RP033 -
Thermoset Process Control: Endpoint Determination with Dielectric
Sensors; Micromet Instruments, Inc., Dr. David R. Day and
David D. Shepard
ABSTRACT
Microdielectric
sensors are widely used for monitoring reactions in a variety
of thermosetting and thermoplastic materials. Software packages
that use dielectric response for closed loop control are now
emerging. This paper utilizes recently developed software routines
for composite process control under a variety of conditons.
The routines measure dielectric loss factor at several frequencies,
extract ionic conduction levels, and monitor the first and
second derivative of conductivity with respect to time. The
operator is given the option to specify time and temperature
windows in which the process condition under control may be
confined. The process under control may be triggered by attaining
a user selected first derivative and second derivative. In
this investigation an epoxy-amine system is cured utilizing
the process control software for dielectric endpoint determination.
Endpoint reproducibility is confirmed using DSC for determining
the sample Tg at end of cure. Data will be presented for various
ramp rates and degrees of cure.
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RP043 -
In-Process End Point Determination of Epoxy Resin Cure; Micromet
Instruments, Inc., Dr. David R. Day, David D. Shepard, and
Kelly J. Craven
ABSTRACT
The use of durable,
implantable dielectric sensors allow measurements to be made
in-process in the adverse environments of autoclaves and presses.
The slope of the Ion Viscosity (resistivity) curve can be used
as a very sensitive indicator of the rate of reaction of a
resin. Previous work has demonstrated a strong relationship
between the log Ion Viscosity and glass transition temperature
(Tg) of epoxy resins during isothermal cure. This allows the
use of dielectric measurements to estimate the Tg of an epoxy
part in real time during production. The dielectric data may
then be used to determine the endpoint of a reaction based
on its reaching a specified slope of the log Ion Viscosity.
In this paper,
a commercially available software package was used to automatically
indicate when the endpoint of Hercules 3501-6 graphite epoxy
prepreg cure was reached. Good reproducibility of the Tg of
the resin at this endpoint was observed using Thermal Mechanical
Analysis (TMA) and Dynamic Mechanical Analysis (DMA). The slope
of log Ion Viscosity vs. Time proved to be a sensitive indicator
of small changes in Tg.
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RP046 -
Production Implementation of Fully Automated, Closed Loop
Cure Control for Advanced Composite Structures; General Dynamics,
Sean Johnson and Nancy Roberts
ABSTRACT
Economics of
advanced composite part production requires development and
use of the most aggressive cure cycles possible without sacrificing
quality. As cure cycles are shortened and heating rates increase,
tolerance windows for process parameters become increasingly
narrow. These factors are intensified by condensation curing
systems which generate large amounts of volatiles.
Management of
the situation requires fully automated, closed loop process
control and a fundamental understanding of the material system
used for the application. No turnkey system for this application
is currently available. General Dynamics Pomona Division (GD/PD)
has developed an integrated closed loop control system which
is now being proofed in production. Realization of this system
will enable cure time reductions of nearly 50 percent, while
increasing yield and maintaining quality.
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RP087 -
Routine QA/QC Testing and Automated Statistical Quality Control
of Thermoset Materials Using Dielectric Analysis, Micromet
Instruments, Inc., Todd A. Senturia and David D. Shepard.
Reprint from American Laboratory Magazine, November 1993
ABSTRACT
The final quality
of parts fabricated from thermosetting resins, compounds and
prepregs can be greatly affected by both batch-to-batch material
variability and by the change in material processing characteristics
brought about by aging effects. This paper examines the sensitivity
of Dielectric Analysis to the key processing characteristics
of thermosetting materials, and explores the use of the Dielectric
technique as a routine QA/QC tool for both pre-production and
incoming material inspection. The application of rigorous statistical
methods to Dielectric QA/QC data, and the promise of automated
Statistical Quality Control (SQC) pass/fail determination are
also discussed.
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RP121 -
End of Cure Sensing using Ultrasonics for Autoclave Fabrication
of Composites, Johns Hopkins University Applied Physics Laboratory,
Paul J. Biermann and Joan H. Cranmer; Edison Welding Institute,
Carol A. Lebowitz; Carderock Division Naval Surface Warfare
Center, Lawrence M. Brown
ABSTRACT
The objective
of this work was to demonstrate the use of ultrasonics to determine
the end-of-cure for autoclave cured, graphite/epoxy composite
laminates. The fundamental benefit of this work will be understanding
when to complete the temperature hold and cool down the autoclave
and, therefore, consistently produce composite laminates with
the desired material properties. An additional benefit is the
ability to follow the changing viscosity of the resin during
the initial part of the cure.
