System and method of detecting a missing tow in a composite layup

A system for detecting a missing tow in a tow band may include a fiber placement head for applying a tow band to a substrate forming a composite layup. The system may further include a heating device for preheating the substrate prior to application of the tow band. The system may additionally include an infrared camera mounted to the fiber placement head and configured to generate a real-time thermal image of the composite layup during the application of the tow band to the substrate.

FIELD

The present disclosure relates generally to composites manufacturing and, more particularly, to a system and method for detecting a missing tow in a composite layup.

BACKGROUND

Composite structures may be fabricated using automated fiber placement machines to apply continuous strips or bands of tows of pre-impregnated fibers onto a tool or mandrel to form a composite layup having a plurality of plies. Each tow may be comprised of several tow segments that may be spliced end-to-end using resin. The tows may be drawn from a plurality of tow spools that may be mounted on a fiber placement head. The fiber placement head may include a tow collimator for aligning the plurality of tows into side-by-side arrangement with one another to form a tow band. From the tow collimator, the tow band may be fed to an application device of the fiber placement head where the tow may be pressed onto the tool or mandrel as the fiber placement head moves along the tool following the contour of the tool surface.

Occasionally, during the process of applying a tow band to a tool surface, a tow may be missing from the tow band such as due to a misfeed of a tow though the collimator or through other components of the fiber placement head. A tow may also be missing due to a break in a splice of the tow. In addition, a tow may be missing due to the tow falling off of the tool surface after the tow is applied to the tool due to insufficient tack between the tow and tool surface or substrate.

Conventional methods of detecting missing tows include visual inspection of the composite layup for the presence of depressions in the layup surface which may be indicative of a missing tow. Unfortunately, detection of a depression in the layup surface may be difficult due to the relatively small thickness (e.g., 0.008 inch) and relatively small width (e.g., 0.125 inch) of each tow. In addition, the difficulty in detecting a depression in the layup surface by visual inspection with the human eye may be compounded when the composite layup is comprised of overlapping plies having tows with the same fiber orientation resulting in minimal contrast due to the black color of the tow. Tactile inspection of the layup surface may be impractical for the relatively large amount of surface area associated with certain composite structures. In addition, tactile inspection may not yield the desired results.

A further drawback associated with conventional methods for detecting missing tows is that the fiber placement machine may continue to apply composite material with a missing tow in a tow band. For example, multiple plies of composite material may be laid over an area with a missing tow before the missing tow is detected and the fiber placement machine is stopped. In order to rework the area of the composite layup with the missing tow, the general area of the missing tow may be generally identified. However, rework of the composite layup may require the removal and replacement of material in a labor-intensive process and time-consuming process at significant cost. Furthermore, because the area of the missing tow(s) is only generally known, large amounts of material may require removal before reaching the exact location of the missing tow.

As can be seen, there exists a need in the art for a system and method for detecting a missing tow in a composite layup with improved accuracy. In addition, there exists a need in the art for a system and method for detecting a missing tow in a composite layup wherein the exact location of the missing tow may be identified prior to minimize the amount of composite material that is removed during the rework process.

SUMMARY

The above-noted needs associated with detection of missing tow are specifically addressed and alleviated by the present disclosure which provides a system for detecting a missing tow in a tow band. The system may include a fiber placement head for applying a tow band to a substrate forming a composite layup. The system may further include a heating device for preheating the substrate prior to application of the tow band. The system may additionally include an infrared camera mounted to the fiber placement head and configured to generate a real-time thermal image of the composite layup during the application of the tow band to the substrate.

In a further embodiment, disclosed is a system for detecting a missing tow in a tow band. The system may include a fiber placement head configured to apply a tow band to a substrate forming a composite layup. The system may further include an infrared heater positioned in front of a compaction roller and being configured to preheat the substrate prior to application of the tow band using the compaction roller. In addition, the system may include an infrared camera mounted to the fiber placement head and configured to generate a real-time thermal image of the composite layup during the application of the tow band to the substrate. The system may also include a display device coupled to the infrared camera for displaying the real-time thermal image of the composite layup.

Also disclosed is a method of detecting a missing tow in a composite layup. The method may include preheating a substrate prior to applying a tow band on the substrate, and applying the tow band to the substrate to form a composite layup. The method may additionally include generating a real-time thermal image of the composite layup while the tow band is being applied to the substrate, and determining whether a tow is missing based upon the real-time thermal image.

