Comparison of joining hole making methods for fiber reinforced FDM 3D printing parts

In this paper, continuous fiber reinforced plastic composite fused deposition modeling (FDM) 3D printing and conventional material removal processing methods were combined to investigate the effects of hole-making methods (printing, drilling and helical milling) and fiber filling patterns (solid pattern and rhombic grid pattern) on the quality and mechanical properties of joining holes in printed parts. This study evaluated the cutting forces during hole machining and assessed hole quality based on defect analysis, diameter accuracy, roundness error, and wall morphology, complemented by cost comparisons. It was observed that holes manufactured by conventional material removal methods were of better quality, but were also more costly. Tensile tests were conducted on the bolted joint structures to evaluate the mechanical properties of the joining holes, and scanning electron microscopy (SEM) examinations were performed on the cross-sections of bolted joints to analyze the tensile damage patterns. It was found that helical milled holes exhibit unique damage patterns and greater ultimate tensile displacements due to the existence of fibers directly involved in load bearing at the hole walls. This leads to a significant increase in energy absorption performance. The tensile properties of the structures consisting of specimens with a fiber filling angle of 0°/90° were superior to those with a fiber filling angle of 45°/135°. Additionally, the mechanical properties were found to be slightly better using the rhombic grid pattern than the solid pattern for the same fiber filling density and fiber filling angle. These findings provide valuable insights into the choice of preparation methods for joining holes in 3D printed parts to achieve optimal performance in a variety of engineering applications.