|Ph.D Student||Peled Alon|
|Subject||"Smart" Deep Drawing|
|Department||Department of Mechanical Engineering||Supervisor||Professor Emeritus Jehuda Tirosh|
The goal of this work is to propose and test a new modified hydroforming process. External loads are applied to the workpiece on different surfaces by two independent fluid pressure sources: (a) the classical hydro-forming fluid pressure, which ‘warps’ the cylindrical portion of the product with a prescribed pressure (about 200 bars in our case); and (b) the fluid rim pressure, which acts radially on the outer edge of the flange with a prescribed pressure (about 1000 bars in our case).
The analysis shows that the modified hydro-forming process preserves the usefulness of the product and postpones, or even eliminates, rupture at the bottom of the product by shifting it (if it occurs) to the product's safer upper-portion. The rim pressure ‘extrudes’ the flange and causes plastic flow inward, resulting in significant reduction of tensile stress in the blank, which otherwise promotes early rupture.
One major complication in the design of the present experimental machine arises from potential leakage of the rim pressure into the flange area, which when it occurs causes a sharp increase of the load on the blank holder. A partial solution of this problem is to let the flange thicken at its rim. Under these conditions, the flange generates its own sealing, provided that the blank-holder is lifted accordingly. One unique feature of this new deep drawing machine is a ‘smart’ control of the blank holder position, which allows for the thickening of the flange and for the decreasing of the punch load (and thus the tensile stresses). Numerous tests were performed using this new machine and the resulting maximal drawing ratios (LDR) obtained were comparable with other published results. In some cases, this machine has produced, what is believed to be, the highest known LDR in a single stroke (reaching the value of 3-3.2).
The essential features of the present fluid assisted deep-drawing processes are modeled by treating the blank as a membrane of metal characterized by a few general constitutive laws for hardening and rate sensitive materials. This modeling procedure is different from the usual procedures based on bounds or perturbation analysis. An exact solution of these model equations is developed which clearly demonstrates that the control of the rim pressure and the blank holder's position are the major factors in reaching high drawing ratios before rupture. Results of numerical simulations using commercial codes (ABAQUS and DYTRAN) also matched the experimental findings.