Patent Description:
Aircraft parts, such as wing components, often comprise composite parts made by a resin infusion process in which a stack of porous material (known as a preform) is filled with a liquid resin. After infusion, the resin matrix is cured to solidify the combined material into a unified rigid composite. The result is a cost-effective way of manufacturing structural materials that exhibit enhanced physical characteristics (e.g., strong, lightweight, resistive to harsh environments, etc.) useful for high-performance applications such as aerospace.

In present resin infusion techniques, a profile of temperature and pressure is set to enable the resin to flow into and fill the preform. After infusion is complete, the profile ramps up the temperature to cure, then cools after cure for demolding the composite part. However, even when adhering closely to the prescribed profile of temperature and pressure, numerous variables can cause the cured thickness of the part to fall outside the strict design tolerances of the part.

The production of a composite part with even a slightly non-conforming thickness is very expensive, as it requires either costly shim or rework procedures to properly fit and assemble the part, or scrap of the part altogether. Current resin infusion techniques produce composite parts with variations in thickness that can lead to high rejection and scrap rate of parts. Therefore, composite part manufacturers seek improvements in producing parts with resin infusion where the final cured thickness consistently meets strict tolerance requirements to mitigate need for shim or rework.

In accordance with its abstract Japanese Patent Application Publication No. <CIT> states: ' PROBLEM TO BE SOLVED: To satisfy both of low working cost and high dimensional accuracy in forming a fiber-reinforced plastic structure having a plurality of regions different in laminate number. SOLUTION: In a process of encapsulating a reinforced fiber fabric cloth laminated in plural sheets on a forming die with a vacuum bag and injecting a liquid resin in the bag inside to cure the resin in a curing control apparatus, thickness sensors <NUM> and <NUM> which can measure a thickness of the reinforced fiber fabric cloth during the resin injection and resin impregnation sensors <NUM> and <NUM> which can quantify a resin impregnation state inside the reinforced fiber fabric cloth are provided as one set on at least two or more portions of regions different in laminate number, and a valve <NUM> is provided which can individually open/close, by remote control, a resin injection channel and a vacuum suction channel communicating respectively to the regions different in laminate number. Confirmation of the measurement value of the thickness sensor and transmission of a control signal based on the confirmation, confirmation of the measurement value of the resin impregnation sensor and transmission of a control signal based on the confirmation, and transmission of switching control signals of all the valves are remote-controlled by a terminal.

The disclosure provides dynamic thickness control of a composite part. Key variables, such as resin viscosity and partial pressure, that are subject to change over the course of infusion, and in the transition period between infusion and cure, may cause an inconsistent per ply thickness and fiber volume fraction across the cured part and between batches of parts manufactured. Accordingly, a network of sensors are positioned around the preform to monitor the thickness of the resin-infused preform during infusion and, optionally, in the transition period between infusion and cure. The sensors generate data for thickness and feedback to a control process. The control process calculates, according to a given material system (e.g., resin and reinforcement) a change in the applied pressure and, optionally, the heat up rate to meet a given thickness. The calculation is based on an empirical body of work that correlates cured part thickness of a given resin and reinforcement to the applied pressure, viscosity, and temperature profile. The applied pressure and temperature are thus varied in-situ during the infusion and, optionally, in the transition period between infusion and cure to ensure that the cured thickness is controlled to fall within a given tolerance range when it is cured.

According to a first aspect there is disclosed a method of fabricating a composite part according to claim <NUM>.

According to a second aspect there is disclosed a composite fabrication system according to claim <NUM>.

Other illustrative examples (e.g., methods and computer-readable media relating to the foregoing examples) may be described below. The features, functions, and advantages that have been discussed can be achieved independently in various examples or may be combined in yet other examples, further details of which can be seen with reference to the following description and drawings.

The present disclosure is now described, by way of example only, and with reference to the accompanying drawings.

