A systematic literature review of control and monitoring systems applied in metal additive manufacturing processes

Abstract Additive manufacturing (AM) is increasingly applied for the fabrication of geometric complex components and intricate shapes which are not readily obtained using conventional powder metallurgy processes. Despite the advantages of AM, for many product applications there are challenges related to process-induced defects which can degrade part material properties and reduce its mechanical performance. The incorporation of effective control systems can help to reduce processing defects, improve processing efficiency, and minimize waste. Designing such systems requires careful consideration of the following key factors: 1) defining the control objectives and selecting appropriate controllable inputs, 2) choosing a suitable control category and selecting a relevant control strategy accordingly, 3) developing a mathematical model for model-based control design, and 4) designing a measurement system to acquire data and provide feedback to the controller for processing. Based on these factors, the objective of this paper is to systematically review publications which have reported on the use of control and monitoring systems during metal AM processing. Additionally, this review examines whether control is applied within a single layer or across multiple layers, to provide better insight into deciding between these two control approaches. In addition to the four factors highlighted due to their importance in the design of control systems, a further factor considered in this review is the identification of research gaps and future directions. By examining how these factors were addressed in the literature, this paper aims to identify best control practices for metal AM processing and highlight the potential of less explored areas.