Process–material optimization for reliable bottom‑up DLP 3D printing with TMPTA–HDDA resin systems

Bottom‑up Digital Light Processing (DLP) enables high‑resolution polymer fabrication but is limited by overcure in fine features and shrinkage‑induced residual stresses that cause warpage and cracking in larger geometries. In this study, practical formulation–process guidelines for cost‑effective acrylate resins based on Trimethylolpropane Triacrylate (TMPTA) and 1,6‑Hexanediol Diacrylate (HDDA) are established, and a comparative assessment of these two economical monomers for bottom‑up DLP 3D printing is presented. The investigation focuses on key factors affecting print quality, including warpage behaviour and curing characteristics, while examining the influence of photoinitiator concentration and UV absorbers (e.g., Tartrazine) on process optimization. Experimental results show that objects with diameters up to 2 cm were successfully printed using both TMPTA and HDDA. TMPTA-based systems exhibited faster curing and lower warpage, making them more suitable for high-precision printing. Conversely, HDDA provided better light attenuation but resulted in greater deformation. Warpage was found to increase with higher photoinitiator concentrations, whereas adding UV absorbers or light blockers (such as Tartrazine) effectively reduced light penetration and scattering. For larger geometries (diameter > 2 cm), polymerization shrinkage induced internal stresses and cracking, which were mitigated by blending HDDA and TMPTA. The optimized formulation – HDDA and TMPTA at a 40:60 wt ratio – achieved balanced adhesion, dimensional stability, and good hardness (Shore D: 82–88) at a recommended exposure time of 9 s. For successful printing of large, complex parts, the addition of 0.2 wt% tartrazine as a light blocker, combined with the use of the HDDA–TMPTA blend, is recommended to effectively eliminate cracking. These findings offer practical guidelines for resin formulation and parameter tuning to improve precision and reliability in DLP-based additive manufacturing.