Residual stress and tensile anisotropy of hybrid wire arc additive-milling subtractive manufacturing

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Hybrid wire arc additive-milling subtractive manufacturing (HWAAMS) is an effective method for the near net formation of complex structures by using the two processes alternately. The effects of milling width (ae) on the surface residual stress and the influence of milling thickness (t) on tensile anisotropy of the HWAAMS were studied using Al5Si aluminum alloy. The mean surface residual stress of HWAAMS in the middle dropped by 93 % relative to WAAM when the ae was 0.4 mm. The tensile elongation anisotropy could be controlled within 5 % when the t < 0.4 mm. However, the anisotropy in the ultimate tensile strength gradually increased to 8.3 % when the t was 0.8–1.6 mm. These results showed that milling-induced compressive stress contributed the most to reduce residual stress, and was induced by burnishing between the cutter and the milling surface. The milling-induced compressive stress reduced the surface residual stress and removed the inside maximum stress point by offsetting the initial residual tensile stress. This caused the remaining material with a previous initial residual stress to reach a new equilibrium at various milling depths that resulted in the changes mentioned above. Furthermore, milling decreased the fusion line spacing between the deposition layers that caused a dense and parallel distribution along the building direction rather than the usual WAAM shape that runs through the cross-section along the feeding direction. This caused a tensile anisotropy increase as the t increased because the stress concentration readily formed at the fusion line. These results are significant to understand the additive-subtractive synergistic effects in the HWAAMS.