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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RP115 -
- In-Mold Dielectric Cure Monitoring Using Ejector Pin Sensors,
Micromet Instruments, Inc., Nathaniel T. Smith
ABSTRACT
Dielectric analysis
has proven its value as a cure monitoring tool in a variety
of industries including the thermoset molding industry. In
the thermoset molding industry limitations to broad acceptance
of the technology have been partially due to the size and cost
of installing sensors in the molding tool. Micromet Instruments
has developed sensor technology that enables dielectric sensor
based injector pins to be used in existing ejector pin locations.
This paper will discuss dielectric cure monitoring principles
and examine data collected with ejector pin sensors.
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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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RP064 -
SMC Molding Cycle-Time Reduction Through Real-Time Control
of Part to Part Variation; Micromet Instruments, Inc., David
R. Day, Huan L. Lee
ABSTRACT
Many factors
influence SMC cure behavior including mold temperature, SMC
temperature, formulation, and aging. Although most of these
factors are controlled to some extent, small uncontrollable
variations will always cause some degree of fluctuation in
cure behavior. The recent development of in-mold cure sensors
allows the analysis and control of these variations from part
to part and from batch to batch. In this study, SMC molding
was monitored for thousands of parts and analyzed using Statistical
Process Control (SPC) methods. The standard deviation in part
to part cure times was found to be on the order of 1 to 5 seconds
depending on factory conditions. A strong correlation of cure
time with mold surface temperature was found, however, other
uncontrolled parameters were found to have an additional significant
influence. The cure sensor and monitoring system was connected
to the press controller thus implementing closed loop control.
Average cycle times were reduced by more than 10% through early
mold opening, automatically triggered by real time cure state
information, while part quality standards were met or surpassed.
Cure state as a function of the thickness of the part was also
investigated and is reported.
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RP106 -
Applications of Dielectric Analysis for Cure Monitoring and
Control in the Polyester SMC/BMC Molding Industry, Micromet
Instruments, David D. Shepard, David R. Day and Kelly J.
Craven
ABSTRACT
Dielectric Analysis
is routinely used for monitoring the cure of thermosetting
resins. Implantable, disposable sensors allow measurements
of the curing process to be made in various locations throughout
a part. Permanent, reusable sensors flush mounted in the mold
allow the measurements to be made automatically during each
molding cycle. This paper discusses development, QA/QC, and
production control in the polyester SMC/BMC industry. The curing
rate through the cross-section of SMC parts of thicknesses
up to 3/4 of an inch is examined. The effect of aging temperature
on the reactivity of BMC demonstrates the use of Dielectric
Analysis as a QA/QC test. Finally, it is shown that overall
cycle times can be reduced by real time identification of the
part-to-part variability in cure times during production molding.
This allows closed-loop feedback to the press controller as
to the proper time to demold the part.
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RP108 -
Dielectric Property of Curing Epoxy Resin and Application
for Casting Process, Toshiba Corporation, Satoshi Matishima,
Toshiyuki Nakano, Mitsuhiko Koyama, Yoshiyuki Inoue
ABSTRACT
Epoxy casting
resin is used in heavy apparatus as insulation and structural
material. To optimize the epoxy casting process, several analytic
techniques are used. Different from other techniques, dielectric
analysis (DEA) has the advantage of nondestructive, on-line
process measurement. We tried to evaluate the cure profile
of bis-phenol A type liquid epoxy casting resin with DEA, DSC
and a viscometer simultaneously, and found that the ionic conduction
portions of the loss factor correlated well with glass transition
temperature and viscosity.
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RP056 -
Automotive/Aerospace Synergism in Computer-Aided Composites
Processing; Advanced Composites Engineering, GM Delco Products
Division, Johnny Gentry
ABSTRACT
In-mold dielectric
cure monitoring techniques pioneered by the aerospace industry
were applied to the manufacturing process of LITEFLEX® springs.
Real-time data was collected in-situ and used to interpret
the progression of cure in an epoxy/fiberglass composite. This
information was used to trigger mold pressurization in an attempt
to lower void content and improve part appearance.