The figures and the following description illustrate the disclosure. It will thus be appreciated that those skilled in the art will be able to devise various arrangements that, although not explicitly described or shown herein, fall within the scope of the claims. Furthermore, any examples described herein are intended to aid in understanding the principles of the disclosure, and are to be construed as being without limitation to such specifically recited examples and conditions.

<FIG> is a side view diagram of a composite fabrication system <NUM>. The composite fabrication system <NUM> is configured to manufacture composite structures, such as a composite part of an aircraft. In doing so, the composite fabrication system <NUM> applies heat and pressure to infuse a resin <NUM> into a preform <NUM>. After the resin is infused, the composite fabrication systems <NUM> cures the resin-infused material into a hardened structure, thereby creating the desired composite part.

Generally, the composite fabrication system <NUM> includes a tool mandrel <NUM>, a vacuum bag <NUM>, one or more heat source(s) <NUM>, one or more pressure source(s) <NUM>, a resin supply <NUM>, and a chamber control system <NUM>. The tool mandrel <NUM> (sometimes referred to as a mandrel, mold tool, or forming tool) provides a base or surface which supports the preform <NUM>. The preform <NUM> may include layers or plies of fibers, such as carbon fibers or fiberglass fibers, that are laid-up on the tool mandrel <NUM> and placed under the vacuum bag <NUM>. The vacuum bag <NUM> seals to the tool mandrel <NUM> via sealing members <NUM>, and encloses the preform <NUM> to form a chamber <NUM>.

During infusion, the chamber control system <NUM> controls the heat source(s) <NUM> and the pressure source(s) <NUM> to apply heat and pressure to the chamber <NUM>, thereby causing the resin <NUM> to flow from the resin supply <NUM> and into the preform <NUM> via a resin distribution medium <NUM>. The pressure source(s) <NUM> (e.g., vacuum pump) couple with an inlet fitting <NUM> and/or an outlet fitting <NUM> to create a pressure differential that draws the resin <NUM> from the resin supply <NUM> and into a resin inlet <NUM> of the resin distribution medium <NUM>. The resin distribution medium <NUM> typically includes a channel with resin outlets and/or a permeable membrane to enable the resin <NUM> to flow and distribute into the preform <NUM>. After the preform <NUM> is sufficiently infused with the resin <NUM>, the preform <NUM> may be cured with a curing temperature and/or pressure to form the composite part.

In previous fabrication systems, the infusion and the cure are performed according to a predetermined profile of temperature and pressure. However, even if the predetermined course of temperature and pressure is closely followed, numerous key variables can undesirably affect the final thickness of the composite part. Examples of key variables including a resin viscosity, partial pressure, oven airflow, and tool design. For instance, even if the infusion pressure applied to the resin reservoir is constant, the partial pressure ahead of the resin flow front and within the preform is subject to change over the course of infusion due to the presence of moisture and a rise in temperature. Additionally, the resin viscosity may also change during infusion due to the thermally activated chemical reaction of the resin.

The composite fabrication system <NUM> is therefore enhanced with sensors <NUM> configured to measure a thickness of the preform <NUM> infused with the resin <NUM>. Using data generated by the sensors <NUM>, the chamber control system <NUM> is configured to adapt at least the pressure source(s) <NUM> and, optionally the heat source(s) <NUM> to dynamically adjust the temperature/pressure in the chamber <NUM> prior to completing the cure process of the composite part. This ensures that the thickness of the final composite part meets a given tolerance according to the design specification of the part. The composite fabrication system <NUM> thus provides a technical benefit in reducing or eliminating costly shim or rework procedures as well as fabrication waste resulting from out of tolerance part thickness.

Generally, the sensors <NUM> are positioned around the preform <NUM> to monitor the thickness of the preform <NUM> infused with the resin <NUM>. In the period during infusion and after infusion but before cure, the preform <NUM> infused with the resin <NUM> may be referred to as a composite preform. After cure, the preform <NUM> infused with the resin <NUM> may be referred to as a composite part. The sensors <NUM> can be positioned around the preform <NUM> at locations where part thickness of the composite part is to be verified post cure. That is, the sensors <NUM> may be strategically located to represent the desired thickness and/or target shape of the composite part. The thickness may include a dimension of the part across any direction of the part as desired, and multiple thickness locations may be analyzed.

