# Experimental Comparison of Fastener Implementation Approaches in Fused Deposition Modeling
## 4 Conclusions  
This study revealed the design and experimental results of four of the most commonly used fastener addition methods in parts manufactured using FDM technology. Two of these designs are the heat mounting of the elements that are injected into plastic. After the printing process is completed, the insert is heated and placed in the designed cavity by melting the surfaces. In the third design, an opening for the assembly of the fastener is designed in addition to a cavity in which the substance will be placed. After the printing process is completed, the square nut is placed into the cavity through this opening. In the fourth design, there is no need for an opening other than the cavity in which the substance will be placed. During printing, the fastener is placed into the part at a suitable layer in the cavity inside the part, and the printing process is to be continued. After the printing is completed, no postprocessing is needed.  
The printing process times are almost the same for each of the four designs. Although the postprocess times were added to print times, differences of up to 10% occur between some samples.  
It can be concluded that the type I.a design is more dependent on the surface rather than the infill, while type I.b is directly related to the infill ratio. The failure characteristic of the basic inserts used in the type I.a samples is by the separation of the bond surface. Failure with more advanced inserts such as the ones used in type I.b is not separating from the surface but disintegrating the infill structure. On the other hand, the longer design of the insert used in type I.b results in lower strength in the flexural tests. This relates to affecting the durability of the overall structure.  
Type II design is also much more dependent on the infill ratio, and the graph is almost linear. Type III design depends on both the infill ratio and the surface. Increasing the strength from 10% to 20% depends on increasing the filling. However, the increase in strength from 20% to 40% is much less due to wall thickness becoming important for loads at this level.  
From the perspective of torque capability, most of the designs investigated in this study are capable enough for basic needs. In addition, the test results reveal that type I.b and type III designs can hold more than standard M4 screw, which is designed for when used with 40% or more infill.  
When manufacturing components for unmanned aerial vehicles (UAVs), prioritizing lightweight construction is paramount, yet the challenge of ensuring robust connections, which endure diverse loads, necessitates the consideration of various assembly techniques. For the assembly of electronic components, hot insert can be preferred, which is the method that least affects the rest of the design, and the captive nut method can be preferred in wing-to-fuselage assemblies or motor mounts, which offer higher strength. In some applications such as prosthetics, expectations from fasteners may vary. In addition to providing high strength, it is also important to avoid situations such as dislocation of the fastener during assembly and disassembly. In addition, the type III application stands out as the method that least affects the visual of the piece.  
F.F.O.: investigation, methodology, formal analysis, validation, visualization, writing. I.K.: writing--review and editing. E.P.O.: visualization, writing--review and editing. All authors have read and agreed to the published version of the manuscript.  
This research received no external funding.  
Not applicable.  
Data availability Statement: Data are contained within the article.  
The authors declare no conflict of interest.