Self-Loosening Characteristics of Three-Dimensional Printed Bolted Joints

A bolt joint is a simple element that joins mechanical components. Self-loosening of bolted joints occurs due to the vibrations caused by motors and engines, resulting in the breakage of machines, deterioration of performance, and potentially serious safety problems. Recently, developments in three-dimensional (3D) printing technologies have enabled the fabrication of detailed components. These technologies can be used for producing fasteners using 3D printed bolts. Many researchers have proposed a theoretical model for self-loosening of the steel bolt, and experimental studies on the self-loosening phenomenon have been advanced. However, studies on the self-loosening of 3D printed bolts have not been conducted. Therefore, this study aims to confirm the self-loosening phenomenon and the safety of 3D printed bolts through experiments and finite element (FE) simulation. The self-loosening phenomenon in the cases of transverse vibration of standard M12 x 1.75 x 70 hex bolts made using stereolithography apparatus printer is observed experimentally. A lateral vibration test system is constructed and self-loosening of the bolt is evaluated by observing the axial force according to the vibration cycle by using a strain gauge. This study confirms the self-loosening of 3D printed bolts by changing the preload and amplitude. In addition, the FE simulation is verified through experimental results. Experimental results show that the 3D printed bolt loses much clamping force due to lateral vibration. Through this study, it is expected that 3D printed bolts will be used more frequently in situations where specially shaped bolts are needed.