• Carlson, Fredrik Bagge
• Holmstrand, Martin
• Johansson, Rolf
• Robertsson, Anders
• Karlsson, Martin
• Backer, Jeroen De

Abstract

Friction stir welding (FSW) is a solid-state welding process where metals are joined without melting. Heat is generated by friction between a rotating non-consumable tool and the work-piece material, and by mechanical deformation of the material. The process, invented in 1991, provides several benefits over arc welding and other fusion processes: No filler material has to be added, low energy consumption, low distortion and excellent mechanical properties, similar to those of the parent material. The FSW process has hitherto been performed mostly by stiff machines of gantry-type. In this work, however, the use of a 6 DOF robot arm for FSW was explored. This allows for processing of a wider range of seam shapes. However, the compliance of the robot introduces challenges in terms of positioning of the tool subject to large external forces. In the FSW process, large contact forces are necessary to produce frictional heat, to move the tool along the seam, and to counteract the torque induced by the rotating tool. In this context, it is not enough to rely on the robot's internal sensors for positioning, and therefore, an external laser sensor was attached adjacent to the tool in order to detect and measure the position of the seam.<br/>The measurements propagated through a PI-controller, yielding changes of the reference positions for the robot. The approach was verified experimentally at TWI Technology Centre Yorkshire, UK, through FSW of thin section aluminium alloys with an ABB IRB 7600 robot.

Topics

• impedance spectroscopy
• aluminium
• aluminium alloy