BACKGROUND

Composites including plies of reinforcing fibers embedded in a matrix are highly desirable for their light weight and high strength. One example of a composite is carbon fiber reinforced plastic (CFRP), where the constituents include carbon fibers embedded in an epoxy matrix.

Layup machines may be used to fabricate complex composite structures, such as aircraft wings and fuselages. These layup machines deposit reinforcing fibers on tool surfaces of layup mandrel tools. The fibers may be pre-impregnated with resin upon deposition ("prepregs"), or they may be dry and subsequently infused with resin.

Different types of layup system may have different configurations. For instance, some systems may include dedicated machines with dedicated end effectors for tape laydown or automated fiber placement (AFP), while other systems may include machines that incorporate interchangeable heads for either tape laydown or AFP. Tape laydown is typically performed by an end effector, which applies a single "tape" between three to twelve inches wide. Fiber placement is typically performed with an end effector having four to thirty two tow paths. The end effector lays down material typically between one-eighth to one -half inches wide. For instance, a thirty two tow machine may have an effective laydown width of sixteen inches.

There may even be different configurations of the same type of laydown machine. For instance, AFP machines may have different numbers of tows, different tow widths, and different compaction roller lengths.

Typically prior to fabrication of a composite part, a machine configuration is selected. Then, that configuration is used to form an initial layup of the composite part. In some instances, that configuration produces an initial layup having puckers or wrinkles. In other instances, that configuration cannot even form an initial layup. Consequently, a new machine configuration is determined, and a new layup is formed. Multiple iterations of redesigning, refabricating and revalidating the layup are performed. Performing the multiple iterations is costly in time and money. It would be desirable to reduce the cost. SUMMARY

According to embodiment herein, a method comprises using a computer to access an engineering definition of a composite part and apply a set of rules governing material laydown to determine a machine configuration for laying up the part. The method may further comprise applying the rules involves performing a trade between different slit tape placement processes wherein the rules may optionally be applied to determine machine configurations that satisfy at least one of design requirements, producibility requirements, and manufacturing flow time target at different tape widths. The method may further comprise applying the rules to determine allowable tape type for the part or to determine different tape widths for different plies of the part or determine different tape widths for different portions of the part. The method may optionally include that at least some of the rules determine penalties for structural performance as a function of a specific tape width or that the rules are derived from empirical data as a function of tape width. The method may further comprise modifying the engineering definition to comply with any of the rules that were violated and then reapplying the rules prior to part layup or comprise accessing a laydown machine having the configuration.

According to another embodiment herein, an apparatus comprises a computer programmed to access an engineering definition of a composite part and apply a set of rules governing material laydown to determine a machine configuration for laying up the part.

According to another embodiment herein, a system comprises a plurality of

manufacturing facilities and a computer programmed to access an engineering definition design of a composite part and apply a set of rules governing material laydown to determine a machine configuration for laying up the part that is further programmed to perform rule- based configuration and trade to select one of the facilities to fabricate the part. This system may further specify that the trade includes identifying those fabrication facilities cells that achieve the best balance between (1) laydown machine configuration and tape width; (2) engineering requirements for composite laminate balance and symmetry, (3) structural performance, (4) weight of the part; and (5) speed of manufacturing the part.

According to another embodiment herein, an article comprises computer-readable memory programmed with data for causing a computer to access an engineering definition of a composite part, and apply a set of rules governing material laydown to determine a machine configuration for laying up the part. The article optionally comprises wherein the rules are applied to produce a plurality of different machine configurations, and wherein the memory is further programmed to cause the computer to perform a trade between different slit tape placement processes to select one of the machine configurations.

According to another embodiment herein, a method of fabricating a composite part, optionally an aircraft part or aircraft fuselage, comprises receiving design data for the aircraft part. The part includes aircraft skin and integrated stiffening elements. The design specifies part geometry, ply boundaries, ply drops, stacking sequence, and fiber orientations within each boundary. The method further comprises applying a set of rules governing slit tape placement processes to determine a machine configuration for laying up the part.

