Sliding Mode Control for Melt Pool Area in Metal Laser Powder Bed Fusion Process

The laser powder bed fusion (LPBF) additive manufacturing process involves fusing powdered metals with a high powered laser moving at a high speed. As this process is governed by a complex multi-phase interaction between multiple physical domains, several models have been developed of varying complexity. This paper adopts a non-linear first order model from the literature governing the surface area of the moving melt pool created by the laser heating of the powder, as control of this state can lead to improved build quality (small melt pool hinders metal fusion, large melt pools lead to material evaporation and stress-concentrations in the final part). The model is reviewed, and a second order state space model is constructed using the error between the actual melt pool size and a desired reference value. The power supplied to the laser is used as a control input, and an exponentially stable sliding manifold is defined. A control law is defined to drive the system states to the manifold in finite time and hold it there, ensuring a desirable melt pool size throughout the duration of the build. Simulated results are presented, indicating the effectiveness of the control design using gains for slow and fast convergence.