Real-time in-process control methods of process parameters for additive manufacturing

Additive Manufacturing, also known as 3D printing, fabricates objects in a layer-by-layer manner. In recent years, extensive efforts have been made to evolve 3D printing technologies from rapid prototyping technologies to enable industrial implementation. To this end, numerous researchers have investigated the effect of process parameters on final properties of printed parts such as mechanical properties or dimensional and geometric accuracy, proposed hardware, and software modifications to improve these properties, or implemented inprocess monitoring capabilities during manufacturing to enable the detection of defects without the need for destructive testing and therefore enable part quality assessment. However, whilst in-process monitoring efforts are essential, these are limited to only flag defects rather than preventing them. Consequently, these efforts do not ensure part quality and do not reduce material waste in the form of scrap parts. As a result, researchers have more recently proposed the implementation of real-time process parameter control in order to correct defects formed during manufacturing and prevent these from continuously occurring. This review summarizes real-time in-process control of process parameters of non-metallic and metallic additive manufacturing technologies. The reviewed work is further classified according to the process parameters that were used for control, mainly dividing these into heat source and non-heat source process parameters.