ATL and AFP: Defining the megatrends in composite aerostructures

For most of its history, most of the aerospace industry has taken advantage of carbon-fiber-reinforced composites at great expense: Individually cut prepreg are painstakingly hand layed by highly trained technicians, the best of whom can place about 2.5 lb of material per hour. Only 10 years ago, if a knowledgeable composite aerostructure pro like Spirit AeroSystems Inc.’s (Wichita, Kan.) Terry George (then a Boeing Commercial Airplanes employee) had been told that within a decade, he’d be building the massive nose and front fuselage barrel section of a new all-composite wide-body commercial aircraft fuselage from carbon-fiber reinforced epoxy, the idea of doing so with the prevailing manual technology would have seemed a practical and financial impossibility. “Ten years ago, I would never have believed we would be building a composite airplane,” says George. Today, George does the impossible as Spirit’s director of operations for his company’s work on The Boeing Co.’s (Seattle, Wash.) 787 Dreamliner. And he’s not alone. Spirit Aerosystems, like the other airframe structure suppliers for the 787, makes the massive Section #41 for the 787 in one piece, using automated tape laying (ATL) and automated fiber placement (AFP) technologies that, in the past decade, have revolutionized the manufacture of  composite aerostructures.

AFP/ATL fundamentals and evolution

The AFP and ATL processes are functionally similar, although each is used differently to achieve specific structure construction goals to provide strength or stiffness where needed. Both processes apply resin-impregnated continuous fiber.
   AFP, an R&D tool for many years before migrating to the production floor with the development of the 787, automatically places multiple individual preimpregnated tows onto a mandrel at high speed, using a numerically controlled placement head to dispense, clamp, cut and restart each tow during placement. Minimum cut length (the shortest tow length a machine can lay down) is the essential ply-shape determinant. The fiber placement head can be attached to an existing gantry system, retrofitted to a filament winding machine or delivered as a turnkey custom system.
   Actually developed more than 20 years ago, ATL machinery lays fiber down in the form of prepregged unidirectional tape or continuous strips of fabric, rather than single tows.  Tape layup is versatile, allowing breaks in the process and easy changes in the direction of fiber orientation. ATL systems also can adapted for both thermoset and thermoplastic materials.
   Typically, with both processes, material is applied via a robotically controlled head, which can weigh from a few pounds to several hundred pounds, depending on application. The head contains many of the mechanics needed for material placement.
   For AFP, multiple tows are supplied from creels located on or near the head. The number of tows used by a head depends on the width requirements of the part and can range from as few as one or two to simultaneous placement of as many as 32.
   For ATL, the head includes a spool or spools of tape, a winder, winder guides, a compaction shoe, a position sensor and a tape cutter or slitter. In either case, the head may be located on the end of a multi-axis articulating robot that moves around the tool or mandrel to which material is being applied, or the head may be located on a gantry suspended above the tool. Alternatively, the tool or mandrel can be moved or rotated to provide the head access to different sections of the tool. Tape or fiber is applied to a tool in courses, which consist of one row of material of any length at any angle. Multiple courses are usually applied together over an area or pattern and are defined and controlled by machine control software programmed with numerical input derived from part design and analysis.
   The first generation of ATL and AFP equipment evolved from technologies developed by some of the traditional computer numerically controlled (CNC) machinery manufacturers, companies already heavily involved in aircraft manufacturing: MAG Cincinnati (Hebron, Ky.) has a heritage in Cincinnati Milacron. Others similarly steeped in machines tool technology include Ingersoll Machine Tools Inc. (Rockford, Ill.), Forest-Linè (Paris, France) and MTorres (Navarra, Spain and Santa Ana, Calif.). Each provides a fiber or tape placement system that is in use producing structures for aircraft ranging from the F-22 military fighter craft to the forthcoming A350 XWB from Airbus (Toulouse, France). And like many composites-related technologies, AFP and ATL first found use in military aircraft applications, proving their mettle on aircraft like the B-2 Spirit bomber, the F-117 fighter, the Eurofighter, the F-22, the C-17 Globemaster cargo plane and the Joint Strike Fighter, now known as the Lightning II.
   MAG Cincinnati offers the Viper FPS for fiber placement applications. The latest model in this line is the Viper 6000, capable of handling mandrels of up to 190,000 lb (86,180 kg). It offers independent control of feed, clamp, cut and start for up to 32 individual tows or slit tape. This allows automated “on-the-fly” adjustment of fiber band width, controlled steering of fiber layout around changing contours, and precise configuration of openings (doors, hatches, etc.). The Viper is currently used to produce fuselage sections, cowls, ducts and nozzle cones; it’s used by Vought Aircraft Industries (Dallas, Texas) to produce the aft fuselage sections of the 787. In the tape laying arena, MAG Cincinnati offers the CHARGER machine, which deposits 3, 6 or 12 inches (75, 150 or 300 mm) of unidirectional preimpregnated tape. CHARGER Contour Tape Layers enable layup of contours and features with angles as acute as 25°. A CNC-guided 10-axis gantry-style system applies, cuts and debulks tape automatically. The system uses what is said to be a unique side-loading head design that provides fast, simple change-out of tape rolls of up to 12 inches/300 mm wide and 25.6 inches/650 mm in diameter.
