Influence of Deposition Strategy and Processing Parameters on the Thermal History of Material Extrusion Parts

This study investigates the effect of reheating on previously deposited layers in material extrusion (MEX) 3D printing, commonly known as Fused Deposition Modeling (FDM), considering the combined effects of deposition sequence (unidirectional and bidirectional) and key process parameters, including printing temperature, printing speed, and layer height. Two temperature measurement methods were used to record changes during printing, and the results from local and global approaches were compared. The temperature of the interface between the first deposited layer and the build platform was measured with thermocouples. The findings show that the reheating effect at the first layer fades with increasing build layer, with no further increase in heating profile after the eighth layer, regardless of the process parameters investigated. The measured minimum temperatures at the investigated location remained above the glass transition temperature, Tg, which is critical for bonding and polymer chain rearrangement to continue taking place. Printing temperature was found to be the strongest observed factor influencing reheating, as it provides the heat for conduction into previous layers. Deposition sequence also played an important role, with bidirectional deposition leading to higher reheating and 25–50% more layers above the crystallization temperature, Tc. Overall, the results confirm that deposited roads undergo cyclic heating, and understanding the influence of process parameters on reheating is important for interpreting bond formation in MEX 3D printing.