Gradient tool system for composite parts

A gradient tool for forming a part, the gradient tool comprising a first tool component comprising a first surface and a second surface. The first surface comprising a first material having a first coefficient of thermal expansion (CTE), and the second surface comprising a second material having a second CTE. The first CTE of the first material is different than the second CTE of the second material.

FIELD

The present disclosure generally relates to methods and equipment for fabricating composite parts, and generally relates to a gradient tool system used in curing composite parts.

BACKGROUND

Composite parts may be cured within an autoclave that applies heat and pressure to the composite part during a cure cycle. Prior to cure, the composite part is typically laid up over a top surface of a tool. During autoclave heating, thermal mismatches or thermal stresses between the composite part and the tool on which the composite part is fabricated oftentimes generates thermal stresses that are locked into the part.

One of the reasons the composite part may warp is that the coefficient of thermal expansion (CTE) of the part and the CTE of the tool might be different. When the CTE of the composite part and the tool are different, the tool and the part may change shape at different rates causing the part to warp. In most situations, the tool is formed from a material having a CTE that approximately matches the CTE of the composite part in an attempt to reduce warping. However, such material is expensive and may not completely eliminate the warping.

Thermal stresses can also result in the bending of the composite part out of its engineering shape as the part cools to room temperature. As just one example, “spring-in” is a common manifestation of this, although “web rise” and twists are frequently observed as well depending on part geometry. When the composite part does not meet its desired engineering shape, shimming may be needed. Alternatively, in extreme cases, the part will be rejected and a new part must be manufactured. In certain known situations, composite part manufacturers may reject at least some of the parts they produce, which may up to double the manufacturing cost of certain composite parts.

In an attempt to reduce such thermal stresses, detailed modeling can be performed to design tooling that accounts for the warping of the part so that the part will warp from the tooling shape to the desired final shape. Certain modeling techniques are known that can be used in an effort to predict thermal stresses. However, the use of such modeling techniques have certain limitations. For example, running such an analysis is expensive and may take multiple weeks to perform. Invar (a specific composition of metal) tools, as well as composite tools, are available that come close to matching the CTE of the composite parts made on them. However, some such tools may be replaced frequently, depending on use. Invar is also expensive, as tools are frequently thousands of pounds. Both Invar and composite tools still may use tool surface compensation.

SUMMARY

In an arrangement, a gradient tool for forming a part is disclosed. The gradient tool comprising a first tool component comprising a first surface and a second surface, the first surface comprising a first material having a first coefficient of thermal expansion (CTE), and the second surface comprising a second material having a second CTE. The first CTE of the first material is different than the second CTE of the second material.

In an arrangement, the first CTE of the first material is lower than the second CTE of the second material.

In an arrangement, the gradient tool comprises a second tool component comprising a first surface, wherein the second tool component is formed from a third material having a third CTE. In an arrangement, the first surface of the second tool component comprises a geometrical surface structure similar to a geometrical surface structure of the first surface of the first tool component.

In an arrangement, the third CTE of the third material of the second tool component is substantially equal to the second CTE of the second material of the first tool component.

In an arrangement, the first tool component is formed integrally with the second tool component.

In an arrangement, the first tool component is coupled to the second tool component such that the second surface of the first tool component is adjacent a first surface of a second tool component.

In an arrangement, the first CTE of the first material of the first tool component is substantially equal to a fourth CTE of the part.

In an arrangement, the first surface of the first tool component has a geometrical surface structure to match a geometrical surface structure of the part.

In an arrangement, the second surface of the first tool component has a geometrical surface structure to match a geometrical surface structure of the part.

In an arrangement, at least one of a third material of a second tool component and the second material of the first tool component comprises aluminum.

In an arrangement, a method of manufacturing a composite part using a gradient tool comprising a first tool component is disclosed. The method comprising the steps of: laying up a composite part along a first surface of the first tool component of the gradient tool; sealing a vacuum bag over the composite part; drawing a vacuum in the vacuum bag so as to compact the composite part; heating the composite part to a predetermined temperature; changing a shape of the first surface of the first tool component at a first rate dependent on a first Coefficient of Thermal Expansion (CTE) of the first surface, and changing a shape of a second surface of the first tool component at a second rate dependent on a second CTE of the second surface, the second CTE of the second surface different than the first CTE of the first surface.

In an arrangement, the method further comprises the step of causing thermal stresses within the first tool component based on the different first CTE and second CTE of the first tool component.

In an arrangement, the method further comprises the step of compressing at least one compressible area defined by the first tool component so as to respond to the difference of thermal expansion between the first surface and the second surface of the first tool component.

