Influence of pre-cure stage upon exothermic overshoot and defects from deposition of continuous CFRP tow in AM

This study investigates the influence of the introduction of a pre-curing stage in Additive Manufacturing of continuous CFRP tows upon the exothermic overshoot and the defects generated during the deposition of the pre-cured material. This additive process aims at combining benefits from AM of CFRP laminates with the necessity of reducing the temperature overshoot during the cure of thermosetting polymers. Thermo-chemical properties of the epoxy resin XB3515 have been characterized. An FE model addressing the cure simulation has been also developed using the FE solver Abaqus, and validated. Pre-cured laminates have been manufactured to investigate the effect of the pre-cure level upon temperature overshoot and deposition-induced defects. The findings point out that the introduction of a pre-curing unit can reduce the temperature overshoot within the Carbon/Epoxy laminate and, therefore, cure-induced residual stresses. However, the following deposition phase limits the choice of the pre-cure level. A value between 20% and 30% reduces the thermal gradient by more than 90% generating in-plane waves with a severity that should not compromise the mechanical performances of the component; in particular, the compressive strength should be reduced by 2%-10%.