Applying Automation to the Fabrication of CFRP for...

Accudyne Systems, Inc. 134 Sandy Drive Newark, DE 19713 Phone: 302-369-5390 Fax: 302-368-8498

APPLYING AUTOMATION TO THE FABRICATION OF COMPOSITE BASED AEROSPACE PARTS

AND DEVELOPING A MACHINE SPECIFICATION

John Melilli Accudyne Systems, Inc.

134 Sandy Dr. Newark, DE 19713 USA

Aircraft and rotorcraft parts made from high performance composite materials are superior to earlier generation metals due to their increased strength, reduced weight, and increased service life. For these reasons most aircraft part designers choose to create new parts out of carbon fiber reinforced plastic despite the challenges involved, namely that the manufacture of CFRP parts are more complex than traditional materials and can therefore make parts more costly to produce. This paper describes the method that Accudyne Systems has created for developing automation equipment to manufacture composite parts economically. This “part centric” approach produces a “part purpose” machine that takes into consideration the specific design of a part with regard to ply orientation, number of laminates, and shape of the part. This paper describes that process and details several part and machine examples that came from the process. More equipment examples can be seen on our website at www.accudyne.com. As shown in Figure 1, traditional part design is a linear process. Downstream steps are constrained by choices made in previous steps, however new decisions are not informed by considerations further down the line.

PARTCONCEIVED

LAYUPSELECTED

MANUALLYFABRICATED

CONFIGURATIONLOCKED

FABRICATIONAUTOMATED

Figure 1 The traditional approach where each step has its own barrier

Accudyne Systems, Inc. • 134 Sandy Drive • Newark, DE 19713

Phone: (302) 369-5390 • FAX: (302) 368-8498 • www.accudyne.com

With each step, the barriers to effective automation intensify because of the increased constraints. Plies that are difficult to place, fiber angle variation, short courses may not cause problems during manual part fabrication; however challenges such as these are the source of difficulties and expense when trying to automate the fabrication of a CFRP part.

Pros and Cons

• Highly versatile• Mature Technology•Application Centric

• Large• Expensive• Slow on

“real” parts

Figure 2. Traditional automated tape and tow placement equipment

which are typically machine centric Tier One and Tier Two part producers have typically considered automation solutions that are “machine centric” meaning that they perform in a broad mode independent of specific part characteristics such as geometry or ply orientation. Many commercially available fiber placement and tape placement machines excel at making large parts such as wings and fuselages. However, these types of machines operate inefficiently if the part has short courses, pad-ups, ply drops, significant contours or other such features. In these cases, and when production rates, reduction of scrap and consistency of quality are most important, the industry requires a bold new paradigm.



CONNECT THE PART DESIGN TO THE AUTOMATION SOLUTION

PARTCONCEIVED

LAYUPSELECTED

MANUALLYFABRICATED

CONFIGURATIONLOCKED

FABRICATIONAUTOMATED

PART

Figure 3. The Future Approach – “Part Centric”

In “part centric” design approach a robust examination of the part design and the planned automation drives the overall design effort. It also leads to a series of steps which lead the part designer to developing a machine specification that is idealized for the manufacture of a specific part or a series of similar parts, hence a “part purpose” machine. Aerospace parts can have complex geometries that complicate their automated manufacture. By taking a part centric approach during initial part design engineers can consider design changes to minimize automation challenges. By working “hand in hand” with a custom automation supplier this process methodology allows harmonization of part and machine design to yield a completely connected process. Although flat parts may seem simple at first examination, the inclusion of internal padups and unusual ply boundaries pose challenges to even the nimblest machine centric machine. If optimizing fabric placement would improve automated production and yield, it may be important to consider processes other than AFP or ATL. In some cases, a complete work cell may be the most appropriate approach as it combines multiple aspects of the manufacturing process. This use of works cells is common in many other manufacturing industries. Clearly, the future of automating the manufacture of composite based parts is going to take a new approach. The following is one option to address the new challenges:

1. Evaluate part requirements including:



a. Part geometry b. Ply orientation c. Desired manufacturing rate d. Material (Uni or fabric) e. Process evaluation and validation

2. Establish a machine timing diagram 3. Develop machine concepts 4. Apply Accudyne’s AT-POS analysis software to predict ply behavior on contoured shaped

parts (for tow/tape placement) 5. Develop a trade study to validate the process and potential machine operation

EVALUATION OF THE PART

Following are examples of various parts and the machines that were produced to manufacture them.

1. Hat Shaped Stringer Stringer

Hat Shaped Stringer

Figure 4 Typical hat shaped stringer used in aircraft design Traditional ATL/AFP machines were deemed to be too expensive and too slow to produce the “hat” shaped stringers used to reinforce the fuselage shown above (Figure 4). After a careful analysis of the part the Flat Charge Laminator was conceived and built. Shown in Figure 5, this machine manufactures the part using a combination of fabric and unidirectional prepreg material at a rate of 25 Kg/hr or a stringer every 15 minutes. This rate will allow the manufacturer to supply their customer with parts to accommodate the rate of 10 planes per month (published target manufacture rate).



Figure 5 Flat Charge Laminator – Capable of laying unitape and fabric at rates of 25 lb/hr

demonstrated

2. Aircraft radome

Figure 6 Composite Radome

Figure 6 shows another common aircraft part, a composite radome. Radomes typically utilize materials that are transparent to radar signals and that, due to the shape and required performance characteristics, are best manufactured using fabrics. The manufacture of these parts entails the use of precut pieces of prepreg fabric which are then hand laid on a mandrel. Making each unit by hand is expensive and time consuming. After careful examination of the part, material type and orientation engineers developed a work cell to manufacture the inner laminates for a radome using glass/epoxy fabric. The concept utilizes a means for manipulating fabrics and adhesive films onto a tool (Figure 7).



