Qualification of Custom Subtractive Gantry Built for Hybridization of Commercial DED System

The hybridization of directed energy deposition (DED) machines is commonly made by integrating an additive head into an existing CNC machine but there is no instance in the literature of the opposite being done. A commercial DED machine was integrated with a subtractive gantry for the in situ repair of components without breaking the inert environment. Since the additive machine’s structure is not optimized for high-speed machining, concerns regarding the quality of the finished product arose. An accelerometer was secured to the subtractive spindle to characterize the stiffness of the system. Meanwhile, artifacts with diverse geometric features were fabricated and measured and a GD&T report was generated. The results were compared to an artifact fabricated with a commercial CNC to assess quality. The results were paired with vibration data to find indications of low-stiffness and chatter. A fast Fourier transform of the vibration analysis showed a higher amplitude spindle frequency in comparison to the tooth passing frequency, indicating a low local stiffness. A high amplitude 2× frequency was observed showing indications of an angular misalignment of the tool. A correlation analysis was done between the acceleration at SF, 2× harmonics and TF frequencies for all axes and the geometrical deviations of the artifact. Most correlation coefficients ranged between 0.3 and 0.4 which means that there was a low to moderate correlation between acceleration at the relevant frequencies and dimensional deviations.