The Use of Evanescent Wave Fluorescence Spectroscopy for Control of the Liquid Molding Process

Fluorescence has been demonstrated to be an accurate measurement of resin cure and is measured using an evanescent wave fiber-optic sensor. An economical optical fiber sensor has been developed with a refractive index in excess of 1.6, permitting evanescent wave monitoring of epoxy resins. In this work, the fluorescence wavelength-shift, which has been correlated with monomer conversion, is monitored during the liquid molding process. A hierarchical control strategy is being developed for liquid molding processes that will use the cure measurement provided by the evanescent wave fluorescence sensor. Single input/single output control loops are implemented at the base level to regulate the mold temperature, the vacuum pressure in the mold, either the inlet flow or pressure during injection, and the final mold pressure. A model-based feedback controller is implemented to control the chemical cure and manipulates the setpoint of the temperature controller to achieve cure control. A general high-level controller is under development to optimize the process under a wide range of operating conditions.

[1]  R. Loutfy.  High-conversion polymerization of fluorescence probes. 1. Polymerization of methyl methacrylate , 1981 .

[2]  G. Martin,et al.  Diffusion and Diffusion-Controlled Kinetics during Epoxy-Amine Cure , 1994 .

[3]  Scott D. Schwab,et al.  Free-Volume-Dependent Fluorescence Probes of Physical Aging in Polymers , 1990 .

[4]  G. A. Pogany.  Gamma relaxation in epoxy resins and related polymers , 1970 .

[5]  L. Mandel,et al.  Absorption and Emission of Evanescent Photons , 1972 .

[6]  Tomas Hirschfeld,et al.  Effect of numerical aperture on signal level in cylindrical waveguide evanescent fluorosensors. , 1987, Applied optics.

[7]  P. Deshpande,et al.  Advanced process control for injection molding , 1991 .

[8]  Hyung‐Joon Paik,et al.  Fiberoptic intrinsic fluorescence for in-situ cure monitoring of amine cured epoxy and composites , 1994 .

[9]  M. Afromowitz,et al.  Fiber optic polymer cure sensor , 1988 .

[10]  J. Andrade,et al.  Remote fiber-optic biosensors based on evanescent-excited fluoro-immunoassay: Concept and progress , 1985, IEEE Transactions on Electron Devices.

[11]  King-Fu Lin,et al.  Fluorescence monitoring of polarity change and gelation during epoxy cure , 1994 .

[12]  N. Sung,et al.  In‐situ cure monitoring of diamine cured epoxy by fiberoptic fluorimetry using extrinsic reactive fluorophore , 1994 .

[13]  S. D. Schwab,et al.  Monitoring the composite curing process with a fluorescence-based fiber-optic sensor† , 1991 .

[14]  Peter Craven,et al.  Smoothing noisy data with spline functions , 1978 .

[15]  John F. Maguire,et al.  Remote Raman spectroscopy as a sensor technology in composite materials processing , 1995 .

[16]  F. Phelan,et al.  Interpretation of 3‐D permeability measurements for RTM modeling , 1995 .

[17]  Chong Sook Paik Sung,et al.  Characterization of epoxy cure by UV-visible and fluorescence spectroscopy: azo chromophoric labeling approach , 1986 .

[18]  In situ sensor monitoring and intelligent control of the resin transfer molding process , 1994 .

[19]  N. J. Harrick,et al.  Internal reflection spectroscopy , 1968 .

[20]  Joseph L. Rose,et al.  In‐line optical monitoring of polymer injection molding , 1994 .

[21]  M. F. Hutchinson,et al.  Algorithm 642: A fast procedure for calculating minimum cross-validation cubic smoothing splines , 1986, TOMS.

[22]  D. Hunston,et al.  Cure Monitoring for Polymer Matrix Composites , 1986 .