3D printing of continuous fiber-reinforced thermoplastic composites (CFRTPCs) enables the fabrication of highperformance complex structures, yet warpage induced by residual-stress release remains an obstacle to dimensional accuracy. Existing studies in conventional composites, automated fiber placement/tape laying, and neat-resin 3D printing have generally attributed this problem to non-uniform thermal shrinkage; however, this explanation fails to reveal the origin and evolution of residual stress in 3D-printed continuous-fiber systems. Here, using multi-scale characterization including computed tomography (CT), morphology scanning, in situ Raman stress measurements, and oil-bath thermal treatment, we investigate the generation of residual-stress differences and warpage during CFRTPC printing. The results show that fiber residual-stress differences originate from nozzle-induced bending and subsequently undergo staged evolution during the resin cooling window and constraint-locking process. After detachment from the substrate, the printed tape undergoes time-dependent deformation jointly driven by resin viscoelasticity and the release of fiber stress differences. In this process, the resin mainly provides a transient constraint that can be weakened by post-treatment, whereas the final warpage level is governed by through-thickness fiber residual-stress differences that cannot be eliminated by posttreatment. On this basis, we establish a four-stage coupled evolution model of fiber-resin residual-stress differences, comprising heating deposition, cooling solidification, constraint locking, and residual-stress balancing. Furthermore, a synergistic process-control strategy designed around the dominant factors in different stages reduces the dimensional error from 5.0% to 0.6%, corresponding to an 8.3-fold improvement in dimensional accuracy. This work provides a mechanism-driven framework and an engineering route for high-precision 3D printing of continuous fiber-reinforced composites.
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