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). A schematic view is shown in Fig. 1.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 the rupture to the product's safer upper-portion. The rim pressure acts on the rim of the flange and `extrudes' the material inward, resulting in significant reduction of tensile stress in the blank, which otherwise promotes undesired 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 to 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 `smart' control of the blank holder position, which allows for thickening of the flange and for decreasing 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 3.2 compared to the conventional LDR of about 2. This great difference is shown in Fig. 2.Another new improvement is based on the idea that surface roughening of the punch (namely higher frictional shear between the punch and the workpiece) in conjunction with hydroforming fluid pressure ensures a certain amount of reduction of the punch load for a given drawing ratio. The combination of normal fluid pressure and rough punch leads to transmission of frictional shear from the punch to the workpiece in the direction of the punch motion. Thus, the normal punch load acting on the bottom of the cup can be diminished, depending on the magnitude of the confining fluid pressure and the roughness of the moving punch. The resulting reduction of the load at the bottom of the cup provides the source for increasing the LDR. The advantage of using a rough punch is verified by numerous experiments using copper and aluminum thin blanks. An example of punch roughness is shown in Fig. 3 and the resulting load reduction in Fig. 4.
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