The strength of incremental sheet forming is its high flexibility. The tool movement performs the forming operation and the geometric information of the product is stored in the tool path. The desired shape can be composed of concave and convex elements. The manufacturing of combined convex-concave shapes requires an additional support beneath the workpiece. This support can be a solid die or a second movable tool. Alternatively, a combined convex-concave shape can be produced by two concave forming operations. However, this strategy requires an intermediate turning of the workpiece. A novel type of incremental sheet forming process for producing combined convexconcave shapes without any solid support or turning steps is presented. This process is called incremental sheet forming with active medium. The combination of tool movement on the upper side and pressurisation by an active medium on the lower side of the workpiece enables convex forming operations. An experimental setup is developed to use pressurised air as active medium. Preliminary experiments successfully prove the feasibility of the new manufacturing process. However, the tool path for convex forming is plane and does not correspond to the three-dimensional target shape. These circumstances make it challenging to accurately produce both convex and combined convexconcave shapes. The subsequent goal is to understand the physical principles of convex forming and find methods to control the manufacturing process. Numerical and analytical techniques are used to identify the forming mechanisms. Experimental investigations reveal that convex forming is limited by cracks as well as grooves along the tool path. Moreover, the use of a constant pressure level does not lead to a steady state in the manufacturing process. Therefore, additional measures are required to achieve the target shape. A two-stage forming strategy and an optimised tool geometry are proposed to improve geometric accuracy. Although these measures have a positive influence on the forming process, they contradict the idea of a flexible manufacturing process without turning steps. Hence, the dynamical adjustment of the pressure during the manufacturing process by means of closed-loop control is a preferable method to reduce geometric deviations. The final experiments validate the effectiveness of the closed-loop control and demonstrate that the vertical forming force is stabilised by adjusting the pressure. The closed-loop control is a vital prerequisite for incremental sheet forming with active medium to exploit the potential of creating combined shapes.weiterlesen