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Abstract This study presented a comprehensive computational fluid dynamics-based model for fused filament fabrication (FFF) three-dimensional (3D) printing multiphase and multiphysics coupling. A model based on the framework of computational fluid dynamics was built, utilizing the front-tracking method for high precision of multiphase material interfaces, a fully resolved simulation at the mesoscale explores the underlying physical mechanism of the self-supported horizontal printing. The study investigated the influence of printing temperature and velocity on the FFF process, exhibiting a certain self-supporting forming ability over a specific range. The results indicated that during the printing of large-span horizontal extension structures, the bridge deck material transitions from initial straight extension to sagging deformation, ultimately adopting a curved shape. The straight extension distance is inversely proportional to the depth of the sagging deformation. Additionally, the study revealed that printing temperature primarily affected the curing time of the molten material, while printing velocity fundamentally affected the relaxation time of both thermal and dynamic characteristics of the material.

In view of the problem that the measurement accuracy of screen gaps is affected by the R region of the transition rounded corner of the large-size flat back cover, a mobile vision system with dual linear motor synchronous drive is designed to realize precise positioning of monocular vision in 16 local image acquisition positions set in the R region. Full-size measurement of the R region is achieved using local information fusion to accurately measure the screen gap. First, to solve the problem of edge breaking and the blurring of local images, a region extraction and segmentation method based on block statistics is proposed to quickly obtain accurate outer edges. Then, an adaptive Hough line detection method based on dichotomy is proposed to accurately locate the outer edges. The experimental results show that the accuracy of region extraction and segmentation is up to 99.68% within 60 ms; the angle error and position error of line detection are less than 0.01° and 0.2 pixels, respectively. With optimal anti-interference performance, the proposed algorithm realizes the adaptive and accurate positioning of the outer edge within 200 ms; the measurement time and the measurement error of the measurement system are less than 6.0 s and 0.03 mm, respectively.

Part-level thermal-mechanical simulation with filament resolution is currently a significant challenge for material extrusion processes. This paper proposed a novel method to achieve part-level and high-fidelity simulation for such processes, where the physical behaviours of heat transfer, viscoelasticity, dynamics, and contact are comprehensively considered. This method integrates a sophisticated thermal-mechanical contact model with a thermo-viscoelastic dynamic model. The kinematic and dynamic behaviours of the filaments were described based on the theory of discrete differential geometry, and the contact force and heat transfer between multiple filaments were modelled by using a newly defined contact element with spring-dashpot forces and heat conduction. The contact parameters were determined, and the accuracy was validated through contact experiments. The contact reheating and temperature distribution were quantified, and the effects of the printing parameters on the contact heat transfer and deformation were examined. Several part-level cases were simulated to demonstrate its capability in industrial applications.