Understanding printing pressure on the mechanical performances of 3D printed thermoplastic composites: modelling and experiments

Printing pressure represents a critical processing parameter that exerts substantial influence on the interlayer adhesion of 3D-printed fiber-reinforced thermoplastic composites, consequently determining their mechanical performance. In this investigation, a non-isothermal computational fluid dynamics (CFD) model was developed, incorporating the non-Newtonian rheological behavior of molten thermoplastic materials during the fused filament fabrication process. The CFD simulations demonstrated remarkable accuracy in predicting printing pressure distributions, which were validated through real-time measurements of printing forces using a high-precision force monitoring system integrated into the build platform. Quantitative analysis revealed that the generation of printing pressure is predominantly governed by two mechanisms: (i) the compressive forces induced by the nozzle head on newly extruded thermoplastic materials, and (ii) the impact forces resulting from the deceleration of molten thermoplastic deposition onto the build platform or previously deposited layers. Furthermore, the CFD model enabled the establishment of a correlation between print quality and printing pressure. Detailed mechanistic analysis was conducted to elucidate the fundamental causes of inadequate interlayer adhesion with respect to various printing parameters. The experimental results conclusively demonstrated that optimized printing pressures effectively eliminate intra-filament voids while simultaneously increasing the interfacial contact area between adjacent layers, thereby significantly enhancing the interlayer adhesion strength in printed composite structures.