   Ingersoll Machine Tools (Rockford, Ill.) has made the strategic choice to focus exclusively on fiber placement machines; since 2005 Ingersoll has installed 11 machines and another eight will be installed by mid-2009. Ingersoll offers the AFPM (Automated Fiber Placement Machine), which features seven primary axes, fiber delivery of up to 32 individually directed fiber tows, Siemens 840D multi-axis CNC control and a Composite Programming System (CPS). Ingersoll production range includes vertical gantry machines with stationary layup tool  and horizontal machines  with 3-D parts fabricated on form tools supported between centers. Other features include rapid interchange of fiber spools, a head/creel module with quick exchange, tow widths of 0.125 inch to 1.000 inch (3.18 mm to 25.4 mm), support for tool weights up to 250,000 lb (115 metric tonnes) and a CATIA Composite Work Bench native interface. In May, Ingersoll reported that its Mongoose H3 fiber placement machine, using 32 tows of 0.5-inch/12.7 mm width, can lay down up to 8000 ft²/hr of carbon fiber. The machine is being delivered to Alenia Aeronautica SpA (Rome, Italy) after qualification tests that proved a layup, cut and add speed of 30 m/min (1,200 in/min). Later in 2008 Ingersoll says it expects to have the next generation of machines available, with layup speed of 60 m/min (2,400 in/min) and cut and add speeds of 50 m/min (2,000 in/min).
   Forest-Liné’s (Paris, France) range of products for the composite industry goes from simple tape layers (WR) to multi-axis tape layers (Atlas/Access), to AFP machines. Forest-Liné’s ATL technology is unique to the industry and actually consists of a double head (ATLAS), one carrying a 12-inch/305-mm bulk prepreg spool for high-volume lamination, the other carrying a cassette containing precut 6-inch/152.5-mm tape for quick layup of complex shapes.
   “In this way,” says Patrick Rousseau, senior composite project manager at Forest-Liné, “the machine is dedicated only to layup. It doesn’t worry about cutting or removing scrap tape.” The precut tape is prepared offline on a cutting machine (Access) and stored on a cassette, thus avoiding layup time for cutting and removing scrap. Tape cutting is done with two ultrasonic knives. The precut tapes allow any shapes to be made to satisfy any design requirements. The bulk head lays tape ranging from 3 to 12 inches (76 to 305 mm), and the precut head lays tape ranging from 3 to 6 inches (76 to 152.5 mm). Speed is 60 m/min, with optimized acceleration/deceleration. Four Atlas and two Access machines from Forest-Liné (with one more of each on order) are used to layup the largest continuous parts on the 787 the wingskins, manufactured by Mitsubishi Heavy Industries (MHI, Nagoya, Japan). Each wing is 6.5m/21.3 ft wide and 36.5m/120 ft long. The dual-head Atlas machine lays down 12-inch/305-mm tape through the primary head, and 6-inch/152.5-mm tape through a secondary head fed by a cassette that holds the precut edges. One Access and one Atlas machine are also used by Fuji Heavy Industries (FHI, Tokyo, Japan) to manufacture the wing box for the 787.
   MTorres (Santa Ana, Calif.) offers the TORRESLAYUP, an 11-axis gantry high-speed ATL, originally designed to manufacture carbon fiber-reinforced composite aerostructures. Developed as a modular concept, each unit is designed and built to customer requirements using commercially available CNC.
   The system reportedly provides the highest possible compacting capacity during the laying process, eliminating the need of frequent vacuum consolidation cycles to achieve optimum laminate compaction. MTorres has signed a multimillion euro contract with Airbus to supply a number of these ATLs to support manufacturing on the A350 XWB. The contract includes different sizes of machines to manufacture the wingskins and wing stringers and spars.  They will be delivered to Airbus UK (Filton, U.K.) and to Airbus Germany (Stade, Germany). The machines will apply tapes 300 mm, 150 mm and 75 mm (12 inches, 6 inches and 3 inches) in width, using two ultrasonic knives for tape-cutting purposes. In addition, the laying heads will feature built-in tape defect detection systems.
   New to fiber placement scene is  ElectroImpact (Mukilteo, Wash.), whose history is primarily in automation and tooling integration, especially in the aerospace industry. In 2003, the company developed a new concept called Modular Fiber Head Placement, whereby all materials needed for a given fiber placement application are located on a modular head that can be quick-changed, much like a toolchanger on a traditional milling machine. The goal is to allow composites manufacturers to buy one machine base, but multiple heads to meet a variety of applications. ElectroImpact’s concept was presented to Boeing in 2003, and in 2004 Boeing placed an order for the system. Since 2004, Electroimpact has built two full-scale prototype AFP machines with three different modular AFP heads: a 0.5-inch by 12-tow head, a 0.25 inch by 12-tow head, and a 3-inch by 4-tow head. All are interchangeable and can be operated on either of the machines with a tool change-type operation. The machines were built under contract to Boeing, but with 50 percent Electroimpact investment. In 2006, Electroimpact received a license from Boeing for the AFP technology developed under contract to Boeing, and other technologies. ElectroImpact is on the verge of delivering its first AFP system — one machine and two modular heads — to Spirit AeroSystems for use in production of the section 41 fuselage section for the 787. Tool changes on the system take 30 seconds; the Spirit device will provide material 0.25 inch to 0.5 inch wide.

