Study on the residual stress and warping of stiffened panel produced by electron beam freeform fabrication

In the present work, the process of depositing stiffeners on a flat plate by electron beam freeform fabrication (EBF) was analyzed by uncoupled thermal-mechanical finite element (FE) simulation. The deposition of the stiffeners was realized by two steps: (I) stiffeners were deposited on the positive side of the panel and cooled to room temperature and (II) stiffeners were deposited on the reverse side of the panel and cooled to room temperature. The simulation results showed that the warping direction of the panel is opposite to the stacking direction of the stiffeners. The transient temperature mainly distributed along the roots of stiffeners, and the lowest temperature occurred at the center of the grid formed by the stiffeners. The maximum residual stress occurred at the intersection point of the stiffeners. After step II, the warping the panel was reduced by 63% comparing to the warping after step I.