The general
approach to this program involved using pulse-echo ultrasonics
to measure the transit time for longitudinal ultrasonic waves
to pass through a graphite/epoxy composite laminate during
cure. Sixteen, 32 and 64 ply [0/90]s graphite/Fiberite 934
epoxy panels were fabricated and cured to various end-of-cure
conditions. Additionally, panels with various starting conditions
were run. Sound speed was calculated using the panel thickness
(number of plies multiplied by the manufacturer specified thichness
of each ply) divided by the measured transit time.
Mechanical (maximum
fiber stress and maximum strain) and glass transition temperature
(Tg) tests are being performed on all the fabricated panels.
Determining the relationships between the velocity profiles,
mechanical properties, and Tg data is in progress. Ultimately,
the goal is to understand the relationship between the ultrasonic
data and state-of-cure, and to incorporate the ultrasonic sensor
into an operational expert system for sensor feedback control
of the autoclave process.
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RP118 -
Effect of Advancement of Epoxy Prepreg Processing - A Dielectric
Analysis, Micromet Instruments, Inc., David R. Day and David
D. Shepard
ABSTRACT
With the relatively
recent trend toward adaptive process control during processing
of structural composites, there is need for an understanding
of the nature of variations during cure that are encountered.
Part-to-part variations can arise because of differences in
thermal exposure arising from part placement or part thickness,
or from chemical differences due to formulation or advancement.
Microdielectric sensors are particularly well suited for monitoring
thermoset cures from initial point of flow, through the liquid
region, and on into the solid state. In this study, microdielectric
sensors are used to systematically study the influence of resin
advancement on cure behavior. Relationships between advancement
and critical cure phenomena such as flow temperature, point
of viscosity minimum, and reaction end point are discussed.
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RP073 -
The Influence of Formulation Variables on the In-Mold Reactivity
of DMC/BMC Compounds; Fiat Central Research, A.Arboletti
and A.Balestrini
ABSTRACT
The increasingly
widespread use of composite materials using unsaturated polyester
resin (SMC, BMC, DMC) for the industrial production of automotive
components, require more sophisticated techniques for the chemical-physical
characterization as exhaustive as possible.
Among the methodologies
available today for industrial application (directly in a manufacturing
context), one of the most promising is one based on changes
of the dielectric properties which take place in the material
during the polymerization of the thermosttting resins.
This paper examined
different BMC compounds produced in CRF with different percentage
variations of some of the standard formulation components:
catalysts (terbuthilperbenzoate and terbuthilperoctoate), inhibitors
(phenolic type and parabenzoquinone) and styrene. The compression
molding of 200x200 mm square plates in a mold equipped with
a TMS dielectric sensor allowed us to evaluate, for each formulation,
the reactivity (gel and cure time) in real time. A statistical
approach (design of experiment) used to study this phenomenon
which make it possible to evaluate the reproducibility of the
measurements, the reliability of the results and the influence
of the compound ageing time on its reactivity characteristics.
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RP052 -
Process Optimization and Quality Assurance through Curing
Control with a Dielectric Sensor; A. Gati (this is a German
language paper)
ABSTRACT
Dielectric sensors
enable cure monitoring in the production environment. This
paper describes the basics of dielectrometry, design of suitable
sensors, comparable rheometric and thermal analysis measurements,
as well as examples of closed loop process control.
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RP134 - F/A-18C/D
and E/F Implementation of Dielectric Sensor Adhesive Staging;
The Boeing Company, John M. Griffith and Tim Hackett
ABSTRACT
Dielectric sensors
have been used in development and laboratory activities for
over 30 years. A large number of polymer demonstrations have
shown dielectric sensors to be a good way to follow viscosity
and degree of cure changes during oven, press and autoclave
cures. One area of dielectrics that has been missing is production
implementation of this sensor technology. This paper addresses
F/A-18C/D and E/F production implementation of dielectric sensors.
Wing skins on the F/A-18 have a titanium root fitting that
transitions into the composite wing. Adhesive is applied to
the transitioned area between the titanium and carbon/epoxy
prepreg before curing. One of the manufacturing steps is to
oven stage this adhesive at elevated temperature to reduce
its flow during cure. This staging operation was controlled
by time at temperature with an accept/reject process control
flow test. The development project objective was to implement
sensor based control of the staging operation into production
on the F/A-18C/D and E/F aircraft. Boeing, Navy, Air Force,
government DCMC, Micromet, and ASC personnel worked as a team
on this project. Results of the building block approach going
from development through certification to successful implementation
is presented in this paper.
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