchmark tests have proved that the IA gives a fairly good strain estimation but a poor stress estimation. The pseudo-inverse approach (PIA) was developed recently by the authors’ group, taking into account the loading history: some realistic intermediate configurations are determined without contact treatment to consider the loading history due to bending; and a new algorithm of plastic integration is proposed to consider bending–unbending effects. These new aspects in the PIA lead to a large improvement of the stress evaluation, which makes possible damage modeling in the sheet forming process. In this study, a simplified model of ductile damage based on continuum damage mechanics is implanted into the PIA. For this first exploration, the authors limit themselves to a material with isotropic hardening and damage. A 3D damage model in deformation is adopted: the assumptions of proportional loading and damage saturation after the damage threshold lead to an integrated damage evaluation method. A more accurate damage rate model is also developed which allows a strong coupling between plasticity and damage. These models are implemented in two ways: the inverse calculation is either coupled or uncoupled with the damage effect. The numerical results obtained show the feasibility of damage consideration in the PIA and the influence of damage effects on the sheet formability.