Types of Defects in FSW

FSW has multiple advantages over traditional welding methods; FSW avoids the defect types that tend to arise with liquid phase cooling in other welding methods. Additional defect types occur mostly as a result of insufficient temperatures or welding conditions; these defects must be correctly identified and sized.

Natural Defects

Different types of defects can occur in friction-stirred welds, such as incomplete continuity of the bond between the material from each side of the weld (referred to as a “kissing-bond”), long tunnel-like defects, and lack-of-penetration. Also, due to the friction-stir welding process, defects can be randomly oriented inside the weld.

Schematic view of the FSW manufacturing process.

Calibration Defects

Longitudinal, transverse, and oblique notches located on the OD and ID are used as references for the calibration process. Side-drilled holes are also employed to build the time-corrected gain (TCG) curve, which will account for signal attenuation inside the material.

Random-oriented defects generated during the manufacturing process.

Robotic Inspection Platform

A complete turnkey inspection station, the FSW system is designed to be directly installed in the production line.

Large cylindrical fuel tank welds are presented to the collaborative robot (Cobot). It positions the inspection head and the tank is rotated until the entire circumferential weld is inspected. The tank is then moved and the cycle repeats on the next weld.

Main components of the system:

• Innovative inspection head that provides uniform and constant pressure of all water wedges on the part for optimal coupling
• Probe and water wedge design includes a water suction port to minimize water loss
• Calibration station to ease pre- and post-inspection validations and enables fast calibration part changes
• Collaborative robot (Cobot) for accurate positioning and pre-post calibration checks
• FOCUS PX phased array ultrasound acquisition unit

Versatile and Efficient System

Advantages

• Innovative inspection head provides precise pressure for constant coupling with the part
• Flexible configuration enables simple adjustment for different inspection angles
• Optimal water coupling and suction minimizes water loss
• No safety parameters required thanks to the use of collaborative robots
• Permanent calibration stand allows quick acoustic validation between shifts
• Weld-dedicated application software with an optimized workflow, from scan plan definition to analysis
• Simple motion software for optimal operation