Friction stir welding (FSW) is a solid-state welding technique. So, it doesn’t involve material melting in the process. This process is quiet popular, especially in aircraft and space vehicle manufacturing industry since it can weld lightweight aluminium alloy with a very good quality. However, the understanding of the welding process condition is still not enough to predict the weld quality and the impact it has to the machine tool’s stiffness in different welding parameters. Since manufacturing companies want to increase productivity without too many additional cost (adding a new production line, etc.), so naturally they want to increase the welding speed, etc. However, changing the welding parameter probably will cause the weld quality drop since there is not enough heat input to the weld, etc. So, the understandingof the welding process in depth is essential.In this thesis a FEM simulation to obtain the forces and temperature during the FSW process has been conducted. The modelling and simulation were conducted in DEFORM3D software. The workpiece which is being welded for the FSW process were modeled as one workpiece in order to avoid contact instabilities during simulation. No movement boundary condition has been placed on the workpiece. The convection to the environment is the only boundary condition. However the simulation result is not good enough to be used in the next step, which is to apply the forces to the design of machine tool’s assembly in order to get the resulting stress and deformation of the design using static structural analysis of Ansys Workbench. But still, the static structural analysis was still conducted using the known maximum force value. This maximum force value was given by the welding company, which propose for this project, based on the welding company’s experience. And the result is the stress received by machine tool’s are still below the tensile yield strength of the material. However the maximum deformation exceeds a little from the required specification of the machine tool.