As their use for many years attests, robots in manufacturing operations have advantages, such as precision, repeatability, consistency, multishift flexibility, reduced safety and health hazards, total cost reduction, and more effective use of consumable materials and energy. According to the Robotics Division of ABB Inc., only recently has the use of robots become more popular in the aerospace industry—especially for paint applications.
The reasons for that are most likely increased market pressure to reduce manufacturing costs while improving productivity and quality, the company says. Other reasons, it adds, are “considerable” improvements in industrial robots regarding precision, reliability, and ease of programming. Paint finishing, sealing, gluing, and other dispensing operations are considered to require the lowest level of precision, as robots in those applications act from a distance and do not touch the part.
ABB claims to have made key contributions to high-performance robotic paint-finishing technology. The developments, it says, have been “predominantly motivated” by applications required for the automotive industry, but they are highly applicable to aerospace applications—for both aircraft assembly and parts manufacturing. Among the developments is the company’s new IRB5500 robot with increased acceleration capability and work envelope.
Painting robots have at least two features that are different and more complex than required of standard industrial robots, according to ABB. They must be explosion-proof, by means of either explosion-proof motors or air purging of standard servo motors. And they must have a well integrated process control, together with motion control, to synchronize the robot motion path and to control atomizer spray parameters on the fly.
To achieve the second requirement, there must be almost perfect robot control not only of the tool center point position, speed, and orientation but also of its acceleration to fulfill stringent requirements regarding paint film uniformity. New programming methods result in improved finishing quality, increased paint application efficiency and productivity, and less process time.
One of the new programming advances is the so-called stay-on method that keeps the atomizer over the area to be painted, reducing overspray and cycle time. The typical robotic paint process is based on parallel passes with an indexing step between each pass. While making the index and reversing direction, robots have to slow down, thus dropping a larger amount of paint in the indexing area. To avoid this scenario, robots are programmed to index outside the painted area, where the atomizer is turned off.
But robots with high acceleration do not slow down in the corners. So, the indexing can be done inside the painting area without turning off the atomizer. The result is a reduction in cycle time, shorter travel for the robot, and reduced overspray.
Other technical advances by ABB include:
• A highly efficient RB1000 paint atomizer family
• Advanced paint-saving cartridge technology, called CBS
• New robotic powder paint application (IC-3) and color change (PCC) equipment
• DispensePac sealant and adhesive robotic dispensing systems including the newest applications of sprayable masking materials
• TrueView vision and force control systems supporting applications in work object location, robot guidance, part cleaning, sanding, polishing, and masking.
While the evolution of robotics use in the aerospace industry will roughly mirror that of the automobile industry’s, ABB says aerospace will probably skip the step of using custom-made machines for paint finishing. However, some rail-supported motions and potentially specific crane-like machinery will still be used for robot repositioning in coatings of large surfaces such as aircraft fuselages. For larger aircraft, there is a need for some further development of larger rails, platforms, and towers for repositioning of a robot or a cluster of robot arms from one coating segment into the other. New methods of precisely locating and positioning robot reference points relative to the substrate segment to be treated are being developed, such as small scale GPS-like systems and vision-guided robotics.
For smaller aircraft, current robotics technology inherited from the automotive industry is sufficient to fulfill all coating operations, according to ABB.
The current high level of public awareness regarding global warming will have a strong influence on environmental compliance of aerospace paint-finishing operations, says ABB. Substitution of solvent-based materials by waterborne coatings and powder coatings will follow the known patterns from the automotive industry. In general, for aerospace paint-finishing processes and equipment, the expectation is “do more with less.” This likely will result in applicators of higher output and performance as well as robots of higher speed and acceleration. Reduction of air emissions and less paint waste will continue to require almost perfect application processes. And reduction of booth size is a strong requirement for two reasons: to reduce investment cost and to reduce energy cost for heating and cooling of ventilation air.
Dragoslav Kosta Milojevic of ABB Inc., Robotics Division, North America, wrote this article for SAE Magazines.