## 1 Introduction  
Binder jetting is a 3D printing process for plastics and metals, in which powder is applied in layers with a roller and then a binder is dispensed into the powder bed via a print head. The component is created completely enclosed in the powder bed, so that excess powder must be removed from the surfaces and from internal structures after printing. The current state of the art is to perform this powder removal manually in a time-consuming manner using a compressed air lance, brush and vacuum [1]. The process is presented in Figure 1. In order to remove unbound powder from voids such as channel structures, openings need to be included in the design for effective depoordering of the parts through which the unwanted powder can trick away during the powder-removal process [2].  
Because final component strength in metal binder jetting is not achieved until undergoing a subsequent sintering process, the unsintered components (also called green parts) are very fragile and can easily be damaged during handling [3, 4]. A particularly high risk of damage to the components arises from the manual depowdering process, e.g., for components with fine external features or internal hollow structures. Depending on the complexity of such a structure, it is sometimes impossible to entirely remove the excess powder. Remaining powder in the channels that is not removed is bonded to the actual part area in the sintering process, thus significantly altering the desired component shape and function [5,6].  
Figure 2 shows an example of this problem. The image shows a cut through a sintered part that features a curved cooling channel. During depowdering it is not possible to clean the entire channel, so unwanted residual powder remains in the middle section of the channel. Compared to the same component produced with the Laser Powder Bed Fusion process, this powder cannot be easily removed by using strong compressed air or tapping the component on a hard surface due to the fragility of the green part. Even light tapping, for example, would break off edges of the binder jetting green part, and if one were to use a compressed air lance to remove excess powder from channels, powder that is being swirled around in the jet of compressed air and hits the part may lead to surface erosion.  
The clogging powder actually sinters more densely than the actual component (compare middle and right image of Figure 2). This is caused by the applied binder. Just as in metal injection molding (MIM), a large amount of the binder is burned on a holding stage for debinding in the sintering furnace at approximately 500 \({}^{\circ}\)C, however, the binder component known as the backbone burns later on and slightly above the temperature at which the first sintering necks are formed between the particles. This is necessary because otherwise the powder particles would no longer be held together in the component geometry [7,8]. The authors assume that the presence of this backbone in this phase of the sintering process could have a significant negative influence on the compaction process, because, for example, distances between the particles are increased or the now evaporating binder interferes with the diffusion processes. A distance of 1 \(\upmu\)m between two particles is sufficient to prevent the particles from sintering [9].