TWI Industrial Member Report Summary 775/2003
S D Smith
Friction Stir Welding (FSW) has advanced considerably since the first welds were made in the early 1990s. Major developments in tool design have led to a significant increase in the maximum possible welding speed. The welding process has a number of parameters that may be varied to achieve good quality welds ( eg linear speed, rotation speed, tool tilt angle, shape of probe, sculpting of shoulder). The improvements that have been made to these variables are the result of incremental progress from the interpretation of test data.
An improved understanding of FSW is now needed. For example, it is recognised that the heat generated during FSW, which is a critical part of the process, is due to the shearing of material under the shoulder and, to a lesser extent, around the probe. Despite this, very little is known about the actual paths taken by material swept past the tool during welding. Markers placed along the weld line can give some indication of the final deformed shape of material, but they do not reveal how the material progressed to the final shape. It is therefore important to investigate possible methods for understanding material movement during welding.
Computer modelling can be used to gain an improved understanding of the established fusion welding processes. For example, models have been used to predict weld pool dynamics and welding residual stresses. Recently, models have been used to investigate FSW. Much work on modelling of heat flow during FSW has been done. Less work has been done on the use of modelling to predict material movement during FSW, but this could provide the improved understanding of FSW that is now needed ( eg for tool design, parameter optimisation, the investigation of difficult to weld materials).
The objectives of this report are as follows:
- To introduce the concepts needed for simulations of FSW.
- To review published models of FSW.