There were other challenges when it came to joining two sections. Although CFRP parts are stiff, they are limp when large and very thin. Manufacturers usually force the parts into rigid shaping jigs for joining, but this creates stress in the part. So the Fraunhofer IFAM researchers developed a flexible jig, a shape and positioning robot with vacuum actuators.
Using precise measurement data, the computer determined the geometry of each fuselage shape for the best fit, then directed the vacuum actuators to gently move the parts into position. This minimized stress on the parts, optimized the forces applied for joining, minimized the gap sizes and allowed more precision in the amount of adhesive used.
“We did all of this using robots off the shelf – the robots the automotive industry uses,” Niermann says. The team “taught” the robot, positioning it in 15 different ways and measuring the difference between its actual position and the ideal one. Using this data, a software program created an individual mathematical model to control the robot in a very precise way. The program even allowed for the bends in the linear track caused by the robot’s weight as it moved along the axis.
“There are other, already known ways to ‘use’ such data, but our unique way – via the adaption of the mathematical model that controls the robot – makes the decisive difference between precise enough for our purpose or not usable for our purpose,” Niermann says. “With this method, we make sure the robots ‘know’ their own deviations and act accordingly.”
Using robots and a camera system for the final quality inspection improved the speed and accuracy of manufacturing. “We used half the time, sometimes one-third the time that the human teams needed to perform the same tasks,” Niermann says. “And this automation has high reliability, which is what the industry looks for. We don’t have the variances of human work.”
The jig with actuators and the robot positioning algorithm offer manufacturers more flexible production processes. “This jig can hold every type of part, and the robot can work on every type of part,” Niermann says, noting that this is a much cheaper solution than any used today.