True strain distribution profile on sheet metal using different punch geometries
Changes are often necessary during the tryout of stamping tools. These changes may range from adjustments on die and punch designs to the selection of a new material with better formability characteristics. All these actions, however, require time and money creating the need for better initial sheet metal evaluation. Hence, increasing attention has focused on the development of laboratory tests that enable stamping companies to know more about the sheet metal stampability or that can, at least in part, ensure that their stamped products are produced without major problems. Identification of high stress region on stamping may allow for better tool stamping adjustment during tests, rendering a more uniform materials deformation and leading to the production of higher quality parts. Increasing attention has focused on the material evaluation based on the tool geometries in order to calculate the strain distribution. This study deals with an evaluation of four punch models with varied geometries in addition to the traditional Nakazima test tool. An evaluation was also made of the major true strain distribution profile at points distributed linearly from the region close to the die shoulder to the punch center.
Effect of friction coefficient in deep drawing of AA6111 sheet at elevated temperatures
Abstract The effect of friction coefficient on the deep drawing of aluminum alloy AA6111 at elevated temperatures was analyzed based on the three conditions using the finite element analysis and the experimental approach. Results indicate that the friction coefficient and lubrication position significantly influence the minimum thickness, the thickness deviation and the failure mode of the formed parts. During the hot forming process, the failure modes are draw mode, stretch mode and equi-biaxial stretch mode induced by different lubrication conditions. In terms of formability, the optimal value of friction coefficient determined in this work is 0.15. At the same time, the good agreement is performed between the experimental and simulated results. Fracture often occurs at the center of cup bottom or near the cup corner in a ductile mode or ductile–brittle mixed mode, respectively.
Prediction of forming limit diagrams with experimentally determined heterogeneity of anisotropic sheets
Abstract The heterogeneity coefficient described by surface roughness was introduced into Jalinier theory of computation of forming limit diagrams. The surface roughness is changed during sheet deformation, and in the same manner the heterogeneity coefficient is altered. Taking into account the changing of heterogeneity coefficient during forming of sheet resulted the better correlation between theory and experiments.