The use of the Finite Element Method in product development is now well established. Its use in manufacturing processes is increasing and is part of the field of new applications in computational mechanics. The most important reason for this development is the industrial need to improve productivity and quality of products and to have better understanding of the influence of different process parameters. The modeled phenomena play an important role at various stages of the production of steel parts, such as welding, heat treatment and casting, among others. The analysis of welding processes involves several branches of physics, and requires the coupling of different models addressed to describe the phenomenological behavior of a system. Many of these models have been implemented numerically and are being used in an efficient way to solve the problems on an individual basis. Friction stir welding is a new solid-state joining technology. It has become a unique technique well suited for joining many hard-to-weld metals and some dissimilar metals. Compared with the conventional welding processes, FSW possesses many advantages over traditional fusion joining techniques, no melting, low defect and low distortion. This new technique is being successfully applied to the aerospace, automobile, and shipbuilding industries and opens up a broad avenue of joining technology development and research. Like any new technology many unanswered questions remain, thermal and thermo-mechanical processes are still not completely understood. The relation between simulation results and properties of the products will be discuss in details
