## 3 Quality Control of Silicon Carbide Printed Part Formation
### The Impact and Control of Key Printing Parameters on Green Part Formation Quality
#### 3.1.2 Uniform and Dense Powder Bed  
Binder deposition within the powder bed represents the most fundamental process in binder jetting 3D printing, governing selective powder bonding and layer-wise fabrication. A powder bed with homogeneous porosity distribution is a prerequisite for precise binder deposition within predefined geometries. As shown in Figure 8, in powder beds with heterogeneous pore distribution, the deposited binder preferentially infiltrates regions with smaller pores, potentially bonding unintended powder particles at structural boundaries and consequently increasing the surface roughness of green components. On the other hand, the cavities formed within the powder bed may hinder the interlayer adhesion from overcoming shear forces, which can easily lead to layer misalignment (this phenomenon is referred to as \"shearing/shifting\") [76]. This results in significant deviations of the printed layers from their intended positions, thereby reducing the dimensional accuracy of the green parts [77]. Furthermore, the non-uniform porosity caused by these cavities can lead to uneven density distribution in the green body, ultimately causing fractures or deformations in the formed printed parts during the subsequent sintering process. Figure 8: The penetration behavior of the binder solution within powders exhibiting uniform porosity (left) and non-uniform porosity [78]. Therefore, constructing a homogeneous and dense powder bed represents a fundamental prerequisite for manufacturing high-precision green bodies. To achieve optimal powder bed uniformity and densification in additive manufacturing processes, it is essential to systematically investigate the governing mechanisms that influence powder packing quality. Key factors requiring particular attention include the detrimental effects of binder-powder interactions on bed homogeneity, the agglomeration behavior and flowability challenges associated with fine powders, and the critical powder spreading dynamics during the deposition process. Binder-powder interaction behavior  
The binder-powder contact tunneling model proposed by [PERSON] [79] vividly demonstrates how binder impact on the powder bed induces distinct particle motion patterns. Figure 9a illustrates incomplete penetration of binder droplets into a loosely packed powder bed, forming dry aggregates and causing surface collapse defects that lead to non-uniform porosity in subsequently spread powder layers. Figure 9c displays the crater effect resulting from high-speed binder droplet impact on a homogeneous powder bed, where droplets spread along crater walls while entraining particles during retraction, ultimately forming more spherical binder particles that penetrate the powder bed. This crater-induced powder splashing is recognized as a primary source of surface roughness, as both the craters and splashed powder compromise current layer accuracy while adversely affecting subsequent layer spreading. Figure 9b demonstrates the desired impact mechanism: under conditions of dense and uniform powder packing, low-speed impacts result in droplet spreading into flattened discs that penetrate downward with minimal surface defects. The universal approach for achieving powder beds with uniform porosity involves adjusting binder parameters to mitigate crater-induced splashing [80], with key control parameters including binder volume, initial velocity, and viscosity [81]. Figure 9: The phenomenon of binder contact with the powder bed [82]. (**a**) The “tunnel effect” of the binder falling onto a loose powder bed. (**b**) The binder penetrates into a uniformly packed powder bed from a low drop height. (**c**) The binder penetrates into a uniformly packed powder bed from a high droplet height, causing splashing. In addition to adjusting binder parameters, the hydrophilicity of the powder material and the selection of binder type also significantly influence the impact of binder-powder interactions on the powder bed state.