Sheet Metal Hydroforming steel research int. 76 (2005) No. 11 891 Introduction Over the last ten years, High-Pressure Sheet Metal Form- ing (HBU) has been forcefully developed and advanced as an alternative to conventional deep drawing. Within the scope of comprehensive investigations the huge capability of HBU could be proved for complex axially symmetric sheet metal parts [1-6]. Based on the acquired knowledge, a unique 100 MN hydroform press including a sophisticated HBU tool system was designed and realised in order to use these potentials for the production of large area drawn parts with complex geometry details (figure 1) [7]. Special features of this machine are the horizontally aligned frame which consists of a cast core reinforced by tensioning wires, the short stroke locking cylinder, a special working media supply, and a tool change system which al- lows the part handling outside the press frame. The working media supply is particularly optimised for sheet metal hy- droforming. A filling cylinder generates a large volume flow by 30 MPa, supplemented by a pressure intensifier which generates low volume flows by pressures up to 200 MPa. High Pressure Sheet Metal Forming of Large Area Parts HBU tool. The main characteristic of working media based processes is the substitution of rigid tool components (i.e. punch or die) by a fluid. Instead of a punch, a pres- surised working medium is used in HBU processes to form the sheet metal into a die. Figure 2 shows an HBU tool with characteristic components: – Supply plate which closes the cavity by a sealing – Die – Multi-Point blank holder system for material flow control in the flange area After applying the necessary locking force, the process is initiated by a pump or a pressure intensifier which generate the required volume flow. Following a free form stage, the final shape is reached by the contact of the sheet with the die during a form-based stage and by calibration. Function sharing. The HBU tool design is based on a function sharing between locking and blank holder func- tion. Consequently, the blank holder force can be set inde- pendently of the locking force with a high accuracy in a wide range. Unlike the hydroforming of twin sheets, a con- flict of goals between material flow and leak tightness can be avoided. Multi point blank holder system. A multi point blank holder system, consisting of 10 membrane short stroke cylinders, can effectively control the local and temporal dis- tribution of the surface pressure, and consequently the ma- terial flow in the flange area. Segmented blank holder plates transmit the blank holder force on the sheet metal flange. Each membrane short stroke cylinder is controlled by a sep- arate proportional valve. Flange draw-in sensors measure the position of the sheet metal edge during the process [8]. The sensors are posi- Flow Control in High Pressure Sheet Metal Forming of Large Area Parts with Complex Geometry Details Michael Trompeter 1) , Erkan Önder 2) , Werner Homberg 1) , Erman Tekkaya 3) , Matthias Kleiner 1) 1) Institute of Forming Technology and Lightweight Construction (IUL), University of Dortmund, Germany 2) Department of Mechanical Engineering, Middle East Technical University (METU), Ankara, Turkey 3) Department of Manufacturing Engineering, ATILIM University, Ankara, Turkey Working media based forming processes show advantages compared to the conventional deep drawing in the range of sheet metal parts with complex geometry details. By High Pressure Sheet Metal Forming (HBU), complex parts can be formed with reduced tool costs, fewer process steps, and improved part properties, particularly by the use of high strength steels. In order to use these advantages to full capac- ity, the material flow into the area of the geometry details needs to be optimised. The key element for the material flow control is a multi-point blank holder. In combination with flange draw-in sensors, a closed loop flange draw-in control can be built up which guarantees a repro- ducible material flow and, consequently, defined part properties. Furthermore, a favourable pre-distribution of sheet metal material can be reached which leads to a widening of the process limits. Considering a large area sheet metal part with a complex door handle element as example, strategies for the material flow control will be discussed in this paper. The conclusions are based on FE-simulations as well as ex- perimental findings. Keywords: sheet metal hydroforming, process control, material flow, oscillating blank holder forces, 100 MN hydroform press, FEM Figure 1: 100 MN Hydroform press and HBU tool system.