Heat Transfer Analysis in Double Diaphragm Preforming Process of Dry Woven Carbon Fibres

Double diaphragm forming (DDF) represents an efficient manufacturing technique leveraging vacuum pressure and heat to form composite material stacks between flexible diaphragms. This study focuses on the critical role of thermal management during preforming, essential for material integrity, defect mitigation, and process efficiency. A comprehensive three-dimensional finite element model (FEM) is developed to investigate the heat transfer dynamics in DDF, incorporating temperature-dependent material properties such as specific heat and thermal conductivity under compaction and varying density conditions. A novel approach is introduced to predict thermal contact conductance (TCC) across multilayer carbon fabric interfaces, validated using four laminate configurations. The resulting effective thermal conductivity of the laminates is applied in production-scale simulations, enabling accurate predictions of temperature distributions, which are corroborated by experimental data. The findings highlight the significant impact of mesoscale interactions, such as yarn-level deformation and surface asperities, on TCC variation. The study provides an enhanced understanding of heat transfer mechanisms in DDF, offering insights to optimise process parameters, improve product quality, and advance manufacturing capabilities for complex geometries.