Extending geometric flexibility in friction welding: A comparative study of orbital and rotary friction welding

Manufacturing processes are increasingly challenged by the demand for complex geometries, locally tailored properties, and a high degree of functional integration. In this context, solid-state joining technologies offer significant advantages due to their low heat input, limited distortion, and favorable microstructural characteristics. Rotary friction welding (RFW) is a well-established and robust process; however, its kinematic characteristics impose inherent limitations on geometric applicability. In RFW, the purely rotational motion results in a relative velocity of zero at the rotation axis, increasing linearly with radius, leading to a non-uniform distribution of heat input. In contrast, orbital friction welding (OFW) is characterized by a constant relative movement between the joining partners, promoting a more uniform frictional heat generation over the entire interface. Furthermore, orbital kinematics enable the joining of non-axisymmetric geometries, overcoming the limitations of RFW. In this work, a comparative experimental study of OFW and RFW is presented. A custom-designed test rig was developed to perform both processes on a single platform under controlled and directly comparable conditions. S235JRC+C steel was used as a reference material system. Mechanical characterization was conducted by tensile testing, while metallographic cross-sections and hardness measurements were used to analyze weld formation and microstructural evolution. The results demonstrate that OFW produces metallurgically sound joints with promising mechanical performance and enables the joining of non-axisymmetric components. In addition, the developed high-speed OFW test rig enables significantly higher relative velocities compared to previous studies, thereby extending the accessible process window and enhancing frictional heat generation.