Robotic drilling, fastening systems gain ground in aerospace/defense as metrology technologies boost robot accuracy
With thousands of fastener locations that need to be drilled and filled to complete a plane, drilling and fastening remain the largest areas of opportunity for automated robotics applications in aerospace. New developments are also making robots more attractive than ever in the aerospace and defense space—especially improved rigidity and accuracy in the robots themselves.
There are other benefits, too. Flexible, agile robotic automation also offer substantial cost advantages over huge, fixed “monument” systems that have been used for decades to perform the thousands of drilling and fastening operations on a large airframe structure. Robots are also viewed by some as a way to speed production to alleviate order backlogs.
“Drilling and fastening operations are the most common application in our manufacturing assembly process as a whole, and that is unlikely to change any time soon,” said Curtis Richardson, Associate Technical Fellow, Robotics and Automation Technology, Manufacturing Research and Development, Spirit AeroSystems Inc. (Wichita, KS).
Government-funded Small Business Innovation Research (SBIR) programs conducted in recent years have started to pay off with development of improved, more accurate robotic drilling and fastening systems. Key technology enablers include metrology- and vision-guided drilling and fastening systems, using secondary encoders that help boost robot accuracy, and force control sensors for robotic painting, coating and sanding applications on large airframes.
“One of the strongest technical trends in aerospace automation is the integration of sensor systems; 2D and 3D vision are still the most common sensing systems used, but integration with metrology systems such as laser trackers and scanners is also becoming more prevalent,” Richardson said. “Accuracy and quality standards in many aerospace applications are driving integration of metrology even for traditional gantry and Cartesian machines, but we’re seeing benefits from metrology integrated with lower-cost automation like robotics as well. Industrial robots themselves have improved to the point that they are now capable of doing some work that 10 or 15 years ago would have required purpose-built machine tools.”
Other areas where robotic automation is gaining ground include processes like nondestructive inspection, part trimming, and surface preparation, Richardson said, which are also getting more automation attention due to the proliferation of large composite aircraft structures.
Aero Automation Surges
Leading a list of highly automated aircraft programs, the F-35 Lightning II Joint Strike Fighter (JSF) is built by several prime contractors and subcontractors working with Lockheed Martin (Bethesda, MD), employing a great deal of robotic automation including robotic drilling cells installed at Northrop Grumman Corp.’s (NGC; El Segundo, CA) Integrated Assembly Line (IAL) at the Palmdale, CA, manufacturing facility that builds the F-35’s center fuselage.
Installed by Kuka Systems Corp. (Sterling Heights, MI), the IAL features an automated workcell for the F-35 Inlet Duct Robotic Drilling (IDRD) project, an SBIR program with the Air Force Research Laboratory that involved automation integrator Comau Aerospace (Southfield, MI) along with partners Variation Reduction Solutions Inc. (VRSI; Plymouth, MI), the Delmia brand of Dassault Systèmes (Auburn Hills, MI), Cenit North America Inc. (Auburn Hills, MI), and Fanuc Robotics America Corp. (Rochester Hills, MI). The F-35 IDRD used a Digital Thread manufacturing concept with software and metrology technology in the Fastener Installation Live Link System (FILLS) that ensures highly accurate automated insertion of the roughly 30,000 fasteners on the F-35 center fuselage.
“The aerospace companies are using robots and automated guided vehicles [AGVs] for automating applications for the same reasons other industries, like automotive, have been using them—improvement in process speed and quality, as well as taking people out of hazardous jobs and making them machine operators instead of manual laborers,” said Dave Masinick, account manager, aerospace, Kuka Robotics Corp. (Shelby Township, MI). “The difference is in the business and applications drivers. Aerospace production is a relatively slow, low-volume, high-value process compared to other manufacturing. The ‘volume’ demand is not the product throughput, but rather the high number of process steps required to complete the plane. The best example of that is drilling and fastening together the frame structures and skins.
“Each plane has many thousands of fastener locations that need to be drilled and filled to complete a plane,” Masinick explained. “In addition to replacing manual processes, aerospace manufacturers are looking at robots as replacements for dedicated-purpose machines that are more costly to procure and less flexible than an integrated robot cell or system.” Some examples, he added, are robotic fiber and tape placement for composite construction, ultrasonic NDI (nondestructive inspection), mechanical routing and trimming, and abrasive waterjet trimming.
