Model-based feedforward control of laser powder bed fusion additive manufacturing

Abstract

Control of laser power to improve part quality is critical for fabrication of complex components via Laser Powder Bed Fusion (LPBF) additive manufacturing (AM) processes. If the laser power is too low, it will result in a small melt pool and lack of fusion; on the other hand, if the laser power is too high, it will result in keyhole and material evaporation. This paper examines a model-based feed-forward control for laser power in LPBF to improve build quality by avoiding the onset of keyhole formation or reducing over-melting. First, an analytical, control-oriented model on the dynamics of melt-pool cross-sectional area in scanning a multi-track part was developed, and then a nonlinear inverse-dynamics controller was designed to adjust laser power such that the melt-pool cross-sectional area can be regulated to a constant set point during the build process. The resulting control trajectory on laser power from the simulated closed-loop controller was then implemented in a LPBF process as a feed-forward (FF) controller for laser power. Multiple bead-on-plate samples of Inconel 625, with different number of tracks and track lengths, were then built on an EOSINT M 280 AM system to evaluate the performance of the resulting FF-Analytic controller. Experimental results demonstrated that the proposed FF-Analytic control of laser power was able to avoid the onset of keyhole formation that occurred under a constant laser power for certain samples. Furthermore, the proposed FF-Analytic control was demonstrated to have significantly reduced over-melting at the returning ends of the laser scan path in scanning a multi-track part compared to applying a constant laser power, albeit with some over-compensation due to modeling imperfection. Overall, the proposed FF-Analytic control of laser power had 23–40% lower average error rate than applying a constant laser power in regulating the melt-pool cross-sectional area to a constant reference value, in terms of measurements of cross-sections at track ends.