JPH02198815A - Manufacture of fiber-reinforced composite product - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION OBJECTS OF THE INVENTION Field of Industrial Application The present invention relates to a method for resin transfer molding of composite products.

BACKGROUND OF THE INVENTION Resin transfer molding (RDM) is a process used to manufacture fiber reinforced composite products.

This manufacturing method involves two steps: manufacturing a fiber preform into the shape of the final product, and impregnating the preform with a thermosetting resin.
It involves two basic processes. The fiber-reinforced composite product produced in this manner exhibits the characteristics of high strength and light weight. Such composite products are commonly used in the aviation industry and other applications requiring lightweight and high strength materials.

The first step in the RTM process is to manufacture the fiber preform into the desired product shape. - Generally, the preform consists of multiple plies of fabric that impart the desired reinforcing properties to the final product. For example, the fabric ply is composed of graphite fibers or KIEVLAR® fibers. Several steps are required to produce the preform. The actual steps required and the optimal order in which to perform them will vary depending on the shape of the preform.

Any successive steps may be performed in any logical order so long as the desired preform is produced. -Generally,
The technology used to form preforms is adapted from the clothing industry. For example, fabric plies are cut according to a predetermined pattern, stacked onto a mandrel having a desired shape, and loosely glued or stabilized to maintain the desired shape after removal from the mandrel.

Once manufactured, the fiber preform is placed in a transfer mold for the second step in the RTM process. This mold is closed using Tactix, manufactured by Dow Chemical Company located in Midland, Michigan, USA.
A resin, typically an epoxy resin such as 123/H41®, is injected under pressure to wet the preform. This resin initially has approximately the same viscosity as water so that it can completely impregnate the preform. Next, the temperature of the mold is raised to increase the viscosity of the resin and finally solidify it. The final fiber-reinforced composite product is generally about 50% to 60% by volume.
It has fibers of Generally, high performance aerospace composite products have about 55% to 60% fiber by volume.

One of the important steps in the RTM process is to stabilize the preform before placing it in the mold.

Stabilization is necessary to ensure that the fabric plies maintain the desired shape and orientation until impregnated with resin.

The stabilization also prevents the fabric ply from unraveling along the cut edge. Significant development efforts have been expended to optimize the stabilization step. The most common methods utilized to stabilize preforms are stitching and hot iron tacking.

Both of these methods are labor and time intensive.

Stitching is a very effective means of stabilizing the preform, but it is difficult to perform after the fabric plies have been stacked on the mandrel. Furthermore, the stitch processing is
Making the fabric plies too stiff so that they do not bend easily makes it difficult to manufacture preforms into complex shapes. Therefore, stitching is not a suitable method for stabilizing preforms with complex shapes.

Tucking is more effective for producing preforms with complex shapes. However, if the preform has many plies of fabric, it is more labor intensive and requires more time than stitching. A thermoplastic polymer is placed between each ply of fabric and melted with a hot iron. This polymer resolidifies to bond the fabric plies together. Tacking requires one fabric ply at a time since heat transfer occurs only by conduction. Tacking one fabric ply at a time is a relatively time consuming process due to the poor thermal conductivity of many reinforcing fibers. Such technology is more (
More et al., US Pat. No. 4,470,862.

As mentioned above, efforts continue in the art to develop less labor intensive and time-intensive RTM preform stabilization methods.

OBJECTS TO BE SOLVED BY THE INVENTION It is an object of the present invention to solve the above-mentioned problems and provide a method for stabilizing RTM preforms with a minimum of effort and time.

[Structure of the Invention] Means for Solving the Problems> The present invention is a method for manufacturing a fiber-reinforced composite product using a resin transfer molding method. The method includes laminating a plurality of plies of dry fabric, forming the plies into a desired shape, and stabilizing the plies to form a dry fiber preform. The stabilized dry fiber preform is then placed into a resin transfer molding means.

A thermosetting resin is injected under pressure into a resin transfer molding means to impregnate the stable fiber preform. The molding means is then heated to cure the thermosetting resin and form a fiber reinforced product. The improvements introduced by the present invention include placing a polymeric binder on adjacent fabric plies and directing a heated air stream toward the surplus plies to melt the binder and unite the fabric plies. to form a stabilized dry fiber preform.

The above-mentioned and other features and advantages of the present invention can be easily understood from the following detailed description taken in conjunction with the accompanying drawings.

EXAMPLE The preform used in the RTM process consists of multiple plies of fabric loosely joined together.

The fibers used to form the preform are of such fibers that impart the desired reinforcing properties to the final product. For example, if high specific strength is required in the final product, the reinforcing fibers are graphite fibers, Kevlar polyamide fibers (Dupon DeNemours, Wilmington, Praue, USA) or glass fibers. Depending on the degree of reinforcement required, the preform generally has from about 2 to about 12 plies. However, according to this manufacturing method, up to 50 plies can be sufficiently stabilized depending on the density of the fiber weave.

