Load-Bearing Assessment of Threads in 3D-Printed Polymer Elements

The article presents a comparative analysis of mechanical properties of M8 threaded joints produced using three different methods, in rectangular nylon (PA 12) specimens manufactured in SLS technology. Threaded holes in specimens were made by direct thread printing (specimens marked PT), thread reinforcement with Helicoil inserts (HT), and the use of heat-set inserts (IT). The specimens were subjected to a tensile testing at a constant displacement rate of 2 mm/min. The maximum force and the displacement at failure were recorded. The results indicated that the lowest load-bearing capacity <i>F</i>_MF was observed in the printed thread specimens, with an average value of 3.41 kN. The use of heat-set inserts increased <i>F</i>_MF to 3.83 kN, representing a 12% improvement. The highest load-bearing capacity was achieved in specimens reinforced with Helicoil inserts, which enhanced joint strength by 40% compared to printed thread specimens, reaching an average <i>F</i>_MF of 4.78 kN. In all cases, failure occurred due to the thread or insert pull-out from the specimen material. Studies have shown that the use of metal inserts significantly enhances the strength of threaded joints in SLS-printed PA12 components. Helicoil inserts provide the highest <i>F_MF</i> load capacity, while heat-set inserts offer better technological advantages. Although printed threads are easier to manufacture, their applicability is limited to larger thread sizes and lower mechanical loads.