Residual Stress Optimization for Laser Powder-Bed Fusion Hastelloy X Parts

Cyclic temporal heating/cooling mechanism during the laser powder-bed fusion (LPBF) additive manufacturing (AM) process, results in high residual stresses in printed parts. Distribution and level of residual stresses are detrimental to the part quality, thus calling for a thorough study on the effect of input process parameters on the residual stresses distributed across the printed. In this article, a central composite design (CCD), as an advanced statistical approach, is used to find the optimal values resulting in the least residual stresses in printed Hastelloy X parts. Residual stresses in the X and Y-direction are measured and fitted to a quadratic regression model. Results from the quadratic regression model are compared to linear regression to identify the shortcomings of linear models. An exhaustive search with multiple initial value vectors is used to confirm the optimum parameter values that achieve the minimum residual stresses in the X and Y directions. Lastly, samples for validation purposes are printed with optimal values to verify the effectiveness of the proposed model. The residual stress measurement from the validation parts, compared to the prediction and confidence intervals, show an excellent agreement. It is concluded that the methodology used in this work can be used to find the optimal parameter values that minimize the residual stresses in the LPBF-made Hastelloy X parts.