The present disclosure generally relates to contour cauls, for example as used in composite manufacturing processes.
A composite structure in the form of a laminate can be made from reinforcing fibers combined with a resin. Uses for such composite structures include aircraft parts, spacecraft parts, and other applications where strong, light, and durable structures are useful.
Vacuum bagging can be used in composite manufacturing processes. For example, a vacuum bag can be placed around a composite structure during manufacturing, and air can be evacuated from the bag. The resulting pressure on the composite structure can help remove entrapped air and excess resin from the laminate and can also compact the laminate. Heat can be applied to enhance these effects and to harden the laminate.
A “contour caul” can be placed between the vacuum bag and the composite structure in order to help even out the pressure on the laminate.
According to certain aspects of the present disclosure, a contour caul is provided. The contour caul includes two or more higher Tg regions that follow geometries of a composite structure and an expansion region located between the higher Tg regions. The expansion region has a lower glass-liquid transition temperature than the higher Tg regions.
According to further aspects of the present disclosure, a method of making a contour caul is provided. The method includes applying a higher Tg material and a lower Tg material to a composite structure, the higher Tg material having a higher glass-liquid transition temperature than the lower Tg material, and the lower Tg material being applied between regions where the higher Tg material is applied. The method also includes allowing the higher Tg material and the lower Tg material to harden to form the contour caul.
According to additional aspects of the present disclosure, a method of making a composite structure is provided. The method includes placing a composite structure in a contour caul. The contour caul includes two or more higher Tg regions that follow geometries of the composite structure and an expansion region located between the higher Tg regions. The expansion region has a lower glass-liquid transition temperature than the higher Tg regions. The method also includes evacuating air from about the contour caul and the composite structure, and applying heat to the contour caul and the composite structure. The heat causes the expansion region to transition at least partially to a more flexible state than the higher Tg regions of the contour caul.
It is understood that other configurations of the subject technology will become readily apparent to those skilled in the art from the following detailed description, wherein various configurations of the subject technology are shown and described by way of illustration. As will be realized, the subject technology is capable of other and different configurations and its several details are capable of modification in various other respects, all without departing from the scope of the subject technology. Accordingly, the drawings and detailed description are to be regarded as illustrative in nature and not as restrictive.
The accompanying drawings, which are included to provide further understanding and are incorporated in and constitute a part of this specification, illustrate disclosed embodiments and together with the description serve to explain the principles of the disclosed embodiments. In the drawings:
In the following detailed description, numerous specific details are set forth to provide a full understanding of the present disclosure. It will be apparent, however, to one ordinarily skilled in the art that the embodiments of the present disclosure may be practiced without some of these specific details. In other instances, well-known structures and techniques have not been shown in detail so as not to obscure the disclosure.
A composite structure in the form of a laminate can be made from reinforcing fibers combined with a resin. Uses for such composite structures include aircraft parts, spacecraft parts, and other applications where strong, light, and durable structures are useful.
Vacuum bagging can be used in composite manufacturing processes. For example, a vacuum bag can be placed around a composite structure during manufacturing, and air can be evacuated from the bag. The resulting pressure on the composite structure can help remove entrapped air and excess resin from the laminate and can also compact the laminate. Heat can be applied to enhance these effects and to harden the laminate.
A “contour caul” according to aspects of the disclosure is placed between the vacuum bag and the composite structure in order to help even out the pressure on the laminate. The caul can be form fitted within the composite structure prior to bonding processes and then removed until needed. For example, after Pi preforms (i.e., it shaped structures that can be used to join two structures) are in place on the structure, the caul can be placed back on the structure.
If the composite structure has a complex geometry, the contour caul applies more pressure to some parts of the structure than others. For example, in some composite structures with pieces joined by Pi preforms, two corners of the structure can be close enough together that a contour caul cannot apply even pressure to both corners. Instead, the caul might be pulled away from one corner by being pressed into another corner, possibly preventing adequate overall compaction.
Aspects of the subject technology address this issue by including an expansion region or joint in a contour caul. The expansion region can be formed in the caul by using a different resin from the rest of the caul that has a lower gas-liquid transition temperature Tg. The gas-liquid transition that occurs at Tg is a reversible transition in amorphous materials from a hard state into a molten or rubber-like state.
A contour caul according to aspects of the disclosure includes two or more higher Tg regions that follow geometries of a composite structure and an expansion region located between the higher Tg regions. The expansion region has a lower glass-liquid transition temperature than the higher Tg regions.
