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Coldworking holes is an established manufacturing procedure in the aerospace industry. There are two coldworking methods used today: split-sleeve and split-mandrel. The intricate steps of these processes are not completely understood. There has been no investigation into the differences in the mechanisms of the two processes. Initial results from an ongoing program reveal that the differences in the mechanisms impart the split-mandrel process with advantages over the split-sleeve process, including the ability to coldwork 7000 series aluminum without shear cracking at the axial ridge, and the ability to effectively automate the process.

An automated, sleeveless method of coldworking used in either a robotic or traversing slide application is discussed. The coldworking end effector, developed by West Coast Industries, uses the split mandrel coldworking process, thus obviating the need for the complex handling of the split sleeve and its associated costs. Sensors mounted on the end effector provide feedback to the robotic controller, and may be used for Statistical Process Control (SPC). The unit may be used to coldwork 2000 and 7000 series aluminum alloys, with hole sizes ranging from 4.4 mm to 12 mm, and 1.5 mm to 50 mm stackup thickness.

Coldworking short edge margin applications, using nominal applied expansion levels, may result in the buckling of the short ligament. This paper describes a new coldworking procedure, Multiple Initial Coldworking, utilizing the split mandrel process. This coldworks the hole three times, instead of the usual one time. Static tests conducted on aluminum and titanium sheets analyzed the effect of the new process on low edge margin applications and other hole quality issues. Fatigue tests determined fatigue life increase on the basic process. Three passes at a lower applied expansion produce fatigue results similar to nominal single pass coldworking.

An automated, sleeveless method of coldworking, used in either robotic or traversing slide applications, is discussed. The coldworking end effector, developed by West Coast Industries, uses the split mandrel process, thus obviating the need for the complex handling of the split sleeve, and its associated costs. Sensors mounted on the end effector provide feedback to the robotic controller, and may be used for Statistical Process Control (SPC). The unit may be used to coldwork 2000 and 7000 series aluminum alloys, with hole sizes from 4.4 mm to 12 mm diameter, and 1.5 mm to 50 mm thick material.