Friction Stir Weld (FSW) inspection using TFM

A T-joint is welded using a FSW process. The sample contains a 0.2 mm side-drilled located between the two welds for calibration and a 3-mm high, 1-mm long EDM notch.

We use a 10-MHz array from flange opposite web and compare a linear scanning using an aperture of 8 elements focused along the backwall (on the left) to a TFM inspection (on the right). For both cases we set the gain to have a 80% screen height for the side-drilled hole and we superimpose a dxf overlay of the component in GEKKO (white lines in the following images).

We can see that the notch is detected for both cases. However, the signal-to-noise ratio measured on the tip diffraction is 10 dB for the linear scanning and 20 dB for TFM.

We see that the dead zone is greatly reduced with TFM going from 2 mm to 0.5 mm. It is thus possible to detect indications closer to the front surface, for example the tip of a longer defect.

The TFM also “draws” the shape of the defect and the rounded contours of the welds.