To increase throughput and reduce production costs on the new F-35 Lightning II , engineers at Northrop Grumman Aerospace Systems are using commercial six-axis robots for drilling and fastening applications.

The F-35 Lightning II (the plane formerly known as the Joint Strike Fighter) is a supersonic, multi-role combat jet that’s scheduled to enter service starting next year. According to some experts, it will probably be the last manned fighter built for the U.S. military.

The single-engine aircraft will be manufactured in three variants: A conventional takeoff and landing version for the U.S. Air Force; a carrier model for the U.S. Navy; and a short takeoff-vertical landing version for the U.S. Marine Corps. Aircraft will also be built for the Royal Air Force, the Royal Navy and other allied military forces.

To increase throughput and reduce production costs, engineers at Lockheed Martin Aeronautics Co. (Fort Worth, TX) are using lean manufacturing principles, such as one-piece flow, just-in-time parts delivery and standardization. For instance, all three versions of the F-35 will share 80 percent of the same parts.

“Three F-35 variants derived from a common design, developed together and using the same sustainment infrastructure worldwide, will replace at least 13 types of aircraft for 11 nations initially, making the Lightning II the most cost-effective fighter program in history,” says Dan Crowley, Lockheed Martin executive vice president and F-35 program general manager.

During the next 20 years, more than 3,000 aircraft will be assembled. Once production ramps up, the goal is to build one F-35 a day. To boost assembly speed and improve quality, Lockheed Martin has outsourced sections of the fuselage to BAE Systems Inc. (Rockville, MD) and Northrop Grumman Aerospace Systems (El Segundo, CA).

The Air Force Research Laboratory (AFRL, Dayton, OH) has been spearheading an effort to use commercial six-axis robots in the F-35 production process. Northrop Grumman’s Palmdale, CA, plant recently shipped the center fuselage for the first production aircraft.

The company “made significant investments in using robotics to speed the flow of center fuselage assembly,” says Mark Tucker, Northrop Grumman’s vice president of tactical systems and F-35 program manager. “Installation of robotic drilling machines during low-rate initial production is expected to reduce drilling times on key assemblies by up to 70 percent.”

For instance, a recent AFRL initiative called the “guided robots and robotic applications in confined spaces” project used a Series 2000/125L robot from FANUC Robotics America Inc. (Rochester Hills, MI). The robot was equipped with a drilling end-effector from Brown Aerospace Manufacturing Systems Inc. (Kimball, MI) that allowed the compact, right-angle spindle to access 90 percent of locations. A vision guidance system allowed the robot to enter the narrow opening in the F-35’s air-inlet duct.

The composite duct is integrated with the center fuselage by attaching aluminum frames that require hundreds of mechanical fasteners. The assembly process requires the drilling and countersinking of 800 holes per duct. Each air duct is approximately 9 feet long, but only 20 inches in internal diameter. Despite the ergonomically challenging space constraints, the operation was initially done manually. Assemblers would crawl inside the duct and use hand tools.

Because each of the 800 drilling points has a unique safe-radius area, the robot used in the research project used a laser tracking system developed by Variation Reduction Solutions Inc. (VRSI, Plymouth, MI) to help locate the correct position within a very narrow tolerance. A laser inspection system was used to evaluate the quality of each hole.

Northrop Grumman eventually plans to install three robotic cells to drill three different sections of the air-inlet duct, which requires approximately 2,400 holes per set. “By using articulated robots, we’ll go from a 50-hour manual process to a 15-hour automated process,” says Scott Gillette, a manufacturing technology development engineer who’s working on the project. “We’ll also reduce floor space. In addition, there are applications for robotic fastening that we’re looking at.”

The AFRL has just implemented phase one of a new automation initiative called the “affordable accurate robot guidance” project. The purpose of the two-year study is to develop robotic technology that can be applied to aerospace drilling and fastening applications. The prototype cell will be used by F-35 engineers to assemble center fuselages.

The project requires the drilling of approximately 4,000 holes per side through various stack-ups of composite and metal. Hole diameters range from 0.190 to 0.250 inches. “This type of drilling has traditionally been done with large gantry machines, which are not as flexible as robots,” says Don Manfredi, VRSI’s chief operating officer.

“The production systems will each contain up to four robots per cell to accomplish the required drilling,” adds Manfredi. A prototype is expected to be ready by the end of this year, while a production version will debut at Northrop Grumman’s Palmdale plant by late next year.

Many observers believe the F-35 applications will eventually trickle down to the commercial aviation sector and spur widespread use of robots. “Robotic drilling is a growing area that has major benefits for the entire aerospace industry,” Gillette points out.

“We’re using commercially available robots to keep the development costs down,” adds Gillette. “Accuracy and reach envelope are the most important attributes that we typically look for in off-the-shelf articulated robots. We want to work with established suppliers, rather than develop robotic technology for our own needs. We just want to use the technology, not own it.”