In an arrangement, a method of fabricating a gradient tool comprising a first tool component is disclosed. The method comprising the steps of: configuring a first surface of the first tool component to interface with a bottom surface of a composite part; selecting a first material of the first surface of the first tool component, the first material having a first coefficient of thermal expansion (CTE); configuring a second surface of the first tool component to interface with a second tool component; and selecting a second material of the second surface of the first tool component wherein the second material has a second CTE. The second CTE is different than the first coefficient of thermal expansion of the first material.

In an arrangement, the method further comprises the step of: defining a desired tool inner mold line along the first surface of the first tool component.

In an arrangement, the method further comprises the step of: selecting the first material of the first surface of the first tool component, such that the first CTE of the first material is generally equivalent to a CTE of the composite part that is configured to interface with the first surface of the first tool component.

In an arrangement, the method further comprises the step of: selecting the second material of the second surface of the first tool component, such that the second CTE of the second material is generally equivalent to a CTE of the second component part.

In an arrangement, the method further comprises the step of: coupling the first tool component to the second tool component such that the second surface of the first tool component is adjacent the first surface of the second tool component.

In an arrangement, the method further comprising the step of: integrally forming the first tool component as one-piece with the second tool component.

DETAILED DESCRIPTION

The embodiments described herein provide tools and methods that may reduce the adverse effects resulting from CTE differentials existing between a composite part and a tool. The herein-described tools and methods may reduce thermal stresses and strains occurring during a cure process of a composite part. The herein-described tools and methods may reduce the number or percentage of parts falling outside of desired tolerances and therefore reduce production costs. The tools and methods may also reduce the overall cost of a tool used for curing composite parts.

More specifically, the tools described herein include a face portion having a coefficient of thermal expansion (CTE) that varies from a CTE equal to the CTE of a base portion to the CTE of the part being made. This variation allows the surface of the tool contacting the composite part being made to have a CTE equal to the CTE of the composite part to prevent thermal stress between the part and the tool surface.

Disclosed embodiments will now be described more fully hereinafter with reference to the accompanying drawings, in which some, but not all of the disclosed embodiments are shown. Indeed, several different embodiments may be provided and should not be construed as limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete and will fully convey the scope of the disclosure to those skilled in the art.

FIG. 1is a diagrammatic representation of a functional block diagram of a gradient tool system10according to disclosed embodiments. Such a tool system10may comprise an autoclave30and a gradient tool20. Referring first toFIG. 1, an uncured composite part15may be supported by way of the gradient tool20within the autoclave30. Specifically, the uncured composite part15may be cured on the gradient tool20placed in the autoclave30in which autoclave heat and pressure are applied to the uncured composite part15. The uncured composite part15comprises a coefficient of thermal expansion (CTE)18.

In this illustrated arrangement, the gradient tool20comprises two components: a first tool component50and a second tool component100. In one preferred arrangement, these two components50,100are coupled to one another. As illustrated, the first component50comprises a first surface60and a second surface80. In this illustrated arrangement, the first surface60of the first tool component50comprises a surface that is located at a top of the first component50and the second surface80comprises a surface that is located at a bottom of the first component50. However, as those of ordinary skill in the art will recognize, alternative first and second surface arrangements may also be used. As just one example, the first surface60could comprise a first side surface of the first component50while the second surface could comprise a second side surface of the first tool component50.

As illustrated, the first surface60of the first tool component is configured to interface or support a bottom surface17of the composite part15. Preferably, the first surface60comprises a desired tool inner mold line70for the composite part15. As illustrated, both the first surface60of the first tool portion and a bottom surface17of the composite part15comprise planar geometrical surface structures. However, as those of skill in the art will recognize, other geometrical surface structures of the composite part, and of surface17, and therefore the desired tool inner mold line70may also be used.

In this illustrated arrangement, the first surface60comprises a first material64wherein this first material64has a first coefficient of thermal expansion (CTE)66. In one preferred arrangement, this first CTE66of the first material64is selected to be generally equivalent to a CTE18of the composite part15.

Similarly, the second surface80of the first tool component50is configured to interface with the second tool component100. A tool component interface82may be defined where the first tool component50interfaces with the second tool component100. Specifically, in this illustrated arrangement, the second surface80of the first tool component50is configured to be coupled to a first surface120of the second tool component100. As illustrated, the first surface120of the second tool component100comprises a top surface of the second tool component100. However, as those of ordinary skill in the art recognize, alternative first and second surface arrangements may also be used. As just one example, the first surface120could comprise a first side surface of the second component100. In this illustrated arrangement, the first tool component50is coupled to the second tool component100such that the second surface80of the first tool component50resides adjacent (i.e., in direct or indirect contact with) the first surface120of the second tool component100.