DETAILED DESCRIPTION

Referring now to the drawings wherein the showings are for purposes of illustrating various embodiments of the present disclosure, shown inFIG. 1is a perspective view of a tow detection system100for detecting a missing tow194(FIG. 4) in a tow band160. The tow detection system100may be implemented in an automated fiber placement machine150for applying a prepreg tow band160or prepreg composite tape onto a substrate166to form a composite layup164for a composite part. The substrate166may comprise a tool surface of a stationary tool168or a rotating mandrel (not shown), or the substrate166may comprise courses162of previously laid tow bands160. The automated fiber placement machine150may include one or more fiber placement heads152for applying the tows154onto the substrate166.

Referring toFIG. 1, as indicated above, each one of the tow bands160may be comprised of a plurality of individual tows154. Each one of the tows154may be formed as a bundle of resin-coated reinforcement fibers. Each tow154may be provided in a relatively small width or diameter such as in the range of from approximately 0.12 to 0.50 inch although larger widths are possible. The tows154may be dispensed from one or more spools (not shown) and threaded through a tow collimator153for alignment of the tows154into a tow band160as shown.

The tow band160may pass between a pair of tow restart rollers170for controlling the stop-and-start movement of the tow band160in accordance with a preprogrammed sequence for applying courses162onto the substrate166. The courses162may be applied in parallel arrangement to one another as illustrated inFIG. 1. The tow band160may also pass through a tow cutter and clamp mechanism172which may be configured to cut the tow154at the end of each course162. A new end of a tow band160may be pushed by the restart rollers toward a compaction roller156. The compaction roller156may apply the tow band160to the substrate166. The compaction roller156may also apply compaction pressure to the tow band160to press the tow band160onto the substrate166as the compaction roller156moves along the surface of the tool168.

InFIG. 1, the fiber placement head152may include a heating device174for elevating the temperature of the substrate166. The heating device174may be positioned in front of the location where the tow band160initially contacts the substrate166. In this regard, the heating device174may be positioned in front of the compaction roller156wherein the tow band160is compacted against the substrate166. The front of the roller may be defined relative to a direction of forward motion of the fiber placement head152.

The heating device174may be configured to preheat the substrate166surface prior to the tow band160contacting the substrate166. The heat in the substrate166may increase the tack or adhesion between the tow band160and the substrate166. By increasing the tack in the tow band160, the individual tows154may be maintained in position on the substrate166during the process of laying up a composite part. The heating device174may be provided as a radiative heater176such as an infrared heater178for heating the substrate166and/or for preheating the tow band160prior to contact of the tow band160with the substrate166. However, the heating device174may be provided in alternative configurations such as a forced hot air heater180.

Referring toFIGS. 1-2, the automated fiber placement machine150may include an infrared camera182. The infrared camera182may be mounted to the fiber placement head152and may be configured to generate a real-time thermal image188of the composite layup164during the application of the tow band160to the substrate166. In an embodiment, the infrared camera182may be configured to record a real-time thermal image188of the composite layup164as the fiber placement head152moves along the tool168. In this regard, the infrared camera182may be positioned behind a location where the tow band160is compacted against the substrate166. For embodiments of the fiber placement head152having a compaction roller156, the infrared camera182may be positioned behind the compaction roller156relative to a direction of forward motion of the fiber placement head152.

InFIG. 2, the infrared camera182may be configured to capture a field of view (not shown) of the composite layup164in the area where the tow band160has been placed by the compaction roller156. In this manner, the infrared camera182may record an image of the tow band160as may be heated in response to heating of the substrate166by the infrared heater178. In this regard, the infrared heater178may heat tow bands160that have been previously applied to the tool168surface. The field of view of the infrared camera182preferably captures at least a width of a tow band160. For example, the infrared camera182may have a field of view that may capture a substantial majority of a tow band160having 32 tows wherein each one of the tows154has a tow154width of approximately one-half inch or more making for a total tow band160width of approximately 8 inches. However, the infrared camera182may have a field of view that may capture a tow band width of any size.