The fabric plies are loosely bonded together, ie, stabilized by a polymeric binder disposed between adjacent fabric plies. As the polymeric binder, a variety of polymers may be used which, when present in the amounts described below, are compatible with the thermosetting resins subsequently used in the RTM process. The polymer binder can be thermoset or thermoplastic. The choice of bonding material is
It is determined by compatibility with the later injected primary matrix, operational effectiveness, control of the manufacturing environment, and final product performance. Although thermoset materials can be used as preform bonding materials, thermoplastic materials are preferred simply because they are more convenient to manipulate. Suitable thermoplastic polymers for use in the present invention include nylon, polyetheretherketone (PEEK), and polyphenylene sulfide (PPS). The most effective thermoplastic polymer for general applications is nylon because it has a relatively low melting point.

The polymeric binder has the form of small particles or thin fibers. Small particles are more effective than thin fibers.
This is preferred because it allows for easier control of the amount of thermoplastic binder used to stabilize the preform. Typical particle sizes are about 100 to about 400 microns in diameter. A preferred method of placing the polymer between the fabric plies is to use a fabric that has the polymer adhered to one side thereof. Pacesa Corporation, located in Chicobee, Massachusetts, USA.
te Corporation) applies the granules to the desired fabric.

The amount of thermoplastic polymer used to stabilize the fabric ply must be small enough that the thermoplastic binder does not have any appreciable adverse effect on the properties of the thermoset. However, the amount of binder placed between the fabric plies must be sufficient to stabilize the preform.

Preferably, the binder is at a concentration of about 5 g/rtf to about 60 g/rd for each pair of adjacent fabric plies. Limiting the amount of binder within this range attempts to balance the somewhat contradictory objectives of stabilizing the preform without appreciably adversely affecting the properties of the final product. be able to.

Most preferably, the binder is at a concentration between about 5 g/rrr and about 20% or more of the thermoplastic polymer disposed between each pair of adjacent fabric plies.

To form the preform, the fabric plies are stacked on top of each other to achieve the desired fiber orientation. The fabric plies are stacked on a flat surface or on a mandrel that conforms to the shape of the desired final product. The fabric plies are cut according to the desired pattern to facilitate stacking. If the binder and fibers are not bonded together, the stacking step places the binder between adjacent plies of fabric. Generally felt or powdered binders are used in the latter case.

The forming surface of the plane or mandrel on which the fabric plies are laid up is generally porous and has a large number of holes, grids, etc. Such a mandrel 10 is shown in FIG. Hole 12
This allows the hot air used to melt the thermoplastic polymer to be easily directed toward the fabric ply. - In general, the area occupied by the holes is 10
It is approximately 20% or more of the total area of the upper plane. The forming surface used to lay up the fabric plies is made of a material that can be formed into the desired shape and easily drilled with holes of the desired size. In another embodiment, the molding surface can be porous. Additionally, the molding surface must be able to maintain its shape and structure after being exposed to a stream of hot air. For example, the molding surface is made of aluminum or similar lightweight metal or plastic material. For applications where it is necessary to make only the surface of the forming means porous. For example, if the plastic binder has a low melting temperature, the mandrel can be covered with a layer of porous material such as cloth or cloth felt.

The forming means may be equipped with vacuum capability. The vacuum pressure behind the perforation surface performs three very important functions. First, during the process of stacking the fabric plies, the vacuum can temporarily hold the fabric plies in place until hot air is applied to stabilize the final preform.

Second, a vacuum can be used to facilitate the flow of hot air through the stack. A hot air path is thus created from the applicator through the preform stack and through the holes in the forming surface to the vacuum space. Third, after hot air is applied to melt the binder, vacuum pressure can be used to draw cold room air through the fabric plies to rapidly solidify the molten plastic binder. Rapid solidification of the ply binder increases the density of the preform and increases production rates.

The forming means may be provided with the ability to blow cold air or cold air in a direction opposite to the hot air flow, thereby facilitating a higher density of the preform.

Once the ply binder is sufficiently melted by the injection of hot air, the supply of hot air is stopped and cold air or cold air is blown through the holes onto the molding surface and circulated through the laminate. Pressure should be maintained while applying cold air.

This method results in a denser preform.

After the fabric plies are laid down on a perforated flat surface or mandrel, they are stabilized with pressurized hot air. The hot air melts the binding material placed between the fabric plies, bonding the plies together.

The temperature of the hot air is a function of the type of binder placed between the fabric plies, the rate at which the polymer melts, and the thickness of the preform laminate. For example, if nylon 12 is placed between about 8 plies of fabric,
Air at temperatures from 0'F to about 204C (400'F) substantially melts all the polymer in about 5 seconds. The hot air is supplied at sufficient pressure to penetrate all fabric plies simultaneously. For example, if the preform consists of about 9 or more plies of fabric, the air pressure should be 0°35 kg.
/cJ (5 p s i ) to 0. 7kg/c (
10 psi) is preferred. Hot air is supplied to the fabric ply for a sufficient period of time to melt the polymer disposed between all fabric layers that contact the forming means. The time required to melt the polymer is determined by the number of fabric plies in the preform, the polymer used and the temperature of the air. Hot air is supplied to the fabric ply from various locations to stabilize the entire preform or localized portions.