BRIEF DESCRIPTION OF THE DRAWINGS

Figure 1 is an illustration of a layup machine.

Figure 2 is an illustration of a method of fabricating a composite part.

Figure 3 is an illustration of an apparatus for applying a set of rules governing material laydown to an engineering definition of a composite part.

Figure 4 is an illustration of an aircraft including a composite fuselage.

Figure 5 is an illustration of a plurality of manufacturing facilities.

Figure 6 is an illustration of a method of using a rule-based approach to select a facility for manufacturing a composite part.

DETAILED DESCRIPTION

Reference is made to Figure 1, which illustrates a machine 10 for using a slit tape placement process to form a layup of composite material. Slit tape placement processes include flat tape laydown, contoured tape laydown, and fiber placement. In some

configurations, the layup machine 10 may include an end effector 16 having a single layup head 12. In other configurations, the layup machine 10 may include an end effector 16 having multiple layup heads 12 and a quick changer 18 or a device for exchanging individual layup heads 12 (as illustrated in Figure 1). In some configurations, the layup machine 10 may have multiple end effectors 16 with layup heads 12 that are not exchangeable. Each layup head 12 may include one or more compaction rollers 16 for compacting the composite material during layup.

Configurable details of the machine 10 include number of tows or slit tape (typically one for a tape layer, and between four and thirty two for fiber placement), width of each tape (typically between three to twelve inches for a tape layer, and one-eighth to one-half inches for fiber placement), compaction roller width, head geometry (which may be determined by the geometry of the part: convex parts are typically fabricated with larger heads whereas concave parts are typically fabricated with more compact heads), quantity of end effectors per head (which may be determined by the desired production flow time and part size), and the number, type and configuration of end effectors per head (which may be determined by part geometry and engineering design requirements).

Reference is made to Figure 2, which illustrates a method of creating a composite part including layers or plies of reinforcing fibers embedded in a matrix. At block 210, an engineering definition of the composite part is accessed. The engineering definition may define surface geometry including contour and features such as holes, trim locations, and engineering edge of part. The engineering definition may also specify ply drops, ply boundaries, stacking sequence and fiber orientations within each ply. The fiber orientations may be specified according to a rosette, which is a reference system for fiber orientation.

The engineering definition may define material specifications for the composite part. The material specifications may specify properties of the composite, including properties of the reinforcing fibers and the matrix. One example of the composite is carbon fiber reinforced plastic (CFRP), where the constituents may include carbon fibers embedded in an epoxy matrix.

The engineering definition may also define process specifications for the composite part. These process specifications may include material laydown instructions, processing instructions, cure instructions, processor qualifications, and inspection instructions. Process specifications may also describe allowable deviations during laydown (e.g., laps, gaps, and angular deviation from the rosette) and allowable defects in the layup (e.g., wrinkles and puckers).

At block 220, a set of rules governing material laydown is applied to the engineering definition to determine one or more layup machine configurations. For instance, the rules are applied to determine machine configurations that satisfy design requirements (structural performance), producibility requirements (e.g., no wrinkles, steering), and manufacturing flow time target (that is, the time for laying up the part) for the specified composite at different widths. There may be more than one acceptable machine configuration for the part. In a first example, if the part has flat geometry, tape or AFP may be an acceptable machine configuration. The widths for AFP or tape may also be unlimited. In a second example, if the part geometry is contoured, AFP may be the only acceptable machine configuration. In this second example, the rules define the AFP tape widths that are acceptable, and the quantity of tows of the acceptable width that can be utilized in accordance with roller compliance.

The rules may include algorithms that generate tape paths for different layers of tape. A tape path includes a series of coordinate positions that determine the movement of a tool (e.g., a fiber placement head) during tape laydown. For example, a tape path generation rule may utilize a ply boundary, and surface, and fill that boundary according to the number of tows and tape width selected.

The rules may include algorithms that indicate whether, based on rosette (direction) and contour of the part, a given machine configuration may lay down material of a given width in the desired direction and position without wrinkles, puckers and other defects.

