Publications and presentations

Friction stir welding is an increasingly used method to join similar and dissimilar materials with excellent mechanical weld seam properties. However, in certain cases, friction stir welding is restricted by high mechanical loads as a result of high forces and torques during the welding process. This relates in particular stiffness-reduced machine concepts which may cause path deviations, massive vibrations and insufficient tool plunging. Against this background, this investigation demonstrates a method to reduce forces and torques by tool scaling. Due to the stepwise diameter reduction of shoulder and probe and a simultaneous adjustment of the process parameters, a significant force and spindle torque reduction was achieved. Furthermore, it could be shown that tool scaling does not affect the mechanical strength properties. The experimental investigations were carried out with EN AW 5754 H11 with a sheet thickness of 8 mm. The weld seams were performed on a robotized friction stir welding setup (KUKA KR500) with a maximum axial force of 10 kN. Based on a 26-mm shoulder and a 10-mm pin diameter, it could be demonstrated that the general weldability of 8 mm EN AW 5754 H11 is restricted (incomplete tool plunge) by the maximum axial force of the robotized friction stir welding setup (10 kN). Due to the stepwise reduction of the shoulder and probe diameter from 26 mm to 20.8 mm and 10 mm to 8 mm, respectively, a general weldability and weld seams without irregularities could be achieved by the equal robotized friction stir welding setup. Furthermore, it could be shown that an axial force and spindle torque reduction from 10 kN to 4 kN and 29 Nm to 10 Nm, respectively, was obtained due to further reduction of the tool diameters.

Metal-Plastic hybrid components and assemblies are gaining importance due to novel lightweight constructions and a growing integration of functions by using the right material at the right place. Thermal joining enables a joining technology for thermoplastic materials and engineering metals without using adhesive or joining elements. The paper provides novel investigations on the interaction between form fit and physicochemical interactions due to the combined use of specifically used oxide layers, interaction barriers and defined surface structuring by laser processing. Thereby, the design of experiments allows the investigation of the form fit as dominant interaction mode.

Nowadays, the use of light alloys in automotive and aerospace industries is increased, due to the higher demand for weight reduction. Substitution of copper by aluminium is widely persuaded in order to save weight and material costs, for battery components and wire connectors. The decreasing in the energy requirements of the manufacturing processes is also desirable, as well as the stability of material cost on the market. Therefore, the development of joining technologies of aluminium and its alloys, with acceptable weld characteristics and minimal energy consumption is demanded [1-3]. Friction stir welding (FSW) is the technique which was developed at The Welding Institute (TWI) UK in 1991 [3-8]. It offers various advantages such as small or no distortion, high mechanical properties, low energy consumption, no consumable material or shielding gas are needed, it offers convenient microstructure and is especially well suited to the welding of aluminium alloys [7]. The basic concept is relatively simple. A rotating tool with a special designed pin and shoulder penetrates the upper side of the sheet in the overlapping area until a certain plunge depth is reached. The process lasts until the sheets are joined. Then the rotational tool retracts, and a keyhole is formed. The keyhole affects surface quality and mechanical properties of the joints, especially on thin aluminium sheets. In this paper, the convex pin-less tool is used to overcome this disadvantage. The aim of this study is to evaluate influence of rotational speed on the microstructure of four-layer lap-joint from ultrathin aluminium-magnesium sheets during friction stir spot welding (FSSW).