# Geometric Benchmarking of Metal Material Extrusion Technology: A Preliminary Study
## 3 Results and Discussion
The technical guidelines provided by the producer of the Ultimaker 316L filament suggest that feature distortion and collapse during debinding and sintering can be prevented by limiting the nominal height-to-width ratio below 3 and 6 for pillars and thin walls, respectively [33]. However, it is noteworthy that our study observed discrepancies with these guidelines. While collapse and distortion were indeed observed when the suggested ratios were exceeded, contrary to expectations, such problems were also encountered below these values. In particular, no dimensional ratio lower than 6 prevented distortions in thin walls, while only a height-to-thickness ratio equal to 1 proved enough to achieve an undistorted pillar feature. Bridges represent the most critical structures in terms of deformations occurring at the end of the metal-MEX production process. Acceptable parallelism values were indeed achieved only by features B1 and B2, whose horizontal beams were shorter than 18 mm, as depicted by the map in Figure 6d. Despite ceramic-based support structures being included to sustain the structures during debinding and sintering, further lengthening the beam resulted in the prominent inflection of elements B3,  
Figure 6: Maps for white-state geometric tolerances achievable with metal-MEX: (**a**) perpendicularity of wall features; (**b**) perpendicularity of pillar features; (**c**) coaxiality of hollow cylinder features; (**d**) parallelism of bridge features. B4, and B5, as shown in Figure 7. However, the Ultimaker guidelines do not provide any effective ratio to prevent the collapse or distortion of horizontally suspended geometries like the beams of bridge features. Based on the results of our study, it is thus not advisable to exceed a nominal length-to-width ratio of 2 when fabricating bridge features with ceramic-based supports through metal-MEX. On the contrary, hollow cylinders appear instead to be characterized by a more stable structure, since no collapse was observed throughout the production process, despite height-to-thickness ratios ranging from as low as 2.40 to as high as 36. Furthermore, the map in Figure 6c shows that finer coaxiality can be achieved not only through thicker and shorter features but also by concurrently increasing both the height and the thickness of the hollow cylinder, thus suggesting that thickness plays a more significant role in achieving structural integrity for these geometries. Interestingly, unsupported hollow protruding geometries are not addressed in the guidelines; thus, no insight or optimal limit ratio is available for comparison. It is crucial to highlight that the success of the printing phase and the entire process is closely tied to the geometry of the nozzle, especially its diameter, as it affects the number of adjacent depositions in each layer. The nozzle's diameter also determines the width of the extruded filament, thereby impacting the minimum size of the features. Therefore, achieving a precise replication of the geometry may be at risk if a feature's dimension is smaller than the nozzle's diameter. This problem emphasizes how the nozzle's diameter might affect the achievable aspect ratio. In the metal-MEX process, as the layer height increases, there might be a restriction on the aspect ratio of features, due to the expansion of the deposited material strand caused by a larger nozzle diameter. Consequently, if the aspect ratio becomes too high, layers could become unstable or fail to adhere correctly. Therefore, smaller nozzles would allow for finer details and smaller features to be printed but might limit achievable aspect ratios due to increased layer width compared to height. On the other hand, larger nozzles would enable faster printing and higher aspect ratios but might sacrifice detail and resolution for smaller features. It is then clear that achieving dimensional accuracy requires a careful balance of nozzle diameter, layer height, print speed, and level of detail suited to a particular project.