The machining of large components by huge machining centers is often a bottleneck in production. In this case, process control is spatially limited to the size of the plant and restricted in flexibility by the design principle. This is avoided by using mobile industrial robots (IR). Moreover, when using CNC-controlled robots, existing programs can continue to be used. The disadvantage of conventional IRs, however, is their lower accuracy compared to a processing machine, which has so far not allowed the required processing tolerances to be maintained.
The experts at Fraunhofer IFAM in Stade have already shown in many projects that the accuracy of jointed-arm robots can be significantly increased by extending the measurement technology, optimizing the software, and making adjustments to the mechanics. They demonstrated sufficient precision in outline machining on original large CFRP aircraft components with tolerances in the submillimeter range. To extend the application range to metal machining processes, further adaptations, including structural ones, to the robot kinematics are necessary.
An innovative approach to optimizing a robot system for machining processes is being pursued by the "Flexmatik 4.1" project (Fraunhofer-internal program designed as market-oriented strategic preliminary research together with Fraunhofer IPK and LBF). While previous projects achieved very good results with continuous milling operations, plunging into the workpiece and two-dimensional machining, if at all, has only been possible through costly and process-slowing adjustments. The robot designed in-house in "Flexmatik 4.1" with an optimized structure and newly developed drive systems overcomes these limitations and achieves a further increase in position and path accuracy. The symmetrical design of the kinematics, double bearing of the joints and additional stiffening of the arm elements make new machining applications conceivable that were previously inaccessible to IR.
Another weakness of previous IR is the low rigidity of the gears in the drive train. An additional direct drive in the newly developed kinematics eliminates their influence on the path accuracy and simultaneously increases the reaction speed and dynamics. Initial tests of the drives show an increase in relative path accuracy by a factor of 10 compared to conventional drives, allowing significantly higher tolerance requirements to be met in the overall process.
With the introduction of robotics in large component machining, a considerable reduction in costs is possible with a simultaneous increase in efficiency. This is a further contribution to improving sustainability in production and strengthening German civil aircraft manufacturing in international competition.