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Induction Heating Assisted Permeation Enhancement for the VARTM Process

Induction Heating Assisted Permeation Enhancement for the VARTM Process. Richard Johnson and Ranga Pitchumani University of Connecticut Composites Processing Laboratory 191 Auditorium Road, Storrs, CT 06269 www.engr.uconn.edu/cml Sponsors: NSF(CTS-9912093), AFOSR(f-49620-01-1-0521)

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Induction Heating Assisted Permeation Enhancement for the VARTM Process

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  1. Induction Heating Assisted Permeation Enhancement for the VARTM Process Richard Johnson and Ranga Pitchumani University of Connecticut Composites Processing Laboratory 191 Auditorium Road, Storrs, CT 06269 www.engr.uconn.edu/cml Sponsors: NSF(CTS-9912093), AFOSR(f-49620-01-1-0521) Presented at the International SAMPE Technical Conference. Nov. 5th 2002. Baltimore, MD

  2. Outline • Introduction to VARTM • Process description • Controlling the mold filling stage • Numerical Modeling • Nonisothermal mold filling with induction heating • Experimental Setup • Model Validation • Results • Questions

  3. Process Description • Vacuum Assisted Resin Transfer Molding (VARTM) • Preform permeation is a critical step • voids and dry spots = poor part quality

  4. Process Difficulties - Filling • Variation in preform permeability from that predicted by theory leads to non-uniform fill • uncertainty in pore structure • heterogeneous preform layups • race tracking • Need for flow control

  5. Control • Boundary control methods show reduced controllability further from the controlled boundary • Need for more localized control D. Nielsen, R. Pitchumani (COMPOS PART A-APPL S: 2001) (COMPOS SCI TECHNOL: 2002) (POLYM COMPOSITE: 2002)

  6. Mold Fill - Heterogeneous Preform Layup • Heterogeneous layups can lead to dry spots • Proposed control scheme: Active localized heating Line Source Low Permeability Patch Line Vacuum

  7. Mold Fill with Heating • Addition of heat to the low permeability area • improved uniformity • elimination of voids and dry spots Line Source Low Permeability Patch Uniformly Heated to 60C Line Vacuum

  8. Heating Methods • Resistive • contact required • Ultrasonic • contact required • possibility of ultrasonic horn melting vacuum bags • Induction • compact, mobile heating unit • requires susceptors • Laser • requires fast scanning of intentionally defocused beam

  9. emfi Induction coil geometry Numerical Modeling - Induction Heating • Induction power calculation • current conservation at the nodes of the susceptor mesh • summation of voltages in a loop = emf I2 I1 I3 I4

  10. Numerical Modeling - Flow • Flow governed by Darcy’s law: • Pressure distribution: • five-point Laplacian scheme • Darcy’s law used to find velocities • volume tracking method used to find the flow front locations • BC’s • Walls impenetrable with no slip • vacuum line defined with negative pressure • inlet defined by atmospheric pressure at the surface of the source container • Permeability • Carman-Kozeny relationship: • Cz values from literature:

  11. Numerical Modeling - Heat Transfer • Energy equation: • 3-D control volume analysis and ADI method (Douglas and Gunn: 1964) • BC’s • mold sides considered adiabatic • top surface of the vacuum bag and bottom surface of the mold considered convective • inlet and outlet at ambient temperature

  12. Numerical Modeling • Coupled by viscosity • Arrhenius equation: • flow is dependent on temperature through viscosity • temperature is dependent on the flow • Iterative solution • convergence based on temperature: • Time step varied • mesh Courant number • mesh Fourier numbers

  13. Experimental Setup

  14. Model Validation Vacuum Level: 77kPa Coil Voltage: 125V Coil Position: 5.08cm P = -77 kPa No Heating Vacuum Level: 77kPa Coil Voltage: 140V Coil Position: 15.24cm

  15. Numerical Study • Parametric study • varied parameters • induction coil location • (stationary in each simulation) • induction coil voltage • vacuum level • permeability ratio

  16. Definition of maximum and quasi-steady-state temperature If the maximum allowed temperature is 100oC then Vmax = 85V Results - Upper Bound

  17. Coil location: 15.24 cm Vacuum level: -77 kPa Coil location: 5.08 cm Vacuum level: -77kPa Results - Lower Bound

  18. Results - Central Patch •  vacuum level  higher allowable voltages • Coil locations closer to the inlet • upper bound  higher allowable voltages • lower bound increases sharply with permeability ratio 10.16 cm 5.08 cm 15.24 cm

  19. Results - Central Patch with Race Tracking • Comparison to non-race tracking cases • similar upper bound • more restrictive lower bound • lower permeability ratios requiring heating • higher required voltages at the same permeability ratio 10.16 cm 5.08 cm 15.24 cm

  20. Numerical Study • Parametric study varied parameters • permeability ratio • induction voltage • coil position Merit function

  21. Ideal coil location and RMS error Ideal coil location and quasi-steady state temperature Results - Side by Side

  22. Summary • Description of the VARTM process • Numerical model for non-isothermal flow in VARTM with induction heating • Experimental setup • Parametric studies • two preform layups • varied parameters: • induction coil location • vacuum level • induction coil voltage • permeability ratio • processing windows • Current work: active control

  23. Questions ?

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