The sensors <NUM> may include pairs of sensors disposed on either side of the preform <NUM> at various locations where thickness of the final part is to be inspected for tolerance conformance (e.g., three tolerance inspection locations as in <FIG>). The distance between a sensor pair may represent a thickness tolerance or tolerance range designed for the composite part. Alternatively or additionally, one or more sensors <NUM> may include a sensor configured to measure the thickness of the composite preform from one side of the preform <NUM>. The sensors <NUM> may include dielectric sensors, ultrasonic sensors, or other type of sensor suitable for measuring the thickness of the composite preform.

One or more sensors <NUM> may additionally be configured to measure alternative metrics such as temperature, pressure, and/or viscosity of the resin <NUM>. The sensors <NUM> may alternatively or additionally be provided to the tool mandrel <NUM>, resin distribution medium <NUM>, vacuum bag <NUM>, and/or various locations of the chamber <NUM> and preform <NUM>. The sensors <NUM> may be communicatively coupled with the chamber control system <NUM> via one or more wired or wireless connections. Details of operation of the chamber control system <NUM> will be described in greater detail below.

It will be appreciated that the composite fabrication system <NUM> of <FIG> is an example fabrication system provide for discussion purposes, and that examples described herein may apply to numerous resin infusion variations known by various names in the industry. Examples of applicable resin infusion variations include Controlled Atmospheric Pressure Resin Infusion (CAPRI), Resin Transfer Infusion (RTI), Resin Transfer Molding (RTM), Resin Injection Molding (RIM), Vacuum-assisted Resin Transfer Molding (VaRTM), and Vacuum Infusion Process (VIP). Accordingly, additional or alternative components of the composite fabrication system <NUM> are possible, including alternative resin reservoir storage and delivery mechanisms, alternate pressure source connections and locations, alternative heat source components (e.g., oven, integral, or induction heating) and locations, etc..

Additionally, the composite fabrication system <NUM> may include various consumable items not shown for ease of illustration, such as a peel ply, vacuum lines, breathers, etc., that may be removed and disposed after demold. Additional and alternative types and locations of resin distribution lines, vacuum bags, sealing members etc., are also possible. Though <FIG> illustrates simple shapes for ease of illustration, the preform <NUM> and resulting composite part may include complex shapes with variations of thickness across dimensions of the structure. For instance, the composite fabrication system <NUM> may include a caul plate and/or the tool mandrel <NUM> may comprise a mandrel with an inner mold line to ensure that the surfaces of the composite preform form a smooth aerodynamic surface and maintain a desired contour or shape. As such, the rate of distribution of the resin <NUM> into the preform <NUM> may be non-uniform and partially dependent upon different thicknesses across preform <NUM>.

The preform <NUM> may generally comprise laminates of fibers (e.g., tape, woven and/or braided fibers) that are stacked in the desired orientations, cut and formed into the desired shape, and debulked. The preform <NUM> may include dry fiber materials, binderized fiber materials, or some combination thereof. The preform <NUM> may also incorporate additional materials such as metals, foams, adhesives, prepregs, sensors, and other specialty materials. Moreover, the preform <NUM> may include interlayers, or veils, of a thermoplastic (e.g., polyamide) that soften or melt as the temperature of the infused preform rises. This change in the physical state of the interlayer architecture may alter the thickness of the veil and thus lead to a change in the cured per ply thickness of the laminate to affect the cured part thickness.

The resin <NUM> may include any liquid resin, such as a thermoset or thermoplastic resin, that solidifies in order to harden into a composite part (e.g., for use in an aircraft). For thermoset resins, the hardening is a one-way process referred to as curing, while for thermoplastic resins, the resin may return to liquid form if it is re-heated. Thus, the resin <NUM> may be a polyimide, an epoxy, a thermoplastic resin, or any other resin suitable for making composite parts. Illustrative details of the operation of the composite fabrication system <NUM> will be discussed with regard to <FIG>.