Such expansion regions form low Tg points within the caul. When heat is applied during a vacuum bag curing process, a glass-liquid transition of an expansion region allows for movement of other parts of a contour caul, thereby permitting the higher Tg and therefore harder portions of the caul to move into complex geometries such as adjacent corners before the laminate hardens. Both lower Tg and higher Tg regions can form enhanced contours at different times during a cure cycle, with the higher Tg regions maintaining a greater degree of rigidity beyond the gel point of the lower Tg regions.
In addition, as the laminate cures and compacts, the expansion regions of the caul permit the harder portions of the caul to move and to continue to apply pressure to the composite structure. This continued movement and pressure can allow the caul to match subtle structures in the laminate.
An arrangement as shown in
Composite structure 130 in
Failure to properly cure a Pi joint can lead to a weakened joint, creating a potential for a catastrophic failure. For example, if the Pi joint is used to join parts of a composite structure for part of an aircraft, a weakened Pi joint could lead to an aircraft crash. The present disclosure is not limited to prevention of catastrophic failures.
Caul 110 according to aspects of the present technology can help with curing of a composite structure. Caul 110 includes both higher Tg (glass or glass-liquid transition temperature) regions 112 and 114 and an expansion joint 116 situated between the higher Tg regions according to aspects of the disclosure. The expansion region has a lower glass-liquid transition temperature than the higher Tg regions. When heated during curing, the expansion region becomes softer and/or more flexible than the higher Tg regions, while the higher Tg regions remains relatively harder. The softer and/or more flexible expansion regions permit the higher Tg regions to be more evenly pressed into corners and other complex geometries of a composite structure according to aspects of the disclosure and/or to concentrate pressure into such corners. The higher Tg materials can also press more evenly or concentrate pressure into other areas containing angles, for example angles near or less than 90 degrees.
In the case of a composite structure made of multiple pieces, a caul can include higher Tg regions following corners and other complex geometries of each piece. This is illustrated in
More than one expansion region can be included in a caul according to aspects of the disclosure. Thus, caul 120 is shown with expansion regions 128 and 129. Expansion region 128 is situated between higher Tg regions 122 and 124. Likewise, expansion region 129 is situated between higher Tg regions 124 and 126. According to aspects of the disclosure, inclusion of multiple expansion regions can help even out pressure applied during curing even for very complex structures. Thus, a caul that includes higher Tg regions and expansion regions according to aspects of the subject technology can function as a singular assembly of pressure intensifiers for curing even complex composites structures.
The regions of contour cauls according to aspects of the disclosure can be made from many materials. One example of a suitable material includes epoxies. One example of a suitable epoxy for an expansion region according to aspects of the disclosure is West Systems 105/206 Epoxy. Other epoxies and materials other than epoxies can be used.
According to further aspects of the disclosure, locating pins can be incorporated into a surface of a contour caul. The locating pins can position the contour caul on a composite structure. Examples of such locating pins are shown in
Contour cauls such as those shown in
Caul 200 in
As the composite structure cures, a laminate forming or being added to the composite structure can compact. The lower Tg regions permit the higher Tg regions to follow this compaction, allowing the contour caul to follow subtle changes and structures within the composite structure. The disclosure is not limited to cauls that follow such subtle changes and structures.
In step 410, a composite structure composed of one or more pieces is positioned and placed in one or more contour cauls according to aspects of the disclosure, for example using locating pins. Such pins do not necessarily have to be used. Alternatively, the contour cauls can be positioned and placed on a composite structure in step 410.
A vacuum bag is placed around the composite structure and caul(s) in step 420. Curing of the composite structure begins in step 430. Curing can begin by evacuating air from the vacuum bag to apply pressure to the composite structure and applying heat. One or more expansion regions in caul(s) according to aspects of the subject technology soften due to the heat, which in turn can improve application of the pressure to complex geometries of the composite structure.
Pressure and heat can be maintained until the composite structure finishes curing in step 440. As the structure cures, the lower Tg regions can permit the higher Tg regions to follow compaction of laminates that make up or are being applied to the composite structure. Both the higher and lower Tg regions can form enhanced contours at different times during curing, with the higher Tg regions maintaining a greater degree of rigidity beyond the gel point of the lower Tg regions. The composite structure can be removed from the caul(s) in step 450.
Contour cauls according to aspects of the subject technology can be used in other ways than those described above with respect to
In step 710, a higher Tg material is applied to a composite structure, for example before curing. The higher Tg material can be applied to more complex structures such as corners according to aspects of the disclosure. A lower Tg material that will form expansion regions is applied in step 720. Examples of higher Tg and lower Tg materials include but are not limited to different epoxies with different transition temperature points. These steps do not have to be performed in any particular order and can be performed simultaneously.