In a preferred arrangement, the first tool component50comprises a non-homogenous portion and may be formed from various compositions. More specifically, the second surface80of the first tool component50is made from a different material than the first surface60of the first tool component50such that the CTE90of the second surface80matches a CTE of the second tool component100. In addition, the CTE66of the first surface60of the first tool component50matches the CTE18of the part15being formed. As just one example, the second surface80of the first tool component50comprises an aluminum surface, and the first surface60of the first tool component50comprises an aluminum-nickel alloy, such as Invar. When placed in an autoclave and cured, such as the autoclave30illustrated inFIG. 1, the different CTE of the first and second surfaces60,80of the first tool component50will cause thermal stress within the first tool component50. Specifically, because the CTE66of the first surface60is different than the CTE90of the second surface50, the first surface60and the second surface80will change shape at different rates (based on the different CTEs66,90) causing thermal stresses within the first tool component50.

In one preferred arrangement, the second tool component100comprises a first or top surface120and a second or bottom surface125. The first surface120is roughly (but preferably not exactly) the final shape of the part15in order to further reduce the cost of the second tool component100. In one preferred arrangement, the first tool component second surface80has the rough shape, and the face top portion has the exact shape of the part.

In one arrangement, the first tool component50may be fabricated by sputtering, additive manufacturing, or successive electroplating, and machining.

In this illustrated arrangement, the second tool component100comprises a rectangular prism configuration but alternative second tool component configurations may also be used. The first surface120of the second tool component100comprises a surface that comprises a rough structure of an inner mold line (IML)140that is generally similar to the desired tool inner mold line70of the first tool component50. The second surface125of the second tool component100may have any type of geometrical surface structure.

This second tool component100could be made of any material124. For example, the material124of the second tool component100may comprise a ceramic, a metal, a thermoset, a thermoplastic, a composite, or perhaps any combination thereof. Preferably, the material124of this second tool component100is selected and/or designed so that it can be manufactured in a cost effective manner. As just one example, the second tool component100may be produced by way of injection molding, additive manufacturing, or subtractive manufacturing. Low tolerance requirements of the rough IML surface face140of the second tool component100enables the use of inexpensive fabrication techniques while also reducing the overall manufacturing costs of the second tool component100.

The first tool component50may comprise an atomic composition across its thickness (e.g., a metal and/or an alloy of metals). Such an alloy could be formed from several metals having compositions that are different from each other. For example, the first material64of the first surface60of the first tool component50may comprise a material having a CTE66that is similar to the CTE18of a particular composite part15undergoing fabrication. The CTE66of the first material64of the first surface of the first composite tool may be selected to be higher or lower than the CTE90of the second surface84of the first tool component50. In addition, the first tool component50may comprise a second surface80that comprises a second material84having a CTE90that is similar to the CTE128of the material124of the second tool component100. Accordingly, the first material64may have a different composition than the second material84.

Advantageously, the first tool component comprises a CTE that varies along a portion of the first tool component. For example, the first tool component50comprises a coefficient of thermal expansion that varies along its height HFC59between the first and second surfaces60,80, respectively.

In order to achieve a thermal gradient within the first tool component50, the first tool component may comprise an alloy formed of a plurality of metals with each metal having a different composition. As just one example, the first tool component50may comprise a first surface comprising Invar (36% Ni) or (38% Ni) which comprises a CTE that is closer to composite parts' CTE than Aluminum does. So, in one exemplary first tool component, the gradient may comprise an Aluminum second surface and an Invar first surface.

In one arrangement, the second component100comprises a homogenous second tool component and may be manufactured from a material selected based mainly on cost. For example, the second tool component100may be formed from aluminum or an aluminum alloy.

The first surface60of the first tool component50may match the rough structure of the IML140of the surface120of the second tool component100. In this illustrated arrangement, the IML70of the first tool component50is defined by the first surface60upon which the composite part15is laid up or placed upon. The second surface80, or the bottom surface, of the first tool component50may have a geometrical surface structure that matches the desired tool IML at its other surface60, or top surface. As such, this first tool component50can be referred to as “a gradient tool component”. That is, the first tool component50comprises a gradient CTE between the first surface60(i.e., the desired tool inner mold line70) and the second surface80. Specifically, this gradient CTE of the first component50provides a gradient change in the value of a CTE along a dimension of the first tool component50. For example, in this illustrated arrangement, the first tool component50provides a gradient change in the value of the CTE along a height HFC54of the first tool component50. Exemplary gradient changes may comprise step intervals (e.g., constant or non-constant step intervals), sinusoidal changes, logarithmic changes, and/or exponential changes.

