تجزیه و تحلیل حساسیت از فرآیندهای ماشین پرس با استفاده از مدل های اصطکاک مختلف مناسب برای مشکلات تماس غیر ثابت

This paper looks at the sensitivity of thickness to variation of friction. The models of friction used are: the classic Amontons–Coulomb; a nonlinear pressure-dependent model proposed by Wriggers, vu Van and Stein; and a velocity-dependent model proposed by Molinari, Estrin and Mercier. They are coded in FORTRAN for use with finite element program ABAQUS. The contact problem is then formulated in the total Lagrangian formulation for contact between an elastic–plastic body and rigid tools. The variational (weak) form of the formulation is given and this is discretized by finite element method. To test and compare the models, one common metal forming processes is simulated: deep drawing of a square-cup. The sensitivity graphs showing each of the three friction models together is given at the end. One other conclusion although not major part of this work is that Amonton–Coulomb is not the best model suited for contact conditions in metal forming processes, because Wriggers et al. model and Molinari et al. model provide better results for modelling bends and corners.

Stamping is a sheet metal forming process. Sheet metal forming is the process of converting a flat sheet of metal into a part of desired shape without fracture or excessive localized thinning. In stamping, a sheet metal called blank, is held on its edges by a blankholder and is deformed by a motion of a punch or die. The movement of the blank into the die cavity is controlled by a programmed pressure between the blankholder and the die, Davies [1]. The major problems encountered in sheet metal forming are fracturing, thinning, buckling and wrinkling, shape distortion, loose metal, and undesirable textures, Davies [1]. The success of these have been studied by a number of researchers. This depends largely on the input i.e., process parameters. The process parameter, that is considered in this paper, is friction i.e., friction models and a model variable. The mathematical problem solved in sensitivity analysis of stamping is the calculation of the change in thickness of a blank due to the friction variations of blanking for various friction models. The formula is equation(1) View the MathML sourceSensitivity=∂outputvariable∂friction, Turn MathJax on

The main achievements of this research are: 1. Sensitivity analysis of stamping processes subject to a variation of friction coefficient. 2. Modelling of one metal forming process, deep drawing of square cup, considering complexities of boundary conditions and models of stamping tools. 3. Investigation of the applicability of various friction models to modelling of metal forming processes. 4. Comparison of numerical results for various friction models. To accomplish this, each friction model was implemented in ABAQUS. The convergence of new dry models are typically higher than that for AC under the FEM program ABAQUS. This is due to the nonlinear nature of these models and slower convergence of the FEM solution. The accuracy of the results is not extensively investigated and no comparison to experiments was done, because of shortages in a budget for numerical calculations.