The infrared camera182may be communicatively coupled to a display device110as shown inFIG. 2for displaying a real-time thermal image188of the tow band160as the fiber placement head152moves along the tool168. With a relatively large display device110such as a monitor having a diagonal dimension of 14 inches, a tow band width of approximately eight (8) inches may be magnified by at least approximately 50 percent which would result in the thermal image of a missing tow194being displayed on the display device110at a width of approximately 0.75 inch. The display device110may be configured for viewing by an operator of the fiber placement machine150. With a relatively high resolution infrared camera182and with magnification of the real-time thermal image188, detection of a missing tow194within a tow band160such as by visual inspection (e.g., by the human eye) of the real-time thermal image188may reveal a localized difference192in the heat signature190of the area of the missing tow194relative to the remainder of the tow band160. In this regard, the tow detection system100disclosed herein represents a significant improvement relative to conventional methods for detecting missing tows194.

InFIG. 2, in an embodiment, the infrared camera182may be communicatively coupled to a processor102(e.g., a computer) to which the display device110may also be coupled. The processor102may include a user interface108such as a keyboard, a graphical user interface, or other device allowing an operator to interface with the processor102and/or to control the infrared camera182such as for changing a zoom or a field of view of the camera during operation of the automated fiber placement machine150. In an embodiment, the infrared camera182may also be configured to autonomously operate on a continuous, intermittent, or periodic basis during the application of tows154to the substrate166.

In a further embodiment, the user interface108may facilitate manual control of the infrared camera182by an operator. For example, the user interface108may facilitate manipulation or control of the inferred camera such as to start and stop the recording of the real-time thermal image188of the composite layup164at any point during the application of tow bands160to the substrate166. The processor102may also be configured to facilitate manual override of a preprogrammed tow application sequence of the automated fiber placement machine150. For example, upon the detection of a missing tow194by visual observation of the real-time thermal image188of the composite layup164on the display device110, an operator may suspend or temporarily halt the operation of the fiber placement machine150to allow for the disposition of the missing tow154.

The processor102may include the display device110for displaying one or more thermal images of a composite layup164to allow an operator to visually observe the real-time thermal images188(e.g., video) recorded by the infrared camera182such as during operation of the automated fiber placement machine150. The processor102may additionally include a comparator104which may be configured to determine whether a tow154is missing from the tow band160by comparing a heat signature190of the composite layup164in a real-time thermal image188(FIG. 4) to the heat signature190of a composite layup164in a baseline thermal image186(FIG. 3) as described below.

Referring toFIGS. 3-4, shown inFIG. 3is a baseline thermal image186of a composite layup164. Shown inFIG. 4is a real-time thermal image188of a composite layup164as may be recorded by an infrared camera182mounted behind a compaction roller156of a fiber placement head152. InFIG. 3, the composite layup164in the baseline thermal image186may have the same configuration as the composite layup164being formed on the tool168by the fiber placement head152and represented by the real-time thermal image188ofFIG. 4. In an embodiment, the baseline thermal image186may represent a composite layup164comprised of at least one tow band160including tows154having the same size, shape, and material configuration and arranged in the same manner (e.g., side-by-side) as at least one tow band160in the composite layup164represented in the real-time thermal image188.

InFIGS. 3-4, the comparator104may be configured to determine whether a tow154is missing from a tow band160by comparing a heat signature190of the composite layup164in the real-time thermal image188to the heat signature190of a composite layup164of the baseline thermal image186. For example, the composite layup164represented in the real-time thermal image188inFIG. 4may include a missing tow. In the real-time thermal image188, the missing tow194may be represented as a localized difference192in the heat signature190in the area of the missing tow194relative to the heat signature190of the remainder of the same tow band160. The difference in the heat signature190in the area of the missing tow194may occur as a result of a greater amount of heat from underlying substrate166(e.g., tool168surface or previously-applied tow) radiating upwardly through the gap in the tow band160due to the missing tow194, relative to the amount of heat radiated upwardly through the tows154on opposite sides (i.e., lengthwise edges) of the missing tow194.

For example, in a baseline thermal image186of a composite layup164, each one of the tow bands160may have a generally uniform color or shade (e g, uniformly black) which may represent substantially uniform heat radiation upwardly through the tow bands160from the underlying substrate166. In a real-time thermal image188of the composite layup164, a tow band160having a missing tow194may have a non-uniform color or shade. More specifically, the region of a missing tow194may appear lighter in color or shade such as gray shade relative to the remaining portions of the tow band160which may appear uniformly black in the real-time thermal image188recorded by the infrared camera182.

