Applicability assessment of thermoset coating onto additively manufactured thermoplastic composite molds

Abstract

Coatings can significantly enhance the surface characteristics of printed molds however, there is no guideline to assess the coating applicability for additively manufactured fiber-reinforced thermoplastic molds. Therefore, the applicability of a thermoset polymer surface coating onto additively manufactured carbon fiber-reinforced Polyphenylene Sulfide (CF-PPS) composite mold was investigated. The coating application temperature should not be higher than the maximum operable temperature of the substrate. Therefore, Dynamic Mechanical Analysis (DMA) of the printed CF-PPS was performed to characterize the dependence of the elastic modulus on temperature as well as to verify the thermal stability of the printed molds at the coating processing temperature. The cure kinetics of the coating material was characterized to guide the design of processing conditions to achieve a complete cure of the thermoset resin. The composite mold needs to withstand multiple thermal cycles for the part manufacturing process. Thermal degradation of the coating was assessed for multiple thermal cycles utilizing Thermogravimetric Analysis (TGA) and the results did not show significant degradation. To provide insights into the coefficient of thermal expansion (CTE) mismatch between the coating and the printed CF-PPS, the CTE was characterized for both material systems. Additionally, the coating adhesion was characterized via pull-off tests after multiple thermal cycles and the results revealed no significant change in the pull-off strength after ten cycles. Finally, the coating was demonstrated on a mold printed with CF-PPS which was subjected to multiple autoclave composite part manufacturing cycles. The durability of the coating and the geometrical deviation of the mold were investigated throughout the manufacturing cycles.