The bond formation among polymer filaments in the fused deposition modeling (FDM) determines the mechanical behavior of resultant parts and structures. A transient updated Lagrangian finite element formulation is proposed to simulate the bond formation among molten filaments in the FDM process with flexibility in dealing with complex geometry, boundary conditions and gravitational load. Qualitative and quantitative validation of the model is carried out by comparing with sintering experiments under both isothermal and non-isothermal conditions. The model is used to investigate the effects of initial configuration and boundary conditions and gravity on the bond formation in the FDM process. Results suggest that fidelity to configuration and boundary is crucial to the prediction of bond formation. Gravity imposes opposite influences on bonds along the vertical and horizontal direction and there is a trade-off between utilizing gravity to enhance the bond formation and keep dimensional accuracy of the printing process.

熔融沉积建模（FDM）中聚合物细丝之间的键形成决定了所得零件和结构的机械性能。提出了一种瞬态更新的拉格朗日有限元公式，以模拟在FDM工艺中熔融长丝之间的键形成，并灵活地处理复杂的几何形状，边界条件和重力载荷。通过与等温和非等温条件下的烧结实验进行比较，对模型进行了定性和定量验证。该模型用于研究FDM过程中初始构型，边界条件和重力对键形成的影响。结果表明，对构型和边界的保真度对于预测键形成至关重要。