FIG. 4illustrates a localized difference192in the heat signature190of the tow band160in the area of the missing tows194. Each missing tow194has a missing tow length198, and a missing tow width196. The missing tow width196is equivalent to the width of the remaining tows154of the tow band160. As indicated above, with a resolution of currently-available infrared cameras182, the missing tow194may be detectable in the real-time thermal image188by visual observation with the human eye due to the localized difference192in the heat signature190as indicated above. Manual detection by the human line may also be facilitated by magnification of the real-time thermal image188recorded by the infrared camera182as mentioned above.

InFIG. 4, the processor102may be configured to identify a location and/or position of a missing tow194such as by reference to a reference point204of the composite layup164. For example, the reference point204may comprise a predetermined longitudinal and/or lateral location of a reference coordinate system208100associated with a tow laydown program106. The tow laydown program106may comprise a computer program such as a numerical control (NC) program having computer-readable instructions for controlling the operation of the automated fiber placement machine150for applying courses162of tow band160to a substrate166. In an embodiment, the tow laydown program106may comprise a NC program for operation of the fiber placement head152. The processor102may be configured to identify a location of the opposite ends of the missing tow194with regard to the reference point204associated with the NC program. In an embodiment, the reference point204may comprise a structural feature206that may be associated with the composite layup164. For example, in a composite layup164over a mandrel for generating a skin panel of a barrel section of a fuselage, the location of a missing tow194in the composite layup164may be identified relative to a stringer or a frame station over which the skin panel may be applied. In this regard, the processor102may be configured to index the location of a missing tow194relative to a tow laydown program106.

Referring toFIG. 5, shown is a side sectional view of the composite layup164illustrating a missing tow band160ofFIG. 4and wherein the missing tow band160is positioned at a ply depth212within the composite layup164. In an embodiment, the infrared camera182may be configured to record a time stamp202(FIG. 2) with a real-time thermal image188recorded by the infrared camera182. In this regard, the infrared camera182may be configured to continuously record the time during the recording of real-time thermal images188of the composite layup164. In an embodiment, the time stamp202may be displayed on the display device110along with the real-time thermal image188of the composite layup164. When a missing tow194is detected, the processor102may be configured to correlate the time stamp202to a ply depth212. In an embodiment, the ply depth212may be defined with regard to the location of the ply below the surface of a ply stack214. The ply stack214may be defined by a stacking sequence200associated with an NC program for controlling the fiber placement head152.

In the event that a depression caused by a missing tow194is detected in the composite layup164surface at a later point during the layup process, a video of a recording of the real-time thermal images188can be reviewed to determine the point in time (i.e., the time stamp202) during the layup sequence when the tow194became missing. The time stamp202(FIG. 2) can be correlated to the ply position in the stacking sequence200associated with an NC program. Rework may be performed by adding an overlay of tows154onto the composite layup164surface in the area of the missing tow194without removing existing ply material and performing an interlaminar repair.

As indicated earlier, the processor102may be configured to identify a longitudinal position (not show) and/or a lateral position (e.g., a course location210—FIG. 4) of the missing tow194in the composite layup164corresponding to the ply depth212of the missing tow194. For example, during the lay-up of a barrel section of a fuselage, a time stamp202on a real-time thermal image188of a missing tow194may indicate a ply sequence216and a position of the missing tow194on the barrel section. In this manner, the processor102provides a means for accurately identify the location of a missing tow and which may reduce the amount of rework on a composite layup164relative to the amount of rework required using conventional method for detecting missing tows. As indicated above, such rework may require removal of one or more of the composite plies overlaying the region of the missing tow194, and replacing the plies with a composite patch to bring the area of the missing tow194to within design tolerances.

Referring toFIG. 6, shown is a block diagram of a tow detection system100for detecting missing tows194in a composite layup164such as on an automated fiber placement machine150. InFIG. 6, the automated fiber placement machine150may include the infrared camera182as indicated above for recording real-time thermal images188of a tow band160applied to a substrate166by the fiber placement head152. The automated fiber placement machine150may be controlled by a tow laydown program106stored on a storage device (not shown) and communicatively coupled to the processor102for controlling the operation of the fiber placement head152. The processor102may include a comparator104for comparing the real-time thermal image188of the composite layup164to a baseline thermal image186of the composite layup164as described above. The real-time thermal image188may be displayed on a display device110along with an optional time stamp202as shown inFIG. 2. The processor102may include a user interface108for controlling the operation of the infrared camera and/or the operation of the fiber placement machine150.

