Plastic article or earthenware shaping or treating: apparatus – Distinct means to feed – support or manipulate preform stock... – Female mold type means
Utility Patent
1998-07-23
2001-01-02
Mackey, James P. (Department: 1722)
Plastic article or earthenware shaping or treating: apparatus
Distinct means to feed, support or manipulate preform stock...
Female mold type means
C425S145000, C425S149000, C264S040300, C264S040700, C264S3420RE
Utility Patent
active
06168408
ABSTRACT:
DESCRIPTION
1. Field of the Invention
The present invention relates to an apparatus for manufacturing composite parts produced by resin transfer molding (RTM).
More precisely, the apparatus according to the invention is designed for producing large-size composite parts that may either have a high fiber content, i.e. 58% or greater, or a lower fiber content, i.e. below 54%.
This type of apparatus is particularly used for applications in the aerospace industry in which large-size parts with a high fiber content are used in conjunction with large-size sandwich parts in which the fiber content of the skins covering the core of the sandwich structure is relatively low.
2. Background Art
The RTM technique has been used for many years in fields such as the automobile and producer's goods industries to produce parts with a relatively low fiber content, i.e. lower than 54%. It consists of inserting a dry fibrous preform into a mold and then using low pressure to inject a liquid organic resin into the mold under negative pressure, thereby impregnating the fibrous preform. The impregnated preform is then heated in order to polymerize it before removing it from the mold.
The RTM technique has a number of advantages over other known composite materials techniques: overall operating time is reduced, the investment cost of the production line is low due to the absence of cooling and autoclave systems, part measurements, particularly thickness, can be accurately calibrated, the technique yields excellent surfaces, and health and safety conditions for operators are very good.
In order to produce the type of parts with a high fiber content greater than 58% required by the aerospace industry, the dry preform onto which the resin is injected in the mold must be strongly compressed. However, the RTM procedures in the known art do not allow for the manufacture of large-sized parts with this degree of compression.
The considerable loss of pressure introduced by the compressed textile fibers in the preform inhibits the penetration of resin into the preform.
Moreover, the resin injection pressure must remain low enough for the orientation of the textile fibers in the preform to remain unaffected during the injection procedure; the mechanical characteristics of the part thereby obtained are essentially determined by the orientation of the textile fibers in the resin matrix.
Consequently, when large parts are being manufactured, the time required for the resin to penetrate into the entire fibrous preform exceeds the time the resin takes to polymerize (normally known as the gel time). The highly compressed textile fibers also constitute an obstacle to the penetration of the resin and may leave entire areas of a part unimpregnated as well as leaving bubbles.
For these various reasons the RTM technique is currently little used for the manufacture of large parts with a high fiber content.
Moreover, existing apparatuses that use the RTM technique are usually designed for series production of parts with relatively uniform characteristics, particularly as concerns their measurements and their fiber content. This characteristic of the existing apparatuses also tends to make them very unsuitable for the aerospace industry in which parts with widely differing characteristics are produced in limited series. For example, large parts such as structural components, require a high fiber content, i.e. greater than 58%. In contrast, the manufacture of sandwich parts comprising a core made of a honeycomb material, or foam covered on both sides with a skin, generally uses a relatively low fiber content i.e. less than 54% for the skins.
In the manufacture of resin parts obtained by injection molding, various techniques have been developed to give improved control over the various injection parameters such as flow-rate, pressure, temperature, etc. while taking the shape of the part produced into consideration. Documents U.S. Pat. Nos. 5,178,805, 5,316,707, 4,850,217 and 5,551,486 all disclose certain of these techniques as examples.
However, the specific drawbacks of the RTM technique described above have hitherto prevented the techniques used for RTM injection molded production being adapted to produce large parts with high or low fiber contents as required.
DISCLOSURE OF THE INVENTION
The invention relates precisely to an apparatus for manufacturing composite parts using the RTM technique that will allow relatively simple, cheap production of large parts with a high or low fiber content while ensuring that the parts thereby obtained have a particularly low porosity level (maximum 1 to 3%) without the risk of premature gelling of the resin or the presence of unimpregnated areas within the parts.
According to the invention, this result is obtained by means of an apparatus for manufacturing composite parts by resin transfer molding, characterized by the fact that it comprises:
at least one mold able to accept a fibrous preform,
means for compressing the preform in the mold,
at least one resin supply vessel,
at least one injection cylinder for injecting the resin into the mold,
control means capable of operating the apparatus in controlled flow-rate mode in which the resin is transferred from the resin supply vessel to the injection cylinder before being injected into the mold by the cylinder at a generally constant rate, and in which the compressing means generally ensure that the fibrous preform is highly compressed, and in a controlled pressure mode wherein the resin is injected directly into the mold by the resin supply vessel at a generally constant rate and wherein the compressing means generally ensure weak compression of the fibrous preform, and
means of switching the control means between the controlled flow-rate and controlled pressure modes.
In the apparatus thus defined, the controlled flow-rate mode is used to produce large parts with a fiber content greater than 58% while controlled pressure mode is used to produce large-size sandwich parts in which the skins have a fiber content less than 54%.
In a preferred embodiment of the invention, the control means act on a three-way valve comprising one inlet connected to the resin supply vessel, a first outlet connected to the injection cylinder and a second outlet connected to the mold. The inlet of the three-way valve is connected to the first outlet in controlled flow-rate mode and to the second outlet in controlled pressure mode.
The control means advantageously act upon means for pressurizing the resin supply vessel so that constant pressure is applied to the vessel in controlled flow-rate mode while variable pressure is applied to the vessel in controlled pressure mode.
In order to manufacture large-size parts while reducing the risk of the resin starting to polymerize in the resin supply vessel (this risk is increased the greater the volume and the diameter of the vessel), several resin supply vessels are preferably used. These vessels are connected in parallel in a tank connected to pressurizing means. Each resin supply vessel is then connected in turn to the inlet of the three-way valve via a valve commanded by the control means.
The injection cylinder is normally controlled by an electric motor fitted with a speed regulator. The control means act on the speed regulator in controlled flow-rate mode so that the injection cylinder injects a controlled flow of resin into the mold.
In the preferred embodiment of the invention a first pressure sensor supplying a first instantaneous signal is located on the mold inlet. The control means also comprise a first comparator means that supply a first input signal representative of the deviation between a maximum pressure setting and the first instantaneous signal, a second comparator means that supplies a second input signal representative of the difference between two consecutive first input signals, and at least one fuzzy logic control card that, in controlled flow-rate mode, uses the first and second input signals to supply a flow-rate control signal.
A second pressure sensor is preferably located on the outlet of
Boime Bernard
Filleul Didier
Aerospatiale - Societe Nationale Industrielle
Burns Doane Swecker & Mathis L.L.P.
Mackey James P.
Nguyen Thukhanh T.
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