Linear direct current sensing system for flow monitoring in Liquid Composite Moulding

Direct Current (DC) resistance measurement is a well-established technique for monitoring Liquid Composite Moulding (LCM) processes. Through on-line resistance measurement of the sensing gap between two crossing wires (i.e. at a node), it is possible to determine the presence of resin and the degree of curing at the node location. Linear Direct Current (LDC) measurement as presented in this paper is based on the same physical principle. The main advantage of the LDC method is that the flow front position can be tracked along the entire length of two contiguous wires and not only at discrete node locations. Preliminary measurements were conducted in a ID flow channel to quantify the sensitivity of the LDC sensing technique and to optimise the experimental set-up. Evaluation criteria include the qualitative comparison of results of visual and LDC monitoring systems with regard to position and shape of the flow front and permeability characterisation. Permeability of the fibre lay-up in the flow channel was determined using output data from the LDC measurement and with conventional methods based on video capture of the flow front position. Comparison of the results shows a difference of 0.02 X 10(-11) m(2) between K-LDC and K-visual which corresponds to a relative difference of 0.45%. The second part of the paper deals with the improvement of measurement accuracy and data handling. A software was developed to display the 2D flow front position based on the information provided by the LDC system. This study has shown the potential of the technique for monitoring LCM injection processes. Next step will include the application of LDC technology in an industrial environment to support the fabrication of complex-shaped 3D structures. (C) 2002 Elsevier Science Ltd. All rights reserved.