Developments in Advanced Coldworking

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.