Means such as that shown in FIGS. 2 and 3 can be used to simultaneously supply hot air to the fabric plies and pressurize them together. These means have a body 14 made of a hard, low thermally conductive material, such as fiberglass or ceramic. The low thermal conductivity of the body 14 prevents it from absorbing heat contained in the airflow. A handle 16 allows the means to be lifted and moved into the appropriate orientation. An air supply connection 18 connects said means to an air supply hose. The body 10 has a number of holes 20 that are used to supply pressurized hot air to the fabric plies.

Large sections of the preform can be stabilized quickly using means with flat surfaces, as shown in FIG. Narrow edge means as shown in FIG. 3 can be used to stabilize the corners and folds of the preform. Although two specific configurations of the stabilizing means are shown in the accompanying drawings, a variety of configurations may be used as long as they are capable of supplying hot air to the fabric plies.

For example, a hot air gun can be used to tack the fabric plies with the binder together.

Example 1 A graphite fiber reinforced composite product having the shape of a mandrel shown in FIG. 1 was manufactured as follows.

First, a dry fiber preform is formed. Four plies of graphite fiber cloth with small particles of nylon dispersed on one side are cut according to a predetermined pattern. The fabric plies are stacked in sequence on a perforated flat surface and hot air is injected onto the fiber laminate using the flat hot air injection means shown in FIG. A 5 second blast of 149°C (300°F) air is used to bond each layer. The flat laminate is then formed with fold lines corresponding to the corners on the mandrel shown in FIG. 1 using means such as those shown in FIG.

FIG. 4 shows an embodiment for forming corner lines on a preformed laminate 26. In FIG. The rVJ groove 23 in FIG. 4 is designed to accommodate stacks of various thicknesses. Additionally, the bonded and creased fiber laminate is transferred to the forming mandrel shown in the first illustration and the seams are then bonded to complete the operation.

The embodiments of the present invention have been described above in detail with reference to the accompanying drawings, but as will be apparent to those skilled in the art, the present invention includes various modifications and changes to the embodiments described above within the technical scope thereof. It can be implemented by

Effects of the Invention By using this hot air to stabilize the preforms used in the RTM process, the required effort and time are significantly reduced compared to conventional means.

Reducing the effort and time required to stabilize RTM preforms can make RTM a practical means of producing fiber reinforced composite products. This is particularly suitable for fiber reinforced products with complex shapes.

[Brief explanation of the drawing]

FIG. 1 is a partially cutaway perspective view of a perforated mandrel used to form a preform. FIG. 2 is a perspective view showing the means used to blow hot air onto the preform to melt the polymer disposed between the fabric plies and stabilize the preform. FIG. 3 is a perspective view of another means used to blow hot air onto the preform. FIG. 4 is a schematic perspective view illustrating the manner in which a fiber preform is creased using the means shown in FIG. 10... Mandrel 12... Hole 14... Body 16... Handle 18... Air supply connection part 20... Hole 23... V groove 26... Laminated body patent applicant Unitedφ Technology Incorporated Representative Patent Attorney Yo Oshima −

Claims (10)

[Claims] (1) Laminating a plurality of dry fabric plies, forming the fabric plies into a desired shape, stabilizing the fabric plies to form a dry fiber preform, and stabilizing dry fabric placing the preform in a resin transfer molding means; injecting a thermosetting resin under pressure into the resin transfer molding means to impregnate the fiber preform with the thermosetting resin; A method for producing a fiber-reinforced composite product comprising heating the stabilized fiber preform and a thermosetting resin to cure the thermosetting resin and forming a fiber-reinforced product, the method comprising: a stabilized dry fiber preform by placing a polymeric binder between the plies of fabric and directing a stream of heated air capable of melting the binder towards the plies of dry fabric to bond the plies of fabric together; A method for producing a fiber-reinforced composite product, comprising the step of forming a fiber-reinforced composite product. (2) The method for manufacturing a fiber-reinforced composite product according to claim 1, wherein the cloth ply is graphite fiber. (3) The method for manufacturing a fiber-reinforced composite product according to claim 1, wherein the cloth ply is made of aramid fiber. (4) The method for manufacturing a fiber-reinforced composite product according to claim 1, wherein the cloth ply is made of glass fiber. (5) The method of manufacturing a fiber-reinforced composite product according to claim 1, wherein the binder is dispersed between the adjacent fabric plies in the form of powder particles or fiber felt. (6) The method for manufacturing a fiber-reinforced composite product according to claim 1, characterized in that about 5 g to about 60 g of the binder is used per 1 m^2 of cloth surface. (7) The method for manufacturing a fiber-reinforced composite product according to claim 1, wherein the thermosetting resin is nylon. (8) The method for manufacturing a fiber-reinforced composite product according to claim 1, wherein the thermosetting resin is polyetheretherketone. (9) the air directed to the fabric ply is about 121
A method of manufacturing a fiber-reinforced composite product according to claim 1, characterized in that the fiber-reinforced composite product is heated between 250°F and 400°F. (10) the air is directed to the fabric ply by means having a body made of a low thermal conductivity material, an air supply connection, and a plurality of holes for channeling the air towards the fabric ply; A method for producing a fiber-reinforced composite product according to claim 1.