Influence of scanning order on residual stress and deformation in laser direct manufacturing of TC4

In order to reduce the substrate deformation and residual stress during laser direct manufacturing of TC4 components, the influence of different scanning orders on the deformation and residual stress of the parts formed by subarea scanning strategy were studied. The newly-defined outside-in and inside-out scanning orders, and a randomized scanning order were applied and compared. The deformation was measured by the surface structure light measurement system and the residual stress was measured by the X-ray diffraction method. The results show that different scanning orders have significant effects on the deformation and residual stress. The maximum substrate deformation is reduced by 60% by the outside-in scanning order compared with that by the randomized scanning order, while larger residual stress is introduced, which is even up to 392 MPa. Oppositely, the randomized scanning order makes a more uniform residual stress distribution and the maximum residual stress is only 93 MPa. Therefore, it is beneficial to balance the substrate deformation and residual stress of large TC4 forming parts by applying the outside-in and randomized scanning orders in the front and back forming period respectively.