Computer simulation helps design 6,000 composite plies on first Premier I business jet while reducing required shopfloor changes by 5 to 1

Citation

DiVito, J., Retz, K. and Tonn, C. (2000), "Computer simulation helps design 6,000 composite plies on first Premier I business jet while reducing required shopfloor changes by 5 to 1", Aircraft Engineering and Aerospace Technology, Vol. 72 No. 5. https://doi.org/10.1108/aeat.2000.12772eaf.004

Computer simulation helps design 6,000 composite plies on first Premier I business jet while reducing required shopfloor changes by 5 to 1

Computer simulation helps design 6,000 composite plies on first Premier I business jet while reducing required shopfloor changes by 5 to 1

Keywords Raytheon, Simulation, Design

Computer simulation made it possible to design over 6,000 ply pieces on the world's first composite-fuselage business jet, the Raytheon Premier I, while reducing the number of changes required on the factory floor by 80 per cent – a 5 to 1 reduction. This is a dramatic improvement over the traditional trial-and-error approach in which plies required substantial rework during manufacturing in order to overcome problems caused by fabric distortion. The time savings were achieved by using FiberSIM^TM software from Composite Design Technologies (CDT), Waltham, Massachusetts, to eliminate the standard trial-and-error process by allowing engineers for the first time to make several virtual iterations of the composite part based on the feedback that the software provided. This resulted in parts with optimum weight, accuracy and quality that could be repeatedly produced exactly as specified. The project was completed from start to finish in three and a half years, 30 per cent less than the normal timeframe.

The Premier I is a swept-wing, all-weather, pressurized twin turbofan engine aircraft that carries up to six passengers and a crew of one or two. By utilizing a composite sandwich construction of carbon-fiber over honeycomb core, the Premier I fuselage eliminates the need for the stringers and frames used in a conventional aluminum fuselage. This yields an additional six to ten inches interior cross-section, resulting in a cabin with 315 cubic feet of interior space – a 33 per cent increase in volume over a similar-sized competitor's aircraft. The 24.1-foot fuselage section, from the nose radar bulkhead to the aft pressure bulkhead, is built as a single piece weighing 25 per cent less than an equivalent aluminum structure.

Improved process

The fuselage is the single largest part of the aircraft and is built using an automated fiber placement machine from Cincinnati Machine, Cincinnati, Ohio. The fiber placement machine steers as many as 24 tows (strands) of carbon fiber on to a complex curved surface, creating a one-piece structure for optimum aerodynamics. Compared to the traditional hand lay-up process, the machine reduces structural weight of the pressure vessel by 20 per cent and reduces material waste by 60 per cent.

While fiber placement provided dramatic improvements to manufacturing the primary structure of the fuselage, Raytheon engineers also endeavored to improve the process of finalizing the geometry, orientation and position of the hundreds of individual plies that make up the reinforcements for the fiber placed fuselage and nearly 400 other composite components on the aircraft. These components include fairings, empennage, cowlings, the majority of the parts on the doors, among others. In previous programs of this type, the engineering department defined the overall geometry and basic ply guidelines for each composite part and turned it over to manufacturing. Since manufacturing had no way to validate ply geometry except by trial and error, the next step was to build the tool. This task took a great deal of lead-time and very little could be accomplished until it was completed. The flat patterns, including darts and cuts required to overcome fabric distortion, were then developed through a long and difficult shopfloor process. Production workers would manually cut out fabric plies and try to fit them on to the tool. In many cases, the plies did not fit together well or they bunched up or tore as they were laid on to contoured areas of the tool. These types of issues took a considerable amount of time and material to resolve. In addition, it proved difficult to maintain accurate documentation of the manufacturing process since changes were frequently being made on the manufacturing floor.

In order to prevent these issues from arising on the Premier I project, Raytheon engineers evaluated several alternatives to improve the ability to evaluate and define the ply lay-up prior to releasing the product to manufacturing. They selected FiberSIM for several reasons. One was that FiberSIM is tightly integrated with the CATIA CAD system that is used as the primary design tool at Raytheon. This eliminated the need for Raytheon designers to learn another user interface and also avoided the need to translate design geometry back and forth between the CAD system and composite design software. The second reason was that FiberSIM had by far the greatest number of successful production users including Boeing, Lockheed Martin, British Aerospace, Sikorsky and many other leading aerospace manufacturers.

