Additive Manufacturing (AM) for metal part can be divided in to different types: The powder technology and the wire technology. Usually, powder is adapted for high precision component whereas wire is used for structural components and large scale part. One of the main benefits of AM is to simplify assemblies by reducing the number of components and also to provide a large freedom of design. A standard AM system consists of a combination of three blocs: a motion system, a heat source and a feedstock. For Wire Arc Additive Manufacturing (WAAM), the heat source is a welding generator and the feedstock is a wire. The motion system could be a 6 axis robot or a CNC machine. The welding process used in this paper is Cold Metal Transfer (CMT). The welding torch is fixed on a 6 axis robot. In contrast with usual AM which is generally limited to planar substrates, the goal of this paper is to manufacture structural stiffeners on curved aluminium alloy sheets. Theses stiffeners are made of walls welded on a substrate having a simple curvature. Before the manufacturing process, the first issue is the curvature measurement of the sheet which is a major problem to deal with. The second issue consists of AM paths generation. These are different from a classic AM paths, which are 2.5D Hence, the layer is a 3D path, depending on the sheet curvature. The third issue is the sheet metal fixation on the manufacturing table: the shape of the sheet must not move and the fixation must not distort the sheet. The final issue is the manufacturing process itself: the heat creates residual stresses and thermal deformation during the deposition. Finally, to improve the mechanical link between the walls and the metal sheet, the strategy on the first layers is different than the rest of the wall. Different welding modes are selected to improve the size of the melted area and the link with the substrate. To quantify the effect of manufacturing strategy, the strength of the different wall is measured by using a tensile machine.