A four stage modelling process has been presented which can be used to accurately represent the thermal and mechanical aspects of the inertia friction welding process through the use of load and displacement controlled phases. Thermal results from the first phase of the model for two different weld parameters have shown a significant difference in heating rate between the two welds and approximately 100◦C difference in interface temperature. The thermal profile and deformed weld shape at the end of the welding process has been used to predict the residual stresses in the remaining two phases of the model which simulate the post-weld cooling and machining of the finished component. Results from the phase volume fields show that the higher weld pressure of Weld 2 results in a narrower HAZ region which is confirmed by the predictions and measurement of the residual stress where the comparison shows that the peak values are well predicted by the model and in the case of Weld 1, where thermal data is available to allow calibration of the model, the HAZ width is well predicted. The HAZ width was reduced in the model when a higher pressure was used for the welding, which is consistent with the shifting of the peak in the experimental hole drilling results, how-ever the model overestimated the HAZ width in this case by less than 1 mm.