## 1 Introduction  
Additively manufactured (AM) components are built layer by layer, which enables the production of products of high complexity as well as filigree, rigid, and high-strength structures. Advantages of this process, such as almost unlimited design freedom and tool-free production, allow for a wide variety of applications in many fields [1]. Innovative foundry manufacturers discovered the benefits of additive manufacturing early on. Additively manufactured patterns, molds, and cores have several advantages, including improved part consolidation, material efficiency and on demand production [2]. Therefore, they are now being increasingly used and have become mainstream in this industry. As the actual component is produced using a conventional casting process, this type of additive manufacturing is referred to as indirect additive manufacturing [3].  
Additive manufacturing of molds and cores in the foundry industry can be based on an organic cold resin system [4]. Another possibility is the use of an inorganic binder system [3]. In this case, an inorganic binder based on water glass is applied to the sand bed. Compared to organic binders, inorganically-bound cores and molds have various advantages [5]. For example, there are no emissions during core production, a significant reduction in emissions during casting, no organic condensate adhesion to the casting, and improved material properties. In addition, the economics of the casting process are improved due to reduced maintenance of casting tools and reduced air treatment [6].  
One challenge in 3D printing with an inorganic molding material system is part quality. The possible drying of individual nozzles on the 3D printer's print head can result in unconnected areas in the part [7], which have lower strength due to the lack of binder. Inorganic binder systems need thermally induced curing [1]. However, inorganic core binders can also be activated by CO\({}_{2}\)[8]. Therefore, the binder in the nozzle can solidify if it is in contact with CO\({}_{2}\) without cleaning it regularly. According to [PERSON] et al., another reason for defective nozzles is buildup on the print head, such as sand grains or misdirected drops [9].  
To counteract the problem of defective nozzles, the condition of print heads is usually checked manually before each print job by printing a test pattern on a pH indicator paper. If the quality of the print head falls below a defined threshold, various cleaning processes can be used to restore the functionality of the nozzles. This procedure allows the condition of the nozzles to be checked and, if necessary, improved before the printing process begins. Another possibility is the continuous optical control of each layer as proposed by [PERSON] et al. [9]. Defective nozzles can be detected by lines without binder in the individual layers.  
This article aims at a feasibility study of acoustic print head monitoring. Modal analysis is a popular way to determine the elastic parameters of materials [10; 11]. However, the monitoring of industrial manufacturing processes is researched in numerous articles as well [12; 13].  
In this article, an acoustic print head analysis is implemented, instead of manual control by means of a test print. This acoustic analysis can be automated easily and has the potential for online monitoring. In a first step, the acoustic data must be recorded by attaching a suitable sensor system for monitoring the print head. In addition, a suitable evaluation methodology must be developed that searches for acoustic patterns in the signal and uses these to draw conclusions about the condition of the nozzles. This evaluation will be performed with Artificial Neural Networks (ANN). ANNs and machine learning have been utilized to evaluate acoustic emissions and structure born noise in an industrial environment for predictive maintenance in numerous articles [12; 14], however there is no study on the analysis of piezo print heads.