Download - Rtm Upm 2011
• Infusión de resina: Práctica 4
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Resin infusion
• Resin infusionDry reinforcement and resin are supplied separately before the manufacturing of the part.A preform of dry reinforcement is manufactured (lay-up and stitching of fabric patterns, braiding,...) and placed into the mould. Then, the mould is closed and the preform is impregnation with the resin by a process of infusion.The infusion can be done using liquid resin (LRI, RTM...), or solid resin integrated together with the preform during the lay-up process (RFI).g p g y p p ( )
LIQUID RESIN FILM OF RESIN
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Resin infusion
• Resin infusionGeneral characteristics
METHOD CHARACTERISTICS PROS CONS
C l t t• High investment in
i t f t i fRTM
(Mould closed by mechanical pressure)
• Complex structures• Good repetitivity: control of
Vf through the shape of the mould
• High surface quality
equipments: manufacturing of performs, moulds presses, injection equipments.
• Require very liquid resins (low damage tolerance)
• Difficult automatisation• Difficult automatisation
RLI (VARTM, MVI) • Tooling similar to “prepreg”
based manufacturing • Require very liquid resins (low
• Dry fabric reinforcement + resin (liquid or film)
• Allow parts with high geometrical
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( , )(vacuum and autoclave
pressure)
g• Investments similar or
lower than prepreg based manufacturing
• Require very liquid resins (low damage tolerance)
complexity (3D) • Storing of
reinforcement at RT • Single or bi-
component resins M di l i
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RFI (Vacuum and autoclave
pressure)
• Medium-large series• Tooling similar to “prepreg”
based manufacturing • Resins similar to those
used in prepreg based manufacturing
• Require the use of resin films: difficult thickness control, complex storing…
• Do not allow very complex t i
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p ) manufacturing • Investments similar or
lower than prepreg based manufacturing.
geometries• High cost of preforms
“Acronym” anarchy !
• CIRTM: co-injection RTM • Crystic VI: vacuum infusion (Scott Bader)• DRDF: double RIFT diaphragm forming (University of Warwick)• LRI: liquid resin infusion• MVI modified vacuum infusion (Airbus)• Quickstep use of liquids for enhanced heat transfer in infusionQuickstep use of liquids for enhanced heat transfer in infusion• RFI: resin film infusion• RIFT: resin infusion under flexible tooling (ACMC Plymouth)• RIRM: resin injection recirculation moulding• SCRIMP Seeman Composites Resin Infusion Molding Process (TPI) • VAIM: vacuum-assisted injection moulding• VAP vacuum assisted processing (patented by EADS)• VARI: vacuum assisted resin injection system (Lotus Cars)
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VARI: vacuum assisted resin injection system (Lotus Cars)• VARIM: vacuum assisted resin injection moulding• V(A)RTM: vacuum (-assisted) resin transfer moulding• VIM: vacuum infusion moulding.
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c • VIMP: vacuum infusion moulding process • VM/RTM Light: a hybrid RIFT/RTM (Plastech)• VIP: vacuum infusion process
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Extracted from “Resin Infusion under Flexible Tooling (RIFT)”. John SummerscalesAdvanced Composites Manufacturing CentreSchool of Marine Science and Engineering - University of Plymouth, UK
Resin infusion
• Resin transfer moulding (RTM)Resin infusion method more used in aerospace applicationsCharacteristics:
– A two-part, matched-metal mould is used as toolas tool
– Liquid resin is pumped into the tool– The part is cured into the tool
RTM at a glimpse
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Resin infusion
• Advantages and drawbacks of RTM
AdvantagesAdvantages– Excellent mechanical properties– High fiber volume– Relatively low capital equipment cost
R l ti l l t f t i l– Relatively low cost of raw materials– Possibility of manufacturing of very complex geometries– High dimensional tolerances (even thicknesses)– Excellent surface control (mould finish over entire part)Excellent surface control (mould finish over entire part)– Near-net shape parts possible– Excellent quality control possible– High repetitivity
Hi h it f t i t ti i i h d l b t i bl
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– High capacity of parts integration, saving weigh and labour costs in assembly– High capability of automatisation
Disadvantages– Size limitations
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c – Size limitations– Manufacturing only with fabric and textile preforms– High tooling cost– Mould deflection during processing
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Resin infusion
• Moulds: basic concepts
S f ti th th ld f ti lSame function than the mould of a conventional process
Parts:B ld d l i ld– Base mould and closing mould
– Internal modules– Sealing system
System for mould alignment closing and compression– System for mould alignment, closing and compression– Systems of injection and vacuum– Heating and cooling system
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This elements configure the tool to achieve the final part with all its geometrical and functional requirements:
G t i l t l di i l t bilit d tiff
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c – Geometrical accuracy, tolerances, dimensional stability and stiffness– Correct filling of the mould– Possibility of extraction of the part
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Aproximación académica: Práctica de RTM
BOMBA DE VACÍO
UTIL+
PREFORMA
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SISTEMA DE INYECCIÓN
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Aproximación académica: Ley de Darcy
resina de frente del velocidad siendo :, uPku ∇−=μ
dadpermeabili:KCondiciones de contorno
l d d l ld
presiones de gradienteviscosidad :
dadpermeabili
:
:
P
K
∇μ
0. =nu en la pared del molde
P = Pinj en el punto de inyección
P = P en el frente de resina0=⋅∇ u Ecuación de continuidad
P = Po en el frente de resina
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En caso de flujo unidireccional, la presión de la resina cae linealmente desde el punto deinyección hasta el frente de resina. El tiempo de inyección será entonces:
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c
2
2L
PKt
Δ=
μ
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2 PK Δ
• Viscosity, Permeability: Some ideas from the U. Delaware
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A typical Resin Transfer Mold is illustrated below.
