This work focuses on the development of a simulation framework based on the meshless Smoothed Particle Hydrodynamics (SPH) method, specifically applied to Friction Stir Welding (FSW) modeling. The framework allows for the numerical investigation of the effects and mechanisms that govern the FSW process. Several interdependent physical phenomena characterizing FSW are explored and incorporated into the simulation framework. These include complex contact conditions with slip-stick friction, nonlinear temperature-dependent plasticity, material coalescence, and multiple thermal contributions. Various numerical aspects, such as the stability of the SPH formulation, are also investigated. The developed SPH framework is initially validated through various reduced examples before being applied to investigate FSW scenarios. The study provides a deeper understanding of the material flow mechanisms in FSW and allows for quantitative assessment of the flow conditions. The newly developed bonding mechanism provides insights into the evolution of weld formation. Additionally, the simulation framework enables the investigation of process parameter influence on the resulting weld quality. Comparison of the results with available experimental and simulation data confirms the capability of the SPH method to reproduce the complex effects of the FSW process. Moreover, the complexity of the joining method provides an opportunity to test and enhance the capabilities of the SPH method, leading to the development of a functional simulation framework capable of representing various industrial scenarios.