Investigation of draping and its effects on the mold filling process during manufacturing of a compound curved composite part

Resin Transfer Molding (RTM) is a composite material manufacturing process during which resin is injected into a mold cavity filled with a fibrous reinforcing preform. Application of woven and stitched fiber mats in fabricating preforms for RTM is a highly viable means of manufacturing affordable composites. Draping, in this paper, refers to the act of bringing a flat workpiece into contact with an arbitrary tool surface. As a result, the draping of woven and stitched mats tends to cause the mat to deform to the tool geometry. This paper details an experimental study designed to demonstrate the effect of draping preforms on mold filling, and final structure of the composite product. A mold was built providing a conical mold cavity. Flow visualization experiments were performed, as well as shearing angle and preform fiber volume fraction measurements from manufactured cone parts. Experimental results show that draping does significantly change fiber orientation, fiber Volume fraction, permeability and hence the injection pressure or flow rate required to fill a mold. This data was compared with numerical prediction codes for preform deformation, permeability calculation, and mold filling. Preform deformation predictions were found to overpredict in areas of high deformation, due to the assumptions made by the numerical algorithm used. Permeability components calculated are reasonable, but are affected by overpredicted preform deformation, and interpolation methods used. Prediction of injection pressure and flow rate histories are good, while predicted flow front shapes fail to capture some experimental features. Difficulties in predicting flow front shapes are attributed to three mechanisms; a decrease in permeability magnitudes due to increased volume fraction, a smaller Volume of fluid required due to increased volume fraction, and reorientation of fiber tows changing the direction of principle permeability components. (C) 1997 Elsevier Science Limited.