AGVs are being used to transport subassemblies and heavy tooling that requires portability, he said. “The mobile robot platforms keep the factory floor clear of stationary ‘monuments’ and give the manufacturers the opportunity to move the automation to the work, rather than moving the work past the automation.”
Metrology Boosts Robotic Accuracy
Many current aerospace automation projects involve a heavy dose of metrology. While some of the aerospace developments mirror robotic automation in the automotive world, there are distinct differences.
“There are two threads that we’ve been following for automation,” said Michael Kleemann, VRSI’s chief engineer-aerospace. “When you look at aerospace, generally you only see automation in either fabrication, more classical machine tools, or in very large, sort of purpose-built automated assembly machines. Assembly-level drilling and fastening has been catching on. But as aerospace primes start to look for greater cost savings and greater quality improvements due to automation, the automation industry needs to provide more flexible solutions.”
VRSI has focused on using robotics combined with metrology systems to use measurement to achieve the close tolerances and requirements of aerospace, Kleemann said.
“In aerospace, your production timelines, or your takt time for any given process, is usually measured in days or weeks. In automotive, it’s measured in seconds, so you can’t have a robot sitting around for a week after it’s done its job. It’s not going to provide a good business case. A lot of the demand in aerospace is either for large-scale systems that can automate an entire process end-to-end, or smaller-scale systems that are flexible enough so that they can be used for different tasks in a process.
“We’ve worked on some projects that require very close tolerances, on the order of 0.010″ [0.25 mm] or less,” said Kleemann. “For something like that, we’ve always used the approach of using a coordinate metrology system integrated into the system to provide a second source of measurement of positional accuracy. That’s the approach we used in the inlet duct project, as well as subsequent projects, and it gets the job done.”
An SBIR Phase II program for the F-35, the Affordable Accurate Robotic Guidance (AARG), teams some of the developers of the earlier FILLS project on the AARG system, which uses metrology-guided drilling technology to automate the F-35’s J450 Wing Overlap drilling at Lockheed. VRSI’s Brett Bordyn, director of technology, presented a paper describing the project at the Defense Manufacturing Conference 2012 in Orlando, FL. The system is designed to fully automate drilling more than 1500 holes per F-35 aircraft, using FARO Vantage laser trackers and laser pointer beacons, Kuka robots, and a Zagar drilling head, to improve hole quality and process repeatability while lowering costs and increasing throughput. VRSI did development work on the system’s integrated inspection capabilities, and in testing, the AARG has drilled holes within a 0.007″ (0.18-mm) radius.
“Another area where we have found that we can bring quality and productivity gains is in integrated feature inspection—not necessarily measuring the positioning of the machine but measuring the feature that the machine creates,” Kleemann said. “The AARG system is a new prototype SBIR we’re working on that has external metrology for positional guidance, but it also has a laser triangulation scanner and a noncontact bore probe integrated into the end effector. As soon as a hole is drilled, we can scan with the laser scanner, measure the countersink quality and surface characteristics in great detail, then insert the noncontact bore probe and measure hole diameter as well as grip length; it can even do a complete scan and see things like liquid shim blowout or exit burr—that’s something that’s required by the process.”
Robots Add Rigidity, Improve Accuracy
Newer, more rigid robots like the new Fanuc Robotics M-900iB/700 shown at IMTS 2012 are geared specifically toward aerospace applications. At IMTS, Fanuc demonstrated the system M-900iB/700, which has a 2.83-m horizontal reach and a 700-kg payload, drilling an airframe fuselage panel while monitored by a laser measurement system to show how little deflection occurred during the drilling process.
“We’re still working on things like making the robots more accurate and more rigid, but we developed the new M-900 robot primarily because of the demands of the aerospace industry from a drilling perspective,” said Chris Blanchette, manager, aerospace integration channels, Fanuc Robotics. “It’s a highly rigid robot, and it’s also a high-accuracy robot, which is part of the trend of robots moving into more machining-type processes, like drilling and riveting.”
