Optimizing the electroforming process for full-shell X-ray optics

Electroforming replication technology at the Marshall Space Flight Center has a long heritage of producing high-quality, full-shell X-ray mirrors for various applications. Nickel alloys are electroformed onto a super-polished mandrel in the electroforming process and then separated to form the replicated full-shell optic. Various parameters in the electroplating configuration could result in the non-uniformity of the shell's thickness. Thickness non-uniformities primarily occur due to the non-uniform electric field distribution in the electroforming tank during deposition. Using COMSOL Multiphysics simulations, we studied the electric field distributions during the deposition process. Using these studies, we optimized the electric field distribution and strength inside the tank using customized shields and insulating gaskets on the mandrel. These efforts reduced the thickness non-uniformity from over 20% to under 5%. Improving the thickness uniformity of the shell aids in better mounting and aligning shells in the optics module. Optimization of the electroforming process, in some cases, improved the optical performance of the shells. Using finite element modeling, we estimated the effect of electroforming stress on the figure errors of the replicated optics. We observed that the electroforming stress predominantly affects the figure toward the ends of the optics. We presented COMSOL optimization of the electroforming process and the experimental results validating these simulations. We also discuss modeling experimental results of the replication figure errors due to electroforming stresses.