A microdielectric
sensor placed on the mold surface collected temperature and
conductivity data that was converted to a cure percentage scale
(cure index). The optimum pressurization point for the epoxy
system was at approximately 40% conversion. Although results
varied somewhat depending on spring geometry, void contents
were reduced to less than 1%, composite shear strength increased
10-15% and surface appearance was also significantly improved.
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RP089 -
Investigation of the In-Mold Viscosity Characteristics of
Electronics Packaging Polymers During Transfer Molding Using
Dielectric Analysis, Motorola and University of Texas, Sheit
Chen, Timothy Skoglund, Mark White, Brian Crowell, David
D. Shepard
ABSTRACT
The viscosity
profile of epoxy molding compound during the transfer molding
of plastic encapsulated semiconductors is critical to the quality
of the package. The viscosity profile of the molding compound
during transfer molding is affected by material, process, and
geometry parameters.
This study used
Ion Viscosity (electrical resistivity) to study the in-mold
viscosity behavior as a function of mold temperature, transfer
speed, and preheat temperature during actual transfer molding.
Miniature dielectric sensors were mounted in six locations
within a package mold. In these studies, the viscosity behavior
in the mold was found to be strongly affected by mold temperature
and mostly unaffected by both transfer pressure and perheat
temperature.
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RP092 -
Real Time Process Monitoring & Control in Liquid Composite
Molding, K.N.Kendall, Ford Research Laboratories
ABSTRACT
Liquid composite
molding (LCM) processes require reliable techniques for detecting
mold fill and component cure to reduce materials waste and
minimize molding cycle times. The use of thermocouples to measure
in-mold temperature is the most widely used method of monitoring
thermoset LCM processes. However, the thermocouple tip must
be located in the centre of the laminate to evaluate peak temperatures
and ensure resin exotherm is not suppressed by the mold.
This intrusive
method leaves a small hole in the laminate when employing re-usable
thermocouples which could be a source of weakness in the composite
and may create a defect in the component. Pressure can be measured
non-intrusively and recent work has shown that key events in
the molding cycle can be monitored in this way. However, the
technique requires specific process parameters to be fulfilled
and is dependant upon the characteristics of the cure reaction.
Dielectric sensors provide an alternative method of monitoring
thermoset LCM processes and can be used to control the process
in real time in addition to providing statistical process control
data. Experimental data is used to illustrate examples of each
technique when applied to the resin transfer molding (RTM)
and structural reaction injection molding (SRIM) processes.
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RP125 -
In-Mold Cure Monitoring of Phenolic Molding Materials, Rogers
Corporation, Vinceent R. Landi, Micromet Instruments, David
D. Shepard, Kim R. Smith
ABSTRACT
A new method
and associated equipment has been developed for non-destructively
following the progress of the cure of thermoset phenolic molding
materials, during a molding operation. It is based on passing
an ultrasonic pulse signal through the material as it is curing.
The velocity of sound in the material increases monotonically
with increases in modulus. Modulus, in turn, increases with
increasing degree of cure. Through this method, it is possible
to determine when a molded part is sufficiently cured to be
removed from the mold. Cure development during compression
molding is reported on four phenolic molding compounds at three
different cure temperatures.
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RP132 -
In-Mold Cure Monitoring of Thermosetting Molding Compounds;
Holometrix Micromet, David Shepard
ABSTRACT
In-mold
cure monitoring provides a valuable tool for research, development,
QA/QC and production monitoring and control of thermosetting
molding compounds. Robust sensors permanently mounted in a
mold can provide information as to the change in material viscosity,
cure rate and cure time of the molding compound. Measurements
can be made in test molds or full-scale production molds. Dielectric
measurements are widely used in the polyester and vinyl ester
molding industries to monitor the cure of SMC and BMC materials.
The change in dissipation factor or electrical resistivity
(Ion Viscosity) during the molding process is used to determine
the time until the compound begins to cure and the time until
the cure is complete. Ultrasonic measurements enable the in-mold
cure monitoring of phenolic and other molding compounds where
reaction by-products interfere with the ability to use the
dielectric technique. Ultrasonic cure monitoring involves measuring
the change in the speed that sound travels through the material
and the change in the attenuation of the sound wave. This provides
a curing curve similar in appearance to that obtained during
the dielectric cure monitoring of polyester molding compounds.
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