Modeling of bonding strength for Fused Filament Fabrication considering bonding interface evolution and molecular diffusion

Fused Filament Fabrication (FFF) is one of the most widely used material extrusion additive manufacturing techniques . Its application is limited by the poor mechanical properties because of the weak bonding interface between strands. Although numerous experimental studies have investigated the effects of process parameters on mechanical performances, the bonding fracture mechanism and the quantitative relationship between process parameters and the bonding strength are not well understood. Here, we report a novel theoretical model considering coupled effects of the bonding interface evolution and molecular diffusion for predicting the bonding strength, which provides a comprehensive insight into the FFF bonding process. The model establishes an accurate relationship between process parameters and the bonding strength parallel/perpendicular to the deposition direction. Predictions agree well with experimental results and the average root mean square error (RMS) is ~5.52%. The fracture mechanism confirms the variation of the bonding interface and molecular diffusion assumed in the model. The bonding interface evolution and molecular diffusion are proved to play an important role in the bonding strength.