This book deals with the thermo-mechanics of welding based rapid prototyping process. A numerical and experimental approach for the analysis of temperatures, heat affected zone, deformation and residual stress are presented. Focus is placed on the investigation of the thermomechanical interaction of molten metal with a substrate at room temperature using, initially, a simplified modeling approach limited to single droplet and than increasing the complexity of the model to include factors like material addition, thermal cycling and moving heat source. The single droplet model or two dimensional axisymmetric model can give insight into the physics of thermo-mechanical interactions however three dimensional models are also included to show that how various factors actually contribute to the overall thermal and structural response.A detail parametric analysis is also conducted to demonstrate how different process variables affect the overall efficiency.