Locating pins can be added to the contour caul in step 730. When the higher and lower Tg materials harden, the pins can become trapped by the materials. Directed force compression stiffeners and other structures also can be added in a like manner. Alternatively, such structures can be added using other approaches, and the structures can be added at other points in the process illustrated by
In step 740, the materials are allowed to harden, for example by drying. The now hardened materials form a compression caul according to aspects of the disclosure. The caul can removed from the composite structure in step 740 for later use, for example after additional parts or elements have been added to the composite structure.
The process shown in
Contour cauls according to aspects of the subject technology can be made in other ways than those described above with respect to
In some aspects, addition components can be added to the higher and lower Tg materials before, during, or after steps 810 and 820. Examples of such structures include but are not limited to directed force compression stiffeners and locating pins.
In step 830, the materials are allowed to harden, for example by drying. The now hardened materials form a compression caul according to aspects of the disclosure.
A laminate is applied to a composite structure or a form in step 840. For example, prepreg (i.e., reinforcing fibers pre-pregnated with resin) can be layed up, sprayed, or applied to the composite structure or form in any other manner. The resin and reinforcing fibers form a laminate on the composite structure. One or more contour cauls are applied to the laminate on the composite structure in step 850.
A vacuum bag is placed around the composite structure and caul(s) in step 860. Curing of the composite structure begins in step 870. Curing can begin by evacuating air from the vacuum bag to apply pressure to the composite structure and applying heat. One or more expansion regions in caul(s) according to aspects of the subject technology soften due to the heat, which in turn can improve application of the pressure to complex geometries of the composite structure.
Pressure and heat can be maintained until the composite structure finishes curing in step 880. As the structure cures, the lower Tg regions can permit the higher Tg regions to follow compaction of laminates that make up or are being applied to the composite structure. Both the higher and lower Tg regions can form enhanced contours at different times during curing, with the higher Tg regions maintaining a greater degree of rigidity beyond the gel point of the lower Tg regions. The composite structure can be removed from the caul(s) in step 890.
Contour cauls according to aspects of the subject technology can be used in other ways than those described above with respect to
In the foregoing, a phrase such as an “aspect” does not imply that such aspect is essential to the subject technology or that such aspect applies to all configurations of the subject technology. A disclosure relating to an aspect may apply to all configurations, or one or more configurations. A phrase such as an aspect may refer to one or more aspects and vice versa. A phrase such as a “configuration” does not imply that such configuration is essential to the subject technology or that such configuration applies to all configurations of the subject technology. A disclosure relating to a configuration may apply to all configurations, or one or more configurations. A phrase such as a configuration may refer to one or more configurations and vice versa.
All structural and functional equivalents to the elements of the various aspects described throughout this disclosure that are known or later come to be known to those of ordinary skill in the art are expressly incorporated herein by reference and are intended to be encompassed by the claims. Moreover, nothing disclosed herein is intended to be dedicated to the public regardless of whether such disclosure is explicitly recited in the claims.
While this specification contains many specifics, these should not be construed as limitations on the scope of what may be claimed, but rather as descriptions of particular implementations of the subject matter. Certain features that are described in this specification in the context of separate embodiments can also be implemented in combination in a single embodiment. Conversely, various features that are described in the context of a single embodiment can also be implemented in multiple embodiments separately or in any suitable subcombination. Moreover, although features may be described above as acting in certain combinations and even initially claimed as such, one or more features from a claimed combination can in some cases be excised from the combination, and the claimed combination may be directed to a subcombination or variation of a subcombination.
Likewise, while operations are depicted in the drawings in a particular order, this should not be understood as requiring that such operations be performed in the particular order shown or in sequential order, or that all illustrated operations be performed, to achieve desirable results.
The previous description is provided to enable any person skilled in the art to practice the various aspects described herein. Various modifications to these aspects will be readily apparent to those skilled in the art, and the generic principles defined herein may be applied to other aspects. Thus, the claims are not intended to be limited to the aspects shown herein, but are to be accorded the full scope consistent with the language claims, wherein reference to an element in the singular is not intended to mean “one and only one” unless specifically so stated, but rather “one or more.” Unless specifically stated otherwise, the term “some” refers to one or more. Pronouns in the masculine (e.g., his) include the feminine and neuter gender (e.g., her and its) and vice versa. Headings and subheadings, if any, are used for convenience only and do not limit the subject disclosure.
All structural and functional equivalents to the elements of the various aspects described throughout this disclosure that are known or later come to be known to those of ordinary skill in the art are expressly incorporated herein by reference and are intended to be encompassed by the claims. Moreover, nothing disclosed herein is intended to be dedicated to the public regardless of whether such disclosure is explicitly recited in the claims.