Consider the following examples. For example, wider tape or slit tape will generally have a smaller minimum steering radius than narrower tape (where minimum steering radius is the smallest radius by which material can be steered material with an acceptable level of wrinkles or puckers). A rule may determine whether a wider tape violates the minimum steering radius. The rules may include algorithms that specify natural paths (that is, paths that produce a state of neutral fiber tension, where the same distance is continuously maintained between both sides of the tape). If a tape path is instructed to follow a natural path, a rule may determine whether the natural path violates an allowable angular deviation from the rosette. The rules may also determine whether the natural path violates maximum lap or maximum gap between tape courses.

The rules may include algorithms that determine concavity of part. A rule may then determine whether a given compaction roller can bridge the concavity and apply sufficient compaction.

The rules may also consider penalties associated with structural performance. For instance, a weight penalty might be incurred if a laminate needs to be thickened because of material knockdown or property reduction relative to other available material types. If the laminate does not satisfy load requirements, additional material (plies) may need to be added. A further penalty may be incurred by adding more plies (and weight) to maintain symmetry and balance within the composite laminate.

The rules may raise violations to established process specifications, and they may identify the type and/or magnitude of deviations. The engineering design may then be accessed to determine whether the deviations would result in unacceptable violations or whether the deviations may be allowed for improved manufacturability. The engineering design may later be modified to minimize these rule violations. For example, the rules predict a wrinkle based on minimum steering radius for a particular tape width in a certain zone of a part, but that zone is non-critical, and the particular tape width will result in faster laydown. In this example, the deviation may be allowed to enable a faster laydown. (In this example, an optimal layup machine configuration may be identified defined in terms of structural performance and manufacturing flow time.)

The rules may indicate allowable tapes per ply or part portion. As a first example, the rules may allow up to a 6" wide tape for a 90 degree fiber orientation, but no more than a one-half inch tape for other fiber orientations (e.g., 0, +45 and -45 degrees).

As a second example, the rules allow a one-half inch wide material for all areas and all fiber orientations of a part, except for one small zone. The rules allow narrower width material (one-quarter inch) for that small zone. Consequently, a layup machine configuration may specify different end effectors to accommodate these two widths. (By using wider tape, the machine configuration may reduce manufacturing flow time.)

These rules are merely provided as examples. Another rule may determine whether minimum steering radius is violated for a tape of a given width. Another rule may determine tow drop offs as ply boundaries are approached.

The rules are derived from process specifications and empirical material performance. For example, minimum steering radius may be obtained for different types (material system, weave, resin content, etc.) and width of composite material by testing on a flat plate and looking for wrinkles, puckers and other defects that are within allowable limits. The type of machine used and process parameters (e.g. tension, compaction force) for the machine may also influence the results. Laminate mechanical property performance (e.g., tension and compression testing) is another example of data that may be provided from testing. Initially, the empirical data may be obtained from testing material coupons. Over time, additional data may be obtained from testing subcomponents, or complete assemblies. In some embodiments, the rules are applied to determine acceptable machine configurations. In other embodiments, the rules are applied to determine configuration options as opposed to complete machine configurations. For instance, the rules may suggest an AFP head that utilizes the maximum number of tows and that satisfies compliance requirements for a tape width that also satisfies structural performance.

At block 225, the method may perform a trade between different slit tape placement processes. As a first example, the rules may determine the machine configuration that provides the shortest production time and lowest fabrication cost. As a second example, the rules may identify deviations and defects that will result if a specific machine configuration is used to lay down material of a given width in a specified direction and position.

A trade based on tape width may be performed as follows. Consider the example of machines that have thirty two one-half inch wide tows or slit tape of material and others that have sixteen one-half inch tows. The compaction roller for a one-half inch thirty two-tow machine is 16 inches, whereas it is 8 inches for a one-half inch sixteen tow machine. For the same width tow, the greater the quantity of tows that can be simultaneously employed, the faster the laydown time, assuming constant speed. In some cases, depending on panel contour, the number of tows out of the total available may be limited. For example, a machine with thirty two tows over a panel with a complex contour may have a limit of eighteen or nineteen tows that can be effectively used because of roller compliance, and in some cases potentially less, so a one-half inch thirty two tow machine may provide unneeded capacity for a given panel configuration. Wider tapes will likely have more challenges in compliance, especially over complex contours. Assuming a common laydown speed, the more tows, the faster material can be laid down and the faster the panel can be fabricated. A layup machine configuration may specify the number of required tows of a certain width. Consequently, money is not wasted on purchasing a layup machine having additional tows that provide no added value. Another layup configuration might specify tows of different widths within a common end-effector. Yet another configuration might specify

interchangeable or fixed end-effectors having different tow widths.

