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Among the sheet hydroforming processes, hydrodynamic deep drawing (HDD) process has been used to form complex shapes and can produce parts with high drawing ratio. Studies showed that radial pressure created on the edge of the sheet can decrease the drawing force and increase drawing ratio. Thus, increasing of radial pressure to an amount greater than chamber pressure, and independent control of these pressures, is the basic idea in this study. In this research, the effect of radial and chamber pressures on formability of St13 and pure copper sheets in the process of hydrodynamic deep drawing assisted by radial pressure (HDDRP) with inward flowing liquid is investigated. Giving that a significant portion of the maximum thinning of the formed part occurs in the beginning of the process, the pressure supply system used in the experimental tests was designed in a way, which provides simultaneous control of the radial and chamber pressures throughout the process. Thickness distribution, forming force, and tensile stresses are the parameters that were evaluated in this study. Results indicated that using a higher radial pressure than the chamber pressure and controlling their values in the initial stages of the process enhances the thickness distribution of the formed part in all regions. A comparison between the thickness distribution and maximum forming force of the formed parts by the HDDRP and HDDRP with inward flowing liquid methods showed that by applying the later method, parts with more uniform thickness distribution and less maximum thinning and forming force can be achieved.

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Hydrodynamic Deep Drawing (HDDRP), the combination of hydroforming and conventional deep drawing, accommodates the advantages of the two processes. A technique, called HDDRP with inward flowing liquid, has been introduced based on the idea of insertion of radial pressure around the blank rim. The radial pressure created on the blank edge, can increase the drawing ratio. Thus, increasing the radial pressure to an amount greater than the cavity pressure, and independent control of these pressures is the basic idea of this research for forming cylindrical parts. To perform the experiments, two independent pumps were used to provide the two pressures independently. The pressure supply system and the die set were designed in a way that provides simultaneous control of the pressures throughout the process. Then, the effects of radial pressure paths on thickness distribution of cylindrical St13 cups were investigated. In addition, a comparison between HDDRP and HDDRP with inward flowing liquid processes has been performed experimentally. Results indicated that using a higher radial pressure than the cavity pressure and controlling their values at any moment of the process enhances the thickness distribution of the formed part in all regions.