Flow-induced fiber displacement in non-bindered UD-NCF during Wet Compression Molding – Analysis and implications for process control

Abstract

Wet compression molding (WCM) provides high-volume production potential for continuously fiber-reinforced composite components with thermoset resins. Reduced cycle times are enabled by simultaneous infiltration, draping and consolidation within a single process step. During compression, the matrix is forced through the macroscopic stack and across its surface. This can cause undesired fiber displacements, which affect the structural performance of the processed part, as local fiber orientations can deviate from the intended one. Since already minor changes in fiber orientation can decrease the part performance, this process defect, often referred to as flow-induced fiber displacement (FiFD), should be avoided during processing. To prevent this, the WCM compression step is comprehensively evaluated by two experimental setups. First, systematic industrial-scale trials provide insight into the correlation between applied mold closing profile and resulting superficial FiFD on macro-scale. Second, a setup with transparent plates is applied to investigate the impact of superficial fluid at the stack surface on the obtained FiFD. Experimental results show positive correlations between velocity and viscosity of superficial fluid flow and observed FiFD. In this context, a more sophisticated closing amplitude of the press in combination with an adapted temperature control of the resin is proposed to minimize undesired fiber displacements.