Thread rolling by the through-feed and in-feed methods

In thread rolling, two profiled rolling dies press the thread into the shank of the workpiece; it is produced by forming, without removing chips. There are two methods for moving the dies and the workpiece. In the in-feed (plunge) method, the dies are parallel to the workpiece, are fed in radially and roll the entire thread length in one go; the thread length is limited by the width of the dies. In the through-feed method, the dies are set at a slight angle, the workpiece travels axially through the dies during rolling, and the thread length is practically unlimited.

Which method when

• In-feed method: Short and medium thread lengths, headed bolts, studs, threads with a runout ahead of a collar, fine threads with high demands on the profile.
• Through-feed method: Long threads, threaded rods, stud bolts with continuous threads, anchor rods, tie rods, anything longer than the width of the dies.

For both methods, every thread needs its own dies: one set per pitch, profile and method. For special threads, it is therefore worth asking about existing die sets; RS Randack keeps a large stock of rolling dies for metric threads, inch threads, UN and UNR, UNJ and MJ for aerospace, and trapezoidal threads.

What sets rolled threads apart

The grain flow remains uninterrupted, the flanks are work-hardened and smooth, and the thread root is under compressive residual stress; this considerably increases fatigue strength compared with cut threads. With final rolling after quenching and tempering, this advantage comes fully into play. For more, see Thread rolling or thread cutting and Rolling after heat treatment.

What you should specify

Thread with pitch and tolerance class, thread length and runout, whether the thread is to be rolled before or after quenching and tempering, coating, and whether a set of rolling dies to drawing is required.