When the aircraft components are sewed, the needle has to maintain a 90° angle to the surface at all times. This also applied to components with convex or concave shapes. For this reason, only a six-axis jointed-arm robot with sufficient freedom of movement and flexibility could come into consideration as an automation solution.

Sewing of carbon-fiber mats

The KUKA robot is mounted in inverted position on a seven meter long linear unit because it also has to sew convex and concave shapes, and in any other position it would not be able to reach all of the points. Working from above expands the robot’s work envelope to 5 meters x 3 meters x 1.5 meters (LxWxH).

The aircraft component to be sewed is brought on a workpiece carrier into the cell, where the operating personnel can leave it in any position, i.e. without reference to any fixed points. The KR 125 “finds” the workpiece carrier and measures it in three dimensions by means of a laser measuring system. The data thus obtained are used by the robot to adjust its sewing program to the position of the workpiece carrier.

• KUKA KR 125 robot
• PC-based KUKA KR C2 robot controller, including control panel with Windows interface
• Linear unit
• Robot programming
• Commissioning
• Three sewing heads (from KSL Keilmann Sondermaschinenbau GmbH)

• High repeatability
  
  The robot works with high repeatability, and its motions are exactly coordinated with the sewing head. Moreover, if the KR 125 has to leave the programmed path due to a broken thread, it will resume work again from the previous position. Such interruptions occur frequently because the needle is subject to heavy wear. Furthermore, the process may be stopped by knots occurring in the thread.
  
  
  
• Flexibility
  
  The KUKA KR 125 demonstrates high flexibility. It has to be able to use three different sewing heads, which are exchanged by means of a quick-change system, while at the same time reliably controlling three different sewing methods. In tufting, the robot inserts the thread into the carbon fiber composite at a 90° angle. In the backstitch method, it joins different layers of material to each other; access from below is necessary if this method is to be used. Such access is not required if blindstitch sewing is used. For this reason, when this single-thread chain stitch is used, the material is left in the mold even after sewing. The mold is closed at the bottom, therefore the material can remain there while resin is being pressed into the carbon fiber composite and during subsequent curing of the CRP. The desired shape of the component is thus obtained.