Friction Stir Welding : Heat Input Calculation

A recent review stated that “an improved understanding of the mechanical properties of joints as a whole and the ability to control mechanical properties are much needed” before the process can be fully accepted by industry. In that sense FSW research have a far way to go. In literature there are analytical model for stir zone (SZ) used for studying the heat transfer and residual stress in friction stir welded joint, but there are still some unsolved problems for the exact calculation of the size of the heat input zone and value of heat input. If the prediction accuracy of the FSW thermal cycle is very low, it is impossible to predict the microstructure and properties in SZ thermo-mechanically affected zone (TMAZ) and heat affected zone (HAZ) accurately and reliably. Welding heat input is the key factor influencing SZ behavior and the welding thermal cycle. According to Askari the heat generation due to plastic work is the dominating term during the steady state FSW process. In his model the friction force around the tool pin surface during steady state FSW process has been neglected as the material in this zone is plasticized and it under go plastic deformation rather than slip at the tool boundary. The model of FSW developed by William’s has been used as the base for the analytical model used in this study. In this present study for FSW heat input in the SZ has three parts: Viscous dissipation transformed in to heat around the tool pin, plastic work around the tool pin converted to heat and work done by tool shoulder friction converted to heat.