Forming characteristic of thread cold rolling process with round dies

Threaded shafts are widely used in modern mechanical equipment as fasteners or transmission parts. Thread cold rolling process with round dies is an efficient way to manufacture threaded shaft due to wide dimension range of the threaded shaft, simple structure of rolling die, and convenient adjustment of rolling process. In this paper, a full three-dimensional finite element model of thread cold rolling process with round dies was developed by comprehensive considering the calculation efficiency and precision, and the forming characteristics of the thread cold rolling process with round dies were studied by using numerical method. The results indicated that the metal flow and plastic deformation mainly occur in the superficial area near the thread profile; and the radial load is the main load of rolling dies, which increases with the increase of radial infeed of rolling dies and decreases gradually after the stop of radial infeed; and the characteristics of metal flow, stress distribution, and strain distribution in the crest, flank, and root of the thread profile are significantly different. The crest areas of the thread profile are mainly formed by radial metal flow, and the flank areas of the thread profile are mainly formed by axial metal flow, and the root areas of the thread profile are mainly formed by radial material flow. The equivalent stress and equivalent strain increase gradually from the crest to the root of the thread profile, and reach their maximum at the root areas of the thread profile. Although the height of the thread profile, strain, and stress in the areas near both ends of the threaded shaft is lower than that in the middle zone of shaft, the profile of the thread, strain, and stress distribute periodically as fluctuation of peaks and valleys along axial direction (i.e., x-axis). However, the peak and valley of the strain (or stress)-x curve are opposite with the crest and root of the thread profile. The metal flow and deformation along axial direction present a short-range effect, which would mainly affect the forming of the adjacent thread profiles, and have little effect on the other thread profiles.