<FIG> is a flowchart illustrating a method <NUM> for fabricating a composite part via resin infusion with dynamic thickness control. The steps of the method <NUM> are described with reference to the composite fabrication system <NUM> of <FIG>, but those skilled in the art will appreciate that the method <NUM> may be performed in other systems as desired. The steps of the flowcharts described herein are not all inclusive, may include other steps not shown, and may be performed in an alternative order.

In step <NUM>, the preform <NUM> is provided to the tool mandrel <NUM>. In step <NUM>, the sensors <NUM> are positioned according to a target shape of the composite part. In step <NUM>, the preform <NUM> is sealed with the vacuum bag <NUM> to form the chamber <NUM>. In step <NUM>, temperature and pressure are applied to the chamber <NUM> to infuse the resin <NUM> into the preform <NUM> to create a composite preform undergoing infusion.

In step <NUM>, a thickness of the composite preform is monitored prior to cure. That is, the sensors <NUM> generate data of the thickness of the composite preform during infusion, and, optionally, during the transition period between infusion and cure, and/or during the cure cycle and prior to completing cure of the composite preform. The timing of the infusion, transition period, and cure is described in greater detail below. The sensors <NUM> may provide real-time feedback of the thickness of the composite preform to the chamber control system <NUM>.

In step <NUM>, the chamber control system <NUM> adjusts at least the pressure during the infusion of the resin and, optionally, the temperature prior to completing cure based on the thickness information provided by the sensors <NUM>. The pressure and, optionally the temperature, are thus dynamically controlled in-situ by monitoring the thickness of the composite preform during the infusion of the resin and prior to completing cure and adjusting the pressure and, optionally, the temperature as necessary during infusion of the resin and prior to completing cure. The method <NUM> therefore provides a substantial benefit over prior techniques by actively controlling the thickness to fall within a given tolerance range regardless of any number of uncontrolled variables that may occur which affect the final cured thickness of the composite part. Further details related to calculation of the adjusted pressure and temperature is described in greater detail below.

<FIG> illustrates a profile <NUM> of temperature <NUM> and pressure <NUM>/<NUM> to apply over time for the infusion and cure of a composite part. The chamber control system <NUM> is configured to direct the heat source(s) <NUM> and pressure source(s) <NUM> to apply the temperature <NUM>, inlet pressure <NUM>, and outlet pressure <NUM> of the profile <NUM> to control the infusion and cure as a function of time. In particular, the chamber control system <NUM> controls: (i) the infusion temperature, Ti, from time t<NUM> to t<NUM>, (ii) the cure temperature, Tc, from time t<NUM> to t<NUM>, (iii) the temperature heat-up rate between Ti and Tc in the transition period between infusion and cure from t<NUM> to t<NUM>, (iv) the temperature cool-down rate between Tc and the demold temperature, Td, from time t<NUM> to t<NUM>, (v) the area under the curve from time t<NUM> to t<NUM>, and (vi) the inlet pressure <NUM> from time t<NUM> to t<NUM>.

During infusion from t<NUM> to t<NUM>, the pressure <NUM>/<NUM> applied by the pressure sources <NUM> draws the resin <NUM> from the reservoir (e.g., resin supply <NUM>) and into the preform <NUM> via the resin distribution medium <NUM>. During this process, resin is prevented from overfilling the preform <NUM> due to pressure from the vacuum bag <NUM>. As the infusion progresses, the infusion rate gradually slows due to increased drag and decreased pressure as fluid wets the preform <NUM>. That is, as described earlier, even if the infusion pressure applied to the resin reservoir is constant, the partial pressure ahead of the resin flow front and within the preform <NUM> is subject to change over the course of infusion due to the presence of moisture and rise in temperature. Additionally, the resin viscosity may also change during infusion due to the thermally activated chemical reaction of the resin <NUM>.

