ORIGINAL ARTICLE The study of forming concave-bottom cylindrical parts in hydroforming process Masoomeh Salahshoor & Abdolhamid Gorji & Mohammad Bakhshi- Jooybari Received: 16 August 2014 /Accepted: 10 February 2015 # Springer-Verlag London 2015 Abstract Among the sheet-hydroforming techniques, hydro- dynamic deep drawing assisted by radial pressure has intro- duced good results for forming parts with high drawing ratio. Forming concave-bottom cylindrical parts is complicated through conventional deep drawing and requires several steps. Hydroforming is one of the techniques that can resolve such problems. In this paper, forming of concave-bottom parts has been studied by using finite element simulation and experi- ment through hydrodynamic deep drawing assisted by radial pressure. The effects of pressure path and geometrical param- eters of the punch on thickness distribution and punch force have also been investigated. The results illustrate that after forming the concave profile of the part, by increasing the maximum fluid pressure, the thickness of critical regions does not change. Thus, the pressure path with the lowest maximum pressure that can form the concave profile of the part is the best pressure path for forming a concave-bottom part. Mean- while, increasing the concavity height and punch corner radius affects thickness reduction in critical regions, but these param- eters do not have any significant effects on maximum punch force. Keywords Concave-bottom part . Cylindrical part . Deep drawing . Sheet hydroforming 1 Introduction Using advanced manufacturing processes with high flexi- bility and new materials is important in technology ad- vancement. Hydroforming is one of the main sheet metal-forming processes that attracted the attention of many researchers. This process has been developed at least since pre-World War II, but its application was lim- ited to some specific fields, but since the 1990s, it has been used in different industries, particularly in automo- tive industry [1]. In comparison to conventional deep drawing, sheet hydroforming contains many advantages, such as the capability of forming complex shapes, lower residual stress, better surface quality, better repeatability, less spring back, and better dimensional accuracy [2]. Many sheet materials can be formed in this process, such as steels, aluminum alloys, magnesium alloys, titanium alloys, copper, and composite sheets [3]. The more famil- iar sheet-hydroforming processes are rubber diaphragm hydroforming, hydro-mechanical deep drawing, hydro- dynamic deep drawing, hydro-rim deep drawing, sheet hydroforming with movable die, and hydrodynamic deep drawing assisted by radial pressure (HDDRP) [4]. Among the sheet hydroforming techniques, HDDRP has introduced good results for forming parts with high drawing ratio [5]. In this method, the fluid pressure is also inserted into the rim of the sheet to increase the drawing ratio and decrease the drawing force [6]. The effective parameters of sheet hydroforming process are the pre- bulging parameters, fluid pressure, die geometry, clear- ance between the punch and the die, and friction coeffi- cient [7]. In order to control the forming process, re- searchers have been trying to study the effect of these M. Salahshoor : A. Gorji (*) : M. B.<. Jooybari Department of Mechanical Engineering, Babol Noshirvani University of Technology, Babol 4714871167, Iran e-mail: hamidgorji@nit.ac.ir Int J Adv Manuf Technol DOI 10.1007/s00170-015-6908-6