G.A. Barandun

Linear direct current (LDC) resistance measurement for online LCM-process monitoring

On-line monitoring of the Liquid Composite Moulding (LCM) process is a key element to improve quality and to reduce manufacturing cost for complex parts. In this context, direct current (DC) resistance measurement is a promising sensing technique allowing to track both flow front position and degree of curing of the resin during injection. One possible geometrical configuration to measure DC resistance in a mould is to dispose two electrically conductive fiber grids orthogonally on non-intersecting planes (DC-SMARTweaveTM technique). On-line resistance measurement of the sensing gap between two wires crossing (i.e. node) allows to determine the presence of resin and the degree of curing at this node location. An original measurement technique (LDC: Linear Direct Current) based on the same physical principle was developed to record the flow front position continuously. Linear DC allows to track the flow front position on the overall length of two contiguous wires and not only at discrete nodes location. Two experiments were conducted in a 2D-glass tool in order: (1) to evaluate the potentiality and reliability of the standard DC-SMARTweaveTM technique. (2) to test in-house developed software, based on LabVIEW, which allows to quantify the time discrepancy between DC-measurement and LCM-simulation. Results and comparison between video capture, LCM-simulation and DC-resistance monitoring has shown a good agreement (see appendix A). A first measurement in a 1D-flow channel was conducted to quantify the sensitivity of the Linear DC (LDC) technique and test an in-house developed software which permits to give, before an injection, the LDC geometrical set-up to optimize data acquisition and data processing. The permeability of the fibers laid-up in the 1D- flow channel can be calculated, first based on the video capture K visual of the flow front position and second directly based on the output voltage of the LDC-measurement KLDC. A discrepancy smaller than 1% between Kvisual and KLDC has shown a good potential of this original LCM- monitoring technique and need to be tested later on a production part to characterize local variation of the permeability due to drape of the fiber material.