FIG. 2is a diagrammatic representation of one example of a plot200of coefficient of thermal expansion (CTE)210for the gradient tool20illustrated inFIG. 1. As illustrated, the second tool component100(also referred to herein as a “base”) is provided. In this illustrated arrangement, the base100comprises aluminum. This aluminum base100has a CTE αAluminum240. Therefore, the CTE αAluminum240is constant from the first surface120of the aluminum base100to the second surface125of the aluminum base. This CTE αAluminum240is graphically represented by a line280provided in the plot200ofFIG. 2.

At the first surface120of the aluminum base100, the base100is coupled to the first tool component50which in this arrangement comprises a gradient face portion (this gradient face portion is same as first tool component50illustrated inFIG. 1). As noted inFIG. 2, the tool component interface82is defined where the first tool component50interfaces with the second tool component100. The gradient face portion comprises a CTE320that varies linearly from the second surface80of the gradient face component (i.e., the tool component interface82) to the first surface60of the gradient face component. More specifically, the gradient face portion50comprises a CTE αAluminum350at the second surface80of the gradient face component50that matches the homogenous CTE280of the base component: CTE αAluminum. In addition, the gradient face portion50comprises a CTE340at the first surface60of the gradient face component50, such as CTE αComposite380. The CTE αComposite380is represented by the dashed line382inFIG. 2. This CTE340is designed or selected to match the CTE380of a composite part15laid up on the second surface60of the gradient face50.

As those of skill in the art will recognize, alternative gradient tools comprising alternative CTE gradients may also be used. As just one example, the second tool component100may have a non-homogenous base component with a CTE280that varies between the first surface120and the second surface125. In an alternative arrangement, the second tool component100may comprise at least two types of metals, with each metal having a different CTE.

In yet another alternative arrangement, the first tool component50may comprise three or more materials.

In one arrangement, the first tool component50may be formed integrally as one-piece with the second tool component100. For example, the first tool component50may be grown on the second tool component100. Alternatively, the first tool component50could be formed separately from the second tool component100and then coupled to the second tool component, such that the second tool component100acts as a base portion for the gradient tool50. Examples of coupling the first tool component50to the second tool component100include but are not limited to: using gravity, thermal lock, snap lock, adhesive, gluing, and bonding.

Preferably, the first tool component50is removably coupled to the second tool component100. One advantage of such a gradient tool construction is that when the separate first tool component is coupled to the second tool component, the first tool component can be replaced without having to replace the second tool component. Such a feature is advantageous when new materials having CTEs that are a better match for the part being formed become available or when a different composite (with a different CTE) is being tested and/or processed on the tool because only the first tool component50will need to be switched out, rather than the entire gradient tool20. In the testing situation, the first tool component can be switched out to another first tool component having a top surface CTE matching the CTE of the test composite, then switched back again to return to making parts from the usual composite.

The first tool component50may or may not comprise one or more compressible areas74. The first tool component50may comprise compressible areas74to relieve the stress by being compressible relative to the tool. Such compressible areas74, which may be open or closed cells and may or may not contain a gas (e.g., air), are generally highly compressible relative to metal. The compressible areas74may also contain other highly compressible materials as well. The placement and orientation of such compressible areas74could be designed and engineered in order to respond to the difference of thermal expansion between the different materials used for the first surface60and the second surface80of the first tool component50without absorbing all of the difference as tool-internal strain during a cure. Such compressible areas74may be provided in a uniform manner along a dimension of the first tool component50, such as the length and/or width. Alternately, such compressible areas74may be provided in only certain portions of the first tool component50. In yet another alternative arrangement, such compressible areas74may comprise the same or different geometrical shapes and/or configurations as each other based on the structure and overall shape of the composite part15being cured.

For example, and as illustrated inFIG. 1, the first tool component50comprises a plurality of compressible areas74A-D having different geometrical shapes. As illustrated, the plurality of compressible areas74A-D are evenly spaced along the same plane and along a length LFC88of the first tool component50. However, compressible area arrangements may be provided wherein the location and number of compressible areas74may be a function of the final shape of the composite part15to be cured. The arrangements and/or orientations of the compressible areas74may also be a function of the composition of or the materials used for the first and second surfaces60,80of the first tool component50. In addition, arrangements and/or orientations of the compressible areas74may be a function of the type of material used in the first or base component100.

