Decomposition-free synchronous multi-layer cooperative 3D printing for enhanced strength and structural integrity

Cooperative 3D printing can accelerate fabrication of large-scale structures by using multiple print heads; however, many cooperative strategies decompose a part into sub-domains, which introduces decomposition seams and alters inter- and intra-layer gap times. These changes can degrade bonding and modify stress evolution, reducing mechanical performance and increasing failure risk. This paper proposes a decomposition-free cooperative strategy, Synchronous Multi-Layer Printing (SMLP), in which each head prints complete layers under a controlled time shift, enabling synchronous deposition paths without geometric partitioning. SMLP is evaluated using thin-wall specimens produced by two extrusion-based additive manufacturing processes to connect strategy-induced timing effects to material integrity. First, SMLP is implemented on a dual-head fused deposition modeling system and compared against a traditional decomposition-based multi-head strategy using tensile and tear tests. Paired comparisons show that SMLP increases interlayer tensile strength by ~ 12.4 MPa (≈ 30%) relative to the traditional multi-head strategy ( p < 0.001), while tear strength is statistically unchanged ( p = 0.831). Second, to assess implications for large-scale construction AM, an analytical model is developed for extrusion-based concrete printing that maps strategy-dependent timing fields to time-dependent yield-stress evolution and compares them against evolving shear stress in straight walls. The polymer and concrete studies are linked at the cooperative-strategy level: in both cases, SMLP modifies the deposition-time history, and that timing history governs a material-specific strength evolution process. The polymer experiments resolve this through interface-limited tensile behavior, whereas the concrete model resolves it through time-dependent yield-stress development and structural stability. The model predicts that, over the parameter ranges considered, SMLP reduces build time by ~ 24% compared with single-head printing and increases the number of buildable layers before collapse by ~ 100–300% compared with traditional multi-head printing. Together, the experimental and analytical results support SMLP strategy improves both strength and structural integrity along with productivity.