The resin is injected under pressure through one or more "gates". The air is expelled through vents. The vents should be located in the region that fills last in order to avoid entrapped air that can cause "dry spots".
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Viscosity is a measure of the resistance of a fluid to flow through the open conduits and pores of a preform. Viscosity is defined by Newton’s law as the material characteristic that relates the stress required to sustain a given strain rate. This law is schematically defined below.
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As a consequence of the temperature dependence of the viscosity, a temperature processing window is imposed on the mold. This window is illustrated in the Figure below.
Initially the viscosity decrease as the monomers become more mobile and less resistant to flow at elevated temperatures. However, a continued increase in temperature causes the resin to react to from higher molecular weight and less mobile species. Eventually the systems begins to gel and form rigid cross linked networks that are resistant to flow and the viscosity increases rapidly. Viscosity is an important factor in selecting resins. If the viscosity is too high, the resin will not flow easily and may not penetrate fiber bundles. If the viscosity is too low, the resin may follow a path of least resistance and leave voids or dry spots. As a rule of thumb, the resin viscosity should be in the range of 100 to 1000 cps.
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Viscosity can be a strong function of temperature. In particular, at higher mold temperatures the resin can begin to cure during filling. In this event, the viscosity will increase dramatically and impede flow. This situations is schematically illustrated below.
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If a preform is isotropic in the in-plane directions such that Kxx = Kyy , then the flow fronts progress as circles. This situation is illustrated in the figure below.
Random fiber mats and symmetric bi-directional fabrics produce isotropic preforms.
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If the preform is anisotropic in the plane with Kxx different from
Kyy, the flow fronts become elliptic and remain elliptic through out filling. This situation is illustrated below.
The major and minor axes of the ellipse coincide with the in-plane principal directions. The ratio of the major and minor axes of the ellipse is equal to the ratio of the square roots of the principal permeability’s. This situation can be encountered with unidirectional stitched mats.
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Preforms are usually assembled by stacking several plies of mats and/or fabrics. The permeability for fluid flow in the plane of the plies is generally much more than the permeability for the fluid flow in the transverse or out-of-plane direction. This situation results in anisotropy of the permeability. Consequently the directional dependence of the permeability must be taken into account. The figure below assigns directional indices to the permeability.
The quantities Kxx and Kyy denote the in-plane permeability’s of
the preform: Kzz denotes the out-of-plane permeability
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For multiple layers of plies, the overall effective permeability’s can be estimated by the relationships shown below.
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A phenomenon called "race tracking" or channeling is observed in most mold filling situations. An example of race tracking is shown below.
In this illustration, the fluid at the edge of the mold is moving ahead of the fluid in the center due to high permeability regions near the edges. This effect usually occurs because it is difficult to place the preform into the mold so that the dimensions exactly match the mold size. High permeability areas can also be created by the unraveling of the fiber bundles during the cutting of the preform. Race tracking can also develop when permeability gradients exist in the preform due to preform deformation or "wash". Race tracking can lead to voids and resin rich areas. However, in some cases race tracking can enhance the uniformity of flow by designing specific channels in the preform
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Aproximación académica: Práctica de RTM
• Los alumnos, en grupos de 4, realizarán un informe con una extensión aproximada de 8 hojas, que deberá incluir al menos los siguiente apartados:
Descripción de la pieza a fabricar representada en la página anterior el panel de 2x1 y 10Descripción de la pieza a fabricar, representada en la página anterior, el panel de 2x1 y 10 mm de espesor presentado en claseDescripción del proceso de inyección. Los parámetros básicos del proceso son
– Presión de inyección: 0 Presión de vacío: 0.5 atmy– Líquido inyectado: agua– Tiempo entre el inicio de la inyección y el inicio de salida del líquido inyectado (asociado a la velocidad
del frente del líquido en los bordes): 10 s– Tiempo de llenado (asociado a la velocidad del frente del líquido a través de la diagonal): 100 sTiempo de llenado (asociado a la velocidad del frente del líquido a través de la diagonal): 100 s
Obtención de las permeabilidades en el borde (race-tracking) y en el centro del panel empleando la expresión de la ley de Darcy para flujo unidireccionalDescargar el programa MyRTM (http://www.myrtm.ch)
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Comparar la ley de Darcy y la definición de permeabilidad empleada por dicho programaCon las permeabilidades obtenidas, y realizando las hipótesis necesarias (detallar):
– Modelizar el panel utilizando el ejecutable gmsh u otro programa CAD (CATIA, por ejemplo)– Realizar un mallado del panel utilizando el ejecutable gmsh
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c – Realizar un mallado del panel utilizando el ejecutable gmsh– Alimentar el programa MyRTM con el modelo y las permeabilidades obtenidas, introduciendo el punto
de inyección mostrado en el ensayo– Ejecutar el programa realizando las hipótesis que el alumno considere necesarias.
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Describir el proceso de inyección simulado, obteniendo los tiempos de proceso, y comparando los resultados con los del ejercicio representado en claseEl informe se entregará una semana después del examen final de la asignatura