Visual observation of effect of tilting tool on forging action during FSW of aluminium sheet

Using a backing plate with prepared grooves of various lengths, the distribution features of forging result and the effect of tool tilt angle on forging action were investigated by visualisation. The height of the profile of Al extruded into the grooves increased with increasing tool tilt angle, showing that the forging effect can be enhanced by tilting tool. It was primarily attributed to the increase in actual forging force, because the measured downward forging forces at 0 and 3° tilt angles were 500 and 1500 N respectively. Moreover, the forging force was found to be composed of static component and dynamic component, and the latter resulted from the horizontal compressive force of moving worktable. Although the width of forging affected zone (FAZ) can reach the area covered by shoulder, the distribution of forging result was not uniform. So, small pin and considerable tool tilt angle are beneficial to eliminating void.