Accordingly, even if the process parameters (i)-(vi) described above are determined in advance for producing a composite part to a given specification, key variables such as physical characteristics of the resin <NUM> and physical characteristics of the interlayers of the preform <NUM> may nonetheless affect the thickness of the cured composite part. Therefore, during the infusion of the resin and prior to completing cure of the part at time t<NUM>, the chamber control system <NUM> adjusts pressure <NUM>/<NUM> and may adjust the temperature <NUM> of the profile <NUM> to compensate for the uncontrolled variables and bring the part back into thickness tolerance before it is cured. As described in further detail below, the chamber control system <NUM>, may dynamically control thickness in the transition period (e.g., from time t<NUM> to t<NUM>) after infusion is complete but before cure begins.

<FIG> is a block diagram of a chamber control system <NUM>. The chamber control system <NUM> is configured to receive thickness data <NUM> from the sensors <NUM>, and to calculate adjusted pressure values <NUM> and, optionally, adjusted temperature values <NUM> to apply with the heat source(s) <NUM> and/or pressure source(s) <NUM>, respectively. In particular, the chamber control system <NUM> is configured to calculate the adjustments by referencing empirical models <NUM> of prior fabrications of composite parts. By collecting the thickness data <NUM> and processing it with respect to the empirical models <NUM> in real time, the chamber control system <NUM> is advantageously enabled to detect that an out of thickness tolerance may be present or possible, and to bring the part back into tolerance before it is cured to a final thickness.

The chamber control system <NUM> may comprise hardware, software, or a combination of hardware and software. For example, the chamber control system <NUM> may include a processor <NUM>, which includes any electronic circuits and/or optical circuits that are able to perform functions. The processor <NUM> may include one or more Central Processing Units (CPU), microprocessors, Digital Signal Processors (DSPs), Application-Specific Integrated Circuits (ASICs), Programmable Logic Devices (PLD), control circuitry, etc. Some examples of processors include Intel® Core ™ processors, Advanced Reduced Instruction Set Computing (RISC) Machines (ARM®) processors, etc. The chamber control system <NUM> may also include memory <NUM> which may include any electronic circuits, optical circuits, and/or magnetic circuits that are able to store data. The chamber control system <NUM> may further include an interface <NUM> to send or receive data, and a graphical user interface <NUM> to display information and receive user input.

<FIG> is a flowchart illustrating a method <NUM> for fabricating a composite part via resin infusion with dynamic thickness control in another example, not falling within the scope of the claims. The steps of the method <NUM> are described with reference to the composite fabrication system <NUM> of <FIG>, the profile <NUM> of <FIG>, and the chamber control system <NUM>/<NUM> of <FIG> and <FIG>, but those skilled in the art will appreciate that the method <NUM> may be performed in other systems and with alternative profiles as desired. Assume, for this example, that sensors <NUM> have been positioned with respect to the preform <NUM> as desired, and that the chamber control system <NUM> has received the appropriate temperature/pressure profile to apply, and desired thickness tolerances for locations of the composite part. Further assume for this example that the infusion process has been initiated according to the profile <NUM> for producing the composite part.

In step <NUM>, the chamber control system <NUM> detects that the preform <NUM> is completely infused with the resin <NUM>. In step <NUM>, the chamber control system <NUM> monitors (e.g., via sensors <NUM>) the thickness of the composite preform during the transition period between infusion and cure. Thus, after infusion, the chamber control system <NUM> may initiate processing of the thickness data <NUM> received by the sensors <NUM> in real time.

