Towards advanced welding methods for the ITER vacuum vessel sectors

The problem of joining the ITER VV sectors, considering the tolerance requirements of the blanket attachments, and the time required for TIG welding, continues to stimulate EU R&D into power beam welding techniques for fewer passes and lower distortion by a factor of up to 5. The work on reduced pressure e-beam welding showed that penetration varied with position, fit-up, distance and pressure and single-pass weld control seemed impractical so work on a combination of rest-current-control root weld followed by wire-fill passes promises a practical solution. The NdYAG laser welding has yielded useful and stable results and demonstrated the possibilities of improved performance over TIG. Design on the welding robot has been simulated by the successful use of computational virtual modeling techniques. A robust, singularity-free, hydraulic, parallel-configuration robot is under construction to demonstrate welding and control scenarios and the possibility of active suppression of vibrations induced by machining forces.