As discussed herein, in one preferred arrangement, the first surface120of the second tool component100will match the IML70of the first tool component50so that the first tool component50and the second tool component100may be coupled to one another. As just one example, the first and second tool components may be coupled by way of an adhesive (e.g., a synthetic bonding agent) or a glue (e.g., a naturally occurring bonding agent). If coupled to one another by an adhesive or glue, this would allow the first tool component50to be replaced with a replacement first tool component so as to extend the life of the second tool component. Also, the ability to switch out the first tool component allows the use of a different material for selection of the second or bottom surface80of the first tool component50. Other methods of coupling the two tool components50,100together include the use of gravity or the use of one or more snap locks or snap fits. Alternatively, a thermal lock could be used to couple the first and second components50,100together. That is, the two portions may be coupled together at elevated temperatures. As those of skill in the art will recognize, a combination of these types of coupling mechanisms may also be used. Moreover, being able to switch out the face portion (e.g., first tool component50), allows selection of different face portions to match different composite materials having a different CTEs without having to purchase or design/fabricate a new base portion.

FIG. 3is a diagrammatic representation of an alternative gradient tool20′ that may be used in a gradient tool system, such as the gradient tool system10illustrated inFIG. 1. Similar to the gradient tool20illustrated inFIG. 1, the alternative gradient tool20′ comprises two components: a first tool component50′ and a second tool component100. As such, like elements fromFIG. 1are represented with like reference numbers inFIG. 3.

In this illustrated arrangement, the first tool component50′ of the gradient tool20′ is coupled to the second tool component100, which acts as a base component for the gradient tool20′. As illustrated, the first component50′ comprises a first surface60and a second surface80. In this illustrated arrangement, the first surface60of the first tool component50′ is located at a top of the first component50′ and the second surface80is located at a bottom of the first component50′. However, in alternative arrangements, the first surface60may comprise a different surface, such as a side surface or a bottom surface of the first component50′. As also illustrated, the first tool component50′ comprises a non-constant height HFC59. That is, the height of the first tool component50′ varies over the length LFC88of the first tool component50.

As illustrated, the first surface60comprises a desired tool inner mold line70′ for a composite part15. As illustrated, the first surface60of the first tool component50′ comprises a non-planar surface. The second surface80of the first tool component50′ comprises a planar surface.

The second surface80of the first tool component50′ is configured to interface with the second tool component100. As illustrated, the first surface120of the second tool component100comprises a top surface of the second tool component100. As also illustrated, the first tool component50′ comprises a plurality of compressible areas74A′-D′. As previously described, such internal compressible areas74A′-D′ are provided in order to respond to the different thermal expansion created by the different materials used for the first and second surfaces60,80of the first tool component50′ without absorbing all of the thermal difference as tool-internal strain during a cure. In this illustrated gradient tool20′, such internal compressible areas74A′-D′ are provided along a first portion112and a second portion114of the first tool component50′. As illustrated, the first and second portions112,114comprise portions of the first tool component50′ having larger heights.

The presently disclosed embodiments of the gradient tool provide a number of advantages. For example, matching the thermal expansion of the part to the first tool component may reduce the spring-in and other cure-induced deformation of parts that can arise during composite part manufacturing. This, in turn, may reduce scrap rates for composite part manufacturers and therefore may reduce overall manufacturing costs. Another advantage of the presently disclosed gradient tools is that they may provide a cost effective tool that matches the thermal expansion of the composite part where the tool interfaces the composite part. This result may be achieved while the gradient tool still provides appropriate support of the part and not requiring the tool to match the thermal expansion of the part where the tool does not interface the part, such as in the tool cart structure.

Another advantage of the presently disclosed gradient tool is that the first tool component and second tool component may be fabricated such that they could be replaced independent of each other. This may present a number of advantages. For example, gradient tool interchangeability may benefit research when a part is fabricated by way of several different material systems. The herein-described gradient tool may also present manufacturing advantages by allowing replacement of only the first tool component or the second tool component as these tool components may wear at different rates.

Attention is now directed toFIG. 4which illustrates the steps of a method420of fabricating a composite part, using the herein described the gradient tools20,20′ comprising a first tool component50,50′ and a second tool component100, as shown inFIGS. 1 and 3. Beginning at step430, a gradient tool20and/or20′ is provided. In one arrangement, the gradient tool20,20′ comprises a first tool component50,50′ coupled to a second tool component100. In one arrangement, the first tool component50,50′ is integrally formed as one-piece with the second tool component100.

