## 4 Discussion  
This work explores influences on the joint quality of sinter-bonded joints. The influence of the various production steps, such as print orientation, and parameters, such as depowdering pressure, can be broken down into influence on the surface roughness. The sintering process can compensate rough surfaces to a small degree, depending on the sinter parameters, but this effect is limited and smooth surfaces are key for an effective bond. Depowdering of the green part cannot be avoided but leads to an increase in surface roughness. Since the absolute roughness values increase with an increase in pressure, it can be assumed that due to the insufficient strength of the green parts, the pressured air removes isolated powder grains or agglomerates bonded by the binder from the green part, thus increasing the roughness. Although a lower pressure achieves a lower roughness, depowdering takes slightly longer. Additionally, a longer manual depowdering process could lead to more variation in surface properties. At low pressures, it can be assumed that manual cleaning affects repeatability more than it does at higher pressures. Due to the manual execution, both time exposure in the compressed air jet and distance of the compressed air nozzle to the component surface may vary, and are a reason for the deviation in the results. Overall, the air pressure of \(3\,bar\) was shown to be the best compromise between quality of powder removal and surface roughness. In addition to the selected pressure, the amount of powder present as dust in the air was also determined to be decisive. This occurs when the ratio between the vacuum power and the secondary air within the depowdering glovebox is not matched, or while depowdering internal structures. Existing powder dust is then blown onto the component with the compressed air lance and leads to erosive removal of surface particles. When dust load in the air is high, a trace of the compressed air lance  
Figure 19: Sintered joint with macroscopic shape deviation. Figure 20: Flatness values distributed over the build area (**left**) and detailed image of the deformation of the components most likely due to the curing process (**right**). movement can even be seen on the component. This relationship should be investigated in further research, but was not the subject of the present study. As already described, the influence of the print orientation on the roughness is known in the literature. The roughness of the sidewards-facing surfaces is higher, since here the stacked layers form the surface. This results in a surface with a roughness that is defined by the peaks and valleys of the powder layers. This strongly influences the surface roughness orthogonal to the layer build-up direction [3, 29, 36]. On the downwards-facing component surface, the applied binder penetrates the powder bed beyond the component contour to a small extent, so that a slight powder adhesion of the underlying layer leads to an increased roughness of the same order of magnitude as for the side surfaces [37, 38, 39]. This so-called bleeding effect could be enhanced by the special curing process of solvent extraction. The roughness of the top surface of the component is only affected by the impingement of the binder droplets when the recoating parameters are properly set, and is therefore smaller [40]. It is surprising that the standard deviations are very high, despite a very large number of samples. This indicates a general process instability and underlines the large influence of the manual depowdering process on surface quality. Although the smoother top surface of the components bonded significantly better in the sintering process relative to the other orientations, not even 20% of the surfaces could be joined. Despite the fact that the roughness of the side faces and the bottom faces are equal in terms of magnitude, the side faces achieve a contact percentage that is just half that of the bottom faces.