The limit forming estimation of multi-stage thin-walled vessel cold forming technological process

Abstract

The multi-stage technological process of cold stamping of a thin-walled vessel made of sheet steel was evaluated taking into account technological heredity. The quality of the product is evaluated by the distance of its deformed state from the limit states on the strain diagram. To calculate the process, the model of large plastic deformations of the anisotropic shell is used, taking into account the dynamics and contact interactions with the tool, which was numerically implemented in the LS-DYNA® package. Models of plastic flow of an anisotropic sheet, associated with the Barlat criterion Yld 2000-2d, with the power law of isotropic strain hardening, the Peng - Landel potential of nonlinear elastic behavior of a polyurethane die, and the Coulomb friction law of contact interaction of the product with the tool are used from the package library. These models constants for low-carbon sheet steel DC04EK 0,7 mm and polyurethane SKU-PFL were identified from experimental data. The forming limit curve was built on the distortion of the coordinate grid near the zones of strain localization and failure of the vessel in the technological process without intermediate annealing and in the failure test under uniaxial tension. The features of the strain paths in the control points of the vessel at each stage of the technological process, including the sequence of operations of drawing, distributing and reduction, are studied. The path calculation was confirmed by an experiment using pressing equipment as a test. It is established that the operation of distributing the workpiece after its drawing quickly leads to the limit state and therefore requires a preliminary recovering the plasticity resource by annealing. There is a preference for forming the relief of the vessel by smaller degrees of distribution and greater degrees of reduction for elimination of the limit states and the operation of intermediate annealing.