# Experimental Comparison of Fastener Implementation Approaches in Fused Deposition Modeling
## 1 Introduction  
Additive manufacturing (AM), usually referred to as 3D printing, is an innovative manufacturing technique that has gained significant acclaim in several industries. Its application spans across various disciplines, such as engineering, materials science, and medicine, demonstrating its adaptability and extensive influence [1, 2, 3]. This technology has profound consequences for design and manufacturing, impacting the qualities of parts, design possibilities, supply chains, manufacturing methods, and business models [4]. AM is a manufacturing technique that utilizes 3D CAD model data to directly produce a physical solid model by adding material layer by layer [5, 6]. This contrasts with conventional techniques of material processing. AM procedures allow for the production of intricate geometric structures, providing a notable benefit compared to traditional machining methods [7, 8]. In addition, AM is utilized for the production of prototypes, tooling,and functioning goods. It also holds significant promise in the optics industry for creating mechanical components [9]. Additionally, technology is causing a shift in manufacturing business models towards the practice of mass customization, responsible production, and sustainable consumption [10; 11]. AM systems can be coupled with other technologies, becoming a hybrid machine. The most common example of hybrid machines is combining AM systems with subtractive systems, such as milling machines. Parts can be manufactured as AM with milled surfaces; also, in some cases, these systems can also be used to repair parts [12]. Fused Deposition Modeling (FDM), alternatively referred to as Fused Filament Fabrication (FFF), is a prevalent AM technique [13; 14; 15]. One of its main advantages is its cost-effectiveness, making it accessible for personal use, education, and small businesses. FDM is compatible with a variety of materials, including ABS, PLA, and nylon, which allows for flexibility in application and functionality [16]. The biggest differences that distinguish FDM are that it can use two or more different materials in one print and that it can form cavities inside the part that are not connected to the outside. Thanks to these properties, we can use flexible and rigid materials in a single piece, 4D composite structures can be obtained with materials that react differently when exposed to temperature, or a functional gap can be created by removing one of the materials with a chemical solvent [17]. In FDM printing, by leaving gaps in the interior of the parts, the part can be made lighter without affecting the external form of the part, and these gaps can also be used for different purposes as they can react differently to sound waves and RF signals [18; 19]. These spaces also allow us to insert functional objects into the part during printing [20]. These functional objects may be a magnet, sensor, or strength-enhancing support structure, or it may be possible to place fasteners such as bolts and nuts. The cavity for the fastener can be designed in the CAD process, and according to some studies, the cavity can also be calculated by the software relevant to the fastener. Using hybrid systems, nuts or other fastener parts can be embedded automatically without human interaction [21]. In many manufactured designs, it is necessary to assemble the parts together. While the bonding method can be used to connect parts produced by AM to each other or to other parts, fasteners are often preferred. In current studies, studies on fasteners produced by AM are included in the literature [22; 23]. Screws and nuts produced with FDM have the ability to be designed according to need, but they also have some limitations brought about by the production method. One of these limitations is the low strength of the plastics used in FDM compared to the materials used in fasteners. Another limitation is the surface roughness caused by the layer thickness of the FDM [24; 25; 26]. This feature leads to both reduced strength and tolerance problems as screw diameters are reduced.