Referring toFIG. 7, shown is a flow diagram illustrating one or more operations that may be included in an embodiment of a method300of detecting a missing tow194in a tow band160. The method may also be implemented for detecting a missing tape in a tape laying operation.

Step302of the method300ofFIG. 7may include comprising preheating a substrate166at a location in front of a point158where the tow154is applied to the substrate166. For example, the preheating may occur and the location directly in front of a compaction roller156of a fiber placement head152. Step302may include preheating the substrate166using a radiative heater176such as an infrared heater178for heating the resin. The method may include preheating the substrate166prior to applying a tow band160of a composite layup164on the substrate166to improve the tack of the tow band160. The substrate166may comprise the surface of a tool168or the substrate166may comprise previously-applied tow bands160.

Step304of the method300ofFIG. 7may include applying the tow band160to the substrate166. In this regard, the method may include applying the tow band160using a fiber placement head152. For example, the tow band160may be applied to the substrate166by pressing or compacting the tow band160against the substrate166with a compaction roller156as shown inFIG. 2. In this regard, the compaction roller156may facilitate partial consolidation of the composite layup164.

Step306of the method300ofFIG. 7may include generating a real-time thermal image188of the composite layup164while the tow band160is being applied to the substrate166. In an embodiment, the method may include generating the real-time thermal image188using an infrared camera182. In this regard, the method may include positioning an infrared camera182behind a point158where the tow154is applied to the substrate166. For example, Step306may include positioning an infrared camera182behind a compaction roller156of a fiber placement head152relative to a direction of head movement184. The method may include generating the real-time thermal image188while moving the fiber placement head152along a direction of head movement184. The infrared camera182may be configured to record or generate real-time thermal images188on a continuous basis or on an intermittent or manually-commanded basis as mentioned above.

In an embodiment, the method may include displaying the real-time thermal image188on a display device110coupled to the infrared camera182. The method may include visually inspecting with the human eye (i.e., manually inspecting), the real-time thermal image188of the composite layup164for a localized difference192in the heat signature190within a tow band160which may be representative of a missing tow194as mentioned above with regard toFIG. 4.

Step308of the method300ofFIG. 7may include comparing the real-time thermal image188to a baseline thermal image186of the composite layup164. For example, the method may include the use of a comparator104which may form part of a processor102of a computer-based system100. The comparator104may perform a comparative analysis of the real-time thermal image188of the composite layup164relative to a baseline thermal image186of the composite layup164. In this regard, the method may include automated inspection of the real-time thermal image188of the composite layup164for a localized difference192in the heat signature190of the composite layup164relative to the heat signature190of a composite layup164in a baseline thermal image186.

Step310of the method300ofFIG. 7may include determining whether a tow154is missing from the tow band160based upon comparing the real-time thermal image188to the baseline thermal image186. The method may further include determining whether one or more of the tow bands160in the composite layup164have a substantially uniform heat signature190in the real-time thermal image188. A non-uniform heat signature190in the real-time thermal image188may be representative of a missing tow194.

In a further embodiment, the method may include indexing a location of a missing tow194relative to a tow laydown program106. For example, the method may include recording a time stamp202when a missing tow194is detected, and correlating the time stamp202to a position of the missing tow194in the composite layup164. For example, the time stamp202may be correlated to a ply depth212of the missing tow194in the stacking sequence200and a lateral or longitudinal position of the missing tow194as mentioned above.

Advantageously, the system and method disclosed herein provides a means for detecting a missing tow194in a composite layup164immediately after the application of the tow band160to the substrate166which may minimize the amount of composite material that may be applied with a missing tow194. In this regard, the system and method disclosed herein may provide the option for automatically or manually suspending the operation of the fiber placement head152pending the disposition and possible rework as a result of the missing tow194. Furthermore, the system and method disclosed herein provides a means for accurately identifying the location of a missing tow194in a composite layup164which may minimize the amount of rework that may otherwise be required.

Additional modifications and improvements of the present disclosure may be apparent to those of ordinary skill in the art. Thus, the particular combination of parts described and illustrated herein is intended to represent only certain embodiments of the present disclosure and is not intended to serve as limitations of alternative embodiments or devices within the spirit and scope of the disclosure.