Additive manufacturing technologies are being increasingly adopted in the manufacturing industries due to their capabilities in producing complex geometries without the need for special tools. Material extrusion (MEX-TRB/P) is a popular additive manufacturing technology due to its simple operation. However, optimization of various process parameters remains a challenge, as incorrect combinations can lead to reduced dimensional accuracy and incapacitated mechanical properties of the fabricated parts. Given that the MEX-TRB/P process relies on the heating and cooling of thermoplastic materials, understanding the role of temperature is critical to optimizing the MEX-TRB/P printed parts. This article reviews existing research on the effects of process parameters, specifically those that are temperature sensitive, on the mechanical properties of the printed parts. The review first classified the process parameters into temperature sensitive and non-temperature sensitive process parameters. Then, the influence of temperature on the bonding quality and material properties is investigated, and a relationship between the thermal conditions and mechanical properties of 3D printed parts is established. This review also summarizes experimental and numerical methods for investigating temperature evolution during printing. This study aims to provide a deep understanding of the optimization of temperature-sensitive process parameters and their role in enhancing the mechanical properties of MEX-TRB/P-printed parts.

In this study, tensile test specimens were fabricated using a material extrusion 3D-printer at various printing temperatures to evaluate the development of physical bonds within the same layer as well as in between previous layers. The tensile test specimens were fabricated using PLA material, with printing temperatures ranging from 180 °C to 260 °C. Experimental investigations were conducted to investigate the dimensional accuracy and physical appearance of the parts across printing temperatures. Uniaxial tensile tests were conducted at a strain rate of 1 mm/min and repeated five times for each variable in accordance with the ASTM D638-14 standard. Results showed that increasing the printing temperatures yielded parts with better tensile properties. An approximate difference of 40% in tensile strength was observed between specimens fabricated under the two most extreme conditions (180 °C and 260 °C). The changes in tensile properties were attributed to bonding mechanisms related to interlayer bonding strength and a reduction in voids within the internal geometry. Analysis of the fracture surface using scanning electron microscopy (SEM) revealed fewer and smaller voids within the internal geometry for parts printed at higher temperature. The percentage area of voids reduced significantly when the printing temperature was increased from 180 °C to 220 °C. The tensile properties continuously improved with the printing temperature, with parts printed at 220 °C exhibiting the highest dimensional accuracy. The findings offer insight into the impact of the printing temperature on both the external physical bonds between printed roads, affecting the physical appearance and dimensional accuracy, and the internal bonds, affecting the tensile properties of the fabricated 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, T_g, 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, T_c. 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.