In the past decade, there has been a significant increase in rocket launches. Fuel tanks used to propel rockets into space are built from large cylindrical components that are welded together using friction stir welding (FSW). FSW is a solid-state joining process that uses a rotating cylindrical tool to heat and mix two pieces of light metal in the jointed area. To prevent safety issues, the weld needs to be inspected in multiple directions for a variety of flaws, including lack of penetration, kissing bonds, wormholes, voids, and root and toe defects.
Olympus has developed a unique robotic inspection system to inspect friction stir welds.
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.
Flexible Inspection Solution
The FSW inspection system’s phased array probes inspect the weld area for multiple defect orientations.
The fully automated system detects the typical defects found in large cylindrical fuel tanks.
- Inspects part thicknesses of 2.5–25 mm
- Can be set to detect multiple defect orientations (0 degrees, 45 degrees, 90 degrees) with minimal mechanical changes
- Detects artificial flaws in longitudinal, transverse, and oblique orientations with the following dimensions:
- – Depth: 0.5 mm
- – Width: 0.25 mm
- – Length: 10 mm
- Detects side-drilled holes (SDHs) equivalent to 1.2 mm in diameter, parallel or perpendicular to the weld
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
Motion and Acquisition Software
Motion software for simple system operation:
- Web-based application
- Preprogrammed calibration and check sequences
- One-click to start sequences
WeldSight™ software for data acquisition and analysis:
- Optimized workflow for FSW inspection
- Embedded scan plan tools:
- – Weld profile editing
- – FSW wedges and probes editing
- – Focal law configuration
- – Raytracing visualization for coverage validation
- Supports large data files, enabling the inspection of large fuel tanks
- – Volumetric views for efficient analysis
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