Robotic Coating, Sanding Solutions
At aerospace supplier St. Louis Metallizing (SLM; St. Louis), robotic thermal spray technologies are used to apply metal and ceramic coatings to a variety of OEM and repair parts to minimize corrosion, erosion and wear to the original substrate and extend part life. SLM currently has 17 robots from ABB Robotics (Auburn Hills, MI) integrated into various cells throughout its facility to accommodate large and small configurations used in commercial and military aerospace applications.
“With thermal spray, you’re putting a coating on a part that serves as a way to provide a good mechanical bond,” said Tom Desloge, SLM director of sales and marketing. “Most of our work is in engine components and landing gear repair. In our process, we’ll remove the coating, then apply thermal spray, and then we do machining as well.”
The company’s thermal spray processes include electric arc, high-velocity oxy-fuel (HVOF), air plasma, electric wire arc and oxy-fuel flame spray in the wire and powder form, notes Bill Bryant, SLM aerospace sales engineer. “It’s a combination of maintenance and repair, and thermal spray is also used a lot on the new OEM side,” Bryant said. “Before an engine is put into service or a landing gear is installed on an aircraft, thermal will be used.”
One of the trends is the elimination of chrome plating for landing gear, Bryant added. “Even though chrome plating has been a popular method for providing corrosion resistance, thermal spray is being used on an increasing basis. Not only does thermal spray eliminate the use of hazardous chemicals found in chrome plating, it is known to last up to three to five times longer than chrome.”
Components from the hot section of jet engines, in particular, need specialized coatings. “That’s where your thermal barriers come into play,” he said, “to protect precious metals, component alloy types, with a thermal spray coating to prevent heat from penetrating into the base metal, distorting or eroding the original substrate.”
SLM also does its own in-house nondestructive testing (NDT) for detecting surface cracks or porosity on coated parts. “We’ve been using robots since the early 1980s, and we’ve built up our business on it,” said Desloge. “We standardized on ABB robots, because the quality is sky-high. Consistent quality is everything, and rework hurts your reputation.”
Force sensing technology from Fanuc helped Aerobotix Inc. (Madison, AL), an authorized Fanuc Robotics integrator, develop and commercialize its robotic sanding solution under the US Air Force Automated Sanding SBIR with the Air Force Research Laboratory for the F-35 program, said Aerobotix President and Owner Kirk McLauchlin. Now in Phase III SBIR status, Aerobotix offers the robotic sanding system to commercial and military customers.
“It’s definitely applicable to other projects, and we’ve had multiple platforms that have shown interest in it,” McLauchlin noted. “We’ve given demonstrations to just about every platform out there—from F/A-18, F-16, F-22 and B-2, as well as the F-35—just about anything where people spray LO [low-observable] coatings on an aircraft, there will almost always be some type of sanding required.”
Aerobotix, which was founded in 2005, started using Fanuc’s force sensor around late 2008, McLauchlin said, noting the sensor previously had been employed mostly for automotive in assembly or grinding. “Just about everything we do is a nonstandard application of a standard product. As an integrator, our art is to take standard off-the-shelf products and put them together in a unique way to achieve a tool with specific capabilities, then program it for use in advanced manufacturing processes,” McLauchlin said.
“Fanuc would typically mount the force sensor to the wrist of the robot and install an assembly tool or something similar on it. We remotely mount the sensor five to six feet from the wrist at the end of a long end-of-arm tool, because we have to reach into narrow, confined areas with the sander, so right away there are challenges in the programming and tuning.”
The Aerobotix system uses a Fanuc M-710 robot equipped with the R-30iA control platform and the Fanuc force sensor. “We can set the application force for the sanding tool to 5 kg and hold that, plus or minus 0.5 kg, which for a vibrating, shaking tool, is very good,” McLauchlin said. “Once you spray on low-observable coatings, it typically leaves a surface finish that’s not acceptable, like an orange peel, for the performance requirements of the coating.
“Between different coatings we may have to sand, just to knock off that rough finish, or there may also be areas where we have to do thickness sanding to remove material that’s put on too heavily. The final finish has to be uniform, so we use the sanding tool to smooth out the finish, and prepare it for proper adhesion of a final top coat application.” ME
This article was first published in the March 2013 edition of Manufacturing Engineering magazine.