Simulated Active Control in a VARTM Process Using Induction Heating

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Simulated Active Control in a VARTM Process Using
Induction Heating

• Richard Johnson and Ranga Pitchumani
• University of Connecticut
• Composites Processing Laboratory
• 191 Auditorium Road, Storrs, CT 06269
• www.engr.uconn.edu/cml
• Presented at the 14th International Conference on
  Composite Materials, July 18, 2003, San Diego, CA
• Sponsors Office of Naval Research, National
  Science Foundation

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Outline

• Introduction
• Experimental setup
• Numerical modeling
• Active control
• Temperature
• Motion
• Numerical Study
• Ongoing work

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Process Description

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

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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)
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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
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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
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Heating Methods

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

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Numerical Modeling - Induction Heating
I2
I1
I3

• Induction power calculation
• current conservation at the nodes of the
  susceptor mesh
• summation of voltages in a loop emf

I4
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Experimental Setup
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Numerical Modeling - Flow

• Flow governed by Darcys law
• Pressure distribution
• five-point Laplacian scheme
• Darcys law used to find velocities
• volume tracking method used to find the flow
  front locations
• BCs
• 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

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Numerical Modeling - Heat Transfer

• Energy equation
• 3-D control volume analysis and ADI method
• (Douglas and Gunn 1964)
• BCs
• mold sides considered adiabatic
• top surface of the vacuum bag and bottom surface
  of the mold considered convective
• inlet and outlet at ambient temperature

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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 Fourier number
• mesh Courant numbers

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Active Control

• Temperature
• Heat the resin to supply aid to flow permeation
• Fundamental challenge Limit temperatures so as
  to not gel the resin during filling

• Motion
• The induction coil must be moved so as to heat
  the appropriate regions
• Only x and y direction motion are considered

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Temperature Control

• Maximize the coil voltage - achieving the fastest
  fill times
• Specified upper bound 100C
• Temperature measurement is difficult
• Lumped capacitance approach

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Motion control

• y - direction motion
• Maintain the coil above filled regions
• Keep the coil just behind the flow front
• Allows for control where the preform layup is not
  know a priori

• x - direction motion
• Keep the coil behind the location of maximum lag
• Use delays to avoid potential problems

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Numerical Study
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Preform Layup Predetermined Random

• Coil path corresponds to
• the low permeability areas
• Improved
• uniformity over
• unheated case

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Preform Layup Side Strip

• Coil location remains at the right side of the
  mold
• Notable improvement
• in uniformity

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Preform Layup Center Patch

• Demonstrates a practical application
• Coil remains centered in the mold
• Can potentially avoid void entrapment

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Preform Layup Computer Selected Random

• Shows improved uniformity
• Coil location follows the
• lag location

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Delay Times

• Minimum RMS error
• 210 second delay
• Physical limitation
• coil power up from standby to 200V 7 sec
• Recommended delay
• 7-10 Seconds

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Summary Ongoing Work

• Summary
• Numerical model of the VARTM process
• Induction heating control
• Ongoing Work
• Implement control logic on physical setup
• Incorporate resin cure kinetics in the numerical
  model
• Replace upper control bound with a function of
  the cure kinetics

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• Questions?