Laser welded lip seal for UHV class fusion vessels–A methodical study

Abstract

Lip seals are considered, the most promising options for the vacuum boundary joints in large size vacuum vessels (like rectangular neutral beam vessel with an opening size of ∼30 m) of fusion machines. Lip seals are designed with the corner welding of 2 mm thickness sheets of SS304L with the welding penetration requirement of 3 mm. With the first phase of development, laser welding parameter optimization and the sensitivity analysis was carried out to understand the effect of manufacturing tolerances (like air gap between the plates, laser beam misalignment and plate misalignment) on the weld quality. To ascertain the defined tolerances, a specialized clamping tool was configured, designed, manufactured and tested by integrating that with the assembly of laser welding head and robotic arm. For the prototype welding demonstration, the Lip seal welding of a rectangular configuration and an elliptical configuration of size 3 m × 1.5 m (∼1/3rd size of Diagnostic Neutral Beam (DNB) vessel lip seal); and 1 m length with 1.2 m diameter (exact size of DNB high voltage bushing lip seal) are considered. Welding qualification was done with the Non-Destructive and Destructive examinations. Further, the camera based feedback system for the seam tracking was incorporated to the system, which enables the remote detection and correction of the weld path. This development also extended to enable the repair of welding operation.