Development and Evaluation of a Robot Guided Friction Stir Welding Gun

Abstract Friction stir welding (FSW) generally involves considerable process forces that require the use of heavy and cost-intensive machines like heavy-duty robots with massive clamping and anvil structures, which limits the flexibility of the application. To address this challenge, the Steppwelder FSW gun was developed at the MPA University of Stuttgart. This innovative welding gun enables the production of short stitch welds that can function as stand-alone alternatives to spot welds or merge seamlessly into continuous welds. The C-shaped frame design enables a closed flux of force within the gun, making it suitable for the attachment to industry standard robots used in automotive body construction processes such as clinching, riveting, or resistance spot welding (RSW). This paper presents the overall design of the welding gun, featuring a spindle and a C-frame optimized for FSW, and examines two design iterations with a focus on their stiffness characteristics. The first design, version 1.5, is an early prototype developed to demonstrate the feasibility of the process. The second version 2.0 incorporates enhancements aimed at increasing stiffness and projection while reducing the installation space to prepare it for broader application. Both frame designs are modeled as digital twins (DT) in the ABAQUS simulation software, incorporating a force-time profile of up to 14 kN based on physical models. The elastic deformation behavior and precise deflection values were then qualitatively and quantitatively analyzed at defined measuring points. These DTs were validated and calibrated by using digital image correlation on their physical counterparts under applied force. The optimized design of the welding gun offers a robust system capable of delivering consistent and reliable results for friction stir stitch welding, addressing the growing demand for flexible joining solutions in lightweight materials and mega-casting applications.