Analysis of Optimization of Blank Holding Force In Deep Drawing By Using LS DYNA

Sheet metal forming problems are typical in nature since they involve geometry, boundary and material non-linearity. Cup drawings involves many parameters like punch and die radius, clearance, lubrication, blank holding force and its trajectories etc. So designing the tools for cup drawing involves a lot of trial and error procedure. To reduce number of costly trial error steps, the process can be simulated by using finite element packages. Even the finite element package gives an approximation towards the solution. The experimentation is inevitable. The aim is to study analysis of optimization of blank holding force developed for cup drawing operation by using explicit finite element package LS DYNA. One of the basic problems in deep drawing is wrinkling. Wrinkling can be avoided by using blank holding force. But higher the blank holding force (BHF), higher is the frictional force, so more will be tensile stresses in cup wall there by promote tearing failure at the punch corner. Hence BHF needs to optimized so as to prevent the wrinkling and at the same time to prevent tearing failure. In this work die design is done for a cup of 30mm diameter and deep with 1 mm thickness. For the same blank holding force is calculated from the empirical formula. The same is simulated on an explicit finite element package LS DYNA. By an iterative procedure the optimum blank holding force is obtained and presented. B H F in deep drawing is an essential parameter to be determined optimally to avoid formation of wrinkles. It is also necessary to at the same time to determine the force in drawing operation and failure of the cup. Higher the B H F, higher is the frictional forces between the blank and blank holder, so higher the loads required for drawing operation and higher the strains developed in the cup walls between the die and punch, thereby reducing thickness of the section. In this thesis optimum blank holding force has been found out by checking the condition of nonformation of wrinkles at different coefficient of friction at (0.045, 0.06, 0.1, 0.13, and 0.15) and at different die radius (2, 3, 4, 5,6mm) and the values of blank holding force has been taken where no wrinkles has been formed for different coefficient of friction and for different die radius and the graphs are plotted and the results are studied. hMethod is used for mesh convergence stability of max vonmises stress is taken as a parameter to check the convergence.