Post-Curing Temperature-Driven Optimization of Flexural Properties in SLA-Printed Photopolymer Resin Grades

Stereolithography (SLA) is increasingly adopted for functional prototyping, test fixtures, and short-run production, but reliable engineering use requires a clear understanding of how post-processing governs the final material state. This study examines how post-curing temperature (PCT) and resin grade (RG) jointly shape the flexural response and failure characteristics of SLA-printed photopolymers. Two commercial RGs were selected, a general-purpose formulation and an engineering “tough” formulation, and specimens were post-cured for 60 min at five PCTs (40-80 °C), using the as-printed green non-post-cured part at room temperature (25 °C) as baseline. Flexural stress-strain curves were used to extract stiffness-, strength-, strain-, and energy-based metrics, complemented by specimen-scale fracture-surface imaging to contextualize post-peak behavior. Beyond reporting absolute properties, the PCT effect is expressed through normalized amplification factors referenced to the 25 °C green part, enabling a process-efficiency view that highlights threshold behavior, saturation windows, and property-dependent divergence. The results show that the first PCT step beyond the baseline accounts for the largest fraction of stiffness and peak-stress improvement, while higher PCTs yield diminishing returns in these metrics yet can remain influential for energy accumulation up to peak stress in a RG-dependent manner. Quantitatively, the strongest stiffening and strengthening were obtained for White V4, which reached 133.6 MPa in flexural strength and 2.06 GPa in flexural modulus at 80 °C, corresponding to increases of +310 % and +329 % relative to the green state. Tough 2000 showed more moderate increases in strength and modulus, reaching 80.0 MPa and 1.52 GPa at 80 °C (+106 % and +145 %, respectively), but displayed a superior energy-absorption response, with EA increasing up to 2.12 times the green-state value. The first PCT step (25 → 40 °C) accounted for most of the mechanical improvement, namely 79–85 % of the total stiffness gain and 60–72 % of the strength gain, confirming a clear threshold–saturation behavior. The combined mechanical trends and fracture-surface observations provide practical guidance for selecting RG and PCT based on application priorities, especially when peak load capacity competes with deformation tolerance and energy absorption requirements.