The “part-purpose” machine

The larger systems previously discussed were developed to handle a wide variety of part sizes and shapes and, therefore, tend to be large, sophisticated and expensive. But there has developed a parallel demand for automated technology that enables series production of large numbers of parts that are identical or similar in size and shape. Several machinery suppliers have developed what have come to be called part-purpose systems, that is, simpler machines that address the manufacture of a very limited range of parts. Unlike the more complex machine that can do many types of parts, these system’s provides a more affordable automated solution for small- to medium-sized, relatively simple composite structures.
The pioneer suppliers in this arena are Accudyne Systems Inc. (Newark, Del.) and Automated Dynamics (Schenectady, N.Y.). According to John Melilli, VP of sales at Accudyne, the focus is on applications in which “traditional AFP/ATL machines are more than a typical part might require.”
   Automated Dynamics’ specialty is part-purpose AFP, using a unidirectional prepreg material in a thermoplastic resin matrix. Fiber can be oriented anywhere from 0° to 90°. The process uses high heat and pressure to consolidate structures in-situ, without postcure. Its fiber placement management (FPM) software uses a 2-D part boundary definition function and ply table entry format for programming.
   However, the company recently introduced its ATL-1117 gantry tape layer, now in use for the flight deck floor on Boeing’s 787 Dreamliner. This ATL has a 3-inch/76-mm thermoset material processing head, and the workcell envelope is 11.0 ft by 17.5 ft (3.3m by 5.3m). Also new is the AFP/ATL-0510 robot, which is based on a Kawasaki robot platform. The standard work envelope is 10 ft by 5 ft by 4 ft (3.0m by 1.5m by 1.2m), and parts can be made to revolve with the addition of a spindle system. The robot is capable of hosting multiple processing-head technologies, including thermoset and thermoplastic automated fiber placement (AFP) and ATL. The AFP/ATL-0510 robot comes standard with the company’s offline FPM and online FPS software. Accudyne’s purpose-built ATLs usually feature a fixed or limited-movement head operating over the tooling surface.
   Accudyne worked with MAG Cincinnati to develop a flat charge laminator for Vought Aircraft Industries (Dallas, Tex.), which was looking to build long, flat parts quickly. The machine has a 60-ft/18.5m-long, flat steel vacuum table and a carriage mechanism that moves from one end to the other under closed-loop servo control. The carriage contains three prepreg heads capable of laying down any combination of thermoset prepreg in the zero or longitudinal direction from either end of the machine, each fed by a spool that can hold a material roll up to 25 inches/625 mm in diameter and 12 inches/300 mm wide. Material can be unidirectional tape, woven fabric or ±90°/±45° bias prepreg. In addition, the carriage holds two rolls of auxiliary material, such as peel ply, foil or vacuum bagging film. Each head is individually controlled by the machine’s operating system. Accudyne optimizes machine efficiency by making the heaviest components stationary, in this case, the table, while lighter elements (the heads) move. To minimize downtime during material changeout, an automated “turret loading system” allows an operator to load new material rolls while the machine is operating, with only a 90-second production delay as spools are automatically exchanged. Material lay down rates of 100 ft/min (30.48 m/sec) and between 50 lb to 60 lb (22.7 kg to 27.2 kg) per hour have been achieved. Reportedly, a finished charge can be produced in 15 minutes, with edge position is accurate to ±0.030 inch/0.75 mm and start/stop accuracy is ±0.030 inch/0.75 mm.
   Subsequently, MAG Cincinnati in May introduced to the general market the Small Flat Tape Layer (SFTL) for the production of long, narrow, flat parts, nested multipart laminates, drape-formed skins and more. Typical structures for which the SFTL is designed include spars, stringers, beams, ply packs, shear ties, frames, flaps and skins. Finally, MAG Cincinnati offers the Flat Charge Laminator (FCL), for processing of long, narrow structural parts. The FCL, says MAG Cincinnati, was especially created address demand for composite stringers, spars and beams in aircraft applications. It accommodates ATL-grade prepreg material up to 12 inches/300 mm wide and features high-capacity laminating heads, heavy-duty carriage and support structures, and a segmented vacuum table.  The multihead function allows layup of prepreg unidirectional tape, prepreg woven fabric and film/foil in a single, variable thickness laminate.
   With the players, machines and capabilities identified, one question, for the potential buyer, remains unanswered. AFP or ATL? Great debate surrounds that issue, and in our September issue, we’ll revisit this subject.