Figure 7 Radome Manufacturing Cell

Within this cell, both the tool and the material move allowing straightforward and accurate application of fabric and film. After the material is placed, a compaction step is required and a butt joint between plies is executed to adhere to the part designers’ specification that all material joints are lapped by other material. The cell also incorporates a novel bladder system for compacting and debulking each fabric ply. AFP and ATL machines cannot effectively or efficiently manufacture this part. The part centric approach recognizes the need to harmonize machine, material, method and operator to increase the rate at which this part can be manufactured.

3. “T” and “Z” SHAPED STRINGERS



Figure 8 Typical Z Stringer used in aircraft design

Some aircrafts utilize a T, Z or C shaped stringer which is placed on the surface of the fuselage and co-cured in an autoclave. The current technology consists of cutting plies on an ultrasonic table, assembling them into a flat laminate and forming them over a tool. In the case of the T shaped stringers, a “radius filler” or “noodle” must be manufactured on a separate machine and inserted into the void created at the base of the T. All of this is done by hand (except the ultrasonic cutting) and is both time consuming and expensive. It also impacts the ability to increase rate.

Figure 9 T & Z Stringer Former Machine capable of forming

1 stringer every 10 minutes



Figure 9 shows a work cell that combines Pick and Place, hot drape forming, debulking and the manufacture and insertion of a noodle. Most of the previous activities done by hand are replaced by automation. Rate is significantly increased as compared to the manual process and each part has consistent, predictable quality.

ACCUDYNE TOW PATH OPTIMIZATION SOFTWARE To develop automation for tow/tape parts that have complex geometries, Accudyne Systems has created a software tool, Tow Path Optimization Software (AT-POS®©), that models a CATIA designed part. The software calculates the effect of strain and steering on individual tows or tapes providing the designer a crucial piece of information about part manufacturability prior to manual fabrication and locking configuration. It also imparts to the automation equipment supplier an understanding of what the fibers will be experiencing during automation. The top of Figure 10 shows a typical part coverage when tows follow a natural path with lap or gap. The same part in which the tows were steered or forced off of the natural path to ensure full coverage is shown in the lower figure. Note that full coverage does not come without significant fiber strain.

Coverage is a function of tow placement constraintsNatural path has limited applicabilityForced path increases coverage but alters fiber angle and strainDesired orientation →Actual tow paths →Actual orientation

Figure 10 Comparison of fiber coverage; natural path (top panel) has limited application. A forced

path must be used to achieve complete coverage. Figure 11 shows the fiber strain experienced in the part in which the tows were steered from their natural path to ensure optimum desired coverage. The blue areas have minimal to no strain and the other colors indicate increasing amounts of strain. With this information the part designer can refine the design to a point where the optimum part can be designed for efficient automated manufacture. The software tool models anticipated fiber strain by changing tow width, ply angle, seed point, etc.



Additionally, the software (AT-POS) when incorporated into an Accudyne Systems machine provides as placed ply information for a completed part which can, in turn, be analyzed using any of several FEA programs.

Models individual tows on actual surfaceVariables include:

Width and number of towsDesired ply orientationSurface curvaturePlacement initiation siteTow steering

Output includes:Coverage modelsIndividual tow paths and orientationBuckling predictionWrinkling predictionTow strain mapping

Figure 11 AT-POS software will visually show low and high fiber

strain areas on a curved part Figure 12 shows a machine concept that utilized the AT-POS approach in which the part and the machine specification were harmonized at the onset. Through extensive discussions with the part and stress engineers and utilization Accudyne Systems’ AT-POS analytical tool, the part was designed for manufacturability in conjunction with the machine design team. The machine design engineers using this data created a machine specification that would produce a part that was designed for high speed manufacturability. In some cases, the machine concept will typically present one or more unique challenges that need to be identified and will require a development program to provide a low risk/cost way of determining if any significant barriers exist in the development of a machine. Such a trade study may also answer other questions such as validating production and scrap rates.



Unique DOF placement to Unique DOF placement to increase throughputincrease throughput

36 end head with 36 end head with ““ONON--THETHE--FLYFLY”” add and cutadd and cut

Fixed creel with auto Fixed creel with auto rewindrewind

Conformable compactionConformable compaction

Projected 25+ lbs/hourProjected 25+ lbs/hour

Figure 12 – A concept of a part purpose machine developed after analyzing the part requirements.

CONCLUSIONS

There are many aerospace composite parts that do not fit elegantly or efficiently into the “machine centric” approach of being manufactured with “off the shelf” ATP or AFP machines. Continued reliance on cutting and kitting as an effective means to manufacture parts can no longer be tolerated as it requires significant amounts of manual labor to turn those kits into composite parts. Automated manufacture of composite parts is going to require a novel approach that begins with the part in the forefront of the machine or automation abstraction effort. Ideally, the earlier in the inception of the part the better, as adjustments to the part design can be made prior to locking the part’s configuration. Additionally many of the parts that can be made using AFP or ATL will benefit from using AT-POS to determine both an optimum part design and a machine specification. Using this process will save the part manufacturer significant costs and will ensure that the machine will be optimized based on not only prior knowledge about the part, but on having influenced the part prior to locking the configuration. See our website a www.accudyne.com or contact the author for more information or an examination of your part using Accudyne Systems “part centric” approach to manufacturing a “part purpose” machine.

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