At step440, composite part15is laid up or assembled on a first surface60,60′ of a gradient tool20. Lay up of the composite part15may take place by way of conventional ply layup techniques, the composite part15may have one or more simple or complex contoured part surfaces. In one preferred arrangement, the composite part15may be laid up manually. In an alternative arrangement, the composite part15may be laid up using advanced fiber placement (“AFP”) or automated tape laying (“ATP”) manufacturing methods (or by any other known method) in the desired positions and orientations as determined during the composite laminate specification and design phase.

At step450, the composite part15, along with the gradient tool20and/or20′ are covered with a flexible bag25such as a vacuum bag. At step460, the flexible bag25is then sealed to the gradient tool20and the composite part15.

At step470, a vacuum is drawn in the flexible bag25by way of a vacuum source, such as source32inFIG. 1. This created vacuum forces the flexible bag25down onto a top surface of the composite part15in order to compact and/or consolidate the composite part15.

At step480, the vacuum bagged composite part15is cured with heat. For example, at step480, the vacuum bagged composite part15may be placed within a conventional or surface-heating systems, such as those found in autoclave30. Curing in such a conventional heating system will heat the composite part15from the outside in, as heat energy is transferred through a thickness of the composite part15. The process duration of a thorough cure, therefore, is determined by the rate of heat flow into the composite part15. As such, the flow rate depends on the specific heat, thermal conductivity, density, and viscosity of the material(s) used in the composite part15. With certain convection heating systems, the composite part15may heat at an uneven rate, which can stress the final cured laminate. Therefore, the temperature in the autoclave30and a convection heating source is typically ramped up and down slowly in an attempt to minimize part stress. Heating the composite part15to a predetermined temperature changes a shape of the first surface64of the first tool component50,50′ at a first rate dependent on a first CTE66of the first surface64. Heating also changes a shape of a second surface84of the first tool component50,50′ at a second rate dependent on a second CTE90of the second surface84.

After the heating step480has taken place, at step490, the flexible bag25, having the composite part15therein, is removed from the autoclave.

At the end of this curing process, the composite part15is substantially cured and the plies within the composite part15are consolidated so as to form a continuous, cured composite laminate. At step490, the cured composite part15may be removed from the flexible bag25. Thereafter, the cured composite part15is allowed to cool before any further finishing processing steps take place.

FIG. 5illustrates a method500of fabricating a gradient tool20(shown inFIGS. 1 and 3) and/or gradient tool20′ (shown inFIG. 3) comprising a first tool component50,50′ and/or50′ and a second tool component100. As illustrated, the method500comprises an initial step504of configuring a first surface60of a first tool component50,50′ to interface with a bottom surface17of a composite part15. In one arrangement, the first tool component50,50′ may be fabricated by sputtering, additive manufacturing, successive electroplating, or machining.

At optional step505, the method500may include the step of defining at least one compressible area74within the first tool component50,50′.

At optional step506, the method500may include the step of defining a desired tool inner mold line70along the first surface60of the first tool component50,50′.

At step508, the method500includes the step of selecting a first material64of the first surface60of the first tool component50,50′. Specifically, the first material64may be chosen to have the first CTE66.

At optional step510, the method500comprises the step of selecting the first material64of the first surface60of the first tool component50, such that the first CTE66of the first material64is generally equivalent to the CTE18of the composite part15that is configured to interface with the first surface60of the first tool component50.

Then, at step512, the method500includes the step of configuring a second surface80of the first tool component50,50′ to interface with a second tool component100. In one arrangement, the method may include the step of fabricating the second tool component100by injection molding, additive manufacturing, or subtractive manufacturing.

Then at step516, the method500includes the step of selecting a second material84of the second surface80of the first tool component50,50′ wherein the second material84has the second CTE90. Specifically, the second CTE90may be selected to have a different CTE than the first CTE66of the first material64.

At optional step518, the method includes the step of selecting the second material84of the second surface80of the first tool component50,50′, such that the second CTE90of the second material84is generally equivalent to the CTE128of the second component part100.

At optional step520, the method500may include the step of coupling the first tool component50,50′ to the second tool component100such that the second surface80of the first tool component50,50′ is adjacent the first surface120of the second tool component100.

At optional step524, the method may comprise the step of integrally forming the first tool component50as one-piece with the second tool component100. Step524is an alternative step to step520.

