# Effect of Filament Material and Printing Temperature on 3D Printing Extrusion Force
## 1 Introduction  
Fused filament fabrication (FFF) is a widely used 3D printing technology. Variability in part quality, influenced by dimensional tolerances, surface roughness, and occasional defects (e.g., porosity, layer delamination), has traditionally limited this technology to non-load-bearing applications. However, advancements have already demonstrated its potential for high-end use. Much of this variability could be improved by proper in-process measurement, real-time control of additive manufacturing [1, 2], and process modelling [3] to improve the process, monitoring printer health [4] and the properties of the printed parts. However, true in-line monitoring of material flow and real-time print correction isstill lacking [5]. Unfortunately, newer industrial systems offer limited, if any, capability for inline control and correction of the nozzle temperature, surrounding temperature, and filament feed rate, although studies with older systems have provided some important insights into their influence [5]. Irregularities during extrusion can be detected by analyzing data obtained from various sensors on the 3D printer: the thermocouple at the hotend, a non-contact infrared (IR) temperature sensor to measure the deposited molten polymer, a borescope camera, three-axis miniature MEMS accelerometers to measure vibrations on the table and extruder head, thermocouples to measure the temperature of the table bed [6], and pressure sensors in the hotend. Different methods are used to measure the extrusion forces and the condition of the printer and monitor the flow through the print nozzle during the printing process--from measuring the forces that occur when the filament is pushed into the hotend to measuring the vibrations--using acoustic emission (AE) sensors, accelerometers, infrared thermometers, and visual cameras to monitor the parameters of the extruder motor [4]. By integrating modern methods like digital twins, in situ monitoring with machine vision, applying machine learning algorithms, and utilizing real-time analysis powered by artificial intelligence, product quality and productivity can be significantly enhanced [7; 8; 9]. The rheology of the polymer melt in the extruder could also be measured using pressure drops in several measurements in specially developed novel online rheometers used for measuring the extensional viscosity [10]. Thus, the combination of measuring power to drive the filament in the hotend, pressure measurement in the nozzle, IR temperature measurement, and modeling could be used to estimate the pressure drop in the nozzle [11]. Pressure values from 140 to 6900 kPa were measured over a range of ABS filament feed rates at 230 \({}^{\circ}\)C, 235 \({}^{\circ}\)C, and 240 and a flow rate of 5 mm\({}^{3}\)/s. The in situ pressure measurements were higher than the theoretical predictions using a power-law fluid model, suggesting that the assumptions used for the theoretical calculations may not fully capture the dynamics in the FFF liquefier [12]. [PERSON] and [PERSON] developed a special in-line rheometer by designing a modified nozzle with a customized pressure transducer and a thermocouple to measure the temperature of the processed melt [13]. After applying the appropriate corrections, the inline rheometer provided an accurate viscosity measurement that could be used for real-time monitoring and process control. FFF printers use feeding rollers to feed the filament into the hot end. Feeding is usually performed by an electric motor-controlled pinch roller mechanism. If the resistance in the hot end is too high (for various reasons, such as clogging of the nozzle, inhomogeneous material, or incorrect temperatures), slippage can occur. Slippage can also occur if the filament diameter is not constant, the knurled feeding roller does not rest on the surface, or the rollers are worn.