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A new, patented process for improving the fatigue lives of holes in metal structures has been developed. The process, known as StressWaveTM, produces residual compressive stresses and fatigue performance comparable to, or better than, those produced by legacy cold working methods and is designed primarily for automated manufacturing, fastening and assembly environments. Eliminating the need for close-tolerance starting holes, consumable sleeves, liquid lubricant cleanup and off-line processing increases speed of operation. These process benefits and associated cost savings satisfy many aspects of lean and continuous improvement program initiatives.

This paper describes a compact, integrated end effector developed by Fatigue Technology Inc. of Seattle Washington for the purpose of split sleeve cold expanding fastener holes in an automated environment. The end effector is designed for use in flexible robotic cells, but can be adapted to work in fixed automated assembly devices. The unit carries fifty sleeves in a quick change magazine. The entire unit is 30.5 cm in diameter, 45.5 cm in length and weighs approximately 40 kg. A programmable logic controller controls all mechanical functions, and communicates with the robot work cell. Operator interaction is provided by a touch screen terminal that monitors robot and end effector operations and fault conditions. Data used for statistical process control can be monitored from the various sensors on the unit. The device is capable of cold expanding holes in aluminum, titanium and steel with diameters ranging from 4.5 mm to 12 mm, and stack thicknesses ranging from 1.5 mm to 50 mm.