Integrated product development

Raytheon established an integrated product development team including both design and manufacturing engineers co-located in Wichita. Using the FiberSIM software as an integrative tool, design and manufacturing engineers worked together to a far greater degree than ever had been done in the past, in essentially a real-time process to define the ply design prior to hand-off to production. Design engineers established the basic geometry, structural properties and rough ply geometries of each component working in CATIA exactly as with the previous method. Then, without waiting for the tool to be built, design engineers immediately began working in conjunction with manufacturing engineers to define the detailed ply geometry. This process began with using FiberSIM to simulate how fibers conform to complex contours, something that was never known in the past until the tool was built and patterns were cut out and laid upon it. As the engineers defined each ply of the components, the software highlighted the areas that would be difficult to lay up in yellow, for mild distortion, or red, for major distortion.

At this point, a team of both design and manufacturing engineers was formed to address the issue. With both disciplines represented, it was possible to make decisions on the spot. The engineers added darts and splices to the virtual plies on the screen and could immediately see the impact on the part, including whether the splice simply caused the problem to move elsewhere. Through an iterative process that took less than a day for all but the most complex components, the team was able to completely define a ply geometry that reduced distortion to acceptable levels and eliminated wrinkles and tears. The trial-and-error process used in the past to define ply geometry typically took one to two weeks for similar parts. In addition, project lead-time was reduced because the ply design process could take place at the same time the tool was being built.

Hand-off to manufacturing

Once the team was satisfied with the ply geometry, the software generated flat patterns for each ply. These ply shapes were then exported from FiberSIM directly to Magestic nesting software. This software orients the plies on sheets of fabric to minimize waste and drives the numerically controlled ply cutters. The creation of a seamless link from the 3D CAD model direct to the cutter made it possible to implement automated cutting without the need to manually program ply geometry. This seamless transfer also significantly reduced the potential for incorrect ply size or orientation. Since FiberSIM produced net shape flat patterns, and the nesting software for the ply cutter optimized the position of the plies on the bed, material waste was significantly reduced compared to the manual process.

Designers also used FiberSIM software to organize the ply lay-up. With the intuitive forms-based user interface, designers recorded critical non-geometric information such as material, orientation, and pertinent markings for each ply. The software helped them keep track of the associated attributes of each ply as well as its location. Engineers then used the software to create illustrated shop-floor lay-up books that include schematic diagrams of the tool and lay-up pattern. Operators used the lay-up books to sequence the lay-up.

Multiple surfaces

Over the three years that FiberSIM was used on this project, its developer made several major improvements to the software, some at Raytheon's request. One of the most important is the capability to have more than one surface active at any given time. This feature is very useful when applying plies over a honeycomb core since it involves two different surfaces – the tool and the honeycomb. Having both surfaces active saves time by eliminating the need to switch between active surfaces.

Also in response to the needs of their customers, CDT formed a close relationship with Cincinnati Machine to develop a seamless interface between FiberSIM and Cincinnati Machine's "AcraPlace" fiber placement programming software. This technology enables engineers to consider manufacturing issues in the early stages of design so they can take complete advantage of the benefits of this advanced manufacturing process. This is just another example of CDT's history of responsiveness to its customer's needs and its ability to provide leading-edge technologies to the composites industry.

The Premier I is now flying, and Raytheon considers the project to be a showcase for the use of computer simulation in composite design. Of all the plies designed in the program, only 5 per cent required redesign on the shopfloor, saving tremendous amounts of time and giving engineers much more control over the final design. The program was completed, from concept to first flight, in three and a half years compared to five years for traditional development projects of this magnitude. Results were so outstanding that Raytheon plans to use the same methods on its new Horizon business jet, which is currently being developed. Early reports from that project indicate that even greater savings are being achieved, due to the experience gained on the Premier project as well as some software improvements that have occurred in the meantime.

For more information contact Composite Design Technologies, 486 Totten Pond Road, Waltham MA 02451. Tel: 781-290-0506, x300; Fax: 781-290-0507; WWW: www.cdt.com

Joe DiVitoProduct ManagerKevin RetzTechnical SpecialistChris TonnManufacturing Engineer, Raytheon Aircraft Company, Wichita, Kansas