A study on the forming of CICC for the superconducting Tokamak device with post-forming predictions via virtual manufacturing

To construct the magnet assembled with the CICC (Cable-In-Conduit Conductor) for the superconducting Tokamak fusion device, the 3-roll bending, that inherently has a difficulty to form the coil with accurate radius of curvature, is used for continuous winding. This difficulty is mainly caused by the spring back after forming. In order to obtain precise dimension, a trial-and-error operation is inevitable. To reduce the effort of tryout, a relation between travel of the bending roller and post-forming displacement was obtained via virtual manufacturing. The radius of CICC after forming was expressed as a function of the bend-roll travel. In addition, the variation of the CICC cross-section (reduction of the conduit cross-section) was investigated during the first turn and during conduit bending with largest curvature to check if the strand can have enough space. To ensure the validity of the computation, prototype coils were manufactured and the coil radii after forming were measured. The data showed similar pattern with some discrepancy for large-sized coils. The residual stress generated by jacketing on the coil before roll bending was measured to investigate if its existence influences the final deformation behavior. A mapping function was proposed to compensate the error caused by the numerical assumptions.