FIG. 6is an illustration of a perspective view of an aircraft600that may incorporate one or more composite parts15or structures manufactured using the gradient tool system10of the present disclosure. As shown inFIG. 6, the aircraft600comprises a fuselage612, a nose614, a cockpit616, wings618coupled to the fuselage612, one or more propulsion units620, a tail vertical stabilizer622, and one or more tail horizontal stabilizers624. Although the aircraft600shown inFIG. 6is generally representative of a commercial passenger aircraft, the one or more composite laminate parts, as disclosed herein, may also be employed in other types of aircraft or air vehicles. More specifically, the teachings of the disclosed embodiments may be applied to other passenger aircraft, cargo aircraft, military aircraft, rotorcraft, and other types of aircraft or aerial vehicles, as well as aerospace vehicles, satellites, space launch vehicles, rockets, and other aerospace vehicles. It may also be appreciated that embodiments of tools and methods in accordance with the disclosure may be utilized in other transport vehicles, such as boats and other watercraft, trains, automobiles, trucks, buses, or other suitable transport vehicles formed from or utilizing the composite laminates as disclosed herein.

Embodiments of the disclosure may find use in a variety of potential applications, particularly in the transportation industry, including for example, aerospace, marine, automotive applications and other application where composite structures may be used. Therefore, referring now toFIGS. 7 and 8, embodiments of the disclosure may be used in the context of an aircraft manufacturing and service method630as shown inFIG. 6and the aircraft600as shown inFIG. 7. Aircraft applications of the disclosed embodiments may include, for example, without limitation, the design and fabrication of composite laminates fabricated by way of one or more of the various gradient tools as disclosed herein.

During pre-production, exemplary method630may include specification and design632of the aircraft600and material procurement634. As just one example, for the specification and design of the aircraft related composite laminate parts, the desired engineering characteristics of the gradient tool may be determined at this step. This might include the selection of the materials to be used for the first and second surfaces of the first tool component, along with the materials' desired CTE. This might also include a determination of whether certain compressible areas will be used in the first tool component. Where it is decided that certain compressible areas are to be used, the desired shape, location, and placement of the compressible areas may be determined at this step.

As another example, during this specification and design step, in one particular gradient tool, the type of material for use in the second tool component may be selected. In yet another example, during this specification and design step, the thickness of the first tool component and its various surfaces and materials may be determined. In addition, during this specification and design step, the coefficient of thermal expansion of the various materials to be used for both the first and second tool components may be determined. As just another example, at this design step, the mechanism for coupling the first and second tool component may be determined. At this step, it may also be determined how the first tool component will be manufactured.

During production, component and subassembly manufacturing636, such as the manufacturing of a composite part utilizing the gradient tool as disclosure herein, takes place. During production, system integration638of the aircraft600also takes place. After such a component and subassembly manufacturing step, the aircraft600may go through certification and delivery640in order to be placed in service642. While in service by a customer, the aircraft600is scheduled for routine maintenance and service644, which may also include modification, reconfiguration, refurbishment, and so on.

As shown inFIG. 8, the aircraft600produced by exemplary method630may include an airframe652with a plurality of high-level systems654and an interior656. Examples of high-level systems654may include one or more of a propulsion system658, an electrical system660, a hydraulic system662, and an environmental system664. Any number of other systems may be included. Although an aerospace example is shown, the principles of the disclosure may be applied to other industries, such as the marine and automotive industries.

Tools and methods embodied herein may be employed during any one or more of the stages of the production and service method630. For example, components or subassemblies corresponding to production process may be fabricated or manufactured in a manner similar to components or subassemblies produced while the aircraft600is in service. Also, one or more apparatus embodiments, method embodiments, or a combination thereof may be utilized during the production stages632and634, for example, by substantially expediting assembly of or reducing the cost of an aircraft600. Similarly, one or more of apparatus embodiments, method embodiments, or a combination thereof may be utilized while the aircraft600is in service, for example and without limitation, to maintenance and service644.

Further, the disclosure comprises embodiments according to the following clauses:

Clause 1. A gradient tool for forming a part, the gradient tool comprising:

a first tool component comprising a first surface and a second surface, the first surface comprising a first material having a first coefficient of thermal expansion (CTE), and the second surface comprising a second material having a second CTE,

wherein the first CTE of the first material is different than the second CTE of the second material.

Clause 2: The gradient tool of clause 1, wherein the first CTE of the first material is lower than the second CTE of the second material.

Clause 3: The gradient tool of clause 1, further comprising: a second tool component comprising a first surface, wherein the second tool component is formed from a third material having a third CTE.