Consequently, the trade may specify interchangeable heads to accommodate these different width requirements for different section, or a minimum common tape width for all sections in order to use a simpler machine. The trade may be in production flow time, where a common narrower tape width may take longer, but this may reduce machine complexity and purchase cost for the machine. Thus, trades may be made of potentially different tape width material, which provides flexibility in layup machine configuration, which ultimately impacts manufacturing flow time and cost.

A trade based on weight penalty may be performed as follows. A rule for weight penalty may be based upon a set of laminate mechanical properties established for laminates made from different tape or slit tape widths of known sizes. A production baseline of a laminate made using tape width X is compared against the same laminate made using tape width Y. Mechanical properties of the laminate made from tape width Y are lower than the laminate made from tape width X. Additional plies would be added to the laminate made with tape width Y to achieve the equivalent laminate mechanical properties of the laminate made with tape width X and also to maintain balance and symmetry. A weight penalty would be incurred by these additional plies.

In some embodiments, the rules may be used to evaluate different part materials, and trades may be performed according to the different materials. The rules may be used to evaluate the part using the material specified in the engineering definition, and it may also evaluate the part if a new part material is selected. Changing the material from a thermoset to a thermoplastic, for instance, may result in a different machine configuration.

Figure 2 shows the rule-based configuration and the trades as being performed separately. However, a method herein is not so limited. In some embodiments, the functions at blocks 220 and 225 may be integrated and performed together.

At block 230, in addition to applying the rules, engineering analysis may be performed to determine if suggested tape widths satisfy engineering requirements (static, fatigue, damage tolerance, etc.). Tape widths may be eliminated for consideration if they do not satisfy the engineering requirements. A dynamic simulation to validate path compliance may also be performed in conjunction with layup analysis to verify whether the kinematics of a machine will be capable of performing the layup. Some machines might have limitations on performing all programmed paths required for laydown. For instance, some machines might have a singularity, reach, or inability to maintain surface normal due to axis limitation. At block 240, once an acceptable machine configuration has been selected, a layup machine is accessed. In some instances, the layup machine may be accessed by purchasing or building it. Or if the machine configuration already exists in a facility, the machine may be accessed by identifying that facility.

In some instances, a part does not pass any rules. It might not be producible at any tape width. Or, there might not be a facility available to produce the part. In these instances, the design may be modified, and the functions at blocks 220 to 240 may be performed again. Thus, the design is modified before attempting to form the initial layup.

At block 250, part programs are generated for the layup machine. A programming and simulation solution may take the requirements from the engineering design and convert them into instructions that can be processed by the procured layup machine. The part programs may be post processed, simulated or directly used by the layup machine to fabricate a part. The programs may include instructions for fiber placement machines (e.g., path for the head, angular position, and cut and add commands for the different tows), machining, etc.

At block 260, the layup machine is programmed and used to form the layup. The automated layup may be wet or dry, or a combination thereof. The fabric may be deposited by an end effector that performs a slit tape placement process. The part layup is then bagged and cured. Afterwards, the cured part may be machined (e.g., trimmed and drilled).

At block 270, feedback may be provided to validate or modify the rules. For instance, if wrinkles are detected during laydown, and the rules had indicated that no wrinkles were expected, the rules would be modified for the future configuration of layup machines.

Reference is now made to Figure 3, which illustrates a computer 310 including a processor 320, and computer-readable memory 330. A program 340 is stored in the memory 330. When executed in the computer 310, the program 340 accesses an engineering definition of a composite part and applies a set of rules governing material laydown. The computer 310 may determine one or more machine configurations/options for forming a layup of the part. By performing the rule-based configuration concurrently with part design, empirical testing is minimized, thereby speeding up part production. Trial and error are avoided.