In step <NUM>, the chamber control system <NUM> analyzes the thickness of the composite preform with respect to historical data of prior composite part fabrications. That is, the chamber control systems <NUM> may employ the empirical models <NUM> in processing the current thickness of the composite preform. The empirical models <NUM> may include historical data that correlates key physical characteristics or variables of prior composite preform characteristics with resulting cured thicknesses of prior composite part fabrications. An example of a physical characteristic of a composite preform is a specific viscosity of the resin <NUM> as a function of temperature. For example, the age of the resin <NUM>, production source of the resin <NUM>, and/or how the resin <NUM> has been mixed (mixture process) may contribute to the specific viscosity of the resin <NUM>. Therefore, the chamber control system <NUM> may be configured to process the current thickness as a function of the physical characteristics of the resin <NUM> infused into the preform <NUM> with respect to prior physical characteristics of prior infused resins and corresponding prior thickness results. The chamber control system <NUM> can be configured to process the measured thickness as a function of the physical characteristics of the interlayer (e.g., softening temperature of the interlayer and/or permeability of the preform <NUM>) in comparison to the physical characteristics of the prior thickness results and corresponding physical characteristics of prior preform interlayer characteristics.

Alternatively or additionally, empirical models <NUM> may include historical data that correlates fabrication process parameters and a cured thickness of the prior composite part fabrications. For example, sensors (e.g., sensors <NUM>) may provide measurement values to a controller (e.g., chamber control system <NUM>) including one or more of the thickness, a measured temperature of the chamber, a measured pressure of the chamber, a measured viscosity of the resin in the composite preform, and a time. Thus, the chamber control system <NUM> may process fabrication parameters in comparison to the parameters of prior fabrications, including comparisons of thickness, pressure, and temperature with respect to time. Thus, in some examples, the chamber control system <NUM> may calculate the adjusted values for at least one of the temperature and the pressure to apply prior to completing the curing based on the measurement values and a correlation in the historical data between prior measurement values (e.g., previously recorded and stored in empirical models <NUM>) and a cured thickness of the prior composite part fabrications.

In step <NUM>, the chamber control system <NUM> predicts a cured thickness of the preform based on the analyzing of the thickness with respect to the historical data. In doing so, the chamber control system <NUM> may detect that an out of tolerance thickness is possible based on the calculations of a predicted thickness of the composite part. In some examples the chamber control system <NUM> may generate a notification of possible out of tolerance thickness. For example, the chamber control system <NUM> may raise triggers, flags, and/or a display on the graphical user interface <NUM> that an out of thickness tolerance may be present or possible.

Then, in step <NUM>, the chamber control system <NUM> adjusts the profile of temperature and pressure during the transition period based on the predicted cured thickness of the preform. Thus, the chamber control system <NUM> may correct the thickness back into tolerance prior to cure completion. In other words, the chamber control system <NUM> is configured to control the thickness with the adjusting to produce the composite part as a cured part having a predetermined cross-sectional part thickness. Advantageously, using the method <NUM>, the profile of temperature and pressure is adjusted during the transition period between infusion and cure to correct the thickness back into tolerance prior to cure.

Claim 1:
A method (<NUM>) of fabricating a composite part, the method (<NUM>, <NUM>) comprising:
providing a preform (<NUM>) on a tool mandrel (<NUM>);
positioning sensors (<NUM>) around the preform (<NUM>) according to a target shape of the composite part;
sealing the preform (<NUM>) with a vacuum bag (<NUM>) to form a chamber (<NUM>);
applying heat and pressure to the chamber (<NUM>) to infuse a resin (<NUM>) into the preform (<NUM>) to create a composite preform (<NUM>) undergoing infusion;
using the sensors, monitoring a thickness of the composite preform (<NUM>) prior to completing cure of the composite preform (<NUM>);
analyzing the thickness of the composite preform (<NUM>) with respect to historical data of prior composite part fabrications;
calculating adjusted values for the pressure to apply prior to completing cure based on the thickness of the composite preform (<NUM>) and the historical data;
calculating the adjusted values based on a correlation in the historical data between physical characteristics of composite preforms (<NUM>) and a cured thickness of the prior composite part fabrications; and
adjusting the pressure during the infusion of the resin and prior to completing cure of the composite preform (<NUM>) based on the adjusted values.