Design of non-assembly joints incorporating randomness generated through a publicly accessible 3D print farm

Abstract

Traditionally, technical hinge joints are made of multiple parts, which need to be assembled. Additive manufacturing (AM) provides the option to overcome these assembly steps since movable mechanisms become manufacturable in a streamlined manufacturing route. The feasibility for such so-called “print-in-place” approaches has been proven and punctual design recommendations are available in additive manufacturing community knowledge. Still, a generalized assessment of the influencing parameters is absent because the layout of the gap of a joint highly depends on the AM boundary conditions. This study considers manufacturing simple hinge joints by the method of fused filament fabrication (FFF) on commercially available 3D printers. In order to generate representative scatter, the manufacturing jobs of the specimens are placed on a 3D print farm in a university fab lab. The machines are utilized and maintained by a public community, which also utilizes different materials suppliers in a randomized manner. Series of print-in-place joints are printed with statistically relevant repetitions under variation of the hinge joint gap, print orientation and AM layer height. After manufacture, the joints are tested to provide statistical information on force necessary for motion. The results indicate that with a reduction of gap width, the forces necessary to initially release and move the joints begins to rise until complete fusion of bushing and hinge axis. If the hinge axis is aligned with the Z-axis of the 3D printing process tighter critical clearances become manufacturable than with a hinge alignment in the XY-plane of the 3D printer. Moreover, reduced scatter of the results is obtained in the Z-axis. As for the layer height, it is seen that layer heights of 0.1 mm might lead to increased release forces while the largest adjusted layer height of 0.3 mm led to increased forces during the hinges’ motion.