Multiple iterations of redesigning, refabricating and revalidating a part are avoided.

Considerable time and cost is saved from the need to form an initial layup and follow an iterative process of redesigning the part and determining a new layup machine configuration that can form an acceptable layup.

The rule-based configuration also enables manufacturing trades to be made between engineering design and machine configuration. In making these trades, the rule-based configuration may be used to identify a machine configuration that is best suited for the application in terms of providing the fastest production flow time and lowest fabrication cost.

This reduction in time is especially significant for new airplane programs, which involve new designs for fuselage, wings, empennage, and other composite structures.

Program level trades may be made between airplane performance and manufacturing cost. A new composite airplane program may requires many expensive layup machines, so the ability to quickly trade between engineering design and machine configuration provides valuable insight into optimizing layup machine configuration, as it is a major component in overall cost. Reference is made to Figure 4, which illustrates an example of a composite aircraft

400. The aircraft 400 generally includes a fuselage 410, wing assemblies 420, and empennage 430. One or more propulsion units 440 are coupled to the fuselage 410, wing assemblies 420 or other portions of the aircraft 400. Landing gear assemblies 450 are coupled to the fuselage 410. Passenger and cargo doors 460 are formed in all sections. Reference is now made to Figure 5, which illustrates a plurality of manufacturing facilities 510 for forming layups of composite aircraft parts. The facilities 510 may be geographically dispersed. Each facility 510 includes one or more layup machines 512 and tooling 514. At least some of the machines 512 have different configurations. These configurations include, but are not limited to, the types of layup (hand versus automated) that may be performed, the type of machines that are available, the type of end effectors that are available, and the widest available tapes that can be deposited. Figure 5 also illustrates a computer 520 for performing a rule-based machine configuration and trades to select facilities 510 for manufacturing different aircraft parts.

Reference is made to Figure 6 which illustrates a method of selecting facilities to manufacture a composite aircraft part. At block 610, an engineering definition of the part is received. For example, the engineering definition is for skin and integrated stiffening substructure.

At block 620, analysis is performed on the part to understand the magnitude of the contour of the part. By understanding the magnitude and contour, choices for tape width can be narrowed. For typical automated fiber placement material, typical material widths of 1/8", 1/4", and ½" may be used. For hand layup and automated tape layup, wider tapes of 3", 6", and 12" may be used. For hand layup, broad materials in typical widths of 36", 48", and up to 60" may be used.

Some of these candidate tape widths can be eliminated at this step. For example, compound contour panels are highly unlikely candidates for hand layup (likelihoods would be based on prior producibility knowledge). Automated layup with narrower tapes (1/8", 1/4", 1/2") would only be considered. On the other hand, panels having relatively uniform surfaces might be candidates for hand layup with 6" tape. The initial analysis reduces the overall analysis time by narrowing the type of layup (e.g., hand layup versus automated layup), candidate tape widths (e.g., 1/2" tape versus 1/4" tape), candidate automated machines (e.g., machines not having capability to lay down ¼" tape would be eliminated from further consideration), and candidate cells (e.g., cells not having capability to lay down ¼" tape would be eliminated from further consideration).

At block 630, a set of rules is applied to the engineering design to determine an optimal layup machine configuration. The rules identify those configurations that achieve the best balance between (1) engineering requirements for composite laminate balance and symmetry, (2) aircraft performance (e.g., range, weight, seat cost/mile), (3) part weight, and (4) speed of manufacturing the part (e.g. within material out time limits, machine capability, machine availability window, labor time/cost, customer need date, etc.). Other factors to be balanced may include, but are not limited to engineering change effort. Engineering change effort refers to modifications from an existing configuration to incorporate different tape widths. This balance involves a trade in design change time for production time.

At block 640, the selected facility may be incorporated into a specification for manufacturers, to enable the equipment to be purchased, installed, commissioned, and used for part production.