## 3 Quality Control of Silicon Carbide Printed Part Formation
### The Impact and Control of Key Printing Parameters on Green Part Formation Quality
#### 3.1.1 Nozzle-Clogging Issues  
During the printing process, clogging of the printhead nozzle can cause the binder to migrate outside the intended geometry, resulting in a phenomenon known as \"feathering\", which decreases the accuracy of the printed parts and is regarded as one of the main sources of shape accuracy issues. Figure 6 illustrates the impact of nozzle clogging on printed parts. Figure 6: Absence of binder in the green part due to nozzle clogging (**left**). The printed part is damaged due to a lack of binder inside (**right**). Cited from [67, 68]. Controlling the viscosity and surface tension of the binder to prevent the formation of satellite droplets [69] or to delay nozzle drying [49] is a common method for addressing nozzle clogging. Normally, droplets fall in a tadpole shape with a tail. Due to the effects of surface tension, the trailing liquid breaks off to form small droplets that trail behind the main droplet, creating a tail-like structure known as a satellite droplet. Figure 7a systematically illustrates the key stages and parameter relationships during droplet formation and satellite droplet generation in the inkjet process, where \(\Gamma\) represents the aspect ratio of the tail at the exit pinch-off, \(\mathrm{V_{j}}\) denotes the mean jetting velocity of the ink, \(\mathrm{L_{p}}\) corresponds to the total length of the ligament during exit pinch-off, and \(\mathrm{t_{2}}\) and \(\mathrm{t_{1}}\) indicate the exit pinch-off time and the initial ink ejection time from the nozzle orifice in each droplet formation cycle, respectively. The right panel of Figure 7a clearly labels the separated states of the primary droplet and satellite droplet, visually demonstrating how tail breakup leads to satellite droplet formation. Figure 7b1-b6 vividly demonstrates the jetting states during droplet formation through comparative illustrations, including no droplet formation, single droplet formation, single satellite droplet formation, and multiple satellite droplet formation. Researchers such as [PERSON] [71] and [PERSON] [72] have provided a detailed explanation of the causes of nozzle clogging due to satellite droplets. In this regard, [PERSON] [67] noted that a distance of 1-3 mm must be maintained b  
Figure 7: (**a**) Morphological features of the forming ligament or droplets, which are depicted individually at the moment of ink ejection beginning, exit pinch-off, front pinch-off, and tail breakup. (**b1–b6**) Representative instantaneous snapshots of the droplet formation regimes: (**b1**) no droplet formation, (**b2,b3**) a single droplet, (**b4,b5**) one satellite droplet (a primary droplet accompanied by one stable satellite droplet), and (**b6**) multiple satellite droplets (a primary droplet accompanied by multiple stable satellite droplets) [70]. the powder bed to ensure that satellite droplets have enough time to merge with the main droplets. Moreover, some smaller satellite droplets may be blown away from the jet axis by lateral airflow and evaporate. When the solvent evaporates and these smaller satellite droplets are suspended in the air as aerosols, they may contribute to \"nozzle clogging\". To better describe the fluid properties of binders, guide the selection or preparation of binders, and regulate binder droplet behavior, parameters such as Reynolds number (Re), Weber number (We), and Ohnesorge number (Oh) are commonly used to measure the liquid properties of binders [73]. These three parameters are related to fluid density, fluid dynamic viscosity, fluid surface tension, droplet velocity, and characteristic length. [PERSON] et al. [74] first proposed the Ohnesorge-related parameter Z = 1/Oh to characterize the printability of binders, which is correlated with the binder's dynamic viscosity, surface tension, fluid density, and characteristic length. Experimental investigations by [PERSON] et al. [75] on the regulation of parameter Z ranges demonstrated that, when Z < 1, the viscous forces of the binder become dominant.