Clause 4: The gradient tool of clause 3, wherein the first surface of the second tool component comprises a geometrical surface structure similar to a geometrical surface structure of the first surface of the first tool component.

Clause 5: The gradient tool of clause 3, wherein the third CTE of the third material of the second tool component is substantially equal to the second CTE of the second material of the first tool component.

Clause 6: The gradient tool of clause 3, wherein the first tool component is formed integrally with the second tool component.

Clause 7: The gradient tool of clause 1, wherein the first tool component is coupled to the second tool component such that a second surface of the first tool component is adjacent a first surface of the second tool component.

Clause 8: The gradient tool of clause 7, wherein the first tool component is coupled to the second tool component by adhering, gluing, mechanically interlocking, thermally interlocking, or being held together by gravity.

Clause 9: The gradient tool of clause 1, wherein the first CTE of the first material of the first tool component is substantially equal to a fourth CTE of the part.

Clause 10: The gradient tool of clause 1, wherein the first surface of the first tool component has a geometrical surface structure to match a geometrical surface structure of the part.

Clause 11: The gradient tool of clause 1, wherein the second surface of the first tool component has a geometrical surface structure to match a geometrical surface structure of the part.

Clause 12: The gradient tool of clause 1, wherein the first tool component comprises at least one compressible area defined therein.

Clause 13: The gradient tool of clause 1, wherein at least one of a third material of a second tool component and the second material of the first tool component comprises aluminum.

Clause 14: The gradient tool of clause 1, wherein the third material of the second tool component comprises an aluminum alloy.

Clause 15: The gradient tool of clause 1, wherein the first tool component comprises a non-constant height.

Clause 16: A method of manufacturing a composite part using a gradient tool comprising a first tool component, the method comprising the steps of:

laying up a composite part along a first surface of the first tool component of the gradient tool;

sealing a vacuum bag over the composite part;

drawing a vacuum in the vacuum bag so as to compact the composite part;

heating the composite part to a predetermined temperature;

changing a shape of the first surface of the first tool component at a first rate dependent on a first Coefficient of Thermal Expansion (CTE) of the first surface, and

changing a shape of a second surface of the first tool component at a second rate dependent on a second CTE of the second surface,

the second CTE of the second surface different than the first CTE of the first surface.

Clause 17: The method of clause 16 further comprising the step of: causing thermal stresses within the first tool component based on the different first CTE and second CTE of the first tool component.

Clause 18: The method of clause 16 further comprising the step of: compressing at least one compressible area defined by the first tool component so as to respond to the difference of thermal expansion between the first surface and the second surface of the first tool component.
Clause 19: The method of clause 16 further comprising the step of integrally forming the first tool component as one-piece with the second tool component.
Clause 20: A method of fabricating a gradient tool comprising a first tool component and a second tool component, the method comprising the steps of:

configuring a first surface of a first tool component to interface with a bottom surface of a composite part;

selecting a first material of the first surface of the first tool component, the first material having a first coefficient of thermal expansion (CTE);

configuring a second surface of the first tool component to interface with a second tool component; and

selecting a second material of the second surface of the first tool component wherein the second material has a second coefficient of thermal expansion (CTE),

wherein the second coefficient of thermal expansion (CTE) is different than the first coefficient of thermal expansion of the first material.

Clause 21: The method of clause 20 further comprising the step of: defining a desired tool inner mold line along the first surface of the first tool component.

Clause 22: The method of clause 20 further comprising the step of: selecting the first material of the first surface of the first tool component, such that the first coefficient of thermal expansion (CTE) of the first material is generally equivalent to a coefficient of thermal expansion (CTE) of the composite part that is configured to interface with the first surface of the first tool component.
Clause 23: The method of clause 20 further comprising the step of: selecting the second material of the second surface of the first tool component, such that the second coefficient of thermal expansion (CTE) of the second material is generally equivalent to a coefficient of thermal expansion (CTE) of the second component part.
Clause 24: The method of clause 20 further comprising the step of fabricating the first tool component by sputtering, additive manufacturing, successive electroplating, or machining.
Clause 25: The method of clause 20 further comprising the step of fabricating the second tool component by injection molding, additive manufacturing, or subtractive manufacturing.
Clause 26: The method of clause 20 further comprising the step of: defining at least compressible area within the first tool component.
Clause 27: The method of clause 20 further comprising the step of coupling the first tool component to the second tool component such that the second surface of the first tool component is adjacent the first surface of the second tool component.
Clause 28: The method of clause 20 further comprising the step of integrally forming the first tool component as one-piece with the second tool component.