Multivariable closed-loop control for layer geometry in Wire Arc Additive Manufacturing
Keywords: Additive manufacturing, process control, nonlinear control, optimal control
AbstractThis paper focuses on modelling and control of mass and heat transfer process for Wire Arc Additive Manufacturing (WAAM). Although similar to arc welding, WAAM is a more complex problem as it involves interaction between deposited layers and a greater concern with final geometry and material properties of the final part. Despite the rich literature regarding modelling and control of arc welding, the efforts to extend the results to WAAM are still few. The layer geometry accuracy during deposition leads to decreased material consumption and post processing machining costs, as well as reducing the occurrence of internal voids in the produced part, thus closed-loop control can be used to guarantee a more accurate deposition geometry. This paper proposes a static model for the deposited layer geometry of thin walls using process variables (wire feed speed, travel speed and contact tip to workpiece distance) and physical variables (arc power, inter-pass temperature) as inputs. The model is based on the Rosenthal solution for the temperature distribution due to a moving heat source in combination with a layer geometry parameterization, which is incorporated in a dynamic model of the GMAW process for control design. A closed loop control is proposed considering the linearized model about a given operating point. Numerical simulation results illustrate the efficacy of the proposed control for the regulation and tracking of both layer height and wall width and a experimental setup for validating the control strategy is also proposed.