Thermal Expansion and Thermomechanical Dimensional Stability in Vat-Printed Photopolymers

Thermomechanical dimensional stability in vat-photopolymerised polymers is controlled by more than a single coefficient of thermal expansion (CTE). Linear expansion can vary with temperature, cure state and network mobility; the response can change near glass transition; repeated heating can reveal residual cure or irreversible strain; and the printed architecture can introduce orientation-dependent behaviour in some systems while other SLA systems show little or no measurable thermal-expansion anisotropy. Direct VPP evidence supports both sides of that boundary. Peterson et al. used thermomechanical analysis in a DLP-printed graded-crosslink system [1]. Sekmen et al. showed that thermo-viscoelastic behaviour and shrinkage depend on degree of cure and temperature in a commercial SLA/DLP photopolymer [2]. Klimtova and Vesely found no orientation-dependent thermal expansion in the SLA epoxy system they tested, despite strong anisotropy in FFF controls [3], whereas Nabavian Kalat et al. reported orientation-dependent thermal expansion and dimensional stability in an SLA shape-memory epoxy [4]. ER-96 therefore treats CTE as a conditioned material-state measurement rather than a universal datasheet constant. The qualification architecture combines specimen-state definition, TMA/dilatometry, temperature-window control, heating/cooling history, orientation comparison where justified, and component-level dimensional checks when inserts or dissimilar materials create CTE mismatch.