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The patented StressWave cold working process improves the fatigue lives of holes in metal structure by locally treating the metal prior to machining the hole. This important feature, as well as other aspects of the process, offers a number of advantages for manufacturing fatigue-resistant components and assembled structure. Existing manufacturing and assembly equipment can be retrofitted to accommodate various StressWave adaptive devices. These adaptive devices can be actively or passively controlled, work effectively over a wide range of processing speeds and production rates, and can be controlled to adjust for varying thickness of the part or assembly. The flexibility of the StressWave cold working process allows it to be used upstream of final assembly allowing order of magnitude cost reductions when compared to mandrel cold working methods.

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.

Fastened joints are an integral part of aircraft design. Due to their complexity and function, they are also the primary source of structural fatigue problems. The incorporation of residual compressive stresses around a fastener hole greatly enhances the fatigue resistance and integrity of a fastened joint. This paper describes the split-sleeve cold expansion method to create residual compressive stresses which extend the fatigue life of holes in both new structure and field repairs. Data from test programs highlight process benefits and crack retardation effects for various specimen configurations. Other process features such as cold expansion to size are explained, along with the status of process automation.

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.