Recent advances of defect-driven hybrid additive manufacturing of extrusion-based polymers: bridging multiscale mechanisms to enhanced structural performance

This review proposes a defect-driven framework to advance extrusion-based polymeric hybrid additive manufacturing, systematically addressing three intrinsic limitations: geometric inaccuracy and surface roughness, high porosity, and weak interlayer bonding. By integrating additive manufacturing (AM) with subtractive machining, dynamic compaction, and multi-energy field assistance, we establish a multiscale process–structure–property linkage that connects interfacial micro-mechanisms to macroscopic structural performance. Three representative hybrid paradigms are highlighted: (1) additive–subtractive hybridization combining FDM/DIW with milling or laser cutting to effectively minimize dimensional deviation and improve surface finish through geometric recalibration; (2) additive–equivalent compaction utilizing roller- or hammer-assisted pressure to activate polymer chain diffusion across interlayer interfaces, markedly reducing porosity and enhancing bonding strength; and (3) multi-energy-field assistance, where ultrasonic, thermal, and magnetic fields modulate crystallization behavior and anisotropic functionality. Experimental studies across various materials and geometries collectively demonstrate that hybrid process integration can suppress defect formation by coupling molecular diffusion dynamics with process optimization. With continuing progress in multi-field coupling and intelligent process control, hybrid additive manufacturing is evolving toward more adaptive, digitally driven, and multifunctional fabrication systems. This technological convergence is expected to provide greater design freedom and improved manufacturing efficiency for next-generation polymers and composites.